VEGF-dependent and PDGF-dependent dynamic neurovascular reconstruction in the neurohypophysis of adult mice.

Hypothalamo-neurohypophysial system (HNS) releases arginine vasopressin (AVP) and oxytocin (OXT) from axonal terminals of the neurohypophysis (NH) into blood circulation for controlling body fluid homeostasis and lactation. Chronic osmotic and suckling stimulations have been shown to cause neurovascular and neuroglial reconstruction in the NH of adult mammals and no study has been reported for vascular dynamics. The aim of this study was to elucidate the occurrence of continuous angiogenesis and growth factor-dependent neurovascular reconstruction in the NH of adult mice. Active proliferation of endothelial cells and oligodendrocyte progenitor cells (OPCs) was observed using the immunohistochemistry of bromodeoxyuridine and Ki-67. Vascular endothelial growth factor A (VEGFA) and VEGF receptor 2 (VEGFR2 (KDR)) were highly expressed at pituicytes and endothelial cells respectively. Moreover, prominent expression of platelet-derived growth factor B (PDGFB) and PDGF receptor beta was observed at OXT-containing axonal terminals and pericytes respectively. Administration of the selective tyrosine kinase inhibitor AZD2171 for VEGFRs and STI571 for PDGFRs significantly decreased proliferation of endothelial cells and OPCs. Moreover, AZD2171 treatment decreased vascular density by facilitating apoptosis of endothelial cells and the withdrawal of its treatment led to remarkable rebound proliferation of endothelial cells, so that vascular density rapidly returned to normal levels. AZD2171 decreased the density of both AVP- and OXT-containing axonal terminals, whereas STI571 selectively decreased the density of AVP-containing ones. Thus, this study demonstrates that the signaling pathways of VEGF and PDGF are crucial mediators for determining proliferation of endothelial cells and OPCs and the density of AVP- and OXT-containing axonal terminals in the HNS.

Endonasal endoscopic pituitary adenoma resection: preservation of neurohypophyseal function.

OBJECTIVES: In the past 10 years, endoscopic resection of pituitary adenomas has become an alternative to microsurgical resection with the additional advantage of increasing the patient's postoperative comfort. This analysis explored whether endoscopic resection can reduce the risk of postoperative neurohypophyseal dysfunction. DESIGN: We rated and compared the need to administer desmopressin during the first four postoperative days and with the need after a follow-up of at least 3 months (chronic administration). SETTING: Three groups of patients were compared: Patients in group 1 were operated on microscopically. Patients in group 2 were operated on endoscopically. Patients in group 3 were operated on endoscopically with intraoperative magnetic resonance imaging (iMRI). PARTICIPANTS: Group 1 was made up of 50 patients treated in 1999; group 2 comprised 50 patients operated on from 2006 to 2007; and Group 3 comprised 50 patients operated on in 2008. MAIN OUTCOME MEASURES: In group 1 the need to use desmopressin postoperatively occurred in eight patients; three needed chronic treatment. In group 2 the need for postoperative application of desmopressin occurred in four patients; none required chronic treatment. In group 3 desmopressin had to be administered postoperatively in five patients but only temporarily. RESULTS AND CONCLUSIONS: Endoscopic surgery is a safe and effective method for the resection of pituitary adenomas. The rate of chronic desmopressin application was reduced. In conjunction with iMRI and navigation, the endoscopic technique allows increased radicality together with fewer adverse effects.

Development of the medial hypothalamus: forming a functional hypothalamic-neurohypophyseal interface.

The medial hypothalamus is composed of nuclei of the tuberal hypothalamus, the paraventricular nucleus of the anterior hypothalamus, and the neurohypophysis. Its arrangement, around the third ventricle of the brain, above the adenohypophysis, and in direct contact with the vasculature, means that it serves as an interface with circulating systems, providing a key conduit through which the brain can sample, and control, peripheral body systems. Through these interfaces, and interactions with other parts of the brain, the medial hypothalamus centrally governs diverse homeostatic processes, including energy and fluid balance, stress responses, growth, and reproductive behaviors. Here, we summarize recent studies that reveal how the diverse cell types within the medial hypothalamus are assembled in an integrated manner to enable its later function. In particular, we discuss how the temporally protracted operation of signaling pathways and transcription factors governs the appearance and regionalization of the hypothalamic primordium from the prosencephalic territory, the specification and differentiation of progenitors into neurons in organized nuclei, and the establishment of interfaces. Through analyses of mouse, chick, and zebrafish, a picture emerges of an evolutionarily conserved and highly coordinated developmental program. Early indications suggest that deregulation of this program may underlie complex human pathological conditions and dysfunctional behaviors, including stress and eating disorders.

