GABA_B受体对位听神经脑干传入通路神经活动的影响

Influences of GABA_B receptors on the neuronal activities of afferent impulses along the vestibulocochlear nerve brainstem pathway

目的本实验旨在探讨GABA能神经递质及GABAB受体对电刺激位听神经传入脑干通路兴奋性变化的影响。方法使用出生后0～5d的ddy/ddy小鼠制备脑干切片。脑片经电压敏感染料NK3041染色,电刺激与脑片相连的位听神经残端,使用16×16像素的硅光电二极管阵列测量膜电位变化引起的电压敏感染料吸光度的改变。观察GABA及GABAB受体拮抗剂2-Hydroxysaclofen (saclofen)对神经活动的影响,使用ARGUS-50PDA软件分析实验数据。结果多部位的光学记录方法显示了从位听神经到耳蜗核和前庭核兴奋性传导的时间-空间分布。神经活动可用电位或色彩的改变显示。每一个像素记录的电信号由快的峰电位样反应和慢反应组成。抑制性神经递质GABA可降低快的峰电位样反应及慢反应的幅度;GABAB受体拮抗剂saclofen能够部分逆转GABA的作用,随着saclofen(50μmolL～100μmolL)的浓度增加,在耳蜗核及小脑可引起去极化电位增强及后超极化电位。结论电刺激位听神经在脑干传入通路可引起兴奋性神经活动,GABA及saclofen对诱发的神经活动有调节作用,提示GABA及GABAB受体在听觉传入通路和小脑担负重要的生理功能。

Objective To explore the influences of GABA ergic neurotransmitter and GABAB receptors on the excitatory changes from the vestibulocochlear nerve afferent brainstem pathway evoked by electro-stimulation. Methods Brainstem slices were prepared using ddy/ddy mice of postnatal 0 - 5th days. The brainstem slices were stained with voltage-sensitive dye NK3041. The cut end of the vestibulocochlear nerve （nⅧ） was stimulated by an electrical pulse through a tungsten electrode; a 16 ×16 pixels silicon photodiode array was used to record the absorbency changes of voltage-sensitive dye induced by depolarization of membrane potentials from auditory brainstem slices. On the neuronal activities, the influences of GABA and an antagonist against GABAB receptors, 2-hydroxysaclofen （saclofen） were observed. The experimental data were analyzed by ARGUS-50/PDA software. Results The spatio-temporal distribution of excitatory propagations from the vestibulocochlear nerve to cochlear nucleus and vestibular nucleus was recorded with a multiple-sites optical recording system. The neuronal avtivities were displayed with changes of electrical potentials or colors. The electrical signals consisted of a fast spike-like response and a following slow response from each pixel. Inhibitory neurotransmitter GABA could decrease the both amplitudes of fast spike-like responses and following slow responses, whereas the saclofen reversed the effects of GABA partially. As the concentration increased （50 μmol/L ~ 100 μmol/L）, saclofen induced a reinforced fast spike-like response and a after-hyperpolarization response which followed the fast spike-like response in the cochlear nucleus and cerebellum. Conclusion The excitatory neuronal avtivities were recorded along the brainstem afferent pathway evoked by electro-stimulation to the cut end of the vestibulocochlear nerve. GABA and saclofen,an antagonist against GABAB receptors modulated the evoked neuronal activities. The present experiment suggests that GABA and saclofen play important physiological roles in the auditory afferent pathway and cerebellum.