Hippocampal serotonin re-uptake and nocturnal locomotor activity after microinjections of 5,7-DHT in the fornix-fimbria.
The role of the hippocampal 5-hydroxytryptamine (5-HT) terminals in the control of locomotor activity was investigated by lesioning 5-HT axons in the fimbria with 5,7-dihydroxytryptamine (5,7-DHT). Rats pretreated with desimipramine (10 mg/kg, i.p.) received microinjections of 5,7-DHT (0, 1, 3, 5 or 10 micrograms in 0.4 microliter ascorbic Ringer's solution) into the fornix-fimbria. On the fourteenth to twenty-first nights after operation, nocturnal locomotor activity was measured in photocell cages. Twenty-eight to thirty days after operation degeneration of 5-HT terminals was assessed by measuring in vitro [3H]5-HT re-uptake in slices of dorsal hippocampus, ventral hippocampus and the septum. Groups injected with 5,7-DHT showed hyperactivity in the night period and increased decrements of activity between tests, both of which were related to the dose of neurotoxin. A reduction of [3H]5-HT re-uptake was found in dorsal hippocampus which was related to the dose of 5,7-DHT), but ventral hippocampal and septal [3H]5-HT re-uptake were not systematically reduced. For each rat, levels of dorsal and ventral hippocampal [3H]5-HT re-uptake were negatively correlated with the mean nocturnal activity from the 7 nights of testing. Levels of dorsal, but not ventral hippocampal [3H]5-HT re-uptake were negatively correlated with the mean nightly decrement of activity. No correlations were found between septal [3H]5-HT and these activity measures. These results, indicate that the increase in nocturnal locomotor activity caused by generalized depletion of 5-HT in the brain may be due to disruption of hippocampal 5-HT terminals supplied by the fornix-fimbria.
D015116:5,7-Dihydroxytryptamine / Q000494:pharmacology*; D000818:Animals; D001369:Axons / Q000187:drug effects; D002940:Circadian Rhythm / Q000187:drug effects*; D004102:Dihydroxytryptamines / Q000494:pharmacology*; D005260:Female; D006624:Hippocampus / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D009043:Motor Activity / Q000187:drug effects*; D009434:Neural Pathways / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D011903:Raphe Nuclei / Q000187:drug effects; D051381:Rats; D012701:Serotonin / Q000378:metabolism*
D004102:Dihydroxytryptamines; D015116:5,7-Dihydroxytryptamine; D012701:Serotonin