SUBMICROSCOPIC TRANSFORMATIONS OF THE HYPOTHALAMUS STRUCTURE UNDER CONDITIONS OF 24-HOUR LIGHTING

Light information that is perceived by the retinal photoreceptors is transmitted along the retinohypothalamic pathway (the retinal ganglion cells present in it) and supraoptic fibers, suprachiasmatic, paraventricular, arcuate nuclei of the hypothalamus, through the trunk of the upper thoracic region and lateral intermedial nuclei of the spinal cord, sym- pathic neurons of the superior cervical ganglion in the pineal gland. In the dark, signals from the suprachiasmatic nucleus enhance the synthesis and release of norepinephrine from sympathetic endings. The experiments were carried out on 40 sexually mature male outbred white rats weighing 0.15-0.18 kg. The animals were kept in cages at a constant temperature, air humidity and free access to water and food. Experimental animals were divided into two series, in each of which the biomaterial was taken at 14.00 and 02.00 h. The selected timing of the experiment is due to the different functional activity of the pineal gland in the indicated time periods of the day. Submicroscopic studies of the supraoptic nuclei of the hypothalamus of intact animals at 14:00 showed that the majority of neurosecretory cells are round-oval in shape with rare invaginations and nuclei of irregular shape with shallow invaginations of the karyolem. The karyoplasm contains lumps of chromatin and a dense osmiophilic nucleolus. Neuroplasm occupies a small volume, in it the tubules of the granular endoplasmic reticulum are tightly packed with a small lumen, where there are many ribosomes and polysomes, as well as a small amount of evenly distributed granules. In the Golgi complex, secretory granules of different sizes are formed. Mitochondria, small with a dense matrix, contain few cristae. Some of them are in an energetically stressed state, are able to hypertrophy and partially lose their cristae or die. The ultramicroscopic organization of neurosecretory cells of the supraoptic nuclei of the anterior hypothalamus of rats was investigated. Under the standard illumination mode (12.00C: 12.00T), the ultrastructure of neurons indicates a decrease in their functional activity during the light period of the day and growth - in the dark period of the day. Light stress (24.00C: 00T) leads to significant desynchronosis and causes destructive changes in the components of the structures under study, more pronounced at 02.00 h.