Central actions of neurohypophysial hormones

Effects of calcium and sodium on ATP-induced vasopressin release from rat isolated neurohypophysial terminals

ATP-receptors (P2X2, P2X3, P2X4 & P2X7) are found in neurohypophysial terminals (NHT). These purinergic receptor subtypes are known to be cation selective. Here we confirm that both sodium (Na+ ) and calcium (Ca2+ ) are permeable through these NHT purinergic receptors, but to varying degrees (91% vs. 9%, respectively). Furthermore, extracellular calcium inhibits the ATP-current magnitude. Thus, the objective of this study was to determine the effects of extracellular Na+ vs. Ca2+ on ATP-induced vasopressin (AVP) release from populations of rat isolated NHT. ATP (200 μM) perfused exogenously for 2 minutes in Normal Locke's buffer caused an initial transient increase in AVP release followed by a sustained increase in AVP release which lasted for the duration of the ATP exposure. Replacing extracellular NaCl with NMDG-Cl had no apparent effect on the ATP-induced transient increase in AVP release but abolished the sustained AVP release induced by ATP. Furthermore, removal of extracellular calcium resulted in no ATP-induced transient increase in AVP release, but had no effect on the delayed, sustained increase in AVP release. The ATP-induced calcium-dependent transient increase in AVP release was >95% inhibited by 10 μM of the P2X purinergic receptor antagonist PPADS, a dose sufficient to block P2X2 and P2X3 receptors but not P2X4 or P2X7 receptors. Interestingly, the ATP-induced calcium-independent, sodium-dependent sustained increase in AVP release was not affected by 10 μM PPADS. The ATP-induced calcium-dependent transient increase in AVP release was not affected by the P2X7 receptor antagonist BBG (100 nM). However, the ATP-induced sodium-dependent sustained AVP release was inhibited by 50%. Therefore, these results show that rat isolated NHT exhibit a biphasic response to exogenous ATP that is differentially dependent on extracellular calcium and sodium. Furthermore, the initial transient release appears to be through P2X2 and/or P2X3 receptors and the sustained release is through a P2X7 receptor. This article is protected by copyright. All rights reserved.

Purinergic receptor types in the hypothalamic-neurohypophysial system

Many different types of purinergic receptors are present in the Hypothalamic-Neurohypophysial System (HNS), which synthesizes and releases vasopressin and oxytocin. The specific location of purinergic receptor subtypes has important functional repercussions for neuronal activity and synaptic output. Yet, until the advent of receptor KOs, this had been hindered by the low selectivity of the available pharmacological tools. The HNS offers an excellent opportunity to differentiate the functional properties of these purinergic receptors in cell bodies vs. terminals of the same physiological system. P2X2, P2X3, P2X4 and P2X7 receptors are present in vasopressin terminals while oxytocin terminals exclusively express the P2X7 subtype. The latter is not functional in the cell bodies of the HNS. These purinergic receptor subtypes are permeable to sodium vs. calcium in varying amounts and this could play an important role in the release of vasopressin vs. oxytocin during bursting activity. Endogenous ATP and its metabolite, adenosine, have autocrine and paracrine modulatory effects on the release of these neuropeptides during physiological stimulation. Finally, we hypothesize that during such action potential bursts, ATP potentiates the release of vasopressin but not of oxytocin, and that adenosine, via A1 receptors, inhibits the release of both neuropeptides. This article is protected by copyright. All rights reserved.

Neuropeptides from concept to online database www.neuropeptides.nl

In the early 1970's the term "neuropeptide" was used for the first time by David de Wied for peptides related to peptide hormones but with non-endocrine biological activity in the brain. This early notion appreciated neuropeptides as a specific class of chemical signals produced by neurons, released in a regulated fashion and acting on other neural cells. As we define them today, neuropeptides are encoded by over 70 genes in mammalian genomes. Neuropeptides can be clustered in at least 10 subfamilies according to structural features, for which often shared or related receptors exist. A complete overview is provided through hyperlinks to bioinformatic databases on genome and transcripts, protein structure and brain expression. Other proteineous signaling molecules in the nervous system which originally were discovered in other biological systems, particularly chemokines, growth factors and peptide hormones, share the hallmarks of classical neuropeptides and may be considered as neuropeptides as well.

Highly regionalized distribution of stromal cell-derived factor-1/CXCL12 in adult rat brain: constitutive expression in cholinergic, dopaminergic and vasopressinergic neurons

The stromal cell-derived factor-1 (SDF-1)/CXCL12 and its receptor CXCR4 are key modulators of immune functions. In the nervous system, SDF-1/CXCL12 is crucial for neuronal guidance in developing brain, intercellular communication and the neuropathogenesis of acquired immunodeficiency syndrome. However, cerebral functions of SDF-1/CXCL12 in adult brain are poorly understood. The understanding of its role in the adult brain needs a detailed neuroanatomical mapping of SDF-1/CXCL12. By dual immunohistochemistry we demonstrate that this chemokine is constitutively expressed not only in astrocytes and microglia but also in neurons, in discrete neuroanatomical regions. Indeed, neuronal expression of SDF-1/CXCL12 is mainly found in cerebral cortex, substantia innominata, globus pallidus, hippocampus, paraventricular and supraoptic hypothalamic nuclei, lateral hypothalamus, substantia nigra and oculomotor nuclei. Moreover, we provide the first evidence that SDF-1/CXCL12 is constitutively expressed in cholinergic neurons in the medial septum and substantia innominata and in dopaminergic neurons in substantia nigra pars compacta and the ventral tegmental area. Interestingly we also show, for the first time, a selective co-localization of SDF-1/CXCL12 with vasopressin-expressing neurons in the supraoptic and paraventricular hypothalamic nuclei. In addition, in the lateral hypothalamic area, SDF-1/CXCL12 was found to be located on melanin concentrating hormone-expressing neurons. Altogether, these original data suggest that SDF-1/CXCL12 could be a modulatory neuropeptide regulating both central cholinergic and dopaminergic systems. In addition, a key role for SDF-1/CXCL12 in neuroendocrine regulation of vasopressin-expressing neurons represents an exciting new field of research.

Comparative physiological features of the regulatory effect of vasopressin on higher nervous activity in an ascending series of mammals

This report provides comparative physiological data on the features of the regulatory effects of the neurohormone vasopressin on higher nervous activity in an ascending series of mammals consisting of insectivores, rodents, and primates. Administration of vasopressin to hedgehogs produced a general facilitatory effect on conditioned reflex brain activity. The effects of vasopressin on memory processes in hedgehogs was minor. In rabbits, vasopressin had greater regulatory effects on conditioned reflex memory than in hedgehogs. However, this was transient in nature. In monkeys, administration of vasopressin had complex differential effects on simple conditioned responses and different types of memory. The effects of vasopressin on memory processes were long-lasting and were different for corticalized and noncorticalized forms of nervous activity. The question of changes in the nature of the regulatory effects of vasopressin during phylogenesis is discussed, as is the question of the increases in its level of involvement in the regulation of higher nervous functions and memory processes.

Glucocorticoid regulation of vasopressin V1a receptors in rat forebrain

Vasopressin V1a receptors (V1aRs) are expressed in the septum of the rat brain where they are thought to mediate several of the physiologic and behavioral effects of this neuropeptide. We have investigated the effects of adrenal steroids on forebrain V1aRs. Rats were bilaterally adrenalectomized (ADX) and hormone replaced with either corticosterone (CORT), dexamethasone (DEX) or aldosterone (ALDO) at different concentrations. V1aR mRNA was evaluated using in situ hybridization, and V1aR binding site density was quantified using a specific iodinated V1aR antagonist [125I]d(CH2)5Sar7-AVP (125I-SAVP). V1aR density in the dorsolateral septum and the bed nucleus of the stria terminalis (BNST) decreased significantly with adrenalectomy, and 5 micrograms/100 g b.wt. of DEX was able to restore V1aR binding to levels comparable to those of sham operated controls in both regions. ALDO replacement also elevated V1aR binding in the BNST but not in the septum. In ADX animals given corticosterone in their drinking water, V1aR mRNA levels detected by in situ hybridization increased significantly over the ADX rats given saline. In order to understand the molecular basis of this effect, a putative genomic clone encoding the rat V1aR was isolated, and sequence analysis of the 5' flanking region has revealed the presence of several putative glucocorticoid response elements (GREs). Gel retardation assays were performed using these putative GREs, and two appear to be active in protein binding in glucocorticoid receptor containing nuclear extracts. The glucocorticoid effects on V1aR mRNA and binding, and the presence of putative active GREs in the promoter of the V1aR gene strongly implicate a role for adrenal steroids in the regulation of V1a receptor gene expression in glucocorticoid receptor and/or mineralocorticoid receptor expressing tissues.

Evidence for glucocorticoid regulation of the rat vasopressin V1a receptor gene

WRK-1 cells express vasopressin V1a receptors. Twenty-four-hour treatment of these cells with dexamethasone (DEX) resulted in an increase in [3H]AVP binding that was maximal at 12 h, and could be blocked by addition of RU 38486. The increases in [3H]AVP binding were paralleled by increases in V1a receptor mRNA. The in vivo effects of glucocorticoids (GCs) on V1a receptor binding in hepatic tissue were also investigated in adrenalectomized and hormone-replaced rats given either DEX or aldosterone (ALDO). DEX effectively increased V1a receptor binding site density whereas ALDO had no effect. The DEX effects on V1a receptor mRNA and binding strongly implicate glucocorticoids in the regulation of V1a receptor gene expression.

Vasopressin and oxytocin in stress

Though oxytocin and vasopressin are similar in structure and are produced in the same brain regions, they show specific responses under stress conditions. In humans, increases in peripheral blood vasopressin appear to be a consistent finding during many acute stress situations, while in rats, vasopressin secretion is unresponsive to several stimuli known to induce ACTH and catecholamine release. Even decreases in vasopressin levels during stress were described. In accordance with others, we observed enhanced vasopressin release in response to stress stimuli with an osmotic component such as hypertonic saline injection but also during exposure of rats to a warm environment. Immobilization stress which fails to induce vasopressin release was reported to increase hypothalamic vasopressin mRNA and plasma vasopressin levels in chronically adreno-demedullated rats. Unlike vasopressin, oxytocin may be considered a typical stress hormone responding to osmotic as well as other stress stimuli. We found that acute exposure of rats to immobilization stress resulted in an increase in oxytocin mRNA level. In addition, we have shown that magnocellular neurons of the paraventricular nucleus, but not the supraoptic nucleus, are essential for oxytocin release during immobilization stress. The release of posterior pituitary hormones represents an important component of the stress response.

