CHANGES IN MORPHODENSITOMETRIC PARAMETERS OF THE PARAVENTRICULAR NUCLEUS OF THE HYPOTHALAMUS IN RATS UNDER STRESS OF DIFFERENT DURATIONS
Paraventricular nuclei of the hypothalamus play the important role in both endocrine regulation of the tropic function of the adenohypophysis and the organism's neuroendocrine response to stress of various origins, particularly sustained photoperiod disturbances. However, morphodensitometric p...
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| Main Authors: | , |
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| Format: | Article |
| Language: | English |
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Bukovynian State Medical University
2025-07-01
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| Series: | Неонатологія, хірургія та перинатальна медицина |
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| Online Access: | https://neonatology.bsmu.edu.ua/article/view/334790 |
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| Summary: | Paraventricular nuclei of the hypothalamus play the important role in both endocrine regulation of the tropic function of the adenohypophysis and the organism's neuroendocrine response to stress of various origins, particularly sustained photoperiod disturbances. However, morphodensitometric properties of the medial parvocellular subnuclei within the rat hypothalamic paraventricular nuclei across varying photoperiod durations have yet to be investigated.
Aim of the study. To investigate the morphodensitometric parameters of the medial parvocellular subnuclei of the hypothalamic paraventricular nuclei in rats across diurnal time points under altered photoperiodic conditions.
Materials and methods. The study was performed on 36 sexually mature, male outbred white rats. The animals were divided into three groups, each comprising two subgroups of six rats. The rats were maintained under a different light-dark cycle for 14 days (light/dark 12:00L:12:00D, 12 hours each, LD), (dark/dark 00L:24:00D, DD), (light/ light 24:00L:00D, LL). Morphodensitometric analysis of hypothalamic neurons in rats was performed using the VIDAS-386 digital image analysis system (Kontron Elektronik, Germany) within the visible spectrum. Quantitative data on the area of neurons, their nuclei and nucleoli, the content of RNA in the cell cytoplasm, nuclei and nucleoli were obtained in a semi-automatic mode.
Scientific research was conducted in compliance with the main provisions of Ukrainian Law No. 3447-IV "On Protection of Animals from Cruelty", the European Convention for the Protection of Vertebrate Animals Used for Experimental and Other Scientific Purposes (18.03.1986), EU Directive 2010/63/EU, Orders of the Ministry of Health of Ukraine No. 690 (23.09.2009), No. 944 (14.12.2009), and Order of the Ministry of Education and Science of Ukraine No. 249 (01.03.2012). The research protocol was approved by the Biomedical Ethics Commission of [BDMU] (24.02.2019).
Statistical analysis was performed using the “STATISTICA” software (StatSoft Inc., USA, Version 10). Quantitative indicators with normal distribution were compared using Student’s t-test. Differences were considered statistically significant at p<0.05.
The research was conducted within the framework of approved research projects of the Department of Medical Biology and Genetics: "Morphofunctional and Biochemical Basis of Dysfunction of Neurosecretory Brain Structures and Endocrine Glands and Hepatorenal System in Rats in Experimental Pathology, in Age Aspect and Ways of Its Correction" (state registration number 0119U101346, implementation period 01.2019-12.2023) and "Morphofunctional Reorganization of Structures of Nervous and Endocrine Systems in Different Periods of Postnatal Ontogenesis and Biochemical Mechanisms of Metabolism of Signaling Molecules, State of Oxidative and Antioxidant Systems under Conditions of Experimental Pathologies and Influence of Glutathione and Melatonin (Experimental Study)" (state registration number 0124U002513, implementation period 01.2024-12.2028).
Results and discussion. Under the LD lighting regime, morphodensitometric analysis revealed a circadian rhythm in the morphofunctional activity of the medial parvocellular subnuclei of the paraventricular nucleus. Peak values were recorded during the daytime interval (14:00 h).
In rats from the DD group that were decapitated at 14:00 h, the neuronal soma area was 54.77±0.605 μm², amounting to a 9.7% decrease compared to the LD group. At the same time, its cytoplasmic area measured 28.91±0.427 μm², representing a 10.4% increase relative to the LD group. A significant reduction was observed in the concentrations of RNA in the nucleus and nucleolus of the studied structures (by 14.4% and 12.1%, respectively) at 14:00 h.
Investigations conducted on samples collected at 02:00 h revealed a 10.4% increase in neuronal soma area compared to the control values, and a 10.9% increase compared to animals from the previous time interval exposed to the same experimental conditions. Nevertheless, the nucleus showed a significantly lower RNA concentration (by 31.8%), attributed to a reduction in the nucleolus (by 21.7%). Additionally, a significant decrease in RNA content was observed in the cytoplasm, where its concentration was 0.10±0.001 o.u.
In rats from the LL group at 14:00 h, no significant changes in the morphometric parameters of the mpsPN were observed. Regarding RNA concentration in the studied neuronal structures, a significant increase was detected only in the nucleolus of neurosecretory cells, where it measured 0.303±0.0023 o.u. at 14:00 h — 2.5% higher than in rats maintained under standard photoperiod conditions. At 02:00 h, no significant differences in neuron size or its structural parameters were found compared to those in the LD group. RNA concentration in the cytoplasm and nucleus of the neurosecretory cells of the mpsPN remained stable, whereas in the nucleolus it was 2.8% lower than in the LD group.
Conclusions: 1. Morphodensitometric parameters of the medial parvocellular subnuclei of the hypothalamic paraventricular nuclei in rats exhibit fluctuations, with peak values occuring during the daytime observation period.
Light deprivation induces a disruption in the rhythm of functional activity of the studied hypothalamic neurons and a shift of peak values from the daytime to the nighttime period, likely attributable to increased levels of melatonin, the primary pineal chronobiotic, in the bloodstream during this phase of the day. As a stress-limiting factor, melatonin suppresses CRH production in the mpsPN of the hypothalamus.
Prolonged exposure to constant illumination (light stress) did not elicit significant changes in the studied morphodensitometric parameters compared to those in rats maintained under LD and DD photoperiods. This suggests a remarkable plasticity of the mpsPN of the hypothalamus in response to experimental conditions.
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| ISSN: | 2226-1230 2413-4260 |