Sex Differences in the Control of Social Investigation and Anxiety by Vasopressin Cells of the Paraventricular Nucleus of the Hypothalamus

Altered vocal communication in adult vasopressin-deficient Brattleboro rats

The neuropeptide, arginine vasopressin (AVP), has been implicated in social communication across a diverse array of species. Many rodents communicate basic behavioral states with negative versus positive valence through high-pitched vocalizations above the human hearing range (ultrasonic vocalizations; USVs). Previous studies have found that Brattleboro (Bratt) rats, which have a mutation in the Avp gene, exhibit deficits in their USVs from the early postnatal period through adolescence, but the magnitude of this effect appears to decrease from the juvenile to adolescent phase. The present study tested whether Bratt rats continue to exhibit USV deficits in adulthood. USVs of adult male and female Bratt and wild type (WT) rats were recorded in two contexts: a novel environment (empty arena) and a social context (arena filled with bedding soiled by same-sex conspecifics). The number, frequency, and duration of 50 kHz USVs were quantified by DeepSqueak after validation with manual scoring. Twenty-two kHz measures were quantified by manual scoring because DeepSqueak failed to accurately detect USVs in this frequency range. Adult Bratt rats did not exhibit deficits in the number of 50 kHz USVs: male Bratt rats emitted similar 50 kHz USVs as male WT rats, whereas female Bratt rats emitted more USVs than female WT rats. USV frequency and duration were altered in adult Bratt rats, but in a context-dependent manner. Twenty-two kHz USVs were less affected by the Bratt mutation. The present study demonstrates how chronic AVP deficiency impacts social communication across the lifespan. The present findings reveal a complex role for AVP in vocal communication, whereby disruption to the Avp gene leads to sex-, context-, and developmental phase-specific effects on the quantity and spectrotemporal characteristics of rat USVs.

Supportive care of female hormones in brain health: what and how?

Female hormones, functioning as neuroactive steroids, are utilized beyond menopausal hormone therapy. The rapid onset of allopregnanolone analogs, such as brexanolone and zuranolone, in treating depression, and the effectiveness of megestrol acetate in addressing appetite and weight gain, prompted the Food and Drug Administration to authorize the use of progesterone for treating postpartum depression and cancer-related cachexia. Progesterone has also been found to alleviate neuropathic pain in animal studies. These off-label applications offer a promising option for patients with advanced cancer who often experience various mood disorders such as depression, persistent pain, social isolation, and physical complications like cachexia. These patients have shown low tolerance to opioids and mood-regulating medications. However, the potential risks and uncertainties associated with hormone therapy treatment modalities can be daunting for both patients and medical professionals. This review aims to offer a comprehensive understanding of the non-reproductive functions and mechanisms of female hormones in brain health.

Sex differences in the structure and function of the vasopressin system in the ventral pallidum are associated with the sex-specific regulation of social play behavior in juvenile rats

Vasopressin (AVP) regulates various social behaviors, often in sex-specific ways, including social play behavior, a rewarding behavior displayed primarily by juveniles. Here, we examined whether and how AVP acting in the brain's reward system regulates social play behavior in juvenile rats. Specifically, we focused on AVP signaling in the ventral pallidum (VP), a brain region that is a part of the reward system. First, we examined the organization of the VP-AVP system in juvenile rats and found sex differences, with higher density of both AVP-immunoreactive fibers and AVP V1a receptor (V1aR) binding in males compared to females while females show a greater number of V1aR-expressing cells compared to males. We further found that, in both sexes, V1aR-expressing cells co-express a GABA marker to a much greater extent (approx. 10 times) than a marker for glutamate. Next, we examined the functional involvement of V1aR-expressing VP cells in social play behavior. We found that exposure to social play enhanced the proportion of activated V1aR-expressing VP cells in males only. Finally, we showed that infusion of a specific V1aR antagonist into the VP increased social play behaviors in juvenile male rats while decreasing these behaviors in juvenile female rats. Overall, these findings reveal structural and functional sex differences in the AVP-V1aR system in the VP that are associated with the sex-specific regulation of social play behavior.

