bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Ibotenic Acid‐Induced Neuronal Degeneration in the Hypothalamus upon Proceptivity and Sexual Receptivity in the Female Marmoset (Callithrix jacchus)
Authors: Dixson A. F. , Hastings M. H.
Published: September 2006

The sexual behaviour of 16, oestradiol‐treated, ovariectomized common marmosets was recorded before and after bilateral microinfusions of ibotenic acid (n = 8) or isotonic saline (n = 8) into the hypothalamus. Ibotenic acid‐induced neuronal degeneration occurred in 5 females, mainly affecting the anterior and dorsomedial hypothalamus. Marked decreases in proceptivity (tongue‐flicking, staring and immobile displays) occurred after ibotenic acid lesions, whereas sexual receptivity (refusals and terminations of male partners' mounts) was unchanged. In 3 females where microinfusions of ibotenic acid were attempted but failed to produce lesions, sexual behaviour was unaffected and resembled that measured in saline‐treated controls. These results provide the first evidence that selective lesions of neuronal cell bodies in the anteromedial hypothalamus disrupt proceptivity whilst sparing sexual receptivity in a primate species.
Luteinizing Hormone‐Releasing Hormone Neurons which are R‐etrogradely Labeled After Peripheral Fluoro‐Gold Administration in the Male Ferret
Authors: Berglund Lee Ann , Sisk Cheryl L.
Published: September 2006

This study identified luteinizing hormone‐releasing hormone (LHRH)‐producing neurons which have access to fenestrated capillaries in prepubertal male European ferrets. Fluoro‐Gold was injected intraperitoneally to retrogradely label neurons with terminals outside the blood‐brain barrier. LHRH neurons were identified by immunofluorescence using a secondary antibody tagged with tetramethylrhodamine isothiocyanate. Cell bodies which demonstrated both tetramethylrhodamine isothiocyanate and Fluoro‐Gold fluorescence were defined as LHRH‐producing neurons with axon terminals in regions containing fenestrated capillaries. The total number and neuroanatomical distribution of immunopositive (LHRH +) cells concurred with previous studies in the ferret in which cell bodies were diffusely distributed from rostral forebrain through caudal diencephalon, with approximately 70% of the LHRH + cell bodies located in retrochiasmatic hypothalamus. In the present study, an average of 59.8% of all LHRH+ neuronal perikarya also contained Fluoro‐Gold. The majority of Fluoro‐Gold filled LHRH+ neurons demonstrated only faint to moderate amounts of Fluoro‐Gold when compared to other Fluoro‐Gold filled neurosecretory neurons. This limited uptake of Fluoro‐Gold may be due to a relative inactivity of LHRH neurons projecting outside the blood‐brain barrier. Double‐labeled LHRH + neurons were dispersed throughout the entire population of LHRH+ cell bodies and no apparent nuclear groups of double‐labeled neurons were found. This observation suggests that the LHRH+ neurons responsible for neurosecretion into the median eminence coexist with the LHRH+ neurons responsible for intracerebral neurotransmission or neuromodulation. One distinguishable population of LHRH + neurons was consistently observed in all the brains. Only 26% of total LHRH+ perikarya within the caudal arcuate nucleus contained Fluoro‐Gold, while at least 50% of LHRH+ neurons in other structures, including the rostral arcuate nucleus, contained Fluoro‐Gold. Thus, in the prepubertal male ferret, the majority of LHRH cell bodies located in the caudal arcuate nucleus may be differentially regulated and/or involved in non‐neuroendocrine functions.
Inhibition of Sexual Maturation in Male Rats by Melatonin: Evidence Linking the Mechanism of Action to Changes in the Regulation of Hypothalamic Neuropeptide Y
Authors: Corder Roger , Walker C. Dominique , Gaillard Rolf G. , Aubert Michel L.
Published: September 2006

Activation of gonadotrophin‐releasing hormone (GnRHJ pathways is a pivotal event in the process of sexual maturation, however the regulatory influences that precipitate this change and lead to the onset of puberty remain poorly understood. Recent studies indicate that neuropeptide Y (NPY) may participate in the regulation of luteinizing hormone secretion by modulating the pattern of GnRH secretion and by directly altering the pituitary responsiveness to GnRH stimulation. To determine whether NPY plays a role in puberty‐associated changes in hypothalamic function, levels of NPY‐like immunoreactivity (NPY‐IR) were measured in a fragment of the hypothalamus encompassing the median eminence and medial portion of the arcuate nucleus (ME‐AN), and also in the remainder of the hypothalamus from male rats of different ages. To identify changes in hypothaiamic NPY linked to the process of sexual development, the effect of delaying sexual maturation by daily afternoon administration of 100 μg melatonin (MT) from 20 to 40 days was investigated. In the hypothalamus and ME‐AN, total NPY content increased progressively with age. Expressed as a concentration (fmol/μg extracted protein), peak values for the ME‐AN (55.4 ± 7.0) were observed at 30 days of age followed by a decline to lower levels (30.2 ± 1.9) at 40 days. Daily afternoon administration of MT from 20 days of age resulted in significant increases (P<0.01) in the levels of NPY‐IR in the ME‐AN compared to control values at 30 and 40 days of age. MT was without effect on NPY‐IR levels in the remainder of the hypothalamus. When MT was administered in the early morning, a procedure which does not delay sexual maturation, NPY‐IR values for the ME‐AN region were not different from control rats indicating that the MT‐induced changes in NPY were related to the effects on sexual maturation. Using pituitary luteinizing hormone content and seminal vesicle weight as indices of sexual development, significant inverse correlation coefficients (P<0.001) between these parameters and the NPY concentration in the ME‐AN were observed (r =−0.79 and −0.70, respectively). From published data it is not possible to conclude whether the main effects of NPY are exerted at the hypothalamic or pituitary level. However, the changes in the NPY content of the ME‐AN observed during the onset of puberty, and the influence of MT on these changes, support assertions that NPY is involved in the regulation of sexual maturation.
Inhibition of Prolactin Release by Gonadotropin‐Releasing Hormone‐Associated Peptide in Benign, Dopamine‐Sensitive and in Malignant, Dopamine‐Resistant Pituitary Tumors
Authors: Forget Hélèns , Lafond Julie , Collu Robert
Published: September 2006

