Responses of Withdrawal Interneurons to Serotonin Applications in Naïve and Learned Snails Are Different

Abstract

Long-term changes in membrane potential after associative training were described previously in identified premotor interneurons for withdrawal of the terrestrial snail Helix. Serotonin was shown to be a major transmitter involved in triggering the long-term changes in mollusks. In the present study we compared the changes in electrophysiological characteristics of identifiable premotor interneurons for withdrawal in response to bath applications of serotonin (5-HT) or serotonin precursor 5-hydroxytryptophan (5-HTP) in preparations from naïve, neurotoxin-injected or associatively trained snails. It was found that 5-HT or 5-HTP applications caused a significant decrease of membrane potential in premotor interneurons of naïve snails, associatively trained snails and snails with impaired serotonergic system by injection of a selective neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) 1 week before the experiments. Applications of 5-HT or 5-HTP did not cause significant changes in the action potential (AP) threshold potential of these neurons in naïve snails. Conversely, applications of 5-HT or 5-HTP to the premotor interneurons of previously trained or 5,7-DHT-injected snails caused a significant increase in the firing threshold potential in spite of a depolarizing shift of the resting membrane potential. Results demonstrate that responsiveness of premotor interneurons to extracellularly applied 5-HT or 5-HTP changes for days after the associative training or serotonin depletion. Similarity of the effects in trained and 5,7-DHT-injected animals may be due to massive release of serotonin elicited by 5,7-DHT injection. Our results suggest that serotonin release due to aversive conditionining or elicited by the neurotoxin administration triggers similar changes in resting membrane potential and AP threshold in response to bath applications of 5-HT or its precursor 5-HTP.

Impairing of Serotonin Synthesis by P-Chlorphenylanine Prevents the Forgetting of Contextual Memory After Reminder and the Protein Synthesis Inhibition

“…It is established that serotonin (5-HT) is a basic neurotransmitter for defensive behavior in mollusks and learning on the basis of defensive reflexes (Balaban et al, 1987 ; Glanzman et al, 1989 ; Gainutdinov et al, 1999 ; Il-Han et al, 2010 ; Bogodvid et al, 2017 ). In behavioral experiments it was shown that the disruption of serotoninergic system by the neurotoxin 5.7-DHT did not change the original memory, however, led to a memory impairment after repeated reactivation (Balaban et al, 2016 ).…”

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“…There is a close relationship between noradrenergic serotonergic systems so that increase in serotonin levels causes an inhibition in receiving noradrenergic signals. The dopaminergic system plays an important role in motional activities and the functioning of dopamine is adjusted by serotonin (Bogodvid et al,2017). In addition, some of the researchers suggest the mediatory role of "Personality traits" which is a factor involved in the relationship between ADHD and Eating disorders.…”

Effects of Thryptophan Hydroxylase Blockade by P-Chlorophenylalanine on Contextual Memory Reconsolidation after Training of Different Intensity

“…Reconsolidation of a contextual memory has been shown in invertebrate animals [49,[56][57][58][59][60][61]. The investigation of the memory formation process and memory reconsolidation in mollusks is also attractive due to the possibility of investigate the correlations between memory mechanisms and changes occurs at the cellular and receptor level [40,[62][63][64][65][66][67][68][69][70][71][72][73][74][75].…”