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[Neuroscience] Re: cell numbers in hippocampus

jonesmat via neur-sci%40net.bio.net (by jonesmat from physiology.wisc.edu)
Thu May 31 15:09:38 EST 2007

On May 31, 9:51 am, Mathias <mathiasDOTfranz... from webDELETEME.de> wrote:
> I'll answer myself in case someone else is interested in the same
> question later. I found an article by Olbrich and Braak (1985) in Anat.
> Embryol. 173:105-110 stating that in the human hippocampal area CA1 less
> than 10% of the neurons are not pyramidal cells. They also cite similar
> results for rats and monkeys in the discussion section.
> Thus I think one can estimate that the rat CA1 (of a single hippocampus)
> has approx. 355.000 pyramidal cells.
> hthsl (hope this helps someone later ;)
>     Mathias


Thanks for those references. They are helpful.

I wonder, though, if the small number of interneurons might be a bit
deceptive, functionally.

They make enormous numbers of synapses onto pyramidal cells and each
other. I think each interneuron may make tens of thousands of
synapses, spanning several hundred microns, and contacting hundreds or
thousands of pyramidal cells. I can't remember the exact papers where
these things were measured in CA1, but I think this is reviewed in the
big Freund & Buszaki "Interneurons of the Hippocampus" paper.

Also, Steve Cobb & Eberhard Buhl (r.i.p.) and colleagues showed that a
single spike in a single interneuron is capable of synchronizing the
firing of the field of pyramidal cells that it contacts.

Just putting in my usual plug for the importance of inhibitory
systems. The mouse that roared, as it were...



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