摘要:

N‐methyl‐D‐aspartic acid (NMDA) is known to stimulate adrenocorticotropin (ACTH) release after peripheral administration in spite of its inability to readily cross the blood‐brain barrier (BBB). The importance of the area postrema, the hindbrain circumventricular organ which lacks a BBB, for NMDA action and ACTH release during stress was evaluated in this study. ACTH response to NMDA injection (4 mg/kg ip) was significantly reduced in rats with ablation of the area postrema compared to sham‐operated animals. Integrity of the area postrema was also found to be required for full ACTH release in response to two stress stimuli (immobilization, handling). The data show that the area postrema is a brain region involved in the control of the hypothalamic‐pituitary‐adrenocortical (HPA) axis mediating, at least partially, the stimulatory action of NMDA and of stress stimuli on

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00151.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Ninety min after intraperitoneal (ip) injection of Cholecystokinin (CCK, 50 μg/kg body wt) Fos‐like protein was expressed in cells throughout the nucleus of the tractus solitarii (NTS) and area postrema, and also in scattered cells in the lateral reticular area of the brainstem. Using dual fluorescent immunocytochemistry for Fos‐like protein and tyrosine hydroxylase (TH), catecholaminergic cells in the A2 region of the NTS and the A1 region of the lateral reticular area were shown to be activ

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00152.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractWe have investigated whether the stress‐induced activation of the medullary catecholaminergic neurons, that was shown previously to provide the main central activation input to the hypothalamo‐pituitary‐adrenocortical axis during an immobilization stress, is sensitive to circulating corticosteroids. Experiments were carried out on adrenalectomized rats that were first maintained on corticosterone in the drinking water for 5 days following surgery and then switched to corticosterone‐free water 15 h before stress application. Some of the latter animals were injected with dexamethasone. Activation of the brainstem Catecholaminergic neurons was estimated by assaying 3,4‐dihydroxyphenylacetic acid (DOPAC), a side metabolite of the noradrenaline and adrenaline biosynthesis pathway that was established previously as a reliable index of the activity of these neurons. In the so‐called A1C1and A2C2Catecholaminergic groups of the medulla, lack of corticosterone under these experimental conditions did not modify the basal level of DOPAC but led to a further enhancement (+ 35% to 40%) of the approximately 2‐fold increase in DOPAC content observed 15 min after the onset of the 5‐min immobilization stress. No significant further enhancement of the stress‐induced DOPAC increase was observed in the locus coeruleus. In these adrenalectomized rats, dexamethasone pretreatment prevented the enhancement of the stress‐induced increase in DOPAC level observed in the medullary cell groups but did not abolish the response to stress. Lack of endogenous corticosteroids led to a 10‐fold enhancement of the adrenocorticotropin increase following immobilization stress. Pretreatment with dexamethasone fully abolished the stress‐induced increase in adrenocorticotropin plasma level.Our results show that circulating corticosteroids reduce the stress‐induced activation of the medullary A1and A2C2groups i.e. those that contribute mainly to the catecholaminergic innervation of the hypothalamo‐pituitary‐adrenocortical axis within the hypothalamic paraventricular nuclei. However, since the feedback regulation of the central catecholaminergic systems is much less efficient than the feedback actually observed on the adrenocorticotropin secretion, we suggest that it is likely to play a minor physiological role in the overall feedback regulation exerted by circulating corticosteroids on the hypothalamo

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00153.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe proto‐oncogene product of the c‐fos gene, cFos, is a useful marker for luteinizing hormone‐releasing hormone (LHRH) neuronal activation. While recent data indicate that in the rat, an LHRH surge plays an active role in stimulating the proestrous luteinizing hormone (LH) surge, the mechanics of the LHRH surge remain unknown. The aim of this study was to determine whether LHRH neuronal activation occurs entirely at the beginning of the LH surge or whether the number of LHRH neurons activated increases during the ascending phase of the surge. To accomplish this aim, we determined the relationship between the number of LHRH neurons expressing cFos and LH concentrations during the ascending limb of the proestrous LH surge. During the estrous cycle in the rat, on the afternoon of proestrus, the number of LHRH neurons expressing cFos increased as plasma LH levels increased to reach peak concentrations. The regression line describing these two variables had a very highly significant correlation coefficient, indicating a linear relationship. Treatment with RU486 to block progesterone's action on the afternoon of proestrus significantly reduced both the number of LHRH neurons expressing cFos and the magnitude of LH secretion during the entire ascending phase of the LH surge. An analysis of covariance with comparison of regression lines from untreated and RU486‐treated animals revealed that while both sets of data established significant linear relationships between the degree of activation of LHRH neurons and plasma LH values, the slopes of the two lines were different (P = 0.031) with no statistical difference in the two intercepts. These data, together with the demonstration of an overall reduction of cFos intensity following removal of progesterone's actions, suggest progesterone alters the dynamics of LHRH neuronal activation by significantly reducing the recruitment of LHRH neurons and suppressing the level of activation of individual LHRH neurons. The results of our study support the hypothesis that the ascending phase of the LH surge results from the gradual recruitment of LHRH neurons into the activ

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00154.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA nocturnal surge of prolactin (PRL) occurs in the dark period preceding parturition in the rat. The roles of oxytocin, vasoactive intestinal peptide (VIP), serotonin and the opioids in controlling the antepartum PRL surge were investigated by examining PRL secretion over the last 2 days of pregnancy in the presence of antagonists to these neurohormonal factors. Serial blood samples were collected from unanesthetized, freely moving rats via indwelling jugular cannulae, and plasma PRL was measured by radioimmunoassay. In control rats PRL levels rose in a nocturnal surge peaking at 223 ± 34 ng/ml (n = 6) at 0500 h on day 21 of pregnancy, the day of parturition. Intra‐arterial infusion of the oxytocin antagonist desGly‐NH2d(CH2)5[Tyr(Me)2, Thr4]‐OVT at a dose sufficient to completely block milk ejection (10 μg/h) had no effect on this PRL surge. Infusion of the VIP antagonist [4Cl‐D‐Phe6,Leu17]‐VIP at 2 μg/h from 2200 h on day 20 until 0500 h on day 21 significantly attenuated the antepartum PRL surge, reducing the peak to 76 ± 28 ng/ml at 0500 h on day 21 (n = 6; P<0.001). Naloxone, the opiate receptor antagonist, inhibited the antepartum PRL surge in a dose‐dependent manner. Infused at 2 mg/h naloxone partially reduced the magnitude of the PRL surge, which peaked at 128 ± 24 ng/ml at 0300 h on day 21 (n = 4; P<0.05), while at 10 mg/h naloxone totally abolished the PRL surge (n = 6; P<0.001). Injection of the serotonin synthesis inhibitor ρ‐chlorophenylalanine (250 mg/kg, sc at 1700 h on days 19 and 20 of pregnancy) increased the magnitude of the antepartum PRL surge to a peak of 327 ± 48 ng/ml at 0500 h on day 21 (n = 5), compared with 244 ± 24 ng/ml at the same time in vehicle‐injected controls (P<0.05; n = 5). The results demonstrate that the antepartum PRL surge is stimulated by an opioid mechanism, and also by VIP. Oxytocin and serotonin have no role in stimulating PRL secret

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00155.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe present experiments sought to characterize the particular stimuli received during mating in the female rat which induce acute increases in luteinizing hormone (LH) and prolactin (PRL) following copulation. Comparisons were made between cycling females mated on the evening of proestrus in partitioned chambers in which spontaneous patterns of approach/withdrawal toward the male served to pace copulatory stimulation (paced), in non‐partitioned chambers in which female regulation of intervals between copulatory mounts was prevented (non‐paced), or under conditions in which they received mounts‐without‐intromission (mounts‐only). Frequent blood samples were withdrawn via surgically implanted intra‐atrial catheters. In experiment 1, blood samples for LH determinations were taken at 15‐min intervals for 1 h prior to and for 2 h after mating on the evening of proestrus. In experiment 2, samples for PRL determinations were taken at 10‐min intervals for 30 min prior to and for 90 min after mating on proestrus and at 0300, 0400 and 0500 h on the day of estrus (reported times corrected for reversed light cycle). LH levels were significantly higher in paced animals 15 min after initiation of mating than in non‐paced and mounts‐only females; no differences in LH were seen between females who subsequently became or did not become pregnant/pseudopregnant (P/PSP). PRL values were not different between groups receiving the different mating treatments at any time; however, P/PSP animals showed significantly higher levels of PRL between 20 to 60 min after mating than did non‐P/PSP females. No differences in PRL were seen between mating treatments or pseudopregnancy condition at 0300 to 0500 h on estrus. Paced females in both experiments received intromissions at a significantly slower rate than did non‐paced females. There was a significant positive correlation (r = 0.619, P<0.001) between LH concentration at 15 min and the inter‐intromission interval (in seconds) in paced and non‐paced groups of females. These data suggest that an LH response to mating is dependent upon the particular characteristics of mating stimulation received. In addition, they demonstrate that PRL increases acutely after mating stimulation in animals destined to become P/PSP but does not increase in response to those characteristics of mating stimulation wh

