CHARACTER OF THE ACTIVITY CHANGES IN THE LARGE CELL NUCLEI OF THE RAT HYPOTHALAMUS AT PHOTOPERIOD MODIFICATION

One of the important links of the hypothalamus neuroendocrine system is the largecell supraorbital nuclei, the neurons of which synthesize vasopressin and oxytocin,transport them to the neurohypophysis. Supraorbital nuclei also take part in theprovision of neuroendocrine response to various types of stress – light, immobilization,traumatic, emotional, painful, hypoxic and stresses of other etiologies.The mechanisms of the circadian pacemaker activity of the neural systems of thesupraorbital hypothalamus nuclei are currently under intensive investigation. Atthe same time, knowledge concerning the effects of photoperiod modifications (inparticular, constant lighting) on the activity of the most vulnerable hypothalamicstructures (supraorbital nuclei), which provide a sequence of neuroendocrine changesunder stress and stress-reactivity of the body, remains relatively limited.The purpose – to determine the influence of photoperiod modifications on the morphofunctional state of the supraorbital nuclei of the rat hypothalamus.Material and methods. The experiments were conducted on 40 nonlinear male whiterats, divided into 2 series of studies. Biomaterial sampling was carried out at 14.00and 02.00 using morphometry, densitometry and statistics research methods.Results. The circadian rhythm of the neurons’ morpho-functional activity of thehypothalamus supraorbital nuclei with maximum activity at a day time (up to 14.00) isregistered in rats under the standard light regime. In animals, subjected to a prolonged light exposure, pronounced changes in morphofunctional state of the neurons of the hypothalamus supraorbital nuclei wereestablished. In particular, at 02.00 h the area of the neuron nucleus was 94.08 ± 9.55μm2 and was probably larger than that in the intact animals. The nuclear-cytoplasmicratio of the neurons in the hypothalamus supraorbital nuclei at 02.00 h was lowerthan that in the intact animals due to a decrease in the specific volume of the nucleus.In comparison with the daytime period (14.00 h), the decrease in the neurons’ bodyarea of the hypothalamus supraorbital nuclei, caused by the probable decrease in thearea of the nucleus and nucleolus of cells, was detected by 02.00 h. This caused anincrease of the nuclear-cytoplasmic ratio in the neurons under study, which made 2.51± 0.023 units. Constant light regime does not cause inversion of the rhythm of morphofunctional activity of the neurons under study.Conclusions. 1. Photoperiod duration significantly influences upon the daily activityof the hypothalamus supraorbital nuclei, and constant light regime does not cause therhythm inversion of morpho-functional activity of the studied neurons.2. Light stress causes a probable increase in the area of the nucleus and nucleolusof neurons in the night interval of observation. At the same time, a decrease in thenuclear-cytoplasmic ratio, an increase in the concentration of RNA in the nucleolusand cytoplasm of the neuron of the supraorbital nuclei of the rat hypothalamus areobserved in the day time period.