Biomedical subjects

H Akil

Publications and source records attributed to H Akil.

At least 145 records · Page 8Linked to original sources

PubMed1993

Altered ratios of beta-endorphin: beta-lipotropin released from anterior lobe corticotropes with increased secretory drive. I. Effects of diminished glucocorticoid secretion.

Previous studies have demonstrated that acute stress or ovine corticotropin-releasing hormone (oCRH) in vivo, or oCRH in vitro, stimulates release of beta-endorphin over beta-lipotropin from anterior pituitary corticotropes. This occurs despite the predominance of beta-lipotropin in corticotrope peptide stores. In vitro studies with primary anterior pituitary cultures suggested that chronic exposure to oCRH results in a shift towards more beta-lipotropin secretion into the media than with short-term exposure. The current studies explored whether increased secretory drive in vivo results in a similar shift towards more beta-lipotropin. We used removal of glucocorticoids by adrenalectomy or metyrapone blockade of corticosterone synthesis, to stimulate endogenous secretion of CRH and vasopressin. Both treatments resulted in shifts of the ratio of beta-endorphin: beta-lipotropin in plasma of experimental animals in comparison to the sham-treated control rats. In vitro testing with oCRH of anterior lobe cultures from adrenalectomized or metyrapone-treated rats demonstrated similar effects of these treatments on the ratio of beta-endorphin:beta-lipotropin. These changes occurred despite similar ratios of beta-endorphin:beta-lipotropin in anterior pituitary peptide stores.

Adrenalectomy↗

PubMed1993

Altered ratios of beta-endorphin:beta-lipotropin released from anterior lobe corticotropes with increased secretory drive. II. Repeated stress.

A number of stimuli including acute footshock and electrically-induced seizures lead to release of beta-endorphin immunoreactivity from the anterior pituitary corticotropes. Gel filtration of this beta-endorphin immunoreactivity indicates that approximately 3-fold more beta-endorphin than beta-lipotropin is released into plasma following these acute stressors. A similar preponderance of beta-endorphin over beta-lipotropin is seen in the media of short-term anterior lobe cell suspensions stimulated with ovine corticotropin-releasing hormone. Previous studies indicated that footshock stress, when administered repeatedly, can increase the biosynthesis of anterior lobe proopiomelanocortin (POMC) as indicated by increased steady state adrenocorticotropin/beta-endorphin content as well as increased POMC mRNA levels and increased POMC biosynthesis and rate of processing as measured by pulse-labeling and pulse-chase studies. The goal of the present studies was to determine whether this increased biosynthetic drive results in an alteration in the end products secreted with repeated stress. Acute footshock in a rat which has received 14 days of chronic footshock releases proportionately more beta-lipotropin than is released in a naive rat. Chronic electrically-induced seizures, which also increase anterior lobe POMC derived peptide stores, lead to a similar shift in the ratio of beta-lipotropin:beta-endorphin released following stress. These data suggest that chronic drive and the subsequent changes in POMC peptide stores may lead to a decrease in the proportion of beta-endorphin size immunoreactivity in the releasable pool of the anterior lobe corticotrope, thus altering the hormonal signal from the anterior lobe corticotrope.

Adrenocorticotropic Hormone↗

PubMed1993

Effects of chronic morphine treatment on beta-endorphin-related peptides in the caudal medulla and spinal cord.

The effects of chronic morphine treatment on beta-endorphin (beta E)-immunoreactive (beta E-ir) peptide levels were determined in the rat caudal medulla and different areas of the spinal cord. Seven days of morphine pelleting had no effect on total beta E-ir peptides in the caudal medulla. In contrast, it significantly increased beta E-ir peptide concentrations in the cervical and thoracic regions of the spinal cord compared with placebo-pelleted controls, whereas in the lumbosacral region this trend did not reach statistical significance. Injections of the opiate receptor antagonist naloxone 1 h before the rats were killed had no effect on the morphine-induced increases in the cord. Chromatographic analyses revealed that enzymatic processing of beta E-related peptides in the spinal cord seemed unaffected by the morphine and/or naloxone treatments. In light of previous data showing that morphine down-regulates beta E biosynthesis in the hypothalamus, the present results suggest that the regulation of beta E-ir peptides in the spinal cord is distinct from that found in other CNS areas. These data provide support for previous results suggesting that beta E-expressing neurons may be intrinsic to the spinal cord.

Animals↗

PubMed1993

Pre- and posttranslational regulation of beta-endorphin biosynthesis in the CNS: effects of chronic naltrexone treatment.

There appear to be two anatomically distinct beta-endorphin (beta E) pathways in the brain, the major one originating in the arcuate nucleus of the hypothalamus and a smaller one in the area of the nucleus tractus solitarius (NTS) of the caudal medulla. Previous studies have shown that these two proopiomelanocortin (POMC) systems may be differentially regulated by chronic morphine treatment, with arcuate cells down-regulated and NTS cells unaffected. In the present experiments, we examined the effects of chronic opiate antagonist treatment on beta E biosynthesis across different CNS regions to assess whether the arcuate POMC system would be regulated in the opposite direction to that seen after opiate agonist treatment and to determine whether different beta E-containing areas might be differentially regulated. Male adult rats were administered naltrexone (NTX) by various routes for 8 days (subcutaneous pellets, osmotic minipumps, or repeated intraperitoneal injections). Brain and spinal cord regions were assayed for total beta E-ir, different molecular weight immunoreactive beta-endorphin (beta E-ir) peptides, and POMC mRNA. Chronic NTX treatment, regardless of the route of administration, reduced total beta E-ir concentrations by 30-40% in diencephalic areas (the arcuate nucleus, the remaining hypothalamus, and the thalamus) and the midbrain, but had no effect on beta E-ir in the NTS or any region of the spinal cord. At the same time, NTX pelleting increased POMC mRNA levels in the arcuate to approximately 140% of control values.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Diurnal CRH mRNA rhythm in the hypothalamus: decreased expression in the evening is not dependent on endogenous glucocorticoids.

Levels of hypothalamic corticotropin-releasing hormone (CRH) mRNA and plasma glucocorticoids vary diurnally as a result of circadian influences on the hypothalamopituitary-adrenal axis. CRH mRNA expression increases from morning to afternoon in rats but decreases rapidly near the onset of dark as glucocorticoids reach peak concentrations in plasma. Since glucocorticoids are normally inhibitory on hypothalamic CRN mRNA expression, we determined whether the glucocorticoid secretion at the diurnal peak reduced CRH mRNA concentration in the evening. We found that adrenalectomy did not prevent the decrease in CRH mRNA levels near the onset of dark. It appears that the drop in CRH mRNA expression occurs via a steroid-independent mechanism. While the mean CRH mRNA level increased after adrenalectomy, the shape of the CRH mRNA rhythm remained unchanged except in the morning. Interestingly, adrenalectomy increased CRH mRNA levels disproportionately in the morning, producing a sharp rise followed by a plateau during the light phase instead of the gradual rise observed in intact animals. We subsequently treated adrenalectomized animals with corticosterone pellets to determine whether a constant steroid signal was sufficient in restoring the normal shape of the mRNA rhythm during the light phase. Results indicate that the endogenous steroid rhythm is not necessary for generating the normal CRH mRNA rhythm during the light phase. Instead, a constant exposure to corticosterone at approximately 50% of the daily mean (2.4-3 micrograms/dl) appears to be sufficient for regulation of the mRNA rhythm.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗

PubMed1993

Tissue-specific and substrate-specific endoproteolytic cleavage of monkey pro-opiomelanocortin in heterologous endocrine cells: processing at Lys-Lys dibasic pairs.

This study compares the processing of pro-opiomelanocortin (POMC) at two Lys-Lys cleavage sites, located in the carboxy-terminal domain of the precursor, one site marking the amino terminus of beta-melanocyte-stimulating hormone (beta-MSH) and the other in the carboxy-terminus of beta-endorphin (beta E). These comparisons were carried out by transfecting monkey POMC cDNA into two heterologous cell lines: AtT-20, which endogenously expresses mouse POMC, and Rin m5F, which has been previously used as a host for transfected POMC. These cells lines are known to process POMC differently at Lys-Arg residues, though less is known about their Lys-Lys cleavage. Our results have demonstrated both tissue-specific and site-specific factors controlling Lys-Lys cleavage. The AtT-20 line appears not to perform either Lys-Lys cleavage. Rin m5F cells, on the other hand, fail to process the site at the carboxy terminus of beta E (beta E28-29) but do process, to a significant extent, the N-terminal site to beta-MSH. That this differential processing is unlikely to be due to a POMC conformation which would make the beta E site inaccessible was demonstrated by mutating the sites from Lys-Lys to Lys-Arg. With such mutants, Rin m5F cells fully processed at both locations. Interestingly, the mutant Lys-Arg sites were not fully processed by AtT-20 cells. These results are discussed in terms of the complement of processing enzymes expressed in each of the cell lines, as well as the role of residues surrounding the diabasic cleavage sites in determining the likelihood of proteolysis.

APUD Cells↗

PubMed1993

Dopamine regulation of swim stress induction of the pituitary intermediate lobe proopiomelanocortin system.

Previous studies have indicated that 30 min of swimming in room temperature water is a potent stimulus for the secretion of beta-endorphin (beta E) from the intermediate lobe (IL) of the pituitary in rodents. Repeated daily challenge with this paradigm over days to weeks leads to a progressive increase in proopiomelanocortin (POMC)-derived IL peptides and POMC mRNA levels as well as an increase in the stimulated secretion of beta E in response to rechallenge with swim. The current studies were undertaken to examine the possible role of dopamine systems in mediating swim stress-induced changes in IL beta E biosynthesis and release. Confirming previous results, a 30 min swim stress exposure caused plasma concentrations of beta E to increase several fold. Apomorphine (APO), a dopaminergic agonist, completely blocked this effect, suggesting that dopamine receptors may mediate the acute IL response to swim stress. Animals that swam once daily for 14 days displayed elevated beta E levels in both the IL and plasma 24 h after the last swim session. In these animals, repeated administration of APO did not reverse swim-stress-induced changes in beta E. Immediately following an acute-swim rechallenge, animals which had been previously swim-stressed for 14 days demonstrated significantly greater beta E release than naive animals. Again, an acute injection of APO inhibited the acute increase in IL secretion, suggesting that repeatedly swum animals are still responsive to the acute effects of APO even though repeated coadministration of APO with swim exposure had no effect on IL beta E peptide stores or plasma beta E concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Pituitary-adrenal response to ether vapor in the weanling animal: characterization of the inhibitory effect of glucocorticoids on adrenocorticotropin secretion.

The hypothalamic-pituitary-adrenal axis is hyporesponsive to stimuli during early life in the rat. Once the adrenocortical response is established, failure to terminate the corticosterone (B) rise is evident after certain stressors, such as ether. The purpose of this study was 2-fold: 1) to investigate the B and ACTH response to ether vapor in young animals and 2) to test the ability of glucocorticoids to inhibit the ether ACTH-stimulated secretion in weanling animals. Rats aged 14, 18, and 25 d and adult rats were subjected to ether vapor for 3 min. Plasma was collected for B and ACTH determination by RIA at 0, 5, 15, 30, 60, and 120; min after ether exposure. Maximum B levels were observed at different times after exposure: 15 min in the adult and 30 min in the younger animals. In addition, B levels were significantly elevated at 60 min in the d 25 and d 18 rats compared with the adult (d 25 = 672.4 +/- 28.9, d 18 = 744.6 +/- 31.7, adult = 323.2 +/- 8.7 mol/L +/- SEM; d 25 = 23.3 +/- 1.0, d 18 = 25.8 +/- 1.1, adult = 11.2 +/- 0.3 micrograms/dL +/- SEM). The B delay observed in the younger animals was not due to a delayed ACTH response because maximal ACTH values were observed 5 min after ether exposure in all ages (d 14 = 21.9 +/- 4.8, d 18 = 35.8 +/- 21.3, d 25 = 82.01 +/- 16.5, adult = 98.9 +/- 25.2 x 10(-12) mol/L +/- SEM). However, in the d 25 rats the ACTH level remained significantly elevated 30 min after the ether vapor challenge (5 min = 86.9 +/- 25.2, 30 min = 61.8 +/- 4.8, 60 min = 15.3 +/- 4.1 x 10(-12) mol/L +/- SEM). The delay to return to resting ACTH levels was consistent with the time delay observed for the B release from the adrenal.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗

PubMed1993

5'-Heterogeneity of the mineralocorticoid receptor messenger ribonucleic acid: differential expression and regulation of splice variants within the rat hippocampus.