Since the gonadotropin‐releasing hormone‐associated peptide (GAP) has been reported to be capable of inhibiting prolactin release from normal lactotrophs, with the present study we have examined the in vitro effects of GAP on prolactin release in an estrone‐induced, dopamine‐sensitive rat pituitary adenoma and two malignant, transplantable and dopamine‐resistant rat pituitary tumors, 7315a and MtTW15. Enzymatically dispersed cells obtained from the three types of tumor were cultured in multiwell dishes for 4 days. On the fifth day, the cells were exposed for 4 h to human GAP 1–56 or to the analog GAP 42–56 or to rat GAP 1–53, at various concentrations. In some experiments, the effect of a pretreatment of the cells for 16 h with pertussis toxin before exposure to human GAP was also evaluated. In the three tissues, rat GAP was able to inhibit prolactin release in a dose‐dependent manner. Human GAP 1–56 and GAP 42–56 were able to inhibit prolactin release in a dose‐dependent manner in all cells except those of the MtTW15 tumor. Furthermore, in adenomatous cells, the inhibitory effects of these peptides were suppressed by pretreatment of the cells with pertussis toxin. These findings indicate that GAP is capable of inhibiting prolactin release even in dopamine‐resistant pituitary tumors. This inhibition is exerted through a pertussis toxin‐sensitive G‐protein‐dependent signaling mechanism in adenomatous cells.
Cellular Levels of Messenger Ribonucleic Acids Encoding Vasoactive Intestinal Peptide and Gastrin‐Releasing Peptide in Neurons of the Suprachiasmatic Nucleus Exhibit Distinct 24‐Hour Rhythms
Authors: Zoeller R. Thomas , Broyles Brad , Earley John , Anderson Earl R. , Alberst H. Elliott
Published: September 2006

There is strong evidence supporting the view that the Suprachiasmatic nucleus (SCN) functions as a circadian clock; however, the neural and molecular events underlying SCN function remain unclear. A specific subpopulation of neurons within the ventrolateral aspect of the SCN that contains three peptides, vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI) and gastrin‐releasing peptide (GRP), play an important role in SCN function. VIP‐containing neurons of the SCN receive synapses from photic projections, and co‐injection of all three peptides mimics the phase‐delaying effects of light on circadian activity rhythms. In principle, the signaling potential of a neuron containing several transmitters may be affected by the concentration ratio of co‐released factors; hence, one mechanism by which VIP/PHI/GRP‐containing neurons could influence SCN function is by changing the concentration ratio of these peptides throughout the light‐dark cycle. The present study was performed to examine this possibility. Relative cellular levels of mRNA encoding both VIP/PHI and GRP were determined within the SCN every 4 h in rats housed in a 14 h light: 10 h dark cycle. Quantitative in situ hybridization revealed a statistically significant (P<0.005) 24‐h profile of changes in VIP/PHI mRNA that peaked during the dark phase, and a significant (P<0.005) 24‐h profile of changes in GRP mRNA that peaked during the light phase. These data support the interpretation that cellular levels of mRNAs encoding VIP/PHI and GRP within the SCN exhibit distinct profiles of changes throughout the light‐dark cycle. Further, these findings are consistent with the hypothesis that the concentration ratio of VIP and PHI to GRP changes over the light‐dark cycle, and that this may be an important mechanism by which circadian rhythms are generated or entrained.
Ovariectomy Increases in vivo Luteinizing Hormone‐Releasing Hormone Release in Pubertal, but not Prepubertal, Female Rhesus Monkeys
Authors: Chongthammakun Sukumal , Claypool Lee E. , Terasawa Ei
Published: September 2006

In pubertal, but not prepubertal, monkeys ovariectomy (OVX) results in an elevation of circulating luteinizing hormone (LH) levels. To determine if the castration‐induced LH increase in pubertal monkeys is due to an increase in pulsatile LH‐releasing hormone (LHRH) release, effects of OVX on in vivo LHRH release in the stalk‐median eminence were examined in fully conscious monkeys using a push‐pull perfusion method. The average ages (± SEM) of female rhesus monkeys in each group at OVX were 14.5±0.6 months (n = 6; prepubertal), 25.0±1.3 months (n = 5; early pubertal) and 37.8 ± 2.1 months (n = 6; midpubertal). Perfusate samples from the stalk‐median eminence were obtained in 10‐min fractions for 6 h in the morning (0600 to 1200 h) and 6 h in the evening (1800 to 2400 h), from the same subjects before OVX, and at 29 days and approximately 100 days after OVX. LHRH levels in perfusates were measured by radioimmunoassay. LH levels throughout the experiment were monitored by periodic blood sampling.

OVX resulted in a significant LH increase in early and midpubertal monkeys (P> 0.001 for both), but not in prepubertal monkeys. Similarly, OVX in early and midpubertal monkeys increased mean LHRH release when examined 29 days after surgery (P> 0.05 and P> 0.01, respectively). The OVX‐induced LHRH increases in early and midpubertal monkeys remained elevated at approximately 100 days postcastration. Furthermore, it was found that effects of OVX on the increased LHRH release were primarily due to the elevation of basal release and pulse amplitude, but not pulse frequency. In contrast, OVX did not cause any significant effects on pulsatile LHRH release in prepubertal monkeys.

