Tag Archives: GABA

How complicated can neuropharmacology be?

A revolution is occurring in our thinking about the neurochemistry and treatment of depression.  Spectacular therapeutic results with ketamine imply that neurotransmission with glutamic acid is involved (see the older post below for the background)  In addition gamma amino butyric acid (GABA) may also be a player.  That’s why a recent review [ Neuron vol. 102 pp. 75 – 94 ’19 ] is worth a careful reading.

Like all new fields, early results are particularly confusing. In particular the statement was made that in addition to NMDA receptor blockers (such as ketamine) positive allosteric modifiers (PAMs) of the NMDAR also are therapeutic in depression (the latter in animal models only, a phase III trial in depression having failed).

So I wrote the lead author ”

Great review, but how do you reconcile the rapid antidepressant action of the NMDAR blocker ketamine and friends and an NMDAR PAM (positive allosteric modifier)”

I got the following back —

We have data indicating that ketamine blocks NMDA receptors on GABA neurons resulting in disinhibition and increased synaptic activity of principle neurons, whereas the PAM (rapastinel) acts directly on NMDA receptors on principle neurons to produce a similar downstream effect

It didn’t make sense that drugs having opposite effects on the same therapeutic target (the NMDAR) would have the same therapeutic effect.

So I wrote

If I understand you correctly, this implies that the subunit composition of the NMDARs at the two sites (GABA interneurons and principal neurons) is different.

I got the following back, which is positively Talmudic in its logical intricacy.

It could be the same receptor complex; because ketamine is an open channel blocker the GABA neurons, which are more active, would be more sensitive because activity is required to remove the Mg+2 block in the channel and thereby allow ketamine to enter and block the channel. The PAM does not require activity and could act at directly on principle neurons.

If this is correct, a lot of neuropharmacology on drug effects will require rethinking.  What does the readership think?

Stock tip — update

The FDA approved esketamine (Spravato) last week (see copy of original post at the end).  I had recommended buying Johnson and Johnson if the FDA approved it.  I think it’s a good long term buy, but there is no rush for the following reason — Esketamine is not a drug you can get a prescription for and take on you own. Because of the psychiatric side effects it must be administered in a SPRAVATO REMS.

Risk Evaluation and Mitigation Strategy (REMS): SPRAVATO™ is available only through a restricted program called the SPRAVATO™ REMS because of the risks of serious adverse outcomes from sedation, dissociation, and abuse and misuse.

Important requirements of the SPRAVATO™ REMS include the following:

  • Healthcare settings must be certified in the program and ensure that SPRAVATO™ is:
    • Only dispensed in healthcare settings and administered to patients who are enrolled in the program.
    • Administered by patients under the direct observation of a healthcare provider and that patients are monitored by a healthcare provider for at least 2 hours after administration of SPRAVATO™.
  • Pharmacies must be certified in the REMS and must only dispense SPRAVATO™ to healthcare settings that are certified in the program.

So you can’t go to some shady practitioner who’ll say you have treatment resistant depression and get some (e.g. the pill pushers for opiates, ‘medical’ marihuana  etc. etc.)

So there aren’t going to be hordes of users right away, although the stuff I’ve read implies that there will be eventually.

If you have a subscription to Cell have a look at vol. 101 pp. 774 – 778 ’19 by the guys at Yale who did some of the original work.  If not content yourself with this.

They are refreshingly honest.

Was the Discovery of Ketamine’s Antidepressant Serendipitous?Of course. However, its discovery emerged from the testing of a novel mechanistic hypothesis related to the pathophysiology of depression.”

