Light microscopic autoradiographic visualization of [3H]-arginine vasopressin binding sites in rat brain

Vasopressin: An output signal from the suprachiasmatic nucleus to prepare physiology and behaviour for the resting phase

Vasopressin (VP) is an important hormone produced in the supraoptic (SON) and paraventricular nucleus (PVN) with antidiuretic and vasoconstrictor functions in the periphery. As one of the first discovered peptide hormones, VP was also shown to act as a neurotransmitter, where VP is produced and released under the influence of various stimuli. VP is one of the core signals via which the biological clock, the suprachiasmatic nucleus (SCN), imposes its rhythm on its target structures and its production and release is influenced by the rhythm of clock genes and the light/dark cycle. This is contrasted with VP production and release from the bed nucleus of the stria terminalis and the medial amygdala, which is influenced by gonadal hormones, as well as with VP originating from the PVN and SON, which is released in the neural lobe and central targets. The release of VP from the SCN signals the near arrival of the resting phase in rodents and prepares their physiology accordingly by down-modulating corticosterone secretion, the reproductive cycle and locomotor activity. All these circadian variables are regulated within very narrow boundaries at a specific time of the day, where day-to-day variation is less than 5% at any particular hour. However, the circadian peak values can be at least ten times higher than the circadian trough values, indicating the need for an elaborate feedback system to inform the SCN and other participating nuclei about the actual levels reached during the circadian cycle. In short, the interplay between SCN circadian output and peripheral feedback to the SCN is essential for the adequate organisation of all circadian rhythms in physiology and behaviour.

Prenatal Testosterone Exposure Decreases Aldosterone Production but Maintains Normal Plasma Volume and Increases Blood Pressure in Adult Female Rats

Plasma testosterone levels are elevated in pregnant women with preeclampsia and polycystic ovaries; their offspring are at increased risk for hypertension during adult life. We tested the hypothesis that prenatal testosterone exposure induces dysregulation of the renin-angiotensin-aldosterone system, which is known to play an important role in water and electrolyte balance and blood pressure regulation. Female rats (6 mo old) prenatally exposed to testosterone were examined for adrenal expression of steroidogenic genes, telemetric blood pressure, blood volume and Na⁺ and K⁺ levels, plasma aldosterone, angiotensin II and vasopressin levels, and vascular responses to angiotensin II and arg⁸-vasopressin. The levels of Cyp11b2 (aldosterone synthase), but not the other adrenal steroidogenic genes, were decreased in testosterone females. Accordingly, plasma aldosterone levels were lower in testosterone females. Plasma volume and serum and urine Na⁺ and K⁺ levels were not significantly different between control and testosterone females; however, prenatal testosterone exposure significantly increased plasma vasopressin and angiotensin II levels and arterial pressure in adult females. In testosterone females, mesenteric artery contractile responses to angiotensin II were significantly greater, while contractile responses to vasopressin were unaffected. Angiotensin II type-1 receptor expression was increased, while angiotensin II type-2 receptor was decreased in testosterone arteries. These results suggest that prenatal testosterone exposure downregulates adrenal Cyp11b2 expression, leading to decreased plasma aldosterone levels. Elevated angiotensin II and vasopressin levels along with enhanced vascular responsiveness to angiotensin II may serve as an underlying mechanism to maintain plasma volume and Na⁺ and K⁺ levels and mediate hypertension in adult testosterone females.

Vasopressin and the output of the hypothalamic biological clock

The physiological effects of vasopressin as a peripheral hormone were first reported more than 100 years ago. However, it was not until the first immunocytochemical studies were carried out in the early 1970s, using vasopressin antibodies, and the discovery of an extensive distribution of vasopressin-containing fibres outside the hypothalamus, that a neurotransmitter role for vasopressin could be hypothesised. These studies revealed four additional vasopressin systems next to the classical magnocellular vasopressin system in the paraventricular and supraoptic nuclei: a sexually dimorphic system originating from the bed nucleus of the stria terminalis and the medial amygdala, an autonomic and endocrine system originating from the medial part of the paraventricular nucleus, and the circadian system originating from the hypothalamic suprachiasmatic nuclei (SCN). At about the same time as the discovery of the neurotransmitter function of vasopressin, it also became clear that the SCN contain the main component of the mammalian biological clock system (i.e. the endogenous pacemaker). This review will concentrate on the significance of the vasopressin neurones in the SCN for the functional output of the biological clock that is contained within it. The vasopressin-containing subpopulation is a characteristic feature of the SCN in many species, including humans. The activity of the vasopressin neurones in the SCN shows a pronounced daily variation in its activity that has also been demonstrated in human post-mortem brains. Animal experiments show an important role for SCN-derived vasopressin in the control of neuroendocrine day/night rhythms such as that of the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes. The remarkable correlation between a diminished presence of vasopressin in the SCN and a deterioration of sleep-wake rhythms during ageing and depression make it likely that, also in humans, the vasopressin neurones contribute considerably to the rhythmic output of the SCN.

Differential increase in Fos immunoreactivity in hypothalamic and septal nuclei by arginine8-vasopressin and desglycinamide9-arginine8-vasopressin

Subcutaneous or intracerebroventricular injection of either arginine8-vasopressin or desglycinamide9-arginine8-vasopressin has been shown to facilitate memory, reduce or reverse the effects of amnesic drugs, and maintain tolerance to some effects of ethanol. These actions of vasopressin (and, by inference, of desglycinamide9-arginine8-vasopressin) are mediated by vasopressin V1 receptors in brain, via a c-fos-dependent mechanism, but the receptors at which the desglycinamide analog acts have not been identified. The precise central sites are also not known, but evidence of several types suggested the anterior hypothalamus and septum as probable loci of vasopressin action. In the present work, this question was studied by immunocytochemistry, using antibodies against Fos and Fos-like proteins. The numbers of Fos-immunoreactive nuclei were counted in several related brain regions and structures, after administration of arginine8-vasopressin, des-Gly9-[Arg8]-vasopressin or saline. A subcutaneous injection of vasopressin, but not of saline, enhanced Fos expression in the paraventricular, supraoptic and suprachiasmatic nuclei of the hypothalamus, but the desglycinamide analog stimulated Fos expression only in the suprachiasmatic nucleus. Vasopressin injection significantly increased the number of Fos-immunoreactive cells in the intermediate lateral septum, medial septum, and dorsal and ventral divisions of the lateral septum. In contrast, the desglycinamide analog increased the numbers of Fos-immunoreactive cells in the dorsal and intermediate portions of the lateral septum, but caused no change in the medial septum, and a decrease in the ventral portion of the lateral septum. Increased Fos expression was also found in the subfornical organ after subcutaneous injection of either vasopressin or the desglycinamide analog. Double labeling with antibodies against Fos protein and against vasopressin revealed that most of the vasopressin-induced Fos-immunoreactive cells in the supraoptic, paraventricular and suprachiasmatic hypothalamic nuclei are also vasopressin immunoreactive, i.e. they are vasopressin-producing neurons. These findings suggest that a circuit involving V1 receptors in the subfornical organ, connecting fibres to the suprachiasmatic nucleus, and vasopressinergic projections from the suprachiasmatic nucleus to the lateral septum, may play a central role in mediating the actions of both vasopressin and its desglycinamide analog in the maintenance of ethanol tolerance.

Vasopressin opposes locomotor stimulation by ethanol, cocaine and amphetamine in mice

The effects of arginine8-vasopressin on the stimulation of locomotor activity induced by ethanol, cocaine and amphetamine were examined in DBA/2N mice. Locomotor activity was measured by photocell beam interruption for a period of 45 min following ethanol, cocaine or amphetamine administration. Pretreatment with vasopressin alone in a dose of 2 (but not 1) microg/mouse s.c. reduced locomotor activity. The low dose of vasopressin did not modify the stimulation of locomotor activity induced by i.p. administration of ethanol in doses of either 1.5 or 2 g/kg. The high dose of vasopressin reduced locomotor activity induced by both doses of ethanol, in an apparently additive manner. Cocaine in doses of 15 and 20 mg/kg strongly stimulated locomotor activity, but this stimulation was completely antagonized by pretreatment with 1 microg of vasopressin. Similarly, the stimulation of locomotor activity induced by amphetamine (5 mg/kg) was also blocked by pretreatment with vasopressin. These findings raise the possibility that the effect of vasopressin varies with the extent and nature of dopaminergic involvement in the drug-induced stimulation of activity. For drugs like cocaine or amphetamine which stimulate locomotor activity primarily through the mesolimbic dopaminergic system, vasopressin can completely antagonize the stimulation. For ethanol, which stimulates locomotor activity through action on a number of other neurotransmitters as well as dopamine, vasopressin treatment only reduces its stimulation of locomotor activity in an additive manner. These results suggest a close interaction between vasopressin and dopamine action.

Central vasopressin blockade enhances its peripheral release in response to peripheral osmotic stimulation in conscious rats

Increased plasma osmolality results in increased central as well as peripheral release of vasopressin. Experiments were carried out to determine whether, in this circumstance, vasopressin can act centrally to modulate its peripheral release. Prior to the start of a thirty-min i.v. infusion of 2.5 M or 0.15 M NaCl, the rats were given an intracerebroventricular (i.c.v.) injection of a peptide V1/V2 vasopressin antagonist (2 micrograms), OPC-31260 (60 micrograms), a non-peptide V2 antagonist, or 1-desamino-8-D-arginine vasopressin (dDAVP, 5 ng), a V2 agonist. Experiments with the peptide antagonist were carried out in male and non-estrous female rats. Since there were no differences between males and females in the measured responses, experiments with the other two drugs were carried out only in males. Pretreatment with either the V1/V2 antagonist or the V2 antagonist enhanced the increase in plasma vasopressin levels in response to the hypertonic saline infusion by about 50% at the end of 30 min. dDAVP, on the other hand, had no effect. None of the i.c.v. drugs had an affect on either the pressor or bradycardic responses to hypertonic saline infusion. These observations suggest that vasopressin can act centrally in a negative feedback fashion to attenuate its own release into the peripheral circulation in response to increased plasma osmolality.

Peripheral injection of arginine8-vasopressin increases Fos in specific brain areas

Learned behaviors and tolerance to ethanol can be maintained by peripheral injection of arginine8-vasopressin (vasopressin) under conditions in which they would otherwise be lost. However, the sites of this action in the brain have not been clearly identified. Using a polyclonal antibody raised against Fos and Fos-like proteins, we have demonstrated increases in immunoreactive Fos and Fos-like proteins in the suprachiasmatic, supraoptic and paraventricular nuclei of the hypothalamus, and lesser increases in piriform cortex and amygdala, of the rat 2 h after a s.c. injection of vasopressin. Our results suggest that the exogenous vasopressin may exert its central action by activating a cellular immediate early gene in specific brain regions.

Effects of testosterone on the rat renal medullary vasopressin receptor concentration and the antidiuretic response

The renal concentrating ability declines with age in humans and animals. Studies suggest that the concentrating defect is due to a decrease in renal vasopressin sensitivity. With ageing, expression of the renal vasopressin V2 receptor in rat is impaired; the normal receptor expression is restored by testosterone treatment. The effect of testosterone on the renal sensitivity to vasopressin was investigated in young rats. Male rats after orchidectomy and chronic antiandrogen cyproterone acetate treatment, and female rats after chronic testosterone phenylpropionate treatment, were used. The plasma arginine-vasopressin (AVP) and testosterone concentrations, and the antidiuretic responses to AVP and the V2 agonist deamino-[8-D-arginine]-vasopressin (dDAVP) after volume loading were measured, and the renal [3H]AVP binding density was determined. The plasma AVP level decreased slightly, but not significantly, in male rats after orchidectomy and cyproterone acetate treatment, but did not alter in female rats after testosterone treatment. The AVP and dDAVP sensitivities decreased in male rats after orchidectomy and cyproterone acetate administration, and increased in female rats treated with testosterone, as compared with the animals with a normal gonadal function. [3H]AVP binding to the renal inner medullary membranes was decreased following orchidectomy or antiandrogen treatment in male rats, and increased in testosterone-treated female rats. The results suggest that testosterone may play a physiological role in maintenance of the V2 vasopressin receptor expression and hence in the normal urinary concentrating ability in rat.

Oxytocin and vasopressin binding sites in the hypothalamus of the rat: histoautoradiographic detection

Localization of oxytocin and vasopressin binding sites has so far been studied in the rat brain by means of film autoradiographs. The availability of selective iodinated ligands with high specific activity allowed us to develop the histoautoradiographical technique and to reinvestigate at the microscopic scale the distribution of these sites in the hypothalamus. Most oxytocin binding sites were localized in delimited nuclei, e.g., the medial preoptic, the ventromedial, the ventral premammillary, the supramammillary, and the medial mammillary nuclei. In addition, a weak diffuse specific labeling occurred in the medial preoptic and the anterior hypothalamic areas. The vasopressin binding sites (of the V1a type) were detected in delimited nuclei, e.g., the suprachiasmatic, the stigmoid, and the arcuate nuclei, but they were also diffusely distributed in the lateral hypothalamic and the dorsochiasmatic areas. The locations of neurohypophysial peptides binding sites detected by light microscopy are compared with those previously obtained by film autoradiography.

Hemorrhage-induced vasopressin release in the paraventricular nucleus measured by in vivo microdialysis

Experiments were carried out, using the technique of in vivo microdialysis in conscious rats, to determine whether hemorrhage, a potent stimulus for the release of vasopressin from the posterior pituitary into the circulation, would also result in a local release of vasopressin from the paraventricular nucleus (PVN), and whether this release is affected by gender. Male and non-estrous female rats were prepared with a microdialysis probe adjacent to the PVN and femoral arterial and venous catheters the day before the experiment. On the day of the experiment, rats was bled either 20% or 30% of blood volume. The concentration of vasopressin in the dialysate increased significantly in the males following both hemorrhages and in the females following the 30% hemorrhage. There were no statistically significant differences in the post-hemorrhage dialysate vasopressin concentration with respect to either gender or magnitude of the hemorrhage. The plasma vasopressin concentration increased markedly in response to the hemorrhage and this response was greater in females following the 30% hemorrhage. There were no gender differences in the reduction in arterial pressure following either hemorrhage. It is concluded that physiological stimuli for the release of vasopressin into the circulation also result in intrahypothalamic release of this hormone.

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.

Pressor response to microinjection of clonidine into the hypothalamic paraventricular nucleus in conscious rats

We have reported that intracerebroventricular (i.c.v.) injection of clonidine causes pressor response in conscious rats. To determine the effective brain site, cardiovascular responses induced by unilateral microinjection of clonidine into various hypothalamic nuclei of conscious rats were studied. Microinjection of clonidine (5-20 micrograms/0.5 microliter) into the paraventricular nucleus (PVN) of conscious rats dose-dependently produced a long-lasting pressor response with a decrease in heart rate, which mimicked the response to i.c.v. injection of clonidine. However, clonidine (10 micrograms) injection into various hypothalamic nuclei (anterior, posterior, ventromedial and dorsomedial nucleus) caused a small or no pressor response. In anesthetized rats, clonidine injected into the PVN induced a long-lasting depressor response concomitant with bradycardia. PVN pretreatment with the alpha 2-adrenoceptor antagonist, yohimbine (1 and 10 micrograms), dose-dependently inhibited the pressor response to PVN injected clonidine, but the alpha 1-adrenoceptor antagonist, prazosin (1 microgram), had no significant effect. Central (i.c.v.) pretreatment with the vasopressin (AVP) V1-receptor antagonist, [d(CH2)5Tyr(Me)]-AVP (0.5 and 2.0 micrograms), dose-dependently inhibited the pressor response to PVN injection of clonidine (10 micrograms), while systemic (i.v.) and local (intra-PVN injection) pretreatments with V1-receptor antagonist (2.0 micrograms) had no effect. These results suggest that the pressor response to microinjection of clonidine into the PVN of conscious rats is mediated by endogenous brain AVP, which is released by activation of alpha 2-adrenoceptors. It is also suggested that the PVN is a possible brain site for the pressor response to i.c.v. injected clonidine.

Arginine vasopressin V1-antagonist and atrial natriuretic peptide reduce hemorrhagic brain edema in rats

BACKGROUND AND PURPOSE

Injection of arginine vasopressin into the cerebral ventricles in animals with brain injury increased brain water, whereas injection of atrial natriuretic peptide reduced water content. Therefore, to determine the role of endogenous arginine vasopressin in brain edema, we attempted to inhibit edema from a hemorrhagic lesion with an arginine vasopressin V1 receptor antagonist or atrial natriuretic peptide.

METHODS

Adult Sprague-Dawley rats with hemorrhages induced by 0.4 IU bacterial collagenase were treated with 75 ng (n = 9) or 8 micrograms (n = 9) of the vasopressin V1 receptor antagonist d(CH2)5Tyr(Me)Arg, 3.2 micrograms (n = 4) atrial natriuretic peptide injected intracerebrally, or 5 micrograms/kg per hour (n = 7) atrial natriuretic peptide intraperitoneally. They were compared with control groups injected with 0.4 IU collagenase only. Brain water and electrolytes were measured 24 hours later. Brain uptake of [14C]sucrose was measured 30 minutes after lesions were induced by 0.4 IU collagenase alone (n = 5) or after collagenase injection and 50 micrograms/kg per hour (n = 5) atrial natriuretic peptide injected intravenously.

RESULTS

The arginine vasopressin V1 receptor antagonist and atrial natriuretic peptide significantly (p < 0.05) reduced water and sodium contents in the posterior edematous regions. Brain uptake of [14C]sucrose was significantly reduced by intravenous atrial natriuretic peptide.

CONCLUSIONS

Antagonists to arginine vasopressin V1 receptors and atrial natriuretic peptide both significantly reduce hemorrhagic brain edema, and atrial natriuretic peptide appears to protect the blood-brain barrier.

Central carbachol stimulates vasopressin release into interstitial fluid adjacent to the paraventricular nucleus

We have used an in vivo double microdialysis probe technique in conscious rats to determine whether the application of carbachol to one paraventricular nucleus (PVN) can result in increased local release of vasopressin from that PVN. Experiments were carried out 24 h after placement of microdialysis probes lateral to each PVN. When both probes were perfused initially with 0.9% NaCl, vasopressin was detected in the outflow (dialysate) from both probes. When carbachol (100 micrograms/ml) was included in the perfusate of one probe for the first 10 min of a 30-min collection period, while the other probe continued to be perfused with saline alone, there was a seven-fold increase in the concentration of vasopressin in the dialysate from the carbachol-perfused probe; the vasopressin concentration in the dialysate from the contralateral probe increased only slightly. The plasma vasopressin concentration was also elevated. When one of the paired probes was perfused with carbachol (100 micrograms/ml) for 30 min, there were similar increases in the concentration of vasopressin in the dialysate from both probes and a sustained increase in the plasma vasopressin concentration. Thus, vasopressin is released into the interstitial fluid adjacent to the PVN under basal conditions, and this release can be substantially increased when vasopressin secretion to the periphery is stimulated.

Neurophysins, rather than Receptors, are Involved in [H]Oxytocin and [H]Vasopressin Binding Detected by Autoradiography in the Hypothalamo-Neurohypophyseal System

Abstract The goal of the present experiments was to analyse the binding of oxytocin (OT) and vasopressin (VP) in the hypothalamo-neurohypophyseal system to determine whether [(3)H]OT and [(3)H]VP binding in this system involved interaction with receptor sites or with neurophysins. Using quantitative autoradiography, several experiments were performed to compare [(3)H]OT- and [(3)H]VP-binding characteristics in this system and in brain areas containing identified receptor sites. Saturation experiments indicated much lower affinity of [(3)H]OT and [(3)H]VP binding in the magnocellular nuclei and neural lobe than on brain receptors. Competition experiments using selective ligands indicated interaction with neurophysins rather than with receptors in the hypothalamo-neurohypophyseal system. This system was never labelled in the presence of a [(125)I]OT antagonist, a selective OT receptor ligand. In contrast with receptors elsewhere in the brain, the magnocellular nuclei were labelled by [(3)H]OT and [(3)H]VP in the absence of MgCI(2). In the pituitary neural lobe, density of binding sites was moreover obviously related to the amount of neurosecretory granules, as seen in acutely dehydrated rats. Taken together, these data strongly suggest that in the hypothalamo-neurohypophyseal system [(3)H]OT and [(3)H]VP bind to neurophysins rather than to specific receptors.

