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Showing posts with label Catterall. Show all posts
Showing posts with label Catterall. Show all posts

Wednesday, 19 August 2015

Low Dose Clonazepam for Autism - SFARI Webinar with William Catterall








This post will be mainly of interest to the small number of people using low-dose clonazepam for autism and those considering doing so.

This therapy modifies the excitatory/inhibitory (im)balance between the GABA and Glutamate neurotransmitters.  The big advantage is that it should be very safe, is extremely inexpensive and, unlike Bumetanide, does not cause diuresis.   The disadvantage is that the effective dose is only in a narrow window, and you have to find it by trial and error.


Does it work?

It certainly does work in some children with autism.

It also appears to have an additional effect over Bumetanide alone, at least my son.

Questions remain:

·        Does it work with everyone who responds to bumetanide?
·        Does it only work in people with a Nav1.1 dysfunction?
·        Will bumetanide work in everyone who responds to Clonazepam?


One of my earlier, detailed, posts on this subject is this one:-



Just google “clonazepam epiphany” or use the site index, for the other posts.


Professor Catterall

I have already covered the science behind low-dose Clonazepam and Professor Catterall’s trials in two mouse models.  It is quite a complex subject and in the end most people just want to know does it work in humans with autism or not.

Catterall’s research was funded by the Simons Foundation, so no surprise really that he made a Webinar for SFARI.  It covers the ground of those two papers and indicates the next steps for his research.

It is a bit lighter going than his papers, but it is a full hour of science.

Catterall plans to trial it in humans with autism, starting with those known to have sodium channel dysfunction. So he is following the same pattern he used with his mice.

The first mouse model he used was Dravet syndrome, a rare condition leading to epilepsy and autism which is caused by a sodium ion channel (Nav1.1) dysfunction.  The second experiment used a standard mouse model of autism called the BTBR mouse model, so no connection with sodium channels.

My question to Catterall was whether this therapy would only work in people with a Nav1.1 dysfunction.  He did respond via the comments on the post, but did not really answer the question.  The fact that he plans to trial his idea on humans with autism with a known sodium ion channel dysfunction, does suggest something at least.

I think that since the actual mechanism of the drug is on a sub-unit of the GABAA receptor, sodium channels may actually be more of a coincidence, meaning that while autism Nav1.1 dysfunction may indeed indicate this therapy, it may be applicable in other autism where GABA is dysfunctional.


Bumetanide Use

The downside of bumetanide use to correct the E/I imbalance often found in autism is the diuresis and excessive loss of potassium in about 20% of people.

If you revisit the original paper suggesting an  E/I imbalance might be fundamental to many kinds of autism, you will see that this E/I imbalance is not just an ongoing issue, it is potentially an avoidable cause of disruption at key points in the brain’s development prior to maturation. In simpler terms, an E/I imbalance during development may cause the physical brain abnormalities often observed in autism.

That would suggest you should try and reverse E/I imbalance as soon as possible, well before maturation of the brain. 

One day an analog of bumetanide may be developed, that avoids the diuresis;  it is already being discussed.


Bumetanide (or low dose Clonazepam) use, even before autism has become established ?


In something like 30% of cases of classic autism there is macrocephaly (a big head), which even shows up on ultrasound scans of the pregnant mother.  A big head does not necessarily mean autism, but specific types of autism are clearly associated with big heads.

There are many other well known risk factors, like siblings with autism, siblings with other disabilities, older parents, family history (schizophrenia, bipolar, auto-immune conditions, COPD, Nobel Laureates, math prodigies) etc.

Since we also know that an indicator of this kind of E/I imbalance is that benzodiazepine drugs can show paradoxical effects (they work in reverse), it should be possible to make some kind of predictive diagnostic test.


So it would not be rocket science to identify many babies at elevated risk of autism and then treatment could be started very early and well before brain maturation.

This is rather like the Japanese researchers in the previous post suggesting that sulforaphane consumption in childhood might prevent susceptible people developing schizophrenia in adulthood.








Monday, 16 March 2015

Bumetanide and/or low-dose Clonazepam for Autism




Today’s post answers a question left un-answered in earlier posts about the best way to treat the imbalance (excitatory vs inhibitory or just E/I) that exists in the function of the key neurotransmitter GABA in many types of autism.

I first started this blog after the pleasant shock of seeing the positive behavioral and cognitive effect caused by Bumetanide.

This was just copying a recent French clinical trial on humans.

Later on in this blog we came across Professor Catterall who made two experiments in mice to show that the same E/I imbalance could be treated using tiny doses of a drug called Clonazepam.  At doses a hundred time higher, Clonazepam is used to treat seizures and anxiety, but at those doses it dose have side effects.

The mechanism is different to Bumetanide, by the effect was claimed to be the same.

Since Bumetanide has actually been shown effective in a human trial, most readers of this blog have this as their first choice.

I commented that in Monty, aged 11 with ASD, there was indeed an additional positive effect of adding clonazepam to existing bumetanide therapy.  Now having several effective treatments, it is harder to quantify the effect of new ones.  

It remained unknown what would be  the effect of low dose Clonazepam without the Bumetanide. 

Since Bumetanide is known to reduce potassium levels, albeit in a minority of cases, to the extent that supplementation is required, it is necessary to monitor blood levels of potassium.  This is a drawback of the therapy, although the majority of people will not actually need supplementation.  So one regular reader of this blog has tried Clonazepam; and I assume, Maja, without Bumetanide.



Tried Clonazepam 0.025mg in one dose, in the evening, before sleep. After whole 3 days, as you predicted, change was amazing - she become self confident, a bit naughty, but in some joyful, playful way. Started to play more often with friends (by report of teacher end assistant in school). They both reported that she is different, but in good way, even she is harder to manage with (i didn't tell them about new therapy in that time)

Started to play differently, not in pattern she's developed over the years (she has great imaginations, wich is a plus, but has stereotype of ideas in the play).

First of all, we noticed that she is capable to sense odors (she had some kind of anosmia before), than she managed to catch a rhythm to dance (that was a real wow!).

She was speaking with people in the shop (briefly, but adequately)...
There is much more...

Change is still present, but after three weeks are slightly paler . There are not so intense. I'm still overwhelmed, just wont to know if I am missing something.


Thank you Maja for sharing.

In Monty, the effect was not this profound, but then he was already on Bumetanide, and so I was rather expecting no effect.


So, bumetanide and/or low-dose clonazepam for Autism?  

I suggest both, for maximum effect.





P.S.  For the scientists among you

There is another drug, Diamox/Acetazolamide, that I think may also have the same effect as Bumetanide and Low dose Clonazepam.  It is a so-called carbonic anhydrase inhibitor, meaning it forces the kidneys to excrete bicarbonate (HCO3-) and thus makes the blood more acidic.  This has the side benefit of increasing the amount of oxygen in the blood, and hence its use off-label to prevent altitude sickness.  In the brain this change in HCO3- should affect Anion exchanger 3 (AE3) and Sodium dependent anion exchanger (NDAE) which sit alongside the GABAa receptors. By reducing Cl- levels within the cell, the effect would be the same as Bumetanide, which affects the NKCC1 transporter.  This might explain why Diamox, a diuretic, is also used to treat some epilepsy and periodic paralysis.  Note Bumetanide is also used to treat periodic paralysis and some seizures.

This was all covered in a very complicated post:-
GABA A Receptors in Autism – How and Why to Modulate Them

If you are one of those who believe that there is mild hypoxia in some cases of autism, then you could also consider Diamox as an alternative to hyperbaric oxygen therapy.
  










  



Thursday, 18 September 2014

GABA A Receptors in Autism – How and Why to Modulate Them


This post will get complicated, since it will look at many aspects of the GABA A receptor, rather than just a small fraction that usually appear in the individual pieces of the scientific literature. 

It was prompted by comments I have received from regular readers, regarding Bumetanide, Clonazepam, epilepsy and whether there might be alternatives with the same effect.  So it is really intended to answer some complex issues. 

There are some new interesting facts/observations that may be of wider interest, just skip the parts that too involved.

Regarding today’s picture, most readers of this blog are female and by the way, while the US is the most common location by far,  a surprisingly high number of page views come from France, Hong Kong, South Africa and Poland.


GABA

We have seen that GABA is one of the brain's most important neurotransmitters and we know that various forms of GABA dysfunction are associated with autism, epilepsy and indeed schizophrenia.

One recurring aspect in the research is the so-called excitatory-inhibitory balance of GABA.

The way the brain is understood to function assumes that GABA should be inhibitory and NMDA should be excitatory.

What makes GABA inhibitory is the level of the electrolyte chloride within the cells.  If the level is “wrong”, then GABA may be excitatory and the fine balance required with the NMDA receptor is lost.  The brain then cannot function as intended.




Source: Sage Therapeutics, a company that is developing new drugs that target GABAA and NMDA receptors

To understand what is going wrong in autism and how to treat it we need to take a detailed look at the GABAA receptor and all the anion transport mechanism associated with it.  Most research looks at either the receptor OR the transporters and exchangers.


Anion Transport Mechanisms of the GABAA receptor

You will either need to be a doctor, scientist or very committed to keep reading here.

We know that level of chloride within the cells is critical to whether GABA behaves as excitatory or inhibitory.  This has all been established in the laboratory.

The usual target in autism is the NKCC1 transporter that lets chloride INTO cells, but as you can see in the two figures below, there are other ways to affect the concentration of chloride.  

·        The KCC2 transporter lets chloride out of the cells

·        The sodium dependent anion exchanger (NDAE) lets chloride out of the cells

·        The sodium independent anion exchanger 3 (AE3), lets chloride in.  It extrudes intracellular HCO3- in exchange for extracellular Cl-.

All this does actually matter since we will be able to link it back to a known genetic dysfunction and it would suggest alternative therapeutic avenues.  We can also see how epilepsy fits into the picture.












NKCC1 in Autism

Without doubt, the transporter that controls the flow of chloride into the brain is the expert field of Ben Ari.

His recent summary paper is below:-


He showed that by reducing the level of chloride in the autistic brain using the common diuretic Bumetanide, a marked improvement in many peoples’ autism could be achieved


This post is really about expanding more on what he does not tell us.


KCC2 in Autism

In typical people, very early in life the KCC2 transporter develops and as a result level of chloride falls inside the cells, since the purpose of the transporter is to extrude chloride.

It appears that in autism this mechanism has been disrupted.  The existing science can show us what has gone wrong.

The following study shows that KCC2 is itself regulated by neuroligin-2 (NL2), a cell adhesion molecule specifically localized at GABAergic synapses.

It gets more interesting because the scientists looking for genetic causes of autism have already identified the gene that encodes NL2, which they call NLGN2 (neuroligin 2) as being associated with autism and schizophrenia (adult onset autism).





  

Abstract

Background

GABAA receptors are ligand-gated Cl- channels, and the intracellular Cl- concentration governs whether GABA function is excitatory or inhibitory. During early brain development, GABA undergoes functional switch from excitation to inhibition: GABA depolarizes immature neurons but hyperpolarizes mature neurons due to a developmental decrease of intracellular Cl- concentration. This GABA functional switch is mainly mediated by the up-regulation of KCC2, a potassium-chloride cotransporter that pumps Cl- outside neurons. However, the upstream factor that regulates KCC2 expression is unclear.

Results

We report here that KCC2 is unexpectedly regulated by neuroligin-2 (NL2), a cell adhesion molecule specifically localized at GABAergic synapses. The expression of NL2 precedes that of KCC2 in early postnatal development. Upon knockdown of NL2, the expression level of KCC2 is significantly decreased, and GABA functional switch is significantly delayed during early development. Overexpression of shRNA-proof NL2 rescues both KCC2 reduction and delayed GABA functional switch induced by NL2 shRNAs. Moreover, NL2 appears to be required to maintain GABA inhibitory function even in mature neurons, because knockdown NL2 reverses GABA action to excitatory. Gramicidin-perforated patch clamp recordings confirm that NL2 directly regulates the GABA equilibrium potential. We further demonstrate that knockdown of NL2 decreases dendritic spines through down-regulating KCC2.

Conclusions

Our data suggest that in addition to its conventional role as a cell adhesion molecule to regulate GABAergic synaptogenesis, NL2 also regulates KCC2 to modulate GABA functional switch and even glutamatergic synapses. Therefore, NL2 may serve as a master regulator in balancing excitation and inhibition in the brain.



KCC2 in Peripheral nerve injury (PNI)

Autism is not the only diagnosis associated with reduced function of the KCC2 transporter; Peripheral nerve injury (PNI) is another.

In this condition researchers sought to counter the failure of KCC2 to remove chloride from within the cell by increasing the flow chloride through the Cl-/HCO3- anion exchanger known as AE3.


Abstract

Peripheral nerve injury (PNI) negatively influences spinal gamma-aminobutyric acid (GABA)ergic networks via a reduction in the neuron-specific potassium-chloride (K(+)-Cl(-)) cotransporter (KCC2). This process has been linked to the emergence of neuropathic allodynia. In vivo pharmacologic and modeling studies show that a loss of KCC2 function results in a decrease in the efficacy of GABAA-mediated spinal inhibition. One potential strategy to mitigate this effect entails inhibition of carbonic anhydrase activity to reduce HCO3(-)-dependent depolarization via GABAA receptors when KCC2 function is compromised. We have tested this hypothesis here. Our results show that, similarly to when KCC2 is pharmacologically blocked, PNI causes a loss of analgesic effect for neurosteroid GABAA allosteric modulators at maximally effective doses in naïve mice in the tail-flick test. Remarkably, inhibition of carbonic anhydrase activity with intrathecal acetazolamide rapidly restores an analgesic effect for these compounds, suggesting an important role of carbonic anhydrase activity in regulating GABAA-mediated analgesia after PNI. Moreover, spinal acetazolamide administration leads to a profound reduction in the mouse formalin pain test, indicating that spinal carbonic anhydrase inhibition produces analgesia when primary afferent activity is driven by chemical mediators. Finally, we demonstrate that systemic administration of acetazolamide to rats with PNI produces an antiallodynic effect by itself and an enhancement of the peak analgesic effect with a change in the shape of the dose-response curve of the α1-sparing benzodiazepine L-838,417. Thus, carbonic anhydrase inhibition mitigates the negative effects of loss of KCC2 function after nerve injury in multiple species and through multiple administration routes resulting in an enhancement of analgesic effects for several GABAA allosteric modulators. We suggest that carbonic anhydrase inhibitors, many of which are clinically available, might be advantageously employed for the treatment of pathologic pain states.

PERSPECTIVE:

Using behavioral pharmacology techniques, we show that spinal GABAA-mediated analgesia can be augmented, especially following nerve injury, via inhibition of carbonic anhydrases. Carbonic anhydrase inhibition alone also produces analgesia, suggesting these enzymes might be targeted for the treatment of pain




Treatment of neuropathic pain is a major clinical challenge that has been met with minimal success. After peripheral nerve injury, a decrease in the expression of the K–Cl cotransporter KCC2, a major neuronal Cl extruder, leads to pathologic alterations in GABAA and glycine receptor function in the spinal cord. The down-regulation of KCC2 is expected to cause a reduction in Cl extrusion capacity in dorsal horn neurons, which, together with the depolarizing efflux of HCO−3 anions via GABAA channels, would result in a decrease in the efficacy of GABAA-mediated inhibition. Carbonic anhydrases (CA) facilitate intracellular HCO−3 generation and hence, we hypothesized that inhibition of CAs would enhance the efficacy of GABAergic inhibition in the context of neuropathic pain. Despite the decrease in KCC2 expression, spinal administration of benzodiazepines has been shown to be anti-allodynic in neuropathic conditions. Thus, we also hypothesized that spinal inhibition of CAs might enhance the anti-allodynic effects of spinally administered benzodiazepines. Here, we show that inhibition of spinal CA activity with acetazolamide (ACT) reduces neuropathic allodynia. Moreover, we demonstrate that spinal co-administration of ACT and midazolam (MZL) act synergistically to reduce neuropathic allodynia after peripheral nerve injury. These findings indicate that the combined use of CA inhibitors and benzodiazepines may be effective in the clinical management of neuropathic pain in humans.

In conclusion, the major finding of the present work is that ACT and MZL act synergistically to inhibit neuropathic allodynia. In light of the available in vitro data reviewed above, a parsimonious way to explain this synergism is that CA inhibition blocks an HCO−3 -dependent positive shift in the Er of GABA and/or glycine-mediated currents and the consequent tonic excitatory drive mediated by extrasynaptic GABAA receptors, while preserving shunting inhibition that is augmented by benzodiazepine actions at postsynaptic GABAA receptors. Obviously, further work is needed at the in vitro level in order to directly examine the cellular and synaptic basis of the ACT-MZL synergism and clinical studies are required to determine the safety of intrathecally applied CA inhibitors in humans. Since MZL and ACT, as well as several other inhibitors of CA [37], are clinically approved, we propose that their use in combination opens up a novel approach for the treatment of chronic neuropathic pain


Midazolam and Acetazolamide

The therapeutic as well as adverse effects of midazolam are due to its effects on the GABAA receptors; midazolam does not activate GABAA receptors directly but, as with other benzodiazepines, it enhances the effect of the neurotransmitter GABA on the GABAA receptors (↑ frequency of Cl− channel opening) resulting in neural inhibition. Almost all of the properties can be explained by the actions of benzodiazepines on GABAA receptors. This results in the following pharmacological properties being produced: sedation, hypnotic, anxiolytic, anterograde amnesia, muscle relaxation and anti-convulsant.


Acetazolamide, usually sold under the trade name Diamox in some countries.  Acetazolamide is a diuretic, and it is available as a (cheap) generic drug.


In epilepsy, the main use of acetazolamide is in menstrual-related epilepsy and as an adjunct in refractory epilepsy.

Acetazolamide is not an immediate cure for acute mountain sickness; rather, it speeds up part of the acclimatization process which in turn helps to relieve symptoms.  I am pretty sure, many years ago, it was Diamox that I took with me when crossing the Himalayas from Nepal into Tibet.  We did not have any problems with mountain sickness.

If periodic paralysis above rings some bells it should.  Two forms already mentioned in this blog are Hypokalemic periodic paralysis and Andersen Tawil syndrome.  We even referred to a paper suggesting the use of Bumetanide.



Acetazolamide is a carbonic anhydrase inhibitor, hence causing the accumulation of carbonic acid Carbonic anhydrase is an enzyme found in red blood cells that catalyses the following reaction:


hence lowering blood pH, by means of the following reaction that carbonic acid undergoes






Anion exchanger 3 (AE3) in autism

Anion exchange protein 3 is a membrane transport protein that in humans is encoded by the SLC4A3 gene. It exchanges chloride for bicarbonate ions.  It increases chloride concentration within the cell.  AE3 is an anion exchanger that is primarily expressed in the brain and heart

Its activity is sensitive to pH. AE3 mutations have been linked to seizures


Bicarbonate (HCO3-) transport mechanisms are the principal regulators of pH in animal cells. Such transport also plays a vital role in acid-base movements in the stomach, pancreas, intestine, kidney, reproductive organs and the central nervous system.



Abstract

Chloride influx through GABA-gated Cl channels, the principal mechanism for inhibiting neural activity in the brain, requires a Cl gradient established in part by K+–Cl cotransporters (KCCs). We screened for Caenorhabditis elegans mutants defective for inhibitory neurotransmission and identified mutations in ABTS-1, a Na+-driven Cl–HCO3 exchanger that extrudes chloride from cells, like KCC-2, but also alkalinizes them. While animals lacking ABTS-1 or the K+–Cl cotransporter KCC-2 display only mild behavioural defects, animals lacking both Cl extruders are paralyzed. This is apparently due to severe disruption of the cellular Cl gradient such that Cl flow through GABA-gated channels is reversed and excites rather than inhibits cells. Neuronal expression of both transporters is upregulated during synapse development, and ABTS-1 expression further increases in KCC-2 mutants, suggesting regulation of these transporters is coordinated to control the cellular Cl gradient. Our results show that Na+-driven Cl–HCO3 exchangers function with KCCs in generating the cellular chloride gradient and suggest a mechanism for the close tie between pH and excitability in the brain.




Abstract

During early development, γ-aminobutyric acid (GABA) depolarizes and excites neurons, contrary to its typical function in the mature nervous system. As a result, developing networks are hyperexcitable and experience a spontaneous network activity that is important for several aspects of development. GABA is depolarizing because chloride is accumulated beyond its passive distribution in these developing cells. Identifying all of the transporters that accumulate chloride in immature neurons has been elusive and it is unknown whether chloride levels are different at synaptic and extrasynaptic locations. We have therefore assessed intracellular chloride levels specifically at synaptic locations in embryonic motoneurons by measuring the GABAergic reversal potential (EGABA) for GABAA miniature postsynaptic currents. When whole cell patch solutions contained 17–52 mM chloride, we found that synaptic EGABA was around −30 mV. Because of the low HCO3 permeability of the GABAA receptor, this value of EGABA corresponds to approximately 50 mM intracellular chloride. It is likely that synaptic chloride is maintained at levels higher than the patch solution by chloride accumulators. We show that the Na+-K+-2Cl cotransporter, NKCC1, is clearly involved in the accumulation of chloride in motoneurons because blocking this transporter hyperpolarized EGABA and reduced nerve potentials evoked by local application of a GABAA agonist. However, chloride accumulation following NKCC1 block was still clearly present. We find physiological evidence of chloride accumulation that is dependent on HCO3 and sensitive to an anion exchanger blocker. These results suggest that the anion exchanger, AE3, is also likely to contribute to chloride accumulation in embryonic motoneurons.



Sodium dependent anion exchanger (NDAE)

Not much has been written about these exchangers, outside of very technical literature.



Sodium-coupled anion exchange is activated by intracellular acidification (Schwiening and Boron, 1994), suggesting that regulation of the chloride gradient by NDAEs may be closely linked to the regulation of cellular pH. As prolonged neuronal activity can cause neuronal acidification by efflux of bicarbonate through GABAA receptors (Kaila and Voipio, 1987), sodium-coupled anion exchange may help to maintain a hyperpolarizing chloride reversal potential and thus promote the inhibitory action of GABA. Thus activation of sodium-coupled anion exchange by acidosis may also contribute to seizure termination by promoting a more negative chloride reversal potential and thus promoting the inhibitory effects of GABA.



The GABAA receptor  (background is cut and paste from Wikipedia)

In order for GABAA receptors to be sensitive to the action of benzodiazepines they need to contain an α and a γ subunit, between which the benzodiazepine binds. Once bound, the benzodiazepine locks the GABAA receptor into a conformation where the neurotransmitter GABA has much higher affinity for the GABAA receptor, increasing the frequency of opening of the associated chloride ion channel and hyperpolarizing the membrane. This potentiates the inhibitory effect of the available GABA leading to sedative and anxiolytic effects.


Structure and function





Schematic diagram of a GABAA receptor protein ((α1)2(β2)2(γ2)) which illustrates the five combined subunits that form the protein, the chloride (Cl-) ion channel pore, the two GABA active binding sites at the α1 and β2 interfaces, and the benzodiazepine (BDZ) allosteric binding site

The receptor is a pentameric transmembrane receptor that consists of five subunits arranged around a central pore. Each subunit comprises four transmembrane domains with both the N- and C-terminus located extracellularly. The receptor sits in the membrane of its neuron, usually localized at a synapse, postsynaptically. However, some isoforms may be found extrasynaptically. The ligand GABA is the endogenous compound that causes this receptor to open; once bound to GABA, the protein receptor changes conformation within the membrane, opening the pore in order to allow chloride anions (Cl) to pass down an electrochemical gradient. Because the reversal potential for chloride in most neurons is close to or more negative than the resting membrane potential, activation of GABAA receptors tends to stabilize or hyperpolarise the resting potential, and can make it more difficult for excitatory neurotransmitters to depolarize the neuron and generate an action potential. The net effect is typically inhibitory, reducing the activity of the neuron. The GABAA channel opens quickly and thus contributes to the early part of the inhibitory post-synaptic potential (IPSP).

Subunits

GABAA receptors are members of the large "Cys-loop" super-family of evolutionarily related and structurally similar ligand-gated ion channels that also includes nicotinic acetylcholine receptors, glycine receptors, and the 5HT3 receptor. There are numerous subunit isoforms for the GABAA receptor, which determine the receptor's agonist affinity, chance of opening, conductance, and other properties.
In humans, the units are as follows:
There are three ρ units (GABRR1, GABRR2, GABRR3), however these do not coassemble with the classical GABAA units listed above,[18] but rather homooligomerize to form GABAA-ρ receptors (formerly classified as GABAC receptors but now this nomenclature has been deprecated[19] ).
Five subunits can combine in different ways to form GABAA channels. The minimal requirement to produce a GABA-gated ion channel is the inclusion of both α and β subunits, but the most common type in the brain is a pentamer comprising two α's, two β's, and a γ (α2β2γ)
The receptor binds two GABA molecules, at the interface between an α and a β subunit



The important subunits for this post are:-
GABRA2,
Very little is written about this subunit.

GABRA3
While the effect of editing on protein function is unknown, the developmental increase in editing does correspond to changes in function of the GABAA receptor. GABA binding leads to chloride channel activation, resulting in rapid increase in concentration of the ion. Initially, the receptor is an excitatory receptor, mediating depolarisation (efflux of Cl- ions) in immature neurons before changing to an inhibitory receptor, mediating hyperpolarization(influx of Cl- ions) later on. GABAA converts to an inhibitory receptor from an excitatory receptor by the upregulation of KCC2 cotransporter. This decreases the concentration of Cl- ion within cells. Therefore, the GABAA subunits are involved in determining the nature of the receptor in response to GABA ligand. These changes suggest that editing of the subunit is important in the developing brain by regulating the Cl- permeability of the channel during development. The unedited receptor is activated faster and deactivates slower than the edited receptor.


Editing of the I/M site is developmentally regulated

A switch in the GABA response from excitatory to inhibitory post-synaptic potentials occurs during early development where an efflux of chloride ions takes place in immature neurons, while there is an influx of chloride ions in mature neurons (Ben-Ari 2002). GABA switches from being excitatory to inhibitory by an up-regulation of the cotransporter KCC2 that decreases the chloride concentration in the cell. However, if GABA itself promotes the expression of KCC2 is still under debate (Ganguly et al. 2001; Ludwig et al. 2003; Titz et al. 2003). Further, the α subunits are critical elements in determining the nature of the GABAA receptor response to GABA (Böhme et al. 2004). The α3 mRNA (Gabra-3) is present at high levels in several forebrain regions at birth with a major decline after post-natal day 12 (P12), when the expression of α1 is going up (Laurie et al. 1992). The change from α3 to α1 may cause the switch in GABA behavior from excitatory to inhibitory post-synaptic potentials during development.
GABAA receptors respond to anxiolytic drugs such as benzodiazepines and are thus important drug targets. The benzodiazepine binding site is located at the interface of the α and γ2 subunits (Cromer et al. 2002). Antagonists that bind to this site enhance the effect of GABA by increasing the frequency of GABA-induced channel opening events. Post-transcriptional modifications of the α3 subunit, such as the I/M editing described here, could be important in determining the mechanistic features that are responsible for the diversity of GABAA receptors and the variability in sensitivity to drugs

Ligands

A number of ligands have been found to bind to various sites on the GABAA receptor complex and modulate it besides GABA itself.

Types

  • Agonists: bind to the main receptor site (the site where GABA normally binds, also referred to as the "active" or "orthosteric" site) and activate it, resulting in increased Cl conductance.
  • Antagonists: bind to the main receptor site but do not activate it. Though they have no effect on their own, antagonists compete with GABA for binding and thereby inhibit its action, resulting in decreased Cl conductance.
  • Positive allosteric modulators: bind to allosteric sites on the receptor complex and affect it in a positive manner, causing increased efficiency of the main site and therefore an indirect increase in Cl conductance.
  • Negative allosteric modulators: bind to an allosteric site on the receptor complex and affect it in a negative manner, causing decreased efficiency of the main site and therefore an indirect decrease in Cl conductance.
  • Open channel blockers: prolong ligand-receptor occupancy, activation kinetics and Cl ion flux in a subunit configuration-dependent and sensitization-state dependent manner.
  • Non-competitive channel blockers: bind to or near the central pore of the receptor complex and directly block Cl- conductance through the ion channel.

The GABAA receptor include a site where benzodiazepine can bind.  These are drugs that include like valium. Binding at this site increase the effect of GABA.  Since this receptor is meant to be inhibitory, giving valium should make it strong inhibitory, ie calming. 

It was noted that in autism the effect of valium was often the reversed, instead of calming it further increased anxiety.

The Valium is working just fine, it is magnifying the effect the effect of GABA, the problem is that the receptor is functioning as excitatory, the Valium is making it over-excitatory.  Now we come to the reason why.

We know that the excitatory-inhibitory balance is set by the chloride concentration within the cells.  We also know that exact mechanism that determines this level.


 Highlights

BTBR mice have reduced spontaneous GABAergic inhibitory transmission
Nonsedating doses of benzodiazepines improved autism-related deficits in BTBR mice
Impairment of GABAergic transmission reduced social interaction in wild-type mice
Behavioral rescue by low-dose benzodiazepine is GABAA receptor α2,3-subunit specific

Summary

Autism spectrum disorder (ASD) may arise from increased ratio of excitatory to inhibitory neurotransmission in the brain. Many pharmacological treatments have been tested in ASD, but only limited success has been achieved. Here we report that BTBR T+ Itpr3tf/J (BTBR) mice, a model of idiopathic autism, have reduced spontaneous GABAergic neurotransmission. Treatment with low nonsedating/nonanxiolytic doses of benzodiazepines, which increase inhibitory neurotransmission through positive allosteric modulation of postsynaptic GABAA receptors, improved deficits in social interaction, repetitive behavior, and spatial learning. Moreover, negative allosteric modulation of GABAA receptors impaired social behavior in C57BL/6J and 129SvJ wild-type mice, suggesting that reduced inhibitory neurotransmission may contribute to social and cognitive deficits. The dramatic behavioral improvement after low-dose benzodiazepine treatment was subunit specific—the α2,3-subunit-selective positive allosteric modulator L-838,417 was effective, but the α1-subunit-selective drug zolpidem exacerbated social deficits. Impaired GABAergic neurotransmission may contribute to ASD, and α2,3-subunit-selective positive GABAA receptor modulation may be an effective treatment.
  
These results indicate that different subtypes of GABAA receptors may have opposite roles in social behavior, with activation of GABAA receptors containing α2,3 subunits favoring and of GABAA receptors with α1  subunits reducing social interaction, respectively.

Because of their broad availability and safety, benzodiazepines and other positive allosteric modulators of GABAA receptors administered at low nonsedating, nonanxiolytic doses that do not induce tolerance deserve consideration as a near-term strategy to improve the core social interaction deficits and repetitive behaviors in ASD.

These results are most consistent with the hypotheses that reduced inhibitory neurotransmission is sufficient to induce autistic-like behaviors in mice and that enhanced inhibitory neurotransmission can reverse autistic-like behaviors.



Epilepsy

I have received various comments about epilepsy.  Epilepsy has many variants, just like autism.  Epilepsy is often comorbid with autism.  GABA dysfunction is known to be closely involved in some types of autism and some types of epilepsy.

It is known that Bumetanide has very different effects in different types of epilepsy.
The question that naturally arises is whether you can give Bumetanide to someone who has autism and epilepsy and if you cannot, is there an alternative with the same desired effect?

Well it appears that any method that changes chloride levels is likely to affect epilepsy.  It appears that all three methods (NKCC1, KCC2 and AE3) would likely have the same impact on epilepsy.

But would it be a good effect or a bad effect?

Would it interact with any existing anti-epilepsy drugs?

I suspect that Bumetanide might be an effective anti-epileptic in people with autism and that other GABA related drugs might no longer be needed.  Quite likely the effect of Bumetanide and the anti-epileptic targeting GABA might be too much.  So the blog reader that pointed out that the bumetanide clinical trial excluded children with epilepsy has highlighted an important point.

While epilepsy is not fully understood and there are various variants, it would seem plausible that the epilepsy common in core classic autism and early regressive autism is the same type and that it is linked to the same excitatory/inhibitory dysfunction.

You may be wonder if other diuretics have anti-epileptic properties. Here is a paper by a Neurologist from Denver on the subject:-




Why is there an excitatory/inhibitory dysfunction in Autism?

People are writing entire books on the GABA excitatory/inhibitory balance.  I was curious as to why this dysfunction exists at all in autism. 

We learnt from Ben-Ari in earlier posts all about this switch from excitatory to inhibitory that is supposed to occur very early on in life, we now have two reasons why this may fail to happen in autism:-

1.     Editing modifies the GABAA receptor subunit α3.  The change from α3 to α1 may cause the switch in GABA behavior from excitatory to inhibitory post-synaptic potentials during development.  This change appears not to occur in some types of autism.  We see from the Clonazepam research that α3 and  α1 have opposite effects in autism.   In autism, activation of GABAA receptors containing α2,3 subunits favours social interaction  and activation of α1  subunits reduces social interaction.

And/Or

2.     The GABA functional switch is mainly mediated by the up-regulation of KCC2, a potassium-chloride cotransporter that pumps Cl- outside neurons.  NL2 also regulates KCC2 to modulate GABA functional switch. Therefore, NL2 may serve as a master regulator in balancing excitation and inhibition in the brain.  The gene that encodes NL2 is called NLGN2 (neuroligin 2).  Dysfunction in gene NLGN2 is known to occur in both autism and schizophrenia (adult onset autism).


Conclusion

We came full circle back to Bumetanide and Clonazepam as most likely the safest and most effective therapy to adjust the E/I (excitatory/inhibitory) balance in autism. KCCI agonists do not seem to exist.  The bicarbonate exchanger agonist Acetazolamide/Diamox is another common diuretic and I see no reason why it would not also be effective, but we would then affect bicarbonate levels.  Since these ions play a role in controlling pH levels, I think we might risk seeing some unintended effects.  We know that Bumetanide is safe in long term use.  We know that all diuretics that change chloride level within the cell and will affect epilepsy; so it is a case of “better the devil you know”. 

I finally understood exactly why tiny dose of Clonazepam are effective and how this fits in with the changes the Bumetanide has produced.  Thankfully, such tiny doses are free of the typical side effects expected from benzodiazepines.  One tablet lasts 10 days.

It also answers somebody else’s question about starting with Clonazepam before the Bumetanide.  If you did that you might well make things much worse, you would magnify the unwanted excess brain cell firing.  Once you added bumetanide things would then reverse and brain cell firing would be inhibited.

I rather like the parallel with neuropathic pain, the other condition we looked at with reduced KCC2 transporter function, the researchers there proposed the combination of a diuretic (Acetazolamide) to lower cellular chloride (via exchanger AE3) and a benzodiazepine (Midazolam) as a positive allosteric modulator.  This is extremely similar to Ben Ari’s bumetanide (diuretic affecting transporter NKCC1) plus Catterall’s tiny doses of clonazepam (benzodiazepine) as a positive allosteric modulator.

As for epilepsy and bumetanide, we know that bumetanide has different effects on different types of autism. It seems plausible that people with autism might tend to have the same type of epilepsy.  In any case Monty, aged 11 with ASD, does not have epilepsy/seizures and I suspect taking bumetanide has decreased the chance he ever will.  Of course I cannot prove this, it is just conjecture.