Re: Brain/Body Weight

[rowe@lepomis.psych.upenn.edu (Mickey Rowe)]

Mike Styzen asks:

>I think I remember reading a few years back that birds have a
>different enzyme in thier synapses than mamals do, one that makes
>thier nervous systems more efficient so a smaller brain does a bigger
>job.

I don't know to what exactly you might be referring, but I suspect
that any claims indicating the above were at best premature, and most
likely inaccurate.  In the first place, there are many many proteins
associated with synapses, and the exact constituency can vary quite a
bit within an individual brain let alone across species.  Second,
unless you mean to include proteins within the cell membranes on
either side of the synapse, I think that most of the proteins
associated with synapses are not enzymes.  Third (and most important),
we don't know enough about "efficiency" in nervous systems to make any
sorts of general claims with any real support, and what we can
reasonably infer suggests that no such sweeping claim is likely to be
borne out in the long run.  If the avian version of, say Acetyl
Cholinesterase (AChE), worked faster than the mammalian version, would
that make the system "more efficient"?  In what sense?  In actuality,
many neurotransmitters work by modulating the effectiveness of other
neurotransmitters.  This can be done, among other ways, by modulating
the amount of enzyme (such as AChE) floating around in the synapse.
In other words, its not like there's a fixed amount of enzyme, or a
fixed amount of enzyme activity for each synapse.  Enzyme activity is
probably modulated constantly at each synapse, and whether having more
or less at any given time is the "efficient" way to do things will
depend on what other neurons (not to mention the whole organism) are
doing at the time.  Sorry, but to me the claim that a single enzyme
difference can predict something about global efficiency sounds about
as far fetched as the claim that we could build a T rex from
mosquitoes in amber.

Just thought I'd take my turn on the soap box :-)

-- 
Mickey Rowe     (rowe@lepomis.psych.upenn.edu)

P.S. If you do remember more, or if anyone else recognizes Mike's
claim and can fill in details, I'd love to hear about it, so that we
can talk in specifics instead of generalities.