Arginine vasopressin and a vasopressin antagonist peptide: opposite effects on extinction of active avoidance in rats

Navigating Monogamy: Nonapeptide Sensitivity in a Memory Neural Circuit May Shape Social Behavior and Mating Decisions

The role of memory in mating systems is often neglected despite the fact that most mating systems are defined in part by how animals use space. Monogamy, for example, is usually characterized by affiliative (e.g., pairbonding) and defensive (e.g., mate guarding) behaviors, but a high degree of spatial overlap in home range use is the easiest defining feature of monogamous animals in the wild. The nonapeptides vasopressin and oxytocin have been the focus of much attention for their importance in modulating social behavior, however this work has largely overshadowed their roles in learning and memory. To date, the understanding of memory systems and mechanisms governing social behavior have progressed relatively independently. Bridging these two areas will provide a deeper appreciation for understanding behavior, and in particular the mechanisms that mediate reproductive decision-making. Here, I argue that the ability to mate effectively as monogamous individuals is linked to the ability to track conspecifics in space. I discuss the connectivity across some well-known social and spatial memory nuclei, and propose that the nonapeptide receptors within these structures form a putative “socio-spatial memory neural circuit.” This purported circuit may function to integrate social and spatial information to shape mating decisions in a context-dependent fashion. The lateral septum and/or the nucleus accumbens, and neuromodulation therein, may act as an intermediary to relate socio-spatial information with social behavior. Identifying mechanisms responsible for relating information about the social world with mechanisms mediating mating tactics is crucial to fully appreciate the suite of factors driving reproductive decisions and social decision-making.

Hypothalamic Vasopressinergic Projections Innervate Central Amygdala GABAergic Neurons: Implications for Anxiety and Stress Coping

The arginine-vasopressin (AVP)-containing hypothalamic magnocellular neurosecretory neurons (VPMNNs) are known for their role in hydro-electrolytic balance control via their projections to the neurohypophysis. Recently, projections from these same neurons to hippocampus, habenula and other brain regions in which vasopressin infusion modulates contingent social and emotionally-affected behaviors, have been reported. Here, we present evidence that VPMNN collaterals also project to the amygdaloid complex, and establish synaptic connections with neurons in central amygdala (CeA). The density of AVP innervation in amygdala was substantially increased in adult rats that had experienced neonatal maternal separation (MS), consistent with our previous observations that MS enhances VPMNN number in the paraventricular (PVN) and supraoptic (SON) nuclei of the hypothalamus. In the CeA, V1a AVP receptor mRNA was only observed in GABAergic neurons, demonstrated by complete co-localization of V1a transcripts in neurons expressing Gad1 and Gad2 transcripts in CeA using the RNAscope method. V1b and V2 receptor mRNAs were not detected, using the same method. Water-deprivation (WD) for 24 h, which increased the metabolic activity of VPMNNs, also increased anxiety-like behavior measured using the elevated plus maze (EPM) test, and this effect was mimicked by bilateral microinfusion of AVP into the CeA. Anxious behavior induced by either WD or AVP infusion was reversed by CeA infusion of V1a antagonist. VPMNNs are thus a newly discovered source of CeA inhibitory circuit modulation, through which both early-life and adult stress coping signals are conveyed from the hypothalamus to the amygdala.

Acute prosocial effects of oxytocin and vasopressin when given alone or in combination with 3,4-methylenedioxymethamphetamine in rats: involvement of the V1A receptor

The neuropeptides oxytocin (OT) and vasopressin (AVP) are recognized for their modulation of social processes in humans when delivered peripherally. However, there is surprisingly little evidence for acute social effects of peripherally administered OT or AVP in animal models. On the other hand, the party drug 3,4-methylenedioxymethamphetamine (MDMA, 'Ecstasy') has powerful prosocial effects in rats that appear to occur through stimulation of central OT release. Here, we directly compared the social effects of peripherally administered OT and AVP with those of MDMA, and examined a possible role for the vasopressin 1A receptor (V1AR) in the observed prosocial effects. Adult male Long-Evans rats were tested in a social interaction paradigm after OT (0.1, 0.25, 0.5, and 1 mg/kg, intraperitoneal (IP)), AVP (0.001, 0.0025, 0.005, 0.01, and 0.1 mg/kg, IP), and MDMA (2.5, 5 mg/kg, IP), or combined low doses of OT and MDMA, or AVP and MDMA. The effects of pretreatment with the non-peptide OT receptor antagonist compound 25 (C25; 5 mg/kg, IP) and the V1AR antagonist SR49059 (1 mg/kg, IP) were also examined. OT (0.5 mg/kg), AVP (0.01 mg/kg), and MDMA (5 mg/kg) potently increased 'adjacent lying', where rats meeting for the first time lie passively next to each other. C25 did not inhibit adjacent lying induced by OT, whereas SR49059 inhibited adjacent lying induced by MDMA (5 mg/kg), OT (0.5 mg/kg), and AVP (0.01 mg/kg). Interestingly, when ineffective doses of OT and MDMA, or AVP and MDMA, were combined, a robust increase in adjacent lying was observed. These results show for the first time acute prosocial effects of peripherally injected OT and AVP in laboratory rats, and suggest a commonality of action of OT, AVP, and MDMA in stimulating social behavior that involves V1ARs.

Peripheral vasopressin accelerates extinction of conditioned taste avoidance

Both peripheral and central administration of vasopressin improves retention and delays extinction when given before or after acquisition of shock avoidance learning. For conditioned taste avoidance, however, vasopressin prolongs extinction when injected peripherally before acquisition tests and accelerates extinction when infused intracerebroventricularly after acquisition. The following experiments were designed to determine whether this inconsistency is based on the route of administration or timing of vasopressin treatment. Because acquisition of conditioned taste avoidance is strengthened when an agent that is capable of inducing avoidance is administered after LiCl injection, it was determined in experiment 1 that a 6 microg/kg dose of vasopressin did not induce conditioned taste avoidance when administered 50 min after consumption of a sucrose solution. In experiment 2, it was determined that this dose of vasopressin accelerated extinction of a LiCl-induced conditioned taste avoidance when given 50 min after LiCl injection. These results suggest that the inconsistency is not based on route of administration. In experiment 3, it was determined that there was a tendency for animals to show prolonged extinction when vasopressin was administered 20 min before access to a sucrose solution. All of the results taken together suggest that the differential effects of vasopressin on extinction are due to the timing of administration. It was suggested that vasopressin accelerates extinction when given after acquisition by reducing the effectiveness of LiCl and it prolongs extinction when given before acquisition by altering neural responsiveness in areas mediating conditioned taste avoidance.

Pinealectomy blocks modulation of active avoidance by central vasopressin application in rats

The inter-relationship between central vasopressin and the pineal gland in the modulation of active avoidance behavior was investigated. In sham-operated (SO) rats, intracerebroventricular (i.c.v) application of 10 ng arginine vasopressin (AVP) after both the last acquisition and the first extinction trials prolonged the extinction of the active avoidance response; application of 50 ng of the V1 antagonist, d(CH2)5Tyr(Me)AVP (AAVP) was without effect in both experiments. In contrast to the SO in pinealectomized (PX) rats neither AVP nor AAVP influenced the extinction of the avoidance response. Intraseptal infusion of 200 pg AVP or 5 ng AAVP either after the last acquisition or the first extinction trial was without effect in both SO and PX rats. Comparison of the acquisition trials revealed no differences between SO and PX rats.

Central infusion of vasopressin in male rats accelerates extinction of conditioned taste avoidance induced by LiCl

In shock avoidance tasks, extinction is prolonged when vasopressin is infused into the lateral ventricle after an acquisition session. Experiments were performed to determine whether a dose of vasopressin that does not induce conditioned taste avoidance (CTA) could prolong extinction of a LiCl-induced CTA when it is infused into the lateral ventricle of Sprague-Dawley male rats after acquisition. The first experiment was designed to determine whether infusion of vasopressin into the lateral ventricle would induce a CTA. Consumption of a sucrose solution was paired with infusion of vasopressin or saline, and even after two pairings, none of the vasopressin-treated rats showed decreases in sucrose consumption. Therefore, in the second experiment, this same dose of vasopressin was infused into the lateral ventricle 50 min after consumption of a sucrose solution was paired with an injection of LiCl. Vasopressin increased the rate of extinction of the LiCl-induced CTA. These results are the opposite of what has been found after peripheral administration of vasopressin before acquisition and/or extinction of a LiCl-induced CTA. Possible reasons for the difference in the direction of the effect on extinction include differential effects of vasopressin depending on the route of administration, the timing of injection, and the presence of aversive effects produced by the neuropeptide.

Neurohypophyseal peptides and social recognition in rats

An encounter between rats results in bouts of social investigation consisting mainly of sniffing, nosing, following and grooming. The assessment of social recognition is based on the tendency of rodents to investigate unfamiliar conspecifics more intensely, than familiar ones. In the laboratory an immature conspecific is normally used as the social stimulus because the use of juveniles eliminates possible sexual and/or aggressive behaviors of the rat whose memory is assessed. When a juvenile is presented for the first time, it is intensely investigated. A second presentation shortly after the first one elicits less attention. This is not due to satiation or fatigue, since the presentation of a novel juvenile triggers the full sequence of investigation. Social recognition is defined as a specific decrease in social investigation during the second encounter of the same individual. This form of memory is short lasting (< 40 min) and based on the olfactory characteristics of the stimulus animal. Social memory is prolonged by repeated exposure to the stimulus juvenile rat and is impaired by retroactively interfering stimuli. It can be facilitated by vasopressin and derivatives as well as by several other memory facilitating compounds, and, depending on the dose, attenuated or facilitated by oxytocin and derivatives. Ethologically oriented memory tests, that are based on olfactory characteristics of the information to-be-remembered, have an advantage over 'classical' ones: they estimate behavioral patterns which are important to an animal and not only to the investigator. Social memory paradigms can reveal information about memory processes in animals that is relevant for memory deficits in humans.

Role of vasopressin in learning and memory in the hippocampus

The involvement of arginine8-vasopressin (VP) in learning and memory in the hippocampus is examined in mice using a discriminative learning task. Bilateral dorsal hippocampal lesion blocks the enhancing effect of intracerebroventricular (i.c.v.) injection of VP on retrieval and relearning processes. An additional study showed that immunoneutralization of dorsal hippocampal endogenous VP inhibited the facilitating effect of i.c.v. injection of VP, suggesting that hippocampus is essential for the expression of VP's behavioral effects. Using in situ microinjection, a greater sensitivity of the ventral part of the hippocampus to the memory enhancing effects of VP has been reported. This effect is mediated by vasopressin V1 type receptors and oxytocin receptors. Then, we examined the effects on behavior of VP applied to the ventral hippocampus, in relation to the time of treatment during learning. When the animals have no previous information about the task to learn, a deleterious effect of VP appears (pre-first session treatment). Regarding memory consolidation, the effects of VP may depend upon the previous level of performance acquired by the animals since, when injected after the first learning session, the peptide slightly delayed performance, whereas when the injection took place after the second learning session, it enhanced learning. Concerning memory retrieval, the effects of VP depend on the quality of the previously stored information. The fact that VP did not generate the same behavioral effects when the treatment was performed at the beginning or in the middle of the learning processes, suggests that mnemonic context is an important factor in understanding the effect of VP on memory in the ventral hippocampus. Finally, the role of hippocampal adrenergic receptors in the enhancing VP effects on memory retrieval has been examined. The facilitatory effects of VP seem to depend upon the functional state of both alpha- and beta-adrenergic receptors, but further studies will be necessary to clarify the role played by each receptor type in retrieval processes, and to determine the relationships that might exist between them.

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.

Effects of arginine8-vasopressin administered at different times in the learning of an appetitive visual discriminative task in mice

A visual discrimination task was used to investigate the effect of the intra-hippocampal injection of arginine8-vasopressin (AVP) in male Balb/c mice at different stages of the learning processes. The peptide was bilaterally microinjected at a dose of 25 pg per animal, i.e. 833 pg/kg, into the ventral hippocampus, in a volume of 0.3 microliter 10 min before either the first or the second learning session, or immediately after the first or second learning session. Following pre-session administration of AVP, no effect of the peptide was observed on the session prior to which it was administered. On the other hand, 48 h after the pre-first session treatment, it seems that AVP animals had trouble learning the task. Following post-session injection of AVP, no effect was observed when the treatment was given after the first learning session and a tendency to improve performance was noted when the treatment was given after the second learning session. Thus, whatever time AVP was injected during learning, little or no effect was observed. These results and previous work on the same behavioral task showing a clear enhancing effect of the peptide on retrieval processes, suggest that prior experience or mnemonic context before AVP treatment is as important a factor in understanding the effects of AVP on memory processes as the administration route or the doses used.

The block of central vasopressin V1 but not V2 receptors suppresses grooming behavior and hypothermia induced by intracerebroventricular vasopressin in male rats

The role of central vasopressin V1 receptors in grooming behavior induced by vasopressin and oxytocin was studied in male rats of the Wistar strain. The intracerebroventricular (ICV) injection of vasopressin (3 micrograms/5 microliters) induced hypothermia and enhanced novelty-induced grooming behavior. Enhanced grooming but not hypothermia was also induced by ICV injection of oxytocin (3 micrograms/5 microliters). The central administration of a selective vasopressin V1 receptor antagonist prevented the stimulating action of vasopressin on novelty-induced grooming and its hypothermic effect. The ICV injection of a selective vasopressin V2 receptor antagonist failed to affect vasopressin-induced grooming and hypothermic effect. An increase in core temperature was observed in oxytocin-injected animals pretreated with the vasopressin V1 receptor antagonist. Furthermore, pretreatment with the antagonist did not affect grooming induced by oxytocin. These results suggest that enhancement of grooming behavior and influence on thermoregulation are differently regulated by central receptors for vasopressin and oxytocin.

Vasopressin deficiency abolishes a sexually dimorphic behavior in Brattleboro rats

The role of vasopressin (VP) in a sexually dimorphic behavior, the extinction of a conditioned taste aversion, was investigated in male and female rats of three different genotypes. This behavior was examined with a two bottle test in the wild-type Long-Evans (LE) rats, and then in partially VP deficient heterozygous (HET-BB) and completely VP deficient homozygous (HO-BB) Brattleboro rats. In Experiment 1, non-deprived male and female LE rats were given aversions to a sucrose solution by pairing it with a LiCl injection. The rate of extinction of the aversion upon reexposure to ad lib sucrose solution was examined and observed to be sexually dimorphic. Female LE rats extinguished at a significantly more rapid rate than males. Experiment 2 compared HET-BB and HO-BB male and female rats using the same paradigm. Neither of these VP-deficient groups showed sexual dimorphism of the extinction behavior. The data suggest that intact VP levels are necessary to observe the expression of this sexually dimorphic behavior.

Vasopressin regulates human sleep by reducing rapid-eye-movement sleep

In two double-blind experiments, effects of intravenous infusion of arginine vasopressin (AVP) on sleep were evaluated in 2 groups of 10 men (20-35 yr). In experiment I, subjects were tested on two occasions, during which they received either placebo or 0.33 IU/h AVP. In experiment II, on three different occasions, subjects received either placebo or 0.66 or 0.99 IU/h AVP. Infusions were administered between 2200 and 0700 h. Nocturnal plasma AVP concentrations were close to the upper limit of the normal physiological range during 0.66 IU/h AVP (16.6 +/- 2.2 pg/ml) but markedly exceeded this range during 0.99 IU/h AVP (25.0 +/- 1.6 pg/ml). Results indicate primary effects of AVP on rapid-eye-movement (REM) sleep, with moderate reductions in REM sleep during 0.33 IU/h AVP (averaging -10.5%) and with substantial reductions in REM sleep (-24.0%) during 0.66 IU/h AVP. During 0.99 IU/h AVP the effect did not further increase (-24.4%). Less consistent effects of AVP were an increase in stage 2 sleep and in time awake. Effects of AVP were not mediated by changes in cortisol or blood pressure. Results suggest AVP to participate in REM sleep regulation under normal physiological conditions.

The enhancement of retention induced by vasopressin in mice may be mediated by an activation of central nicotinic cholinergic mechanisms

Immediate post-training subcutaneous administration of lysine vasopressin (LVP, 0.003-1.00 microgram/kg) enhanced retention, whereas the vasopressin antagonist AAVP (0.01-0.30 microgram/kg) impaired it, in male Swiss mice tested 48 h after training in an inhibitory avoidance task. Both effects were dose-dependent. Neither LVP nor AAVP affected response latencies in mice not given the footshock on the training trial. The simultaneous administration of AAVP at a dose (0.01 microgram/kg) which had no effect on retention shifted the dose-response curve of LVP to the right. Nicotine (1.0-30.0 micrograms/kg, sc), a central nicotinic cholinergic agonist, also facilitated retention in a dose-related manner without affecting the retention performance of unshocked mice. The effect of nicotine was prevented by the central acting nicotinic cholinergic receptor antagonist mecamylamine (5 mg/kg, sc.). In contrast, neither hexamethonium (5 mg/kg, sc), a peripheral acting nicotinic receptor blocker, nor atropine (0.5 mg/kg, sc) or methylatropine (0.5 mg/kg, sc), two anticholinergic drugs which are known to act on muscarinic cholinergic receptors, prevented the effect of post-training nicotine. The effects of LVP and nicotine were time-dependent, suggesting that both treatments enhanced retention by influencing post-training processes involved in memory storage. Low doses of nicotine (1.50 microgram/kg, sc) or the central anticholinesterase physostigmine (35 micrograms/kg, sc) and LVP (0.003 microgram/kg, sc), which had no effect on retention when administered alone, produced a synergistic interaction when given together following training. The influence of LVP (0.03 microgram/kg, sc) on retention was prevented not only by AAVP (0.01 microgram/kg, sc) but also by mecamylamine (5 mg/kg, sc), whereas the effects of nicotine (10.0 micrograms/kg, sc) were prevented only by mecamylamine. These results suggest that the enhancement of retention induced by vasopressin is probably due to an activation of central nicotinic cholinergic mechanisms which are critical for memory formation.

Interactive effects of neurohypophyseal neuropeptides with receptor antagonists on passive avoidance behavior: mediation by a cerebral neurohypophyseal hormone receptor?

The neurohypophyseal neuropeptides (Arg8)-vasopressin (AVP) and [pGlu4,Cyt6]AVP-(4-8) (where pGlu is pyroglutamic acid and Cyt is cystine) facilitate the retention of one-trial-learning passive avoidance behavior in rats when administered into the cerebral ventricle immediately after the learning trial. The fragment [pGlu4,Cyt6]AVP-(4-8) was considerably more effective than AVP. Oxytocin (OXT) and [pGlu4,Cyt6]OXT-(4-8) have the opposite effect and attenuate passive avoidance behavior also when administered into the cerebral ventricle after the learning trial. Again the fragment was more active than the parent molecule. The ancient arginine-containing neurohypophyseal hormone vasotocin in "high" doses (10ng) had a vasopressin-like effect and in "low" doses (0.1 ng) had an OXT-like effect on passive avoidance behavior. Because both vasopressinergic (V1) and oxytocinergic receptors have been demonstrated in the central nervous system, we asked whether specific antagonists of the V1, V2, and OXT receptor could antagonize the effects of these neuropeptides on passive avoidance behavior. The three antagonists were approximately equally active in blocking the effect of vasopressin, whereas the fragment [pGlu4]AVP-(4-8) and the high dose of vasotocin were more readily blocked by the OXT antagonist. The attenuating effect of OXT, the fragment [pGlu4,Cyt6]OXT-(4-8), and the low dose of vasotocin was markedly reduced by the OXT antagonist. This effect could also be reduced by pretreatment with the V1 antagonist but not with the V2 antagonist. These results suggest the existence of a separate neurohypophyseal hormone receptor complex in the brain affecting memory processes that differs from the peripheral V1, V2, and OXT receptor.

Vasopressin in the septal area of the golden hamster controls scent marking and grooming

Microinjection of arginine vasopressin into the lateral septum and bed nucleus of the stria terminalis of male hamsters stimulates intense flank marking and flank gland grooming, while microinjections of vasopressin in sites immediately adjacent to these areas or in the lateral ventricle are ineffective. Microinjections of oxytocin, angiotensin II and the behaviorally active C-terminal fragment of vasopressin, metabolite neuropeptide, by comparison, do not stimulate flank marking. Effective sites for vasopressin injection are clearly superimposable upon autoradiographically defined sites of high V1-receptor density. Furthermore, vasopressin-sensitive neurons in the lateral septum and bed nucleus of the stria terminalis are necessary for the expression of naturally elicited flank marking since the microinjection of a V1-receptor antagonist into these sites was able to temporarily block flank marking triggered by odors from conspecifics.

Role of neuropeptides in learning versus performance: focus on vasopressin

Neuropeptides that have classical hormonal functions via the pituitary have been implicated in cognitive function. Systemically and centrally administered arginine vasopressin (AVP) has been well documented to prolong extinction and improve consolidation in avoidance tasks. However, major questions have centered on the physiological mechanism of action for these effects and whether these cognitive enhancing actions reflect learning or performance. Work with vasopressin antagonists has led to the hypothesis that the effects of systemically administered AVP may be mediated peripherally and may be secondary to increases in blood pressure and activating effects. Centrally administered AVP, however, can also facilitate memory and recent work using an olfactory social memory task suggests that these effects may be mediated, at least in part, by AVP systems in the lateral septum. These results suggest that the cognitive enhancing actions of AVP may involve two parallel, but ultimately homologous, systems at the functional level. Pituitary-derived AVP may facilitate memory actions through more nonspecific (performance) effects, whereas centrally derived AVP may facilitate memory actions through more direct effects on the neural substrates of memory processing in the limbic system.

Inhibition of vasopressin-stimulated flank marking behavior by V1-receptor antagonists

Flank marking, a form of olfactory communication displayed by hamsters, is dependent upon vasopressin-sensitive neurons in the anterior hypothalamus. In the present study two vasopressin type-1 (V1) receptor antagonists, d(CH2)5Tyr(Me)AVP and dPTyr(Me)AVP were tested for their ability to block flank marking stimulated by the microinjection of arginine vasopressin (AVP) into the anterior hypothalamus. Dose-response curves were established for AVP and flank marking in the presence or absence of different concentrations of each antagonist. DPTyr(Me)AVP was microinjected into the anterior hypothalamus 1 h before the microinjection of AVP while d(CH2)5Tyr(Me)AVP and AVP were prepared together and delivered as a single microinjection. This procedure was necessary because dPTyr(Me)AVP, but not d(CH2)5Tyr(Me)AVP, had agonist activity when initially injected into the anterior hypothalamus in concentrations ranging from 0.90-900 microM. The ED50 values (microM) for dPTyr(Me)AVP and AVP were 17.9 and 0.90, respectively. The initial agonist activity of dPTyr(Me)AVP was always followed by blocker activity. Both V1-receptor antagonists caused a dose-dependent decrease in AVP-stimulated flank marking. Maximal inhibition of AVP-stimulated flank marking was produced with approximately 1.0 mM of either antagonist. Both antagonists blocked AVP-stimulated flank marking behavior for over 12 h following their microinjection.

Vasopressin modulates the activity of nicotinic cholinergic mechanisms during memory retrieval in mice

Lysine vasopressin (0.03 micrograms/kg, sc) enhanced retention test performance on a one-trial step-through inhibitory avoidance task when injected into male Swiss mice 20 min before the retention test. Tests were done 48 h following training. A low dose of the vasopressin antagonist AAVP (0.01 microgram/kg, sc, 20 min prior to testing) did not significantly affect retention test performance, whereas a higher dose (0.03 microgram/kg, sc) impaired it. Neither lysine vasopressin nor AAVP when given prior to testing modified latencies to step-through of mice that had not received a footshock during training. The simultaneous administration of AAVP (0.01 microgram/kg, sc) prevented the enhancement of retention test performance induced by lysine vasopressin. The influence of lysine vasopressin on retention test performance was antagonized by the simultaneous administration of mecamylamine (5 mg/kg, sc) but not by hexamethonium (5 mg/kg, sc), atropine (0.5 mg/kg, sc), or methylatropine (0.5 mg/kg, sc). A modulatory role of vasopressin on the activity of central cholinergic nicotinic mechanisms which probably operate at the time of testing is suggested.

Neonatal treatment with vasopressin antagonist dP[Tyr(Me)2]AVP, but not with vasopressin antagonist d(CH2)5[Tyr(Me)2]AVP, inhibits body and brain development and induces polyuria in the rat

Two vasopressin antagonists, d(CH2)5[Tyr(Me)2]AVP and dP[Tyr(Me)2]AVP, were given to Wistar rats from postnatal day 1 to 21 in order to investigate the influence on development and later diuresis. The latter antagonist significantly reduced body growth from day 3 postnatally onwards. At postnatal day 35 body, total brain, cerebellar and kidney weights were significantly reduced compared with controls. Diuresis, measured at one month of age, was four- to five-fold higher than the control group. Combined treatment with vasopressin failed to abolish the weight disturbances or polyuria. However, animals treated with the vasopressin antagonist d(CH2)5[Tyr(Me)2]AVP did not show developmental or diuretic deficits. Allometric analysis of brain/body relationship of the young animals indicated a disturbance of brain development by dP[Tyr(Me)2]AVP. Although the body and brain growth retardation induced by dP[Tyr(Me)2]AVP supports the hypothesis of a role for vasopressin in brain ontogeny, it can also be the result of a nonAVP-related toxic effect, since it could not be prevented by concomitant treatment with vasopressin.

Neonatal administrations of a vasopressin analog (DDAVP) and hypertonic saline enhance learning behavior in rats

Groups of newborn Wistar rats received daily 1-desamino-8-D-arginine-vasopressin (DDAVP), oxytocin (OXT), hypertonic saline or normal saline for 14 days from day 1 to day 14 of life. One or three months later they were trained in a maze for brightness discrimination (BD). A group of untreated adult male rats received posttrial DDAVP or normal saline for brightness discrimination. Subsequently all the retentions of BD were tested after one month. We found that the neonatal treatments with both DDAVP and hypertonic saline facilitated acquisition and subsequent maintenance of brightness discrimination in immature and mature rats, and also that posttreatment with DDAVP enhanced retention of BD in adult rats. Oxytocin and normal saline had no effect on these parameters. The results are interpreted as showing that endogenous AVP and its synthetic analog enhance the development and adult function of central neural substrates involved in learning behaviors.

Mecamylamine prevents the enhancement of retention induced by lysine vasopressin in mice

Lysine vasopressin (0.03 microgram/kg, sc) enhanced retention of a one-trial, step-through inhibitory avoidance task when injected into male Swiss mice immediately post-training, as indicated by retention performance 48 h later. A low dose of the vasopressin antagonist, AAVP (0.01 microgram/kg, sc), did not significantly affect retention, whereas a higher dose (0.03 microgram/kg, sc) impaired retention. Neither lysine vasopressin nor AAVP modified latencies to step-through of mice that had not received a footshock during training. The simultaneous injection of AAVP (0.01 microgram/kg, sc) prevented the enhancement of retention induced by lysine vasopressin. The influence of lysine vasopressin on retention was antagonized by the simultaneous administration of mecamylamine (5 mg/kg, sc) but not by hexamethonium (5 mg/kg, sc), atropine (0.5 mg/kg, sc), or methylatropine (0.5 mg/kg, sc). A modulatory role of vasopressin on the activity of central cholinergic nicotinic mechanisms which participate in memory formation is suggested.

Centrally injected arginine vasopressin (AVP) facilitates social memory in rats

'Memory' for a juvenile conspecific in male rats can be measured by variation in duration of investigation times when the same juvenile is presented at different intervals. Typically, exposure of an adult male rat to a juvenile results in transient investigatory activity that rapidly declines with repeated exposures at short interexposure intervals (30 min). Longer interexposure intervals (120 min) result in re-investigation with durations similar or greater than the original investigation. Arginine vasopressin (AVP) injected into adult male rats intracerebroventricularly in doses of 0.5-2.0 ng immediately after investigation of the juvenile decreased social investigation of the same juvenile at the long (120 min) interexposure interval. This decrease in investigatory time was similar to that observed after a 30-min interexposure interval in untreated animals. These results support the hypothesis that increasing the availability of AVP in the central nervous system can improve the consolidation of olfactory information and improve conspecific recognition in rats.

Hypertonic saline mimics the effects of vasopressin on inhibitory avoidance in the rat

Rats tested in a step-through inhibitory avoidance task were administered hypertonic saline (2 ml of 0.25. 0.5, and 1.0 M intraperitoneally) or arginine vasopressin (1.0, 2.0, and 4.0 micrograms) injected subcutaneously (sc) after the training trial where the rats received a mild footshock (0.2 mA, 3 s). Both hypertonic saline and vasopressin produced significant increases in latency to reenter 24 h later. These treatments failed to increase reentry latencies in animals that received the same procedure but no shock. The facilitation of inhibitory avoidance produced by hypertonic saline was reversed by sc administration of 25 micrograms of the vasopressor (V-1) vasopressin antagonist, dPtyr(Me)AVP. The results suggest that the endogenous release of vasopressin can be behaviorally significant in situations of acute homeostatic challenge.

Central injections of arginine vasopressin prolong extinction of active avoidance

Behavioral and physiological effects of arginine vasopressin (AVP) were examined following intracerebroventricular (ICV) injection in the rat. ICV injections prolonged extinction of active avoidance at doses of 1.0 and 10.0 ng/rat and this effect was blocked by peripheral injection of the vasopressor antagonist of vasopressin [dPtyr(Me)AVP] at a dose of 30 micrograms/kg (SC). However, 1.0 ng of AVP ICV failed to alter systemic blood pressure and also failed to produce taste aversions in a one or two bottle test. Results suggest that central AVP has a central action independent of systemic changes in blood pressure, but that the receptor mediating this action is functionally similar to the AVP V1 (vasopressor) receptor.

Vasopressin metabolite, AVP4-9, binding sites in brain: distribution distinct from that of parent peptide

Binding sites for the vasopressin metabolite peptide, (AVP4-9), were detected in the rat brain. These binding sites were present in the hilus of the hippocampal formation, superior and inferior colliculus, pontine reticular nuclei, brainstem nuclei, lateral mammillary nucleus, choroid plexus and subfornical organ. The distribution of AVP4-9 binding sites was distinct from that of the parent peptide (1-3). This distinction was apparent in both the regional and intra-regional distribution.

Elimination of vasopressin analgesia following lesions placed in the rat hypothalamic paraventricular nucleus

Pain thresholds are increased following central administration of arginine vasopressin (AVP), an effect which appears not to be mediated through opioid analgesic processes. In addition to magnocellular projections to the posterior lobe of the pituitary gland and parvocellular projections to the zona externa of the median eminence, the paraventricular nucleus (PVN) of the hypothalamus contains VP parvocellular neurons which also project to extrahypothalamic structures involved in pain inhibition. The present study examined whether AVP analgesia as measured by the tail-flick test was altered in animals with lesions placed in the PVN at either 7 or 35 days after surgery. VP levels in the pons-medulla and the lumbo-sacral spinal cord were measured by radioimmunoassay, as well as VP-like immunoreactivity in the PVN and spinal cord with immunocytochemistry. Lesions placed in the PVN eliminated AVP analgesia on the tail-flick test at both 7 and 35 days after surgery, and decreased radioimmunoassayable VP by 59% in the lumbo-sacral spinal cord and 36% in the pons-medulla. The extent of the lesions ranged from complete destruction of the PVN to partial sparing of ventro-medial PVN cells with VP-like immunoreactivity. These data indicate that the PVN is a critical structure for the integrity of AVP analgesia.

A mnemonic role for vasopressin: the evidence for and against

This review critically evaluates the animal and human research concerning vasopressin's putative mnemonic role. Weaknesses in the interpretations of the early animal experiments as well as the implications of the later inconsistent findings are discussed. It is concluded that both the initial enthusiasm and the subsequent skepticism concerning this hypothesized role were premature. This conclusion applies equally to the human research. A review of these studies reveals that almost all of the negative reports involved cognitively-impaired individuals. The relatively few studies that have been conducted concerning vasopressin's effects in unimpaired human subjects are consistent with the hypothesis that vasopressin does affect cognition, though both the mechanism of action and the specific cognitive processes which are altered have yet to be elucidated.

Osmotic stress mimics effects of vasopressin on learned behaviour

It has been suggested that arginine vasopressin (AVP) is involved in the retention of learned responses, in addition to its classical physiological functions of water retention and modulation of blood pressure. AVP administered subcutaneously (s.c.), intraventricularly or intracerebrally can prolong extinction of active avoidance behaviour and can enhance retention in inhibitory (passive) avoidance. These effects have been interpreted as a direct action of AVP on the central nervous system to facilitate memory consolidation. AVP also has facilitatory effects on cognitive function in humans, and marked deficits in AVP function have been associated with certain types of psychopathology. Alternative hypotheses for the behavioural actions of AVP have involved motivational constructs such as arousal, and our recent work has focused on the role of arousal resulting from the activation of peripheral visceral signals in the behavioural effects of peripherally administered AVP. The development of a specific antagonist for AVP, 1-deaminopenicillamine-2-O-methyl tyrosine arginine vasopressin (dPTyr(Me)AVP), which can reverse the behavioural effects of exogenously administered AVP, has provided a powerful tool for examining the role of AVP in the behavioural responses produced by physiological challenges known to release vasopressin. However, the relationship between the behavioural effects of exogenously administered AVP and the behavioural function of endogenously released AVP has not been evaluated. We report here that a potent peripheral osmotic stimulus, the intraperitoneal (i.p.) injection of hypertonic saline, at doses known to release AVP both centrally and peripherally, will produce behavioural effects similar to those of exogenously administered AVP. Furthermore, the prolongation of active avoidance induced by this osmotic stimulus is reversed by pretreatment with dPTyr(Me)AVP, suggesting that endogenously released AVP may also produce behavioural effects.

Vasopressin pressor antagonist injected centrally reverses behavioral effects of peripheral injection of vasopressin, but only at doses that reverse increase in blood pressure

Previous work in rats (Ader, R. and De Wied, D., Psychon. Sci., 29 (1972) 46-48) has established that subcutaneously (s.c.) injected arginine vasopressin (AVP) prolongs extinction of active avoidance and that this effect could be prevented by pretreatment with the vasopressin antagonist analog [1-deaminopenicillamine, 2-(O-methyl)tyrosine]-beta-arginine vasopressin (dPtyr(Me)AVP). The purpose of the present study was to determine if peripherally administered AVP acts via a peripheral blood pressure effect or by a direct action in the central nervous system. We therefore tested the effects of the antagonist injected intracerebroventricularly (i.c.v.) on the prolongation of active avoidance and on blood pressure effects of s.c. injected AVP. The antagonist (i.c.v.) blocked the behavioral effects of systemically injected AVP only at dose sufficient to block the peripherally mediated pressor response of systemically administered AVP. The results show that peripherally injected AVP acts on peripheral systems and support our hypothesis that the peripheral visceral action of AVP contributed significantly to its behavioral action.

Arginine vasopressin, stress, and memory

Arginine vasopressin (AVP) has been shown to have several non-renal actions including the potentiation of learned avoidance behavior in rats and improvement in cognitive functioning in humans. Research in our laboratory has confirmed these behavioral effects in rats using both peripheral and central injection of AVP. We have begun to examine the physiological basis for these effects. Peripheral administration of a vasopressor AVP antagonist reversed the prolongation of extinction produced by peripherally administered AVP in both active and passive avoidance, but also reversed the aversive unconditioned effects of AVP. However, central administration of the vasopressor AVP antagonist reversed peripheral effects of AVP only at doses shown to act peripherally to reverse vasopressor effects of AVP. An osmotic stress in doses known to liberate endogenous AVP mimicked the behavioral effects of exogenously administered AVP, and this stress effect was reversed by the AVP antagonist. These results support our hypothesis of separate but parallel AVP systems in the pituitary and brain with a role in behavioral adaptation to certain types of stress.

Inhibition of flank-marking behavior in golden hamsters by microinjection of a vasopressin antagonist into the hypothalamus

Microinjection of arginine-vasopressin (AVP) into the medial preoptic area of the hypothalamus of the hamster stimulates flank marking, a complex stereotypic motor behavior involved in olfactory communication. Microinjection of an antagonist of AVP, [1-deaminopenicillamine-2-(O-methyl)-tyrosine]arginine-vasopressin, into the same site blocks both the effect of microinjected AVP as well as the natural flank-marking behavior normally elicited by placing a hamster into the recently vacated home cage of another hamster. This finding supports the notion that AVP is a transmitter in the expression of flank marking.

EEG effects of subcutaneous and intracerebroventricular injections of arginine vasopressin in the rat

Several studies have suggested that arginine vasopressin (AVP) may act centrally as a neurohormone or neuromodulator to produce electrophysiological and behavioral effects. However, there are few reports of EEG effects of AVP in unanesthetized, behaving animals. In the present study the EEG effects of "behaviorally relevant" subcutaneous (SC) doses of AVP (6 micrograms/kg) known to raise blood pressure were compared to "behaviorally relevant" intracerebroventricular (ICV) doses (0.1-1.0 ng) and multiple "toxic" ICV doses (1.0 microgram) of AVP. Central injections of toxic doses of AVP produced behavioral arrest, bodily barrel rolling, and EEG slowing, but did not induce electrographic signs of seizure activity. Comparison of the spectral characteristics of the EEG revealed some similarities in the distribution of power between SC and the 1.0 ng ICV dose; whereas ICV doses of 0.1 and 0.5 ng produced power distributions that were different from those seen following saline or SC doses of AVP. The similarities in EEG activity between SC injections and the 1.0 ng ICV dose suggest a common brain state may be induced by the two routes of administration in those dose ranges.

Further evidence for a dissociation of peripheral and central effects of vasopressin

The influence of AVP on open field behavior was studied at 15 and 60 min after s.c. injection. AVP injected 15 min before the session modified all patterns of behavior in the open field. Locomotion and rearing along the wall were significantly decreased, while locomotion in the center was increased. AVP also reduced grooming and defecation. Injection 60 min prior to the session did not affect the open field behavior. AVP increased resistance to extinction of pole-jumping avoidance behavior independent of whether the first acquisition session was given at 20 min after injection at the height of the behavioral depression or at 65 min when these effects had disappeared. However, the rats trained at 20 min after AVP administration made significantly more avoidances on the second day of acquisition training than did the controls. The vasopressin fragment DGAVP, which exhibits almost no peripheral effects, did not cause gross behavioral changes in the open field as did AVP, but it did increase resistance to extinction of the avoidance response comparable to that of AVP. These findings indicate that, although peripheral effects may contribute to the effects of AVP on modulation of memory processes, such effects are not essential.

Vasopressin receptor subtypes in dorsal hindbrain and renal medulla

We have investigated the ability of a series of synthetic vasopressin analogues and related peptides to compete with (3H)-arginine8 vasopressin for binding sites in rat renal medulla and dorsal hindbrain. In renal medulla, arginine8 vasopressin and deamino arginine8 vasopressin, a selective antidiuretic, were equipotent while two antagonists of the pressor action of arginine vasopressin were less potent. In the dorsal hindbrain, arginine8 vasopressin and the pressor antagonists were more potent than the synthetic antidiuretic. Potency profiles of these and other analogues suggest that the renal medulla and dorsal hindbrain vasopressin receptors represent different subtypes.