Posterior pituitary functions are not altered after growth hormone replacement therapy in hypopituitarism due to Sheehan's syndrome.

OBJECTIVE: The aim of the present study was to investigate the effects of growth hormone (GH) replacement on posterior pituitary functions of GH-deficient Sheehan's syndrome (SS) patients. DESIGN: Ten patients with SS and 14 healthy control women were included in this prospective study. All patients were given appropriate hormone replacement therapy other than GH, according to present hormone deficiencies. Patients were euthyroid and eucortisolemic at the time of baseline evaluation. Patients and the control group were evaluated with water-deprivation and saline-infusion tests at baseline and the tests were repeated in patients with SS after 3 months of GH replacement therapy. RESULTS: According to the water deprivation test, 3 patients had partial central DI at baseline. Urine osmolalities of the patients were slightly lower and plasma osmolalities were significantly higher than the control group at baseline, after water deprivation and following DDAVP injection and after hypertonic saline infusion. The osmotic threshold of serum for thirst perception was found to be significantly higher in SS patients than the control group, GH replacement therapy did not influence the results of water deprivation and saline infusion tests in SS patients. CONCLUSION: Patients with SS have subtle abnormalities in posterior pituitary functions and the threshold for thirst perception is increased. However GH replacement therapy does not seem to reverse or adversely affect the mildly deteriorated posterior pituitary functions of SS patients.

Modulation/physiology of calcium channel sub-types in neurosecretory terminals.

The hypothalamic-neurohypophysial system (HNS) controls diuresis and parturition through the release of arginine-vasopressin (AVP) and oxytocin (OT). These neuropeptides are chiefly synthesized in hypothalamic magnocellular somata in the supraoptic and paraventricular nuclei and are released into the blood stream from terminals in the neurohypophysis. These HNS neurons develop specific electrical activity (bursts) in response to various physiological stimuli. The release of AVP and OT at the level of neurohypophysis is directly linked not only to their different burst patterns, but is also regulated by the activity of a number of voltage-dependent channels present in the HNS nerve terminals and by feedback modulators. We found that there is a different complement of voltage-gated Ca(2+) channels (VGCC) in the two types of HNS terminals: L, N, and Q in vasopressinergic terminals vs. L, N, and R in oxytocinergic terminals. These channels, however, do not have sufficiently distinct properties to explain the differences in release efficacy of the specific burst patterns. However, feedback by both opioids and ATP specifically modulate different types of VGCC and hence the amount of AVP and/or OT being released. Opioid receptors have been identified in both AVP and OT terminals. In OT terminals, µ-receptor agonists inhibit all VGCC (particularly R-type), whereas, they induce a limited block of L-, and P/Q-type channels, coupled to an unusual potentiation of the N-type Ca(2+) current in the AVP terminals. In contrast, the N-type Ca(2+) current can be inhibited by adenosine via A(1) receptors leading to the decreased release of both AVP and OT. Furthermore, ATP evokes an inactivating Ca(2+)/Na(+)-current in HNS terminals able to potentiate AVP release through the activation of P2X2, P2X3, P2X4 and P2X7 receptors. In OT terminals, however, only the latter receptor type is probably present. We conclude by proposing a model that can explain how purinergic and/or opioid feedback modulation during bursts can mediate differences in the control of neurohypophysial AVP vs. OT release.

Socially modulated cell proliferation is independent of gonadal steroid hormones in the brain of the adult green treefrog (Hyla cinerea).