The mineralocorticoid receptor (MR) cDNA we previously isolated from the rat hippocampus differs from the clone isolated from the kidney at the 5'-untranslated (5'UT) region. The kidney clone (alpha MR mRNA) and the hippocampal clone (beta MR mRNA) possess unique 5'UT sequences of 220 and 300 nucleotides, respectively, but share an invariant peptide-coding domain and appear to encode an identical MR protein. The two mRNA variants may represent tissue-specific forms of the MR or may be coexpressed in the rat hippocampus along with other 5'UT variants. Here, we report that three mRNA subtypes were found in the hippocampus; their relative abundance was as follows: alpha = beta >> gamma. The three mRNA variants were differentially distributed within the hippocampal subfields, with the alpha form being highly enriched in CA2, dentate, the fasciculum cinereum, and the indusium griseum, whereas beta and gamma forms were evenly distributed through CA1-4. Adrenalectomy selectively increased alpha MR mRNA content, but the changes were restricted to CA1, CA2, and CA3 regions. We conclude that multiple MR mRNAs are differentially expressed in the rat hippocampus. The expression of alpha MR mRNA is specifically increased during adrenalectomy, suggesting that the increase in total MR mRNA content documented previously arises from a substantial increase in a single MR variant that elevates the total MR mRNA content, with the apparent elevation reflecting the average of regulated and unregulated transcripts. It is suggested from our data that a complex mechanism involving transcription and translation regulates MR expression in the rat hippocampus.

Adrenalectomy↗

PubMed1993

Prodynorphin gene expression in the rat intermediate pituitary lobe: gender differences and postpartum regulation.

The distribution of prodynorphin (proDyn) messenger RNA (mRNA) was examined in the rat pituitary using Northern and in situ hybridization analysis. Anterior pituitary gonadotrophs are known to express ProDyn, but the present study demonstrated that proDyn mRNA was also expressed in the intermediate lobe melanotrophs and was colocalized with POMC mRNA. The 2.6-kilobase proDyn transcript observed in the intermediate lobe was shown to be translatable by polysome analysis. Immunohistochemical studies showed dynorphin (Dyn)-like immunoreactivity in all intermediate lobe melanotrophs. Intermediate lobe proDyn gene expression was not regulated by dopamine, in contrast to intermediate lobe POMC mRNA levels, which were increased with haloperidol and decreased with bromocriptine treatment, as expected. A gender difference in ProDyn gene expression was noted, since intermediate lobes of male rats had nearly 2-fold higher proDyn mRNA levels than intermediate lobes of female rats. In contrast, no gender difference of intermediate lobe POMC mRNA levels were detected. ProDyn mRNA levels were up-regulated by 3- to 4-fold in the intermediate lobes of postpartum females as compared to pregnant or nonpregnant female rats, whereas POMC mRNA levels were unchanged, suggesting a role for intermediate lobe ProDyn in the postpartum period of the female rat. Although our results demonstrate proDyn and POMC coexpression in the pituitary intermediate lobe melanotrophs and show a differential regulational control for each gene in this tissue, the present data also strengthen the notion that proDyn is a precursor that has a role to play in reproductive functions.

Animals↗

PubMed1993

Corticosteroids regulate brain hippocampal 5-HT1A receptor mRNA expression.

Using in situ hybridization techniques, the expression of 5-HT1A receptor mRNA was measured within the hippocampal formation after bilateral adrenalectomy (ADX). After 24 hr ADX, 5-HT1A receptor mRNA expression was significantly increased in all hippocampal subfields in ADX animals relative to sham-operated controls (SHAM). The magnitude of the increase was most pronounced within CA2 (127%) and CA3/4 (94%)-subfields of dorsal hippocampus, intermediate in the dentate gyrus (73%), and least within CA1 (60%). Administration of exogenous corticosterone (CORT) at the time of ADX maintained the level of 5-HT1A receptor mRNA expression within the range of SHAM animals. In vitro receptor autoradiographic analysis of 5-HT1A receptors in adjacent sections from the same animals indicated a simultaneous increase in 5-HT1A binding throughout the hippocampus in response to ADX. 5-HT1A binding increased to a similar extent (approximately 30%) in CA subfields and dentate gyrus but remained within SHAM levels in CORT-replaced animals. 5-HT1A receptor mRNA levels were also increased in hippocampal subregions of 1 week ADX animals relative to SHAM animals. Within both CA1 and CA2 subfields, the increments were approximately double those observed after 1 d ADX. 5-HT1A receptor binding was increased in every hippocampal subfield to a similar extent as that observed after 1 d ADX. Increases in both 5-HT1A receptor mRNA expression and 5-HT1A receptor binding were preventable by administration of exogenous CORT at the time of ADX. Hippocampal 5-HT1C receptor mRNA and D1 receptor mRNA expression were not significantly altered by either acute or chronic ADX treatment. These data indicate that adrenal steroids may selectively regulate hippocampal 5-HT1A receptors at the level of 5-HT1A receptor mRNA expression.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1992

Selective forebrain fiber tract lesions implicate ventral hippocampal structures in tonic regulation of paraventricular nucleus corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) mRNA expression.

The hippocampus appears to be involved in tonic regulation of the hypothalamo-pituitary-adrenocortical axis via interactions with corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP)-containing neurons of the hypothalamic paraventricular nucleus (PVN). To further investigate the anatomical basis of such interactions, lesions were made to forebrain fiber tracts in position to communicate inhibitory information from the hippocampus to the PVN. Total fimbria-fornix transections (TFF) and lateral fimbria-fornix lesions (LFF) both significantly increased CRH mRNA levels in the medial parvocellular PVN, as assayed by semi-quantitative in situ hybridization histochemistry. Medial fimbria-fornix lesions or section of the medial corticohypothalamic tracts (MCHT) did not influence CRH mRNA levels. The LFF group showed increases in both AVP mRNA and ACTH secretion, whereas no other lesion was effective in this regard. The results suggest: (1) hippocampal efferents conferring tonic inhibition of the HPA axis probably originate in regions contributing to the lateral extent of the fornix, representing structures in the ventral subiculum and ventral extent of CA1; (2) projections from the hippocampus to the medial basal hypothalamus (travelling in the MCHT) are unlikely to affect HPA function; (3) hippocampus may influence the PVN CRH/AVP neuron at multiple levels, in that LFF and TFF lesions have differential effects on PVN AVP mRNA levels and ACTH secretion.

Adrenocorticotropic Hormone↗

PubMed1992

Site-directed mutagenesis of the human dopamine D2 receptor.

Based on amino acid sequence and computer modeling, two conflicting three-dimensional models of the dopamine D2 receptor have been proposed. One model (Dahl et al., 1991, Proc. Natl. Acad. Sci. USA 88, 8111) suggests that dopamine interacts with aspartate 80 of transmembrane (TM) 2 and asparagine 390 of TM6 with the transmembranes arranged in a clockwise manner, while a second model (Hibert et al., 1991, Mol. Pharmacol. 40, 8) suggests that dopamine interacts with aspartate 114 of TM3 and the serines of TM5 (194 and 197) with the transmembranes arranged in a counterclockwise manner when viewed from the extracellular space. The present study tests the latter model by selectively mutating aspartate 114 and serines 194 and 197 of the human dopamine D2 receptor by site-directed mutagenesis. In addition, two methionines (116 and 117) were mutated to evaluate whether residues near aspartate (114) of the dopamine D2 receptor are critical in differentiating dopamine receptor agonists from adrenoceptor agonists. Removal of the negative charge with the mutation of aspartate (114) to either asparagine or glycine led to a total loss of both agonist and antagonist binding. Individual or dual methionine mutations in positions 116 and 117, to make the dopamine D2 binding pocket more closely resemble the beta 2-adrenoceptor, did not result in a change in selectivity toward noradrenergic agonists or antagonists. The serine mutations revealed interesting differences between the dopamine D2 receptor and the adrenoceptors. In particular, serine 197 appeared more important than serine 194 for agonist binding. In addition, the binding of one agonist (N-0437) was unaffected by individual serine mutations, while the binding of some antagonists, such as raclopride and spiperone, was significantly altered. These findings are discussed in relation to ligand structure and their interactions with the putative binding pocket.

Amino Acid Sequence↗

PubMed1992

Evidence that beta-endorphin is synthesized in cells in the nucleus tractus solitarius: detection of POMC mRNA.

Evidence from a number of sources indicates that the major site of pro-opiomelanocortin (POMC)-producing cells in the CNS is the arcuate nucleus of the hypothalamus. Using immunocytochemical techniques, a second, smaller group of POMC cells has been detected in the nucleus tractus solitarius (NTS) area of the caudal medulla. However, POMC mRNA has never been reported in the NTS even though it has been found in other extrahypothalamic brain regions. Thus, there is some uncertainty as to whether POMC peptides are actually synthesized de novo in the NTS. In the present study, we used biochemical and anatomical techniques to examine whether POMC mRNA is localized in the NTS. Using in situ hybridization, cells containing POMC mRNA were found in the caudal portion of the NTS. The nucleic acid distribution correlated well with the anatomical distribution of 16k POMC peptide immunoreactivity as determined by immunocytochemistry. Northern analysis revealed that the apparent size of POMC mRNA in the NTS was similar to that found in the arcuate nucleus or the pituitary gland. Results of RNase protection assays using a POMC riboprobe complementary to the 5' end of exon 3 suggested that POMC mRNA in the NTS and arcuate nucleus are identical in this region of the message at least. We also calculated POMC peptide product to mRNA ratios in different tissues and found that NTS cells appear to produce less peptide per mRNA molecule than those in the arcuate nucleus or pituitary gland.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

A comparison of D1 receptor binding and mRNA in rat brain using receptor autoradiographic and in situ hybridization techniques.

D1, a subtype of the dopamine receptors, is widely distributed in the nervous system and has been shown to be positively coupled to adenylate cyclase. Using a combination of in vitro receptor autoradiographic and in situ hybridization techniques, the present study examines the co-distribution of D1 receptor binding sites and D1 receptor mRNA in adjacent rat brain sections. D1 receptor binding sites were labeled using the selective antagonist [3H](R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzaz epin- 7-ol (SCH23390) (4.6 nM), in the presence of 1 microM ketanserin, while the D1 receptor mRNA was visualized with a 35S-labeled riboprobe corresponding to a region between transmembrane domains III and VI of the rat D1 receptor (base pairs 383-843). Analysis of serial sections suggested a good agreement between D1 receptor binding and mRNA in several brain regions, including the paleocortex, caudate-putamen, nucleus accumbens, amygdala, and suprachiasmatic nucleus. Marked discrepancies between D1 receptor binding and mRNA were observed in other brain regions including the entopeduncular and subthalamic nuclei, substantia nigra (pars reticulata), hippocampus, and cerebellum. While technical considerations may contribute to these results, much of the discordance between the distributions is probably due to the differential localization of D1 receptor mRNA in cell bodies and receptor binding sites on fibers and may provide insights into receptor synthesis, transport, and membrane insertion. In the basal ganglia, for instance, D1 receptors are synthesized in the striatum and are either transported to efferent projections in areas such as the substantia nigra, or remain localized in striatal cells bodies. Ibotenic acid lesions in the striatum are consistent with these conclusions and demonstrate a coordinate loss of D1 receptor binding and mRNA in the caudate-putamen that is accompanied by a degeneration of fibers projecting to substantia nigra and a loss of D1 binding in the pars reticulata. Neurons in the dentate gyrus and in the granular layer of the cerebellum, on the other hand, synthesize D1 receptors and transport them entirely to either their dendritic or axonal fields, respectively, in the molecular layer. This analysis provides a better understanding of dopaminergic receptor systems in the CNS and their anatomical organization.

Animals↗

PubMed1992

Diurnal corticotropin-releasing hormone mRNA variation in the hypothalamus exhibits a rhythm distinct from that of plasma corticosterone.

