Neurons of the Paraventricular Hypothalamic Nucleus Under Normal and Modified Illumination Conditions: Immunohistochemical and Morphometric Parallels |
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Authors: | R E Bulyk D A Vasilenko V P Pishak O V Timofey |
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Institution: | 1. Bukovyna State Medical University, Chernovtsy, Ukraine 2. Bogomolets Institute of Physiology of the NAS of Ukraine, Kyiv, Ukraine
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Abstract: | Using an immunohistochemical technique and densitometric analysis in experiments on rats, we examined the expression of an
early-response protein, c-Fos, in the medial parvicellular subnucleus of the hypothalamic paraventricular nucleus (mpcPVN).
During 7 days, the animals were kept under conditions of (i) normal photoperiod (group LD), (ii) continuous illumination (group
LL), and (iii) continuous darkness (light deprivation, group DD). It was found that both normal photoperiodicity and artificial
modifications of the latter result in significant changes of c-Fos immunopositivity in the nuclei of mpcPVN neurons (cells
that synthesize corticotropin-releasing factor). Changes in the indices of concentration and amount of c-Fos in mpcPVN neurons
were, from some aspects, similar to those observed under analogous experimental conditions in neurons of a leading pacemaker
of the circadian periodicity, the suprachiasmatic nuclei (SChNs) of the hypothalamus 10], but, at the same time, demonstrated noticeable specificity from other aspects. In all experimental groups, the concentration
and amount of c-Fos in mpcPVN neurons were greater during daytime than at night. Dramatic increases in the above parameters
observed at daytime in rats subjected to light deprivation were the most significant effect of modifications of the photoperiod.
Both continuous illumination and light deprivation resulted in some increase of the number (density) of c-Fos-immunopositive
units in the mpcPVN. The nuclei of neurons of this structure demonstrated the phenomenon found earlier in SChN neuron; geometrical
dimensions of the cell nuclei of these structures depended noticeably on both illumination conditions and periodicity. Probable
mechanisms of the dependence of c-Fos expression in the hypothalamic nuclei on the photoperiod and its modifications, interdependence
of such changes observed in the circadian pacemaker (SChN) and an important component of the system controlling the stress
reactions (mpcPVN), and the relation of the above phenomena to the level of melatonin produced by the epiphysis cerebri (main neuroendocrine intermediator organizing the above-mentioned periodicity) are discussed. |
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