Intracerebroventricular application of a vasopressin antagonist peptide prevents the behavioral actions of vasopressin

Three experiments were conducted to test the hypothesis that the memory-improving properties of peripherally-applied vasopressin (AVP) were related to its aversive (i.e. arousing) actions. The memory effects of AVP were observed in a one-trial food-finding task where non-deprived rats were briefly exposed to a large open field that contained an alcove in which a high-incentive familiar food reward (sweetened milk) was freely available. AVP injections immediately upon removal from the open-field produced faster latencies to refind the alcove (compared to vehicle controls) when tested 48 h later. The aversive actions of AVP were demonstrated in two behavioral assays: (1) a conditioned taste aversion test in which rats learned to avoid a preferred saccharin solution after it had been paired with injections of AVP; and (2) a conditioned place test in which rats learned to avoid a distinctive environment associated with AVP administration. Both the memory and aversive responses to AVP were prevented, in a dose-dependent manner, by immediate pretreatment with intracerebroventricular infusions of the pressor antagonist analog 1-deaminopenicillamine-2-(O-methyl)-tyrosine AVP. The large antagonist doses required to block AVP's behavioral effects suggest that the critical site of action may be far removed from the lateral ventricles. The possibility that AVP-induced improvements in memory result from peripheral arousing actions is discussed.

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.

Antagonism of effects of vasopressin (AVP) on inhibitory avoidance by a vasopressin antagonist peptide [dPtyr(Me)AVP]

After training in two different passive avoidance tasks, the platform box of Ader and De Wied (1972) and the Jarvik box of Jarvik and Kopp (1967), rats injected with vasopressin immediately following the training trial showed a significant enhancement of retention 24 hours later. This vasopressin effect was reversed by high doses of the vasopressor antagonist, dPtyr(Me) AVP. These results support the hypothesis that the visceral afferent signals may be involved in the apparent memory-enhancing effects of AVP, but the high doses of antagonist required suggest that factors other than a simple reversal of the pressor effects of AVP may be important.

Vasopressin antagonists block peripheral as well as central vasopressin receptors

The aim of the present study was to differentiate between the postulated central behavioral effects of vasopressin and its pressor response, which is mainly mediated by peripheral vascular receptors. Thus, the interaction between the vasopressor antagonists dPTyr(Me)AVP (AAVPa) and d(CH2)5Tyr(Me)AVP (AAVPb) with the effects of [Arg8]vasopressin (AVP-(1-9)) and [pGlu4,Cyt6]AVP-(4-8) (referred to as AVP-(4-8)) was examined using passive avoidance behavior and the pressor response as parameters. AVP-(4-8) was approximately 4 and 200 times more potent than AVP-(1-9) in facilitating passive avoidance behavior after subcutaneous (SC) or intracerebroventricular (ICV) administration respectively. This effect of SC injected AVP-(1-9) and AVP-(4-8) could be prevented by both vasopressor antagonists following SC treatment. A similar antagonistic action was found when AVP-(1-9) or AVP-(4-8) and the antagonist AAVPb were administered ICV. SC injection of AAVPb prevented the behavioral effect of ICV administered AVP-(1-9) while ICV treatment with the antagonist blocked the behavioral action of systemically injected AVP-(1-9) and AVP-(4-8). In contrast to SC injected AVP-(1-9) which dose-dependently increased blood pressure and decreased heart rate, AVP-(4-8) injected SC in identical doses did not affect blood pressure and heart rate, neither did AVP-(1-9) and AVP-(4-8) when injected ICV in behaviorally active doses. A SC, but not an ICV injection of the antagonist AAVPb could prevent the blood pressure increase and bradycardia induced by SC AVP-(1-9).(ABSTRACT TRUNCATED AT 250 WORDS)

Vasopressin effects on food-rewarded learning tasks might be due to its action on carbohydrate/lipid metabolism, not memory

Vasopressin (VP) has been implicated in memory processes on the basis of effects observed in aversively motivated learning situations. Therefore researchers have tried to confirm this role by using food-motivated learning tasks. However, the well-established physiological influences of VP on carbohydrate and lipid metabolism were not taken into consideration. At various times following administration, VP might act as a feeding stimulant or as a satiating agent. Experimental designs should allow for these effects when food-rewarded learning paradigms are used to determine whether VP acts on memory.

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.

Vasopressin impairs or enhances retention of learned submissive behavior in mice depending on the time of application

The effects of vasopressin on learning and memory were investigated in a paradigm using adaptive capabilities of interacting male mice. Test animals of the DBA/2 strain which were not submissive in a confrontation with a non-aggressive subordinate C57BL/6 mouse on day 1 (baseline), were defeated on day 2 (learning) by an aggressive dominant C57 mouse, and showed learned submissive behavior upon mere contact with a non-aggressive C57 mouse on day 3 (retest). Pretrial injections of lysine-vasopressin (0.01, 0.1 or 1.0 I.U., s.c.) 20 min before defeat on day 2 resulted in less submissive behavior on day 3 compared to controls, with 0.1 I.U. (equal to 370 ng) being the most effective dose. Post-trial injections of vasopressin (0.1 I.U.) immediately after defeat on day 2 significantly improved retention on day 3. Preretention injections of vasopressin (0.1 I.U.) 20 min before testing on day 3 significantly increased learned submissive behavior. The amnesic effect observed after pretrial injections of vasopressin was neither due to state dependency nor to an acquisition deficit, nor to antinociception. It is concluded that processing of the stressful experience of defeat is differently influenced by vasopressin given before or after training, resulting in an impaired or facilitated retention, respectively. Among the hypothetically discussed underlying mechanisms, one suggestion is that exogenous vasopressin interacts with an assumed discriminative stimulus function of endogenously released vasopressin. Another possibility might be that exogenous vasopressin interferes with the defeat-activated opioid peptide system.