摘要:

AbstractOf the reproductive hormones it has been suggested that relaxin may play an important role in the increased sodium appetite of pregnancy. ICV injection of porcine relaxin caused water‐replete male and female Wistar rats with access to water and 0.9% or 2.7% NaCl to drink on average about 3 to 8 ml of water within 1 h of injection. By 24 h the cumulative intake of water was no different from the control intake. The amounts of water drunk were similar after doses of 50, 100, 250 and 500 ng of relaxin. A dose of 5 ng was ineffective. Male rats generally drank more water than female rats after ICV injection of angiotensin or relaxin. Male SH rats which drink more water than male WKY rats in response to ICV angiotensin also drank more after ICV relaxin. Intakes of 0.9% or 2.7% NaCl were unaffected for up to 24 h after injection of relaxin, whereas angiotensin‐injected rats showed a significant increase in 0.9% NaCl 1 h after injection though this difference was no longer evident in the 24 h cumulative intake. Relaxin did not cause any increase in NaCl intake in SH rats. Insulin, which is similar in structure and molecular weight to relaxin, was without effect on drinking when doses comparable to dipsogenically effective doses of relaxin were injected ICV. In male Wistar rats treated with DOCA for 5–15 days, relaxin retained its weak stimulatory action on water intake but did not affect NaCl intake despite the increased baseline NaCl intake during DOCA. These results indicate that relaxin is a dipsogen in the rat but that it seems to have little short‐term effect on sodium a

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00743.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractPrevious studies from this laboratory have shown that progesterone (PROG) treatment in ovariectomized rats produces an anti‐anxiety response similar to that observed after the administration of prototypical anxiolytic benzodiazepine (BDZ) compounds. The PROG‐induced anxiolytic response was highly correlated with an increased level of 3α‐hydroxy‐5α‐pregnan‐20‐one (allopregnanolone) in the blood and brain, and was also associated with a facilitation of GABA‐stimulated chloride ion (Cl−) influx in cortical synaptoneurosomes. This correlative evidence suggested that the anxiolytic effect of PROG was a result of its in vivo reduction to the neuroactive steroid, allopregnanolone. In this report, a series of studies was conducted to determine the mechanism(s) by which PROG alters behavior in animal models of anxiety. In the first experiment, ovariectomized rats were injected with PROG (1 mg/0.2 ml, SC) 4 h prior to a test in the elevated plus‐maze. Some animals also received an injection of picrotoxin (0.75 mg/kg, IP), a GABAAreceptor‐gated Cl−channel antagonist, whereas other animals were pretreated with RU 38486 (5 mg/0.2 ml, SC), a progestin receptor antagonist. PROG elicited anxiolytic behavior in the plus‐maze, an effect that was blocked by picrotoxin administration. Pretreatment with RU 38486 was not effective in altering PROG‐induced anxiolytic behavior in the plus‐maze. In a second experiment, the effect of PROG on behavior in the plus‐maze was determined in the presence of N,N‐diethyl‐4‐methyl‐3‐oxo‐4‐aza‐5α‐androstane‐17β‐carboxamide (4‐MA; 10 mg/0.2 ml, SC), a 5α‐reductase inhibitor. The enzyme inhibitor was potent in preventing the anxiolytic effect observed in the plus‐maze after PROG administration. In the defensive burying paradigm, PROG treatment also produced anxiolysis by reducing the duration of burying behavior, and this effect was prevented by 4‐MA pretreatment, but not by RU 38486 administration. After the completion of the behavioral assays, analysis of blood allopregnanolone levels revealed a marked increase in PROG‐treated females. The PROG‐induced elevation in circulating allopregnanolone was blocked by pretreatment with 4‐MA. In cortical synaptoneurosomes, the sensitivity (inverse of the EC50) and the maximal response (Emax) in GABA‐stimulated36Cl−uptake were increased in PROG‐treated females. The potentiation of PROG on both of these neurochemical measures was not observed in animals pretreated with 4‐MA. Together, these studies provide evidence that the anxiolytic effect of PROG is not associated with an intracellular steroid receptor that initiates genomic‐mediated responses. The evidence is consistent with a nongenomic mechanism whereby PROG is metabolized to allopre