Co-localization of putative vasopressin receptors and vasopressinergic neurons in rat hypothalamus

Vasopressin and oxytocin are synthesized by neurons in the paraventricular and supraoptic nuclei of hypothalamus. Dense concentrations of vasopressin binding sites have also been localized in these nuclei. Using a vasopressin anti-idiotypic antiserum, a dual immunocytochemical labeling procedure has been employed to elucidate the distribution of putative vasopressin receptors in anatomical relation to vasopressin and oxytocin immunoreactive cells in rat brain. Putative vasopressin receptors are observed in relation to magnocellular neurons in hypothalamus that are vasopressin immunoreactive. They do not appear to be associated with parvocellular vasopressinergic cells or oxytocin immunoreactive neurons. The presence of these presumed autoreceptors would support evidence that vasopressin may autoregulate the activity of magnocellular vasopressinergic neurons in hypothalamus.

Paraventricular nucleus injections of noradrenaline: cardiovascular effects in conscious Long-Evans and Brattleboro rats

The cardiovascular effects of noradrenaline injected into the hypothalamic paraventricular nucleus (PVN) were investigated in conscious Long-Evans (control) rats and homozygous vasopressin (AVP)-deficient Brattleboro rats. Unilateral microinjection of noradrenaline (3-30 nmol) into the PVN produced dose-dependent increases in systolic and diastolic blood pressure of Long-Evans rats, and a concomitant decrease in heart rate. Only the highest dose of noradrenaline tested (30 nmol) caused a significant pressor response in Brattleboro rats (9 +/- 4/9 +/- 4 mm Hg, systolic/diastolic, n = 7) which was significantly smaller than the response produced by the same dose of noradrenaline in Long-Evans rats (32 +/- 8/27 +/- 6 mm Hg, n = 7). Intravenous pretreatment of Long-Evans rats with the V1-receptor antagonist, d(CH2)5Tyr[Et]DAVP, almost completely abolished the pressor effect of noradrenaline (10 nmol) without significantly attenuating the bradycardia. The alpha 2-adrenoceptor antagonist, idazoxan (4 nmol), injected into the PVN abolished the pressor response produced by noradrenaline (10 nmol) in Long-Evans rats but had no significant effect on the bradycardia. Pretreatment with the alpha 1-adrenoceptor antagonist, prazosin (0.7 nmol), significantly attenuated both the pressor and bradycardic effects of noradrenaline in Long-Evans rats. These results suggest that the pressor response produced by microinjection of noradrenaline into the hypothalamic PVN of conscious Long-Evans rats is mediated largely through stimulation of alpha 2-adrenoceptors and is dependent, in part, on release of AVP into the circulation. A component of the bradycardia seen with this intervention may be mediated through stimulation of alpha 1-adrenoceptors in the PVN.

Autoradiographic localization of V1 vasopressin binding sites in rat brain and kidney

Monoiodination of the V1 vasopressin antagonist [Mca1,Sar7]AVP did not alter its high-affinity binding to liver plasma membranes. Monoradioiodinated [Mca1,125I-Tyr2,Sar7]AVP was therefore used to label V1-specific binding sites in the rat brain and kidney. The accumbens nucleus, the septal nucleus, the central amygdala, the bed nucleus of the stria terminalis, the stigmoid hypothalamic nucleus and the nucleus of the solitary tract exhibited specific labeling with both the radioiodinated V1 antagonist and tritiated AVP. Of the circumventricular structures only the choroid plexi and the area postrema showed V1-specific binding sites. The subfornical organ and hypothalamic loci of AVP synthesis such as the paraventricular nucleus, the supraoptic nucleus and the suprachiasmatic nucleus were not marked by the V1 antagonist while bearing [3H]AVP binding sites. As demonstrated by HPLC and binding to liver plasma membranes, the radiolabeled antagonist remained intact during tissue incubation. In addition to renal cortical and medullary [3H]AVP binding sites, medullary tubular and vascular structures could be labeled with the V1 antagonist, indicating the presence of both V1 and V2 AVP receptor subtypes in the rat kidney.

Autoradiographic localization of binding sites for vasotocin in the brain and pituitary of the sea bass (Dicentrarchus labrax)

Specific binding sites for vasotocin (VT) were detected in brain and pituitary of a teleost fish, the sea bass, after in vitro incubation of tissue sections with [3H]arginine-vasopressin (AVP) and light microscopic autoradiography. Conditions for the binding assay were optimized and as a result the binding was saturable and specific. In the brain [3H]AVP binding was found to occur in the pars lateralis and the pars ventralis of the ventral telencephalon, in the pars centralis of the dorsal telencephalon, in the hypothalamic region (especially in the nucleus preopticus, in the tuberal hypothalamus and around the posterior recess), in the tectum opticum and in the noncellular layer of the corpus cerebelli. In the pituitary a high density of [3H]AVP binding was observed in the areas of the pars distalis (PD) occupied by ACTH-, TSH- and GH-cells and also in the pars intermedia (PI). The present study presents the first anatomical evidence for the presence of VT specific binding sites in teleost brain and pituitary.

Enhanced phosphoinositol hydrolysis in response to vasopressin in the septum of the homozygous Brattleboro rat

Arginine8-vasopressin (AVP) receptors in the septum of the Long-Evans rat have been shown to be both pharmacologically (displacement profiles) and functionally (ability to stimulate phosphoinositide hydrolysis) similar to the peripheral V1-type receptor for AVP. Previous binding studies of AVP receptors in the septum of heterozygous (HE) and homozygous (vasopressin-deficient, HO) Brattleboro (BB) rats revealed an increased number of receptors with a lower affinity for AVP in the HO-BB rat when compared to the HE-BB rat. To determine the effect of these receptor changes in the HO-BB rat septum on the postreceptor response of the tissue to AVP, concentration-response relationships for AVP-stimulated phosphoinositide hydrolysis were examined in septal slices from age-matched, adult male HE- and HO-BB rats. AVP-stimulated accumulation of [3H]inositol-1-phosphate (IP1) was significantly greater in the HO-BB (43.7%) than in the HE-BB (13.7%) at AVP concentrations of 10(-08) to 10(-05) M. The two groups did not, however, differ in their ability to stimulate [3H]IP1 accumulation in response to 2.0 mM carbachol. When the AVP-stimulated phosphoinositide response in both genotypes was compared to that obtained for the Long-Evans (LE) rat (the parent strain of the Brattleboro rat) septum under the same assay condition, it was found that the response in the HE-BB was much lower than in the LE. AVP receptor binding capacity (Bmax) correlated (r = 0.975) with release of IP1 ([3H]IP1 accumulation) for all 3 groups studied (LE, HE, HO).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of hypothyroidism on high-affinity vasopressin binding sites in developing hippocampal synaptosomes

Binding sites of vasopressin (VP) have been characterized in the hippocampal synaptic plasma membranes of developing normal and hypothyroid rats using a highly specific tritiated VP antagonist, d(CH2)5Tyr(Me)VP (V1 type). This antagonist bound to an apparently homogeneous population of specific sites with an affinity ten times higher than that of VP itself. The total amount of synaptosomal protein in 15-day-old normal rats represented about 50% of the adult value, but the density of binding sites was already maximal and remained constant thereafter, supporting the concept of an early development of an extrahypophyseal vasopressinergic hippocampal system. Thyroid deficiency specifically reduced the amount of synaptosomal protein. However, the binding site density in the synaptsomal fraction appeared to be relatively well preserved from hypothyroidism, although there was a transient decrease in the apparent affinity of the ligand. These data suggest that thyroid hormones are slightly involved in the early development of high-affinity VP receptors.

Localization of vasopressin binding sites in rat brain by in vitro autoradiography using a radioiodinated V1 receptor antagonist

Vasopressin may act in the brain as a neurotransmitter or neuromodulator to influence blood pressure, memory, body temperature and brain development. In order to localize probable central nervous system sites for these actions, we have used 125I-labelled 1-d(CH2)5, 7-sarcosine-8-arginine vasopressin, a specific V1-receptor antagonist, and in vitro autoradiography to map brain vasopressin binding sites. High levels of binding were found in the choroid plexus, blood vessels, lateral septum, bed nucleus of stria terminalis, accumbens nucleus, central nucleus of amygdala, stigmoid hypothalamic nucleus, suprachiasmatic nucleus, arcuate nucleus, nucleus of the solitary tract, area postrema and parts of the hippocampus, thalamus, superior colliculus, and inferior olivary nuclei. Many of these regions are known to be vasopressin-sensitive and to contain vasopressin fibres. Significantly there was no binding to the paraventricular nor the supraoptic nuclei. Displacement of the radioligand from the lateral septum with unlabelled vasopressin analogues gave a rank order of potencies: d(CH2)5-D-Tyr2(Et)Val4-desGly9-arginine-vasopressin approximately equal to d(CH2)5-Tyr2-(Me)arginine-vasopressin approximately equal to arginine-vasopressin approximately equal to d(CH2)5-Sar7-arginine-vasopressin greater than [1-deamino, 8-D-arginine]-vasopressin approximately equal to oxytocin much greater than vasopressin4-9, consistent with binding to V1 receptor subtype. These studies confirm and extend previous findings of V1 receptors in the rat brain. In particular, several new regions of vasopressin receptor binding have been identified, possibly due to the advantages of a radioiodinated ligand with high receptor affinity without binding to neurophysins. Future study of these regions may prove fruitful in elucidating the central actions of vasopressin.

Testosterone alters the behavioral response of the medial preoptic-anterior hypothalamus to microinjection of arginine vasopressin in the hamster

The medial preoptic-anterior hypothalamus (MPOA-AH) is necessary for expression of several testosterone-dependent behaviors including a form of hamster scent marking, called flank marking. Since arginine vasopressin (AVP) plays a critical role in the control of flank marking by the MPOA-AH the present study examined whether testosterone can influence the amount of flank marking produced by AVP microinjected into the MPOA-AH. The dose-dependent induction of flank marking by AVP was found to be reduced by approximately 50% in castrated male hamsters when compared to intact or testosterone-treated castrates. These data demonstrate that testosterone influences the amount of flank marking produced by AVP within the MPOA-AH.

Quantitative autoradiographic mapping of neurohypophysial hormone binding sites in the rat forebrain and pituitary gland--I. Characterization of different types of binding sites and their distribution in the Long-Evans strain

Oxytocin and vasopressin binding sites were localized and characterized by quantitative autoradiography on consecutive sections of Long-Evans rat forebrains and pituitary glands, incubated in the presence of 5 nM [3H]oxytocin or 5 nM [3H]vasopressin. In the forebrain, two types of neurohypophysial hormone binding sites were thus defined. (1) Oxytocin/vasopressin sites with similar nanomolar-range affinities for [3H]oxytocin and [3H]vasopressin; both tritiated peptides were displaced from these sites in the presence of 10 microM of either oxytocin or vasopressin. The main areas bearing such sites were the ventral subiculum, several nuclei of the amygdala, the ventromedial hypothalamic nucleus, the bed nucleus of the stria terminalis and the olfactory tubercle. (2) Selective vasopressin sites, binding [3H]vasopressin with nanomolar-range affinity and [3H]oxytocin with a much lower affinity; these sites were not labelled in the presence of 5 nM [3H]oxytocin, and 10 microM oxytocin displaced [3H]vasopressin binding by 80%. Such sites occurred in several thalamic nuclei, in the dopaminergic A13 cell group of the zona incerta, the suprachiasmatic nucleus, the fundus striati and the lateral septal nucleus. No selective oxytocin sites were detected. Different oxytocin and vasopressin binding characteristics were found in the hypothalamo-neurohypophysial system. In the paraventricular and supraoptic nuclei and in the pituitary neural lobe the [3H]vasopressin binding density was twice that of [3H]oxytocin; vasopressin was always more potent than oxytocin in displacing both [3H]vasopressin and [3H]oxytocin binding from those sites. Interaction of the tritiated peptides with neurophysins cannot be completely ruled out in these locations. The present data are discussed in correlation with the functional roles of the neurohypophysial peptides in the brain and the pharmacological characteristics of their receptors.

[3H]arginine vasopressin binding to rat brain: a homogenate and autoradiographic study

Arginine-vasopressin (AVP) has been implicated as a putative central neurotransmitter or neuromodulator in some brain functions. This study demonstrates binding of [3H]AVP to rat brain homogenates that is pH and temperature dependent, is saturable (Kd = 0.77 nM, Bmax = 0.374 pmol/mg) and reversible. A number of AVP analogues competitively displaced the [3H]AVP binding, indicating that central AVP binding sites may have a resemblance to the peripheral (V1) AVP vasopressor receptor. Homogenate binding occurred predominantly in the microsomal fraction (P3) of the hypothalamus while in the hippocampus and septum binding was predominantly in the synaptosomal fraction (P2). Autoradiographic methods showed displaceable [3H]AVP binding in the lateral septum, amygdala, supraoptic, paraventricular and suprachiasmatic nuclei of the hypothalamus supporting the results of homogenate binding in preparations of these regions.

Subcellular localization and characterization of vasopressin binding sites in the ventral septal area, lateral septum, and hippocampus of the rat brain

[Arg8]-Vasopressin (AVP) has been shown to exert characteristic central physiological actions in the ventral septal area of the rat brain. This study reports the characterization of receptors for AVP in synaptic plasma membranes prepared from the ventral septal area, the lateral septum, and the hippocampus. Binding of [3H]AVP was temperature and time dependent, linearly related to protein concentration, saturable, and specific. Scatchard plot analysis suggested the presence of a population of binding sites in the three brain areas with dissociation constants and maximal binding capacities, respectively, of 1.06 +/- 0.39 nM and 24.0 +/- 7.01 fmol/mg of protein (mean +/- SEM; n = 3 for the ventral septal area, 0.92 +/- 0.13 nM and 47.0 +/- 4.96 fmol/mg of protein (n = 3) for the lateral septum, and 0.91 +/- 0.14 nM and 25 +/- 5.02 fmol/mg of protein (n = 3) for the hippocampus. In all three brain regions, the rank order of potencies of several vasopressin analogs, unrelated peptides, and other compounds for competitive displacement of ligand indicated a receptor with properties resembling those of the V1-like receptor for AVP. These data document the presence of a high-affinity, V1-like vasopressin receptor in the rat ventral septal area for which the pharmacological properties are similar to those previously reported in physiological studies.

Staining of magnocellular neurons of the supraoptic and paraventricular nuclei with vasopressin anti-idiotype antibody: a potential method for receptor immunocytochemistry

A vasopressin anti-idiotype antibody was generated by immunization with a primary anti-vasopressin IgG. This antibody was capable of immunostaining vasopressinergic neurons in the supraoptic and paraventricular nuclei of the hypothalami of normal and Brattleboro rats. Staining was eliminated by preabsorption or coincubation of the antibody with a vasopressin binding protein prepared from rat neural membranes. The anti-idiotype also inhibited binding of [3H]vasopressin to this neural membrane protein in a dose-dependent manner. These experiments suggest that the anti-idiotype antibody recognizes a receptor associated with vasopressinergic neurons.

Neonatal administration of vasopressin antiserum induces long-term deficits on active and passive avoidance behaviour in rats

Two-day-old male rats received a subcutaneous injection of arginine-vasopressin (AVP) antiserum and avoidance behaviour was studied 3 months later. Rats treated with the antiserum showed a clear retention deficit in a one-trial learning, step-through passive avoidance situation. Anti-AVP treatment also induced an impairment on the acquisition of a two-way active avoidance task. Systolic blood pressure was lower than normal in these animals. The results obtained appear to be indicative of the high vulnerability of the developing nervous system, and are discussed in the context of the different hypothesis on the role of central or peripheral mechanisms in the behavioural effects of AVP. Although no definite conclusions may be drawn in this regard, the present data strongly suggest that neonatal administration of AVP antiserum exerts long-lasting effects upon the functionality of several physiological mechanisms related to the behavioural adaptation of the organism.

Pharmacological characteristics and anatomical distribution of [3H]oxytocin-binding sites in the Wistar rat brain studied by autoradiography

Oxytocin-binding sites were detected by autoradiography on rat brain sections incubated in the presence of the [3H]oxytocin. These sites were characterized pharmacologically using quantitative autoradiography. High pressure liquid chromatography controls of the incubation media indicated that labelling was due to the intact [3H]oxytocin molecule. Pharmacological analysis of different locations (central amygdaloid nucleus, ventral subiculum and ventromedial hypothalamic nucleus) showed that the sites detected had a high affinity for oxytocin and also for arginine-vasopressin. In contrast, some areas known to bind vasopressin intensely, such as suprachiasmatic and lateral septum nuclei, had little or no affinity for oxytocin. Autoradiographs revealed [3H]oxytocin-binding sites in already known brain areas (olfactory centres, ventral subiculum, central amygdaloid nucleus, bed nucleus of the stria terminalis) albeit with more extensive labelling of some of these formations, in particular, the amygdaloid complex. In addition, specific [3H]oxytocin-binding sites were found in areas not yet reported to bind oxytocin, such as the paraventricular thalamic and caudate nuclei. In the hypothalamus, specific binding sites were not detected in the supraoptic and paraventricular nuclei: the only structure labelled was the ventrolateral part of the ventromedial nucleus. Discrepancies between the concentrations of [3H]oxytocin-binding sites, the known distribution of oxytocin-containing endings and electrophysiological data indicate that autoradiography, under our conditions, apparently only reveals some of the oxytocin receptors in the brain. Thus, in the hypothalamus, no relationship can be established between the known effect of oxytocin on oxytocinergic magnocellular neurons and detection of specific [3H]oxytocin-binding sites. Autoradiography may reveal mainly oxytocin-binding sites in areas receiving diverse "parasynaptic" information, where oxytocin might play a modulatory role rather than exerting rapid, short-term effects of the neurotransmitter type.

Immunocytochemistry of magnocellular neurons of supraoptic and paraventricular nuclei of normal and Brattleboro rats with vasopressin anti-idiotype antibody

A vasopressin anti-idiotype antibody was generated by immunization with purified IgG of a primary vasopressin antiserum. The anti-idiotype antibody immunostained neurons in the supraoptic and paraventricular nuclei of the hypothalamus of normal and Brattleboro rats. The distribution of immunostained perikarya in these hypothalamic nuclei together with the staining of fibers in median eminence and neural lobe was similar to that observed in normal rats with anti-vasopressin and suggests strongly that vasopressinergic neurons are being stained. Absorption studies with vasopressin and a vasopressin-binding receptor protein further indicate that a receptor associated with vasopressinergic neurons is recognized by the anti-idiotype antibody.

Immunocytochemically-stained vasopressin binding sites in rat brain. Ventricular application of vasopressin/Accurel in the Brattleboro rat

An immunocytochemical procedure was developed to localize binding sites for vasopressin (VP) in the brain of Brattleboro (di/di) rats after 2 weeks of continuous ventricular administration of the peptide. Accurel-polypropylene tubing loaded with 0.15, 1.5 or 15 micrograms vasopressin was implanted into the lateral ventricle. Subsequently, bound VP was detected immunocytochemically in 2 distinct patterns: in perineuronal structures and dots between cells, in the lateral septum (dorsorostral part), striatum, cingulate cortex, granular cells of the dentate gyrus of the hippocampus, pyramidal cells of CA1 and CA3 hippocampal areas and around cerebellar Purkinje cells. The high dose (15 micrograms) loaded implants revealed the most intense staining; in the cytoplasm of neuronal cell bodies in the lateral and medial septum, striatum, cingulate cortex, bed nucleus of the stria terminalis, organum vasculosum of the laminae terminalis and locus coeruleus. The most intense staining in cell bodies was observed in brains which had low-loaded implants (0.15-1.5 microgram). A variety of controls, proved that no aspecific uptake was involved in the present procedure. The distribution of VP binding sites was only partly coincident with known sites of VP fiber innervation, and largely agrees with data obtained by autoradiographic techniques for [3H]VP binding. The present immunocytochemical technique gave a higher resolution than the currently used autoradiographic techniques. The differences in pattern and intensity of staining due to increasing the dosage rate of the in vivo vasopressin treatment, might mean that the current procedure retains preferentially either low or high affinity populations of binding sites depending on the implanted dose.

