Ultrastructural Changes in the Hypothalamus and Neurohypophysis of Rats After Chronic Morphine Treatment

Abstract

Ultrastructural changes in neurons of the supraoptic and paraventricular nuclei, and in fibers of the neurohypophysis of the rat were observed after 60 days of administration of morphine hydrochloride in a dose of 5 mg/kg body wt. In the neurons of the supraoptic and paraventricular nuclei a decrease of secretory activity was observed, manifested morphologically by the decrease of the number of secretory granules. At the same time, the Golgi apparatus was well developed; in its vicinity one could observe numerous coated vesicles, multivesicular bodies, and lysosomes. In the fibers of the neurohypophysis the accumulation of neurosecretory granules was smaller than normal. Numerous fibers contained an abundance of lysosomelike structures and multilamellar bodies. These occurrences are indicative of the digestion of neurosecretory granules. In addition, many neurosecretory fibers showed degenerative changes, manifested by an irregular shape of the fibers, the disappearance of the tubular system, and the absence of secretory granules. Twelve days after morphine withdrawal, the neurons of the supraoptic and paraventricular nuclei and fibers of neurohypophysis revealed a normal appearance. On the basis of these studies it may be assumed that chronic administration of morphine causes great damage to nervous structures in the hypothalamo-hypophyseal system, which is a cause of decreased neurosecretion. However, these changes appear to regress after morphine withdrawal.