大鼠上丘到外膝体P－物质投射的机能

已知大鼠外膝体内有中脑上丘来的含Ｐ－物质的神经末梢，其机能不明。在离休的大鼠外膝体脑片上用单电极电压箝位的方法研究了Ｐ－物质对外膝体神经元电压依赖性离子通道的作用。结果表明，Ｐ－物质可以使静息膜去极化，并降低膜电导。这提示Ｐ－物质抑制了线性钾漏电流。此外，Ｐ－物质还抑制去极化激活的慢失活的钾电流、低阈值钙电流和超极化激活的内向整流（Ｈ或Ｑ）电流。Ｐ－物质还可能抑制早钾（Ａ）电流。因此，Ｐ－物质在外膝体视觉信号传递中的作用是使外膝体神经元从爆发反应方式或振荡状态转化为中继反应方式，易化突触传递，使视网膜的视觉信号忠实地传递到大脑皮层。

FUNCTION OF SUBSTANCE-P PROJECTION FROM SUPERIOR COLLICULUS TO LATERAL GENICULATE NUCLEUS OF RATS

Substance P immunoreactive terminals arising from the superior colliculus havebeen observed in the dorsal lateral geniculate nucleus of the rat. However, the functionsal role of this tachykininergic projection is still unknown. We studied the effects of substance P on voltage--dependent ion channels of lateral geniculate neurons in rat's in vitrobrain slice with a single-electrode-voltage-clam technique. It was found that substanceP caused a depolarizing shift of membrane potential with a decrease of membrane conductance, suggesting that substance P depressed the linear potassium leak current. In addition, substance P inhibited the slowly inactivated potassium current, low threshold(T-) calcium current and inward rectifier (H- or Q-) current. Probably, the transientpotassium (A-) current was also depressed by substance P. Therefore, the effects ofsubstance P were considered to transfer activities of lateral geniculate neurons fromburst response mode or oscillatory state to relay response mode, and to facilitate mynastie transmission, so that retinal visual signals could be relayed to the visual cortex withless distortion faithfully.