Autistic-like behaviour in Scn1a+/−mice and rescue by enhanced GABA-mediated neurotransmission
"Remarkably, treatment with
low-dose clonazepam, a positive allosteric modulator of GABAA
receptors, completely rescued the abnormal social behaviours and deficits in
fear memory in the mouse model of Dravet’s syndrome, demonstrating that they
are caused by impaired GABAergic neurotransmission and not by neuronal damage
from recurrent seizures. These
results demonstrate a critical role for NaV1.1 channels in
neuropsychiatric functions and provide a potential therapeutic strategy for
cognitive deficit and autism-spectrum behaviours in Dravet’s syndrome."
Experiment number two
In a recent
experiment, Catterall used a standard mouse model of autism called the BTBR
mouse. This is essential a specially
bred mouse that exhibits very many traits of autism. Nobody has purposefully interfered with its
SCN1A genes or NaV1.1 ion channels.
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
In this
study, Catterall repeated his use of low-dose clonazepam to try to “cure” the autistic
mouse. He not only was able to reduce
the autistic deficits, but he was able to make cognitive improvements. In effect he made the mice less autistic and
smarter.
The following
excepts from his paper are quite technical and you may wish to skip past them.
Increased GABAergic Inhibitory Neurotransmission in Response to
Benzodiazepines
"Attempts to reverse autistic-like traits by rebalancing the ratio of
excitatory to inhibitory neurotransmission through pharmacological treatments
that reduce excitatory neurotransmission have met with only partial success
because of their limited efficacy and unwanted side effects in control groups.
The increased GABAergic signaling after treatment with
clonazepam led to a decrease in frequency of spontaneous EPSCs (Figures 1G and 1H),
without change in amplitude in BTBR hippocampal slices (Figure S1D).
Interestingly, the frequency of spontaneous EPSC was also decreased by
clonazepam (Figure S1K), without change in amplitude (Figure S1L) in
C57BL/6J slices.
These data support the idea
that low-dose clonazepam can reverse the underlying deficit in spontaneous
GABAergic inhibitory neurotransmission in BTBR mice."
Improvement of Social
Interaction by Treatment with Clonazepam
"To test the behavioral effects of enhancing inhibitory
neurotransmission in BTBR mice, we injected low nonsedating/nonanxiolytic doses
of clonazepam intraperitoneally 30 min prior to behavioral tests. In the
three-chamber social interaction test, acute clonazepam treatment had no effect
on social interactions of C57BL/6J mice (Figures 2A and S2A) but
increased social interactions in BTBR, with a maximal effect at 0.05 mg/kg (Figures 2B and S2B) and no
sedation (Figure S2H). Measurements of the time of interaction of the test
mouse with a stranger mouse versus a novel object during three-chamber tests
showed that the C57BL/6J mice are unaffected by any of the test doses (Figure 2C), whereas
improvement of the social deficit in BTBR mice by clonazepam is strikingly dose
dependent (Figure 2D). Interestingly, the improved social interactions in
BTBR mice were lost at higher doses of clonazepam (Figures 2B and 2D).
Other behaviors in BTBR mice were also rescued by low-dose clonazepam. In the
open-field test, a single injection of 0.05 mg/kg clonazepam significantly
reduced hyperactivity, measured as the total distance moved (Figure 2E), and
stereotyped circling behavior, measured as the number of 360_ rotations (Figure 2F).
In contrast, these behaviors in C57BL/6J mice were
unaffected by low-dose clonazepam. These low doses of clonazepam had little
effect on anxiety-like behaviors of C57BL/6J mice, such as avoidance of the
center of an open field or the open arms of an elevated plus maze (Figures 2G and 2H).
However, compared to C57BL/6J, BTBR mice visited the center in the open field significantly
more frequently and spent more time in open arms during the elevated plus-maze
test under control conditions, as if they were less anxious than C57BL/6J mice,
and these indicators of abnormally low anxiety in BTBR mice were changed toward
the values for C57BL/6J mice after treatment with 0.05 mg/kg clonazepam (Figures 2G and 2H)
without sedation (Figure S2I).
Amelioration
of Cognitive Deficits by Treatment with Clonazepam
"Cognitive problems are often associated with ASD and
BTBR mice are known to have impaired fear memory. To test the effects of low dose
clonazepam on cognitive deficits, we performed context dependent fear
conditioning after treatment with increasing doses of clonazepam in both BTBR
and C57BL/6J mice (Figures 3A and 3B). Short-term (30 min) and
long-term (24 hr) memory performance in fear conditioning to the spatial
context in BTBR mice were improved by treatment with 0.05 mg/kg clonazepam, but
no significant effects were observed after treatment with 0.0125 mg/kg or 0.1
mg/kg clonazepam (Figures 3B and S3B). In
contrast, no cognitive changes were observed in C57BL/6J mice at any dose (Figures 3A and S3A)."
Rescue by a2,a3-Specific Positive
Allosteric Modulators of GABAA Receptors
"Diversity of GABA receptor function is conferred by more than 20 different
subunits, and receptors with different a subunits play distinct roles in the
physiological and pharmacological actions of GABA and benzodiazepines."
