Glucocorticoid regulation of proopiomelanocortin messenger ribonucleic acid content of rat hypothalamus.

We have verified the possibility that the POMC gene of the rat hypothalamus might be subject to regulation by glucocorticoids. Adrenalectomy increased the concentration of POMC mRNA in anterior pituitary and in hypothalamus, but not in the neurointermediate lobe of the pituitary gland. Dexamethasone and, to a slightly lesser extent, corticosterone treatments reversed the adrenalectomy-induced increase in POMC mRNA concentrations in both anterior pituitary and hypothalamus. Dexamethasone caused a slight decrease of POMC mRNA levels in the neurointermediate lobe of the pituitary gland, while corticosterone had no effect. These results indicate that the POMC gene of the rat brain hypothalamus is also under negative control by glucocorticoids.

Effect of luteinizing hormone releasing hormone (LHRH) and [D-Trp6, des-Gly-NH2(10)]LHRH ethylamide on alpha-subunit and LH beta messenger ribonucleic acid levels in rat anterior pituitary cells in culture.

The effect of incubation with LHRH and its agonist [D-Trp6, des-Gly-NH2(10)]LHRH ethylamide has been measured on the concentrations of mRNAs for the common alpha-subunit of glycoprotein hormones and beta-LH in rat anterior pituitary cells in primary culture. After incubation, total RNA was analyzed by Northern blot or dot blot hybridization with alpha- and LH beta 32P-labeled cRNA probes and mRNA levels were quantified by autoradiography. Short-term treatment (4-6 h) of pituitary cells with 100 nM LHRH led to a marked stimulation of LH release but no effect was observed on alpha-subunit or LH beta mRNA levels. Longer (24-72 h) incubation periods with LHRH led to complete desensitization of the LH response to the neurohormone and induced 2- to 3-fold increases in alpha-mRNA cell content while LH beta mRNA levels remained unchanged. Maximal induction of alpha mRNA accumulation was observed with an LHRH concentration as low as 0.1 nM. Incubation with the LHRH agonist [D-Trp6, des-Gly-NH2(10)]LHRH ethylamide for 24-72 h also increased alpha mRNA but did not modify LH-beta mRNA levels. It is concluded that long-term exposure of anterior pituitary cells to LHRH or to an LHRH agonist positively regulates alpha-subunit gene expression in the absence of change in LH beta mRNA levels. This observation can provide an explanation for the high plasma levels of free alpha-subunits found in patients treated chronically with LHRH agonists.

Effect of neonatal thyroid deficiency on the catecholamine, substance P, and thyrotropin-releasing hormone contents of discrete rat brain nuclei.

The effects of neonatal thyroidectomy and thyroid hormone replacement therapy on the development of catecholamine-, TRH-, and substance P-containing neurons in discrete rat brain nuclei were studied. Newborn male rats were rendered hypothyroid by the injection of 125 muCi 131I and, after 45 days, were compared with normal littermate controls and 131I-injected animals subsequently maintained on T4 injections. The peptide or catecholamine content of discrete brain nuclei removed by punches of frozen brain slices was measured by RIA or radioenzymatic assay, respectively. The success of the thyroidectomy was verified by criteria of weight, length, plasma T4, and pituitary GH content. Animals receiving T4 replacement therapy were indistinguishable from normal littermates. Substance P was measured in 32 different brain nuclei and was significantly increased in 19 of these areas in hypothyroid animals. No changes in norepinephrine were detected, and the dopamine content of all but 3 brain nuclei was increased by thyroidectomy. The TRH concentration was drastically reduced in the median eminence of hypothyroid animals and also changed in 3 other extrahypothalamic areas. All of the changes seen in catecholamine, TRH, and substance P distribution in hypothyroid animals were completely reversed by T4 replacement therapy. These results demonstrate changes in brain peptide neurotransmitters during the hypothyroid state and open new vistas for comprehension of biochemical mechanisms underlying central nervous system malfunction.

Characteristics of the beta-adrenergic receptor in the rat ventral prostate using [125I]cyanopindolol.

The binding characteristics of the beta-adrenergic receptor in the rat ventral prostate homogenate have been studied using the highly potent beta-adrenergic antagonist [125I]cyanopindolol (CYP) as ligand. The bound ligand was separated from the free moiety by precipitation with polyethylene glycol (PEG-6000). This technique is simple, accurate, fast and more advantageous than filtration of the hormone-receptor complex on glass fiber filters or direct centrifugation. [125I]CYP binds to a single class of high affinity sites at an apparent KD value of 23 pM. Using 0.1 microM (-)propranolol to determine non-specific binding, a number of sites of 600 fmol/mg protein were measured. The observed order of potency of adrenergic agonists (KD values) in competing for [125I]CYP binding was: (-)isoproterenol (25 nM) greater than (-)epinephrine (74 nM) much greater than (-)norepinephrine (1900 nM). Detailed study of the binding potency of a large series of beta 1- and beta 2-adrenergic agonists and antagonists showed the presence of a typical beta 2-subtype adrenergic receptor in the rat ventral prostate. The best estimate indicates that the proportion of beta 2-adrenergic receptors in rat ventral prostate is more than 95% of the total population of beta-adrenergic receptors in this tissue. The high selectivity and density of beta 2-adrenergic receptors in rat ventral prostate suggest a physiological role of circulating and/or locally secreted catecholamines in the control of prostatic growth and function.

CRF stimulates adenylate cyclase activity in the intermediate lobe of the pituitary gland.

Ovine corticotropin-releasing factor (CRF) stimulates adenylate cyclase activity in homogenate of the intermediate lobe of the bovine pituitary gland at an ED50 value of 150 nM. GTP increases the stimulatory effect induced by CRF as well as by the beta-adrenergic agonist isoproterenol on [32P]cyclic AMP formation in rat pars intermedia homogenate. In addition, GTP is required for inhibition by dopamine of the stimulatory action of both CRF and isoproterenol. The present data show that CRF stimulates adenylate cyclase activity in the intermediate lobe of the pituitary gland at least partly through a GTP-dependent mechanism. Moreover, dopamine can interfere with the action of CRF as well as that of isoproterenol, thus indicating that the neurohormone could be involved, in addition to beta-adrenergic agents, as stimulator of pars intermedia cell activity.

Genome-wide search for linkage of bipolar affective disorders in a very large pedigree derived from a homogeneous population in quebec points to a locus of major effect on chromosome 12q23-q24.

We completed a genome-wide scan for susceptibility loci for bipolar affective disorders in families derived from a rather homogeneous population in the Province of Québec. The genetic homogeneity of this population stems from the migration of founding families into this relatively isolated area of Québec in the 1830s. A possible founder effect, combined with a prevalence of very large families, makes this population ideal for linkage studies. Genealogies for probands can be readily constructed from a population database of acts of baptism and marriage from the early 1830s up to the present time (the BALSAC register). We chose probands with a DSM III diagnosis of bipolar affective disorder and who may be grouped within large families having genealogical origins with the founding population of the Saguenay-Lac-St-Jean area. Living members (n approximately 120) of a very large pedigree were interviewed using the Structured Clinical Interview for DSM III (SCID I), SCID II, and with a family history questionnaire. A diagnostic panel evaluated multisource information (interview, medical records, family history) and pronounced best-estimate consensus diagnoses on all family members. Linkage, SimAPM, SimIBD, and sib-pair analyses have been performed with 332 microsatellite probes covering the entire genome at an average spacing of 11 cM. GENEHUNTER and haplotype analyses were performed on regions of interest. Analysis of a second large pedigree in the same regions of interest permitted confirmation of presumed linkages found in the region of chromosome 12q23-q24.

Effects of chronic estrogen treatment on dopamine concentrations and turnover in discrete brain nuclei of ovariectomized rats.

We investigated the effects of chronic estrogen treatment in ovariectomized rats on the concentration of dopamine in 33 discrete brain nuclei. In order to assess estrogen's influence on dopamine turnover, some of the rats were administered alpha-methyl-p-tyrosine. Estrogen treatment reduced the concentrations of dopamine in the nucleus accumbens septi, striatum, median eminence, nucleus anterior hypothalami, nucleus suprachiasmaticus, nucleus arcuate IV-V, area ventralis tegmenti, interpeduncular nucleus and nucleus interstitialis striae terminalis. Treatment was without effect on dopamine turnover in all areas studied.

Chronic estradiol treatment increases anterior pituitary but not striatal D2 dopamine receptor mRNA levels in rats.

The effect of chronic 17 beta-estradiol treatment (10 micrograms, twice each day, for 2 weeks) of ovariectomized rats on D2 dopamine (DA) receptor mRNA levels was investigated in striatum and anterior pituitary gland tissues. We used 32P-labeled probes specific for D2 receptor and beta-actin mRNAs in Northern blot analysis. The ratio of D2 DA receptor mRNA/beta-actin mRNA level was significantly increased in the anterior pituitary of estradiol-treated rats compared to vehicle-treated animals. The D2 DA receptor mRNA/beta-actin mRNA ratio in the striatum was not affected by estradiol treatment. However, the medial portion of the striatum showed a significantly lower ratio compared to the lateral portion of the striatum in both vehicle- and estradiol-treated rats. Thus, the estradiol effect on anterior pituitary D2 receptors may implicate transcriptional regulation, whereas our results do not support this hypothesis for the estradiol action on striatal D2 receptors.

Growth hormone-releasing factor stimulates adenylate cyclase activity in the anterior pituitary gland.

Synthetic human pancreatic growth hormone-releasing factor (hpGRF)(1-40)-NH2 stimulates adenylate cyclase activity in rat anterior pituitary particulate fraction at an ED50 value of approximately 150 nM. GTP more than doubles the stimulatory effect of hpGRF and PGE2 on [32P] cyclic AMP formation. The present data show that hpGRF as well as PGE2, another potent stimulus of GH secretion, act at least partly, through GTP-dependent mechanisms in their coupling with adenylate cyclase.

Corticotropin-releasing factor stimulants adenylate cyclase activity in the anterior pituitary gland.

Ovine corticotropin-releasing factor (CRF) stimulates adenylate cyclase activity in rat anterior pituitary homogenate at an ED50 value of 70 nM. GTP increases the stimulatory effect of CRF on ]32p] cyclic AMP formation in a rat adenohypophysial particulate fraction and in bovine anterior pituitary plasma membranes. The present data show that CRF stimulates adenylate cyclase activity in the anterior pituitary gland at least partly through a guanyl nucleotide-dependent mechanism.

Characteristics of the beta-adrenergic stimulation of adenylate cyclase activity in rat ventral prostate and its modulation by androgens.

Beta-adrenergic agents cause a 2.5-3-fold stimulation of adenylate cyclase activity in rat ventral prostate membrane preparations with an order of potency (KD values) typical of a beta 2-subtype receptor: (-)isoproterenol (20 nM) greater than (-)epinephrine (70 nM) much greater than (-)norepinephrine (1 microM) much greater than dopamine (70 microM). The stimulatory effect exerted by high concentrations of dopamine (greater than 0.1 mM) is completely reversed by propranolol but not by haloperidol or sulpiride, thus indicating an action of dopamine mediated by the beta-adrenergic receptor. One week after castration, basal adenylate cyclase activity in prostatic membranes is 50% reduced. In the same group, the stimulation by isoproterenol is completely abolished in the absence of GTP, while the effect of GTP alone is reduced by 75%. The inhibitory effect of castration on basal as well as isoproterenol- and GTP-stimulated adenylate cyclase activity can be completely reversed by treatment of castrated animals with dihydrotestosterone, thus demonstrating the marked androgen dependency of adenylate cyclase activity in prostatic tissue. Since the response to direct stimulation of adenylate cyclase activity (assessed by NaF and forskolin) is only reduced by 33%-60% while the response to isoproterenol is 100% abolished, the present data indicates that the complete loss of beta-adrenergic responsiveness of prostatic adenylate cyclase following castration includes many steps, including those preceding adenylate cyclase activity, namely the beta-adrenergic receptor itself and/or its coupling via the GTP-binding protein. The large amplitude of the effects observed should facilitate study of the mechanisms involved in the marked regulation of the beta-adrenergic receptor-adenylate cyclase system by androgens in prostatic tissue.

[3H]Apomorphine binding to a GTP-sensitive dopaminergic site in bovine anterior pituitary gland.

The characteristics of binding of the potent dopaminergic agonist [3H]apomorphine have been studied in bovine anterior pituitary membranes. A high affinity binding site with an apparent dissociation constant (KD) of 0.7 nM and a number of binding sites of 56 fmol/mg protein has been measured when 10(-5) M dopamine was used to assess nonspecific binding. The order of potency of various agonists to compete with [3H]apomorphine binding is consistent with an interaction at a typical dopaminergic receptor: apomorphine greater than dopamine greater than (-)-epinephrine = (-)-norepinephrine much greater than (-)-isoproterenol. Competition for [3H]apomorphine binding by antagonists shows marked stereoselectivity, (+)-butaclamol being 4000 times more potent than (-)-butaclamol. Dihydroergocryptine, a potent dopaminergic agonist on prolactin release, as well as the dopaminergic antagonists spiroperidol, haloperidol, and (+)-butaclamol, compete for [3H]apomorphine binding at nanomolar concentrations. By contrast, adrenergic (phentolamine, propranolol, and clonidine) and serotonergic (serotonin, cyproheptadine, and methysergide) agonists and antagonists do not compete or are weak competitors at micromolar concentrations. Guanosine triphosphate (GTP) decreases [3H]apomorphine binding, the affinity of this ligand for the receptor being decreased 10 times by 300 microM GTP. The close correlation observed between the affinity of a series of agonists and antagonists for the [3H]apomorphine binding sites and their potency as modulators of prolactin release suggests that [3H]apomorphine binding sites are those involved in the control of prolactin secretion.

Identification of beta adrenergic receptors in rat hypothalamus.

(-)-[3H]-Dihydroalprenolol((-)[3H]DHA) binding in the rat hypothalamus appears to possess all the characteristics expected of physiologically relevant beta-adrenergic receptors. Binding of (-)-[3H]DHA to the hypothalamic sites was rapid (k1 = 1.3 X 10(-7) min-1) and also rapidly reversible. Binding was saturable at low concentrations of ligand (approximately 50-100 nM). The dissociation constant (KD) of (-)-[3H]DHA binding determined by equilibrium analysis was 19 nM. Binding displayed beta-adrenergic specificity. beta-Adrenergic agonists inhibited binding in the following order of potency: (-)-isoproterenol congruent to (-)-epinephrine greater than (-)-norepinephrine. Specific beta-adrenergic antagonists (-)-propranol and (-)-alprenolol inhibited binding at low concentrations (KD = 25-50nM) whereas the alpha-antagonist phentolamine inhibited binding at very high concentration (KD = 42 micron). Interactions of both agonists and antagonists with the sites showed stereoselectivity. The (-)-isomers of all beta-adrenergic agents tested were more potent than their respective (+)-isomers. These results suggest that specific receptor sites for beta-adrenergic catecholamines are present in rat hypothalamus.

Thyroarytenoid muscle electrical activity during spontaneous apneas in preterm lambs.

Laryngeal dynamics plays a major role during perinatal life, a period of respiratory control immaturity. Continuous electromyographic (EMG) activity of a laryngeal adductor muscle (thyroarytenoid [TA] muscle), was recently observed throughout provoked central apneas, either isolated or during induced periodic breathing, in full-term lambs. The aim of the present study was to test if continuous TA EMG activity was also present during spontaneous apneas in nonsedated preterm lambs. We studied 7 premature lambs (term 131 +/- 1 d of postconceptional age). Premature birth was induced after acceleration of fetal lung maturation. Electrodes for diaphragm, inferior pharyngeal constrictor (IPC), and TA electromyograms, electrocardiogram, electroencephalogram, eye movement, and airflow recordings were implanted. Radiotelemetry recordings were repeated from 135 to 149 +/- 8 d of postconceptional age. A total of 2,088 apneas (2,020 central and 68 mixed) >/= 3 s were recorded in the lambs, including 57 epochs of periodic breathing. Continuous TA EMG activity was present throughout 88.4% of all apneas and 98.4% of apneas during periodic breathing, regardless of the sleep stage. These results suggest that active glottic closure is frequent during spontaneous central apneas in this model of prematurity. This unique model will allow us to study controlling mechanisms and consequences of glottic closure during neonatal apneas.

Multiple factors involved in the control of ACTH and alpha-MSH secretion.

Alpha 1-adrenergic agents are potent stimulators of ACTH secretion directly at the pituitary level as observed using anterior pituitary cells in primary culture and by in vivo studies. On the other hand, beta-adrenergic as well as antidopaminergic agents are also potent stimulators of ACTH secretion but at a suprapituitary level, since no effect of these compounds are observed in vitro. CRF administration has been found to lead to rapid and parallel increases in ACTH and alpha-MSH concentrations in rat plasma and the mechanism of action of CRF has been studied in vitro using rat anterior and intermediate lobe of pituitary gland for ACTH and alpha-MSH secretion, respectively. In both cases, CRF stimulates adenylate cyclase activity at ED50 values of 70 and 350 nM for ACTH and alpha-MSH, respectively. CRF stimulates adenylate cyclase activity at least partly through a guanyl nucleotide-dependent mechanism. Using rat pars intermedia cells in culture, we have demonstrated the presence, in addition of a CRF receptor, of a beta 2-adrenergic receptor which stimulates cyclic AMP accumulation and alpha-MSH secretion and of a dopaminergic receptor which inhibits cellular activity. These results have been confirmed in in vivo studies where isoproterenol and thioproperazine (a dopamine antagonist) lead to a rapid increase of alpha-MSH secretion.