Immunocytochemical Localization of the Vertebrate Cyclic Nonapeptide Neurohypophyseal Hormones and Neurophysins

Abstract

Staining of the hormones and neurophysins can be obtained with immunocytochemical methods. The function of the endocrine neurons of the hypothalamic magnocellular neurosecretory system is to synthesize, transport, and secrete neurohypophyseal hormones and neurophysins in response to a variety of physiological stimuli. This chapter introduces a precursor model for the neurohypophyseal hormone biosynthesis. According to this model, the biosynthesis of the peptide bonds of these cyclic nonapeptide hormones would occur solely in the cell body, on ribosomes, via pathways common to the biosynthesis of other peptide chains. Initially, the hormone would be constructed as part of a large precursor molecule, a protein, in which the hormone would be present in a bound, biologically inactive form. Neurophysin(s) and hormone(s) are made as part of the same precursor molecule(s). The activity of the hypothalamic magnocellular endocrine neurons is controlled by humoral and neurogenic stimuli. Neurohormones play an important role in the control of the release of the hormones of the pars distalis of the hypophysis. Like the neurohypophyseal hormones, the releasing and release-inhibiting hormones present in the neurohypophysis are contained in nerve fibers. These nerve fibers are terminals of axons belonging to different parvocellular peptide hormone-producing neuron systems the cell bodies of which are located in the hypothalamus, and possibly in other parts of the brain.