NEUROSECRETORY ACTIVITY IN RATS UNDER CONDITIONS OF CONTINUOUS LIGHT OR DARKNESS

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Abstract
Cytological study of the posterior pituitary and hypotha-lamic areas of male and female rats kept under usual laboratory conditions (controls), in continuous light, or in constant darkness for eight weeks revealed differences in neurosectrtory activity. While the paraventricular neclei seemed to be unaffected by the varied light treatment, the cells of the supraoptic nuclei were largest and appeared to most active in the lighted rats, smallest and least active in the rats housed in darkness. The amount of neurosecretory material in hypothalamo-hypophysial tract in two areas, namely, in the region ventral to the supraoptic nuclei and in the median eminence, was estimated from serial sections. It was apparent that Gomori-positive substance was most abundant and occurred in larger clumps along the hypothalamo-hypophysial tract in the continuously lighted rats. It was least in amount in the rats kept in darkness. The neurosecretory material in the posterior lobe was plentiful in the controls, but was reduced in both the other groups. The Herring bodies in the lighted animals were very small. In light-treated rats large amounts of neurosecretory material appeared to be moving along the neurosecretory axones, while the pars nervosa of such animals was relatively depleted of Gomori-positive substance. This suggests that under the influence of added lighting, the rat both secretes and releases increased amounts of neurosecretory material. At least a partial separation in function between the paraventricular nuclei and the supraoptic nuclei was indicated by the difference in response of these two nuclei.