The hypothalamopituitary-adrenal axis exhibits a diurnal rhythm as witnessed by the daily excursion of corticosterone in plasma. The rhythm appears to be mediated largely by the stimulation of CRH neurons in the paraventricular nucleus (PVN) of the hypothalamus. In the present study, we investigated the effects of circadian influence on CRH mRNA levels in the paraventricular hypothalamus. Animals were sacrificed through a 24-hour period to establish a detailed time course of CRH mRNA fluctuations. Levels of both type I and type II corticosterone receptor mRNAs were also measured in this area to see whether changes correlate with that of CRH mRNA. Plasma levels of ACTH were quantified as an index for CRH peptide secretion. The results indicate that changes in ACTH closely paralleled alterations in corticosterone levels with an increasing trend starting at 1 PM, suggesting that the diurnal secretory drive commences around this time. The CRH mRNA rhythm as determined by RNase protection assays appeared to change in an anticipatory fashion to these endocrine fluctuations, increasing during the light phase and reaching maximal levels just prior to dark (5-6 PM). An abrupt decrease of 30% in the CRH mRNA content was detected in the hypothalamus within 2 h after dark (8 PM) and coincided with the peak of plasma corticosterone levels. However, other periodic variations in the CRH mRNA content were not accompanied by changes in plasma corticosterone. Neither types of corticosterone receptor mRNAs showed any diurnal change suggesting that the expression of steroid receptors in the hypothalamus is not regulated by circadian influences. We conclude that CRH mRNA levels fluctuate diurnally but are inversely related to corticosterone levels only in the early evening.

Adrenocorticotropic Hormone↗

PubMed1992

Development of pituitary pro-opiomelanocortin gene and peptide expression: characterization and effect of repeated intermittent maternal isolation.

The dynamics of pro-opiomelanocortin (POMC) biosynthesis in the adult rat are altered by demands imposed on the system, such that acute stress increases in the efficiency of anterior pituitary (AP) posttranslational events, while repeated stress increases pretranslational events. In contrast, the developing animal has a limited adrenocortical response to acute stress during the first 2 weeks of life (stress nonresponsive period). In this study, we investigated how the maturing AP and intermediate lobe (IL) POMC cells respond to repeated demand. Measurements of AP and IL POMC mRNA and POMC peptides were performed using Northern gels and radioimmunoassay, respectively. Plasma ACTH and corticosterone measurements were also performed. Maternal isolation, for 1 h on 3 consecutive days, was used as a repeated stress stimulus. The developing AP and IL exhibit an age-related increase in POMC mRNA and peptide levels. On the other hand, AP and IL do not respond to repeated intermittent maternal isolation during the first 2 weeks of life. However, a significant corticosterone release is seen in the 14 and 21-day-old animals. A change in POMC mRNA level is only detected in the 21-day-old AP where levels decrease. Therefore, an adrenocortical response to repeated intermittent maternal isolation predates the appearance of glucocorticoid inhibition of POMC expression in the 21-day-old animal. We propose that an immature neuronal inhibitory circuit during the 3rd week of life causes a sustained corticosteroid response which may in turn trigger AP-delayed feedback.

Animals↗

PubMed1992

Localization and quantification of pro-opiomelanocortin mRNA and glucocorticoid receptor mRNA in pituitaries of suicide victims.

Suicidal behavior has been associated with hypothalamic-pituitary-adrenal overactivity in humans, as measured by increased corticosteroid secretion. To investigate whether this overactivity is reflected at the pituitary level, we have studied the localization of pro-opiomelanocortin (POMC) mRNA, and glucocorticoid receptor (GR) mRNA, in human anterior pituitaries, and quantified these messages relative to controls. Pituitaries from 7 suicide victims and 11 cardiac deaths were sectioned into 10-microns slides, stained with thionin and processed for in situ hybridization using a riboprobe complementary to human POMC mRNA. To correct for possible postmortem cell loss, hybridization with P1B15, a cDNA complementary to rat cyclophillin mRNA, was used in adjacent sections. POMC mRNA containing cells were found to be localized in clusters and were highly associated with corticotropin-releasing hormone (CRH) receptors. In contrast, GR mRNA containing cells were distributed through the pituitary, although areas of increased density were associated with POMC mRNA cells. Quantification with a computerized image analysis system revealed a 25% increase in POMC message in suicide victims. Analysis of the corticotrophic cell clumps showed that the suicide victims had higher POMC mRNA density per cell (p = 0.04) and larger corticotrophic cell size (p = 0.04) than the cardiac death victims. No differences in GR mRNA were detected between the two groups, although GR and POMC mRNA levels were highly and significantly correlated (r = 0.8, p < 0.001). There were no differences in P1B15 message between the two groups. We conclude that in situ hybridization is a useful tool to study gene regulation in human neuroendocrine tissue and that suicide victims show evidence of chronic hypothalamic-pituitary-adrenal axis activation.

Adult↗