Effect of adrenal steroids on preproneurokinin-A gene expression in discrete regions of the rat brain

Fasting Enhances Pyroglutamyl Peptidase II Activity in Tanycytes of the Mediobasal Hypothalamus of Male Adult Rats

Fasting down-regulates the hypothalamus-pituitary-thyroid (HPT) axis activity through a reduction of TRH synthesis in neurons of the parvocellular paraventricular nucleus of the hypothalamus (PVN). These TRH neurons project to the median eminence (ME), where TRH terminals are close to the cytoplasmic extensions of β2 tanycytes. Tanycytes express pyroglutamyl peptidase II (PPII), the TRH-degrading ectoenzyme that controls the amount of TRH that reaches the anterior pituitary. We tested the hypothesis that regulation of ME PPII activity is another mechanism by which fasting affects the activity of the HPT axis. Semiquantitative in situ hybridization histochemistry data indicated that PPII and deiodinase 2 mRNA levels increased in tanycytes after 48 hours of fasting. This increase was transitory, followed by an increase of PPII activity in the ME, and a partial reversion of the reduction in PVN pro-TRH mRNA levels and the number of TRH neurons detected by immunohistochemistry. In fed animals, adrenalectomy and corticosterone treatment did not change ME PPII activity 72 hours later. Methimazole-induced hypothyroidism produced a profound drop in tanycytes PPII mRNA levels, which was reverted by 3 days of treatment with T4. The activity of thyroliberinase, the serum isoform of PPII, was increased at most fasting time points studied. We conclude that delayed increases in both the ME PPII as well as the thyroliberinase activities in fasted male rats may facilitate the maintenance of the deep down-regulation of the HPT axis function, despite a partial reactivation of TRH expression in the PVN.

Glucocorticoids and Stress-Induced Changes in the Expression of PERIOD1 in the Rat Forebrain

The secretion of glucocorticoids in mammals is under circadian control, but glucocorticoids themselves are also implicated in modulating circadian clock gene expression. We have shown that the expression of the circadian clock protein PER1 in the forebrain is modulated by stress, and that this effect is associated with changes in plasma corticosterone levels, suggesting a possible role for glucocorticoids in the mediation of stress-induced changes in the expression of PER1 in the brain. To study this, we assessed the effects of adrenalectomy and of pretreatment with the glucocorticoid receptor antagonist, mifepristone, on the expression of PER1 in select limbic and hypothalamic regions following acute exposure to a neurogenic stressor, restraint, or a systemic stressor, 2-Deoxy-D-glucose (2DG) in rats. Acute restraint suppressed PER1 expression in the oval nucleus of the bed nucleus of the stria terminalis (BNSTov) and the central nucleus of the amygdala (CEAl), whereas 2DG increased PER1 in both regions. Both stressors increased PER1 expression in the paraventricular (PVN) and dorsomedial (DMH) nuclei of the hypothalamus, and the piriform cortex (Pi). Adrenalectomy and pretreatment with mifepristone reversed the effects of both stressors on PER1 expression in the BNSTov and CEAl, and blocked their effects in the DMH. In contrast, both treatments enhanced the effects of restraint and 2DG on PER1 levels in the PVN. Stress-induced PER1 expression in the Pi was unaffected by either treatment. PER1 expression in the suprachiasmatic nucleus, the master circadian clock, was not altered by either exposure to stress or by the glucocorticoid manipulations. Together, the results demonstrate a key role for glucocorticoid signaling in stress-induced changes in PER1 expression in the brain.

Functional effects of polymorphisms on glucocorticoid receptor modulation of human anxiogenic substance-P gene promoter activity in primary amygdala neurones

Expression or introduction of the neuropeptide substance-P (SP; encoded by the TAC1 gene in humans and Tac1 in rodents) in the amygdala induces anxiety related behaviour in rodents. In addition, pharmacological antagonism of the main receptor of SP in humans; NK1, is anxiolytic. In the current study, we show that the Tac1 locus is up-regulated in primary rat amygdala neurones in response to activation of the glucocorticoid receptor (GR); a classic component of the stress response. Using a combination of bioinformatics, electrophoretic mobility shift assays (EMSA) and reporter plasmid magnetofection into rat primary amygdala neurones we identified a highly conserved GR response sequence (2GR) in the human TAC1 promoter that binds GR in response to dexamethasone (Dex) or forskolin. We also identified a second GR binding site in the human promoter that was polymorphic and whose T-allele is only found in Japanese and Chinese populations. We present evidence that the T-allele of SNPGR increases the activity of the TAC1 promoter through de-sequestration or de-repression of 2GR. The identification of Dex/forskolin response elements in the TAC1 promoter in amygdala neurones suggests a possible link in the chain of molecular events connecting GR activation and anxiety. In addition, the discovery of a SNP which can alter this response may have implications for our understanding of the role of regulatory variation in susceptibility to stress in specific populations.

Behavioral and hormonal regulation of expression of the clock protein, PER2, in the central extended amygdala

PER2, a key molecular component of the mammalian circadian clock, is expressed rhythmically in many brain areas and peripheral tissues in mammals. Here we review findings from our work on the nature and regulation of rhythms of expression of PER2 in two anatomically and neurochemically defined subregions of the central extended amygdala, the oval nucleus of the bed nucleus of the stria terminalis (BNSTov) and the central nucleus of the amygdala (CEA). Daily rhythms in the expression of PER2 in these regions are coupled to those of the master circadian pacemaker, the suprachiasmatic nucleus (SCN) but, importantly, they are sensitive to homeostatic perturbations and to hormonal states that directly influence motivated behavior.

Motivational Modulation of Rhythms of the Expression of the Clock Protein PER2 in the Limbic Forebrain

Key molecular components of the mammalian circadian clock are expressed rhythmically in many brain areas and peripheral tissues in mammals. Here we review findings from our work on rhythms of expression of the clock protein Period2 (PER2) in four regions of the limbic forebrain known to be important in the regulation of motivational and emotional states. These regions include the oval nucleus of the bed nucleus of the stria terminalis (BNSTov), the central nucleus of the amygdala (CEA), the basolateral amygdala (BLA), and the dentate gyrus (DG). Daily rhythms in the expression of PER2 in these regions are controlled by the master circadian pacemaker, the suprachiasmatic nucleus (SCN), but, importantly, they are also sensitive to homeostatic perturbations and to hormonal states that directly influence motivated behavior. Thus, circadian information from the SCN and homeostatic signals are integrated in these regions of the limbic forebrain to affect the temporal organization of motivational and emotional processes.

Glucocorticoid rhythms control the rhythm of expression of the clock protein, Period2, in oval nucleus of the bed nucleus of the stria terminalis and central nucleus of the amygdala in rats

We investigated the involvement of the adrenal glucocorticoid, corticosterone, in the control of the rhythmic expression of the circadian clock protein, Period2, in forebrain nuclei known to be sensitive to glucocorticoids, stressors and drugs of abuse, the oval nucleus of the bed nucleus of the stria terminalis and the central nucleus of the amygdala. We found previously that the daily rhythm of Period2 in these nuclei is uniquely dependent on the integrity of the adrenal glands (Amir S, Lamont EW, Robinson B, Stewart J (2004) A circadian rhythm in the expression of PERIOD2 protein reveals a novel SCN-controlled oscillator in the oval nucleus of the bed nucleus of the stria terminalis. J Neurosci 24:781-790; Lamont EW, Robinson B, Stewart J, Amir S (2005) The central and basolateral nuclei of the amygdala exhibit opposite diurnal rhythms of expression of the clock protein Period2. Proc Natl Acad Sci U S A 102:4180-4184). We now show that, in rats, in the absence of the adrenals, corticosterone replacement via the drinking water, which is associated with daily fluctuations in corticosterone levels, restores the rhythm of Period2 in the oval nucleus of the bed nucleus of the stria terminalis and central nucleus of the amygdala. Corticosterone replacement via constant-release pellets has no effect. These results underscore the importance of circadian glucocorticoid signaling in Period2 rhythms in the oval nucleus of the bed nucleus of the stria terminalis and central nucleus of the amygdala and suggest a novel mechanism whereby stressors, drugs of abuse, and other abnormal states that affect the patterns of circulating glucocorticoids can alter the functional output of these nuclei.

The central and basolateral nuclei of the amygdala exhibit opposite diurnal rhythms of expression of the clock protein Period2

There is considerable evidence that circadian rhythms in mammals can be modulated by emotional state, but how emotional state modulates specific circadian outputs is poorly understood. We analyzed the expression of the circadian clock protein Period2 (PER2) in three regions of the limbic forebrain known to play key roles in emotional regulation, the central nucleus of the amygdala (CEA), the basolateral amygdala (BLA), and the dentate gyrus (DG). We report here that cells in all three regions exhibit daily rhythms in expression of PER2 that are under the control of the master clock, the suprachiasmatic nucleus (SCN). The rhythm in the CEA and the rhythms in the BLA and DG are diametrically opposite in phase and are differentially affected by adrenalectomy. Adrenalectomy completely abolished the PER2 rhythm in the CEA but had no effect on the PER2 rhythms in the BLA and DG. We previously reported a rhythm in PER2 expression in the oval nucleus of the bed nucleus of the stria terminalis that is identical in phase and sensitivity to adrenalectomy to that found in the CEA. Together, these findings show that key structures of the limbic forebrain exhibit daily oscillations in clock gene expression that are controlled not only by input from the SCN but, importantly, by hormonal and neurochemical changes that normally accompany motivational and emotional states. Thus, cells within these areas are strategically positioned to integrate the inputs from the SCN and emotional states to modulate circadian rhythms downstream from the SCN clock.

A circadian rhythm in the expression of PERIOD2 protein reveals a novel SCN-controlled oscillator in the oval nucleus of the bed nucleus of the stria terminalis

Circadian rhythms in mammals are regulated not only globally by the master clock in the suprachiasmatic nucleus (SCN), but also locally by widely distributed populations of clock cells in the brain and periphery that control tissue-specific rhythmic outputs. Here we show that the oval nucleus of the bed nucleus of the stria terminalis (BNST-OV) exhibits a robust circadian rhythm in expression of the Period2 (PER2) clock protein. PER2 expression is rhythmic in the BNST-OV in rats housed under a light/dark cycle or in constant darkness, in blind rats, and in mice, and is in perfect synchrony with the PER2 rhythm of the SCN. Constant light or bilateral SCN lesions abolish the rhythm of PER2 in the BNST-OV. Large abrupt shifts in the light schedule transiently uncouple the BNST-OV rhythm from that of the SCN. Re-entrainment of the PER2 rhythm is faster in the SCN than in the BNST-OV, and it is faster after a delay than an advance shift. Bilateral adrenalectomy blunts the PER2 rhythm in the BNST-OV. Thus, the BNST-OV contains circadian clock cells that normally oscillate in synchrony with the SCN, but these cells appear to require both input from the SCN and circulating glucocorticoids to maintain their circadian oscillation. Taken together with what is known about the functional organization of the connections of the BNST-OV with systems of the brain involved in stress and motivational processes, these findings place BNST-OV oscillators in a position to influence specific physiological and behavioral rhythms downstream from the SCN clock.

Preprotachykinin-A gene expression in the forebrain of Sardinian alcohol-preferring and -nonpreferring rats

Increasing evidence suggests that TKergic mechanisms might play a role in ethanol intake control. Preprotachykinin-A (PPT-A) mRNA brain levels were measured in Sardinian alcohol-preferring (sP) and Sardinian alcohol-nonpreferring (sNP) rats. PPT-A mRNAs were about 50% lower in sP than in sNP rats in the bed nucleus of the stria terminalis (BNST), whereas levels in the olfactory tubercle (Tu) were about 30% higher in sP than in sNP rats. Our findings suggest that altered PPT-A gene expression might contribute to the different ethanol preference and intake of sP opposite to sNP rats.

Adrenalectomy-induced neuronal degeneration

The binding of glucocorticoids to CNS receptors results in the modulation of many processes, ranging from neurotransmission to cell birth and death. It is of no surprise, therefore, that the removal of these steroids following adrenalectomy disrupts a variety of physiological functions throughout the brain. It is the aim of this review to briefly describe the findings of research examining some of these glucocorticoid-mediated CNS effects; however, as many of these areas have been reviewed extensively by others, this review will focus on the recently described phenomenon, adrenalectomy-induced hippocampal cell death.

In situ hybridization analysis of preprotachykinin-A and -B mRNA levels in short-term sodium depletion

Tachykinins inhibit salt appetite when applied intracranially in a number of brain regions and may function as endogenous inhibitors of sodium intake. To test the hypothesis that induced increases in salt appetite might involve disinhibition via a reduction in endogenous tachykinin expression, we used a semi-quantitative in situ hybridization analysis to investigate changes in brain areas expressing preprotachykinin-A (PPT-A) and preprotachykinin-B (PPT-B) mRNAs of rats after 1 day of sodium depletion (1d Na dep). PPT-A mRNA levels were detected in neurons of the olfactory tubercle (Tu), the nucleus of the olfactory tubercle (LOT), the dorsal and ventral caudate-putamen (d-CPu and v-CPu), the bed nucleus of the stria terminalis (BNST), the medial preoptic area (mPOA), the habenula (Hb) and the postero-dorsal part of the amygdala (MePD). PPT-B mRNA levels were measured in fundus striati (FStr), d-CPu, v-CPu, BNST, mPOA, dorsomedial hypothalamic nucleus (DMD), arcuate nucleus (Arc), central amygdaloid nucleus (CeL), basolateral amygdaloid nucleus (BLV), LOT, Hb and basal nucleus of Meynert (B). 1d Na dep reduced by 33-61% the mean number of PPT-A grains/cell in Tu, LOT, d-CPu, BNST, mPOA, Hb and MePD compared to control animals. Levels of PPT-B mRNA were not reduced as much by 1d Na dep, although statistically significant reductions of 26, 34 and 17% were found in v-CPu, BNST and B, respectively. These findings, therefore, support the hypothesis that endogenous tachykinins exert an inhibitory influence over sodium appetite.

Regulation of preprotachykinin-A mRNA in genetic hypertensive and normotensive rats

It is well-known that central administration of tachykinins (Tks) inhibit salt intake in rats. Recent studies have shown that conditions that arouse salt appetite, such as adrenalectomy and sodium depletion, induce a decrease in preprotachykinin-A (PPT-A) mRNA in discrete regions of the rat brain, suggesting that reduced levels of PPT-A mRNA in the brain may have a permissive role on the expression of salt appetite. It has also been shown that spontaneously hypertensive rats (SHR) show higher avidity for salty solutions than their normotensive control Wistar-Kyoto (WKY) rats. In this regard, the present study tested whether SHR and WKY rats differ in expression of the gene coding for PPT-A, the precursor for Tks peptides. Using semi-quantitative in situ hybridization histochemistry, we examined the level of PPT-A mRNA in discrete rat brain regions of SHR and WKY rats under no treatment, after 1 or 3 days of Na+ depletion. Levels of PPT-A mRNA were analysed in the olfactory tubercle (Tu), in the lateral olfactory tubercle (LOT), in the dorsal and ventral caudate putamen (d/v CPu), in the medial preoptic area (mPOA), in the bed nucleus of the stria terminalis (BNST), in the habenula (Hb) and in the postero-dorsal part of the amygdala (MePD). Semi-quantitative analysis of silver grains revealed a 27.5% lower expression of the PPT-A mRNA levels in SHR opposite to WKY rats under no treatment in v-CPu, mPOA, BNST and Hb. 1 day of Na+ depletion reduced PPT-A mRNA levels when opposite to Na+-repleted animals in Tu and mPOA in both SHR and WKY rats. On the other hand, when comparing SHR and WKY rats after 1 day of Na+ depletion, a 26% lower level of PPT-A mRNA was detected in Tu and d-CPu of SHR opposite to WKY rats whereas a 14% and an 18% lower level was detected in v-CPu and Hb, respectively. A lower expression of PPT-A mRNA in SHR compared to WKY rats was also found in BNST and MePD, although no statistical significance was detected in these two brain areas. In the last experiment, 3 days of Na+ depletion reduced PPT-A mRNA levels in mPOA while negligibly increased mRNA levels in d-CPu and v-CPu, in BNST, Hb and MePD, both in SHR and WKY rats. Conversely, when making comparisons between the two strains, a 35% lower level of PPT-A mRNA in SHR with respect to WKY rats was found after 3 days of Na+ depletion in d-CPu, v-CPu and mPOA. A lower gene expression, even though not statistically significant, was found in Tu, LOT, MePD. These findings show a consistent difference of PPT-A mRNA levels in discrete regions of the SHR brain opposite to WKY rats and confirm that 1 day of Na+ depletion reduces PPT-A mRNA in discrete brain regions. Since SHR are notoriously more salt-avid than WKY rats and Tks are potent inhibitors of sodium intake, the down-regulation of PPT-A mRNA may contribute to the higher natriophilia and, therefore, to the etiology of the hypertensive disease.

