Development of visual input to superior colliculus in fetal rats : in vivo optical imaging.

本实验旨在研究胎鼠上丘(SC)神经元的功能发育。为此，我们用压敏染料光学成像系统研究了胎鼠SC在体内神经活动的时空模式，这些神经活动仍由完整的脐带连接。在本实验中，利用光学成像系统研究了聚焦刺激吻侧SC引起的信号在胎儿SC中的传播。每只孕鼠(3个月龄)取2~3只胎鼠(胎龄21~22天)。用以前开发的方法将胎头固定在传统的立体定位仪上(Nakamura和Sakaguchi，1990；Sakata等人，1998)。对于SC的电刺激，在SC的吻部植入双极刺激电极。刺激以单个(1ms持续时间)或10个序列脉冲(100ms持续时间)进行。将电压敏感染料RH795溶液涂抹于SC表面1小时。刺激SC可使兴奋从刺激部位向尾端传播。抑制信号在SC中广泛传播，在SC表面应用TTX(3mU M)后，这些信号的传播完全消失。CNQX(非NMDA受体拮抗剂)阻断了刺激SC所引起的兴奋性传播的早期，而NMDA受体拮抗剂AP-5减弱了兴奋的晚期，但不影响兴奋的早期。荷包牡丹碱可显著减弱抑制突触的传递。这些结果表明，在大鼠胚胎发育的晚期，兴奋性突触传递通过非NMDA受体和NMDA受体进行，而抑制性突触传递由GABA受体介导。

The purpose of the present experiments is to study the functional development of neurons in the superior colliculus (SC)in fetal rats. For this purpose, the opticaI imaging system using a voltage-sensitive dye was employed in elucidating spatio- temporaI patterns of in vivo neural activity of the SC in fetal rats which were still connected with the dam by the intact umbilical cord. In the present experiments, signal propagation in the fetal SC caused by focal stimulation of the rostral SC was examined using the optical imaging system. Two to three fetal rats (embryonic day 21- 22 day) in each pregnant rat (Sprague-Dawley, 3 months) were used for each experiment. The fetal head was fixed to a conventional stereotaxic apparatus by the previously developed method (Nakamura and Sakaguchi, 1990 ; Sakata et al., 1998). For electrical stimulation of the SC, a bipolar stimulating electrode was implanted in the rostral part of the SC.Stimulation was given with single (1 msec duration) or ten train pulses (100 msec duration). Solution of a voltage-sensitive dye RH795 was applied to the surface of the SC for 1 hour. SC stimulation produced propagation of excitation rostro- caudally from the stimulating site. Inhibitory signal propagated diffusely in the SC.These signal propagation totally disappeared after application of TTX (3 mu M) to the surface of the SC.CNQX(non-NMDA receptor antagonist) blocked an early phase of excitatory propagation induced by focal SC stimulation, while the NMDA receptor antagonist AP-5 attenuated a late phase of excitation without affecting the early phase of excitation. The inhibitory propagation was remarkably attenuated by application of bicuculline.These results suggest that at late stages of the prenatal period in the rat SC, excitatory synaptic transmission occurs through both non-NMDA and NMDA receptors, while inhibitory synaptic transmission is mediated by GABA receptors.