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00744.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe newly synthesized GH‐releasing peptide, GHRP‐2 (D‐Ala‐D‐βNal‐Ala‐Trp‐D‐Phe‐Lys‐NH2), was studied in somatotroph‐enriched populations of ovine pituitary cells in primary culture. Nystatin‐perforated whole‐cell recordings were made on identified somatotrophs after 4–14 days of culture. Using a standard bath solution (containing Na+, Ca2+) and an electrode solution containing K+in current‐clamp recordings, GHRP‐2 (10 nM) depolarized the membrane potential of the cells triggering a burst of action potentials. Voltage‐clamp recordings indicated that GHRP‐2 produced a slowly inactivated inward current with a slight reduction in outward current. The inward current was blocked by the Ca2+channel blocker, Co2+(0.5 mM). Ca2+currents were then isolated using tetraethylammonium bath solution and an electrode solution containing Cs+. Ovine somatotrophs possess transient (T type) and long lasting (L type) Ca2+currents. The L type current was abolished by addition of nifedipine (3 μM) to the bath solution and T type current was isolated on this basis. Current‐voltage relationships indicated an increase in both T and L type Ca2+currents in response to GHRP‐2. The voltage‐dependent inactivation curve for T type Ca2+current was shifted towards a less negative level by the peptide. Intracellular free Ca2+concentration ([Ca2+]i) in somatotroph‐enriched populations was specifically increased by GHRP‐2 but this effect was totally abolished by blockade of membrane Ca2+channels. These data show that GHRP‐2 causes an influx of Ca2+leading to an increase in [Ca2+]i in ovine somatotrophs. The Ca2+currents were both L type and T type with a shift in the inacti

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00745.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractEnzymes in the avian brain irreversibly catalyze the conversion of androgens into either active metabolites (aromatase and 5α‐reductase) or inactive metabolites (5β‐reductase). 5β‐reductase is thought to influence the formation of active metabolites by reducing the concentration of androgenic substrate available for these reactions. However, because these enzymes have different regional, cellular and subcellular distributions in brain, the traditional method to measure enzyme activity in brain homogenates may be inaccurate because of artificial mixing of enzymes. Recently, we have prepared primary cell cultures from the telencephalons of developing zebra finches. Cell cultures offer the advantage that enzyme activity can be measured in live cells in which the relative distribution of enzymes may more closely reflect that foundin vivo.We have previously reported that aromatase is expressed at high levels in these cultures, and that it is active in both neurons and in glia. Here we report on the activities of 5α‐ and 5β‐reductase in these cell cultures. Along with aromatase, 5β‐reductase was expressed at high levels in these mixed cell cultures, including cultures highly enriched in glia. This suggests that 5β‐reductase is present in non‐neuronal cells in brain, possibly co‐localized with aromatase. However, despite the presence of 5β‐reductase, aromatase was detected reliablyin vitroeven when the concentration of substrate was low. Thus, 5β‐reductase does not prevent the synthesis of estrogen in the telencephalon of developing zebra finches. By contrast, 5α‐reductase activity was very low or absent in these cultures. Thus, cells expressing 5α‐reductase may be poorly represented in these cultures. Alternatively, 5α‐reductase and aromatase together may interfere with the synthesis of 5α‐reduced

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00746.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractNeuropeptide Y (NPY) synthesized in the arcuato‐paraventricular projection in the rat hypothalamus is thought to play an important role in controlling energy homeostasis. The factors that regulate hypothalamic NPY are not known but, amongst others, insulin has been postulated as an inhibitory modulatory agent. To test this hypothesis, normal male rats were given either insulin (2 units/day) or saline via subcutaneous osmotic minipumps for 3 days. Euglycaemia was maintained by a concomitant glucose infusion in insulin‐infused rats which had peripheral insulin levels 5–8 times higher than saline‐infused controls. Hyperinsulinaernic rats ate 42% less than controls, but their total energy intake (food intake plus glucose infusion) was higher than that of controls, and they gained more weight than controls during the experimental period. Hyperinsulinaemia had no significant effect on hypothalamic NPY mRNA or NPY levels in the arcuate nucleus. NPY concentrations in the paraventricular nucleus were, however, significantly increased by 73% in hyperinsulinaemic rats, but were closely similar to controls in all other areas. Insulin may act as a satiety factor in that hyperinsulinaemic rats ate less, but the fact that these animals had increased total energy intake and gained excessive weight suggests that insulin may not function as an overall regulator of energy balance. In addition, physiological hyperinsulinaemia does not apparently inhibit NPY gene expression in the arcuate nucleus. Due to the lack of effect of hyperinsulinaemia on NPY synthesis in the arcuate nucleus, the elevated NPY concentrations in the paraventricular nucleus could result from a reduction of its release, which would be in keeping with the reduction in food

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00747.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe pineal hormone, melatonin, transduces photoperiodic information to the neuroendocrine axis of seasonally breeding mammals to regulate reproduction. It is not known where or how melatonin achieves this effect, but the recent identification of the pars tuberalis (PT) as the area with the highest density of melatonin binding sites suggests that this pituitary subdivision may be an important target for the actions of this indoleamine on luteinizing hormone (LH) and prolactin release. The present study was designed to test this hypothesis. Ovariectomized oestradiol‐implanted ewes were exposed to inhibitory long days for 85 days and then received melatonin micro‐implants (Day 0) in the mediobasal hypothalamus (MBH; n = 7) or PT (Melatonin‐PT; n = 5). The effect of these micro‐implants was compared to ewes receiving empty micro‐implants in the PT (Sham‐PT; n = 5). For LH, bi‐weekly jugular blood samples were collected and for prolactin, samples were collected every 20 min for 5 h, with the first hour discarded, on Days ‐4, 26 and 69. Melatonin implanted in the MBH stimulated LH secretion in 3 ewes by Day 46±0 after implantation, and one ewe by Day 67 after implantation. In contrast, no Melatonin‐PT or Sham‐PT ewes exhibited an increase in LH secretion by the end of the study (Day 70). A subsequent experiment, in which the Sham‐PT ewes were implanted with melatonin both subcutaneously and in the PT showed that the micro‐implants did not impair the ability of the ovine reproductive neuroendocrine axis to respond to melatonin. For prolactin, both the Melatonin‐PT ewes and MBH ewes (which had displayed an increase in LH secretion) exhibited a significant decrease in prolactin secretion by Day 26 and this decrease persisted until the end of the study. This result suggests that melatonin may have two sites of action on prolactin secretion; the MBH and PT, or, if melatonin diffused from the MBH to the PT, or vice versa, that only one of these sites is important. In contrast, these data suggest that the PT is not an important target for the action of

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00748.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe presence of soluble guanylate cyclase in the pineal and its regulation by adrenergic pathways has been well documented. Recent evidence points to adrenergically stimulated nitric oxide generation as a mechanism for coupling this pathway. To what extent nitric oxide (NO) signalling can influence adrenergically stimulated melatonin synthesis has not been investigated. Cyclic guanosine 3′,5′‐monophospate (cGMP) signal transduction in the bovine pineal has also received little attention. We describe in the present report: 1) a dose‐dependent elevation of cGMP in response to the nitrovasodilators, sodium nitroprusside (SNP) and 3‐morpholino‐sydnonimine (SIN‐l), 2) a dose‐dependent inhibition of melatonin synthesis by SNP and SIN‐1, but not by 8‐Br‐cGMP in both bovine and rat pineal cell cultures, which is not due to cytotoxicity as judged by two different approaches, and 3) immunohistochemical evidence for the presence of nitric oxide synthase (NOS) (EC 1.14.23.‐) in the intact bovine pineal gland and in cultured bovine pinealocytes. These data support the view that NOS is a component of the cGMP‐generating system in mammalian pinealocytes. Although NO‐donor molecules are also potent activators of cGMP accumulation, they may have other important actions in the pineal, namely the inhibition of adrenergic‐stimulated melatonin synthesis. As SNP and SIN‐1 exerted this inhibitory effect on cells regardless of whether they were stimulated by isoproterenol, forskolin or 8‐Br‐CAMP it would appear that NO‐donors can act ‘downstream’

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00749.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe pineal hormone melatonin is a potent regulator of seasonal and circadian rhythms in vertebrates. In order to characterize potential target tissues of melatonin, the distribution of iodomelatonin (IMEL)‐binding sites was examined within neurochemically and anatomically defined subdivisions of the suprachiasmatic nucleus (SCN), a structure necessary for seasonal and circadian rhythms in mammals. Studies were carried out in both the adult Syrian (Mesocricetus auratus) and Siberian (Phodopus sungorus) hamster. The retinoreceptive zone of the SCN was identified anatomically by immunocytochemical (ICC) visualization of cholera toxin B subunit tracer (ChTB‐ir) following its intra‐ocular injection. Photically‐responsive SCN cells were identified by immunostaining for the protein product of the immediate‐early genec‐fos(Fos‐ir) following exposure of the animal to light. The non‐photoresponsive zone of the SCN was identified usingin situhybridization (ISH) for arginine vasopressin (AVP) mRNA, whilst sites of IMEL‐binding in the SCN were identified byin vitrofilm autoradiography using the specific ligand 2‐[125l]‐iodomelatonin. To compare directly the distribution of IMEL‐binding sites and one of the functional zones of the nucleus, alternate serial coronal sections through the SCN were processed for autoradiography for IMEL and one of the following: ICC for ChTB‐ir or Fos‐ir, or ISH for AVP mRNA. Overall, the regional distribution of the various markers within the SCN was comparable in the two species. The retinorecipient (ChTB‐ir) and photically‐responsive (Fos‐ir) zones of the SCN mapped together to the middle and caudal thirds of the nucleus, predominantly in its ventro‐lateral division. IMEL‐binding was present throughout the full rostro‐caudal extent of the SCN, but by far the most extensive area of IMEL‐binding was in the rostral half of the nucleus, leading to a clear dissociation along the rostro‐caudal axis of the principal zone of IMEL‐binding and the retinorecipient zone of the nucleus. In the Syrian hamster, in coronal sections of the caudal SCN which did contain significant amounts of both IMEL‐binding and Fos‐ir, IMEL‐binding was confined to the medial zone, distinct from the Fos‐ir region of the ventro‐lateral SCN. The segregation was less clear‐cut in the Siberian hamster where the area of IMEL‐binding was more extensive. The dissociation of IMEL‐binding and photically‐responsive cells in the Syrian hamster was confirmed in a series of sagittal sections which were processed alternately for Fos‐ir and IMEL‐binding. Whereas Fos‐ir was confined to the ventro‐lateral SCN, IMEL‐binding was concentrated in the medial zone of the nucleus. In both species, mRNA for AVP was found throughout the rostro‐caudal extent of the SCN, but the peak area was located in the rostral half, and so was segregated from the principal retinorecipient zone. The distribution of mRNA for AVP along the rostro‐caudal and medio‐lateral axes was in direct register with the IMEL‐binding in both species. These studies suggest that melatonin acts upon pathways within the SCN different to those addressed by light, and that it may influence directly the e

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00750.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIt is well established that estrogens are potent stimulators of prolactin (PRL) secretion. It has also been demonstrated that estradiol (E2) can increase the expression and the anterior pituitary levels of the vasoactive intestinal peptide (VIP), a peptide which also acts as a potent PRL‐releasing factor. It thus remained unknown whether the effects on pituitary VIP were due to E2 itself or to E2–induced hyperprolactinemia (HPRL). In order to test this hypothesis, various plasma PRL levels were induced in rats either with ectopic pituitary grafts, PRL secreting tumours or E2 implants, and VIP mRNA expression in the anterior pituitary was measured byin situhybridization and Northern blot analyses. Whereas decreases in VIP mRNA can be observed in pituitaries of rats with pure HPRL, a 6‐fold increase in VIP mRNA can be seen in E2‐treated rats. E2 increased both 1.0 and 1.7 Kb VIP mRNA species. The presence of the graft in E2‐treated rats significantly reduced the increase in VIP mRNA observed following E2. The direct stimulation by E2 of VIP mRNA expression was further demonstrated by the fact that statistical analysis of the data indicated that both E2 and graft were acting independently of each other, and that a new selective antiestrogen, RU 58668, almost totally blocked the effect of E2. Moreover, under similar experimental conditions, pituitary PRL mRNA levels were reduced in the graft group and a marked up‐regulation was observed similarly in both E2 and in E2 rats bearing ectopic grafts. We observed furthermore that not only levels of the mature 1.0 Kb PRL mRNA but also the 1.7 and 3.8 KbPRL precursor RNAs were increased. Such changes were associated with modifications in PRLmRNA size due to an increase in 3′polyA tail lenghts. The present data demonstrate that E2 directly affects VIP mRNA and PRL mRNA expression in the pituitary and support the hypothesis that VIP may play a role in the hypersecretion of PRL associated with the formation of E2‐induce

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00751.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe neuroactive steroid 5α‐pregnane‐3α,21‐diol‐20‐one (5α‐tetrahydrodeoxycorticosterone; 5α‐THDOC) has been shown to potentiate GABA‐induced chloride currents in cell cultures and subcellular preparations.In this study, we recorded from pyramidal neurons in anin vitroslice preparation of the adult rat frontal neocortex using intracellular microelectrodes. 5α‐THDOC (10 μM) increased and prolonged the inhibitory postsynaptic potential (IPSP). The mean maximal synaptic conductance of the early, GABAAreceptor‐mediated, IPSP was enhanced to more than 700%, the one at the maximum of the late, partially GABAAreceptor‐mediated, IPSP to approximately 400%. The progesterone/glucocorticoid receptor antagonist RU 38486 did not prevent the IPSP increase. At a concentration of 1 μM 5α‐THDOC increased only the early IPSP to about 125%.Responses to the iontophoretically applied specific GABAAreceptor agonist muscimol but not to the specific GABABreceptor agonist L‐baclofen were enhanced by 5α‐THDOC (10 μM). In the giga‐seal whole‐cell configuration when the GABABreceptor‐mediated IPSP component was absent due to intracellular perfusion, 5α‐THDOC (10 μM) increased IPSPs to a similar extent as in the conventional microelectrode recordings. Excitatory postsynaptic potentials, resting membrane potential, input resistance and action potential amplitude were not affected by 5α‐THDOC (10 μM).These data demonstrate that in neocortical tissue of the rat 5α‐THDOC enhances GABAergic inhibition by interacting with postsynaptic GABAAreceptors while synaptic excitation an

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1995.tb00752.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY