Time-Dependent Changes in Excitability Following One-Trial Conditioning of Hermissenda. Terry Crow and Vilma Siddiqi. Department of Neurobiology and Anatomy, The University of Texas Medical School, P.O. Box 20708, Houston, TX 77225.
APStracts 4:228N, 1997.
ABSTRACT
The visual system of Hermissenda has been studied extensively as a site of cellular plasticity produced by classical conditioning. A one-trial conditioning procedure consisting of light paired with the application of 5-HT to he exposed, but otherwise intact nervous system produces suppression of phototactic behavior tested 24 hrs after conditioning. Short- and long-term enhancement (STE and LTE) of excitability in identified type B-photoreceptors is a cellular correlate of one-trial conditioning. LTE can be expressed in the absence of STE suggesting that STE and LTE may be parallel processes. To examine the development of enhancement, we have studied its time-dependent alterations following one-trial conditioning. Intracellular recordings from identified type B photoreceptors of independent groups collected at different times following conditioning revealed that enhanced excitability follows a biphasic pattern in its development. The analysis of spikes elicited by 2 sec and 30 sec extrinsic current pulses at different levels of depolarization showed that enhancement reached a peak 3 hrs after conditioning. From its peak, excitability decreased toward baseline control levels 5-6 hrs after conditioning followed by an increase to a stable plateau at 16 to 24 hrs post- conditioning. Excitability changes measured in cells from unpaired control groups showed maximal changes 1 hr post-treatment that rapidly decremented within 2 hrs. The conditioned stimulus (CS) elicited significantly more spikes 24 hr post-conditioning for the conditioned group as compared to the unpaired control group. The analysis of the time-dependent development of enhancement may reveal the processes underlying different stages of memory for this associative experience. 

Received 11 July 1997; accepted in final form 3 September 1997.
APS Manuscript Number J575-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 7 October 1997