Gene expression in the forebrain of dexamethasone-treated pigs: effects on stress neuropeptides in the hypothalamus and hippocampus and glutamate receptor subunits in the hippocampus

Differential Expression of Hypothalamic and Gill-crh System With Osmotic Stress in the Euryhaline Black Porgy, Acanthopagrus schlegelii

The local gill production of corticotropin releasing hormone (crh) and crh-receptor (crhr) is hypothesized to play important roles during seawater (SW) and freshwater (FW) acclimation in euryhaline black porgy (Acanthopagrus schlegelii). The mRNA expression of crh, crhr, and Na +/K + -ATPase (a-nka) was examined in SW and FW diencephalon (Dien) and in the gills at different exposure time by Q-PCR analysis. The in situ hybridization results indicate that crh mRNA hybridization signals were more abundant in FW fish in the gigantocellular (PMgc) and parvocellular (PMpc) part of the magnocellular preoptic nucleus versus SW fish. The crh and crhr-expressing cells were located in basal cells of gill filament. Furthermore, in vitro dexamethasone (DEX) treatment could increase the crh-system in the gill. Increased transcripts of the crh-system in the gill via in vitro and in vivo CRH treatments suggest that CRH may regulate the system in a local manner. The a-Nka cells were localized in the filament and secondary lamellae mitochondria rich cells (MRCs) of FW fish at 8 h and 1 day. a-Nka cells were seen in both filament and lamellae in the FW but much less in SW fish indicating that gills play key roles in black porgy osmoregulation. Gill crh and crhr play important roles in the response to salinity stress.

The use of pigs in neuroscience: Modeling brain disorders

The use of pigs in neuroscience research has increased in the past decade, which has seen broader recognition of the potential of pigs as an animal for experimental modeling of human brain disorders. The volume of available background data concerning pig brain anatomy and neurochemistry has increased considerably in recent years. The pig brain, which is gyrencephalic, resembles the human brain more in anatomy, growth and development than do the brains of commonly used small laboratory animals. The size of the pig brain permits the identification of cortical and subcortical structures by imaging techniques. Furthermore, the pig is an increasingly popular laboratory animal for transgenic manipulations of neural genes. The present paper focuses on evaluating the potential for modeling symptoms, phenomena or constructs of human brain diseases in pigs, the neuropsychiatric disorders in particular. Important practical and ethical aspects of the use of pigs as an experimental animal as pertaining to relevant in vivo experimental brain techniques are reviewed. Finally, current knowledge of aspects of behavioral processes including learning and memory are reviewed so as to complete the summary of the status of pigs as a species suitable for experimental models of diverse human brain disorders.

Chronic dexamethasone-treatment alters mineralocorticoid receptor, truncated trkB and selected glutamate receptor subunit mRNA expression in the porcine hippocampus

Prepubertal boars (n = 4/treatment) were killed 24 h after a 5 day course of intravenous injections of dexamethasone (Dex, 1 and 5 mg kg(-1)), or saline vehicle. Gene expression was quantified in brain sections following in situ hybridisation histochemistry. The objective was to determine whether chronic glucocorticoid treatment would alter the expression of mRNAs for gluco- and mineralocorticoid receptors (GR and MR), brain-derived neurotrophic factor (BDNF), its receptor, trkB, and selected ionotropic glutamate receptor (iGluR) subunits in the hippocampus. Although Dex did not alter GR message, the higher dose reduced MR mRNA in all hippocampal subfields studied. There was no effect of Dex on the expression of BDNF, or the full-length form of its receptor but there was evidence to suggest that mRNA for the truncated form of trkB was increased. Expression of mRNA for glutamate receptor subunits was either unaffected (NR1) or decreased (GluR2 and GluR3). These findings indicate that acute and chronic glucocorticoid treatment has differential effects on hippocampal gene expression in the porcine brain.

Down-regulation of BDNF mRNA, with no effect on trkB or glucocorticoid receptor m RNAs, in the porcine hippocampus after acute dexamethasone treatment

Glucocorticoids bind to hippocampal mineralo-(MR) and gluco-(GR) corticoid receptors and, at high concentrations (e.g. as seen following treatment with pharmacological doses of corticosteroids or during stress), may affect hippocampal neuronal function. Such actions could involve brain-derived neurotrophic factor (BDNF), its receptor, trkB, and the excitatory neurotransmitter, glutamate. This experiment investigated the effect of a single intravenous (i.v.) injection of the synthetic glucocorticoid, dexamethasone (Dex, 5 mg kg(-1)) on gene expression for MR s, GR s, BDNF, trkB, and selected ionotropic glutamate receptor subunits (iGluRs), in the porcine hippocampus. Quantification of m RNA s in the brains of pigs (n = 4/treatment) killed 24 hours after saline or Dex administration indicated a significant Dex-induced decrease in BDNF m RNA in all hippocampal regions. However, gene expression for MR s, GR s, trkB and iGluRs was unaffected at this time-point.

Hippocampal gene expression in the pig: upregulation of corticotrophin releasing hormone mRNA following central administration of the peptide

Corticotrophin releasing hormone (CRH) and glucocorticoids affect hypophysiotrophic regions of the brain and influence limbic system activity. Since the latter mediates emotional responses, changes in gene expression in regions such as the hippocampus may provide new information on neural stress mechanisms. In this study, mRNA for CRH and selected ionotropic glutamate receptor (iGluR) subunits (NR1, GluR2, GluR3) was quantified in the hippocampus of pigs in which stress was simulated by central administration of CRH (100 microg). Increases in hippocampal CRH mRNA were detected in the CA3 subfield 4 h later, and in the CA1, CA2 and CA3 subfields 24 h post-treatment. However, there were no associated changes in iGluR subunit mRNAs, although the ratio GluR3: GluR2 increased in the dentate gyrus after 4 h. These results, together with a recent similar finding in rats subjected to restraint, point to an involvement of hippocampal CRH in the neuronal response to stress.