Enkephalin—Glial Interaction and Its Consequence for Vasopressin and Oxytocin Release from the Rat Neural Lobe

Abstract

Publisher Summary The nerve fibres contain not only vasopressin, oxytocin, and their associated neurophysins but also various other peptides, amines, and amino acids. This chapter discusses the role of pituicytes in the release of hormones from the neurohypophysis with emphasis on the enkephalin–glial interaction and its consequence for vasopressin and oxytocin release from the rat neural lobe. The nervous input of the neural lobe not only consists of vasopressin and oxytocin but is more complex, for example, somatostatin, neurotensin, and the enkephalins have been reported to occur. It is proposed that opiate peptides would inhibit the release of vasopressin and oxytocin at the level of the neural lobe. Moreover, stereospecific opiate receptor binding is found in the bovine neural lobe. At the light microscope level, it is shown in the chapter that Leu-enkephalin immunoreactive fibres occur all over the neural lobe. However, no co-existence in the same terminal of immunoreactivity for the enkephalins and vasopressin or oxytocin is found at the electron microscope level. Immunoreactive Leu-enkephalin fibres surround the pituicytes and make synaptoid contacts upon their soma and processes. The reaction product is localized both in dense core vesicles of 100 nm and diffusely spread over the cytoplasm. A working hypothesis is submitted in which pituicytes play an intermediary role in the regulation of vasopressin and oxytocin release by opiate peptides. The activity of pituicytes would be modulated by opiate peptides and vasopressin or oxytocin.