ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00200.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00201.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractSyrian hamsters exhibit a form of scent marking behavior called flank marking. Flank marking, which is elicited during social contact with other hamsters and by the odors of other hamsters, communicates socially important information such as mate choice and dominance status. Vasopressinergic activity within the medial preoptic‐anterior hypothalamic continuum (MPOA‐AH) is essential for the expression of flank marking. In female hamsters, an inverse relationship exists between the expression of flank marking and sexual receptivity during the 4‐day estrous cycle. Since norepinephrine (NE) appears to facilitate sexual receptivity, the present study investigated whether NE might have an inhibitory effect on flank marking by acting on Vasopressinergic activity within the MPOA‐AH. Microinjection of 9.0 μM arginine vasopressin (AVP) into the MPOA‐AH stimulated high levels of flank marking. Microinjection of 9.0 μM AVP combined with NE in concentrations of 4.0, 0.4 or 0.2 nM, drastically reduced or eliminated flank marking. In contrast, AVP in combination with 0.09, 0.04 or 0.004 nM NE produced no significant reductions in flank marking. In addition, microinjection of 9.0 μM AVP, in combination with epinephrine (4.0 nM), but not dopamine (4.0 nM), serotonin (4.0 nM) or neuropeptide Y (900 μM), significantly reduced AVP‐induced flank marking. In male hamsters, microinjection of NE (4.0 nM) combined with AVP (9.0 μM) into the MPOA‐AH was not found to inhibit AVP‐stimulated flank marking. These results suggest that NE is involved in regulating the expression of flank marking during the estrous cycle by acting on Vasopressinergic activit

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00202.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractIn the present paper we demonstrate the effect of immobilization stress on c‐fos‐like immunoreactivity (Fos‐LI) in the rat amygdaloid complex. Furthermore, since the subnuclei of the amygdaloid complex contain numerous glucocorticoid receptor‐immunoreactive (GR‐IR) neurons, we also studied the possible colocalization of GR‐ and Fos‐LI ie. Fos‐Lls and the action of a synthetic glucocorticoid, dexamethasone, and an anti‐glucocorticoid, RU 38486, on Fos‐LI. Immobilization stress caused a remarkable increase in the number of the Fos‐IR neurons in all the subnuclei of the amygdaloid complex except in the lateral nucleus. The majority of Fos‐IR neurons also contained GR‐LI, with the highest colocalization in the central amygdaloid nucleus. A similar induction of Fos‐LI after immobilization was seen in the hypothalamic paraventricular nucleus and almost all the Fos‐IR neurons in this nucleus also exhibited GR‐LI. Treatments with dexamethasone or RU 38486 prior to stress did not have any marked effect on Fos‐LI when compared to stress alone. The present findings suggest that Fos may function as a transcriptional regulator in the amygdaloid complex after stress and affect the synthesis of neurotransmitters and receptors in the amygdaloid neurons. Since we did not observe any effect of dexamethasone or RU 38486 on Fos‐LI, it is likely that glucocorticoids do not directly regulate the expression of the c‐fos gene or the formation of Fos protein. In view of the fact that Fos is capable of forming a stabile complex with GR and repress the transactivational capacity of GR, Fos may inhibit the negative feedback effect of circulating glucocorticoids and thus maintain elevated p

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00203.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe pars tuberalis (PT) of the pituitary may be an important target for melatonin action, but the secretory output of the melatonin‐responsive cells is unknown. Using [35S]methionine, protein synthesis and secretion have been studied in primary cultures of ovine PT cells, and analysed by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis. Only 4% of the labelled proteins appeared in the medium with the majority retained in the cells. Stimulation of the cells with 10μM forskolin increased the accumulation of several labelled proteins in the medium without corresponding changes in the cell (72, 62, 44, 39, 29, 24, 23, 18 and 14 kd). Two‐dimensional gel electrophoresis showed the proteins to have mildly acidic isoelectric points. Melatonin (1 μM) counteracted the stimulatory effect of forskolin on all but one (23 kd) of these secreted proteins. Immunoprecipitation showed this to be prolactin. Furthermore, melatonin alone appeared to have an inhibitory effect on the synthesis and release of proteins into the medium. The synthesis and secretion of the melatonin‐responsive proteins was not inhibited by actinomycin D (1 μg/ml), indicating control at the translational level. This contrasts with the regulation of prolactin which is actinomycin D‐sensitive. Pulse‐chase experiments demonstrated that it requires 30 min for the secretory proteins to appear in the medium, consistent with intracellular processing and packaging prior to secretion. The secretory proteins labelled in the ovine PT, and responsive to melatonin, did not appear to be specific to the PT, as a similar profile of labelled secretory proteins was produced in primary cultures of pars distalis cells. However, melatonin had no effect on the synthesis and secretion of proteins by the pars distalis. These results demonstrate that in the ovine PT melatonin regulates the synthesis and export of several secretory proteins. These are possibly packaging proteins of secretory granules, similar to the granin family of proteins. Thus, the results confirm that melatonin‐responsive cells are secretory cells and further imply that the PT‐specific produc

