Reversal of relative thresholds for synaptic facilitation and increased excitability induced by serotonin and tail nerve stimulation in Aplysia sensory neurons

Neurobiology of Learning and Memory
S A BungeThomas J Carew

Abstract

Tail shock induces reflex sensitization in Aplysia and, in parallel, induces a number of modulatory effects in central neurons, such as increased excitability in tail sensory neurons (SNs) and facilitation of synaptic transmission from SNs to motor neurons. Both of these modulatory effects are mimicked by exogenous application of serotonin (5HT) or electrical stimulation of the tail nerve P9. In the present study we examined the activation thresholds for increased excitability and synaptic facilitation induced by either 5HT or P9 stimulation. We found that the concentration of 5HT sufficient to produce a significant increase in excitability produced no significant synaptic facilitation and, conversely, that the intensity of nerve stimulation sufficient to produce significant synaptic facilitation produced no excitability changes. This reversal of relative thresholds for these modulatory effects may reflect the differential access of exogenous 5HT and endogenous 5HT (released by tail nerve stimulation) to the SN cell body and synaptic terminals, respectively.

Citations

May 26, 1999·The Journal of Comparative Neurology·N J ErixonW G Wright
May 14, 2004·Journal of Neurophysiology·Stéphane MarinescoThomas J Carew
Nov 24, 1999·Canadian Journal of Physiology and Pharmacology·C H Bailey

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