The bilevel chamber revealed differential involvement of vasopressin and oxytocin receptors in female mouse sexual behavior

Arginine vasopressin (AVP) and oxytocin (OT) are well-known as neuropeptides that regulate various social behaviors in mammals. However, little is known about their role in mouse female sexual behavior. Thus, we investigated the role of AVP (v1a and v1b) and OT receptors on female sexual behavior. First, we devised a new apparatus, the bilevel chamber, to accurately observe female mouse sexual behavior. This apparatus allowed for a more precisely measurement of lordosis as receptivity and rejection-like behavior (newly defined in this study), a reversed expression of proceptivity. To address our research question, we evaluated female sexual behavior in mice lacking v1a (aKO), v1b (bKO), both v1a and v1b (dKO), and OT (OTRKO) receptors. aKO females showed decreased rejection-like behavior but a normal level of lordosis, whereas bKO females showed almost no lordosis and no change in rejection-like behavior. In addition, dKO females showed normal lordosis levels, suggesting that the v1b receptor promotes lordosis, but not necessarily, while the v1a receptor latently suppresses it. In contrast, although OTRKO did not influence lordosis, it significantly increased rejection-like behavior. In summary, the present results demonstrated that the v1a receptor inhibits proceptivity and receptivity, whereas the v1b and OT receptors facilitate receptivity and proceptivity, respectively.

Sex differences in responses to aggressive encounters among California mice

Despite how widespread female aggression is across the animal kingdom, there remains much unknown about its neuroendocrine mechanisms, especially in females that engage in aggression outside the peripartum period. Although the impact of aggressive experience on steroid hormone responses have been described, little is known about the impact of these experiences on female behavior or the subsequent neuropeptide responses to performing aggression. In this study, we compared behavioral responses in both male and female adult California mice based on if they had 0, 1, or 3 aggressive encounters using a resident intruder paradigm. We measured how arginine vasopressin and oxytocin cells in the paraventricular nucleus responded to aggression using c-fos immunohistochemistry. We saw that both sexes disengaged from intruders with repeated aggressive encounters, but that on the final day of testing females were more likely to freeze when they encountered intruders compared to no aggression controls - which was not significant in males. Finally, we saw that percent of arginine vasopressin and c-fos co-localizations in the posterior region of the paraventricular nucleus increased in males who fought compared to no aggression controls. No difference was observed in females. Overall, there is evidence that engaging in aggression induces stress responses in both sexes, and that females may be more sensitive to the effects of fighting.

Effects of arginine vasopressin on human anxiety and associations with sex, dose, and V1a-receptor genotype

RATIONALE

Arginine vasopressin (AVP) has dose- and sex-specific effects on social behavior, and variation in social responses is related to variation in the V1a receptor gene in animals. Whether such complexity also characterizes AVP effects on anxiety in humans, or whether V1a genotype is related to anxiety and/or AVP's ability to affect it, remains to be determined.

OBJECTIVE

To test if AVP has dose-dependent effects on anxiety in men and/or women and if a particular allele within the RS3 promoter region of the V1a receptor gene is associated with anxiety and/or AVP effects on anxiety.

METHOD

Men and women self-administered 20 IU or 40 IU intranasal arginine vasopressin (AVP) and placebo in a double-blind, within-subjects design, and State (SA) and Trait (TA) anxiety were measured 60 min later. PCR was used to identify allelic variation within the RS3 region of the V1a receptor gene.

RESULTS

AVP decreased SA in men across both doses, whereas only the lower dose had the same effect, across sexes, in individuals who carry at least one copy of a previously identified "risk" allele in the RS3 promoter of the V1a receptor gene. Additionally, after placebo, women who carried a copy of the allele displayed lower TA than women who did not, and AVP acutely increased TA scores in those women.

CONCLUSIONS

Exogenous AVP has modest sex- and dose-dependent effects on anxiety/affect in humans. Further, allelic variation in the V1a promoter appears associated with responsiveness to AVP's effects and, at least in women, to stable levels of anxiety/affect.

Dexmedetomidine Inhibits Paraventricular Corticotropin-releasing Hormone Neurons that Attenuate Acute Stress-induced Anxiety-like Behavior in Mice

BACKGROUND

Dexmedetomidine has repeatedly shown to improve anxiety, but the precise neural mechanisms underlying this effect remain incompletely understood. This study aims to explore the role of corticotropin-releasing hormone-producing hypothalamic paraventricular nucleus (CRHPVN) neurons in mediating the anxiolytic effects of dexmedetomidine.

