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.
"Interestingly, the reduction of VIP and VP expression in rats was restored in aged animals after treatment with the neurotrophin nerve growth factor (NGF; Pereira, Cardoso & Paula-Barbora, 2005). Importantly, the reinstatement of VIP-and VPimmunoreactive fibers in the SCN in aged rats did not clearly restore the circadian rhythmic impairments induced by aging (Pereira et al., 2005). Studies have reported substantial changes in temporal VIP and VP expression in the SCN in elderly nonhuman primates (Microcebus murinus) compared with adults (Cayetanot et al., 2005a; Aujard, Cayetanot, Bentivoglio & Perret, 2006). "
[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: The hippocampus plays a role in new learning, memory and emotion and is a component of the neuroanatomical stress circuit. The structure is involved in terminating hypothalamic-pituitary-adrenocortical (HPA) axis responses to stress and attenuates stress responses by shutting off this axis. The immunoreactivity (-ir) of c-Fos, NGF and its receptor TrkA following acute and chronic open-field stress were studied in CA1-CA3 and the DG of the hippocampus. The material consisted of 21 male adult rats divided into three groups: nonstressed (control) animals and rats exposed to acute (15 min once) and chronic (15 min daily for 21 days) aversive stimulation (open-field exposure). The brains were stained with use of immunohistochemical methods for c-Fos, NGF or TrkA. In the animals exposed to acute open-field stress the number of c-Fos-, TrkA and NGF-ir cells was higher in all the structures studied than in the control animals. However they were differentiated only in c-Fos immunoreactivity. In the rats exposed to chronic open-field stress the number of c-Fos-ir cells in the structures of the hippocampal formation studied was smaller than in rats exposed to acute stress and was comparable to that in the control group. No differences were observed between the groups exposed to acute and chronic stress in the number of TrkA-ir cells in the structures under investigation. The number of NGF-ir neurons in CA1 and CA2 was lower after exposure to chronic than after exposure to acute stress but was still higher than that in the control group. Our findings indicate that neurons of CA1-CA3 and the DG are engaged in the stress response after acute as well as chronic open-field exposure. This is probably related to the important role of the hippocampus in processing new spatial information as well as in the habituation processes, although these appear to have different mechanisms.
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