The alteration in extrinsinc ganglion nodosum caused by arterial hypertention in very old spontaneously hypertensive and Wistrar-Kayoto rats

Abstract

With a projected 22% rise in the elderly population by 2030, particularly susceptible to cardiovascular diseases (CVDs) like hypertension (HPT), understanding the underlying mechanisms becomes crucial. The aetiology of HPT is a result of imbalance in sympathetic and parasympathetic regulation of the CVS [1]. HPT manifests as endogenous neural substances such as calcitonin gene-related peptide (CGRP) - the most potent microvascular vasodilator, important in vascular-related stress, nitric oxide synthase (nNOS) - also known as endothelium-derived relaxation factor, release [2]. Aim. This study explored the link between aging and hypertension in male rats using very old (60-63 weeks) spontaneously hypertensive rats (SHR) and its age-matched Wistar-Kyoto (WKY) models in terms of area, nodal volume, and expression of CGRP and nNOS proteins. Method. Cryosections of nodose ganglion (NG) were prepared by immunohistochemical reactions with primary antibodies against CGRP / nNOS proteins and PGP9,5 (marker for all neuronal bodies). Secondary antibodies were conjugated with fluorochrome Cy3 and AF488. Sections were examined using fluorescence microscope. The ganglia area was measured and neurons, positive to PGP9,5, CGRP and nNOS were counted using AxioImage and ImageJ programs. Statistical data was analysed using T-test and one-way ANOVA tests. Results. Surprisingly, no significant differences (p>0.05) were found in nodal ganglion area, volume, or CGRP/nNOS expression between SHR and age-matched control rats. These findings suggest the greater the age of the mouse the less difference they exhibit in terms of CGRP and NOS expression, area, and volume of ganglion. The tendency between the groups shows higher expression of nNOS in SHR rats – 42.9%, whereas in WKY nNOS - 39.3%. Expression of CGRP in SHR group also showed lower results than WKY - 29.5% compared to 35.2%. The SHR rats also showed higher area of the ganglia by 3%, however smaller volume of neural bodies by 29.8%, compared to the WKY rats. Interestingly, the significant difference (p<0.05) was found in measurements of an area of NG in WKY rats between right and left ganglia. Right ganglia were bigger than left by 32,1% but no difference between node sides was found in SHR rats. Conclusion. Even though, the results did not show a significant difference in SHR and WKY rats, they still exhibit different morphology and levels of CGRP and nNOS protein expressions. These distinctions are not significant due to the age of the rats. However, the tendency of SHR rats to higher nNOS and lower CGRP expression, smaller volume of the ganglion, is due to long term pathological action of HPT on blood vessels, compared to WKY rats who underwent natural ageing process [1]. Difference in WKY NG area might indicate slight difference in parasympathetic innervation and type of nerve fibres [3]. Similarly in humans, the older the human the greater the risk of naturally occurring hypertension because of morphological changes of the cardiac plexuses, this explains the huge rise of CVDs in elderly population.