"These results indicate that different subtypes of GABAA receptors
may have opposite roles in social behavior, with activation of GABAA receptors
containing a2,3 subunits favoring
and activation of GABAA receptors with a1 subunits reducing social interaction,
respectively."
"Altogether, these experiments show that treatment with an a2,3-selective positive
allosteric modulator of GABAA receptors is sufficient to rescue autistic-like
behaviors and cognitive deficit in both a monogenic model of autism-spectrum
disorder and the BTBR mouse model of idiopathic autism."
"Subunit-selective GABAA receptor modulators may also have an
important effect on cognitive behaviors."
"The bell-shaped dose-response curves observed for both L-838,417 and
clonazepam may explain why high-dose benzodiazepine treatment for prevention of
anxiety and seizures has not been reported to improve autistic traits in ASD
patients."
Discussion
"Our results on mouse models of autism support the hypothesis that
social and cognitive deficits in ASDs may be caused by an increased ratio of
excitatory to inhibitory synaptic transmission."
"Therapeutic approaches to treat autistic traits in
animal studies or in clinical trials have primarily focused on reducing
excitatory neurotransmission in glutamatergic synapses to rebalance E/I ratio
in autistic brain. However,
autistic-like behaviors in ASD mouse models are only partially reversed by
drugs that inhibit excitatory neurotransmission, and these drugs also have
unwanted side effects on wild type mice. To overcome these drawbacks, we
focused on the opposing side, the GABAergic inhibitory transmission in
autistic brain. Our results highlight the potential for therapy of autistic like
behaviors and cognitive deficit in ASD by low-dose treatment with
subunit-selective benzodiazepines and other positive allosteric modulators of
GABAA receptors. At low
doses that do not induce sedative or anxiolytic effects, we found that
clonazepam, clobazam, and L-838,417 all improved autistic-like behaviors and cognitive
deficit in BTBR mice, supporting the hypothesis that a2,3-subunit-selective up regulation of GABAergic neurotransmission could
be an effective treatment for these core features of autism."
"Consistent with this view, Astra-Zeneca and the National
Institutes of Health have initiated clinical trials of the a2,3-selective
positive allosteric modulator of GABAA receptors, AZD7325, for efficacy in
autism."
Experiment number three
Experiment
number three is of course to test Dr Catterall’s idea about Clonazepam on humans. This has not yet been done, although a trial is planned with a similar drug AZD7325.
He suggests trialing
a low dose of clonazepam, but it is not clear exactly how low. There is mention of 10% of the normal dose. In
large doses, clonazepam is already prescribed in autism to reduce anxiety,
particularly in the US. At even larger
doses, clonazepam is used to treat seizures; given about 30% of people with
autism also have seizures, it would be fair to assume that some of those are
also prescribed clonazepam.
The downside
is that clonazepam is a benzodiazepine, and this class of drug
is habit forming. In extremely low doses,
perhaps this will not be a problem. For
anxiety, plenty of people have been prescribed it for 10+ years; the problem is
they cannot stop taking it.
The pharmacological property of clonazepam is modulation
of the GABAA receptor; based on the
mice, the effect is extremely dose dependent.
The wrong dose gives no beneficial effect. Bumetanide, which is affecting GABA in a very
similar way to make it inhibitory rather than excitory, seems to work like an
on/off switch. A low dose is
ineffective, the correct dose works and a larger dose works just the same.
The optimal dose of clonazepam will be hard to find, too
little does not work and neither does too much.
So for the time being it is rather trial and error.
By my calculations, a good place to start would be 0.8
Mcg (micrograms) per Kg per day and then titrate upwards gradually increasing the frequency and size of the doses.
The drug has a half-life that varies from person to
person; the average is 30 hours but can vary between 18 and 50 hours. This means that one child might need nearly 3
times as much as another, of similar weight.
To be an effective treatment the concentration of
clonazepam would have to be maintained within the effective range. This would need some clever maths, and might result
in 3 unequal daily doses, and that during sleep the concentration might be above range, and during daytime it be
held in range with one or two smaller top-up doses.
If you get the maths wrong, the drug would not work.
Conclusion
The jury is
out until we see the results of experiment three, or anecdotal evidence of some
home trials. One question I have is how this relates to the NaV1.1 ion channels referred to at the beginning
of this post. We know that a defect in
this ion channel will produce autism-like symptoms and that these can be
reversed (in mice) using the correct type of benzodiazepine,
such as clonazepam. If we find that in a
particular child with autism, clonazepam reduces their symptoms and increases
cognitive performance, can we claim the route cause was a dysfunction with NaV1.1 ion
channels? It is a bit of a leap of
faith, but I think it is a fair conclusion.
In which case of course, the logical next step would be to look at the
underlying gene, SCN1A; that I will leave to people much cleverer than
me.
The next
question is whether this therapy, which is reducing excitability of the
neurotransmitter GABA, is alternative or complementary to bumetanide which is,
in effect, doing exactly the same thing.
For that we would need Dr Catterall to talk to Dr Ben-Ari.
In case you
are wondering if there is another connection between Dr Catterall (Clonazepam) and Dr Ben-Ari (Bumetanide), there
is. The same man is part-funding both of
these research efforts – Jim Simons, via his Simons Foundation. As a former hedge fund manager, his is very
cleverly hedging his bets.