Electrical stimulation of specific brainstem nuclei suppresses growth hormone-releasing hormone-induced growth hormone secretion in the pentobarbital anaesthetized rat.

Abstract To clarify the neural mechanism related to suppression of growth hormone (GH) secretion, biphasic electrical stimulation was delivered into several brainstem nuclei in the pentobarbital anaesthetized rat. A concentric bipolar stimulating electrode was implanted chronically one week prior to the electrical stimulation. Ninety min before the electrical stimulation, the rats were anaesthetized by ip injection of pentobarbital and a silastic cannula was inserted into the right atrium for blood sampling. Blood samples were withdrawn five times (0, 10, 20, 30 and 60 min) during the experiment. Electrical stimulation was delivered for 10 min just after the first blood sampling. One min after the onset of the stimulation, human GH-releasing hormone was injected iv to induce GH secretion. Electrical stimulation of several brainstem nuclei, i.e. the locus coeruleus, the rostral portion of the nucleus tractus solitarius and the lateral reticular nucleus suppressed GH secretion and the central gray of the pons showed a tendency for the suppression of GH secretion. On the other hand, electrical stimulation of the parabrachial nucleus and the caudal portion of the nucleus tractus solitarius did not suppress GH secretion. These suppressions were nullified by prior electrolytic lesioning of the hypothalamic periventricular nucleus where the major cell bodies of somatostatin immunoreactive fibres in the median eminence originate. These results indicate that electrical stimulation of several brainstem nuclei excites somatostatin neurons in the periventricular nucleus which are responsible for the suppression of GH secretion.