Gonadal steroid hormones have been shown to influence adult neurogenesis in addition to their well-defined role in regulating social behavior. Adult neurogenesis consists of several processes including cell proliferation, which can be studied via 5-bromo-2'-deoxyuridine (BrdU) labeling. In a previous study we found that social stimulation altered both cell proliferation and levels of circulating gonadal steroids, leaving the issue of cause/effect unclear. In this study, we sought to determine whether socially modulated BrdU-labeling depends on gonadal hormone changes. We investigated this using a gonadectomy-implant paradigm and by exposing male and female green treefrogs (Hyla cinerea) to their conspecific chorus or control stimuli (i.e. random tones). Our results indicate that socially modulated cell proliferation occurred independently of gonadal hormone levels; furthermore, neither androgens in males nor estrogen in females increased cell proliferation in the preoptic area (POA) and infundibular hypothalamus, brain regions involved in endocrine regulation and acoustic communication. In fact, elevated estrogen levels decreased cell proliferation in those brain regions in the implanted female. In male frogs, evoked calling behavior was positively correlated with BrdU-labeling in the POA; however, statistical analysis showed that this behavior did not mediate socially induced cell proliferation. These results show that the social modulation of cell proliferation can occur without gonadal hormone involvement in either male or female adult anuran amphibians, and confirms that it is independent of a behavioral response in males.

Ghrelin immunoexpression in the human hypophysis.

The aim of this study was to immunohistochemically localize ghrelin in autopsy-obtained, nontumoral human pituitaries. Double immunostaining was also undertaken to determine the pituitary cell type expressing both adenohypophysial hormones and ghrelin. Results showed that ghrelin is present in the adenohypophysis, its immunoexpression being cytoplasmic, weak-to-moderate, and localized to a subset of cells. Double immunostaining showed that ghrelin is present in 51% to 90% of growth hormone-producing, luteinizing-producing, and α-subunit-producing cells. Ghrelin immunoexpression was less frequently observed in other adenohypophysial cell types, being seen in 30% of adrenocorticotropin and follicle-stimulating hormones, 15% of thyrotropin, and 10% of prolactin-immunoreactive cells. Ghrelin immunopositivity was also seen in nerve fibers and Herring bodies of the neurohypophysis and pituitary stalk. More work is needed to elucidate the role of ghrelin in adenohypophysial and neurohypophysial endocrine activity. It may well be that ghrelin exerts an autocrine/paracrine effect and can modulate hormone synthesis and release.

Distribution of osmoregulatory peptides and neuronal-glial configuration in the hypothalamic magnocellular nuclei of desert rodents.

The desert rodents Psammomys obesus and Gerbillus tarabuli live under extreme conditions and overcome food and water shortage by modes of food and fluid intake specific to each species. Using immunohistochemistry and electron microscopy, we found that the hypothalamic magnocellular nuclei, and in particular, their vasopressinergic component, is highly and similarly developed in Psammomys and Gerbillus. In comparison to other rodents, the hypothalamus in both species contains more magnocellular VP neurons that, together with oxytocin neurons, accumulate in distinct and extensive nuclei. As in dehydrated rodents, many magnocellular neurons contained both neuropeptides. A striking feature of the hypothalamic magnocellular system of Psammomys and Gerbillus was its display of ultrastructural properties related to heightened neurosecretion, namely, a significant reduction in glial coverage of neuronal somata and dendrites in the hypothalamic nuclei. There were many neuronal elements whose surfaces were directly juxtaposed and shared the same synapses. Their magnocellular nuclei also showed a high level of sialylated isoform of the Neural Cell Adhesion Molecule (PSA-NCAM) that underlies their capacity for neuronal and glial plasticity. These species thus offer striking models of structural neuronal and glial plasticity linked to natural conditions of heightened neurosecretion.

Changes in angiotensin II receptor bindings in the hen neurohypophysis before and after oviposition.