The results indicate that an increase in LHRH release and a concomitant increase in circulating LH occurs after OVX in pubertal monkeys, but not in prepubertal monkeys. These data are consistent with the hypothesis that the low level of LH in circulation before the onset of puberty is due to a low amount of LHRH release which is independent of ovarian steroid feedback and that the maturity of the neuronal control system for the pulsatile LHRH release is responsible for the onset of puberty. After the onset of puberty, the negative feedback of ovarian steroid hormones becomes important to the regulation of gonadotropin release.
Acetyl‐L‐Carnitine Effect on Pituitary and Plasma β‐Endorphin Responsiveness to Different Chronic Intermittent Stressors
Authors: Bidzinska Bozena , Petraglia Felice , Angioni Stefano , Genazzani Alessandro D. , Criscuoio Mario , Ficarra Guido , Gallinelli Andrea , Trentini Gian Paolo , Genazzani Andrea R.
Published: September 2006

The aims of the present study were: 1) to compare the effect of two different chronic intermittent stressors i.e. cold‐swimming versus ether, on the pituitary opioidergic system; 2) to evaluate the response of pituitary and plasma β‐endorphin (βS‐EP) to an acute stress in chronically stressed rats; and 3) to evaluate the effect of acetyl‐l‐carnitine treatment (10 mg/day/rat per os at night) on pituitary and plasma β‐EP changes induced by two different types of chronic stress. The stressors were applied twice a day for 10 days. Rats were killed either before, during or after the last swimming or ether stress session. β‐EP was measured by radioimmunoassay in anterior pituitary and in neurointermediate lobe extracts and in plasma. The following observations were made; 1) Chronic intermittent cold‐swimming stress increased anterior pituitary contents and plasma β‐EP levels; 2) both chronic intermittent cold‐swimming stress and ether stress caused an increase of neurointermediate lobe β‐EP contents; 3) as in control animals, rats exposed to chronic intermittent swimming stress reduced pituitary β‐EP contents and raised plasma β‐EP levels in response to the last acute swimming stress; 4) in contrast to control animals, rats exposed to chronic intermittent ether stress did not show any significant response of the pituitary‐plasma opioidergic system to the last acute ether session; 5) the acetyl‐l‐carnitine treatment counteracted the changes evoked by chronic intermittent cold‐swimming stress on the pituitary and plasma β‐EP levels. The present data show that chronic intermittent ether stress impairs the capacity to respond to the acute stress and that acetyl‐l‐carnitine may modulate the changes of β‐EP levels following chronic cold‐swimming stress exposure.
Corticotropin‐Releasing Hormone Neurons in the Paraventricular Nucleus Project to the External Zone of the Median Eminence: A Study Combining Retrograde Labeling with Immunocytochemistry
Authors: Lennard David E. , Eckert William A. , Merchenthaler Istvan
Published: September 2006

Corticotropin‐releasing hormone (CRH) is the major regulator of the pituitary‐adrenal axis. CRH‐immunoreactive perikarya are widely distributed in the central nervous system; however, only those which participate directly in the regulation of adrenocorticotropin are connected to the portal circulation in the external zone of the median eminence. The present study describes the identification of these hypophysiotropic neurons using retrograde labeling and CRH immunocytochemistry. Fuoro‐Gold was injected peripherally then, 5 days later, the animals were treated with colchicine. Twenty‐four hours later the animals were sacrificed, and their brains were immunostained for CRH with the indirect immunofluorescence technique. The results indicate that the vast majority of the Fluoro‐Gold‐accumulating and CRH‐immunopositive perikarya (hypophysiotropic neurons) are located in the medial parvicellular subdivision of the paraventricular nucleus (PVN). However, not each CRH‐immunoreactive neuron contains Fluoro‐Gold, i.e. a small portion of these neurons project to areas of the brain other than the median eminence. The anterior, lateral and periventricular subdivisions of the PVN also contain hypophysiotropic CRH‐immunoreactive perikarya, however, their number is much less than in the medial parvicellular subdivision. Scattered double‐labeled cells are also present in the medial preoptic area and the dorsal hypothalamus, just behind the PVN. These results support previous observations that the PVN, particularly the medial parvicellular subdivision, is the predominant source of the hypophysiotropic CRH neurons.
α2 and β Adrenoceptors in the Mediobasal Hypothalamus and α2 Adrenoceptors in the Preoptic‐Anterior Hypothalamus Stimulate Prolactin Secretion in the Conscious Male Rat
Authors: Kapoor Ranjna , Chapman Ian M. , Willoughby John O.
Published: September 2006

Plasma prolactin concentrations were measured in unanaesthetized male rats before and after stereotaxic microinjection of adrenergic agents into the mediobasal and preoptic‐anterior hypothalamus.

In the mediobasal hypothalamus injection of the α2 agonist clonidine produced a dose‐dependent increase in prolactin secretion over the dose range 0.1 to 10 nmoles, the stimulation due to 1 nmole being blocked by idazoxan (α2 antagonist). Stimulation of prolactin release was also caused by isoprenaline (β agonist) and was significantly reduced by the β antagonist propranolol. The β2 agonist salbutamol was also effective in stimulating prolactin secretion. However, the adrenergic agonists, noradrenaline (mixed α and β), phenylephrine (α1) and tyramine (sympathomimetic) failed to affect prolactin secretion.

In the preoptic‐anterior hypothalamus clonidine caused a dose‐dependent increase in prolactin secretion over the dose range 0.001 to 10 nmoles, the stimulation due to 0.1 nmole being abolished by idazoxan. While prolactin levels were significantly elevated by noradrenaline and tyramine, phenylephrine was ineffective.

We conclude that the activation of α2 and β2 adrenoceptors in the mediobasal hypothalamus and of α2 adrenoceptors in the preoptic‐anterior hypothalamus, on or near prolactin‐regulating neurons, results in increased prolactin secretion. An α1 inhibitory action in the mediobasal hypothalamus has however not been ruled out. Adrenergic inputs in the preoptic‐anterior hypothalamus appear to exert a predominant facilitatory effect on prolactin secretion.
Radioimmunocytochemical Distribution of Neutral Endopeptidase (Enkephalinase E.G.3.4.24.11) at the Ultrastructural Level in the Rat Median Eminence
Authors: Vandenbulcke Franck , Pollard Hélène , Mitchell Valérie , Beauvillain Jean‐Claude
Published: September 2006

Neutral endopeptidase (E.G. 3.4.24.11) was visualized at the ultrastructural level in the external zone of the rat median eminence by using 125|‐labelled IgG of a monoclonal serum.

A precise analysis of the localization of the immunolabelling, which appears in the form of individual stray silver grains, was undertaken. Among the 1,045 grains counted, 82% were localized over membrane appositions involving nerve endings only and nerve endings plus tanycytes. The difference between the real and a randomly generated population of grains was statistically significant. Our results provide morphological arguments in support of the view of a paracrine action of neuropeptides present in the median eminence especially enkephalins but possibly, substance P, angiotensin, cholecystokinin and neurotensin. These neuropeptides are known to be inactivated by neutral endopeptidase. The action of these peptides may be exerted on nerve endings (autocrine or paracrine) but an intervention on tanycytes cannot be excluded.
Melatonin and the Circadian Clock in Mink: Effects of Daily Injections of Melatonin on Circadian Rhythm of Locomotor Activity and Autoradiographic Localization of Melatonin Binding Sites
Authors: Bonnefond Catherine , Monnerie Régine , Richard Jean‐Pierre , Martinet Lise
Published: September 2006

The present study examines a putative effect of exogenous melatonin on the Circadian organization of the mink. Two approaches were used to determine first whether entrainment of free‐running rhythms of locomotor activity in constant darkness can be obtained by daily melatonin injections, thus demonstrating a control of melatonin on the clock generating Circadian rhythms, the suprachiasmatic nucleus of the hypothalamus. Entrainment was never obtained in the 8 vehicle‐injected females and 7 out of the 8 melatonin injected‐ones. In 3 females free‐running in constant darkness, a phase advance followed by a few days of transient effect was observed when melatonin injections coincided with the onset of activity. However, the comparison of the regression of the daily activity onset related to successive days by covariance analysis revealed that true entrainment was effective in only 1 female. Second, we examined the distribution of melatonin binding sites within the brain of juvenile and adult mink using an in vitro autoradiographic procedure with [125l]2‐iodomelatonin. No binding sites were observed in the suprachiasmatic nucleus of any of the animals. However, all animals displayed a high density of melatonin binding sites in the pars tuberalis of the pituitary. The relation between a modulatory control of melatonin on the Circadian clock and the presence and density of melatonin binding sites in the clock is discussed. In mink, melatonin does not seem to act as an internal Zeitgeber.
Sex and Species Differences in the Vasopressin Innervation of Sexually Naive and Parental Prairie Voles, Microtusochrogasterand Meadow Voles,Microtus pennsylvanicus
Authors: Bamshad Maryam , Novak Melinda A. , De Vries Geert J.
Published: September 2006

To study whether central systems that are implicated in functions associated with reproduction show different changes in males and females that become parental, the central vasopressin (AVP) innervation was compared in two species of voles: prairie voles, in which males and females provide parental care, and meadow voles, in which only females provide parental care. For both species, the densities of AVP‐immunoreactive (AVP‐ir) fibers in the lateral septum, lateral habenular nucleus, medial preoptic area and paraventricular nucleus of the thalamus were compared in males and females that were sexually inexperienced or had become parents 6 days before sacrifice. The lateral septum and lateral habenular nucleus presumably receive their projections from the bed nucleus of the stria terminalis and medial amygdaloid nucleus, while the other two areas presumably receive their projections from the suprachiasmatic nucleus. Differences between sexually naive and parental animals were found only in the presumed projections of the bed nucleus of the stria terminalis and medial amygdaloid nucleus. In both species, AVP‐ir fiber densities in the lateral habenular nucleus and the lateral septum were much greater in males than in females regardless of parental state. In prairie voles, AVP‐ir fiber density in the lateral septum and lateral habenular nucleus was reduced in parental males, while no differences were found in females. In parental meadow voles, the AVP‐ir fiber density in the lateral septum did not show changes, while the fiber density in the lateral habenular nucleus was increased. The reduction in AVP‐ir fiber density in parental prairie vole males and the absence of such a reduction in meadow vole males may be related to differences in their contribution to parental care.
Endogenous Opioid Regulation of Oxytocin Secretion Through Pregnancy in the Rat
Authors: Douglas A. J. , Dye S. , Leng G. , Russell J. A. , Bicknell R. J.
Published: September 2006

We have investigated the influence of endogenous opioids on oxytocin secretion during pregnancy. In blood‐sampled consciousrats on days 18 and 21 of pregnancy plasma oxytocin concentration, measured by radioimmunoassay, was significantly increased compared to non‐pregnant or post‐partum rats. On days 15, 18 and 21 of pregnancy, but not in non‐pregnant, early pregnant or post‐partum rats, the opioid antagonist naloxone caused a significant increase in plasma oxytocin compared to vehicle injection, indicating activation of an endogenous opioid restraint over oxytocin secretion.

Electrically stimulated neural lobes isolated from 16‐ and 21‐day pregnant rats released more oxytocin than those from non‐pregnant rats. However, naloxone (10−5 M) was less effective at potentiating, and the k‐opioid agonist U50,488 (10−5 M) was less effective at inhibiting, stimulated release at the end of pregnancy than in non‐pregnant rats suggesting desensitization of oxytocin nerve terminals to actions of endogenous opioids. Neural lobes from male rats drinking 2% saline for 4 days also showed desensitization of oxytocin nerve endings to naloxone.

Neither neural lobe content of dynorphin A(1–8), an endogenous k‐opioid, nor prodynorphin mRNA expression, measured by in situ hybridization histochemistry in the supraoptic nucleus altered during pregnancy. However, neural lobe content of Met5enkephalin significantly decreased by day 21 of gestation suggesting enhanced release. We conclude that an endogenous opioid, possibly a product of proenkephalin A in oxytocin cells may be responsible for auto‐inhibition of oxytocin release during gestation, and that this mechanism desensitizes in late pregnancy at a time when other opioid inputs to the oxytocin neurons become activated to provide an overall increase in opioid restraint of the system. The changes in opioid input through pregnancy may be involved in initiation and regulation of oxytocin secretion at parturition. A similar opioid mechanism, but possibly involving dynorphin, could explain desensitization in saline drinking rats and indicates that desensitization may be a consequence of chronic activation of secretion from the oxytocin nerve terminals rather than a phenomenon peculiar to pregnancy.
Effects of Novelty Stress on Vasopressin and Oxytocin Secretion by the Pituitary in the Rat
Authors: Onaka Tatsushi , Yagi Kinji
Published: September 2006

Effects of novel environmental stimuli on vasopressin and oxytocin secretion by the pituitary were studied in dehydrated male rats. As the novel environmental stimuli, rats were transferred to an experimental room, placed in a box painted black and given a pure tone auditory stimulus of 2 kHz. Exposure of rats to the novel environmental stimuli for a period of 2 min decreased plasma concentrations of vasopressin and increased plasma levels of adrenocorticotrophic hormone (ACTH) and prolactin, but did not significantly change the plasma level of oxytocin. The stimuli, however, became ineffective for producing the suppressive vasopressin response as the period of exposure was prolonged to more than 5 and up to 30 min, although the prolonged stimuli were still effective for inducing facilitatory ACTH and prolactin responses. After repeated exposures of rats to the environmental stimuli once a day for 5 or 10 days, the stimuli became disabled from producing the suppressive vasopressin response. However, the rats were still capable of responding to the novel stimuli of another kind. All these data suggest that novelty stress suppresses vasopressin secretion but does not change oxytocin secretion. In order to test the possibility that glucocorticoids expectedly secreted by the adrenals in response to the stress might have suppressed vasopressin secretion, a large amount of dexamethasone was administered to the rat before testing. Dexamethasone pretreatment depressed plasma levels of ACTH and vasopressin as reported previously and blocked the facilitatory ACTH response to the novelty stress. However, dexamethasone treatment did not affect the suppressive vasopressin response to the novelty stress. Thus, it is likely that the suppressive vasopressin response to novelty stress does not primarily depend upon endogenous glucocorticoids.
Hypothalamic Neuropeptide Y Messenger Ribonucleic Acid Levels in Pre‐Obese and Genetically Obese (fa/fa) Rats; Potential Regulation Thereof by Corticotropin‐Releasing Factor
Authors: van Huijsduijnen OlfaBchini‐Hooft , Rohner‐Jeanrenaud Françoise , Jeanrenaud Bernard
Published: September 2006

Neuropeptide Y (NPY) is a 36 amino‐acid peptide. It is localized within the brain but is also present peripherally. It is a well substantiated orexigenic peptide with several other endocrine and behavioural effects. In this study NPY mRNA levels were measured, using the polymerase chain reaction amplification technique, in the hypothalamus of pre‐obese (unweaned 13‐day‐ old), young (weaned 28‐day‐old) and adult (11‐week‐old) obese fa/fa rats and compared to those of lean age‐matched controls. Before weaning, pre‐obese pups had the same NPY mRNA levels as controls. After weaning NPY mRNA levels were increased 2‐fold in young 28‐day‐old and 4‐fold in adult obese rats, relative to corresponding controls. When adult obese rats were intracerebroventricularly‐treated with ovine corticotropin‐releasing hormone (oCRF) for 7 days, they stopped gaining body weight elative to vehicle‐infused obese controls. Upon measuring NPY mRNA levels in the hypothalamus of these two groups of animals, it was shown that the high NPY mRNA levels of vehicle‐treated (control) obese rats were decreased by 3‐fold following the intracerebroventricular oCRF administration. It is proposed that: 1) hypothalamic NPY may play a role in the establishment and maintenance of the genetic obesity syndrome of the fa/fa rat, and 2) hypothalamic NPY could be partly regulated by central CRF.
The Actions of Endothelin on Single Cells in the Anteroventral Third Ventricular Region and Supraoptic Nucleus in Rat Hypothalamic Slices
Authors: Yamamoto Shigeki , Inenaga Kiyotoshi , Kannan Hiroshi , Eto Sumiya , Yamashita Hiroshi
Published: September 2006

Endothelin (ET), a peptide consisting of 21 amino‐acid residues was recently isolated from the culture supernatant of porcine aortic endothelial cells. ET has been reported to be a more potent vasoconstrictor than angiotensin II. Other studies suggest that ET is involved in central control of the autonomie nervous system and body water regulation. Extracellular recordings were made from neurons in the anteroventral third ventricle (AV3V) and supraoptic nucleus (SON) in rat hypothalamic slice preparations. ET‐3 was applied at concentrations of 10−10 M to 3x 10−7 M. Of 226 AV3V neurons tested, 48 (21%) were excited, 8 (4%) were inhibited, and 170 (75%) were unaffected by ET‐3 at 10−7 M. The threshold concentration to evoke the responses was approximately 10−9 M. Of 144 SON neurons tested, 64 had a phasic firing pattern and 80 had a non‐phasic firing pattern. Of 64 phasic neurons tested, 39 (61%) were inhibited by ET‐3 at 10−7 M, 25 (39%) were non‐responsive and none was excited. Of 80 non‐phasic neurons tested, 14 (17.5%) were inhibited by ET‐3 at 10−7 M, 66 (82.5%) were non‐responsive and none was excited. The effects of ET‐1 were compared with those of ET‐3. The number of neurons responding to ET‐1 and their responsiveness were almost the same as for ET‐3. To investigate whether the ET responses are dependent on Ca2+ influx, a Ca2+ free medium and the Ca2+ antagonist, nicardipine, were used. The excitatory responses of AV3V neurons to ET were maintained in the Ca2+ free medium. Nicardipine at 10−5 M suppressed neither the excitatory responses of AV3V neurons nor the inhibitory responses of SON neurons to ET‐3. After 8 to 12 h preincubation of slices with islet activating peptide (IAP: pertussis toxin) at 10−7 M, none of the 48 AV3V neurons tested was excited by either ET‐3 or ET‐1. On the other hand, inhibitory responses were still observed in 12 (52%) out of 23 phasic SON neurons tested after IAP treatment. These results suggest that ET has a direct action as a neuropeptide on hypothalamic neurons through the ETB receptor and that the mechanisms underlying the responses may be different in the AV3V and the SON.
Activation of Magnocellular Vasopressin Responses to Non‐Osmotic Stress After Chronic Adrenal Demedullation in Rats
Authors: Aguilera Greti , Kiss Alexander
Published: September 2006

Increases in plasma VP in response to osmotic stimulation are critical for water conservation, while VP released into the pituitary portal circulation is an important regulator of ACTH secretion and does not contribute to plasma VP levels. The role of the adrenal medulla in the specificity of these responses was studied in rats subjected to osmotic and non‐osmotic stress two months following adrenal demedullation or sham operation. Basal and stimulated plasma corticosterone, aldosterone, ACTH and PRA levels in adrenal demedullated rats were similar to those in the sham operated groups indicating recovery of adrenocortical function. Basal plasma VP levels were similar in sham operated controls and adrenal demedullated rats (0.93±0.13 and 1.0 ± 0.1 pg/ml, respectively) and rose to comparable levels in both groups following 48 h osmotic stimulation by water deprivation (14.4+1.3 and 20.7 + 3.4, respectively). On the other hand, while in sham operated rats, immobilization for 15 min, a non‐osmotic stress, had no effect on plasma VP levels in control or water deprived (2.0±0.9 and 15.0±2.7 pg/ml), in adrenal demedullated rats, caused dramatic increases in plasma VP from 1.0±0.1 to 126.0 + 29.9 pg/ml in controls, and from 20.7 + 3.4 to 155 + 37 pg/ml in water deprived rats. Intraperitoneal hypertonic saline injection, a combination of osmotic and painful stress, caused much higher increases in plasma VP in adrenal demedullated rats (138.0 + 22.1 compared with 34.7 + 3.7 pg/ml in sham operated rats). Water deprivation potentiated this response to 70.0 + 8.3 and 295 + 24 pg/ml in sham operated and adrenal demedullated rats, respectively. VP mRNA measured by in situ hybridization, and irVP measured by immunohistochemistry, were elevated in magnocellular neurones in the hypothalamus of adrenal demedullated rats. The demonstration of marked plasma VP responses to non‐osmotic stimuli in adrenal demedullated rats, suggests a modulatory role for the adrenal medulla in the specificity of the secretory responses of the magnocellular and parvicellular vasopressinergic systems.
Vasopressin Anti‐Idiotypic Antibody Staining in the Rat Brain: Colocalization with [35S][pGlu4, Cyt6]AVP(4–9) Binding Sites
Authors: Jurzak M. , Fahrenholz F. , Gerstberger R.
Published: September 2006

Vasopressin and its fragment peptides such as [pGlu4, Cyt6]AVP(4–9) (AVP(4–9)) represent putative neuromodulators within central nervous homeostatic, memory and behavioural circuits. To localize their central receptor systems, the previously characterized monoclonal anti‐idiotypic antibody mAb 237 was employed in immunocytological investigations of rat brain tissue sections. This antibody was raised to the monoclonal idiotypic anti‐AVP antibody mAb 113 which preferentially binds to the acyclic C‐terminal portion of the AVP molecule and is therefore also capable of binding the naturally occurring AVP(4–9) fragment. Immunoreactive magnocellular neurones were detected in the AVP‐synthesizing supraoptic but not paraventricular nuclei. Dense staining was observed within circumventricular organs lacking a blood‐brain barrier (BBB). These structures include the subfornical organ, the organum vasculosum laminae terminalis, the internal layer of the median eminence, the body of the pineal gland, the choroid plexus and the area postrema, where immunoreactivity was found on capillaries, neurones and fibres. Further staining was found in the nucleus of the solitari tract and the arcuate nucleus, endowed with a leaky BBB. Distinct cell patches in the ependymal lining of the third ventricle as well as dendritic processes of juxtaependymal neurones were labelled by the anti‐idiotypic antibody mAb 237. The observed staining pattern did not parallel that obtained in autoradiographic studies performed using either radiolabelled AVP or a V1‐receptor antagonist, but that found with the [35S]‐labelled AVP(4–9) fragment. Using [35S]‐labelled AVP(4–9) fragment, specific high density binding sites could be localized autoradiographically in structures within and outside the BBB, in complete agreement with the anti‐idiotypic immunoreactivity.

Since the anti‐idiotypic methodology is based on transfer of complementary structures, and the epitope recognized by the corresponding idiotypic antibody resembles the sequence of AVP(4–9), the anti‐idiotypic antibodies might recognize the AVP(4–9) receptor with high affinity.
Neurons in the Paraventricular Nucleus of the Hypothalamus that Project to the Sexually Dimorphic Lower Lumbar Spinal Cord Concentrate 3H‐Estradiol in the Male Rat
Authors: Wagner Christine K. , Sisk Cheryl L. , Clemens Lynwood G.
Published: September 2006

The location and distribution of estradiol‐concentrating neurons in the hypothalamus afferent to segments of lumbar spinal cord that contain the sexually dimorphic spinal nucleus of the bulbocavernosus (SNB) were determined by combining retrograde fluorescent tract tracing with steroid hormone autoradiography. Injections of Fluorogold were made into segments of L5‐L6 of the spinal cord of adult male rats and 12 days later animals were castrated. One week following castration, males received injections of [3H]estradiol and were perfused. Their brains were then processed for steroid hormone autoradiography. Following exposure times of 11 to 12 months, autoradiograms were developed and the hypothalamus was analyzed for neurons that concentrate estradiol and project to the spinal cord.

Numerous neurons in the hypothalamus projected to the spinal cord, specifically neurons in the paraventricular nucleus (PVN), the lateral hypothalamus and the dorsal area of the hypothalamus. Although many subnuclei of PVN, as well as lateral hypothalamus, contained Fluorogold labelled neurons and estradiol concentrating neurons, the majority of double labeled cells were found in the lateral parvocellular (lp) subnucleus of PVN. Approximately 30% of the neurons in the lp subnucleus that projected to spinal cord also concentrated estradiol. Up to one half of the estradiol‐concentrating neurons in Ip sent axons to the lower lumbar spinal cord. These results suggest that some of the effects of gonadal steroid hormones on SNB development, plasticity and function may in fact, be indirect, via steroid‐sensitive afferents.
Electrophysiological Effects of Pressure‐Ejected Bombesin‐Like Peptides on Hamster Suprachiasmatic Nucleus Neurons in vitro
Authors: Piggins Hugh D. , Rusak Benjamin
Published: September 2006

The suprachiasmatic nuclei (SCN) of the rodent hypothalamus function as a light entrainable circadian pacemaker. The SCN contain moderate to high concentrations of a number of neuropeptides including peptides showing structural homology with the amphibian derived tetradecapeptide, bombesin (BN), called bombesin‐like peptides (BNLPs). BNLPs include the 27 amino acid peptide, gastrin releasing peptide (GRP,1–27), a smaller decapeptide (GRP18–27) and another decapeptide with less structural homology, neuromedin B (NmB). Immunoreactivity for BN and receptors for BNLPs have been demonstrated in the region of the rat SCN receiving photic input. We studied the effects of local pressure ejections of BNLPs dissolved in saline/1% bovine serum albumin (BSA) vehicle on the extracellularly recorded firing rates of Syrian hamster SCN neurons in a hypothalamic slice preparation. In one study, an ejecting electrode containing BN (10−8 to 10−4 M) was positioned 20 to 60 μm from a recording electrode. Of 74 cells tested with BN, 50 (67.6%) showed significant increases in firing rate, while 3 of 19 cells (15.8%) tested with vehicle ejections were activated. In a second study, a single electrode was used for both recordings and pressure ejections. Of 48 cells tested, BN (10−6 to 10−4 M) activated 30 (62.5%) and suppressed firing in 4 (8.3%). Of 208 cells tested with GRP1–27 (10−9 to 10−4 M), 105 (50.5%) were activated and 2 (1.0%) were suppressed. The percentage of cells responding increased with the concentration of GRP1–27 used in the electrode. No circadian variation in responsiveness to GRP1–27 was detected. GRP18–27 (5 ± 10−5 to 10−4 M) activated 10 out of 18 cells tested (55.6%), while NmB (10−4 M) activated 2 out of 30 cells tested (6.7%) and vehicle ejections activated 1 out 36 cells tested (2.8%). GRP1–27, GRP18–27 and BN, the BNLPs showing the greatest degree of structural homology, activate ∼50% of SCN cells, apparently via the BN/GRP‐preferring receptor subtype, and may play a role in photic entrainment.
Dynorphin 1–17 Delays the Vasopressin Induced Mobilization of Intracellular Calcium in Cultured Astrocytes from the Rat Neural Lobe
Authors: Boersma C. J. C. , Van Leeuwen F. W. , O'Brien W. G. , Law G. J. , Mason W. T. , Bicknell R. J.
Published: September 2006

Opioid peptides are present in nerve terminals in the rat neural lobe where they partially coexist with vasopressin. Morphological findings suggest that these neuropeptides are released onto pituicytes, which is in agreement with a possible role for the pituicyte in oxytocin and vasopressin release from the neural lobe.

Pituicytes in culture respond to vasopressin with a mobilization of calcium from intracellular stores. In the present study this vasopressin induced increase in intracellular free calcium levels was both delayed and decreased by pre‐exposure to dynorphin 1–17, while dynorphin 1–17 by itself did not affect basal calcium levels. All effects of dynorphin 1–17 could be blocked with naloxone. The present results suggest that opioid receptors are present on pituicytes and are coupled to a second messenger pathway by which opioid peptides may inhibit inositol phosphate dependent calcium mobilization by other neuropeptides, such as vasopressin.
Immunocytochemical and Biochemical Evidence for Aromatase in Neurons of the Retina, Optic Tectum and Retinotectal Pathways in Goldfish
Authors: Gelinas Danielle , Callard Gloria V.
Published: September 2006

Using an animal model in which neural aromatase is apparently overexpressed (the goldfish, Carassius auratus) and an antihuman placental antibody which specifically crossreacts with goldfish brain aromatase, aromatase‐immunoreactive neuronal cell bodies and fibers have been localized within the retina. These include a subset of horizontal cells, bipolar cells, and amacrine cells of the inner nuclear layer, some fibers of the outer and inner synaptic layers and certain cells of the ganglion cell layer; photoreceptors were never labeled. Some ganglion cell projections to the brain via the optic nerve and optic tract were aromatase‐positive, as were small neurons of the stratum periventriculare (SPV) and fibers of two other strata of the optic tectum. Aromatase activity, as measured by [3H]estrogen formation from [3H]androgen by tissue homogenates and cell cultures, confirmed the presence of aromatase in retina and in brain regions containing the optic tectum. This localization of the rate‐limiting enzyme in estrogen biosynthesis suggests that neuroestrogen derived from circulating androgen may modulate transmission and integration of visual information important for reproduction in this species.
Effects of Excitatory Amino Acid Receptor Agonists and Antagonists on the Secretion of Melatonin, Luteinizing Hormone and Prolactin in the Ram
Authors: Kumar V. , Lincoln G. A. , Tortonese D. J.
Published: September 2006

To assess the role of excitatory amino acids (EAA) as neurotransmitters in the transmission of light information from the retina to the pineal gland, we have determined whether the systemic injection of EAA agonists in Soay rams will mimic the suppressive effect of light on the secretion of melatonin, and whether pretreatment of rams with EAA antagonists will block this effect. In addition, the efficacy of the drugs in affecting neuroendocrine systems was investigated by measuring the changes in the secretion of luteinizing hormone (LH) and prolactin.

Injections of the EAA receptor agonist, NMDA (N‐methyl‐D,L‐aspartate: 4.0 mg/kg iv), and the non‐NMDA type EAA receptor agonist, AMPA (DL‐α‐amino‐3‐hydroxy‐5‐methylisoxazole‐propionic acid : 0.2 mg/kg iv) given at night to rams exposed to long days (16 h light:8 h darkness), caused no change in the blood plasma concentrations of melatonin. The treatments induced an acute increase in the concentrations of LH, and NMDA, but not AMPA, caused a sustained increase in the concentrations of prolactin. Injections of the specific NMDA‐type receptor antagonist, CGP (CGP 37849: 1.0 mg/kg iv) and the non‐NMDA‐type receptor antagonist, DNQX (6,7 Dinitroquinoxaline‐2,3‐dione: 0.5 mg/kg iv), given prior to a 1‐h light period at night, in rams under long days, caused no change in the light‐induced decrease in blood plasma concentrations of melatonin. The drug treatments had no effect on the plasma concentrations of LH, but CGP, and not DNQX, stimulated an acute increase in the plasma concentrations of prolactin.

These results provide support for the hypothesis that EAA mechanisms operate in the hypothalamus to regulate the release of peptides and catecholamines which control the secretion of LH and prolactin from the pituitary gland; different sub‐types of EAA receptors are involved in the control of the two pituitary hormones. The failure of the treatments to affect the secretion of melatonin may indicate that EAA receptor activation is not involved in the photic relay to the pineal gland, or may merely reflect the inability of the drugs to penetrate into the retina/SCN/pineal neural circuits to produce a response.
Facilitation and Feedback in the Hypothalamo‐Pituitary‐Adrenal Axis during Food Restriction in Rats
Authors: Garcia‐Belenguer Sylvia , Oliver Charles , Morméde Pierre
Published: September 2006

After 4 weeks of food restriction to 50% of ad libitum intake in rats, plasma corticosterone levels were increased, without any change in adrenal weight, and with no evidence of sympathetic nervous system activation (as measured by Tyrosine Hydroxylase and Phenylethanolamine N‐Methyl Transferase activities in the adrenal gland). Plasma corticosterone levels were normalized with the addition of 35% of the calories as sugar. The adrenocortical axis activity was therefore investigated in more detail (nycthemeral cycle of corticosterone levels, ACTH and corticosterone response to a CRF challenge) in ad libitum fed rats and in animals fed 85% or 50% of the intake of the control animals, just before switching the lights off in order to maintain the diurnal rhythm of food intake. Food restriction to 85% did not change mean plasma corticosterone levels but sharpened the peak of corticosterone measured in the evening, indicating that the adrenocortical axis is more sensitive to the endogenous signals responsible for its diurnal cycle of activity. Indeed, the ACTH response to CRF was also increased. A 50% food restriction regimen increased mean corticosterone levels and attenuated the day/night difference, with high corticosterone levels maintained throughout the day. However, the ACTH response to CRF was not different from that measured in ad libitum fed rats, but the corticosterone response was lower, confirming that the adrenal gland is hyposensitive to ACTH. The results are discussed in terms of the balance between inhibiting/activating mechanisms and endocrine/neural influences at each level of the hypothalamo‐hypophyso‐adrenal axis, depending on the level of food deprivation.