Traumatic stress-induced persistent changes in DNA methylation regulate neuropeptide Y expression in rat jejunum.

BACKGROUND: Stress-induced chronic neuropsychiatric conditions such as anxiety are often co-morbid with gastrointestinal malfunctions. While we find enduring anxiety-like symptoms following minimal traumatic brain injury (MTBI) in rats, gastrointestinal consequences of MTBI remain elusive. METHODS: In this study, we examined the effects of MTBI on a major gut peptide, neuropeptide Y (NPY) and gut motility. DNA methylation was studied as a possible epigenetic mechanism operative in the regulation of NPY expression in the gut. KEY RESULTS: Minimal traumatic brain injury reduced the gut motility 48 hours and 30 days after trauma. The expression of DNA methyltransferase isoforms (DNMT1, DNMT3a, and DNMT3b) was altered in the jejunum 48 hours and 30 days after MTBI. However, the mRNA levels of growth arrest and DNA damage 45 (GADD45) isoforms, GADD45a, and GADD45b, which are believed to be involved in active DNA demethylation, initially decreased at 48 hours but subsequently increased after 30 days of trauma. Similarly, DNA hypomethylation at the NPY promoter region in the jejunum was correlated with the increase in NPY mRNA and protein levels 30 days post-trauma. On the other hand, DNA hypomethylation at 48 hours was associated with a decline in NPY expression. Treatment with 5-azacytidine (5-AzaC), a DNMT inhibitor, retarded DNA methylation and restored the NPY mRNA levels in the jejunum of MTBI-induced rats. CONCLUSIONS & INFERENCES: These results suggest that DNA demethylation could be operative as an epigenetic mechanism in the long-term regulation of NPY gene expression to alter the gut motility during traumatic stress.

Neuropeptide Y attenuates anxiety- and depression-like effects of cholecystokinin-4 in mice.

We investigated the involvement of neuropeptide Y (NPY) in the modulation of cholecystokinin-4 (CCK-4)-evoked anxiety and depression. Adult male mice were injected with vehicle, CCK-4, NPY, NPY Y1 receptor agonist [Leu(31), Pro(34)]-NPY or antagonist BIBP3226, via intracerebroventricular route, and subjected to social interaction or forced swim test (FST) for the evaluation of anxiety- and depression-like phenotypes, respectively. To assess the interactions between the two systems, if any, NPYergic agents were administered prior to CCK-4 and the animals were subjected to these behavioral tests. Treatment with CCK-4 or BIBP3226 dose-dependently reduced social interaction time, while NPY or [Leu(31), Pro(34)]-NPY produced opposite effect. CCK-4 treatment increased immobility time in FST. This effect was reversed by NPY and [Leu(31), Pro(34)]-NPY, although BIBP3226 per se did not alter the immobility time. In a combination study, the anxiogenic or depressive effects of CCK-4 were attenuated by NPY or [Leu(31), Pro(34)]-NPY and potentiated by BIBP3226. The brains of CCK-4 treated rats were processed for NPY immunohistochemistry. Following CCK-4 treatment, the nucleus accumbens shell (AcbSh), ventral part of lateral division of the bed nucleus of stria terminalis (BSTLV), hypothalamic paraventricular nucleus and locus coeruleus showed a reduction in NPY-immunoreactive fibers. Population of NPY-immunopositive cells was also decreased in the AcbSh, BSTLV, prefrontal cortex and hypothalamic arcuate nucleus (ARC). However, NPY-immunoreaction in the fibers of the ARC and cells of the central nucleus of amygdala was unchanged. We conclude that, inhibition of NPY signaling in the brain by CCK-4 might be causal to anxiety- and depression-like behaviors.

Agmatine in the hypothalamic paraventricular nucleus stimulates feeding in rats: involvement of neuropeptide Y.

BACKGROUND AND PURPOSE: Agmatine, a multifaceted neurotransmitter, is abundantly expressed in the hypothalamic paraventricular nucleus (PVN). Our aim was to assess (i) the effect of agmatine on feeding behaviour and (ii) its association, if any, with neuropeptide Y (NPY). EXPERIMENTAL APPROACH: Satiated rats fitted with intra-PVN cannulae were administered agmatine, alone or jointly with (i) α2-adrenoceptor agonist, clonidine, or antagonist, yohimbine; (ii) NPY, NPY Y1 receptor agonist, [Leu³¹, Pro³4]-NPY, or antagonist, BIBP3226; or (iii) yohimbine and NPY. Cumulative food intake was monitored at different post-injection time points. Furthermore, the expression of hypothalamic NPY following i.p. treatment with agmatine, alone or in combination with yohimbine (i.p.), was evaluated by immunocytochemistry. KEY RESULTS: Agmatine robustly increased feeding in a dose-dependent manner. While pretreatment with clonidine augmented, yohimbine attenuated the orexigenic response to agmatine. Similarly, NPY and [Leu³¹, Pro³4]-NPY potentiated the agmatine-induced hyperphagia, whereas BIBP3226 inhibited it. Moreover, yohimbine attenuated the synergistic orexigenic effect induced by the combination of NPY and agmatine. Agmatine increased NPY immunoreactivity in the PVN fibres and in the cells of the hypothalamic arcuate nucleus (ARC) and this effect was prevented by pretreatment with yohimbine. NPY immunoreactivity in the fibres of the ARC, dorsomedial, ventromedial and lateral nuclei of the hypothalamus was not affected by any of the above treatments. CONCLUSIONS AND IMPLICATIONS: The orexigenic effect of agmatine is coupled to increased NPY activity mediated by stimulation of α2-adrenoceptors within the PVN. This signifies the importance of agmatine or α2-adrenoceptor modulators in the development of novel therapeutic agents to treat feeding-related disorders.

Central regulation of feeding behavior during social isolation of rat: evidence for the role of endogenous CART system.

OBJECTIVE: Although hyperphagia and body weight gain are well-recognized consequences of social isolation, the underlying mechanisms are not understood. The aim of this work is to test the possibility that the endogenous cocaine- and amphetamine-regulated transcript peptide (CART) may be involved in the process. DESIGN: Socially isolated rats were screened for increase in food intake and body weight, and the modifications of these parameters by CART were evaluated. Furthermore, isolated animals were re-socialized and screened for reversal of these effects. Response of the endogenous CART system, in certain hypothalamic nuclei of the isolated and re-socialized rats, was evaluated with immunohistochemistry. SUBJECTS: Fifty days old naive male Sprague-Dawley rats were used. MEASUREMENTS: The effects of CART/CART antibody on the social isolation and subsequent re-socialization on feeding and body weight changes were monitored. Moreover, the immunohistochemical response of endogenous CART system to social isolation and re-socialization was analyzed morphometrically. RESULTS: While social isolation of rats for a period of 6 weeks caused progressive increase in food consumption and body weight gain, these rats showed a significant reduction in food intake and body weight when injected daily with CART via intracerebroventricular (i.c.v.) route, for the following 7 days. The re-socialization of isolated rats reduced food intake and body weight to the control levels. These effects of re-socialization were attenuated by immunoneutralization of the endogenous CART by i.c.v. CART antibody. Social isolation also resulted in a drastic reduction in CART immunoreactivity in the cells and/or fibers in the hypothalamic areas like dorsomedial, ventromedial, lateral, paraventricular and arcuate nuclei, recognized for their role in feeding. On the other hand, the CART immunoreactivity profile was fully restored following 7 days of re-socialization of the isolation-reared rats. CONCLUSION: Social isolation might down-regulate the hypothalamic CART-containing system, which in turn may lead to increase in food intake and body weight.