The present study was performed to elucidate whether the angiotensin II (ANG II) receptor exists in the plasma membrane fraction of the neurohypophysis in hens, to estimate the time of action of ANG II on the neurohypophysis before and after oviposition, and to examine relationships between the action of ANG II on the neurohypophysis and those of estrogen and prostaglandin F(2α) (PGF(2α)) in relation to arginine vasotocin (AVT) release. The specific binding had a binding specificity to chicken ANG II (cANG II), reversibility, and saturation in the [(125)I]cANG II binding assay. Scatchard analysis revealed that the binding sites are of a single class. The equilibrium dissociation constant (K(d)) obtained by kinetic analysis and Scatchard analysis suggested a high affinity, and the maximum binding capacity (B(max)) obtained by Scatchard analysis suggested a limited capacity. These results suggest that an ANG II receptor exists in the neurohypophysis of hens. The K(d) and the B(max) value was significantly smaller in laying hens than in nonlaying hens, which suggests that bindings of the cANG II receptor change, depending on the difference in laying condition. Values of the K(d) and the B(max) decreased approximately 15 min before oviposition in laying hens, and decreased 1 h after an intramuscular injection of estradiol-17ß and 5 min after an intravenous injection of cANG II in nonlaying hens. The amount of specific binding of PGF(2α) receptor in the neurohypophysis also decreased and AVT concentration in blood increased after the cANG II injection. It seems likely that the action of cANG II in the neurohypophysis increases due to the effect of estrogen approximately 15 min before oviposition, and the cANG II action stimulates AVT release through the increase in the PGF(2α) action in this tissue.

Effect of estradiol-17ß on calcitonin receptor bindings in the hen neurohypophysis.

The present study was performed to elucidate whether estradiol-17ß (E2) would affect calcitonin (CT) receptor binding in the hen neurohypophysis. The equilibrium dissociation constant (K(d)) and the maximum binding capacity (B(max)) of the CT receptor in the plasma membrane fraction of the hen neurohypophysis were examined by Scatchard analysis of specific binding of (125)I-labeled chicken CT. A single i.m. injection of E2 into nonlaying hens caused a decrease in K(d) and B(max) values of the CT receptor. The K(d) and B(max) values of the CT receptor were smaller in laying hens than in nonlaying hens. The present study suggests that E2 may increase the action of CT on the neurohypophysis in hens.

Properties of estrogen binding components in the plasma membrane of neurohypophysis in hens and changes in its binding before and after oviposition.

The present study was performed to elucidate whether the estrogen binding component regarded as a receptor exists in the plasma membrane fraction of neurohypophysis in hens and whether the binding of receptor changes with relation to oviposition. The specific binding for estradiol-17beta (E2) in the neurohypophysis of hens was demonstrated by the use of radioligand binding assays on the plasma membrane fraction of the tissue. The binding to [3H]E2 had a binding specificity to E2 and diethylstilbestrol, reversibility, and saturation. Scatchard analysis revealed that the binding sites are of a single class. The equilibrium dissociation constant obtained by Scatchard analysis and kinetic analysis suggested a high affinity, and the maximum binding capacity obtained by Scatchard analysis suggested a limited capacity. These properties are characteristics of a receptor, which suggests that an estrogen receptor exists in the plasma membrane of hen neurohypophysis. The equilibrium dissociation constant value of estrogen receptor of the neurohypophysis was not significantly different between laying hens and nonlaying hens, but the maximum binding capacity value was statistically smaller (the binding affinity is higher) in laying hens than in nonlaying hens. The specific binding of estrogen receptor showed a decrease at 1 h after an injection of diethylstilbestrol in nonlaying hens. The specific binding also decreased 3 h before oviposition in laying hens and maintained low value until just after oviposition. The present study suggests that estrogen may act directly on the neurohypophysis during 3 h before oviposition in hens.

Salsolinol is present in the bovine posterior pituitary gland and stimulates the release of prolactin both in vivo and in vitro in ruminants.