METHODS

A social defeat stress mouse model was used to evaluate the anxiolytic effects induced by dexmedetomidine through the elevated plus maze, open-field test, and measurement of serum stress hormone levels. In vivo Ca2+ signal fiber photometry and ex vivo patch-clamp recordings were used to determine the excitability of CRHPVN neurons and investigate the specific mechanism involved. CRHPVN neuron modulation was achieved through chemogenetic activation or inhibition.

RESULTS

Compared with saline, dexmedetomidine (40 µg/kg) alleviated anxiety-like behaviors. Additionally, dexmedetomidine reduced CRHPVN neuronal excitability. Chemogenetic activation of CRHPVN neurons decreased the time spent in the open arms of the elevated plus maze and in the central area of the open-field test. Conversely, chemogenetic inhibition of CRHPVN neurons had the opposite effect. Moreover, the suppressive impact of dexmedetomidine on CRHPVN neurons was attenuated by the α2-receptor antagonist yohimbine.

CONCLUSIONS

The results indicate that the anxiety-like effects of dexmedetomidine are mediated via α2-adrenergic receptor-triggered inhibition of CRHPVN neuronal excitability in the hypothalamus.

EDITOR’S PERSPECTIVE

Hypothalamic vasopressin sex differentiation is observed by embryonic day 15 in mice and is disrupted by the xenoestrogen bisphenol A

Arginine vasopressin (AVP) neurons of the hypothalamic paraventricular region (AVPPVN) mediate sex-biased social behaviors across most species, including mammals. In mice, neural sex differences are thought to be established during a critical window around birth ( embryonic (E) day 18 to postnatal (P) day 2) whereby circulating testosterone from the fetal testis is converted to estrogen in sex-dimorphic brain regions. Here, we found that AVPPVN neurons are sexually dimorphic by E15.5, prior to this critical window, and that gestational bisphenol A (BPA) exposure permanently masculinized female AVPPVN neuronal numbers, projections, and electrophysiological properties, causing them to display male-like phenotypes into adulthood. Moreover, we showed that nearly twice as many neurons that became AVP+ by P0 were born at E11 in males and BPA-exposed females compared to control females, suggesting that AVPPVN neuronal masculinization occurs between E11 and P0. We further narrowed this sensitive period to around the timing of neurogenesis by demonstrating that exogenous estrogen exposure from E14.5 to E15.5 masculinized female AVPPVN neuronal numbers, whereas a pan-estrogen receptor antagonist exposed from E13.5 to E15.5 blocked masculinization of males. Finally, we showed that restricting BPA exposure to E7.5-E15.5 caused adult females to display increased social dominance over control females, consistent with an acquisition of male-like behaviors. Our study reveals an E11.5 to E15.5 window of estrogen sensitivity impacting AVPPVN sex differentiation, which is impacted by prenatal BPA exposure.

A vasopressin circuit that modulates mouse social investigation and anxiety-like behavior in a sex-specific manner

One of the largest sex differences in brain neurochemistry is the expression of the neuropeptide arginine vasopressin (AVP) within the vertebrate brain, with males having more AVP cells in the bed nucleus of the stria terminalis (BNST) than females. Despite the long-standing implication of AVP in social and anxiety-like behaviors, the circuitry underlying AVP's control of these behaviors is still not well defined. Using optogenetic approaches, we show that inhibiting AVP BNST cells reduces social investigation in males, but not in females, whereas stimulating these cells increases social investigation in both sexes, but more so in males. These cells may facilitate male social investigation through their projections to the lateral septum (LS), an area with the highest density of sexually differentiated AVP innervation in the brain, as optogenetic stimulation of BNST AVP → LS increased social investigation and anxiety-like behavior in males but not in females; the same stimulation also caused a biphasic response of LS cells ex vivo. Blocking the vasopressin 1a receptor (V1aR) in the LS eliminated all these responses. Together, these findings establish a sexually differentiated role for BNST AVP cells in the control of social investigation and anxiety-like behavior, likely mediated by their projections to the LS.

