Oxytocin Excites Neurons Located in the Ventromedial Nucleus of the Guinea‐Pig Hypothalamus

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Abstract
The area of the ventromedial nucleus of the hypothalamus in the guinea‐pig was shown in autoradiographs to contain high affinity binding sites for oxytocin. In order to ascertain whether these sites may represent neuronal receptors, single‐cell extracellular recordings were obtained from ventromedial neurons in coronal slices of the hypothalamus of adult guinea‐pigs. Oxytocin applied in the nanomolar range excited about half of the neurons tested; none were inhibited. The response to the peptide was reversible and concentration‐dependent. It was exerted directly since it persisted under the condition of synaptic isolation. Moreover, the effect was specific since it could be mimicked by a selective oxytocin agonist and since vasopressin was usually at least 10‐fold weaker than oxytocin. These findings suggest that the binding sites for oxytocin detected by light microscopic autoradiography in the guinea‐pig hypothalamic ventromedial nucleus represent functional receptors.

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