Basically the authors rejected the regnant theory of depression, namely that the cause was to be found in monoamine neurotransmission (e.g. by dopamine, norepinephrine, serotonin).  There was some evidence that the cerebral cortex was involved in depression (not just the monamine nuclei of the brainstem), so they looked at the two major neurotransmitters in brain (glutamic acid, and GABA), and chose to see what would happen if they blocked one of the many receptors for glutamic acid, the NMDA receptor.  They chose ketamine to do this.
Here’s what they found,  A single dose of ketamine produced antidepressant effects that began within hours peaked in 24 – 72 hours and dissipated within 2 weeks (if ketamine wasn’t repeated).  This was in 50 – 75% people with treatment resistant depression.  Remarkable 1/3 of treated patients went into remission.    There simply has never been anything like this, which is why I thought the drug would be a blockbuster.
There is a lot of speculation about just which effect of esketamine is crucial (increase in glutamic acid release with AMPAR stimulation, brain derived neurotrophic factor (BDNF) release, TrkB receptor stimulation, mTORC1 activation, local protein synthesis, restoration of functional connectivity in functional MRI.   In animals one sees a rapid proliferation of dendritic spines.
As promised – here’s a copy of the first post

Stock tip

The past performance of stock recommendations is no guarantee that it will continue — which is fortunate as my first tip (ONTX) was a disaster.  I knew it was a 10 to one shot but with a 100 to 1 payoff.  People play the lottery with worse odds.  Anyway ONTX had a rationale — for the gory details see — https://luysii.wordpress.com/2016/06/01/in-a-gambling-mood/

For those brave souls who followed this recommendation (including yours truly) here’s another.

On 4 March 2019 if the FDA approves esketamine for depression, buy Johnson and Johnson.  Why?  Some people think that no drug for depression works that well, as big Pharma in the past only was reporting positive studies.  The following is from Nature 21 February 2019.

Depression drug A form of the hallucinogenic party drug ketamine has cleared one of the final hurdles towards clinical use as an antidepressant. During a 12 February meeting at the US Food and Drug Administration (FDA) in Silver Spring, Maryland,an independent advisory panel voted 14 to 2 in favour of recommending a compound known as esketamine for use in treating depression.

What’s so hot about esketamine?  First its mechanism of action is completely different than the SSRIs, Monoamine oxidase inhibitors, or tricyclic antidepressants.

As you likely know, antidepressants usually take a few weeks to work at least in endogenous depression.  My clinical experience as a neurologist is slightly different, as I only used it for patients with disease I couldn’t help (end stage MS etc. etc.) where the only normal response to the situation was depression.  They often helped patients within a week.

I was staggered when I read the following paper back in the day.  But there was no followup essentially.

archives of general psychiatry volume 63 pp. 856 – 864 2006
The paper is not from St. Fraudulosa Hospital in Plok Tic, but from the Mood Disorders Research Unit at the National Institute of Mental Health.
Here are the basics from the paper

Patients  Eighteen subjects with DSM-IV major depression (treatment resistant).

Interventions  After a 2-week drug-free period, subjects were given an intravenous infusion of either ketamine hydrochloride (0.5 mg/kg) or placebo on 2 test days, a week apart. Subjects were rated at baseline and at 40, 80, 110, and 230 minutes and 1, 2, 3, and 7 days postinfusion.

Main Outcome Measure  Changes in scores on the primary efficacy measure, the 21-item Hamilton Depression Rating Scale.

Results  Subjects receiving ketamine showed significant improvement in depression compared with subjects receiving placebo within 110 minutes after injection, which remained significant throughout the following week. The effect size for the drug difference was very large (d = 1.46 [95% confidence interval, 0.91-2.01]) after 24 hours and moderate to large (d = 0.68 [95% confidence interval, 0.13-1.23]) after 1 week. Of the 17 subjects treated with ketamine, 71% met response and 29% met remission criteria the day following ketamine infusion. Thirty-five percent of subjects maintained response for at least 1 week.

Read this again: showed significant improvement in depression compared with subjects receiving placebo within 110 minutes after injection, which remained significant throughout the following week.

This is absolutely unheard of.  Yet the paper essentially disappeared.

What is esketamine?  It’s related to ketamine (a veterinary anesthetic and drug of abuse) in exactly the same way that a glove for your left hand is related to a right handed glove.  The two drugs are optical isomers of each other.

What’s so important about the mirror image?  It means that esketamine may well act rather differently than ketamine (the fact that ketamine worked is against this).  The classic example is thalidomide, one optical isomer of which causes horrible malformations (phocomelia) while the other is a sedative used in the treatment of multiple myeloma and leprosy.

If toxic side effects can be avoided, the market is enormous.  It is estimated that 25% of women and 10% of men will have a major depression at some point in their lives.

Initially, Esketamine ( SPRAVATOTM)  will likely be limited to treatment resistant depression.  But depressed people will find a way to get it and  their docs will find a way to give it.  Who wants to wait three weeks.  Just think of the extremely sketchy ‘medical indications’ for marihuana.

 

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Stock tip — update

The FDA approved esketamine (Spravato) last week (see copy of original post at the end).  I had recommended buying Johnson and Johnson if the FDA approved it.  I think it’s a good long term buy, but there is no rush for the following reason — Esketamine is not a drug you can get a prescription for and take on you own. Because of the psychiatric side effects it must be administered in a SPRAVATO REMS.

Risk Evaluation and Mitigation Strategy (REMS): SPRAVATO™ is available only through a restricted program called the SPRAVATO™ REMS because of the risks of serious adverse outcomes from sedation, dissociation, and abuse and misuse.

Important requirements of the SPRAVATO™ REMS include the following:

  • Healthcare settings must be certified in the program and ensure that SPRAVATO™ is:
    • Only dispensed in healthcare settings and administered to patients who are enrolled in the program.
    • Administered by patients under the direct observation of a healthcare provider and that patients are monitored by a healthcare provider for at least 2 hours after administration of SPRAVATO™.
  • Pharmacies must be certified in the REMS and must only dispense SPRAVATO™ to healthcare settings that are certified in the program.

So you can’t go to some shady practitioner who’ll say you have treatment resistant depression and get some (e.g. the pill pushers for opiates, ‘medical’ marihuana  etc. etc.)

So there aren’t going to be hordes of users right away, although the stuff I’ve read implies that there will be eventually.

If you have a subscription to Cell have a look at vol. 101 pp. 774 – 778 ’19 by the guys at Yale who did some of the original work.  If not content yourself with this.

They are refreshingly honest.

Was the Discovery of Ketamine’s Antidepressant Serendipitous?Of course. However, its discovery emerged from the testing of a novel mechanistic hypothesis related to the pathophysiology of depression.”

Basically the authors rejected the regnant theory of depression, namely that the cause was to be found in monoamine neurotransmission (e.g. by dopamine, norepinephrine, serotonin).  There was some evidence that the cerebral cortex was involved in depression (not just the monamine nuclei of the brainstem), so they looked at the two major neurotransmitters in brain (glutamic acid, and GABA), and chose to see what would happen if they blocked one of the many receptors for glutamic acid, the NMDA receptor.  They chose ketamine to do this.
Here’s what they found,  A single dose of ketamine produced antidepressant effects that began within hours peaked in 24 – 72 hours and dissipated within 2 weeks (if ketamine wasn’t repeated).  This was in 50 – 75% people with treatment resistant depression.  Remarkable 1/3 of treated patients went into remission.    There simply has never been anything like this, which is why I thought the drug would be a blockbuster.
There is a lot of speculation about just which effect of esketamine is crucial (increase in glutamic acid release with AMPAR stimulation, brain derived neurotrophic factor (BDNF) release, TrkB receptor stimulation, mTORC1 activation, local protein synthesis, restoration of functional connectivity in functional MRI.   In animals one sees a rapid proliferation of dendritic spines.
As promised – here’s a copy of the first post

Stock tip

The past performance of stock recommendations is no guarantee that it will continue — which is fortunate as my first tip (ONTX) was a disaster.  I knew it was a 10 to one shot but with a 100 to 1 payoff.  People play the lottery with worse odds.  Anyway ONTX had a rationale — for the gory details see — https://luysii.wordpress.com/2016/06/01/in-a-gambling-mood/

For those brave souls who followed this recommendation (including yours truly) here’s another.

On 4 March 2019 if the FDA approves esketamine for depression, buy Johnson and Johnson.  Why?  Some people think that no drug for depression works that well, as big Pharma in the past only was reporting positive studies.  The following is from Nature 21 February 2019.

Depression drug A form of the hallucinogenic party drug ketamine has cleared one of the final hurdles towards clinical use as an antidepressant. During a 12 February meeting at the US Food and Drug Administration (FDA) in Silver Spring, Maryland,an independent advisory panel voted 14 to 2 in favour of recommending a compound known as esketamine for use in treating depression.

What’s so hot about esketamine?  First its mechanism of action is completely different than the SSRIs, Monoamine oxidase inhibitors, or tricyclic antidepressants.

As you likely know, antidepressants usually take a few weeks to work at least in endogenous depression.  My clinical experience as a neurologist is slightly different, as I only used it for patients with disease I couldn’t help (end stage MS etc. etc.) where the only normal response to the situation was depression.  They often helped patients within a week.

I was staggered when I read the following paper back in the day.  But there was no followup essentially.

archives of general psychiatry volume 63 pp. 856 – 864 2006
The paper is not from St. Fraudulosa Hospital in Plok Tic, but from the Mood Disorders Research Unit at the National Institute of Mental Health.
Here are the basics from the paper

Patients  Eighteen subjects with DSM-IV major depression (treatment resistant).

Interventions  After a 2-week drug-free period, subjects were given an intravenous infusion of either ketamine hydrochloride (0.5 mg/kg) or placebo on 2 test days, a week apart. Subjects were rated at baseline and at 40, 80, 110, and 230 minutes and 1, 2, 3, and 7 days postinfusion.

Main Outcome Measure  Changes in scores on the primary efficacy measure, the 21-item Hamilton Depression Rating Scale.

Results  Subjects receiving ketamine showed significant improvement in depression compared with subjects receiving placebo within 110 minutes after injection, which remained significant throughout the following week. The effect size for the drug difference was very large (d = 1.46 [95% confidence interval, 0.91-2.01]) after 24 hours and moderate to large (d = 0.68 [95% confidence interval, 0.13-1.23]) after 1 week. Of the 17 subjects treated with ketamine, 71% met response and 29% met remission criteria the day following ketamine infusion. Thirty-five percent of subjects maintained response for at least 1 week.

Read this again: showed significant improvement in depression compared with subjects receiving placebo within 110 minutes after injection, which remained significant throughout the following week.

This is absolutely unheard of.  Yet the paper essentially disappeared.

What is esketamine?  It’s related to ketamine (a veterinary anesthetic and drug of abuse) in exactly the same way that a glove for your left hand is related to a right handed glove.  The two drugs are optical isomers of each other.

What’s so important about the mirror image?  It means that esketamine may well act rather differently than ketamine (the fact that ketamine worked is against this).  The classic example is thalidomide, one optical isomer of which causes horrible malformations (phocomelia) while the other is a sedative used in the treatment of multiple myeloma and leprosy.

If toxic side effects can be avoided, the market is enormous.  It is estimated that 25% of women and 10% of men will have a major depression at some point in their lives.

Initially, Esketamine ( SPRAVATOTM)  will likely be limited to treatment resistant depression.  But depressed people will find a way to get it and  their docs will find a way to give it.  Who wants to wait three weeks.  Just think of the extremely sketchy ‘medical indications’ for marihuana.

Memories are made of this ?

Back in the day when information was fed into computers on punch cards, the data was the holes in the paper not the paper itself. A far out (but similar) theory of how memories are stored in the brain just got a lot more support [ Neuron vol. 93 pp. 6 -8, 132 – 146 ’17 ].

The theory says that memories are stored in the proteins and sugar polymers surrounding neurons rather than the neurons themselves. These go by the name of extracellular matrix, and memories are the holes drilled in it which allow synapses to form.

Here’s some stuff I wrote about the idea when I first ran across it two years ago.

——

An article in Science (vol. 343 pp. 670 – 675 ’14) on some fairly obscure neurophysiology at the end throws out (almost as an afterthought) an interesting idea of just how chemically and where memories are stored in the brain. I find the idea plausible and extremely surprising.

You won’t find the background material to understand everything that follows in this blog. Hopefully you already know some of it. The subject is simply too vast, but plug away. Here a few, seriously flawed in my opinion, theories of how and where memory is stored in the brain of the past half century.

#1 Reverberating circuits. The early computers had memories made of something called delay lines (http://en.wikipedia.org/wiki/Delay_line_memory) where the same impulse would constantly ricochet around a circuit. The idea was used to explain memory as neuron #1 exciting neuron #2 which excited neuron . … which excited neuron #n which excited #1 again. Plausible in that the nerve impulse is basically electrical. Very implausible, because you can practically shut the whole brain down using general anesthesia without erasing memory. However, RAM memory in the computers of the 70s used the localized buildup of charge to store bits and bytes. Since charge would leak away from where it was stored, it had to be refreshed constantly –e.g. at least 12 times a second, or it would be lost. Yet another reason data should always be frequently backed up.

#2 CaMKII — more plausible. There’s lots of it in brain (2% of all proteins in an area of the brain called the hippocampus — an area known to be important in memory). It’s an enzyme which can add phosphate groups to other proteins. To first start doing so calcium levels inside the neuron must rise. The enzyme is complicated, being comprised of 12 identical subunits. Interestingly, CaMKII can add phosphates to itself (phosphorylate itself) — 2 or 3 for each of the 12 subunits. Once a few phosphates have been added, the enzyme no longer needs calcium to phosphorylate itself, so it becomes essentially a molecular switch existing in two states. One problem is that there are other enzymes which remove the phosphate, and reset the switch (actually there must be). Also proteins are inevitably broken down and new ones made, so it’s hard to see the switch persisting for a lifetime (or even a day).

#3 Synaptic membrane proteins. This is where electrical nerve impulses begin. Synapses contain lots of different proteins in their membranes. They can be chemically modified to make the neuron more or less likely to fire to a given stimulus. Recent work has shown that their number and composition can be changed by experience. The problem is that after a while the synaptic membrane has begun to resemble Grand Central Station — lots of proteins coming and going, but always a number present. It’s hard (for me) to see how memory can be maintained for long periods with such flux continually occurring.

This brings us to the Science paper. We know that about 80% of the neurons in the brain are excitatory — in that when excitatory neuron #1 talks to neuron #2, neuron #2 is more likely to fire an impulse. 20% of the rest are inhibitory. Obviously both are important. While there are lots of other neurotransmitters and neuromodulators in the brains (with probably even more we don’t know about — who would have put carbon monoxide on the list 20 years ago), the major inhibitory neurotransmitter of our brains is something called GABA. At least in adult brains this is true, but in the developing brain it’s excitatory.

So the authors of the paper worked on why this should be. GABA opens channels in the brain to the chloride ion. When it flows into a neuron, the neuron is less likely to fire (in the adult). This work shows that this effect depends on the negative ions (proteins mostly) inside the cell and outside the cell (the extracellular matrix). It’s the balance of the two sets of ions on either side of the largely impermeable neuronal membrane that determines whether GABA is excitatory or inhibitory (chloride flows in either event), and just how excitatory or inhibitory it is. The response is graded.

For the chemists: the negative ions outside the neurons are sulfated proteoglycans. These are much more stable than the proteins inside the neuron or on its membranes. Even better, it has been shown that the concentration of chloride varies locally throughout the neuron. The big negative ions (e.g. proteins) inside the neuron move about but slowly, and their concentration varies from point to point.

Here’s what the authors say (in passing) “the variance in extracellular sulfated proteoglycans composes a potential locus of analog information storage” — translation — that’s where memories might be hiding. Fascinating stuff. A lot of work needs to be done on how fast the extracellular matrix in the brain turns over, and what are the local variations in the concentration of its components, and whether sulfate is added or removed from them and if so by what and how quickly.

—-

So how does the new work support this idea? It involves a structure that I’ve never talked about — the lysosome (for more info see https://en.wikipedia.org/wiki/Lysosome). It’s basically a bag of at least 40 digestive and synthetic enzymes inside the cell, which chops anything brought to it (e.g. bacteria). Mutations in the enzymes cause all sorts of (fortunately rare) neurologic diseases — mucopolysaccharidoses, lipid storage diseases (Gaucher’s, Farber’s) the list goes on and on.

