幼小蝙蝠下丘神经元的听反应特性

实验在出生6—8天的8只幼龄鲁氏菊头蝠(Rhinolophus rouxi)上进行。使用玻璃微电极记录中脑下丘听神经元对超声信号的反应。共观察了162个听单位,它们对超声反应的最佳频率分布范围为25.8—60.9千赫,多数集中在43.0—47.0千赫。反应的潜伏期在6.0—38.0毫秒,平均为15.4±5.2毫秒。反应的最低阈值在25—84dB,平均为69.8±10.3dB.这些神经元对超声刺激的调谐曲线都较宽阔,故Q10-dB值都较小。当微电极由下丘表面垂直下插时,所记录到的神经元的最佳频率与记录深度之间不存在相关关系,即没有音调筑构现象。听神经元的这些特性与同种成年动物构成显著差异。

AUDITORY RESPONSE PROPERTIES OF INFERIOR COLLICULAR NEURONS OF JUVENILE BATS,Rhinolophus rouxi

Under free-field acoustic stimulus conditions, we studied the responses of inferior collicular neurons(IC)to acoustic stimulus(40ms, 0.5ms rise-decay times)in the adult and juvenile(6-8days)rufous horseshoe bat,Rhinolophus rowxi.A total of 162 and 471 IC neurons were isolated from the juvenile and adult bats respectively.In general,IC neurons from the juvenile bats had higher minimum thresholds and longer response latencies than those from the adult bats.The best frequencies(BFs)of the overwhelming majority of IC neurons of the adult bats were 88 to 90 kHz but they were 43 to 47 kHz in the juvenile bats.Although the BFs of IC neurons sequentially isolated by the advancement of an orthogonally penetrating electrode systematically increased from low to high in the adult bats.such a tonotopic organization along the dors-oventral axis of the IC was not observed in the juvenile bats.IC neurons of juvenile bats also tuned to a broader band of frequencies than those of adult bats.These data provide evidence for a postnatal developmental change of auditory signal processing in bats.