Immunoreactive somatostatin content in the pineal gland increases after lesion of the hypothalamic periventricular nucleus in male rats.

Immunoreactive somatostatin (IRS) content in the pineal gland increased about two-fold when the hypothalamic periventricular nucleus (Pe) of male rats, which contains many tuberoinfundibular somatostatin (SRIF) neuron cell bodies, was lesioned. However, the mechanism by which this increase takes place remains to be elucidated. Using 125I-Tyr11-SRIF-14 as a ligand and autoradiography, specific binding was detected in several brain areas. However, we were unable to detect specific SRIF binding sites either in the pineals of control or lesioned animals. This undetectable binding of SRIF-14 could be due to the localization of low-affinity receptors that were not demonstrated by the present method. Another possibility for the undetectable binding of the radioligand to the pineal could be due to the fact that the majority of IRS may be within the nerve terminals and the receptors in a different location.