摘要:

AbstractUsing a modified immunocytochemistry protocol with enhanced sensitivity, we were able to visualize a population of neurons in the tectum of the developing mouse that contained GnRH‐like immunoreactivity. In microscopic studies conducted using 100 pm sections cut in sagittal or horizontal planes, 10–20 lightly‐stained neurons were first detected in the tectum at E 13.75 (morning of plug = E0.5). The number of immunostained cells increased exponentially reaching a peak at E 15.75 before decreasing in number. No positive neurons were seen in the tectum at PN20 or later. The GnRH cells were located medially along the dorsoventral axis of the tectum in a region of the brain distinct from that containing GnRH neurons that migrate into the CNS from the olfactory placode. To determine the nature of the immunoreactivity, two approaches were used. Analysis of tissue from an hpg mutant strongly supports the hypothesis that these cells make mammalian GnRH. lmmunocytochemical data suggest that although the precursor protein is synthesized, the cleaved and amidated decapeptide may be absent or be present at an undetectable level. Our results demonstrate that in addition to the GnRH neurons from the placade, a population of GnRH neurons exists in the mouse tectum. This population is developmentally regulated, appearing only during embryonic and early postnatal ages but not in the

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00733.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractPrevious studies have shown a parallel relationship between pituitary vasopressin (VP) receptor content and responsiveness of the corticotroph during chronic stress. The regulation of pituitary VP receptors was further studied by analysis of V1b VP receptor mRNA levels in pituitaries of rats subjected to chronic immobilization, i.p. hypertonic saline injection (physical stress paradigms associated with increased pituitary responsiveness), and water deprivation, or to 2% saline in the drinking water (osmotic stress paradigms associated with decreased pituitary responsiveness). Northern blot hybridization with a 363 bp32P‐labelled fragment of the rV1b receptor cDNA coding sequence revealed two bands of about 3.7 and 3.2 Kb, whereas a probe directed to the 5′ untranslated region recognized only the 3.7 Kb band. Repeated i.p. hypertonic saline injection, 3 times in 24 h at 8 h intervals, or daily for 8 days, increased the intensity of the 3.7 Kb band by 155 ± 17.5% (P<0.01) and 118 ± 14.6% (P<0.01), respectively, while the 3.2Kb band increased by 122 ± 39.3% (P<0.01) only after 3 times injection. Smaller increases of 39 ± 11 and 33 ± 9% (P<0.05) in the 3.7 Kb band were found after repeated immobilization 3 times in 24 h and 2 h for for 8 days respectively.In situhybridization studies confirmed significant increases (P<0.05) in V1b receptor mRNA levels after 8 and 14 days repeated immobilization (63 ± 19% and 83 ± 10%) or i.p. hypertonic saline injection (110 ± 13% and 73 ± 20%). In response to acute stress, V1b receptor mRNA increased by 77 ± 5% (3.7 Kb band) after 4 h immobilization for 1 h, whereas both bands were reduced by 49 ± 5% and 45 ± 5%, 4 h after a single i.p. hypertonic saline injection. The decrease in V1b receptor mRNA following a single i.p. hypertonic saline injection was prevented by pretreatment with a V1 receptor antagonist, suggesting that increased VP secretion may account for this effect. In spite of the decrease in V1 b receptor mRNA following i.p. hypertonic saline injection, VP binding in pituitary membrane rich fractions, and VP‐stimulated inositol phosphate formation in quartered hemipituitaries were increased by 24 and 39%, respectively. V1b receptor mRNA levels were unchanged or decreased following prolonged osmotic stimulation.These studies suggest that increased V1b receptor mRNA levels contribute to the VP receptor upregulation observed during repeated immobilization and i.p. hypertonic saline injection, whereas the lack of parallelism between V1b receptor mRNA and VP binding indicates that regulation of steady‐state levels of V1b receptor mRNA is not a primary determinant in the control of pituitary VP receptor concentr

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00734.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractEffects of pentobarbital sodium (PB) on the electrical activity of LHRH pulse generator were investigated in the ovariectomized (OVX) rat fitted with chronically implanted electrode arrays in the arcuate‐median eminence region of the hypothalamus. PB was injected intraperitoneally (i.p.) at a dose of 32 mg/kg bw, which has blocked the surge of LH secretion when injected at 13.45 on the day of proestrus, presumably by blocking the activity of the LHRH surge generator. After i.p. injection of PB, the first characteristic increase (volley) in the hypothalamic multiunit activity (MUA), each of which was associated with the initiation of an LH pulse, appeared at the mean interval of 42 min, which was significantly greater than the value, 30 min, in the rat given i.p. injection of saline. The second and third MUA volleys appeared, however, at similar intervals to those in rats given saline. There were no significant changes in the amplitude of LH pulses which followed. In the OVX rat implanted with a silastic tube packed with estradiol‐benzoate (E2) for 1 day, MUA volleys were unclear, mingled with high background activities, but clear volleys appeared after PB injection. The mean interval of LH pulses in the rat given i.p. injection of saline was 51 min, by 24 min longer than the value in the E2‐unimplanted OVX rat. But, after PB injection, the 1st LH pulse appeared at the interval of 37 min, which was by 25 min smaller than that after saline and the overall mean of 3 intervals was 34 min, showing a significant shortage. No PB effect was seen in the LH pulse amplitude in the E2‐implanted OVX rat. The presults show that the LHRH pulse generator is much more resistant to PB than the surge generator in the OVX rat either with or without estrogen priming, and in the rat with estrogen priming, the pulse generator is rather activate

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00735.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractPrevious studies by us and others led us to hypothesize that there are separate LHRH pulse and surge generators in the rat brain. The present study was designed to detect the activity of LHRH pulse generator by checking changes in LH secretion and the multiunit activity (MUA) of the arcuate‐median eminence region of the hypothalamus during infusions of naloxone (NAL, 2 mg/h) in the proestrous rat in which the LHRH surge generator activity was blocked by pentobarbital sodium (PB, 32 mg/kg bw, ip). The animals were subjected to blood sampling in the morning (1000–1300 h) or afternoon (1400–1700), and injected with PB at 09.45 or 13.45, respectively. During saline infusions in the rat given PB injection at either 09.45 or 13.45, serum LH levels were low but fluctuated significantly, suggesting a pulsatile secretion in either the morning or the afternoon period. The pulse intervals were an average 28.2 min in the morning and 42.2 min in the afternoon. NAL infusions decreased the pulse interval significantly, to 22.0 min in the morning and to 27.0 min in the afternoon. In the electrophysiological experiment, characteristic increases in the MUA (volleys), which occur in association with the initiation of an LH pulse and therefore are considered to represent an increased activity of the LHRH pulse generator, appeared during NAL (5 mg/h) infusions in either the morning or the afternoon. These results strongly suggest that separate LHRH pulse and surge generators exist in the brain, and that, even during the critical period of proestrus, the activity of LHRH pulse generator is disclosed by PB, which, on the other hand, arrests the surge gene

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00736.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractAdrenomedullin (ADM) is a 52 amino‐acid peptide which is a potent vasodilator in rats, and suppresses basal and CRF‐induced ACTH release from cultured pituitary cells. The present study examines the hemodynamic and hormonal actions of human ADM (1–52) infusion in conscious, chronically instrumented sheep. Five sheep were infused intravenously (IV) or intracerebroventricularly (ICV) with ADM at 100 pg/h for 60 min, and mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), stroke volume (SV), total peripheral conductance (TPC), coronary blood flow (CF), coronary conductance (CC), peak aortic flow (Fmax), and left ventricular dF/dt were monitored by a computer‐based data collection system every 2 min. Plasma concentrations of adrenocorticotropin (ACTH), arginine vasopressin (AVP) and renin were measured after 60 min of infusion. IV ADM produced a small fall in MAP of 3 ± 1 mmHg, associated with a reflex increase in HR of 14 ± 3 b/min. CO increased by 1.3 ± 0.3 1/min, whereas SV remained unchanged. TPC was markedly increased by 20 ± 3 ml/min/mmHg. Changes in CF were also seen with an increase of 10 ± 2ml/min, and CC increased in parallel by 0.15 ± 0.02 ml/min/mmHg. Fmax and dF/dt showed small increases of 2.1 ± 0.5 Vmin and 85 ± 20 1/min/sec respectively. Plasma concentrations of ACTH and cortisol were reduced by 58% and 55% respectively, whereas plasma renin concentration increased by 106%. There was no change in plasma levels of AVP. ICV infusion of ADM had no effect on any parameter measured. These data suggest that systemic ADM produces a sustained vasodilator action to lower blood pressure in sheep, and this is the first study to report the ACTH‐suppressor action of ADM in conscious animals. ADM may therefore be an important hormone involved in the regulation of pituitary/adrenal function, in addition to its cardiovascular and fluid regulatory a

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00737.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIn the sheep, it has been shown that the pars tuberalis of the pituitary may mediate the photoperiodic control of seasonal changes in prolactin secretion. High concentrations of melatonin receptors are present on the ovine pars tuberalis and melatonin is known to inhibit forskolin‐stimulated cyclic AMP production in this tissue. Other hormonal inputs to the ovine pars tuberalis have not yet been identified. In the rat mRNA for the IGF‐I receptor has been identified in the pars tuberalis usingin situhybridization. In order to define whether IGF‐I may influence the function of the ovine pars tuberalis the presence of receptors for IGF‐I has been investigated. Usingin vitroautoradiography specific [125I]IGF‐I binding was found in high concentrations over the ovine pars tuberalis particularly associated with certain of the capillaries. Homogenate receptor assays showed saturable specific binding of [125I]IGF‐I with a mean dissociation constant (Kd) of 0.5 ± 0.1 nM (n=4). Competition studies revealed a rank order of potency of IGF‐I>IGF‐II>>>insulin, in displacing [125I]IGF‐I binding, indicative of a mixed population of IGF‐I and IGF‐II/rnannose‐6‐phosphate receptors and insulin‐like growth factor binding proteins (IGFBPs). Cross‐linking of [125I]IGF‐I to pars tuberalis membrane homogenates and analysis by SDS‐PAGE under reducing conditions confirmed the presence of both IGF‐I receptors and binding proteins. Autophosphorylation of a 97 kDa substrate, compatible with the β‐sub‐unit of the IGF‐I receptor, was increased in the presence of IGF‐I, indicating the existence of functional IGF‐I receptors on the ovine pars tuberalis. In contrast in the rat [125I]IGF‐I binding was restricted to the median eminence region of the bra

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00738.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractAtrial Natriuretic Factor (ANF) action is mediated by highly selective and specific receptors. Three subtypes have been characterized and cloned: ANF receptor‐A, ‐B and ‐C. These subtypes are all expressed in the anterior pituitary of the rat. In the present study, the mRNA for each subtype was detected byin situhybridization. The amounts of ANFR‐A and ‐B mRNA were found to be similar, and to be twice that of ANFR‐C mRNA. At the ultrastructural level, the three types of ANFR mRNA were expressed in three anterior pituitary cell types, namely lactotrophs, corticotrophs, and gonadotrophs, identified by their hormonal content. No signal was revealed in somatotrophs or thyrotrophs. The different forms of mRNA were similar in terms of subcellular localization: in the cytoplasmic matrix and the nuclear euchromatin.These data indicate that the anterior pituitary is an important target tissue for

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00739.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractMelatonin has been proposed to exert some regulatory actions within the pineal gland itself. The present study examined the effect of melatonin on the release of serotonin (5‐HT) and 5‐hydroxyindoleacetic acid (5‐HIAA) from rat pineal glands by using anin vitroperifusion system. Melatonin induced a concentration‐dependent stimulatory effect on 5‐HT secretion from 10−6M to 10−3M. Maximal effects were obtained with melatonin 10−3M and concentrations lower than 10−6M were without effect. The secretion of 5‐HIAA was inhibited by melatonin 10−3and 10−4M, but it was increased when pineals were incubated with 10−5and 10−6M of melatonin. The indoleamine secretion was also studied on peripherally denervated rat pineal glands. Basal output of 5‐HT from these glands was increased when compared with those from control rats. In contrast, the secretion of 5‐HIAA was strongly reduced after removal of the sympathetic input to the pineal gland. Melatonin 10−3M failed to stimulate 5‐HT release from denervated pineal glands, although it inhibited 5‐HIAA secretion. In contrast, melatonin 10−5M enhanced 5‐HT release without altering 5‐HIAA output. Fluoxetine, a 5‐HT uptake inhibitor, produced similar effects than mM concentrations of melatonin on the indoleamine secretion from control pineal glands, but it had no effect on glands taken from peripherally denervated rats. These data suggest that mM concentrations of the pineal hormone are able to stimulate 5‐HT release from the pinealocyte, while mM concentrations of melatonin increase extracellular 5‐HT by inhibiting its reuptake in the adrenergic nerve endings. These findings are discussed in relation to the possible role of melatonin regulating the intra‐ and extracellular availability of 5‐HT in the pin

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00740.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractInsulin producing cells of the pancreas (beta cells) and neuronal cells share a large number of similarities. For example, different molecules, thought to be specific of neuronal cells, are expressed by beta cells. The factors regulating the expression of these molecules in beta cells are poorly understood. In the present work, we have studied the effect of dexamethasone, a synthetic glucocorticoid, on the expression of three different neuronal traits expressed by INS‐1 cells, a highly differentiated beta cell line. We demonstrate that dexamethasone treatment decreases the steady state levels of mRNAs coding for both the low‐and the high‐affinity NGF receptors and of mRNA coding for NF‐H, an intermediate neurofilament specific of neurons. This effect was time‐dependent, the decrease being detectable after 4–8 h treatment. The decrease in NGF receptors mRNAs steady state levels was paralleled by a decrease in the number of NGF binding sites as demonstrated after Scatchard analysis. We further focused on the mechanisms by which dexamethasone affects the expression of the low affinity NGF receptor. The effect is countered by the glucocorticoid antagonist RU486, indicating that it is mediated by the glucocorticoid receptor. Finally, the decrease in the low‐affinity nerve growth factor receptor mRNA steady state level after dexamethasone treatment is not due to mRNA destabilization but can be rather explained through a change in gene

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00741.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00742.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY