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.

Gene expression studies advance our understanding of the effects of stress and glucocorticoids on brain function and give a new direction to animal welfare research. In this context, the presence of messenger RNA s (m RNA s) for corticotrophin releasing hormone (CRH) and vasopressin (VP) in the porcine hypothalamus has recently been documented. This study investigated the expression of CRH, VP and ionotropic glutamate receptor (iGluR) subunit m RNA s in the brains of pigs treated with the synthetic glucocorticoid dexamethasone (Dex; 5 mg kg(-1)i.v.). In the hypothalamus, VP, but not CRH, m RNA was reduced 3 hours after Dex. In the hippocampus, expression of m RNA s for some iGluR subunits appeared to be differentially regulated 6 hours after Dex. In addition, CRH message was detected in the hippocampus and significantly upregulated in the CA1 region 3 hours after Dex. The relevance of these findings to stress neurobiology of the growing pig is discussed.

Vasopressin and oxytocin gene expression in the porcine forebrain under basal conditions and following acute stress.

This study, the first using the pig, examined expression of mRNAs for vasopressin (VP), oxytocin (OT), preproenkephalin (PENK) and pro-opiomelanocortin (POMC) in the forebrain, and of POMC and prolactin in the pituitary. High basal expression of VP and OT mRNAs was present in the paraventricular (PVN) and supraoptic (SON) nuclei. In the PVN, VP was found in magnocellular regions whereas OT was also seen in the parvocellular portion; the distribution of VP and OT mRNAs in the SON was as reported in other species. The suprachiasmatic nucleus contained VP mRNA but only OT message was present in the dorsomedial SON, a structure peculiar to swine. Gene expression for PENK occurred in the caudate putamen (CPu), for POMC in the mediobasal hypothalamus (MBH) and for prolactin and POMC in the hypophysis. Following restraint, VP message increased in the magnocellular PVN, as did PENK in the CPu and POMC in the MBH.

Bacterial endotoxin-induced gene expression in the choroid plexus and paraventricular and supraoptic hypothalamic nuclei of the sheep.

The febrile and neuroendocrine responses to circulating endotoxin are effected, at least in part, by a central action of prostaglandins with interleukins serving as intermediaries. Data from rodents suggest that prostaglandin and interleukin (IL-1 beta) synthesis in response to endotoxin challenge may occur within the circumventricular organs of the brain, especially the choroid plexus; the present study investigated this possibility using the sheep as an experimental model. A pyretic dose of bacterial endotoxin (40 micrograms lipopolysaccharide) was given intravenously to sheep (n = 5) and the effect on gene expression in the choroid plexus after a 40 min interval was compared with that observed in vehicle-treated animals (n = 5) using in situ hybridisation histochemistry. Evidence of activational and synthetic events following endotoxin administration was provided by significant increases in c-fos (P < 0.05) and IL-1 beta (P < 0.01) mRNA expression. Constitutive cyclooxygenase (cox-1 mRNA) and inducible cyclooxygenase (cox-2 mRNA) synthesis were unchanged. The investigation also sought to provide evidence for endotoxin effects on neuroendocrine activity in this species by examining changes in hypothalamic gene expression. The results showed that c-fos mRNA increased in the paraventricular (P < 0.01) and supraoptic (P < 0.05) nuclei and that CRH mRNA was upregulated in the paraventricular nucleus (P < 0.001). However, in agreement with previous work, there was no change in vasopressin gene expression although oxytocin mRNA was enhanced throughout the paraventricular nucleus (P < 0.05). These findings suggest the following: (1) possible involvement of the choroid plexus in the response of sheep to immunological challenge: (2) endotoxin-induced changes in gene expression in the ovine hypothalamus similar in those caused by other stressors: and (3) possible changes in oxytocin synthesis concomitant with fever in the sheep.

Cyclo-oxygenase mediation of endotoxin-induced fever, anterior and posterior pituitary hormone release, and hypothalamic c-Fos expression in the prepubertal pig.

Prepubertal pigs (n = 8) treated with bacterial endotoxin (20 micrograms lipopolysaccharide; LPS) exhibited a sustained (4 h) hyperthermia, increased plasma concentrations of cortisol, prolactin, growth hormone and vasopressin, but no change in adrenaline or noradrenaline levels was observed. All these effects were prevented or attenuated when the animals were pretreated intravenously with the cyclo-oxygenase inhibitor indomethacin (IND; 2 mg/kg). Similarly, in pigs (n = 3 per treatment) given IND, LPS or IND + LPS, parallel changes in the neuronal expression of c-Fos were observed in hypothalamic regions concerned with thermoregulation, neurohypophysial secretion, and the control of pituitary-adrenocortical function. The stimulatory action of LPS in the median preoptic, supraoptic and paraventricular nuclei was prevented by IND, whereas IND given alone was without effect. These findings suggest that inducible cyclo-oxygenase pathways are responsible for the febrile and neuroendocrine effects of endotoxin in this species.

Increased body temperature, cortisol secretion, and hypothalamic expression of c-fos, corticotrophin releasing hormone and interleukin-1 beta mRNAs, following central administration of interleukin-1 beta in the sheep.

There is evidence to indicate that cytokines of the interleukin series act within the brain to influence physiological responses to pathological states or stressful events. This investigation examined the effects of intracerebroventricular (lateral ventricle) injection of human recombinant interleukin-1 beta (IL-1 beta) on body temperature, hormone (catecholamine, cortisol, prolactin, growth hormone) release and hypothalamic expression of c-fos, corticotrophin-releasing hormone (CRH), vasopressin (AVP) and IL-1 beta mRNAs in the sheep. A preliminary study showed that central administration of 10 micrograms IL-1 beta significantly (P < 0.05) increased body temperature (by 1.2 degrees C) over a 140 min period but did not affect catecholamine secretion. A second experiment using graded doses (100 ng, 1 microgram, 10 micrograms) of IL-1 beta indicated that only the highest dose significantly (P < 0.01) increased cortisol concentrations and that none of the treatments altered the secretion of prolactin or growth hormone. In a third study, changes in gene expression in the hypothalamus were examined using in situ hybridization histochemistry following treatment with 10 micrograms IL-1 beta. The results showed that IL-1 beta increased c-fos mRNA in the paraventricular (PVN, P < 0.05) and supraoptic (SON, P < 0.05) nuclei, CRH mRNA in the PVN (P < 0.01) and IL-1 beta mRNA in the PVN (P < 0.05). There was, however, no change in AVP mRNA in either the PVN or the SON.

The effects of ether stress and betamethasone treatment on the concentrations of noradrenaline and dopamine in various regions of the rat brain.

1. The effects of ether stress on noradrenaline (NA) and dopamine levels in different regions of the rat brain were studied. 2. Exposure to ether vapour (90 s) caused a significant decrease in the concentration of hypothalamic NA but had no effect on catecholamine (CA) concentrations in the other regions studied. 3. Treatment with betamethasone alone (20 microgram/ml) given in the drinking water for 24 h, had no effect on CA levels in the cerebral cortex, midbrain or hypothalamus. However, pretreatment with this dose of steroid prevented the decreases in hypothalamic NA which were normally seen after ether stress and also induced significant increases in the concentration of midbrain NA. 4. The data provide further support for the involvement of NA in the regulation stress-induced corticotrophin (ACTH) release and indicate that centres other than the hypothalamus may be involved in mediating the inhibitory action of betamethasone on the response to ether stress.

The effect of reserpine on hypothalamo-pituitary-adrenocortical function in the rat.

1. The effect of reserpine on hypothalamo-pituitary-adrenocortical (HPA) function in the rat was investigated by the use of direct and indirect indices of pituitary adrenocorticotrophic activity. 2. Administration of a single dose of the drug induced prolonged hypersecretion of corticotrophin (ACTH). 3. Corticotrophin release in response to the drug no longer occurred after repeated daily injections, indicating that some form of 'adaptation' occurred. 4. The increase in HPA activity normally caused by exposure to cold was prevented by reserpine once 'adaptation' to the drug had been produced. 5. Inhibition of stress-induced ACTH release was due neither to depletion of pituitary stores of the hormone, nor to a corticosteroid feedback effect.