So I’ve always thought of the structure as a Pandora’s box best kept closed. I always thought of them as confined to the cell body, but they’re also found in dendrites according to this paper. Even more interesting, a rather unphysiologic treatment of neurons in culture (depolarization by high potassium) causes the lysosomes to migrate to the neuronal membrane and release its contents outside. One enzyme released is cathepsin B, a proteolytic enzyme which chops up the TIMP1 outside the cell. So what. TIMP1 is an endogenous inhibitor of Matrix MetalloProteinases (MMPs) which break down the extracellular matrix. So what?

Are neurons ever depolarized by natural events? Just by synaptic transmission, action potentials and spontaneously. So here we have a way that neuronal activity can cause holes in the extracellular matrix,the holes in the punch cards if you will.

Speculation? Of course. But that’s the fun of reading this stuff. As Mark Twain said ” There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.”

Thrust and Parry about memory storage outside neurons.

First the post of 23 Feb ’14 discussing the paper (between *** and &&& in case you’ve read it already)

Then some of the rather severe criticism of the paper.

Then some of the reply to the criticisms

Then a few comments of my own, followed by yet another old post about the chemical insanity neuroscience gets into when they apply concepts like concentration to very small volumes.

Enjoy
***
Are memories stored outside of neurons?

This may turn out to be a banner year for neuroscience. Work discussed in the following older post is the first convincing explanation of why we need sleep that I’ve seen.https://luysii.wordpress.com/2013/10/21/is-sleep-deprivation-like-alzheimers-and-why-we-need-sleep-in-the-first-place/

An article in Science (vol. 343 pp. 670 – 675 ’14) on some fairly obscure neurophysiology at the end throws out (almost as an afterthought) an interesting idea of just how chemically and where memories are stored in the brain. I find the idea plausible and extremely surprising.

You won’t find the background material to understand everything that follows in this blog. Hopefully you already know some of it. The subject is simply too vast, but plug away. Here a few, seriously flawed in my opinion, theories of how and where memory is stored in the brain of the past half century.

#1 Reverberating circuits. The early computers had memories made of something called delay lines (http://en.wikipedia.org/wiki/Delay_line_memory) where the same impulse would constantly ricochet around a circuit. The idea was used to explain memory as neuron #1 exciting neuron #2 which excited neuron . … which excited neuron #n which excited #1 again. Plausible in that the nerve impulse is basically electrical. Very implausible, because you can practically shut the whole brain down using general anesthesia without erasing memory.

#2 CaMKII — more plausible. There’s lots of it in brain (2% of all proteins in an area of the brain called the hippocampus — an area known to be important in memory). It’s an enzyme which can add phosphate groups to other proteins. To first start doing so calcium levels inside the neuron must rise. The enzyme is complicated, being comprised of 12 identical subunits. Interestingly, CaMKII can add phosphates to itself (phosphorylate itself) — 2 or 3 for each of the 12 subunits. Once a few phosphates have been added, the enzyme no longer needs calcium to phosphorylate itself, so it becomes essentially a molecular switch existing in two states. One problem is that there are other enzymes which remove the phosphate, and reset the switch (actually there must be). Also proteins are inevitably broken down and new ones made, so it’s hard to see the switch persisting for a lifetime (or even a day).

#3 Synaptic membrane proteins. This is where electrical nerve impulses begin. Synapses contain lots of different proteins in their membranes. They can be chemically modified to make the neuron more or less likely to fire to a given stimulus. Recent work has shown that their number and composition can be changed by experience. The problem is that after a while the synaptic membrane has begun to resemble Grand Central Station — lots of proteins coming and going, but always a number present. It’s hard (for me) to see how memory can be maintained for long periods with such flux continually occurring.

This brings us to the Science paper. We know that about 80% of the neurons in the brain are excitatory — in that when excitatory neuron #1 talks to neuron #2, neuron #2 is more likely to fire an impulse. 20% of the rest are inhibitory. Obviously both are important. While there are lots of other neurotransmitters and neuromodulators in the brains (with probably even more we don’t know about — who would have put carbon monoxide on the list 20 years ago), the major inhibitory neurotransmitter of our brains is something called GABA. At least in adult brains this is true, but in the developing brain it’s excitatory.

So the authors of the paper worked on why this should be. GABA opens channels in the brain to the chloride ion. When it flows into a neuron, the neuron is less likely to fire (in the adult). This work shows that this effect depends on the negative ions (proteins mostly) inside the cell and outside the cell (the extracellular matrix). It’s the balance of the two sets of ions on either side of the largely impermeable neuronal membrane that determines whether GABA is excitatory or inhibitory (chloride flows in either event), and just how excitatory or inhibitory it is. The response is graded.

For the chemists: the negative ions outside the neurons are sulfated proteoglycans. These are much more stable than the proteins inside the neuron or on its membranes. Even better, it has been shown that the concentration of chloride varies locally throughout the neuron. The big negative ions (e.g. proteins) inside the neuron move about but slowly, and their concentration varies from point to point.

Here’s what the authors say (in passing) “the variance in extracellular sulfated proteoglycans composes a potential locus of analog information storage” — translation — that’s where memories might be hiding. Fascinating stuff. A lot of work needs to be done on how fast the extracellular matrix in the brain turns over, and what are the local variations in the concentration of its components, and whether sulfate is added or removed from them and if so by what and how quickly.

We’ve concentrated so much on neurons, that we may have missed something big. In a similar vein, the function of sleep may be to wash neurons free of stuff built up during the day outside of them.

&&&

In the 5 September ’14 Science (vol. 345 p. 1130) 6 researchers from Finland, Case Western Reserve and U. California (Davis) basically say the the paper conflicts with fundamental thermodynamics so severely that “Given these theoretical objections to their interpretations, we choose not to comment here on the experimental results”.

In more detail “If Cl− were initially in equilibrium across a membrane, then the mere introduction of im- mobile negative charges (a passive element) at one side of the membrane would, according to their line of thinking, cause a permanent change in the local electrochemical potential of Cl−, there- by leading to a persistent driving force for Cl− fluxes with no input of energy.” This essentially accuses the authors of inventing a perpetual motion machine.

Then in a second letter, two more researchers weigh in (same page) — “The experimental procedures and results in this study are insufficient to support these conclusions. Contradictory results previously published by these authors and other laboratories are not referred to.”

The authors of the original paper don’t take this lying down. On the same page they discuss the notion of the Donnan equilibrium and say they were misinterpreted.

The paper, and the 3 letters all discuss the chloride concentration inside neurons which they call [Cl-]i. The problem with this sort of thinking (if you can call it that) is that it extrapolates the notion of concentration to very small volumes (such as a dendritic spine) where it isn’t meaningful. It goes on all the time in neuroscience. While between any two small rational numbers there is another, matter can be sliced only so thinly without getting down to the discrete atomic level. At this level concentration (which is basically a ratio between two very large numbers of molecules e.g. solute and solvent) simply doesn’t apply.

Here’s a post on the topic from a few months ago. It contains a link to another post showing that even Nobelists have chemical feet of clay.

More chemical insanity from neuroscience

The current issue of PNAS contains a paper (vol. 111 pp. 8961 – 8966, 17 June ’14) which uncritically quotes some work done back in the 80’s and flatly states that synaptic vesicles http://en.wikipedia.org/wiki/Synaptic_vesicle have a pH of 5.2 – 5.7. Such a value is meaningless. Here’s why.

A pH of 5 means that there are 10^-5 Moles of H+ per liter or 6 x 10^18 actual ions/liter.

Synaptic vesicles have an ‘average diameter’ of 40 nanoMeters (400 Angstroms to the chemist). Most of them are nearly spherical. So each has a volume of

4/3 * pi * (20 * 10^-9)^3 = 33,510 * 10^-27 = 3.4 * 10^-23 liters. 20 rather than 40 because volume involves the radius.

So each vesicle contains 6 * 10^18 * 3.4 * 10^-23 = 20 * 10^-5 = .0002 ions.

This is similar to the chemical blunders on concentration in the nano domain committed by a Nobelist. For details please see — https://luysii.wordpress.com/2013/10/09/is-concentration-meaningful-in-a-nanodomain-a-nobel-is-no-guarantee-against-chemical-idiocy/

Didn’t these guys ever take Freshman Chemistry?

Addendum 24 June ’14

Didn’t I ever take it ? John wrote the following this AM

Please check the units in your volume calculation. With r = 10^-9 m, then V is in m^3, and m^3 is not equal to L. There’s 1000 L in a m^3.
Happy Anniversary by the way.

To which I responded

Ouch ! You’re correct of course. However even with the correction, the results come out to .2 free protons (or H30+) per vesicle, a result that still makes no chemical sense. There are many more protons in the vesicle, but they are buffered by the proteins and the transmitters contained within.

Just when you thought you understood neurotransmission

Back in the day, the discovery of neurotransmission allowed us to think we understood how the brain worked. I remember explaining to medical students in the early 70s, that the one way flow of information from the presynaptic neuron to the post-synaptic one was just like the flow of current in a vacuum tube — yes a vacuum tube, assuming anyone reading knows what one is. Later I changed this to transistor when integrated circuits became available.

Also the Dale hypothesis as it was taught to me, was that a given neuron released the same neurotransmitter at all its endings. As it was taught back in the 60s this meant that just one transmitter was released by a given neuron.

Retrograde transmission was just a glimmer in the mind’s eye back then. We now know that the post-synaptic neuron releases compounds which affect the presynaptic neuron, the supposed controller of the postsynaptic neuron. Among them are carbon monoxide, and the endocannabinoids (e. g. what marihuana is trying to mimic).

In addition there are neurotransmitter receptors on the presynaptic neuron, which respond to what it and other neurons are releasing to control its activity. These are outside the synapse itself. These events occur more slowly than the millisecond responses in the synapse to the main excitatory neurotransmitter of the brain (glutamic acid) and the main inhibitory neurotransmitter (gamma amino butyric acid — aka GABA). Receptors on the presynaptic neuron for the transmitter it’s releasing are called autoreceptors, but the presynaptic terminal also contains receptors for other neurotransmitters.

Well at least, neurotransmitters aren’t released by the presynaptic neuron without an action potential which depolarizes the presynaptic terminal, or so we thought until [ Neuron vol. 82 pp. 63 – 70 ’14 ]. The report involves a structure near and dear to the neurologist the striatum (caudate and putamen — which is striated because the myelinated axons of the internal capsule go through its anterior end giving it a striated appearance).

It is the death of the dopamine containing neurons in the substantial nigra which cause Parkinsonism. They project some of their axons to the striatum. The striatum gets input elsewhere (from the cortex using glutamic acid) and from neurons intrinsic to itself (some of which use acetyl choline as their neurotransmitter — these are called cholinergic interneurons).

The paper makes the claim that the dopamine neurons projecting to the striatum also contain the inhibitory neurotransmitter GABA.

The paper also says that the cholinergic interneurons cause release of GABA by the dopamine neurons — they bind to a type of acetyl choline receptor called nicotinic (similar but not identical to the nicotinic receptors which allow our muscles to contract) in the presynaptic terminals of the dopamine neurons of the substantial nigra residing in the striatum. Isn’t medicine and neuroanatomy a festival of terms? It’s why you need a good memory to survive medical school.

These used optogenetics (something I don’t have time to explain — but see http://en.wikipedia.org/wiki/Optogenetics ) to selectively stimulate the 1 – 2% of striatal neurons which use acetyl choline as a neurotransmitter. What they found was that only GABA (and not dopamine) was released by the dopamine neurons in response to stimulating this small subset of neurons. Even more amazing, the GABA release occurred without an action potential depolarizing the presynaptic terminal.

This literally stands everything I thought I knew about neurotransmission on its ear. How widespread this phenomenon actually is, isn’t known at this point. Clearly, the work needs to be replicated — extreme claims require extreme evidence.

Unfortunately I’ve never provided much background on neurotransmission for the hapless chemists and medicinal chemists reading this (if there are any), but medicinal chemists must at least have a smattering of knowledge about this, since neurotransmission is involved in how large classes of CNS active drugs work — antidepressants, antipsychotics, anticonvulsants, migraine therapy. There is some background on this here — https://luysii.wordpress.com/2010/08/29/some-basic-pharmacology-for-the-college-student/