The aims of the present study were to determine whether salsolinol (SAL), a dopamine-related compound, is present in the bovine posterior pituitary (PP) gland, and to clarify the effect of SAL on the secretion of prolactin (PRL) in ruminants. SAL was detected in extract of bovine PP gland using high-pressure liquid chromatography with electrochemical detection (HPLC-EC). A single intravenous (i.v.) injection of SAL (5 and 10mg/kg body weight) significantly and dose-dependently stimulated the release of PRL in goats (P<0.05). Plasma PRL levels reached a peak 10min after the injection, then gradually returned to basal values in 60-80min. The PRL-releasing pattern was similar to that in response to sulpiride (a dopamine receptor antagonist). The intracerebroventricular (i.c.v.) injection of 1mg of SAL had no significant effect on the release of PRL in calves, however, 5mg significantly stimulated the release (P<0.05) with peak values reached 30-40min after the injection. Moreover, SAL significantly stimulated the release of PRL from cultured bovine anterior pituitary cells at doses of 10(-6) and 10(-5)M, compared to control cells (P<0.05). Taken together, our data clearly show that SAL is present in extract of the PP gland of ruminants, and has PRL-releasing activity both in vivo and in vitro. Therefore, this endogenous compound is a strong candidate for the factor having PRL-releasing activity that has been previously detected in extract of the bovine PP gland.

Hypertrophy and increased kisspeptin gene expression in the hypothalamic infundibular nucleus of postmenopausal women and ovariectomized monkeys.

CONTEXT: Human menopause is characterized by ovarian failure, gonadotropin hypersecretion, and neuronal hypertrophy in the hypothalamic infundibular (arcuate) nucleus. Recent studies have demonstrated a critical role for kisspeptins in reproductive regulation, but it is not known whether menopause is accompanied by changes in hypothalamic kisspeptin neurons. OBJECTIVES: Our objective was to map the location of neurons expressing kisspeptin gene (KiSS-1) transcripts in the human hypothalamus and determine whether menopause is associated with changes in the size and gene expression of kisspeptin neurons. In monkeys, our objective was to evaluate the effects of ovariectomy and hormone replacement on neurons expressing KiSS-1 mRNA in the infundibular nucleus. SUBJECTS: Hypothalamic tissues were collected at autopsy from eight premenopausal and nine postmenopausal women and from 42 young cynomolgus monkeys in various endocrine states. METHODS: We used hybridization histochemistry, quantitative autoradiography, and computer-assisted microscopy. RESULTS: Examination of human hypothalamic sections revealed that KiSS-1 neurons were located predominantly in the infundibular nucleus. In the infundibular nucleus of postmenopausal women, there was a significant increase in the size of neurons expressing KiSS-1 mRNA and the number of labeled cells and autoradiographic grains per neuron. Similar to postmenopausal women, ovariectomy induced neuronal hypertrophy and increased KiSS-1 gene expression in the monkey infundibular nucleus. Conversely, in ovariectomized monkeys, estrogen replacement markedly reduced KiSS-1 gene expression. CONCLUSIONS: The cynomolgus monkey experiments provide strong evidence that the increase in KiSS-1 neuronal size and gene expression in postmenopausal women is secondary to ovarian failure. These studies suggest that kisspeptin neurons regulate estrogen negative feedback in the human.

Anterior and posterior pituitary function testing with simultaneous insulin tolerance test and a novel copeptin assay.

CONTEXT: Posterior pituitary function in patients with suspected diabetes insipidus is usually assessed by a water deprivation test. Alternatively, a nonosmotic stimulus such as hypoglycemia may be used to stimulate vasopressin [arginine vasopressin (AVP)] secretion. Plasma AVP measurement may aid in the diagnosis and, especially, differential diagnosis of diabetes insipidus and polydipsia. However, AVP measurement is cumbersome. Copeptin, the stable C-terminal glycopeptide of the AVP prohormone, is stoichiometrically secreted from the posterior pituitary. OBJECTIVE: The aim was to study the value of copeptin levels in the diagnosis of diabetes insipidus during insulin-induced hypoglycemia. PATIENTS AND METHODS: A total of 38 patients were studied during insulin-induced hypoglycemia as part of a combined pituitary function test for possible anterior pituitary disease. There were 29 patients who had normal posterior pituitary function, and nine had central diabetes insipidus. Blood sampling was done before and 30, 45, and 90 min after iv insulin injection. Copeptin was measured with a new sandwich immunoassay. RESULTS: Patients with intact posterior pituitary function had basal copeptin levels of 3.7 +/- 1.5 pm, with a maximal increase to 11.1 +/- 4.6 pm 45 min after insulin injection. Copeptin levels in patients with diabetes insipidus were 2.4 +/- 0.5 pm before insulin injection, with a maximum increase to 3.7 +/- 0.7 pm. Both basal and stimulated copeptin levels were lower in patients with diabetes insipidus as compared with patients with intact posterior pituitary function. A stimulated copeptin level 45 min after insulin injection of less than 4.75 pm had an optimal diagnostic accuracy to detect diabetes insipidus. CONCLUSION: Copeptin measurement may be used to assess posterior together with anterior pituitary function during insulin-induced hypoglycemia.

Possible involvement of brain-derived neurotrophic factor (BDNF) in the innervation of dopaminergic neurons from the rat periventricular nucleus to the pars intermedia.

Developing neurons are guided to their appropriate targets by specific guidance substances that have neurotrophic actions. The aim of the present study was to elucidate the mechanism by which hypothalamic neurons reach the pars intermedia (PI) by correlating the development of dopaminergic (DA) neurons arising in the periventricular nucleus (PeV) of fetal rats with the expression of brain-derived neurotrophic factor (BDNF) in the rat pituitary. The differentiation of DA neurons was observed by immunohistochemistry using an antibody against tyrosine hydroxylase (TH), whereas the ontogenesis of BDNF mRNA in the PI was examined by in situ hybridization and RT-PCR. Immunoreactive TH-neurons were first observed in the PeV at embryonic day (E) 16.5, following which time their axons elongated toward the pituitary. TH-positive reactions were observed in the connective tissue between the PI and the pars nervosa at E20.5. Innervation of the PI by TH-positive neurons was determined at postnatal day (P) 1.5; however, BDNF mRNA was first detected in the PI cells at E17.5, with an increase in its expression clearly visible at E21.5 and continuing high expression levels in the PI thereafter. These results suggest that BDNF is a specific guidance cue for DA neurons elongating from the PeV to the PI.

Evidence of haematopoiesis within the developing human diencephalon. Correlations with vertebrate phylogeny.

AIM: The sites of haematopoiesis during human ontogeny can be correlated to the sites where haematopoiesis occurs in vertebrate phylogeny. As haematopoiesis has been described in the diencephalon and pituitary gland of water-inhabiting vertebrates we wanted to find out whether such a phenomenon also occurs in human embryos. MATERIAL AND METHODS: Paraffin-embedded specimens from the diencephalon and pituitary gland of human embryos at the 7th to 22nd gestational week and from adults were investigated by conventional histology and immunohistology for the presence of haematopoietic cells. RESULTS: Cellular accumulations predominantly of erythroid and megakaryocytic lineage were identified in the floor of the developing diencephalon of the 7th/8th gestational week. At the older developmental stages of the 18th to 22nd gestational week loose aggregates of haematopoietic cells within the leptomeningeal spaces adjacent to the hypophyseal infundibulum were detected in 2 out of 7 cases analyzed. CONCLUSIONS: As it has been proposed that lymphohaematopoietic clusters occasionally occur within the brain in bone marrow-less vertebrates as a response to noxious agents, we speculate that this temporal appearance of haematopoietic cell clusters within the diencephalon floor in early human ontogeny could also be due to fetal immunomodulations.

Long form leptin receptor mRNA expression in the hypothalamus and pituitary during early pregnancy in the pig.

OBJECTIVE: The aim of this study was the detection and location of long form leptin receptor (OB-Rb) in different area of hypothalamus and pituitary in the pig during early pregnancy. SETTINGS AND DESIGN: Expression of OB-Rb was examined by RT-PCR in the different area of hypothalamus: medial basal hypothalamus (MBH), preoptic area (POA), stalk median eminence (SME), as well as pituitary: the anterior (AP) and posterior (NP) lobe collected from gilts at days 14-16 (n=4) and 30-32 (n=4) of pregnancy. RESULTS: The results showed that OB-Rb mRNA was expressed in the hypothalamus (MBH, POA and SME), pituitary (AP, NP) and adipose tissue in the pig during early pregnancy (at days 14-16 and 30-32). CONCLUSION: These findings support the idea that leptin might play a role in the regulation of the hypothalamic-pituitary axis activity, and consequently in the control of pregnancy during critical period of embryo implantation in the pig.

ATP elicits inward currents in isolated vasopressinergic neurohypophysial terminals via P2X2 and P2X3 receptors.