Facilitation of avoidance behavior by vasopressin fragments microinjected into limbic-midbrain structures

Effects of arginine vasopressin (AVP1-9) and its behaviorally active fragments [Cyt6]AVP5-9 and [Cyt6]AVP5-8 were studied on the retention of one-trial learning passive avoidance behavior in rats. Peptides were microinjected into various limbic and midbrain structures (ventral or dorsal hippocampus or the dorsal raphe nucleus) and were administered either immediately after the learning trial (post-learning treatment) or shortly before the 24 h retention session (pre-retention treatment). Doses for intracerebral microinjections were selected after preliminary experiments with subcutaneous and intracerebroventricular peptide administration. AVP1-9 facilitated passive avoidance behavior when the peptide was microinjected into either brain structure, however, the ventral hippocampus appeared to be the most sensitive. In this limbic region, AVP1-9 facilitated passive avoidance behavior in an amount of 8 pg (bilaterally), both when given as post-learning or pre-retention treatment. [Cyt6]AVP5-9 and [Cyt6]AVP5-8 were more effective than the parent nonapeptide in terms that a lower amount of these peptide fragments facilitated passive avoidance behavior in all brain regions investigated. The ventral hippocampus appeared to be the most sensitive brain site for the behaviorally active vasopressin fragments as well. Following microinjections into the ventral hippocampus, [Cyt6]AVP5-8 was more effective in a post-learning than in a pre-retention treatment schedule. [Cyt6]AVP5-9 on the other hand was more effective when injected shortly before the retention trial. The data indicate that limbic-midbrain structures are sensitive to AVP1-9 and behaviorally active putative metabolites of this neuropeptide. The active fragments selectively influence different phases of information processing upon limbic microinjections.

Long-term hyperalgesia in rats induced by neonatal administration of vasopressin antiserum

Vasopressin antiserum was given to two day old rats and the nociceptive thresholds were evaluated three months later. The rats were hypersensitive to pain when electrical current, but not heat, was used as the noxious stimulus. These animals were also insensitive to cold-water swim, a non-opioid form of stress analgesia. The vasopressin content in the pituitary or in the hypothalamus was not however modified by the neonatal treatment. The present results suggest a physiological role for vasopressin in non-opioid pain inhibitory systems.

Prevention of arginine-vasopressin-induced motor disturbances by a potent vasopressor antagonist

The antivasopressor analog d(CH2)5Tyr(Me) arginine-vasopressin completely blocked the convulsive-like behavior and other severe motor disturbances which are normally observed following a second central arginine-vasopressin injection. This vasopressor antagonist appears to be selective for arginine-vasopressin-induced motor disturbances, in that the convulsive and motor effects of pentylenetetrazol and somatostatin were not altered significantly by pretreatment with the central antagonist. Results suggest that arginine-vasopressin-induced motor disturbances are mediated via central receptors. The classic antidiuretic (V2) type of arginine-vasopressin receptor does not appear to be involved, since the agonist 1-desamino-8-D-arginine-vasopressin did not elicit convulsive-like behavior or other severe motor disturbances 2 days following a first ('priming') injection of arginine-vasopressin.

Two classes of arginine vasopressin binding sites on rat brain membranes

Specific binding sites for arginine vasopressin (AVP) were demonstrated on rat brain membranes using [3H]AVP of high specific activity. At pH 7.4 in the presence of 5 mM MgCl2, one class of sites was measured with a KD of 0.56 nM and a Bmax of 4.3 fmol/mg protein. At pH 8.0 in the presence of MgCl2, two distinct sites were observed, having KD values of 0.42 and 13 nM and Bmax values of 5.6 and 68 fmol/mg protein, respectively, and similar results were obtained at pH 7.4 after repeatedly freezing and thawing the membranes. Binding increased with pH, apparently representing increased occupancy of the high capacity, lower affinity site. Binding to the lower affinity site was also enhanced by freezing and thawing membranes, or by adding 5 mM NiCl2 or 10 microM ZnCl2 to the incubation medium, whereas binding to the high affinity site was dependent on the addition of Mg. AVP was over 35 times more active in displacing 0.4 nM AVP than oxytocin or arginine-vasotocin, and 10,000 times more active than somatostatin. A number of other peptides had no effect on [3H]AVP binding at concentrations up to 10(-5) M. Autoradiography and regional dissection studies revealed a marked concentration of high affinity AVP-binding sites in the supraoptic and paraventricular nuclei of the hypothalamus, and Mg significantly enhanced the binding in these regions.

Strategies in neuropeptide receptor binding research

Strategies and general approaches used in neuropeptide receptor binding assays are described. Special attention is given to the nature of the ligand, its physical and chemical stability and the demonstration of an appropriate ligand selectivity pattern. Examples are given to illustrate critical aspects of neuropeptide receptor binding assays. Strong correlation between binding and bioassay data is also stressed.

Administered peptides inhibit the degradation of endogenous peptides. The dilemma of distinguishing direct from indirect effects

Virtually all peptides are biologically active following central administration as a consequence of both direct and indirect cellular actions. Direct effects are mainly interactions with specific membrane receptors but may include unions with other components of the receptor/effector complex. Significant indirect biological effects of exogenous peptides, including apparent secretagogue effects on endogenous peptides largely overlooked in practice, result from extensive competition with endogenous peptides for degradative enzymes (peptidases). A consequence of this competition is enhancement of tonic or intermittent activity of endogenous peptides. The pharmacological profile of any peptide reflects or includes, therefore, the spectrum of endogenous peptides that is protected from peptidase action. It is likely that certain pharmacologically active peptides, including a large number of di-, tri- and oligo-peptides, elicit responses mainly or exclusively by competing for peptidases. Therefore, reliable estimates of the relative contributions of direct and indirect actions of exogenous peptides may be difficult, if not impossible, to obtain.

Potentiation of vasopressin analgesia in rats treated neonatally with monosodium glutamate

The analgesic response elicited by central administration of arginine vasopressin (AVP) appears to be dependent upon the integrity of the hypothalamic paraventricular nucleus (PVN), since lesions placed in the PVN eliminate AVP analgesia. A projection to the zona externa of the median eminence constitutes one of the VP-containing efferents of the PVN. Neonatal treatment with monosodium glutamate (MSG) destroys perikarya of the arcuate nucleus and median eminence. The present study examined whether AVP analgesia was affected in the MSG-treated rat and whether these alterations were accompanied by specific changes in VP immunoreactivity in the zona externa of the median eminence. Female rats, neonatally treated with either MSG or a saline control, were tested as adults on the tail-flick test following intracerebroventricular injections of 0, 75, 150 and 500 ng doses of AVP. After testing, selected animals were prepared for AVP and oxytocin immunocytochemistry of the median eminence. Significant potentiations in the magnitude of AVP analgesia were observed in MSG-treated rats. AVP and oxytocin immunoreactivity in the zona interna and oxytocin immunoreactivity in the zona externa of the median eminence were similar in MSG-treated and control rats. In contrast, AVP immunoreactivity in the zona externa of the median eminence was markedly reduced in the MSG-treated rat. These data suggest that VP analgesia may normally be inhibited by those medial-basal hypothalamic neurons affected by neonatal MSG treatment.

Topography of binding sites for neurohypophyseal hormones in rat brain

Binding sites for arginine-vasopressin (AVP) and oxytocin (OT) were detected in neuroanatomically defined regions of rat brain by using in vitro incubation of 32 micron brain sections with the tritium-labelled ligands and autoradiography with LKB Ultrofilm. Sites were quantified by computerized densitometry of the film images. The highest amount of [3H]AVP-labelled binding sites were observed in the ventral subiculum of the hippocampus, central amygdala nucleus, lateral septum, olfactory nucleus and nucleus tractus solitarii, while the dentate gyrus contained a large amount of low affinity binding. The binding pattern of [3H]OT was more discrete. Relatively high concentrations of OT binding sites were observed in the central amygdala, ventral subiculum and olfactory nucleus. The lateral septum and the nucleus tractus solitarii were virtually devoid of displaceable OT binding while no significant association of OT with the dentate gyrus was found. The topography of binding sites for neurohypophyseal hormones corresponds to the localization of responsive sites in behavioural, biochemical and electrophysiological studies.

Site of interaction of serotonin and desglycinamide-arginine-vasopressin in maintenance of ethanol tolerance

Rats trained to walk in a moving belt apparatus were subjected to a partial (fornix-fimbria (FF] or total (fornix-fimbria + cingulum bundles (FF + CB] chemical denervation of the dorsal serotonergic afferent pathways to the hippocampus. After chronic alcohol treatment that resulted in tolerance development to the motor-impairing effects of ethanol, desglycinamide-arginine8-vasopressin (DGAVP) or saline treatment was started and the residual tolerance measured at several intervals after ethanol withdrawal. DGAVP administration resulted in a virtually complete retention of ethanol tolerance when given to sham-operated controls or FF-lesioned rats. The peptide treatment failed, however, to prolong tolerance in rats bearing a complete FF + CB lesion, that reduced serotonin (5-HT) levels in the hippocampus and overlying parietal cortex to 10 and 45% of controls respectively. These results suggest that the serotonergic innervation of these areas is necessary for the action of DGAVP in the maintenance of ethanol tolerance.

Atrial natriuretic factor (ANF) binding sites in brain and related structures

Visualization of [125I]ANF binding sites in rat brain by an autoradiographic technique demonstrated that these sites are highly localized in areas such as the olfactory bulb, subfornical organ, area postrema and nucleus tractus solitarius. This distribution suggests that certain cardiovascular effects of ANF could be centrally mediated and that the existence of brain ANF-related peptides should be considered. Finally, moderate densities of [125I]ANF binding sites are found in the rat and guinea pig eye while low densities are seen in pituitary and pineal gland.

Regional distribution of putative vasopressin receptors in rat brain and pituitary by quantitative autoradiography

Quantitative light microscopic autoradiography was used to map and characterize the distribution of [3H]arginine vasopressin [( 3H]AVP) binding sites in the rat brain. HPLC analysis for possible degradation of AVP during binding indicated that addition of specific peptidase inhibitors prevented metabolism of AVP. Binding sites for [3H]AVP were observed in the hypothalamus and pituitary as well as in brain regions where AVP may act as a neuroregulator. Within the hypothalamus, dense AVP binding sites were seen in the suprachiasmatic, supraoptic, and paraventricular nuclei. High specific binding was also apparent in the median eminence tubero-infundibular region and in the posterior lobe of the pituitary. [3H]AVP labeling at possible neuroregulatory sites was observed in the hippocampus, lateral septum, superficial cortex, cerebellum, nucleus tractus solitarious, adenohypophysis, and spinal cord.

Quantitative receptor autoradiography with tritium-labeled ligands: comparison of biochemical and densitometric measurements

Tritium-labeled receptor ligands are commonly used for quantitative receptor autoradiography with LKB Ultrofilm. In this study, we compared estimates of tritium concentrations by optical density measurements with direct measurements of tritium concentrations by scintillation counting. We found that predominantly grey matter regions of rat brain showed similar tritium concentrations when measured by either method, but that optical density reading of white matter regions indicated a lower tritium concentration than determined by direct measurement with scintillation counting. We also compared measurements of receptor density by quantitative autoradiography with radioligand-binding measurements on microdissected brain regions. Higher per milligram protein levels of muscarinic receptors were obtained by quantitative autoradiography, comparable to the specific activity of receptors found in purified membranes.

Vasopressin analgesia: specificity of action and non-opioid effects

Recent neuroanatomical and behavioral evidence has indicated that vasopressin (VP) increases pain thresholds. In the present study intracerebroventricular (ICV) administration of both arginine VP (AVP: 75-500 ng) and 1-deamino-8-D-arginine vasopressin (DDAVP: 150-500 ng) elevated tail flick latencies. Oxytocin (OXY, ICV), also elevated tail-flick latencies (150-1000 ng); however this increase was accompanied by "barrel-roll" seizure activity. VP analgesia was eliminated by pretreatment with 1-deamino-penicillamine-2(O-methyl)tyrosine-AVP (dPTyr(me)AVP: 500 ng, ICV), a VP antagonist, but not naloxone (1 or 10 micrograms, ICV), suggesting that VP modulates nonciceptive thresholds through its own binding sites. Conversely, pretreatment with naloxone (1 micrograms, ICV) but not dPTyr(me)AVP (1 microgram, ICV) attenuated the analgesic efficacy of systemic morphine (10 mg/kg), further dissociating VP and central opiate analgesic processes. Finally, systemic pretreatment with dexamethasone potentiated VP analgesia. These data support the notion that VP is a specific non-opioid pain inhibitor.

Levels of arginine-vasopressin in cerebrospinal fluid during passive avoidance behavior in rats

The concentration of immunoreactive arginine-vasopressin (IR-AVP) was measured in the cerebrospinal fluid (CSF) during acquisition and retention of passive avoidance behavior. IR-AVP level in CSF of male Wistar rats immediately after the learning trial was increased; the rate of which was related to the intensity of the electric footshock during the learning trial and the avoidance latency as measured 1 day after the learning trial. Immediately after the 24 h retention test IR-AVP levels were significantly increased in rats subjected to the low (0.25 mA) shock intensity during the learning trial, but IR-AVP levels of rats exposed to the high shock (1.0 mA) were under the limit of detection. If the retention test was postponed till 5 days after the learning trial, the increase of IR-AVP level in the CSF was related to avoidance latencies which reflect the intensity of aversive stimulation (electric footshock). The results suggest an association between central AVP release and passive avoidance behavior and may be indicative of the role of this peptide in neuronal mechanisms underlying learning and memory processes.

Arginine-vasopressin binding sites in rat brain: a quantitative autoradiographic study

Specific binding sites for arginine-vasopressin (AVP) were detected in rat brain after incubation of tissue sections with [3H]AVP. AVP and two selective AVP antagonists are capable of displacing [3H]AVP with an IC50 in the 10(-8)-10(-7) molar range, while oxytocin and ACTH4-10 were much less effective. The neuroanatomical distribution of [3H]AVP-labeled sites was studied with autoradiography utilizing tritium-sensitive LKB film and computerized densitometry for quantitative analyses of the film images. The highest density of [3H]AVP binding sites was observed in hippocampal regions, the lateral septum, olfactory and amygdaloid nuclei, and the nucleus tractus solitarii (NTS) of the brainstem.