Effects of deoxycorticosterone acetate and diazepam on neuropeptidergic neurons in rat striatum

The neurosteroid tetrahydrodeoxycorticosterone (THDOC) interacts with gamma-aminobutyric acid (GABA)/ benzodiazepine (BZ) receptors. To test the hypothesis that THDOC works partially through mechanisms associated with GABAA/BZ receptor function, deoxycorticosterone acetate (DOCA) and the benzodiazepine, diazepam (DZ), were administered short- (1 day) and long-term (11 days). Levels of mRNA for dynorphin, preprotachykinin and preproenkephalin in the striatum of adult male Sprague-Dawley rats were measured by in situ hybridization. Acute DOCA and DZ treatment produced parallel neuropeptide mRNA profiles, whereas chronic DOCA and DZ treatment yielded different patterns of neuropeptide gene expression. Chronic DZ treatment resulted in no significant increase in salt intake whereas chronic DOCA activated salt appetite. We suggest that acute DZ and DOCA interact with GABAA/BZ receptors; however, the results of chronic treatment suggest that DZ and DOCA operate through dissimilar mechanisms.

Regulation of angiotensinogen gene expression in the rat forebrain by adrenal steroids and relation to salt appetite

The renin-angiotensin system (RAS) is present in the brain where it participates in regulation of fluid-electrolyte homeostasis and possibly plays a role in arousal of salt appetite. In the present studies using quantitative in situ hybridization histochemistry we examined the level of the angiotensinogen (ANG) mRNA in the forebrain areas associated with fluid-electrolyte balance in adrenalectomized (ADX) rats and ADX rats supplemented either with selective glucocorticoid type II receptor agonist RU 28362 or with the selective type I receptor agonist, aldosterone (ALDO). RU 28362 and ALDO were administered for 7 days via Alzet 2001 osmotic minipumps at the rates of 10 micrograms/microliters/h and 1 microgram/microliter/h, respectively. Following adrenalectomy, rats were maintained on a standard rat chow, water and 3% NaCl ad lib. In situ hybridization was performed either with a synthetic [33P]- or [32P]-3' end-labeled oligonucleotide probe and the level of ANG mRNA was detected by grain counting over a single cell or by quantitative film autoradiography, respectively. Seven days post ADX the ANG mRNA level in all studied forebrain areas -septum-diagonal band of Broca (SEPT/DBB), the areas immediately adjacent to the organum vasculosum of the lamina terminalis (OVLT), the median preoptic nucleus (MnPO), and the medial preoptic area (mPOA)-of ADX rats decreased by 50-60%. ALDO treatment, which did prevent ADX-induced saline ingestion, did not prevent this decrease. However, supplementation with RU 28362 maintained normal levels of ANG mRNA in all the above regions of the brain. Thus the expression of the ANG gene in the studied areas of rat forebrain is predominantly under the control of the adrenal glucocorticoids via the type II receptor and not regulated by an ALDO dose that stabilizes natriuresis from the kidney.