Temporal synergism of neurotransmitter affecting drugs and seasonal reproductive responses of Indian Palm Squirrel,Funambulus pennanti

Abstract

Daily injections of L-dihydroxyphenylalanine (L-DOPA, dopamine precursor) given 12 hour after 5-hydroxytryptophan (5-HTP, serotonin precursor) eliminated annual testicular regression in seasonally breeding sub-tropical Palm Squirrel that undergoes seasonal changes in responsiveness to day-length and humidity. Other temporal relations (L-DOPA given 0, 4, 8, 16 and 20 hours after 5-HTP administration) decreased/delayed the rate of regression and maintained the reproductive system at intermediate level. 12-hour-relation maintained full breeding condition (maximum gonad and accessory sex organs) unlike control, which exhibited complete atrophy of primary and accessory sex organs. It seems likely that these injections entrained the circadian serotonergic and dopaminergic oscillations and the interaction/phase relation of these two systems through their many circadian expressions (neural/hormonal) accounts for the seasonal interpretation of environmental factors. It is suggested that response in the present study is not a pharmacological effect of drugs but temporal synergism of neural activities affected the seasonality of reproduction as only 12-hour-relation of 5-HTP and L-DOPA maintained breeding activity during post reproductive phase of annual gonad cycle in Palm Squirrel.

Elimination of testicular regression by 12-hr temporal relationship of serotonergic and dopaminergic activity in Indian Palm Squirrel,Funambulus pennanti

“…25~ long. 83~ in the month of July and acclimatized for two weeks in Laboratory condition (Chaturvedi and Jaiwal, 1990). They were fed with soaked gram seeds and water ad libitum.…”

“…Study by Chaturvedi and Jaiwal (1990) indicates that daily injections of 5-HTP and L-DOPA in several specific temporal relations, markedly influenced reproductive and hormonal conditions in Indian Palm Squirrel maintained under NDL (natural day length i.e. exposed to natural photoperiod and environmental conditions) following neurotransmitter precursor treatment.…”

“…Specific physiological conditions may be duplicated out of the season by giving timed daily injections of neurotransmitter precursor drugs (Miller and Meier, 1983;Wilson and Meier, 1989). To test the validity of this hypothesis in subtropical species a preliminary experiment (Chaturvedi and Jaiwal, 1990) was performed in Indian Palm Squirrel. This subtropical species differs from temperate hamsters (syrian and Golden) in certain respects.While photoperiod has full control on the breeding cycle of hamsters (Reiter, 1975) in Indian Palm Squirrel, other environmental factor (humidity) determines the termination of seasonal breeding (Haldar and Saxena, 1988).…”

Suppression of annual testicular development in Indian Palm Squirrel,Funambulus pennanti by 8 hr temporal relationship of serotonin and dopamine precursor drugs

“…In Indian Palm squirrel, Funarnbulus pennanti, L-DOPA injected 12 hr after 5-HTP (12 hr relationship) eliminated seasonal gonadal regression (Chaturvedi and Jaiwal, 1990) and squirrels were maintained continuously in breeding conditions even in non-breeding season. Second study in this series reported that L-DOPA injected 12 hr after 5-HTP may even induce redevelopment of gonad up to full breeding condition when given in sexually quiescent phase of annual cycle (Jaiwal and Chaturvedi, 1991).…”

Temporal Phase Relation of Circadian Neural Oscillations Alters RFamide-Related Peptide-3 and Testicular Function in the Mouse

“…A number of studies have reported that the temporal phase relation of circadian serotonergic and dopaminergic oscillations affects gonadal development in many seasonally breeding birds and mammals [1,2,3,4,5,6]. Administration of a dopamine precursor ( L -dihydroxyphenylalanine; L -DOPA) 12 h after the injection of a serotonin precursor (5-hydroxytryptophan; 5-HTP) in a 24-hour period (12-hour relation) has been reported to induce breeding conditions in these species, as well as the advancement of puberty (in the Japanese quail) [7].…”