Identification and Characterization of Catecholaminergic Neuron B65 that
Initiates and Modifies Patterned Activity in the Buccal Ganglia of Aplysia.
E.A.Kabotyanski, D.A.Baxter and J.H.Byrn.
Laboratory of Origin: Department of Neurobiology and Anatomy, The
University of Texas-Houston Medical School, Houston, TX 77030.
APStracts 4:286N, 1997.
ABSTRACT
Catecholamines are believed to play an important role in regulating the
properties and functional organization of the neural circuitry mediating
consummatory feeding behaviors in Aplysia. In the present study, we
morphologically and electrophysiologically identified a pair of
catecholaminergic neurons in the buccal ganglia. The somata of these
interneurons, referred to as B65, are located under the caudal surface of
thein the buccal ganglia. Their processes innervate both the ipsi- and
contralateral neuropil, and separate branches of B65 appeared to innervate the
somata of both ipsi- and contralateral B4/5 neurons. B65 was typically silent,
with an average resting potential of -52.2 +1.1 mV (mean +S.E.M.). The cell
exhibited patterned burst(s) of activity along with other buccal neurons
during spontaneous cycles of patterned activityfictive feeding. Patterned
activity in B65 was also elicited by stimulation of the radula nerve, by
depolarization of the pattern initiating neurons B31/32 or B63, and by bath
application of L-3,4-dihydroxyphenylalanine (DOPA). B65 appeared to be a
member of the protraction group of neurons. Action potentials in B65 elicited
fast one-for-one excitatory postsynaptic potentials (EPSPs) in neurons B4/5,
B8A/B, B31/32, B63, and B64. In turn, B31/32 and B63 excited B65, and B64
inhibited B65. Some of the synaptic connections of B65 were plastic. For
example, the fast EPSPs elicited in B4/5 and B64 by B65 decremented, whereas
those in B31/32 and B8A/B facilitated. In addition to fast EPSPs, B65 elicited
slow postsynaptic potentials in some of its follower cells.
A brief dDepolarization of B65 could elicited a single cycles of patterned
activity indicative of fictive feeding, whereas sustained depolarization could
elicit multiple cycles in buccal neurons, including B65 itself. During
repeated series of B65-induced cycles patterns, the properties of the buccal
motor programs appeared to change. In particular, the activity of radula
closure motor neurons B8A/B, which initially coincided mainly with the
protraction phase of a cycle, gradually extended into overlap mostly with the
retraction phase. This observation suggests that prolonged activity in B65 may
play a role in transitioning from rejection-like to ingestion-like fictive
feeding. The phase shift of the increased activity of B8A/B during the
retraction phase appears due, at least in part, to a decrease in activity of
B4/5, and thus a reduction in inhibition from B4/5 onto B8A/B, during the
retraction phase. The functional properties and synaptic connections of B65
suggest that it may play an important role in determining features of
patterned neural activity in the buccal ganglia.
Received 13 June 1997; accepted in final form 14 October 1997.
APS Manuscript Number J495-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 29 October 1997