A vasopressin circuit that modulates sex-specific social interest and anxiety-like behavior in mice

One of the largest sex differences in brain neurochemistry is the male-biased expression of the neuropeptide arginine vasopressin (AVP) within the vertebrate social brain. Despite the long-standing implication of AVP in social and anxiety-like behavior, the precise circuitry and anatomical substrate underlying its control are still poorly understood. By employing optogenetic manipulation of AVP cells within the bed nucleus of the stria terminalis (BNST), we have unveiled a central role for these cells in promoting social investigation, with a more pronounced role in males relative to females. These cells facilitate male social investigation and anxiety-like behavior through their projections to the lateral septum (LS), an area with the highest density of sexually-dimorphic AVP fibers. Blocking the vasopressin 1a receptor (V1aR) in the LS eliminated stimulation-mediated increases in these behaviors. Together, these findings establish a distinct BNST AVP → LS V1aR circuit that modulates sex-specific social interest and anxiety-like behavior.

Peptidergic and functional delineation of the Edinger-Westphal nucleus

Many neuronal populations that release fast-acting excitatory and inhibitory neurotransmitters in the brain also contain slower-acting neuropeptides. These facultative peptidergic cell types are common, but it remains uncertain whether neurons that solely release peptides exist. Our fluorescence in situ hybridization, genetically targeted electron microscopy, and electrophysiological characterization suggest that most neurons of the non-cholinergic, centrally projecting Edinger-Westphal nucleus in mice are obligately peptidergic. We further show, using anterograde projection mapping, monosynaptic retrograde tracing, angled-tip fiber photometry, and chemogenetic modulation and genetically targeted ablation in conjunction with canonical assays for anxiety, that this peptidergic population activates in response to loss of motor control and promotes anxiety responses. Together, these findings elucidate an integrative, ethologically relevant role for the Edinger-Westphal nucleus and functionally align the nucleus with the periaqueductal gray, where it resides. This work advances our understanding of peptidergic modulation of anxiety and provides a framework for future investigations of peptidergic systems.

Uncovering the brain-wide pattern of synaptic input to vasopressin-expressing neurons in the paraventricular nucleus of the hypothalamus

Arginine vasopressin (AVP) is a neuropeptide critical for the mammalian stress response and social behavior. AVP produced in the hypothalamus regulates water osmolality and vasoconstriction in the body, and in the brain, it regulates social behavior, aggression, and anxiety. However, the circuit mechanisms that link AVP to social behavior, homeostatic function, and disease are not well understood. This study investigates the circuit configurations of AVP-expressing neurons in the rodent hypothalamus and characterizes synaptic input from the entire brain. We targeted the paraventricular nucleus (PVN) using retrograde viral tracing techniques to identify direct afferent synaptic connections made onto AVP-expressing neurons. AVP neurons in the PVN display region-specific anatomical configurations that reflect their unique contributions to homeostatic function, motor behaviors, feeding, and affiliative behavior. The afferent connections identified were similar in both sexes and subsequent molecular investigation of these inputs shows that those local hypothalamic inputs are overwhelmingly nonpeptidergic cells indicating a potential interneuron nexus between hormone cell activation and broader cortical connection. This proposed work reveals new insights into the organization of social behavior circuits in the brain, and how neuropeptides act centrally to modulate social behaviors.

Modulation of social behavior by distinct vasopressin sources

The neuropeptide arginine-vasopressin (AVP) is well known for its peripheral effects on blood pressure and antidiuresis. However, AVP also modulates various social and anxiety-related behaviors by its actions in the brain, often sex-specifically, with effects typically being stronger in males than in females. AVP in the nervous system originates from several distinct sources which are, in turn, regulated by different inputs and regulatory factors. Based on both direct and indirect evidence, we can begin to define the specific role of AVP cell populations in social behavior, such as, social recognition, affiliation, pair bonding, parental behavior, mate competition, aggression, and social stress. Sex differences in function may be apparent in both sexually-dimorphic structures as well as ones without prominent structural differences within the hypothalamus. The understanding of how AVP systems are organized and function may ultimately lead to better therapeutic interventions for psychiatric disorders characterized by social deficits.

Sex-related brain connectivity correlates of compensation in adults with autism: insights into female protection

The male preponderance in autism spectrum disorder (ASD) led to the hypothesis that aspects of female biology are protective against ASD. Females with ASD (ASD-F) report more compensatory behaviors (i.e. "camouflaging") to overcome ASD-related social differences, which may be a mechanism of protection. No studies have examined sex-related brain pathways supporting camouflaging in ASD-F, despite its potential to inform mechanisms underlying the ASD sex bias. We used functional connectivity (FC) to investigate "sex-atypical" and "sex-typical" FC patterns linked to camouflaging in adults with ASD and examined multimodal coherence of findings via structural connectometry. Exploratory associations with cognitive/emotional functioning examined the adaptive nature of FC patterns. We found (i) "sex-atypical" FC patterns linked to camouflaging in the hypothalamus and precuneus and (ii) "sex-typical" patterns in the right anterior cingulate and anterior parahippocampus. Higher hypothalamic FC with a limbic reward cluster also correlated with better cognitive control/emotion recognition. Structural connectometry validated FC results with consistent brain pathways/effect patterns implicated in ASD-F. In summary, "male-typical" and "female-typical" brain connectivity patterns support camouflaging in ASD-F in circuits implicated in reward, emotion, and memory retrieval. "Sex-atypical" results are consistent with fetal steroidogenic/neuroinflammatory hypotheses. However, female genetics/biology may contribute to "female-typical" patterns implicated in camouflaging.

Oxytocin, Vasopressin, and Social Behavior: From Neural Circuits to Clinical Opportunities

Oxytocin and vasopressin are peptide hormones secreted from the pituitary that are well known for their peripheral endocrine effects on childbirth/nursing and blood pressure/urine concentration, respectively. However, both peptides are also released in the brain, where they modulate several aspects of social behaviors. Oxytocin promotes maternal nurturing and bonding, enhances social reward, and increases the salience of social stimuli. Vasopressin modulates social communication, social investigation, territorial behavior, and aggression, predominantly in males. Both peptides facilitate social memory and pair bonding behaviors in monogamous species. Here we review the latest research delineating the neural circuitry of the brain oxytocin and vasopressin systems and summarize recent investigations into the circuit-based mechanisms modulating social behaviors. We highlight research using modern molecular genetic technologies to map, monitor activity of, or manipulate neuropeptide circuits. Species diversity in oxytocin and vasopressin effects on social behaviors are also discussed. We conclude with a discussion of the translational implications of oxytocin and vasopressin for improving social functioning in disorders with social impairments, such as autism spectrum disorder.

Knockdown of sexually differentiated vasopressin expression in the bed nucleus of the stria terminalis reduces social and sexual behaviour in male, but not female, mice

The neuropeptide arginine-vasopressin (AVP) has long been implicated in the regulation of social behaviour and communication, but the sources of AVP release relevant for behaviour have not been precisely determined. Ablations of the sexually dimorphic AVP cells within the bed nucleus of the stria terminalis (BNST), which are more numerous in males, affect social behaviour differently in males and females. However, it is unknown whether these behavioural effects are caused by a reduction of AVP or of other factors associated with these cells. To test the role of AVP specifically, we used an shRNA viral construct to knock down AVP gene expression within the BNST of wild-type male and female mice, using scrambled sequence virus as a control, and evaluated subsequent changes in social behaviours (social investigation, ultrasonic vocalization (USV), scent marking, copulation, and aggression), or anxiety-like behaviours (elevated plus maze). We observed that, in males, knockdown of AVP expression in the BNST strongly reduced investigation of novel males, aggressive signalling towards other males (tail rattling, USV), and copulatory behaviour, but did not alter attack initiation, other measures of social communication, or anxiety-like behaviours. In females, however, BNST AVP knockdown did not alter any of these behaviours. These results point to differential involvement of AVP derived from the BNST in social behaviour.

Contrasting central and systemic effects of arginine-vasopressin on urinary marking behavior as a social signal in male mice

Arginine-vasopressin (AVP) is a neurohypophyseal peptide that plays a critical role in the regulation of social behavior in mammals. Neuronal AVP regulates male-specific social signaling processes, such as exocrine urinary scent deposition and marking behavior in mice. In the periphery, AVP is transported to the portal bloodstream and acts as an antidiuretic hormone. These AVP dynamics imply that the central role of AVP in the stimulation of urinary marking is dissociated with the peripheral role of AVP in the retention of osmotic conditions. Using male BALB/c mice as subjects, peripheral injection of AVP decreased urinary marking and urination. In contrast, a central infusion of AVP facilitated urinary marking with no effect on urination, while an antagonist of the AVP 1a receptor inhibited marking. Centrally AVP-injected mice also exhibited typical behaviors, such as hiccough/sneeze-like reactions and flash scratching, particularly when confronted with a stimulus mouse through a wire mesh screen. Significant expression of these typical reactions in these mice resulted in the disruption of marking deposition. Further analysis of AVP synthesis illustrated that AVP levels increased in the midbrain but not in the circulation immediately after the test, particularly when confronted with a stimulus mouse. The central AVP regulates urinary marking and other typical behaviors in a dose- and situation-dependent manner. The sequential process implies that centrally synthesized AVP may be secreted into the circulation following immediate neuronal processes, and then peripheral AVP acts as an antidiuretic hormone on urinary marking behavior.

Exocrine scent marking: Coordinative role of arginine vasopressin in the systemic regulation of social signaling behaviors

Arginine vasopressin (AVP) is a neurohypophysial hormone that coordinatively regulates central socio-emotional behavior and peripheral control of antidiuretic fluid homeostasis. Most mammals, including rodents, utilize exocrine or urine-contained scent marking as a social signaling tool that facilitates social adaptation. The exocrine scent marking behavior is postulated to fine-tune sensory and cognitive abilities to recognize key social features via exocrine/urinary olfactory cues and subsequently control exocrine deposition or urinary marking through the mediation of osmotic fluid balance. AVP is implicated as a major player in controlling both recognition and signaling responses. This review provides constructive hypotheses on the coordinative processes of the AVP neurohypophysial circuits in the systemic regulations of fluid control and social-communicative behavior, via the expression of exocrine scent marking, and further emphasizes a potential role of AVP in a common mechanism underlying social communication in rodents.

Sex differences in anxiety and depression: circuits and mechanisms

Epidemiological sex differences in anxiety disorders and major depression are well characterized. Yet the circuits and mechanisms that contribute to these differences are understudied, because preclinical studies have historically excluded female rodents. This oversight is beginning to be addressed, and recent studies that include male and female rodents are identifying sex differences in neurobiological processes that underlie features of these disorders, including conflict anxiety, fear processing, arousal, social avoidance, learned helplessness and anhedonia. These findings allow us to conceptualize various types of sex differences in the brain, which in turn have broader implications for considering sex as a biological variable. Importantly, comparing the sexes could aid in the discovery of novel therapeutics.

Vasopressin regulates daily rhythms and circadian clock circuits in a manner influenced by sex

Arginine vasopressin (AVP) is a neurohormone that alters cellular physiology through both endocrine and synaptic signaling. Circadian rhythms in AVP release and other biological processes are driven by the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. Loss of vasopressin signaling alters circadian behavior, but the basis of these effects remains unclear. Here we investigate the role of AVP signaling in circadian timekeeping by analyzing behavior and SCN function in a novel AVP-deficient mouse model. Consistent with previous work, loss of AVP signaling increases water consumption and accelerates recovery to simulated jetlag. We expand on these results to show that loss of AVP increases period, imprecision and plasticity of behavioral rhythms under constant darkness. Interestingly, the effect of AVP deficiency on circadian period was influenced by sex, with loss of AVP lengthening period in females but not males. Examining SCN function directly with ex vivo bioluminescence imaging of clock protein expression, we demonstrate that loss of AVP signaling modulates the period, precision, and phase relationships of SCN neurons in both sexes. This pattern of results suggests that there are likely sex differences in downstream targets of the SCN. Collectively, this work indicates that AVP signaling modulates circadian circuits in a manner influenced by sex, which provides new insight into sexual dimorphisms in the regulation of daily rhythms.

Removal of vasopressin cells from the paraventricular nucleus of the hypothalamus enhances lipopolysaccharide-induced sickness behaviour in mice

Vasopressin (AVP) cells in the paraventricular nucleus of the hypothalamus (PVN) are activated during sickness and project to multiple nuclei responsible for the anxiety, social and motivated behaviours affected during sickness, suggesting that these cells may play a role in sickness behaviours, typically expressed as reduced mobility, increased anxiety, anhedonia and social withdrawal. In the present study, we selectively ablated AVP neurones in the PVN of male and female mice (Mus musculus) and induced sickness behaviour via injection of bacterial lipopolysaccharide (LPS). We found that PVN AVP ablation increased the effects of LPS, specifically by further decreasing sucrose preference in males and females and decreasing the social preference of males, monitored within 24 hours of LPS injection. These results suggest that PVN AVP contributes to the change in motivated behaviours during sickness and may help promote recovery from infection..