摘要:

AbstractIt has been previously demonstrated that activation of A1adenosine receptors in frog melanotrophs causes inhibition of spontaneous action potential discharges and alpha‐melanocyte‐stimulating hormone secretion. In the present study, we have investigated the effect of adenosine on high‐voltage‐activated (HVA) calcium currents in cultured melanotrophs, using the whole‐cell variant of the patch‐clamp technique with barium as a charge carrier. Adenosine and the specific A1adenosine receptor agonist R‐PIA (50 μM each) produced a decrease of the amplitude of the barium current, while the selective A2adenosine receptor agonist CGS 21680 did not affect the current. The inhibitory effect of R‐PIA was observed throughout the activation range of the current, with stronger responses at more positive potentials. R‐PIA inhibited both the L‐ and N‐type components of the current, the effect on the N‐component being two‐fold higher than on the L‐component. The inhibitory effect of R‐PIA was rendered irreversible by addition of GTPyS (100 μM) to the intracellular solution. Pre‐treatment of the cells with pertussis toxin (1 μg/ml; 12 h) totally abolished the effect of R‐PIA on the HVA calcium channels. Conversely, addition of a high concentration of cAMP (100 μM) together with the phosphodiesterase inhibitor IBMX (100 μM) to the intracellular solution did not modify the effect of R‐PIA on the current.It is concluded that, in frog melanotrophs, adenosine induces inhibition of L‐ and N‐calcium currents and that this effect is mediated by a pertussis toxin‐sensitive G protein. Our data also indicate that the inhibitory effect of adenosine on the calcium currents is

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00827.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractIt has been suggested that the hypothalamic‐pituitary‐adrenocortical (HPA) system contributes to individual differences in sensitivity towards drug abuse. Therefore, we studied the effects of the prototypic drug morphine in transgenic mice with impaired glucocorticoid receptor function. This mouse model has a profoundly dysfunctional HPA feedback. Since morphine‐induced locomotor stimulation is positively correlated with the rewarding effects of morphine, we examined morphine‐induced locomotor activity of transgenic mice and control mice (B6C3F1), Because morphine‐induced locomotor activity depends on an intact mesolimbic system, dopaminergic (DAergic) neuronal activity was also estimated within the mesolimbic system. Results indicated that the activity after vehicle injection do not differ between these two mouse lines. Compared to vehicle injections, morphine (7.5 and 15mg/kg; i.p.) dose‐dependently increased motor activity for 3 h in control and transgenic mice. However, morphine‐induced locomotion was significantly more pronounced in transgenic mice. Further, morphine‐induced mesolimbic DAergic activity was enhanced in transgenic animals as compared to control animals. These results parallel endocrine data that show that the plasma ACTH level of transgenic mice reach higher levels compared to those levels observed in control mice after morphine injections. Altogether, this transgenic mouse line shows an enhanced locomotor‐stimulant effect to morphine, a response that is reflected by an enhanced DAergic activity within the mesolimbic system and is also associated with increased HPA activity. We submit that the dysregulation of the HPA system in these transgenic mice influences the enhanced vulnerability to drug

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00828.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe effect of the α‐subunit of luteinizing hormone (LHα) on lactotroph growth in 14‐day‐old rat pituitary was studiedin vitrousing a reaggregate pituitary cell culture system. LHα significantly expanded both the total population of cells expressing prolactin mRNA and the number of [3H]thymidine incorporating prolactin mRNA expressing cells. No such effect could be elicited by LH. Both effects were inhibited by simultaneous addition of an anti‐LHα antiserum but not by normal rabbit serum. Anti‐LHα antiserum added alone to the cultures caused a small decrease in the number of prolactin mRNA expressing cells and in [3H]thymidine labelling of the latter. It is concluded that LHα may be a trophic factor of lactotrophs not only during fetal development, as suggested by others previously, but also during the rapid expansion of this cell type during postnatal

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00829.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe role of afferent innervation to the hypothalamic paraventricular nucleus (PVN) on CRH mRNA and CRH receptor mRNA levels was studied in control and stressed rats. Groups of rats were subjected to unilateral transection of the stria terminalis (ST), the medial forebrain bundle at the rostral hypothalamic level (RMFB), or the lower brainstem through the medulla oblongata between the obex and the locus coeruleus (CBs). Twelve days after surgery, each group of rats was further divided into controls (basal conditions) and stressed (1 h immobilization), before collecting brains for mRNA analysis byin situhybridization histochemistry. While ST and RMFB cuts had no effect on basal CRH mRNA levels in the PVN, CBs cut decreased CRH mRNA in the PVN ipsilaterally to the knife cut but it was without effect on the contralateral side (– 40% and –37%vscontralateral and sham‐operated, respectively, P&0.01). Acute stress (rats were killed 3 h after immobilization) increased CRH mRNA levels by about 30% bilaterally, an effect which was unchanged by any of the three hemisections. Under basal conditions, CRH receptor mRNA levels in the PVN were indistinguishable from the surrounding areas in sham‐operated controls, ST and RMFB operated rats. However, brainstem hemisection resulted in clear expression of CRH receptor mRNA in areas consistent with the dorsal, medial‐ventral and lateral parvicellular subdivisions of the PVN, ipsilateral to the transection. CRH neurons in these subdivisions project to the lower brainstem and the spinal cord. Expression of CRH receptor mRNA in the medial‐dorsal and anterior parvicellular divisions (CRH neurons with median eminence projections) was not affected by CBs cut. In these subdivisions, immobilization stress markedly increased CRH receptor mRNA levels but it did not influence CBs cut‐induced CRH receptor expression. ST and RMFB hemisections were without effect on PVN CRH receptor mRNA levels under basal or stress conditions. Oxytocin (OT) and vasopressin (VP) mRNA levels in the magnocellular subdivision of the PVN were unchanged after immobilization, or following ST, RMFB or CBs cuts, whereas OT mRNA in the medial‐ventral and caudal parvicellular subdivisions was decreased by 52% after CBs cut. The data demonstrate that: 1) basal CRH mRNA levels in the PVN are under tonic stimulatory influence of the lower brainstem (and/or spinal cord) afferents; 2) CRH receptor mRNA expression in PVN subdivisions (pituitaryvslower brainstem/spinal cord projecting neurons) is under different control mechanisms, and 3) immobilization‐induced changes in CRH mRNA and CRH receptor mRNA levels are mediated either by neural inputs from brain areas other than those investigated here, or b

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00830.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe mechanism whereby testosterone (T) reduces pulsatile LHRH and LH release is unknown. We tested the hypothesis that hypothalamic levels of LHRH mRNA decrease and proopiomelanocortin (POMC) mRNA increase coincident with reduced LHRH release induced by either long‐term or short‐term T treatment in male sheep. Experiment 1 examined the effect of long‐term T exposure on LHRH and LH release and LHRH and POMC mRNA levels. Yearling Suffolk rams were castrated and assigned to one of four treatments: 1) castrated (n = 4); 2) castrated, portal cannula (n = 5); 3) castrated +T (n = 4) and 4) castrated+T, portal cannula (n = 4). T‐treated males received ten 10‐cm silastic T‐implants immediately after castration. Surgical placement of devices for collecting hypophyseal‐portal blood occurred 2 to 3 months after castration. Seven to 10 days after surgery, blood samples were collected at 10‐min intervals for 8h from portal cannulated males or for 5 h from non‐cannulated males to assess pulsatile LHRH and/or LH release. Immediately after blood sample collection, hypothalamic tissue was collected forin situmeasurement of LHRH or POMC mRNA. T‐treatment decreased (P<0.01) mean LHRH and LH and decreased (P0.10) silver grain area per LHRH neuron, but decreased (P0.10) LHRH cell numbers while reducing (P<0.01) silver grain area per POMC neuron and POMC cell numbers. A second experiment examined the effect of 72 h of T‐infusion on LHRH and POMC mRNA levels. Castrated yearling males were assigned to receive either vehicle (n = 4) or T (768 ug/kg/day;n=4). Blood samples were collected at 10 min intervals for 4h prior to and during the final 4 h of infusion. Infusion of T decreased (P0.10) silver grain area per LHRH neuron or LHRH cell numbers. T reduced (P0.10) POMC cell number. We reject our hypothesis and conclude that reduced LHRH or heightened POMC gene expression are not mechanisms whereby T reduces pulsatile LHRH

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00831.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractWe have previously isolated a cleaved prolactin variant, secreted by rat pituitary cells in culture, that stimulated [3H]thymidine incorporation into DNA in gonadotrophs and thyrotrophs when added to pituitary aggregate cell cultures of 14‐day‐old female rats. Using synthetic peptides homologous to the new C‐ and N‐termini of the cleavage site, we made antisera recognizing this cleaved variant without significant cross reaction with native prolactin. Addition of these antisera to pituitary aggregate cell cultures decreased [3H]thymidine incorporation into DNA in gonadotrophs and thyrotrophs but not in the other pituitary cell types. These data are further evidence that this prolactin variant, cleaved between Tyr‐145 and Leu‐146, may have an important role as growth regulator of the gonadotrophs and thyrotrophs in the ra

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00832.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractWe studied the effect of corticosterone on interleukin (IL)‐1β synthesis, body temperature, general activity, food consumption and fluid intake in rats treated with bacterial lipopolysaccharide (LPS). Radiotelemetry was used to assess body temperature and locomotor activity in combination with continuous automated recordings of feeding and drinking. This technique was developed as a novel method to identify and measure sickness behavior in rodents. The animals were (a) sham‐operated, (b) adrenalectomized or (c) sham‐operated and treated with corticosterone (10 mg/kg, subcutaneously). They were then intraperitoneally injected with vehicle or LPS at a dose (100 μg/kg) that in sham‐operated rats induced fever and anorexia, reduced spontaneous activity and increased IL1‐β mRNA in spleen and adrenals as determined by Northern blot analysis. Adrenalectomized rats produced larger amounts of splenic IL‐1β mRNA, reduced their general activity much more and developed a mild adipsia as compared with adrenal‐intact animals. Administration of corticosterone 1 h before LPS lowered the splenic IL‐1β mRNA content compared to LPS‐treated adrenal‐intact rats that did not receive corticosterone and inhibited fever and anorexia, whereas the glucocorticoid did not attenuate the endotoxin‐induced suppression of locomotor activity. Our data suggest that during inflammatory conditions body temperature, sickness behavior and the synthesis of IL‐1β are controlled by corticosterone. Different components of sickness behavior seem to be independently regulated and are under differenti

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00833.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractTo establish the role of pituitary adenylate cyclase activating polypeptide (PACAP), a member of vasoactive intestinal polypeptide (VIP) family, as a neurotransmitter/neuromodulator in the central nervous system, the effects of PACAP38, PACAP27 and VIP on the single neuron activity in the magnocellular portion of the hypothalamic paraventricular nucleus (mg.PVN) were examined in rat brain slice preparations. Extracellular recordings were made from 111 neurons in the mg.PVN, which fired spontaneously at an average rate of 1.85 ± 0.2 spikes/s (mean ± SEM). PACAP38 and PACAP27 were applied to 78 and 33 of the 111 neurons, respectively. Perfusion with PACAP38 in doses between 10 nM and 1 μM increased the firing rate of 56 (71.8%) of the 78 neurons in a dose‐dependent manner. The threshold dose of PACAP38 to excite the neurons seemed to lie below 10 nM. The application of PACAP27 (1 μM) also increased the firing rate of 19 (57.6%) of the 33 neurons tested. Eleven (52.4%) of 21 neurons which were excited by PACAP38 also showed excitation following perfusion with VIP (1 μM). The responses to PACAP38 in 12 of 20 neurons and those to VIP in 6 of 9 neurons tested were still observed in a low Ca2+and high Mg2+medium. Although there was no difference in the mean latency between the responses to PACAP38 (1 μM) and VIP (1μM) (2.1 ± 0.1 min and 2.4 ± 0.4 min, respectively), the duration of the PACAP38‐induced excitation (59.0 ± 5.0 min) was much longer than that of the VIP‐induced one (18.8 ± 3.1 min). The PACAP38 (30 nM)‐induced excitation was reversibly blocked by a concurrent application of PACAP5‐38 (300 nM), a PACAP receptor antagonist. While a selective VIP receptor antagonist, [Lys1, Pro2,5, Arg3,4, Tyr6]‐VIP (1μM), did not affect the excitatory responses to PACAP38 (300 nM), it completely blocked the VIP (1μM)‐induced excitation. These findings suggest that PACAP may therefore modulate the secretion of the pituitary hormones at least partly by its action on the neurons in the mg.PVN through the activation of sp

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00834.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractWe have examined the influence of natural variations in endocrine status on the ability to generate a prostaglandin‐induced fever in virgin female, pregnant and lactating rats and compared responses to those in male rats. Endocrine status of virgin female rats was assessed from examination of vaginal smears and time of parturition noted to enable accurate dating of pre‐ and postparturient fevers. Unanesthetized rats, previously prepared with intraventricular guide cannulas and intraperitoneal telemetry thermistors, were given intraventricular injections of prostaglandin E, (2–100 ng/5 μl) and temperatures monitored for 3 h after injection. Virgin females developed significantly larger fevers than did males at higher doses. There were no significant alterations in either fever height or duration as a function of the phase of the reproductive cycle in the females. Both pregnant and postparturient rats within the several days around birth displayed significantly lower fevers than did virgin females, but there was no further reduction in the immediate periparturient period. These data indicate that there are sex‐, and possibly hormone‐dependent differences in the central mechanisms involved in fever generation and a

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00835.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe physiological factors that govern activity of the caudal neurosecretory system in teleost fish are poorly understood. Immunocytochemical evidence indicates that the neurosecretory Dahlgren cells are innervated by descending monoaminergic fibres. Using intracellular recording techniques in an isolated preparation of the posterior spinal cord of the flounder(Platichthys flesus)we have demonstrated that superfusion of adrenaline or noradrenaline (10−7–10−3M) causes hyperpolarization of Dahlgren cells (up to −30 mV). This hyperpolarization is likely to reflect an inhibitory effect of noradrenergic nerves on the neurosecretory systemin vivo, reducing the rate of hormone release. Fluctuations in the input resistance and membrane time constant suggest involvement of a multiplicity of cellular mechanisms, including the opening and closing of populations of ion‐selective channels. Superfusion with dopamine (10−7–10−3M) had no effect. Superfusion with the β‐adrenoreceptor agonist, isoprenaline, caused hyperpolarization but to a markedly lesser extent than the maximum effect of adrenaline or noradrenaline, suggesting that their effects are mediated, only in part, by a β‐adrenoreceptor subtype. Superfusion of the preparation with a membrane permeable, non‐hydrolysable cyclic AMP analogue (8‐[4‐chlorophenylthio]‐cAMP) resulted in a slight hyperpolarization which was accompanied by a small, but significant, increase in input resistance. These data are consistent with at least part of the β‐adrenoreceptor mediated effect involving closure of cAMP‐sensitive ion channels. Superfusion with the β‐adrenoreceptor agonist, phenylephrine, had no effect on any electrophysiological parameter studied. However, the α2‐adrenoreceptor agonist, clonidine, caused hyperpolarization which again failed to reach the maximum level produced by adrenaline or noradrenaline. Together, these data suggest that the adrenergic inhibition of Dahlgren cell activity is mediated

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00836.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY