Electrophysiological identification of cell bodies of the tubero-infundibular neurones in the rat.

1. Electrical stimulation of the median eminence induced unit responses in the suprachiasmatic, the ventromedial and the arcuate nuclei of the hypothalamus in the female rat anaesthetized with urethane.2. Arcuate units with constant latency responded in one to one fashion to repetitive stimuli up to 286 Hz.3. A conditioning stimulus just above threshold increased the threshold and latency for responses produced by a test stimulus given within 6 msec after the conditioning stimulus. Absolute refractory period was 1.4-2.0msec.4. A conditioning stimulus just below threshold did not alter the threshold and latency of the responses to test stimuli at any interval.5. A stimulus given within a time period following a spontaneously occurring spike failed to induce a unit response.6. It is concluded that the arcuate nucleus of the hypothalamus includes cell bodies of origin of the tubero-infundibular axons in the rat.