Endogenous serotonin contributes to a developmental decrease in long-term potentiation in the rat visual cortex.
The primary visual cortex shows synaptic plasticity during a postnatal "critical period," and its plasticity declines with development. Indeed, we found a developmental decrease in the induction of long-term potentiation (LTP) in the rat visual cortex. In visual cortex slices obtained from 2- to 3-week-old rats, tetanic stimulation (100 Hz for 1 sec, twice at an interval of 30 sec) of the white matter reproducibly induced LTP of field potentials in layer II/III. However, in slices from 5-week-old rats, the same tetanic stimulation failed to induce LTP. We hypothesized that endogenous serotonin (5-HT) is responsible for the developmental decrease in visual cortex LTP, because the induction of visual cortex LTP was suppressed by the addition of exogenous 5-HT (10 microm) and because the amount of 5-HT in the visual cortex increased during development. To test this hypothesis, we investigated the effect of methysergide, a 5-HT receptor antagonist, on the induction of visual cortex LTP. When visual cortex slices from 5-week-old rats were perfused with 50 microm methysergide, tetanic stimulation of the white matter induced robust LTP in layer II/III. Furthermore, serotonergic neurons were lesioned by intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT). LTP was induced in visual cortex slices from 5,7-DHT-treated, 5-week-old rats. These results suggest that the induction of visual cortex LTP in 5-week-old rats is suppressed by endogenous 5-HT. 5-HT may be a factor that determines a critical period for synaptic plasticity in the rat visual cortex.
Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan.
Y
Y
Edagawa
H
H
Saito
K
K
Abe
D015116:5,7-Dihydroxytryptamine / Q000008:administration & dosage; D000375:Aging / Q000378:metabolism*; D000818:Animals; D001923:Brain Chemistry; D066298:In Vitro Techniques; D007276:Injections, Intraventricular; D017774:Long-Term Potentiation / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008784:Methysergide / Q000494:pharmacology; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D018490:Serotonin Agents / Q000008:administration & dosage; D012702:Serotonin Antagonists / Q000494:pharmacology; D014793:Visual Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D018490:Serotonin Agents; D012702:Serotonin Antagonists; D015116:5,7-Dihydroxytryptamine; D012701:Serotonin; D008784:Methysergide