Activity of No Synthase Neurons in the Lateral Hypothalamic Nucleus Following Long-Term Ethanol Consumption

Objective of the study – is to determine the characteristic changes in the activation of nitric oxide synthase (NOS) neurons in the lateral hypothalamic nucleus during the development of alcohol addiction.Material and methods. The experimental study was conducted on 24 adult male Wistar rats (250–280 g, aged 5–6 months), under conditions of acute alcohol intoxication and chronic alcohol dependence. Brain sections corresponding to anterior-posterior (AP) coordinates −1.3 to −2.8 mm from the bregma were analyzed. Histochemical detection of nitric oxide synthase (NOS) activity was performed using NADPH-diaphorase staining. Quantitative analysis was carried out to assess the density and distribution of NOS-positive neurons in the lateral hypothalamic nucleus.Results. The applied histochemical method for nitric oxide synthase (NOS) detection using NADPH-diaphorase staining enabled the identification of specific changes in the number and density of NO-positive neurons across experimental groups. In the acute alcohol intoxication (AAC) group, the number of NOS-positive neurons increased by 30% compared to controls. In contrast, the chronic alcohol dependence (CAD) group showed a 17% reduction in NOS-positive neurons. Predominantly small (≤5 μm) and medium-sized (12–15 μm) neurons were observed within the cytoplasm in 40-μm-thick sections over an area of 200 × 200 μm².In the AAC group, at the AP level of −1.3 to −2.12 mm, the density of NOS-positive neurons was notably higher. The highest average densities were recorded in the ventral lateral hypothalamic nucleus (LHV) with 73 ± 1.7 cells, and in the dorsal lateral hypothalamic nucleus (LHD) with 57 ± 2.2 cells per test area. The lowest densities were observed in the same nuclei: LHV – 19 ± 0.7 cells, and LHD – 16 ± 3.8 cells. At the AP level of −2.3 to −2.8 mm, the density of NOS-positive neurons did not differ significantly from the control group (P > 0.05). In the CAD group, the most pronounced decrease in NOS neuron density was observed in the LHV nucleus at −2.12 to −2.8 mm from the bregma, reaching 8 ± 0.2 cells (P < 0.05), and in the LHD nucleus at −2.3 to −2.8 mm with 7 ± 3.8 cells (P < 0.05). At the level of −2.12 mm, NOS neuron density did not differ significantly from control values (P > 0.05).Conclusions. The results of this study demonstrate that NO-synthase (NOS) neurons in the lateral hypothalamic nucleus (LH) respond both upon acute alcohol intoxication and during the development of alcohol addiction. Upon acute alcohol intoxication, NOS neuron density increased by 30% at the AP level of −1.3 to −2.12 mm from the bregma, with the highest densities observed in the ventral LH (LHV) at 73 ± 1.7 cells and in the dorsal LH (LHD) at 57 ± 2.2 cells. The lowest densities in this group were also recorded in the LHV and LHD (19 ± 0.7 and 16 ± 3.8, respectively). At the posterior level (−2.3 to −2.8 mm), NOS neuron density did not differ significantly from control values (P > 0.05). In the chronic alcohol dependence group, the density of NOS neurons decreased by 17%, with the greatest reductions observed in the LHV at −2.12 to −2.8 mm (8 ± 0.2, P < 0.05) and in the LHD at −2.3 to −2.8 mm (7 ± 3.8, P < 0.05). At −2.12 mm, values did not significantly differ from control (P > 0.05). These findings suggest that the lateral hypothalamus (LH) plays a modulatory role in alcohol-induced neural activity. However, its precise contribution to alcohol-related behavior remains to be fully elucidated. It is plausible that upon acute alcohol intoxication, increased NOS activity in the LH—potentially through the involvement of dopaminergic circuits related to motivation and reward—leads to vasodilation and enhanced local blood flow, reinforcing alcohol-associated stimuli and promoting the formation of addiction. In contrast, chronic alcohol exposure may suppress NOS activity due to reduced dopamine release, NO receptor desensitization, or the neurotoxic effects of acetaldehyde, thereby disrupting the balance of the brain’s reward system.