Localization of the Endogenous Benzodiazepine Receptor Ligand Octadecaneuropeptide and Peripheral Type Benzodiazepine Receptors in the Rat Pituitary

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Abstract
An association of octadecaneuropeptide, an endogenous ligand at the benzodiazepine receptor, with the peripheral type benzodiazepine receptor has been reported in brain as well as a few peripheral tissues. In order to verify whether or not such an association occurs in the rat pituitary gland, we have proceeded to the immunocytochemical localization of octadecaneuropeptide as well as the autoradiographic localization of peripheral type benzodiazepine receptors in rat pituitary, octadecaneuropeptide immunoreactive material was found in high concentrations in the posterior lobe, whereas only a very few cells were labelled in the intermediate lobe. The anterior lobe did not show any specific staining. Immunoelectron microscopy revealed that in the posterior lobe labelling was restricted to pituicytes. Autoradiographic studies demonstrated a strong and uniform labelling in the posterior lobe after incubation with [3H] PK11195, a ligand selective for peripheral type benzodiazepine receptors. In the intermediate lobe, the autoradiographic reaction was restricted to a narrow band adjacent to the hypophysial cleft. No labelling was detected in the anterior lobe. These results demonstrate a close association between octadecaneuropeptide and peripheral type benzodiazepine receptors in the intermediate and posterior lobes of the rat pituitary gland.