Nerve growth factor restores the expression of vasopressin and vasoactive intestinal polypeptide in the suprachiasmatic nucleus of aged rats
ABSTRACT Aging leads to a decrease in the number of neurons expressing vasopressin (VP) and vasoactive intestinal polypeptide (VIP) in the suprachiasmatic nucleus (SCN) of the rat. Similar results were observed following prolonged alcohol consumption and withdrawal. In the latter circumstances, the administration of nerve growth factor (NGF) restored the synthesis and expression of those neuropeptides despite the absence of TrkA receptors in SCN neurons. Thus, we decided to test whether the administration of NGF would improve the expression of neuropeptides in the SCN of aged rats. For this purpose, NGF was delivered intraventricularly to aged rats over a period of 14 days. The somatic volume and the total number of VP- and VIP-immunostained SCN neurons were estimated by applying stereological methods. No age-related variations were found regarding the volume of the neuronal cell bodies. Yet, a striking reduction in the number of VP- and VIP-immunoreactive neurons was detected in aged animals and found to be completely retrieved by NGF. This finding shows that exogenous NGF administered to aged rats restores the neurochemical phenotype of the SCN. This might occur either through direct signaling of SCN neurons via p75NTR or through enhancement of the cholinergic input to the SCN.
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ABSTRACT: Animals have neural structures that allow them to anticipate environmental changes and then regulate physiological and behavioral functions in response to these alterations. The suprachiasmatic nucleus of the hypothalamus (SCN) is the main circadian pacemaker in many mammalian species. This structure synchronizes the biological rhythm based on photic information that is transmitted to the SCN through the retinohypothalamic tract. The aging process changes the structural complexity of the nervous system, from individual nerve cells to global changes, including the atrophy of total gray matter. Aged animals show internal time disruptions caused by morphological and neurochemical changes in SCN components. The effects of aging on circadian rhythm range from effects on simple physiological functions to effects on complex cognitive performance, including many psychiatric disorders that influence the well-being of the elderly. In this review, we summarize the effects of aging on morphological, neurochemical, and circadian rhythmic functions coordinated by the main circadian pacemaker, the SCN.Psychology and Neuroscience 06/2013; 63(3):287-29707. DOI:10.3922/j.psns.2013.3.07
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ABSTRACT: The amygdala is a critical component of the neuroanatomical stress circuit. It plays a role in the generation of responses to emotional stimuli. The central (CeA) and medial (MeA) amygdaloid nuclei are implicated in activation of the hypothalamic-pituitary-adrenocortical (HPA) axis. The immunoreactivity (-ir) of c-Fos, NGF and its receptor, TrkA, following acute and chronic open-field stress were studied in the CeA and MeA nuclei of the amygdala. The material consisted of 21 male adult rats divided into three groups: non-stressed (control) animals, rats exposed to acute (once only lasting 15 min) and chronic (15 min daily over 21 days) aversive stimulation (open-field exposure). The brains were stained with the use of immunohistochemical methods for c-Fos, NGF or TrkA. In the control rats c-Fos-, TrkA- and NGF-ir cells were observed in the nuclei studied, but the quantity varied, being moderate or high (immunoreactive to TrkA and NGF) or low (immunoreactive to c-Fos). In the animals exposed to acute open-field stress the number of c-Fos-ir, NGF-ir and TrkA-ir cells in the nuclei under examination was differentiated but higher than that in the control animals. In the animals exposed to chronic open-field stress the number of c-Fos-ir cells in the nuclei studied was similar and was smaller than those in animals exposed to acute stress. The number of TrkA-ir neurons was also lower in comparison to that in animals exposed to acute stress. However, no significant differences in the number of NGF-ir cells were observed between the groups exposed to acute and chronic stress. Diverse expression of c-Fos protein following both acute and chronic stress stimulation may prove the functional heterogeneity of the amygdaloid nuclei investigated. The decrease observed in both c-Fos- and TrkA-ir in MeA (only TrkA in CeA) of animals exposed to chronic stress may indicate the phenomenon of habituation.Folia morphologica 06/2006; 65(2):145-51. · 0.52 Impact Factor