Brain proteolysis of oxytocin in vitro and in vivo changes during aging in male rats

Oxytocin proteolysis was studied in vitro with purified synaptic membranes and in vivo after injection into the hippocampus of male Wistar Kyoto rats of different ages. When oxytocin was incubated in vitro with brain synaptic membranes obtained from 2-, 6-, and 12-month-old rats, no difference in the content of C-terminal and N-terminal fragments formed by membrane-bound aminopeptidase-like and endopeptidase-like enzymes, respectively, was found after high performance liquid chromatography separation and quantification by amino acid analysis. In contrast, the content of all fragments decreased by about 20%-25% when membranes obtained from 18- and 24-month-old rats were used. When [3H-Tyr2]oxytocin was injected in vivo in the hippocampus of 2-, 6-, 12-, and 18-month-old rats, no difference in the content of free [3H]-tyrosine and other [3H]-labelled fragments was found in the hippocampal peptidic extract after high performance liquid chromatography fractionation. However, the content of all radioactive fragments was about 50% lower in the extract from 24-month-old rats. The findings suggest that oxytocin proteolysis in brain decreases during aging. Such a decrease might counterbalance the impairment of central oxytocinergic transmission caused by the age-related decrease of oxytocin content in brain.

Proteolytic conversion of oxytocin in vivo after microinjection in the rat hippocampus

Since previous studies in vivo have shown that oxytocin is metabolized by rat synaptic membrane-bound aminopeptidase- and endopeptidase-like enzymes, the proteolytic conversion of oxytocin was studied in vivo after microinjection in the rat hippocampus, a brain area that contains oxytocinergic nerve endings and receptors. Isolation of the formed peptide fragments from the injected brain area after homogenization and adsorption on a Sep-Pak cartridge by high performance liquid chromatography, and their characterization by amino acid analysis, revealed that, when oxytocin (50 nmol in 0.5 microliter) was microinjected in the CA1 field of the rat hippocampus, only the N-terminal fragment oxytocin(1-8) was formed in such amount that could be characterized. The microinjection of [3H-Tyr2]oxytocin (10 pmol) revealed that in addition to oxytocin(1-8), free [3H]tyrosine was formed. Taken together with previous findings showing that C-terminal oxytocin fragments as well oxytocin(1-8) are formed by membrane-bound aminopeptidases and endopeptidases in vitro, respectively, the results suggest that, in addition to aminopeptidases, endopeptidase-like enzymes are involved in the proteolysis of endogenous brain oxytocin.

An evaluation of human neurophysin production in Alzheimer's disease: preliminary observations

The concentrations of human neurophysins in the cerebrospinal fluid (CSF) of nine patients with Alzheimer's disease: Preliminary observations. (AD), and one patients with Pick's disease, were determined using specific radioimmunoassays (RIAs). Concentrations of vasopressin and oxytocin were also measured. Values were compared with those from 20 age-matched mentally normal individuals who were being treated for back pain. CSF levels of vasopressin-associated human neurophysin (VP-HNP) and oxytocin-associated human neurophysin (OT-HNP) in patients with AD (22 +/- 4 fmol/ml and 104 +/- 17 fmol/ml) were only 42% and 58% of those in the control subjects (p less than 0.0001, p less than 0.0004). Vasopressin levels for these patients (3.6 +/- 0.4 fmol/ml) were also significantly reduced to 51% of controls (p less than 0.007) and oxytocin levels were marginally (p = 0.092) reduced to 70% of controls. Because neurophysins and neuropeptides are gene-related products of vasopressin-neurons and oxytocin-neurons, the data indicate that these neurons are functionally impaired in patients with AD. Plasma neurophysin values suggest this impairment is confined to neurons with centrally-directed axons. Data from the one patient with Pick's disease demonstrates that reduced CSF levels of neurophysins and hormones is not confined to Alzheimer-type dementia.

Central functions of oxytocin

Oxytocin, the peptide well-known for its hormonal role in parturition and lactation, is present in several extrahypothalamic brain areas besides the neurohypophyseal system. The peptide is found in neurons which send their projections to brain areas containing specific oxytocin-binding sites. Oxytocin is also released from its synapses in a calcium-dependent fashion and may be the precursor of potent behaviorally active neuropeptides. These findings suggest that this ancient neuropeptide acts as a neurotransmitter in the central nervous system. We have attempted to review the most recent behavioral, morphological, electrophysiological and neurochemical studies providing evidence that oxytocin plays an important role in the expression of central functions, such as maternal behavior, sexual behavior (penile erection, lordosis and copulatory behavior), yawning, memory and learning, tolerance and dependence mechanisms, feeding, grooming, cardiovascular regulation and thermoregulation.

Cardiovascular depression and stabilization by central vasopressin in rats

The role of endogenous vasopressin in cardiovascular homeostasis was examined using vasopressin-deficient rats (Brattleboro) (n = 194) and their parent strain, Long-Evans rats (n = 181). Mean arterial pressure (blood pressure) and heart rate were measured every 4 seconds with or without infusion of drug solution for 21 hours, and mean values and their standard deviations (lability) were calculated. Blood pressure in Brattleboro rats (116 +/- 1.1 mm Hg, mean +/- SEM) was significantly higher than that in Long-Evans rats (96 +/- 0.7 mm Hg, p less than 0.001), whereas heart rates (381 +/- 3.3 and 375 +/- 2.9 beats/min, respectively) were similar. The lability of blood pressure and heart rate in Brattleboro rats (9.2 +/- 0.1 mm Hg and 42.3 +/- 0.7 beats/min) was also greater than that in Long-Evans rats (6.7 +/- 0.1 mm Hg, p less than 0.001 and 38.4 +/- 0.8 beats/min, p less than 0.01, respectively). In Brattleboro rats, intravenous vasopressin (0.1 ng/kg/min or 0.6 ng/kg/min) did not affect blood pressure, although it did reduce heart rate and decreased lability of blood pressure and heart rate. Intracerebroventricular (central) infusion of vasopressin (2 pg/kg/min) in Brattleboro rats induced initial hypertension and tachycardia followed by long-lasting hypotension and bradycardia, whereas in Long-Evans rats it induced only hypertension and tachycardia. In both strains, central vasopressin dramatically decreased the lability of blood pressure and heart rate. Neither intravenous (0.2 ng/kg/min) nor central desmopressin (2 pg/kg/min or 0.2 ng/kg/min), a V2 renal receptor agonist, changed any of these parameters in Brattleboro rats, although both diminished urinary volume. Neither intravenous (50 ng/kg/min) nor central (3.3 pg/kg/min) d(CH2)5-Tyr(Me)-arginine vasopressin, a vasopressin V1 receptor antagonist, modulated any of these parameters in Long-Evans rats. These results suggest that endogenous as well as exogenous vasopressin acts centrally as a cardiovascular inhibitor and stabilizer through a receptor mechanism other than V1 or V2 receptor mechanisms.

Neuropeptide gene expression in hypothalamic magnocellular neurons of normal and hypophysectomized rats: a combined immunohistochemical and in situ hybridization study

Hypothalamic magnocellular neurons of the paraventricular and supraoptic nuclei contain several peptides and non-peptide putative neurotransmitters co-existing with vasopressin and oxytocin. However, the functional role of these substances is still unknown. In the present paper the temporal course of changes in the expression of vasopressin, oxytocin, galanin, cholecystokinin, dynorphin and tyrosine hydroxylase in magnocellular hypothalamic neurons of rats subjected to hypophysectomy was examined. Following different survival times the animals were processed either for immunohistochemistry with antibodies against the above mentioned peptides or for in situ hybridization with synthetic oligonucleotide probes complementary to the mRNAs encoding for the peptides. The results obtained showed a marked rise in vasopressin mRNA levels at two days followed by a decrease up to 36 days of survival. Oxytocin mRNA responded to the lesion with a transient decrease, with its lowest values between five and seven days. This was followed by a recovery which almost reached normal values at 36 days of survival. The results also showed a marked, transient activation of the synthetic pathway for galanin and cholecystokinin. The numbers of cells expressing these peptides were maximal between five and seven days, and the respective mRNA levels were significantly increased at these survival times. This was followed by a decrease in the amount of galanin- and cholecystokinin-like immunoreactivity as well as in the levels of their respective mRNAs. Dynorphin-like immunoreactivity showed a course similar to that of galanin and cholecystokinin in operated animals. However, the amounts of dynorphin mRNA were significantly increased at two days, but were followed by a reduction at five days and remained low throughout the different survival times tested. The experiments performed with the tyrosine hydroxylase antibodies and probe showed undetectable levels of the enzyme and its mRNA in normal and hypophysectomized animals. These results demonstrate that, in magnocellular hypothalamic neurons, expression of several peptides occur in differential ways after hypophysectomy. The possibility is discussed that these changes represent part of the mechanisms underlying the process of degeneration and regeneration known to occur in magnocellular hypothalamic neurons after hypophysectomy.

Vasopressin and oxytocin systems in the brain and upper spinal cord of Macaca fascicularis

This paper describes the vasopressin (VP) and oxytocin (OXT) immunoreactive structures in the brain and upper spinal cord of the adult male and female Macaca fascicularis. Immunocytochemistry following intraventricular application of colchicine displayed VP neurons in the diagonal band of Broca (DBB), bed nucleus of the stria terminalis (BST), medial amygdaloid nucleus, dorsomedial hypothalamic nucleus, area of the locus coeruleus (LC), solitary tract nuclei (NTS), and the dorsal horn of the cervical spinal cord in addition to those known to exist in the paraventricular, supraoptic, and suprachiasmatic hypothalamic nuclei. Furthermore, a dense accumulation of VP fibers was observed in areas such as the DBB, medial septum, BST, amygdala, hippocampus, ventral tegmental area, periaquaductal gray, dorsal and ventral raphe, area of Forel, LC region, parabrachial nuclei, and NTS. The lateral septum and lateral habenula displayed no and very few VP fibers, respectively. No extrahypothalamic OXT neurons were found in the brain of this macaque monkey. Dense concentrations of OXT fibers were demonstrated in the amygdala, NTS, and marginal layer of the cervical spinal cord. No sexual dimorphism was found in this primate VP or OXT system. The results show a distribution of the central VP and OXT systems in this primate which is quite different from that in the rat. However, in various aspects it agrees with current data on the VP and OXT systems of the human brain. The present results suggest, therefore, that this monkey might serve as a better model for the human VP system than the rat.

In vivo conversion of vasopressin after microinjection into limbic brain areas of rats

The nonapeptide [Arg8]vasopressin was rapidly degraded with a half-life of lower than 1 minute after local administration into the hippocampus. During the conversion of vasopressin C-terminal fragments were transiently generated. The profile of these metabolites indicated that they were formed by aminopeptidase activity. The aminopeptidase inhibitor amastatin partially inhibited the conversion of vasopressin. A minor pathway involved cleavages in the C-terminus. The results indicate a predominant involvement of aminopeptidase activity in the in vivo metabolism of exogenous vasopressin in the brain. Since products of this metabolic route have been shown to have potent behavioral activities, the behavioral effects seen after microinjection of vasopressin in the brain may be partially due to generation of vasopressin fragments.

N-acetyl-vasopressin- and N-acetyl-oxytocin-like substances: isolation and characterization in the rat neurointermediate pituitary and presence in the brain

Abstract Post-translational modifications of vasopressin and oxytocin in pituitary and brain were investigated in view of recent evidence that oxytocin is partly N(alpha)-acetyfated in the bovine pineal gland. Two peptides were isolated from the neurointermediate lobe of the rat pituitary gland and characterized as N(alpha)-acetyl-vasopressin and N(alpha)-acetyl-oxytocin, based on chromatographic and immunological properties as well as the blocked N-terminus. In the neurointermediate pituitary the acetylated forms represented approximately 1% of the vasopressin and oxytocin contents. These two peptides were also detected in some, but not all, investigated brain areas. The highest degree of acetylation was found in the pineal gland. In all regions acetylation of oxytocin was more abundant than that of vasopressin. The data indicate that acetylation of vasopressin and oxytocin generally occurs as a post-translational modification. They support the concept that acetylation may represent a mechanism aimed to control bioactivity of the neurohypophyseal hormones.

Changes in vasopressin-converting aminopeptidase activity in the rat pineal gland during summer: relationship to vasopressin contents

Vasopressin (VP)-converting aminopeptidase (VP-AP) activity and VP contents were measured in single rat pineal glands during the summer of two successive years. The peptidase activity decreased significantly in August. The lowest activity (+/- SEM) of 0.18 +/- 0.02 pmol.hour-1 was recorded on August 14, compared to the basal activity of 0.25 +/- 0.01 pmol.hour-1 in July and September of 1986. The change with similar percentage occurred in the same period of 1987. The specific activity of the enzyme in the crude homogenate, 15,000 g pellet and supernatant fraction of rat pineal glands, exhibited the same pattern of variations. The decrease in peptidase activity coincided with the previously reported dramatic rise in pineal VP content in early August which was confirmed in this series of experiments. Another peptidase, the so-called gamma-endorphin generating endopeptidase (gamma-EGE) activity, and beta-endorphin-related peptides in the pineal gland did not change in this period. The results show that the variations of pineal VP contents and VP-AP activity during summer are not general for other peptides and peptidases. The coincidence of opposite changes in VP content and VP-AP activity of the pineal gland may indicate a role of the peptidase activity to regulate the VP content.

Diurnal variation in vasopressin and oxytocin messenger RNAs in hypothalamic nuclei of the rat

Diurnal changes in the expression of the vasopressin (VP) and oxytocin (OT) genes in the supraoptic (SON), paraventricular (PVN) and suprachiasmatic nuclei (SCN) of the rat were investigated by dot-blot and in situ hybridization of the VP and OT mRNAs. A significant diurnal variation in VP mRNA level was measured in the SCN, with highest levels around 17.00 h and lowest levels around midnight. No variations in levels of VP mRNA and OT mRNA were detected in SON and PVN. The data indicate that the regulation of the VP gene in the SCN is independent of that in the magnocellular nuclei.

Circadian variations of vasopressin level and vasopressin-converting aminopeptidase activity in the rat pineal gland

Vasopressin levels and vasopressin-converting aminopeptidase activity were measured in the rat pineal gland during the 24 hr light-dark cycle. A rhythmic variation in peptide levels and peptidase activity occurred. At the onset of light at 6.00 hr, the peptidase displayed a significant, short-lasting (approximately 3 hr) increase of about 35% in activity, while a decrease of 28% in pineal vasopressin levels was observed. The changes in peptidase activity and peptide level were not triggered by light per se, since they persisted to occur at the same time point in animals which were not exposed to light, indicating the circadian nature of the rhythmicity. These changes were specific to the pineal gland, since other tissues, like hippocampus and pituitary gland, did not show these daily variations. The data suggest a relationship between vasopressin levels and vasopressin-converting aminopeptidase activity.

Physiological effects of arginine vasotocin and mesotocin in cockerels

1. The effects of continuous infusion of 0.1, 1.0 and 10.0 mU/min/kg body weight of arginine vasotocin (AVT) or mesotocin (MT) on cardiovascular and thermoregulatory responses, on plasma osmolality and ionic composition and on plasma concentrations of AVT, MT, prolactin and aldosterone, were investigated in conscious White Leghorn cockerels. 2. Neither of the peptides, at any dose, affected cardiovascular functions, plasma ions and osmolality. Infusion of MT at the rate of 10 mU/min/kg body weight increased respiratory rate. Both peptides at doses of 1 and 10 mU/min/kg reduced the temperatures of the comb and shank but had no effect on the skin and cloaca. 3. Doses of 0.1 and 1.0 mU MT/min/kg reduced plasma aldosterone and at 10 mU/min/kg increased plasma AVT. At any given dose MT had no effect on plasma prolactin. AVT at 0.1 and 1.0 mU/min/kg of AVT reduced plasma MT. AVT at 1.0 mU/min/kg increased plasma prolactin and at 10 mU/min/kg reduced plasma aldosterone. 4. During saline infusion, plasma MT was positively correlated with plasma AVT and negatively correlated with respiratory rate and cloacal temperature. Plasma AVT showed a positive correlation with plasma MT and aldosterone and a negative correlation with respiratory rate and skin temperature. 5. During saline infusion, there was no significant correlation between cardiovascular functions, or plasma osmolality and ionic composition and plasma MT or AVT. 6. The present study suggests that interrelationships between circulating concentrations of AVT and MT do exist and that AVT affects aldosterone secretion. These neurohypophysical peptides are involved in thermoregulation.

Vasopressin cells in the medial amygdala of the rat project to the lateral septum and ventral hippocampus

The rat brain contains a large number of vasopressin (VP) immunoreactive fibers, the sites of origin of which have not yet been established completely. For instance, the sources of VP fiber systems in the amygdala, ventral hippocampus (VH), mediodorsal thalamic nucleus, ventral tegmental area, and dorsal raphe yet remain obscure. These VP fibers may originate in any of the recently described extrahypothalamic VP cell groups, viz., medial amygdaloid nucleus (AME), dorsomedial hypothalamic nucleus, or locus coeruleus, since VP efferents from these cells still remain to be demonstrated. In search of AME VP efferents three approaches were followed: (1) the Phaseolus vulgaris anterograde tracing method, (2) immunocytochemistry after AME lesioning, and (3) retrograde transport of a fluorescent dye in combination with immunofluorescence. The results demonstrate that VP cells in the AME project to (1) the lateral septum (LS) by the ventral amygdalofugal pathway and (2) the VH via the amygdalohippocampal transition zone. In addition, the VP projection from the bed nucleus of the stria terminalis (BST) to the LS was confirmed. There was no indication that VP cells in the AME project through the amygdalotegmental pathway to the medulla oblongata and spinal cord. The results support the possibility that the BST and AME are an anatomical entity that may be part of the central loci controlling sexual processes in the rat.

The hypothalamic suprachiasmatic nuclei: circadian patterns of vasopressin secretion and neuronal activity in vitro

The suprachiasmatic nuclei (SCN) are intrinsic pacemakers which organize circadian rhythms in mammals. When the SCN of Long-Evans rats are surgically isolated and perifused in vitro, they retain the ability to express a 24 hr rhythm of neuronal firing rate. We find that the SCN are also capable of secreting the peptide vasopressin (VP) in a circadian pattern. The pattern of VP secretion is similar to that of SCN neuronal electrical activity measured during perfusate collection. The temporal profile of VP levels in SCN perfusate parallels that seen in cerebrospinal fluid, suggesting that the SCN might be both the pacemaker and a secretory contributor to this rhythm.

Effects of treadmill running and swimming on plasma and brain vasopressin levels in rats

The influence of treadmill or swimming exercise on resting values of plasma and brain arginine vasopressin (AVP), and plasma sodium, potassium, osmolality and proteins was studied after 5 weeks of training using female Wistar rats. The duration of daily training sessions was progressively increased to reach 6 h/day for swim training (S) and 3 h/day for treadmill running (T). Compared to their untrained controls, treadmill and swim training were respectively associated with: a significant lower body weight; a decreased plasma AVP (36.4% for T and 47.4% for S) and hypothalamic AVP (20% for T and 16% for S); a higher hypophyseal AVP (145% for T and 36.3 for S); a decreased plasma osmolality (6.7% for T and 6.1% for S), sodium (1.2% for both) and potassium (15% for T and 22.4% for S); and no change in protein concentration. For T, rectal temperature increased (38.5 +/- 0.20 to 39.7 +/- 0.5) and for S rectal temperature decreased from 38.6 +/- 0.12 to 37.74 +/- 0.10). The differences observed in AVP contents of the pineal and Harderian glands (enhanced only in the treadmill groups) could be explained by the supposed role of these glands in thermoregulation. Two conclusions could be drawn from this study: there are no parallel changes in the hypothalamo-hypophyseal system (where AVP plays its endocrine role) and the brain (where AVP is a neurotransmitter); plasma changes could be explained by an extracellular fluid expansion with Na and K loss leading to a decrease in AVP secretion.

Quantitation of vasopressin mRNA and oxytocin mRNA in hypothalamic nuclei by solution hybridization assays

Concentrations of vasopressin (VP) precursor and oxytocin (OT) precursor mRNA were measured in magnocellular cell groups of the rat hypothalamus by newly developed solution hybridization assays. The assays employed single-stranded 35S-labeled VP-specific and OT-specific DNA probes that were prepared by primer extension on recombinant M13 DNA templates. Solution hybridization assays were standardized by known amounts of cloned DNA. The detection limit was less than 1 pg DNA equivalent of the respective mRNA. In total RNA preparations of microdissected supraoptic nucleus (SON) mean (+/- SEM) basal levels of 1.37 +/- 0.18 pg VP mRNA and 1.95 +/- 0.14 pg OT mRNA were measured. RNA of the microdissected paraventricular nucleus (PVN) contained 0.35 +/- 0.02 pg VP mRNA and 1.77 +/- 0.15 pg OT mRNA. Elevation of plasma osmolality induced by drinking of 2% saline for 25 days resulted in a 1.85-fold increase in VP mRNA levels of the SON and a 1.6-fold increase in VP mRNA levels of the PVN. The solution hybridization assays are suitable tools to study the regulation of VP and OT mRNAs in magnocellular neurons of the brain.

Septal release of vasopressin in response to osmotic, hypovolemic and electrical stimulation in rats

The central release of vasopressin was studied in anesthetized rats using push-pull perfusions and radioimmunoassay of the hormone. A basal release was observed in the lateral septum and in the lateral ventricle, whereas no vasopressin was detected in the perfusates from the caudate nucleus. Under osmotic stimulation, vasopressin release increased up to 12 and 60 times basal levels following i.p. injections of 5 ml and 10 ml/kg b.wt. of 2 M NaCl, respectively. This increase was blocked by using a calcium-free perfusion medium containing 0.1 mM EGTA. In the lateral ventricle, osmotic stimulation (5 ml/kg of 2 M NaCl i.p.) had the same effect as in the septum. In the caudate nucleus, no release was observed. Hemorrhage also increased the septal release of vasopressin in 5 out of 6 animals tested. Electrical stimulation of the pituitary stalk and of the supraoptic nucleus was used to evoke the release of vasopressin into the bloodstream. Septal release slightly decreased during pituitary stalk stimulation, whereas it did increase during stimulation of the supraoptic region. Our results show that systemic stimuli for vasopressin release evoke both a peripheral and a septal release of the hormone. The dissociation of the effects of electrical stimulation of the pituitary stalk and of the supraoptic nucleus suggests, however, that the vasopressinergic neurones responsible for septal release are distinct from those which project to the neurohypophysis.

Behavioral characteristics of Roman high avoidance rats homozygous for diabetes insipidus (RHA: di/di)

These experiments studied the behavior of an inbred strain of vasopressin-deficient rat, the Roman high avoidance rat homozygous for diabetes insipidus (RHA: di/di). The RHA: di/di rat has been bred to be congenic with the parent normal Roman high avoidance (RHA: +/+) strain, differing from it only by the gene(s) coding for diabetes insipidus. Therefore, the RHA: +/+ strain represents an improved model system with which to study the behavioral effects of vasopressin-deficiency, given recent findings suggesting that considerable behavioral variation exists within the Long-Evans derived Brattleboro strain of vasopressin-deficient rat. We examined the behavior of RHA: di/di and RHA: +/+ rats in the open field and on tests of approach-avoidance, spatial memory and passive avoidance. RHA: di/di rats showed retarded habituation of ambulation and elevated incidence of rearing, defecation, and ambulation in the central area of the open field, relative to RHA: +/+ rats. The RHA: di/di and RHA: +/+ rat did not differ on measures of adaptation to a novel straight runway and both groups increased latencies to enter the goal box of the runway following shock, indicating memory. RHA: di/di rats did exhibit substantial recovery of goal-approach following shock, whereas RHA: +/+ rats did not. Both groups were able to solve a delayed non-match to sample task to receive reward. RHA: di/di rats showed a slower acquisition of the contingency and significantly faster run times of choice trials of the paired run procedure. No differences were evident between groups in memory of passive avoidance. The results of these experiments suggest that hereditary deficiency of vasopressin may influence physiological processes which determine arousal or attentiveness. The effects of vasopressin deficiency on performance of memory-indicating tasks appears to be secondary to modulations in arousal.

Arginine-vasopressin stimulates inositol phospholipid metabolism in rat hippocampus

The hippocampal vasopressin receptors have been characterised by measuring the stimulated accumulation of inositol monophosphate in the presence of 10 mM LiCl after hippocampal slices were prelabelled with [3H]inositol. Arginine-vasopressin caused a dose-dependent increase in inositol monophosphate accumulation (ED50 = 7.1 nM). The response was unchanged in the absence of Ca2+ and significantly reduced in the presence of a V1-receptor antagonist. Equimolar oxytocin was ineffective as a stimulus. This suggests that the hippocampal receptors are of the V1 type.

Vasopressin inhibition of cyclic AMP accumulation and effects on the learned response in inbred mouse strains

The effects of a single injection of arginine vasopressin on the cyclic AMP responses of cerebral cortex slices to noradrenaline, forskolin and 2-chloro-adenosine were tested in six inbred mouse strains. The noradrenaline response was reduced in one strain and that to 2-Cl-adenosine in 2 strains. There was a positive correlation between the differences in the cyclic AMP response to 2-Cl-adenosine between control and AVP-treated mice and the differences in latencies during the extinction period of conditioned avoidance response learning.

Vasopressin neuron survival in neonatal Brattleboro rats; critical factors in graft development and innervation of the host brain

Previously it was found that grafts of supraoptic plus paraventricular areas from 19-day-old foetal normal rats survived in the third ventricle of the brain of 4- to 6-day-old, vasopressin-deficient Brattleboro pups, but could not alleviate their polyuria. In the present series, factors important in graft development were analysed. Again using day-19 fetuses as donors, anterohypothalamus grafts as well as grafts placed near a crushed median eminence survived relatively poorly, but showed the presence of vasopressin neurons immunocytochemically one month post-grafting. Homotopic grafting in the supraoptic nucleus, however, even failed to show surviving vasopressin neurons. Graft survival was improved by the use of donor tissue of fetuses younger than day 19. Parvocellular vasopressin cells were frequently seen, organized into clusters resembling the normal suprachiasmatic nucleus. However, magnocellular neurons, as normally seen in supraoptic and paraventricular nuclei, only survived grafting when taken between days 11 and 15 of fetal age. It was concluded that only immature vasopressin neurons survived grafting under the condition employed. Magnocellular neurons had a limited fiber outgrowth into the host brain and median eminence. Most large neurons only stained with non-specific neurophysin antiserum, not with specific vasopressin-associated neurophysin antiserum. Thin fibers of the parvocellular vasopressin neurons provided only occasional and sparse innervation of the host median eminence and lateral septum (one case), but several examples of massive fiber bundles running dorsally from graft into host brain were observed. These fibers terminated in the thalamic periventricular area, a nucleus that is normally innervated by the vasopressin neurons of the suprachiasmatic nucleus. The failure of the grafts to provide adequate vasopressinergic innervation of the host median eminence probably explains why none of the nearly 200 Brattleboro neonates operated upon showed any sign of relief of their diabetes insipidus. It suggests, however, that the present procedures might be useful in restoring central vasopressinergic functions in the developing Brattleboro rat.

Vasopressin and brain development: studies using the Brattleboro rat

Anomalies in hormonal and neurotransmitter status during early stages of brain development, can lead to lifespan alterations in the functioning of central systems. The neuropeptide vasopressin is nowadays recognized as a putative neurotransmitter, after years of study on its neurosecretory hormonal aspect in water metabolism. Since vasopressin is moreover present early in the brain, and has various mitogenic, metabolic and physiological actions, one might expect vasopressin to be of importance for normal brain development as well. Indeed, the absence of brain vasopressin in the Brattleboro mutant rat coincides with impaired brain development, and some physiological and behavioral defects of these rats are not adjusted by treatment with vasopressin. Regionally the cerebellum seems to be the most affected brain area, both morphologically and biochemically. Only when vasopressin supplementation was done prenatally, this disturbed growth could be restored, which suggests an early role for vasopressin in neurogenesis. Enhanced levels of vasopressin during the perinatal period on the other hand, have been shown to affect permanently the 'setting' of peripheral vasopressin functions in cardiovascular and renal regulatory systems. It is not excluded as yet that after such treatments central organization of vasopressin systems is not impaired as well.

Differences in learning and extinction in response to vasopressin in six inbred mouse strains

Vasopressin was found to enhance acquisition of conditioned avoidance responses in one inbred mouse strain and to retard extinction; in another inbred mouse strain vasopressin depressed the acquisition of conditioned avoidance; in four additional inbred mouse strains vasopressin had no effect on conditioned avoidance learning.

The effect of chronic vs. acute injection of vasopressin on animal learning and memory

The effect of chronic and acute treatment with DDAVP, a vasopressin analog, was studied in 2 month old male rats, using an active avoidance test in a shuttle box. The experiment lasted 6 weeks: an acquisition period of 4 weeks and an extinction period of 2 weeks. Rats were treated one hour before behavioral testing 3 times a week for 6 weeks with either DDAVP 20 micrograms/rat/day for the whole period (chronic group) or with DDAVP for the first week and again once only on the first day of the extinction period (acute group) or with saline. Chronic treatment with DDAVP resulted in better acquisition and in a marked retardation of extinction compared with the acute treatment group. These results were obtained both in normal rats and in rats pretreated at age 5 days of life with intracisternal 6-OH dopamine.