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00156.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe physiological factors that regulate the levels of oxytocin (OT) mRNA in the rat hypothalamo‐neurohypophyseal system during lactation are unknown. The major objective of the present studies was to test whether afferent stimuli provided by the offspring influence the level of OT mRNA in the magnocellular nuclei of the hypothalamus, i.e. the paraventricular nucleus (PVN), supraoptic nucleus (SON) and anterior commissural nucleus (ACN), during lactation. In addition, these studies provide a detailed description of the changes that occur in OT mRNA levels in these nuclei during pregnancy and lactation. Levels of OT mRNA were determined in the total RNA extracted from pooled PVN/SON/ACN, which were microdissected from pregnant and lactating Holtzman rats, by slot‐blot hybridization. RNA blots were hybridized sequentially with a [32P]5’end‐labeled, 25‐base oligonucleotide probe complementary to bases 912–936 of the OT gene and with a random primer‐labeled cDNA complementary to α‐tubulin mRNA, which was used for normalization. Autoradiographs were quantitated by scanning laser densitometry. Compared to the levels on day 1 of pregnancy (the day of mated estrus) the relative levels of OT mRNA were decreased on pregnancy days 7 and 14, and then returned to the mated estrus value on days 16 to 20. The level of OT mRNA again declined prior to parturition on day 23, although it was restored to the estrus value the day after parturition and generally remained at this level throughout lactation. To assess the influence of stimuli provided by the offspring for the regulation of OT mRNA levels during lactation, lactating females were separated from their litters immediately after parturition or on lactation day 8. As compared to nonseparated, time‐matched controls, removal of the litters immediately after parturition resulted in a statistically significant reduction of approximately 25% in the levels of OT mRNA 24 and 48 h later, which returned to control levels by 72 h. In contrast, removal of the litters on lactation day 8 did not significantly alter the level of OT mRNA in the PVN/SON/ACN over the next 3 days. These findings suggest that the level of OT mRNA in hypothalamic magnocellular nuclei is influenced to some extent by afferent stimuli provided by the offspring during an early period of lactation but, thereafter, becomes unresponsive to removal of this influence. Afferent suckling stimuli may be one component of a multifactorial regulation responsible for the maintenance of OT mRNA expressio

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00157.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractMelatonin binding sites in the pars tuberalis of the European hamster (Cricetus cricetus) have been characterized using the radioligand 2‐[125I]iodomelatonin. Specific 2‐[125I]iodomelatonin binding was assessed using radioreceptor studies of pars tuberalis membrane preparations. Saturation studies revealed a single, high affinity site (Kd39.8 (± 7.6 SEM) pM and Bmax4.1 (± 0.5 SEM) fmol/mg protein, n=4). Kinetic experiments showed the 2‐[125I]iodomelatonin binding to be rapid, saturable and reversible. The Kdcalculated from the dissociation and association rate constants was 19.4 pM. The order of potency of different indoles for inhibition of 2‐[125I]iodomelatonin binding was 6‐chloromelatonin>melatonin>6‐hydroxymelatonin>N‐acetylserotonin>5‐methoxytryptophol>serotonin>5‐methoxytryptamine. GTP caused a dose‐dependent inhibition of the 2‐[125I]iodomelatonin binding. A saturation study showed that GTP reduced the number of binding sites by a third without altering their affinity. These results imply the presence of a G‐protein‐coupled melatonin receptor in the pars tuberalis of sexual

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00158.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe present study was done to determine whether the vasopressinergic neurons in the hypothalamus controlling flank marking behavior are distinct from the magnocellular neurons comprising the hypothalamo‐neurohypophysial system. Animals were either hypophysectomized or injected with a suicide transport lectin, volkensin, into the neurohypophysis. Both procedures resulted in a pronounced loss of vasopressin‐immunoreactive perikarya throughout the hypothalamus concomitant with increases in water intake and urine output and decreases in circulating levels of vasopressin. The loss of the hypothalamo‐neurohypophysial system was most pronounced in volkensin‐treated animals that presented with frank diabetes insipidus and exceedingly low levels of plasma vasopressin. However, the vasopressinergic fibers and magnocellular neurons in and around the anterior hypothalamus implicated in the control of flank marking survived the volkensin treatment. Volkensin‐treated animals exhibited levels of flank marking typical of untreated animals. These data suggest the presence of anatomically and functionally distinct populations of vasopressinergic magnocellular neurons in the hypothalamus of the golde

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00159.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractGonadotropin‐releasing hormone (GnRH) regulates the secretion of pituitary gonadotropins and facilitates the display of sexual behavior. We report that in doves, following a brief period of courtship, non‐neuronal cells containing GnRH‐like immunoreactivity (ir) are seen in the habenula of both male and female doves. These cells appear to be translocated from either the cerebrospinal fluid or from capillaries in the pia or choroid plexus into the parenchyma of the brain. Immunoreactive cells are virtually absent in the habenula in control animals housed alone. The identity of the ir cells that enter the habenula is unknown but they would appear to be of either the macrophage or the mast cell lineage. Both of these blood‐derived cells have heterochromatic nuclei and irregular cell surfaces with many filamentous processes, as do the GnRH‐ir cells. The vacuolated granules of the ir cells could be indicative of mast cell degranulation or of endocytic vesicles of a phagocytosing cell. These data suggest that there is a population of cells within the habenula that are of similar size and morphology to the GnRH‐ir ceils and are metachromatic when stained with toluidine blue. The latter is a property of heparin‐containing mast cells. Lineage specific markers that permit a double‐label study will be required to determine the exact nature of the GnRH‐ir cells. Whatever their lineage, the translocation of non‐neuronal cells into the undamaged adult central nervous system has not been described previously, and may provide a means of delivering biologically active substances into spe

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1992.tb00160.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY