Rj. Frysztak et T. Crow, ENHANCEMENT OF TYPE-B AND TYPE-A PHOTORECEPTOR INHIBITORY SYNAPTIC CONNECTIONS IN CONDITIONED HERMISSENDA, The Journal of neuroscience, 14(3), 1994, pp. 1245-1250
Intrinsic changes have been identified in isolated and intact type A a
nd type B photoreceptors following classical conditioning of the nudib
ranch mollusk Hermissenda. Aspects of various intrinsic, nonsynaptic m
odifications are expressed by alterations in the excitability of ident
ified photoreceptors in response to the conditioned stimulus. In addit
ion to changes in cellular excitability, changes in synaptic strength
between identified neurons have been proposed as a possible mechanism
of associative learning in several invertebrate preparations. Here we
report that classical conditioning produces differential effects upon
the strength of inhibitory monosynaptic connections between identified
pairs of type B and type A photoreceptors. The amplitude of IPSPs eli
cited by an action potential in the medial type B photoreceptor and re
corded from medial type A photoreceptors was significantly enhanced in
conditioned animals as compared to pseudorandom controls. In contrast
, the amplitude of IPSPs elicited by an action potential in the latera
l type B photoreceptor and recorded from lateral type A photoreceptors
did not show significant synaptic enhancement following conditioning.
These results provide additional evidence for differential effects of
conditioning upon cellular modifications in identified type A and typ
e B photoreceptors, and further indicate that multiple sites of cellul
ar plasticity exist in the visual system of conditioned Hermissenda.