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00204.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe effect of a 6‐h infusion of gonadotrophin‐releasing hormone (GnRH) or its analogues on dispersed anterior pituitary cells from male or female rats was investigated. The cells were stimulated with 3‐min pulses of K+and GnRH. Thereafter GnRH (1 nM) or GnRH analogues ([D‐Trp6]GnRH‐ethylamide ([D‐Trp6]GnRH, 50 pM), [D‐Phe6, Gln8]GnRH‐ethylamide (Folligen, 100 pM) and [Asu6]GnRH‐ethylamide ([Asu6]GnRH, 33 pM)) were applied for 6 h. In cells from female rats this treatment resulted in a 20‐fold increase in luteinizing hormone (LH) secretion during the first 90‐min period of the 6‐h incubation. Following this a gradual decrease in LH release occurred, and during the fourth 90‐min period the amount of LH secreted was only one‐third or less of the initial value. The pituitary cells of male rats responded to the same treatment with only a 7‐fold rise of LH secretion during the first period. In the second 90‐min of the 6‐h incubation a 20% to 30% increase was observed. Even in the fourth 90‐min period the amount of LH secreted was two‐thirds or more greater than that of the first 90‐min period. When using 10‐fold greater concentrations of the same peptides in males, the increase in hormone secretion in the second 90‐min was not seen and the hormone release decreased to around 50%. We found definite differences in the responses of male and female rat pituitary cells to the 6‐h infusion of GnRH or its analogues: the initial amplitude of the response in females was higher but desensitization was stronger. In males, the initial response was weaker; however, even using doses one magnitude greater, the level of desensitization did not reach the values obtained in females. The results were similar both with GnRH and the analogues. The responses to 3‐min K+and GnRH stimuli given after the 6‐h incubation were strongly reduced in cells from female rats compared to the initial responses; however, in cells from male rats the reaction was higher or unchanged. The ratio of LH released by the final K+stimulus relative to the actual LH content of the cells decreased in females but increased in males. Our data show that the differences between the pattern of desensitization in cells from male and female rats may be caused by the differences in the amount and ratio of immediately releasable hormo

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00205.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractIn lactating rats, suckling elicits the milk ejection reflex which consists of an intermittent synchronous activation of hypothalamic oxytocin neurons which releases oxytocin into the bloodstream. We here investigated the electrophysiological behaviour of spinal cord neurons linked to mammary innervation in relation to suckling and the suckling‐induced milk ejection reflex. Experiments were carried out on 58 urethane‐anaesthetized rats, paralysed with gallamine triethiodide and artificially ventilated. Fixation of the spinal cord and laminectomy significantly slowed down the reflex, which occurred in only 27% of the animals. In these rats, 31 dorsal horn neurons at the thoraco‐lumbar level were found to be excited by nipple stimulation. During suckling by a litter of at least nine pups, they displayed an irregular pattern of brief bursts of activity (peak firing rate 22.0 ± 3.2 Hz, mean ± SD) correlated to the bouts of suckling of the pups. Seventeen out of 19 cells tested by stimulation of at least 2 adjacent nipples received convergent input from different ipsilateral nipples. Out of 11 cells tested, 8 were also activated by stimulation of a contralateral nipple. Fourteen out of 30 units were recorded through at least one reflex milk ejection. Their firing rate was significantly higher than the firing rate of cells recorded in animals which failed to milk eject (4.4 Hz ± 2.8 versus 1.5 Hz ± 0.7). At the moment of the high frequency discharge of action potentials, occurring in oxytocinergic cells 10 to 15 s before each milk ejection, spinal neurons showed no systematic change in electrical activity. In contrast, the stretch reaction of the pups, which corresponds to an intense period of suckling when milk ejection has started, induced, in 12 cells, a considerable increase in electrical activity. One unit was found to be inhibited by suckling and during the stretch reaction. Ten more units, which were not activated by stimulation of the nipples but responded to stimulation of excitatory receptive fields near the last three pairs of nipples, were recorded through reflex milk ejections: 8 remained silent during reflex milk ejections but 2 were activated when the pups stimulated their excitatory receptive field. We conclude that some dorsal horn neurons, able to respond readily to the suckling movements of pups, appear to receive an ungated input from the nipples. At the time of the activation of oxytocin neurons, they present no particular pattern of activation or inhibition which could account in a simple manner for the intermittence of the high frequency discharge in oxytocinergic cells. However, in so far as these dorsal horn neurons may be part of the milk ejection reflex pathway, their activity, showing convergence and summation of input, and being facilitated in milk ejecting animals, indicates that the reflex does undergo a certain degree of processing at the spinal c

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00206.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractNeuropeptide Y (NPY), a 36 amino‐acid peptide found within the hypothalamus, is thought to be an important regulator of food intake. Hypothalamic NPY gene expression, synthesis and secretion are all known to be increased in models of increased metabolic demand in which serum glucocorticoids are also elevated. The present studies were designed to test the hypothesis that glucocorticoids are required for increased hypothalamic preproNPY mRNA levels induced by food deprivation (FD). First, animals underwent bilateral sham‐adrenalectomy (sham) or not (control), and were subjected to 72 h FD, or not. Total RNA was isolated from hypothalamic tissue blocks and the content of preproNPY mRNA was measured by solution hybridization/RNase protection analysis. This study revealed that there was no significant difference in hypothalamic preproNPY mRNA content between shamfed and control‐fed groups, or between sham‐FD and control‐FD groups. In the second experiment, animals underwent bilateral adrenalectomy (ADX), were allowed to feed adlibitumand were sacrificed 1 day, 4 days and 7 days after ADX. Nuclease protection analysis revealed no significant effect of ADX on hypothalamic preproNPY mRNA levels over this time‐course. Finally, we examined the role of glucocorticoids in regulating NPY gene expression following FD. Animals underwent bilateral ADX, or not. At the time of surgery, ADX animals received placebo, or corticosterone (B) replacement in the form of constant release pellets, at one of two doses. Food was removed from half of the animals in each group 24 h after surgery; all animals were sacrificed 72 h thereafter. There was no difference in preproNPY mRNA content between the ADX‐FD and ADX‐fed groups, relative to the fed controls. Replacement with corticosterone [ADX(B)] did not alter preproNPY mRNA content in fed animals, however preproNPY mRNA content in FD animals was increased 2.5‐fold. These studies demonstrate that glucocorticoids are necessary and serve a stimulatory role in the increase in hypothalamic preproNPY mRNA levels observed under conditions of FD, and suggest that hypothalamic NPY gene expression may be directly responsive to peripheral metabolic and

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00207.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe most recently discovered member of the family of natriuretic peptides, C‐type natriuretic peptide (CNP), exerts many pharmacologic actions similar to its structural homolog A‐type natriuretic peptide (ANP). Like ANP it failed to significantly alter prolactin release from dispersed, rat anterior pituitary cells incubated under static or dynamic conditions. Unlike ANP, however, which inhibits prolactin secretionin vivoby a hypothalamic action, CNP injection into the third cerebroventricle significantly stimulated prolactin secretion in ovariectomized, conscious rats. The effect was highly significant 15 min after injection and transient, lasting 30 min in animals injected with 2 nmole CNP. In a companion group of rats, significant inhibition of plasma prolactin levels was observed after central administration of similar doses of ANP. These results suggest differing hypothalamic actions of the CNP and ANP perhaps mediated by multiple natriuretic peptide receptors present in the tissue. Further, they provide additional support for unique roles exerted within the central nervous system by these structural homol

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00208.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractNorepinephrine (NE) turnovers (an index of secretion) increase in the hypothalamus of proestrous rats concomitant with luteinizing hormone surges, whereas, neither of these events are observed in diestrous nor in androgen‐sterilized rats. Increased hypothalamic NE release may occur as a consequence of the withdrawal of local inhibitory γ‐aminobutyric acid and opiate controls on specific presynaptic NE terminals and/or as a result of an increase in activity within noradrenergic neurons. Tyrosine hydroxylase (TH) is the rate‐limiting enzyme for the synthesis of NE and our earlier studies revealed that increases in TH mRNA in A1 and locus ceruleus (LC) neurons can serve as an index of increased activity within these cells. In the present study, we evaluated whether TH message levels change in A1 and LC neurons prior to and during the hours when luteinizing hormone surges and increased NE turnovers are observed. As controls, TH mRNA levels in A1 and LC neurons were evaluated at the same hours of day in diestrous day 2 and in androgen‐sterilized rats.In situhybridization histochemistry and quantitative image analysis methods were used to measure changes in TH mRNA levels.Luteinizing hormone surges in proestrous rats began at 1500 h, peaked between 1600 and 1700 h and declined, thereafter, to 2000 h. In contrast, plasma luteinizing hormone remained basal throughout the day in diestrous and androgen‐sterilized rats. While A1 neuronal TH mRNA levels did not differ in the three groups of rats during the morning (0930 to 1030 h), these message levels were significantly elevated in proestrous rats during the afternoon (1645 to 1715 h) and remained high at 2000 to 2030 h. In contrast, no changes in TH mRNA levels were observed in A1 neurons throughout the afternoon in diestrous animals or androgen‐sterilized rats. TH mRNA levels in the LC did not differ in the three groups of rats and they remained unchanged throughout the afternoon hours we examined. From these observations we conclude that concomitant with afternoon proestrous luteinizing hormone surges and the accompanying increase in hypothalamic NE secretion, there is an increase in activity within A1 but not LC neurons. These data suggest that the proestrous increase in hypothalamic NE turnover we previously observed is not due solely to withdrawal of local inhibitory controls of presynaptic NE release but it also involves an increase in activity within A1 but no

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00209.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY