Interaction of vasopressin with the nigro-striatal dopamine system: site and mechanism of action

Long term osmotic stress exposure outcomes on rat dopaminergic innervations and the associated motor behavior

The osmotic stress is a powerful stimulus that elicits profound peripheral and central disturbances. In the mammalian brain, osmotic stress has been associated to several glial and neuronal changes. The lack of data regarding the impact on the dopaminergic system and locomotion led us to investigate the effect of prolonged water deprivation in rat on the midbrain dopaminergic system and locomotor performance by dehydrating rats for one and two weeks. Locomotor activity and tyrosine hydroxylase (TH) expression were assessed using the open field test and immunohistochemistry respectively. Water deprivation was accompanied with a significant increment of TH expression within substantia nigra compacta (SNc) and ventral tegmental area (VTA) gradually as the duration of dehydration increases. While locomotor activity showed the inverse tendency manifested by a drop of crossed boxes number following one and two weeks of water deprivation. Our data suggest a substantial implication of midbrain dopaminergic system in the central response to the osmotic stimuli accompanied with locomotor deficiencies.

The role of the vasopressin system and dopamine D1 receptors in the effects of social housing condition on morphine reward

BACKGROUND

The association with opioid-abusing individuals or even the perception of opioid abuse by peers are risk factors for the initiation and escalation of abuse. Similarly, we demonstrated that morphine-treated animals housed with only morphine-treated animals (referred to as morphine only) acquire morphine conditioned place-preference (CPP) more readily than morphine-treated animals housed with drug-naïve animals (referred to as morphine cage-mates). However, the molecular mechanisms underlying these effects are still elusive.

METHODS

Mice received repeated morphine or saline while housed as saline only, morphine only, or cage-mates. Then, they were examined for the expression levels of D1 dopamine receptor (D1DR), D2 dopamine receptor (D2DR), dopamine transporter (DAT), oxytocin, and Arginine-vasopressin (AVP) in the striatum using qPCR. Additionally, we examined the effects of the AVP-V1b receptor antagonist, SSR149415, on the acquisition of morphine conditioned place-preference (CPP).

RESULTS

Increased striatal expression of D1DR and AVP was observed in morphine only animals, but not morphine cage-mates. No significant effects were observed on the striatal expression of D2DR, DAT, or oxytocin. Antagonizing the AVP-V1b receptors decreased the acquisition of morphine CPP in the morphine only mice, but did not alter the acquisition of morphine CPP in the morphine cage-mate mice.

CONCLUSIONS

Housing with drug-naïve animals protects against the increase in striatal expression of D1DR and AVP elicited by morphine exposure. Moreover, our studies suggest that the protective effect of housing with drug-naïve animals on the acquisition of morphine reward might be, at least partially, mediated by AVP.

Upregulation of striatal dopamine-2 receptors in Brattleboro rats with prepulse inhibition deficits

BACKGROUND

Brattleboro rats (BRATs) have natural deficits in prepulse inhibition (PPI) of the startle response similar to those exhibited by schizophrenia patients, which are reversed by antipsychotics. We sought to determine whether they also have increases in striatal dopamine-2 (D2) receptors found in some studies examining the brains of schizophrenia patients.

METHODS

Several days after startle testing, the brains of BRAT and Long Evans (LE) rats were removed, and D1 and D2 receptor levels were measured by autoradiography.

RESULTS

PPI was lower in BRATs consistent with previous reports. D2, but not D1, receptor binding was significantly higher in the nucleus accumbens shell and the dorsomedial caudate of BRAT compared with LE rats, consistent with some findings in schizophrenia patients. Furthermore, individual rat PPI was inversely correlated with D2 binding density.

CONCLUSIONS

These findings suggest that the dopamine system in BRATs is dysregulated and these abnormalities may contribute to the PPI deficits observed in these rats.

In vivo characterization of the angiotensin-(1-7)-induced dopamine and gamma-aminobutyric acid release in the striatum of the rat

The effect of angiotensin (Ang)-1-7 on dopamine, gamma-aminobutyric acid (GABA) and glutamate release in the striatum of the rat was examined using in vivo microdialysis. Ang-(1-7) was administered locally in the striatum through the microdialysis probe. At a concentration of 100 microm, Ang-(1-7) caused a significant increase in extracellular dopamine and GABA but had no effect on glutamate release. The Ang-(1-7)-induced dopamine release was blocked by EC33, an inhibitor of aminopeptidase A, an enzyme which converts Ang-(1-7) into Ang-(3-7), suggesting that this effect occurs after metabolism into Ang-(3-7). Indeed, administration of Ang-(3-7) (10-100 microm) into the striatum caused a more potent increase in the striatal dopamine release than Ang-(1-7). Because Ang-(3-7) is an inhibitor of insulin-regulated aminopeptidase (IRAP) and because Ang IV, another IRAP inhibitor, also causes a concentration-dependent increase in dopamine in the rat striatum, IRAP may be involved in this effect. In contrast, EC33 had no effect on the Ang-(1-7)-induced GABA increase but the GABA release was blocked by the putative AT(1-7) receptor antagonist A779 (0.1 microm) and by the nitric oxide synthase inhibitor L-NAME (1 mm). These drugs could not block the effect of Ang-(1-7) on the striatal dopamine release suggesting that only the observed effects on GABA release are mediated by the AT(1-7) receptor and/or are associated with a release of nitric oxide.

Desmopressin and vasopressin increase locomotor activity in the rat via a central mechanism: implications for nocturnal enuresis

PURPOSE

Nocturnal enuresis is characterized by nocturnal urine volumes exceeding bladder capacity and by inability to wake up to the stimulus of a full bladder. Desmopressin (DDAVP) is believed to be efficient in treating nocturnal enuresis by reducing nocturnal urine production. However, clinical observations indicate an additional mode of action since the drug appears to modify sleep architecture, apparently improving the patient's ability to awaken to the stimulus of a full bladder. Because of this, a possible arousing effect of DDAVP was studied.

MATERIALS AND METHODS

The tentative ability of DDAVP and the endogenous hormone vasopressin (AVP) to produce locomotor stimulation in resting rats after both intracerebroventricular and subcutaneous administration was used as an animal model of arousal. In addition brain monoamine biochemistry was analyzed.

RESULTS

The intracerebroventricular injection of AVP (0.1 and 1 microgram.) and the intracerebroventricular (0.1, 1, 10 and 100 microgram.) and subcutaneous (90 and 180 microgram.) injections of DDAVP were both associated with a significant increase in the locomotor activity of the animals compared with controls. The biochemical analysis of cerebral monoamines indicated that DDAVP lowers brain dopamine levels after both types of administration.

CONCLUSIONS

These results suggest that DDAVP exerts a stimulatory effect in the CNS, which is also observed after peripheral administration. There are also indications for an increase in central dopamine turnover which could explain the registered increase in locomotor activity.

A facilitatory role of vasopressin in hypoxia/hypoglycemia-induced impairment of dopamine release from rat striatal slices

The excitatory amino acid, glutamate plays a crucial role in the pathogenesis of brain damage caused by anoxia and/or hypoglycemia. Although vasopressin (VP) also acts as an excitatory transmitter in the CNS, little is known about its effect on hypoxic and/or ischemic brain damage. In this study, we investigated the effect of arginine vasopressin (AVP) on hypoxia/hypoglycemia-induced impairment of dopamine release from striatal slices. Striatal slices were incubated in hypoxia-/hypoglycemia-inducing medium with or without AVP (0.01-1.0 microM) for 20 min. After 1-3 h of washout in normal medium, high K(+)-evoked dopamine release from the slices were examined. Hypoxia/hypoglycemia-induced decrease of striatal dopamine release was reversed by the removal of Ca2+ in the medium, but not by VP1- or VP2-receptor antagonist. In contrast, AVP potentiated the hypoxia/hypoglycemia-induced decrease of dopamine release in the striatum. This AVP-induced deterioration of the striatal response was antagonized by VP2 receptor antagonist, but not by VP1 receptor antagonist. The present results suggest that AVP may play a facilitatory role in hypoxia/hypoglycemia-induced dopamine release deficit mediated through the activation of VP2 receptor.

Antidiuretic effects of neurotensin in chloralose anaesthetized dogs

1. Effects of cerebroventricular and/or intravenous infusions of neurotensin (NT), an endogenous tridecapeptide, on haemodynamics and renal function were investigated in chloralose anaesthetized dogs. 2. Cerebroventricular infusions (i.c.v.) of NT (10-6 mol/L and 10-5 mol/L, 0.1 mL/min) for 30 min did not produce any significant alterations in the measured variables. In the vagotomized dogs, intravenous (i.v.) infusion of NT (10(-5) mol/L) at a rate of 0.1 mL/min for 30 min significantly lowered the arterial blood pressure and glomerular filtration rate; these effects were accompanied by pronounced reductions in the urine flow and urinary sodium excretion and marked increases in urine osmolality. 3. In the dogs with vagi intact, i.v. infusions of NT failed to produce any alterations in the blood pressure; however, renal effects of NT were essentially identical to those observed in the vagotomized dogs. 4. Infusions of NT (10(-6) mol/L) and/or NT-metabolites NT1-8 and NT8-13 (10(-5) mol/L) directly into the renal artery failed to produce any significant alterations in the urine flow. Antidiuretic effects of i.v. NT were not prevented by acute renal denervation, adrenalectomy, or pretreatment of the animals with naloxone. However, morphine pretreatment completely abolished the hypotensive and anti-diuretic effects of NT. 5. It is proposed that i.v. infusion of NT rapidly facilitates the secretion of an endogenous substance possessing potent antidiuretic properties and opiate mechanisms are involved in mediating such an effect. Although it appears unlikely, a role for vasopressin cannot be ruled out.

Effect of some peptides on dopaminergic function in man

Thyrotropin-releasing hormone (TRH) (200 micrograms iv) and 1-desamino-8-D-arginine vasopressin (DDAVP) (4 micrograms iv) antagonized the growth hormone (GH) response to apomorphine HCl (Apo) (0.5 mg sc) in 10 normal men. Apo had no effect on basal prolactin (PRL) levels but antagonized the PRL response to TRH. DDAVP plus Apo decreased PRL compared to placebo or DDAVP alone. These observations are compatible with (a) an inhibitory effect of TRH on hypothalamic and pituitary lactotrophe dopamine (DA) function (b) a facilitory effect of DDAVP on lactotrophe DA function and an inhibitory effect on hypothalamic DA function. Whether these are direct or indirect effects on DA mechanisms is unclear.

Effect of vasopressin on the induction of adrenal tyrosine hydroxylase and phenylethanolamine N-methyltransferase

We have assessed the effect of arginine vasopressin (AVP) on adrenal tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) activities. Both enzymes show marked increases after systemic administration of AVP in the range of 66 and 100 micrograms/day. To determine whether the pituitary gland plays a role in these inductions, the effect of AVP (66 micrograms per day, given divided into 3 doses for 4 days) on the adrenal enzymes was studied in hypophysectomized rats. These animals showed induction of TH but not PNMT. This indicates that a pituitary factor(s) mediates the increase in PNMT caused by AVP. Adrenal TH activity was measured after the injection of AVP (1 or 2 micrograms per rat) into the lateral ventricle: there was a statistically significant increase in TH. TH was not induced in the denervated adrenal gland of rats administered AVP systemically. These findings suggest that AVP may act centrally to induce the enzyme. The continuous s.c. infusion of AVP by osmotic minipump at the rate of 1 microgram/day for 6 days led to a striking increase in adrenal TH activity. However, PNMT did not increase significantly. It can be concluded that different mechanisms are involved in the induction of adrenal TH and PNMT caused by AVP. A neural mechanism is involved in TH induction, whereas PNMT induction requires release of a pituitary factor, presumably ACTH, but innervation of the adrenal is not needed for it. Moreover, the inductions of these two enzymes are differentially sensitive to the concentration of circulating AVP.

Depletion of central catecholamines reduces pressor responses to arginine vasopressin

Previous reports that central administration of arginine vasopressin (AVP) increases turnover of brain catecholamines raise the possibility that the pressor responses which follow central administration of AVP may be mediated, in part, by central catecholamines. To test this hypothesis, rats were given intraventricular injections of vehicle, or of the neurotoxin, 6-hydroxydopamine, which resulted in significant depletions of hypothalamic and medulla oblongata noradrenalin and hypothalamic dopamine, but not of medullary dopamine or of hypothalamic and medullary 5-hydroxytryptamine. Following a one week recovery, these conscious rats, fitted with indwelling arterial catheters, were given intraventricular injections of AVP; the increases in arterial pressure and heart rate were significantly reduced in the catecholamine-depleted animals. These data support the hypothesis that the pressor and tachycardia responses to intraventricular AVP are mediated, in part, by central catecholamine-containing neurons.

Microinjection of anti-vasopressin serum into limbic structures of the rat brain: effects on passive avoidance responding and on local catecholamine utilization

Rats which had received bilateral microinjections of 1:50 diluted anti-vasopressin serum into the dorsal or ventral hippocampus, immediately after the learning trial of a one-trial passive avoidance test, showed a reduction in avoidance latency scores during subsequent retention tests 24 and 48 h later. Postlearning microinjection of anti-vasopressin serum into either the dorsolateral septum or the caudate nucleus was without effect on the retention of passive avoidance behavior. Microinjection of anti-vasopressin serum 1 h before the 24-h retention session into either the dorsal hippocampus, the ventral hippocampus or the dorsolateral septum attenuated avoidance responding during both the 24-h and 48-h retention sessions, whereas preretention microinjection of the serum into the caudate nucleus was not effective. Intracerebroventricular administration of the anti-vasopressin serum in amounts similar to those used in the microinjection experiments did not affect retention scores when given either immediately after the learning trial or before the first retention session. One week after the behavioral experiments, a repeated microinjection of anti-vasopressin serum decreased the local alpha-methyl-p-tyrosine methylester (alpha-MPT)-induced disappearance of noradrenaline in the ventral hippocampus and the dorsal hippocampus respectively. Microinjection of the antiserum in the dorsolateral septum enhanced noradrenaline disappearance in this brain region. No effect was found on alpha-MPT-induced dopamine disappearance in the caudate nucleus following local microinjection of anti-vasopressin serum.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced monoaminergic neurotransmission by desglycinamide-arginine-vasopressin in human subjects

The effect of desglycinamide-arginine-vasopressin (DGAVP) on monoaminergic neurotransmission was studied in human subjects. Samples of cerebrospinal fluid (CSF) were collected during 240 min after DGAVP (2 mg) had been administered intranasally, and monoamine metabolites in CSF were measured with HPLC using electrochemical detection. Levels of homovanillic acid and 5-hydroxyindoleacetic acid increased (P less than 0.05) 150 min after DGAVP administration, whereas levels of 3-methoxy-4-hydroxyphenylglycol were stable during the time monitored. These results suggest that in human subjects the mechanism of action of DGAVP may involve dopaminergic and serotonergic systems.

Vasopressin in Alzheimer's disease: a study of postmortem brain concentrations

Vasopressin (AVP) and its analogues are reported to improve learning- and memory-related performance in experimental animals, and perhaps also in humans. Memory impairment is a clinical hallmark of the dementing disorder, Alzheimer's disease. We have examined AVP concentrations in postmortem brain tissue from 12 patients with histologically confirmed Alzheimer's disease and 13 control subjects. AVP was measured by a highly specific and sensitive radioimmunoassay, validated by parallel inhibition curves and high-performance liquid chromatography. Alzheimer brains had either normal or slightly increased AVP levels in the neocortex, which does not have AVP cell bodies. Significant reductions in AVP content were found in the hippocampus, nucleus accumbens, and globus pallidus interna. Levels were normal in all other regions studied. Abnormalities of the brain vasopressin system may contribute to the memory deficit associated with Alzheimer's disease.