[From: Bruce Nevin (Mon 930322 14:47:19)]
Belated note about an article on nervous systems of lobsters,
plus some stuff on leeches. Looks like a good place to look for
useful neurobiology literature because of the simplicity of these
systems, e.g. about 1000 neurons in the lobster's stomach, in
four ganglia.
The article is in _New Scientist_ for 27 February 1993, 24-28.
Although it is marred by a PopSci tone and lack of references,
and even more by commitment to presuppositions about "neural
commands" it does name major players to follow up in the
literature, and describes some intriguing findings. They were
looking for pattern generators for stomach rhythms (lobster) and
heart rhythms (leech). In each case, they talk about how
neurotransmitters affect how motor neurons "reinterpret" the
"commands" issued to them from the CNS. It would take someone
better versed by far than I in the issues to fathom what might be
going on in PCT terms. There does seem to be a CPG in the
lobster for its pylorus, which functions as a kind of filter
between the teeth in the first part of the stomach (the "gastric
mill") and the midgut, a single neuron called the "anterior
burster":
The main reason the neuron fires rhythmically is that its
membrane contains a complement of different ion channels that
open and close in a sequence that alterntely drives the neuron
to fire impulse bursts and then suppresses this activity. (26)
In the leech heart, on the other hand, there are pairs of
neurons, each of which in turn inhibits the other. "In effect,
the neurons act as a biological version of a simple electric
oscillator." (27)
What they go on most about is variation of these rhythms
determined by neurotransmitters, some with long-lasting effect in
the environment of many cells in a network, others with
short-term effects at a synapse (I may be overstating the
short-term/nearby long-term/widespread correlation). And some
hints about multifunctionality of supposedly specialized neurons.
Authors: Michael Nusbaum, Physiology & Biophysics at U. Alabama
Birmingham, Ronald Calabrese, Biophysics, Emory, Atlanta, GA.
Bruce
bn@bbn.com