Edagawa Y, Saito H, Abe K
Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan.
J Neurosci. 2001 Mar 1;21(5):1532-7. doi: 10.1523/JNEUROSCI.21-05-01532.2001.
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.
初级视皮层在出生后的“关键期”表现出突触可塑性，且其可塑性随发育而下降。事实上，我们发现大鼠视皮层中长时程增强（LTP）的诱导存在发育性降低。在从2至3周龄大鼠获取的视皮层切片中，对白质进行强直刺激（100 Hz，持续1秒，间隔30秒重复两次）可重复性地诱导II/III层场电位的LTP。然而，在5周龄大鼠的切片中，相同的强直刺激未能诱导出LTP。我们推测内源性5-羟色胺（5-HT）是导致视皮层LTP发育性降低的原因，这是因为添加外源性5-HT（10微摩尔）会抑制视皮层LTP的诱导，且视皮层中5-HT的含量在发育过程中增加。为了验证这一假设，我们研究了5-HT受体拮抗剂麦角新碱对视皮层LTP诱导的影响。当用50微摩尔麦角新碱灌注5周龄大鼠的视皮层切片时，对白质的强直刺激在II/III层诱导出了强烈的LTP。此外，通过脑室内注射5,7-二羟色胺（5,7-DHT）损毁了5-羟色胺能神经元。在经5,7-DHT处理的5周龄大鼠的视皮层切片中诱导出了LTP。这些结果表明，5周龄大鼠视皮层LTP的诱导受到内源性5-HT的抑制。5-HT可能是决定大鼠视皮层突触可塑性关键期的一个因素。
