Somatostatin produces apnea and is localized in medullary respiratory nuclei: a possible role in apneic syndromes.

Immunocytochemical studies on the nucleus of the tractus solitarius and adjacent areas of the dorsal medulla of the rat demonstrate the existence of somatostatin immunoreactive nerve cell bodies and nerve terminals within the ventrolateral and ventral subnuclei of the nucleus of the tractus solitarius. Injections of somatostatin (6 nmol in 10 microliters) into the cisterna magna of chloralose-anesthetized rats produced an apnea with a latency of 5-7 min. This apnea was preceded by slow deep breathing, a reduction in heart rate and fall of arterial blood pressure. The apnea was usually irreversible leading to death of the animal. These respiratory and cardiovascular effects of somatostatin were not abolished either by bilateral vagotomy or by low decerebration (below the inferior colliculus). It is suggested that activation of somatostatin receptors linked to neurons in medullary respiratory nuclei might be responsible for the inhibition of respiratory neuronal activity and thus may mediate apneic conditions.