抄録
The effect of γ-aminobutyric acid (GABA) on antidromically identified tuberoinfundibular (TI) neurons was examined in hypothalamic slices of ovariectomized female rats. Twenty antidromically evoked spikes were obtained in the medial basal hypothalamus, including the arcuate and ventromedial nuclei, by electrical stimulation the median eminence. Sixteen of them had a notch in the rising phase and fractionation of the initial segment (IS)-and somatodendritic (SD)-spikes was elicited by repeated stimulation at frequencies higher than 10Hz. The application of 0.5-1.5mM GABA to the incubation medium inhibited SD spikes in 7 of these 16 neurons. The latency, amplitude and threshold of IS spikes were not affected by GABA except for one spike whose latency fluctuated. On the remaining 9 neurons having the notch, effect of 5-10 mM GABA was discernible. Four of 20 antidromically evoked spikes, which had a smooth rising phase and a shorter duration, were notinhibited 5-10 mM GABA, but a fluctuation of the latency was observed in one neuron.
Fifteen neurons having spontaneous unit activity were also obtained in the arcuate nucleus and its adjacent area and tested with GABA. In 10 of the 15 neurons, spontaneous unit activity disappeared following 0.1-1.5 mM GABA perfusion, while the firing rate in the remaining 5 neurons was not affected by 5-10 mM GABA.
These results provide evidence for a direct inhibitory effect of GABA on TIneurons and support the involvement of GABAergic neurons in regulating neuroendocrine functions.
