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Notes: Abstract: Entorhinal cortex lesions destroy an important hippocampal input and lead to axonal sprouting in the dentate gyrus. Glucocorticoids are known to inhibit this reinnervation process. In the present study, we examined changes in hippocampal glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) mRNA expression using in situ hybridization following unilateral entorhinal cortex lesioning (ECL) in the rat. As early as 1 day postlesioning, a 33% bilateral decrease in GR mRNA expression was observed in the dentate gyrus. By contrast, a 36% bilateral increase in GR mRNA expression was detected in the CA1 cell field. GR mRNA levels in both regions returned to those of control animals 2 days postlesioning, indicating that these effects were transient. Adjacent sections hybridized with probes to MR mRNA revealed no changes in hippocampal MR gene expression as a result of ECL. The selective decrease in GR mRNA expression observed in the dentate gyrus following ECL is specific to the hippocampal subregion targeted for reactive synaptogenesis and thus may serve to attenuate the inhibitory actions of circulating glucocorticoids.

Notes: Neuropeptides synthesized in dorsal root ganglia (DRG) have been implicated in neurogenic inflammation and nociception in experimental and clinical inflammatory arthritis. We examined the very early changes in response to adjuvant injection in a rat model of unilateral tibio-tarsal joint inflammation and subsequent monoarthritis. Within 30 min of adjuvant injection ipsilateral swelling and hyperalgesia were apparent, and marked increases in β-preprotachykinin-A (β-PPT-A) and α-calcitonin gene-related peptide (CGRP)-encoding mRNAs were observed in small-diameter L5 DRG neurones innervating the affected joint. This response was augmented by recruitment of additional small-diameter DRG neurones expressing β-PPT-A and CGRP transcripts. The increased mRNA was paralleled by initial increases in L5 DRG content of the protein products, substance P and calcitonin gene-related peptide. Within 15 min of adjuvant injection there were increases in electrical activity in sensory nerves innervating a joint. Blockade of this activity prevented the rapid induction in β-PPT-A and CGRP mRNA expression in DRG neurones. Increased expression of heteronuclear (intron E) β-PPT-A RNA suggests that increases in β-PPT-A mRNA levels were, at least in part, due to transcription. Pre-treatment with the protein synthesis inhibitor cycloheximide had no effect upon the early rise in neuropeptide mRNAs. This and the rapid time course of these changes suggest that increased sensory neural discharge and activation of a latent modulator of transcription are involved.

Notes: Glucocorticoids may underlie the association between prenatal stress, low birth weight and adult stress-associated disorders, e.g. hypertension and type 2 diabetes, increased hypothalamic–pituitary–adrenal (HPA) activity and affective dysfunction. Normally, 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) rapidly inactivates glucocorticoids in placenta and many foetal tissues, thus acting as a ‘barrier’ to maternal steroids. We investigated the effect of inhibiting foeto-placental 11β-HSD in rats, using carbenoxolone (CBX), on subsequent HPA activity and regulation and stress-induced behaviour in adult offspring. Pregnant Wistar rats were injected with CBX (12.5 mg s.c.) or vehicle daily throughout pregnancy. CBX treatment reduced birth weight. Adult offspring of CBX-treated dams had persistently reduced body weight, increased basal corticosterone (CORT) levels, increased corticotropin-releasing hormone (CRH) and reduced glucocorticoid receptor (GR) mRNA in the hypothalamic paraventricular nucleus, though hippocampal GR and mineralocorticoid receptor (MR) mRNA expression were unaltered. In addition, these animals showed less grooming and rearing in an open field and reduced immobility in a forced swim test, and had increased GR mRNA expression in the basolateral (BLA), central (CEA) and medial (MEA) nuclei of the amygdala, with unaltered MR mRNA. These data suggest that disturbance of the foeto-placental enzymatic barrier to maternal glucocorticoids reduces birth and body weight, and produces permanent alterations of the HPA axis and anxiety-like behaviour in aversive situations. The behavioural and HPA effects may reflect GR gene programming in amygdala and hypothalamus, respectively. Foetal overexposure to endogenous glucocorticoids (prenatal stress or reduced activity of foeto-placental 11β-HSD) may represent a common link between the prenatal environment, foetal growth and adult neuroendocrine and affective disorders.

Notes: Glucocorticoids, acting via the mineralocorticoid receptor, are required for granule neuronal survival in the rat dentate gyrus. Whether this mineralocorticoid receptor-mediated neuroprotective effect has more general applicability is unknown. Here we report increased mineralocorticoid receptor expression in rat hippocampal and cortical neurons exposed in vitro to low levels of staurosporine and in rat hippocampal pyramidal neurons exposed in vivo to hypothermic transient global ischaemia. In both the cell culture system and the in vivo system increased mineralocorticoid receptor expression is associated with increased neuronal survival, and this increase is reversed by mineralocorticoid receptor antagonism. Modulation of mineralocorticoid receptor gene expression may therefore be an important target for reduction of brain injury in conditions caused by cerebral ischaemia including brain damage following cardiac arrest and stroke.

Notes: This study aimed at evaluating changes in expression of immediate early genes in a new photothrombotic focal ischemia model that exhibits late spontaneous reperfusion and morphological restoration in the region-at-risk within the cerebral cortex. Gene expression was studied with Northern blots, in situ hybridization and immunohistochemistry. At early time points (1–4 h), nerve growth factor-induced gene A and B, and c-fos mRNAs, were quickly induced throughout the ipsilateral cortex, with no obvious differences between the region-at-risk and remote cortical areas. High concentrations of nerve growth factor-induced gene A and c-Fos proteins were present within the region-at-risk even when cortical cerebral blood flow was as low as 40% of control values. At 4 h the nerve growth factor-induced gene A mRNA and protein expression was significantly decreased in the hippocampus vs. naive controls. However, a small decrease was also found in sham-operated and anaesthetized controls. A late induction, at 5 days, of c-fos and nerve growth factor-induced gene B mRNAs was seen bilaterally in the hippocampus and also, in the case of nerve growth factor induced-gene B, in the contralateral cortex. A complex pattern of changes in immediate early gene expression occurs after reversible focal cortical ischemia. This may be important for tissue recovery as well as neuropsychiatric symptoms after stroke.

Notes: Chronic glucocorticoid excess or deficiency is associated with hippocampal dysfunction and neuronal death. 11β-hydroxysteroid dehydro-genase (11β-OHSD), which catalyses the reversible conversion of corticosterone to inactive 11 -dehydrocorticosterone, regulates glucocorticoid access to receptors in the kidney and liver in vivo. The enzyme is also present in the hippocampus where it might modulate glucocorticoid action. We examined the effects of corticosteroid manipulations on hippocampal and peripheral 11β-OHSD. In the hippocampus, chronic adrenalectomy (10 days) had no effect on 11β-OHSD activity, compared to sham-operated controls. Treatment of adrenalectomized animals with dexamethasone (200 μg/kg.day−1), but not aldosterone (20 μg/kg.day−1), for 10 days significantly increased hippocampal 11β-OHSD activity compared with sham or adrenalectomized rats (22% and 23% rise respectively, P〈0.05). These effects reflect changes in transcription of the liver-type 11β-OHSD gene, with dexamethasone significantly increasing 11β-OHSD mRNA expression in the hippocampus compared with sham or adrenalectomized animals (32% and 70% higher respectively, P〈0.05). In the liver, adrenalectomy significantly reduced 11β-OHSD activity (16% lower), which was restored to sham levels by dexamethasone, but not aldosterone. Similar trends were seen in 11β-OHSD mRNA expression, although these did not reach significance. None of the manipulations altered 11β-OHSD activity or mRNA expression in the kidney. The hippocampal effects of dexamethasone were similar to those of chronic stress (arthritis) which increased 11β-OHSD activity (20% rise, P〈0.05), although this was not reflected at the level of mRNA. Thus, hippocampal (and hepatic, but not renal) 11β-OHSD appears to be regulated by chronic glucocorticoid manipulations and stress. Hippocampal 11β-OHSD may thus ensure optimal long-term corticosterone exposure of glucocorticoid-sensitive neurons.

Notes: Using mono - and bilateral tarsal arthritic models in the rat, we have previously shown increases in the expression of mRNAs encoding substance P and calcitonin gene-related peptide (CGRP) in primary sensory neurons innervating inflamed joints. Dorsal root ganglion (DRG) neuropeptide content in rats is altered by glucocorticoids, and since glucocorticoids regulate the expression of preprotachykinin (PPT) gene, the substance P precursor in other tissues, these effects may be mediated at the level of transcription. Indeed adrenalectomy potentiates disease in polyarthritis although the relationship to joint disease itself is unclear. Secretion of corticosterone in both mono -and bilaterally inflamed rats showed a loss of the normal diurnal nadir with no elevation of evening values. However, there were no changes in glucocorticoid target organs (adrenal gland, thymus and spleen) suggesting the stress was intermittent. Adrenalectomy in mono - and bilaterally inflamed rats did not significantly alter either the severity of inflammation or its spread. Bilaterally inflamed animals did, however, show reduced weight gain. Adrenalectomy had no effect on the induction of PPT and CGRP mRNA expression in innervating DRG neurons in monoarthritis (14 days after adjuvant injection), the unilateral increase in both PPT and CGRP mRNA expression in ADX animals being similar to SHAM arthritic rats. (PPT: ADX 140 ± 13 left; 99 ± 6 right % control; SHAM 160 ± 22 left, 100 ± 5 right % control. CGRP: ADX 177 ± 6 left, 97 ± 3 right % control; SHAM 147 ± 21 left, 100 ± 5 right % control). In bilaterally arthritic rats adrenalectomy potentiated the increase in CGRP mRNA expression (SHAM 168 ± 6% left, 271 ± 23% right; ADX 217 ± 38% left, 193 ± 4% right; control 100 ± 5%) but significantly attenuated the contralateral (right) increase in PPT mRNA expression seen in sham-operated rats (SHAM 136 ± 21% left; 140 ± 11% right; ADX 145 ± 28% left, 86 ± 15% right; control 100 ± 5%). Inflammation-associated changes in somatostatin mRNA expression were similar in sham-operated and adrenalectomized rats. We conclude, therefore, that whilst adrenalectomy exerts subtle effects on the expression of PPT and CGRP mRNAs in DRG neurons in bilateral arthritis, the presence or absence of high circulating endogenous corticosteroids in these animals, with limited arthritis, do not modulate the arthritic process.

Notes: 11β-Hydroxysteroid dehydrogenase (11β-OHSD) metabolizes corticosterone to inactive 11-dehydrocorticosterone and thus protects non-specific mineralocorticoid receptors from exposure to corticosterone in the kidney in vivo. Clearly, 11β-OHSD might also regulate corticosterone access to glucocorticoid receptors. We have investigated cerebellum, a tissue with high glucocorticoid receptor, but very low mineralocorticoid receptor levels and have shown marked 11β-OHSD bioactivity with similar co-substrate requirements and inhibition kinetics to the renal enzyme. 11β-OHSD messenger ribonucleic acid was expressed in cerebellum and was localized in Purkinje and granule cells. This distribution was confirmed immunohistochemically. Thus, we provide evidence for 11β-OHSD in cerebellum and suggest that it may regulate the access of corticosterone to glucocorticoid receptors in addition to mineralocorticoid receptors.

Notes: Corticosteroids exert effects on the hippocampus by binding to intracellular glucocorticoid and/or mineralocorticoid receptors, but the relative importance of each receptor type in mediating corticosteroid effects is poorly understood. There is an extensive serotoninergic (5-HT) innervation of the hippocampus which interacts with corticosteroid-sensitive cells. We have investigated the effect of intracerebroventricular 5,7-dihydroxytryptamine lesions of 5-HT neurons on glucocorticoid and mineralocorticoid receptor messenger ribonucleic acid (mRNA) expression in the rat hippocampus using in situ hybridization histochemistry. In controls, glucocorticoid receptor mRNA was highly expressed in dentate gyrus granule cell neurons, and in pyramidal cells of CA1 and CA2, but levels in CAS and CA4 were significantly lower. 5,7-dihydroxytryptamine-lesioned animals showed significantly less glucocorticoid receptor mRNA in the dentate gyrus (76% decrease), CA1 (42% decrease) and CA2 (52% decrease; all P〈0.05 compared with controls). Mineralocorticoid receptor mRNA was expressed at a similar level in all hippocampal subregions in control rats. 5,7-dihydroxytryptamine lesioning led to a significant decrease in mineralocorticoid receptor mRNA expression in CA3 (56% fall) and CA4 (45% fall; both P〈0.05), but not in the other subregions. Thus the 5-HT innervation regulates hippocampal corticosteroid receptor mRNA expression.