摘要:

Oxytocin (OT) release within the brain is thought to play a major role in inducing maternal behaviour in a number of mammalian species but little is known about the sites of release which are important in this respect. We have investigated whether the paraventricular nucleus of the hypothalamus (PVN) is a site of OT action on maternal behaviour in the sheep.In vivomicrodialysis and retrodialysis was used to determine whether OT is released in the region of the PVN during the post‐partum induction of maternal behaviour and if its release at this site can stimulate maternal behaviour in non‐pregnant animals.In vivosampling showed that OT concentrations increased significantly in the region of PVN at birth. When OT was retrodialysed bilaterally into the PVN (1 or 10 μM) of multiparous ewes treated with progesterone and oestradiol to stimulate lactation, maternal behaviour was induced in a significant number of animals (1 μM, 6/8 and 10 μM, 5/8) compared with controls (0/8 ewes). Similar infusions of the ring structure of OT, tocinoic acid (TOC—10 μM), also induced maternal behaviour in a significant proportion of animals (5/6 ewes) as did intracerebroventricular (ICV) OT (6/8 ewes) and artificial stimulation of the vagina and cervix (VCS, 8/9 ewes). On the other hand, vasopressin (AVP) 1 μM did not induce maternal behaviour in any ewes and a 10 μM dose only induced it in 2/8 animals. The neurochemical changes accompanying the above treatments were also investigated. Noradrenaline concentrations increased in the PVN after the retrodialysis administration of OT 1 μM and 10 μM, TOC 10 μM and AVP 1 μM, OT ICV and VCS. Dopamine concentrations were also increased by OT 10 μM, TOC 10 μM, AVP 1 μM and OT ICV. Aspartate and glutamate concentrations were significantly reduced by retrodialysis infusions of OT 1 μM and AVP 1 and 10 μM but not by any other treatment. Finally, the retrodialysis infusions of OT and TOC, as well as ICV OT, significantly increased plasma OT release whereas AVP infusions did not. These results provide evidence that OT is released in the PVN during parturition and is important for the induction of maternal behaviour. It seems probable that OT release at this site has a positive feedback effect on both parvocellular and magnocellular OT neurones to facilitate co‐ordinated OT release both in central OT terminal regions (to facilitate maternal behaviour) and peripherally into the blood (to facilitate uterine contractions/milk let down). The potential functional roles for the actions of OT on monoamine and ami

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04411.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Galanin mRNA levels in GnRH neurons increase in association with a steroid‐induced LH surge in female rats. Both the steroid‐induced LH surge and the concomitant increase of galanin mRNA in GnRH neurons are blocked by non‐specific inhibition of central nervous system activity imposed by pentobarbital and specific central alpha‐adrenergic receptor blockade. Based on these observations, we hypothesized that galanin gene expression in GnRH neurons is induced whenever GnRH neurons become activated to generate an LH surge. If this were the case, thenanyneurotransmitter receptor blocking agent that inhibits the LH surge by central mechanisms would likewise block the associated increase in galanin mRNA in GnRH neurons. We tested this hypothesis by examining the effects of an N‐methyl‐D‐aspartate (NMDA) receptor antagonist on the steroid‐induced LH surge and on levels of galanin mRNA in GnRH neurons. Three groups of ovariectomized rats were used: Group 1‐treated with estradiol and progesterone (E/P) and sacrificed at the peak of the LH surge; Group 2‐treated the same as Group 1 except that dizocilpine (MK801, an NMDA receptor antagonist) was used to block the LH surge; and Group 3‐treated the same as Group 1 except they received vehicle instead of E/P. Double‐and single‐labelin situhybridization followed by computerized image analysis were used to measure levels of galanin mRNA and GnRH mRNA in GnRH neurons [as grains/cell (g/c)]. E/P treatment induced a 3‐fold increase in LH levels and a 5‐fold increase in the galanin mRNA signal content of GnRH neurons. Treatment with MK801 completely prevented the LH surge in all animals and also blocked the steroid‐induced increase in galanin mRNA in GnRH neurons. As assessed by 2 independent GnRH single‐labeled assays, neither GnRH message content nor the number of identifiable GnRH neurons differed among the experimental groups. We conclude that the increase in galanin mRNA levels in GnRH neurons is tightly coupled to the occurrence of a steroid‐evoked LH surge, and we infer that induction of galanin gene expression in GnRH neurons is induced as a consequence of

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04462.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

On the day of proestrus in the rat, rising plasma levels of estradiol (E) act in concert with progesterone (P) to trigger a preovulatory release of gonadotropins. Cellular levels of galanin mRNA in GnRH neurons are increased in association with the proestrous surge of gonadotropin secretion; however, the relative contribution made by E and P to the induction of galanin mRNA expression in GnRH neurons is unknown. We investigated the role of E and P in the induction of galanin gene expression in GnRH neurons by examining the effects of different combinations of E (estradiol benzoate; 50 μg and P (5 mg)) on the LH surge and the concomitant induction of galanin mRNA in GnRH neurons. We sacrificed ovariectomized adult rats after 1 of 4 treatments: Group 1: vehicle control (n=6); Group 2: P alone (n=7) Group 3: E alone (n=7); Group 4: combined E/P (n=6); the animals were killed at 18.00 h at the time of the LH surge. The brains from these animals were processed by double‐labelin situhybridization to allow measurement of galanin mRNA levels in GnRH neurons. GnRH neurons were identified with a digoxigenin‐labeled cRNA probe for GnRH mRNA, and galanin mRNA was detected and measured simultaneously with an35S‐labeled cRNA probe coupled with computerized grain counting. Estimation of cellular levels of GnRH mRNA was accomplished with single‐labelin situhybridization, an35S‐labeled GnRH cRNA probe and computerized grain counting. We observed a 3‐fold induction of galanin mRNA in the GnRH neurons of animals treated with E alone compared with those treated with the vehicle alone (vehicle: 13±2vsE: 42±4 grains/cell (g/c); P<0.01); LH levels in the E‐treated animals were elevated, albeit moderately, with respect to the vehicle controls. Compared with vehicle‐treated animals, those treated with the combination of E and P showed a 5‐fold induction of galanin mRNA in GnRH neurons (68±9 g/c), which was significantly (P<0.01) greater than that observed in the animals treated with E alone; in addition, the magnitude of the LH surge was much greater (P<0.05) in the E/P‐treated group compared with the E alone group. In contrast, compared to the vehicle controls, animals treated with P alone (15±2 g/c) showed no discernable effect on galanin mRNA levels; moreover, no LH surge occurred in the P alone group. Neither the number of identified GnRH cells nor their content of GnRH mRNA differed significantly among the experimental groups (GnRH mRNA signal: vehicle controls: 153±6vsE: 159±6vsE/P: 153±3vsP: 148±8 g/c). We conclude that while E is the primary ovarian signal inducing galanin mRNA expression in GnRH neurons and the LH surge itself, P plays a facilitato

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04473.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The purpose of this experiment was to determine if there are sex differences in cytosolic androgen receptors (AR) in individual brain nuclei. Bilateral 500 μ diameter samples from 300 μ thick frozen brain sections were micropunched from males and females 2–3 weeks following gonadectomy. Tissue samples were taken from 12 brain nuclei: lateral septum, bed nucleus of the stria terminalis, medial preoptic nucleus, anterior hypothalamic area, arcuate nucleus, corticomedial nucleus of the amygdala, lateral preoptic area, parietal cortex, medial nucleus of the amygdala, dorsomedial nucleus of the hypothalamus, ventromedial nucleus of the hypothalamus, and dorsal hippocampus. Cytosolic ARs were higher in males than in females in each of these 12 areas, but this sex difference was significant only in the first 6. Sex differences in ARs were found in brain regions involved in the neuromodulation of androgen dependent responses. These data suggest that behavioral differences in male reproductive responses may be the result of a sexually dimorphic distribution of androgen receptor containing

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04494.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Aromatase enzyme is essential for the expression of normal sexual behavior in many mammals and birds. Here we report that vorozole (R83842), a non‐steroidal aromatase inhibitor, blocks sexual behavior in the female musk shrew. In addition, vorozole treatment lowers aromatase activity in male and female preoptic area, and reduces plasma estradiol concentrations in females. Our findings confirm and extend results demonstrated in other species, conducted with the active enantiomer (R83842), or the racemic mixture (R76713, racemic vorozole). We also report that vorozole treatment affects the immunocytochemical distribution of aromatase immunoreactivity (AROM‐ir) in musk shrew brain. The histological identification of neurons that contain this enzyme has been difficult in mammals. Several aromatase enzyme antisera have been developed and used in brain, and each gives a different pattern of immunoreactivity. Moreover, despite the fact that aromatase activity is very high in the bed nucleus of the stria terminalis, several amygdala nuclei, the preoptic area and hypothalamus, AROM‐ir in these regions has been very limited. The distribution of AROM‐ir in female musk shrew brain tissues is modified by treatment with vorozole prior to sacrifice. Female musk shrew brains contain aromatase immunoreactive cell bodies, as reported previously, in the central amygdala, lateral septum and to a limited extent in the bed nucleus of the stria terminalis (BST). Brains of females treated with vorozole show additional immunoreactivity in the preoptic area, hypothalamus, and medial amygdala, and have a broad distribution of AROM‐ir in several subdivisions of the BST. Several sexual dimorphisms are apparent in musk shrews brains after treatment with vorozole. We have quantified this sexual dimorphism in the medial preoptic area (MPO) by counting immunoreactive cells. In both the rostral and caudal portions of the MPO, female brains contain significantly fewer AROM‐ir cell bodies than males. These data are in complete agreement with sex differences in biochemical analyses of aromatase activity in the MPO. At this time we do not know if these dimorphisms are the result of differences in circulating levels of steroids in males and females, and/or if the AROM‐ir nuclei regulate sexually dimorp

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04505.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Pituitary transcription factor‐1 (Pit‐1 or GHF‐1), a transcription factor specific to the anterior pituitary, is involved in the expression and regulation of the growth hormone (GH) and prolactin (PRL) genes. Post‐pubertally, the expression of both GH and PRL becomes sexually dimorphic with males having higher GH levels and females higher PRL levels; however, little is known about the postnatal regulation of their common transcription factor. Furthermore, whether the Pit‐1 gene is differentially expressed in somatotrophs and lactotrophs remains to be elucidated. In this study, we usedin situhybridization histochemistry to examine Pit‐1, GH and PRL mRNA levels in the anterior pituitaries of male and female rats throughout development (0, 5, 10, 20, 30, 40 and 60 days of age) to determine when GH and PRL production becomes sexually dimorphic and if this is accompanied by a dimorphism in Pit‐1 gene expression. In addition, the level of Pit‐1 mRNA was determined separately in both GH mRNA and PRL mRNA containing cells during the various developmental stages. We found that in both males and females the mRNA levels of Pit‐1, GH and PRL remain relatively unchanged until around the time of pubertal onset (30–40 days) when there is a significant increase in all three mRNA species, which is followed by a decrease to adult levels. Also around the time of puberty, both GH and PRL mRNA levels become sexually dimorphic, with males having higher levels of GH mRNA and females higher PRL mRNA levels. In contrast, at no time during development were overall Pit‐1 mRNA levels found to differ between the sexes. However, when Pit‐1 mRNA content was measured separately in specific cell types, significant differences between the sexes became evident. Throughout development Pit‐1 mRNA levels are higher in lactotrophs of females than in those of males, whereas in somatotrophs males have higher Pit‐1 mRNA levels than females. Furthermore, within a sex there is differential expression of Pit‐1 in the two cell types with females having significantly higher levels of Pit‐1 in lactotrophs than in somatotrophs and males having higher levels in somatotrophs than in lactotrophs. These data support the hypothesis that a sexual dimorphism exists in the expression of the pituitary specific transcription factor Pit‐1; however, this dimorphism is not manifest as a difference in overall mRNA levels, but in the differential expression of this gen

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04526.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Oxytocin is released within the supraoptic nucleus during parturition and suckling. During suckling, such release is important in positive feedback stimulation of oxytocin neurons. We have investigated whether oxytocin released within this hypothalamic nucleus during parturition (1) acts on local receptors to further amplify its own release in a positive feedback manner and (2) is critically involved in the regulation of the delivery process.  To examine the effect of the oxytocin antagonist on oxytocin release within the supraoptic nucleus, microdialysates were sampled before and during parturition and either vehicle or the antagonist was infused adjacent to the microdialysis probe directly into the supraoptic nucleus after delivery of the second pup. Intranuclear infusion of an oxytocin receptor antagonist (des‐Gly‐NH2d(CH2)5[Tyr(Me)2Thr4]OVT; 50 ng/0.5 μl) significantly (P<0.01) diminished the parturition‐related rise in oxytocin release within the supraoptic nucleus and reduced the number of pups delivered during the first and second 30‐min dialysis period compared to vehicle‐treated controls.  Bilateral infusion of the oxytocin receptor antagonist into the supraoptic nucleus after delivery of the second pup significantly slowed parturition (P<0.05), although the parturition‐related rise in plasma oxytocin concentration was unchanged. In addition, the onset of suckling was significantly affected by the antagonist as indicated by fewer live pups and fewer surviving pups with milk in their stomachs 24 hours after parturition (P<0.05).  To seek other, periventricular sites of oxytocin action during parturition, oxytocin or the oxytocin antagonist was infused into the lateral cerebral ventricle from the birth of pup 2. Via this route, oxytocin speeded up parturition, but the antagonist was ineffective; thus it appears that periventricular oxytocin‐sensitive sites are not normally active in promoting parturition, but can do so.  The findings indicate a receptor‐mediated positive feedback action of oxytocin on its own release within the supraoptic nucleus during parturition, which seems to be involved in the progress of parturition without significantly affecting circulating oxytocin levels. Oxytocin released within the supraoptic nucleus might be important for the coordinated activation of oxytocin neurons and for the synergistic central and peripheral oxytocin effects involved in the regulation of parturition‐related events necessary for the survival of the newborn, in

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04557.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Cultured pituicytes, derived from the neurohypophysis of adult rats, have previously been reported to change from a non‐stellate form to a stellate form when incubated in medium containing aβ‐adrenoreceptor agonist. This study was designed to determine whether the same morphological change could be induced by direct activation of adenylate cyclase or of soluble guanylate cyclase. The fraction of stellate cells was normally low (<0.25) when the pituicytes were incubated (90 min) in a HEPES buffered salt solution (HBSS); most pituicytes had an amorphous protoplasmic appearance. The fraction of stellate cells was significantly increased when pituicytes were incubated in HBSS supplemented with isoproterenol (10 μM) or forskolin (5 μM) or with either of the nitric oxide donors nitroprusside (10–25 μM) and 3‐morpholinosydnonimine (SIN‐1; 10 μM). The effect of forskolin was mimicked by 8‐bromo cyclic AMP, a membrane permeable analog of cyclic AMP, but not by the inactive forskolin analog 1, 9 dideoxyforskolin. The effect of nitroprusside was blocked by methylene blue, an inhibitor of soluble guanylate cyclase, and was mimicked by 8‐bromo cyclic GMP, a membrane permeable analog of cyclic GMP. These results demonstrate that activation of adenylate cyclase and also of soluble guanylate cyclase can induce pituicytes to undergo morphological changesin vitro. The data suggest that the activity of both enzymes may be important in control of the plastic relationship that exists between neuronal and glial elements i

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04538.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY