Modulation of defensive reflex conditioning in snails by serotonin.

Vyatcheslav V. Andrianov,Lyudmila N. Muranova,Khalil L. Gainutdinov,Irina B. Deryabina,Tatiana K. Bogodvid,Aleksandra N. Golovchenko,Roza R. Tagirova,Aliya K. Vinarskaya

doi:10.3389/fnbeh.2015.00279

Abstract

Highlights Daily injection of serotonin before a training session accelerated defensive reflex conditioning in snails.Daily injection of 5-hydroxytryptophan before a training session in snails with a deficiency of serotonin induced by the “neurotoxic” analog of serotonin 5,7-dihydroxytryptamine, restored the ability of snails to learn.After injection of the “neurotoxic” analogs of serotonin 5,6- and 5,7-dihydroxytryptamine as well as serotonin, depolarization of the membrane and decrease of the threshold potential of premotor interneurons was observed.We studied the role of serotonin in the mechanisms of learning in terrestrial snails. To produce a serotonin deficit, the “neurotoxic” analogs of serotonin, 5,6- or 5,7-dihydroxytryptamine (5,6/5,7-DHT) were used. Injection of 5,6/5,7-DHT was found to disrupt defensive reflex conditioning. Within 2 weeks of neurotoxin application, the ability to learn had recovered. Daily injection of serotonin before a training session accelerated defensive reflex conditioning and daily injections of 5-HTP in snails with a deficiency of serotonin induced by 5,7-DHT restored the snail's ability to learn. We discovered that injections of the neurotoxins 5,6/5,7-DHT as well as serotonin, caused a decrease in the resting and threshold potentials of the premotor interneurons LPa3 and RPa3.

Highlights

One of the widespread and well-investigated transmitters in the nervous system is serotonin (Kandel and Schwartz, 1982; Sakharov, 1990; Crow, 2004; Gillette, 2006)
It was found that the injection of the neurotoxin 5,7-DHT led to a significant decrease in the withdrawal reflex caused by tail shock and inhibited the heterosynaptic facilitation between the sensory neuron and the subsequent cells in Aplysia (Glanzman et al, 1989)
The defensive reflex conditioning on shell tapping was achieved within 6 days with the use of 300–350 repetitions of a combination of shell tapping and air blowing into pneumostome in the case of the second protocol (Figures 1A,B, saline solution (SS) + T) or within 3 days with the use of 150 combinations in the case of first protocol (Figure 2B, SS + T)

Summary

Introduction

One of the widespread and well-investigated transmitters in the nervous system is serotonin (Kandel and Schwartz, 1982; Sakharov, 1990; Crow, 2004; Gillette, 2006). The questions regarding to the specific mechanisms (and/or pathways) of 5HT participation in associative learning and the role of specific neurons in these processes remain open These findings and questions motivated us to investigate the role of 5-HT in the mechanisms of learning by behavioral and electrophysiological methods, using the “neurotoxic” analogs of serotonin 5,6/5,7DHT, and the precursor of 5-HT syntheses, 5-hydroxytryptophan (5-HTP)

Methods

Results

Discussion

Conclusion