Early secretory activity in the hypothalamic nuclei and neurohypophysis in the rat; determined by selective staining

Abstract

Visualization of stainable material in the neural lobe of the rat provided the most reliable index of the age at which secretory activity can first be recognized, though preceded by both hypothalamic synthesis and axonal transportation. A problem of interpretation was encountered in the neural lobes of fetal an3 infant animals, due to different staining responses obtained during this age period, to the two methods of staining employed; chrome alum hematoxylin-phloxin and aldehyde fuchsin after oxidation by either acidified potassium permanganate or performic acid. With aldehyde fuchsin the material of the neural lobe is stainable selectively from the eighteenth day of fetal life to adulthood. With hematoxylin phloxine the first staining response also occurred in the posterior lobe but much later, at the end of the first postnatal week. The staining situation i n the pars neuralis has its counterpart in the differentiating hypothalamic nuclei; complicated by the differentiation of the supraoptic nuclei some days in advance of the paraventricular nuclei. After aldehyde fuchsin staining, evidences of neurosecretory activity were present in the perikarya of the supraoptic nuclei at birth, but mature neurons were rarely seen in the paraventricularis until at least 24 hours later. Nuclei of fetal hypothalami were not studied, but the demonstration of stainable material in the fetal neural lobes constitutes circumstantial evidence of functional competence of some neurons of either one or both types of nucleus, most likely the supraoptic.Some time ago (Dawson, '53) a brief record was made of evidences of early neurosecretory activity in the hypothalamoneurohypophyseal neurosecretory system of the rat, shortly after a comparable study had been reported by Green, Catalan0 and Van Breemen ('53), with a more extended account in 1955 (Green and Van Breeman). There was some disparity in our findings probaly due to reliance on different methods of selective staining of neurosecretory material. These authors and many others who subsequently sought to demonstrate neurosecretory material in newborn and infantile rats used only Gomori's chrome alum hematoxylin phloxine while I used, in addition, Halmi's ('52) aldehyde fuchsin method and variants thereof, especially in the kind and degree of oxidation before staining.These early observations based on histological methods have been supplemented by other studies on the occurrence and amount of neurohypophyseal hormones present in the neural lobes of fetal, newborn, infantile and adult rats, as deter-J. MORPH., 118: 549-564.mined by extraction and the use of standard assays. At the present time there are sufficient quantitative data to permit a limited correlation to be made between density of staining and the number of units of extractable hormone.The hypothalamo-hypophyseal system of the rat probably does not provide optimal material for a study of this type which seeks to gain evidence of early functional activity by determining the time, and place of appearance, and quanti...