Response of Medial Preoptic/Anterior Hypothalamic Neurones to Ventrolateral Medulla Stimulation and Its Attenuation by Adrenoceptor Antagonists

Summary

Extracellular single-unit recordings were made from medial preoptic/anterior hypothalamic (MPOAH) neurones in urethane-anaesthetized female rats, and the responses of these neurones to electrical stimulation of the ventrolateral medulla (VLM) were investigated. Of 189 neurones tested, 20% were excited and 21% were inhibited following VLM stimulation. The latency of inhibitory responses showed a normal distribution and the mean latency was 47 ms, whereas the latency of excitatory responses showed a bimodal distribution with peaks in the ranges of 0-10 ms and 40-50 ms, respectively. Excitatory responses with latencies >15 ms and inhibitory responses were significantly attenuated by intravenous injections of the α-adrenoceptor antagonist phenoxy-benzamine but not the β-adrenoceptor antagonist propranolol. In the light of these observations and the known anatomical and electrophysiological findings, it is suggested that A1 noradrenergic and/or C1 adrenergic inputs from the VLM to MPOAH neurones are, at least in part, mediated by α-adrenoceptors.

Key words

Ventrolateral medulla - Medial preoptic/anterior hypothalamic neurones - Poststimulus time histogram - Phenoxybenzamine - Propranolol