LIGHT-MICROSCOPIC OBSERVATIONS ON THE HYPOTHALAMUS AND PITUITARY GLAND OF THE RAT FIXED IN OSMIUM TETROXIDE

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Abstract
SUMMARY: The ventral hypothalamus and the pituitary gland of the rat were examined with the light microscope in sections fixed in an osmium tetroxide solution without further staining. The histology of the neurohypophysis could be observed with remarkable clarity. Herring bodies and axons of the supra-optico-neurohypophysial tract show as grey homogeneous structures. Pituicytes appear as round or variously shaped cells whose cytoplasm is crowded with osmiophilic granules. The granules vary in size from 0·5 to about 2·5 μ, and present either as solid or as ring-shaped black structures. They stained neither with aldehyde-thionine, nor with chrome-alum haematoxylin, nor with the PA-Schiff techniques but stained with Sudan black B. They were found in profusion in the median eminence of the hypothalamus and the infundibular stem in an apparent extracellular location surrounding fibre bundles and capillaries of the hypophysial portal plexus. Two types of cells were identifiable in the supraoptic nucleus of the hypothalamus. Smaller, angular neurones stained densely with osmium and with aldehyde-thionine and larger, more rounded neurones stained only lightly with osmium and did not stain with aldehyde-thionine. A peculiar laminated arrangement of structures in the infundibular recess in the region of the arcuate nucleus was noted. Several distinct types of cells in the adenohypophysis were identifiable on morphological grounds: thyrotrophic basophils, gonadotrophic basophils, acidophils and chromophobes. The possibility of a neuroendocrine role of the pituicytes is discussed.