Effects of extracellular adenosine tri-phosphate (ATP) on ionic currents were investigated using the perforated-patch whole-cell recording technique on isolated terminals of the Hypothalamic Neurohypophysial System (HNS). ATP induced a current response in 70% of these isolated terminals. This inwardly-rectifying, inactivating current had an apparent reversal near 0 mV and was dose-dependent on ATP with an EC50=9.6+/-1.0 microM. In addition, current amplitudes measured at maximal ATP concentrations and optimum holding potentials had a current density of 70.8 pA pF(-1) and were greatly inhibited by suramin and PPADS. Different purinergic receptor agonists were tested, with the following efficacy: ATP > or = 2-methylthioATP > ATP-gamma-S > Bz-Bz-ATP > alpha,beta-methylene-ATP > beta,gamma-methylene-ATP. However, UTP and ADP were ineffective. These data suggest the involvement of a P2X purinergic receptor in the ATP-induced responses. Immunocytochemical labeling in vasopressinergic terminals indicates the existence of P2X(2,3,4, and 7), but not P2X6 receptors. Additionally, P2X(2 and 3) were not found in terminals which labeled for oxytocin. In summary, the EC50, decay, inactivation, and pharmacology indicate that a functional mixture of P2X(2 and 3) homomeric receptors mediate the majority of the ATP responses in vasopressinergic HNS terminals. We speculate that the characteristics of these types of receptors reflect the function of co-released ATP in the terminal compartment of these and other CNS neurons.

Oestrogen receptor beta: role in neurohypophyseal neurones.

The robust expression of oestrogen receptor beta (ER-beta) in magnocellular vasopressin neurones has focused attention on the role of this receptor and the gonadal steroids in the regulation of vasopressin secretion. Although the effects of gonadal steroids on vasopressin secretion have been the subject of many studies, there is no consensus in the literature as to their role. Possible reasons for the diverse findings are discussed, including diversity in the types, site and level of expression of steroid receptors across species, gender and physiological conditions. The physiological regulation of expression is of particular interest because ER-beta mRNA expression in vasopressin neurones is inversely correlated to the osmotic state of the animal. Chronic hyperosmolality inhibits ER-beta mRNA expression in magnocellular vasopressin neurones, while chronic hypo-osmolality enhances expression. This is consistent with an inhibitory role for ER-beta because hyperosmolality is a potent stimulus for vasopressin secretion, whereas vasopressin secretion is maximally inhibited by chronic hypo-osmolality. An inhibitory role is also indicated by in vitro experiments demonstrating inhibition of osmotically stimulated vasopressin secretion by oestrogen and testosterone, and ER-beta mediated inhibition of NMDA-stimulated vasopressin secretion. The challenge remains to elucidate the mechanism of this inhibition, and to understand its significance for maintenance of whole-body fluid and electrolyte homeostasis.

Hypophyseal gene expression profiles of FSH-beta, LH-beta, and glycoprotein hormone-alpha subunits in Ictalurus punctatus throughout a reproductive cycle.

A determination of the seasonal changes in the expression of the genes encoding the subunits of gonadotropic hormones is an important first step in the understanding of the molecular control of the onset of puberty and the reproductive cycle in fish. In this study, the abundance of transcripts encoding the glycoprotein hormone alpha (GpH-alpha), follicle-stimulating hormone beta (FSH-beta), and luteinizing hormone beta (LH-beta) subunits in pituitaries of female channel catfish were systematically tracked throughout an annual reproductive cycle. All three genes showed a concurrent elevation coinciding with the onset of ovarian recrudescence but then each showed a second elevation at different times of the ovarian cycle. In addition to the initial peak at recrudescence, the expression of FSH-beta and GpH-alpha gene peaked again during mid- and late-vitellogenic growth, respectively. The LH-beta gene expression remained low during the phases of regression and vitellogenic growth but was moderately elevated (7-fold) at the onset of ovarian recrudescence and dramatically elevated (36-fold) just prior to spawning (June-July) when the FSH-beta levels were at their lowest. The expression patterns of FSH-beta and LH-beta are remarkably similar to the ovarian expression of their respective receptors.