Amphetamine reward in the monogamous prairie vole

Higher exploratory and vigilant behaviors related to higher central dopaminergic activities of Formosan wood mice (Apodemus semotus) in light-dark exploration tests

Formosan wood mice (Apodemus semotus) are endemic rodents in Taiwan. Recently Formosan wood mice exhibit similar locomotor behaviors in the laboratory environment as in the field environment has shown. Contemporaneously, Formosan wood mice have higher moving distances of and central dopaminergic (DAergic) activities than C57BL/6 mice in behavioral test. This study tried to compare the behavioral responses between male Formosan wood mice and male C57BL/6 mice in the light-dark exploration tests. We also measured the levels of DA and 3,4-dihydroxyphenylacetic acid (DOPAC), the primary metabolite of DA, to assess the dopaminergic activity of the medial prefrontal cortex, striatum, and nucleus accumbens. Our data show that Formosan wood mice revealed higher exploration and central DAergic activities than did C57BL/6 mice in the light-dark exploration tests, and diazepam (an anxiolytics) treatment reduced the exploratory activity and central dopaminergic activities in Formosan wood mice, but not in C57BL/6 mice. After repeated exposure to light-dark exploration tests, the latency to dark zone was increased, and the duration in light zone as well as the central DAergic activity were decreased in C57BL/6 mice. This study provides comparative findings; Formosan wood mice showed the higher exploratory activities than C57BL/6 mice did, and their central DAergic activities were related to the behavioral responses in these two mice. This could potentially shed light on the reasons behind the prevalence of higher exploration and central dopaminergic activities. Using Formosan wood mice as a model to study human diseases related to hyperactivity adds significant value to the potential research.

Amphetamine exposure alters behaviors, and neuronal and neurochemical activation in the brain of female prairie voles

Previous studies have shown that 3-day d-amphetamine (AMPH) treatment effectively induced conditioned place preferences (CPP) and impaired pair bonding behaviors in prairie voles (Microtus ochrogaster). Using this established animal model and treatment regimen, we examined the effects of the demonstrated threshold rewarding dose of AMPH on various behaviors and their potential underlying neurochemical systems in the brain of female prairie voles. Our data show that 3-day AMPH injections (0.2 mg/kg/day) impaired social recognition and decreased depressive-like behavior in females without affecting their locomotion and anxiety-like behaviors. AMPH treatment also decreased neuronal activation indicated by the labeling of the early growth response protein 1 (Egr-1) as well as the number of neurons double-labeled for Egr-1 and corticotrophin-releasing hormone (CRH) in the dentate gyrus (DG) of the hippocampus and paraventricular nucleus of the hypothalamus (PVN) in the brain. Further, AMPH treatment decreased the number of neurons double-labeled for Egr-1 and tyrosine hydroxylase (TH) but did not affect oxytocinergic neurons in the PVN or cell proliferation and neurogenesis markers in the DG. These data not only demonstrate potential roles of the brain CRH and dopamine systems in mediating disrupted social recognition and depressive-like behaviors by AMPH in female prairie voles, but also further confirm the utility of the prairie vole model for studying interactions between psychostimulants and social behaviors.

Functional Connectivity Differences Between Two Culturally Distinct Prairie Vole Populations: Insights Into the Prosocial Network

BACKGROUND

The goal of this study was to elucidate the fundamental connectivity-resting-state connectivity-within and between nodes in the olfactory and prosocial (PS) cores, which permits the expression of social monogamy in males; and how differential connectivity accounts for differential expression of prosociality and aggression.

METHODS

Using resting-state functional magnetic resonance imaging, we integrated graph theory analysis to compare functional connectivity between two culturally/behaviorally distinct male prairie voles (Microtusochrogaster).

RESULTS

Illinois males display significantly higher levels of prosocial behavior and lower levels of aggression than KI (Kansas dam and Illinois sire) males, which are associated with differences in underlying neural mechanisms and brain microarchitecture. Shared connectivity 1) between the anterior hypothalamic area and the paraventricular nucleus and 2) between the medial preoptic area and bed nucleus of the stria terminalis and the nucleus accumbens core suggests essential relationships required for male prosocial behavior. In contrast, Illinois males displayed higher levels of global connectivity and PS intracore connectivity, a greater role for the bed nucleus of the stria terminalis and anterior hypothalamic area, which were degree connectivity hubs, and greater PS and olfactory intercore connectivity.

CONCLUSIONS

These findings suggest that behavioral differences are associated with PS core degree of connectivity and postsignal induction. This transgenerational system may serve as powerful mental health and drug abuse translational model in future studies.

Raised without a father: monoparental care effects over development, sexual behavior, sexual reward, and pair bonding in prairie voles

Around 5 % of mammals are socially monogamous and both parents provide care to the pups (biparental, BP). Prairie voles are socially monogamous rodents extensively used to understand the neurobiological basis of pair bond formation and the consequences that the absence of one parent has in the offspring. Pair bonding, characterized by selective affiliation with a sexual partner, is facilitated in prairie voles by mating for 6 h or cohabitation without mating for 24 h. It was previously shown that prairie voles raised by their mother alone (monoparental, MP) show delayed pair bond formation upon reaching adulthood. In this study we evaluated the effects of BP and MP care provided on the offspring's development, ability to detect olfactory cues, preference for sexually relevant odors, display of sexual behavior, as well as the rewarding effects of mating. We also measured dopamine and serotonin concentration in the nucleus accumbens (ventral striatum) and dorsal striatum after cohabitation and mating (CM) to determine if differences in these neurotransmitters could underlie the delay in pair bond formation in MP voles. Our data showed that MP voles received less licking/grooming than BP voles, but no developmental differences between groups were found. No differences were found in the detection and discrimination of olfactory cues or preference for sexually relevant odors, as all groups innately preferred opposite sex odors. No differences were found in the display of sexual behavior. However, CM induced reinforcing properties only in BP males, followed by a preference for their sexual partner in BP but not MP males. BP males showed an increase in dopamine turnover (DOPAC/DA and HVA/DA) in the nucleus accumbens in comparison to MP voles. No differences in dopamine, serotonin or their metabolites were found in the dorsal striatum. Our results indicate that MP voles that received less licking behavior exhibit a delay in pair bond formation possibly because the sexual interaction is not rewarding enough.

Differences in Diffusion-Weighted Imaging and Resting-State Functional Connectivity Between Two Culturally Distinct Populations of Prairie Vole

BACKGROUND

We used the highly prosocial prairie vole to test the hypothesis that higher-order brain structure-microarchitecture and functional connectivity (FC)-would differ between males from populations with distinctly different levels of prosocial behavior. Specifically, we studied males from Illinois (IL), which display high levels of prosocial behavior, and first generation males from Kansas dams and IL males (KI), which display the lowest level of prosocial behavior and higher aggression. Behavioral differences between these males are associated with overexpression of estrogen receptor alpha in the medial amygdala and bed nucleus of the stria terminalis and neuropeptide expression in the paraventricular nucleus.

METHODS

We compared apparent diffusion coefficient, fractional anisotropy, and blood oxygen level-dependent resting-state FC between males.

RESULTS

IL males displayed higher apparent diffusion coefficient in regions associated with prosocial behavior, including the bed nucleus of the stria terminalis, paraventricular nucleus, and anterior thalamic nuclei, while KI males showed higher apparent diffusion coefficient in the brainstem. KI males showed significantly higher fractional anisotropy than IL males in 26 brain regions, with the majority being in the brainstem reticular activating system. IL males showed more blood oxygen level-dependent resting-state FC between the bed nucleus of the stria terminalis, paraventricular nucleus, and medial amygdala along with other brain regions, including the hippocampus and areas associated with social and reward networks.

CONCLUSIONS

Our results suggest that gray matter microarchitecture and FC may play a role the expression of prosocial behavior and that differences in other brain regions, especially the brainstem, could be involved. The differences between males suggests that this system represents a potentially valuable model system for studying emotional differences and vulnerability to stress and addiction.

Formosan wood mice (Apodemus semotus) exhibit more exploratory behaviors and central dopaminergic activities than C57BL/6 mice in the open field test

Three-quarters of the lands in Taiwan are over 1000 m above sea level. Formosan wood mice (Apodemus semotus), also called Taiwanese field mice, are largely found at altitudes of 1400 ~ 3700 m and are the dominant rodents in these areas. Notably, Formosan wood mice show high levels of exploratory behaviors, not only in the wild but also in laboratory situations. Therefore, in this study, we examined the behavioral responses and central dopaminergic activities of male C57BL/6J mice and Formosan wood mice in the open field test. Dopamine and its major metabolite 3,4-dihydroxyphenylacetic acid were used as indices of dopaminergic activities. Formosan wood mice showed higher levels of exploration and locomotor activity than C57BL/6J mice in the open field test. Higher central dopaminergic activities in the nucleus accumbens, striatum, and medial prefrontal cortex were found in Formosan wood mice than in C57BL/6J mice in the open field test. Higher levels of locomotion and central dopaminergic activities in Formosan wood mice were consistent after two exposures to the open field test; however, dramatic decreases in levels of locomotion and central dopaminergic activities in C57BL/6J mice were found after two exposures to the open field test. The present study found that Formosan wood mice exhibited higher levels of locomotor activity and exploration and central dopaminergic activities than C57BL/6J mice after one or two exposures to the open field test.

Effects of methamphetamine on alloparental behavior in male and female prairie voles

Psychostimulant abuse is associated with a variety of impairments in social functioning, including an increased frequency of depression and aggression and deficits in social cognition. Psychostimulants reduce social investigation in rats and mice; however, it is less clear how other forms of social behavior (e.g., prosocial behavior) are affected. Females are also generally more sensitive to the effects of psychostimulants on locomotion and stereotyped behavior, which suggests that females might also display greater disruption of prosocial behavior. In order to test the hypothesis that psychostimulants reduce prosocial behavior and that females are more vulnerable, we treated adult male and female prairie voles with methamphetamine for three days (0, 0.2 or 2.0mg/kg, i.p.) and examined effects on locomotion and alloparental behavior. The lower methamphetamine dose increased activity in the open field in males and reduced locomotion in females. Methamphetamine-treated males took longer to enter the pup chamber, but both sexes displayed reduced pup contact following treatment with the lower methamphetamine dose. The methamphetamine-induced reduction in prosocial behavior was not associated with changes in pup-directed aggression in males or females. In order to investigate potential mechanisms underlying these changes in behavior, we measured adrenal weights as a proxy for activation of the hypothalamic-pituitary-adrenal (HPA) axis. The higher methamphetamine dose increased adrenal weights. Collectively, these data demonstrate that methamphetamine administration reduces alloparental behavior in both sexes and that females are more sensitive to some of the effects of this drug (e.g., locomotion/stereotyped behavior and possibly stimulation of the HPA axis).

Exploratory and agile behaviors with central dopaminergic activities in open field tests in Formosan wood mice (Apodemus semotus)

Taiwan is a mountainous island, and nearly 75% of its lands are 1000 m above sea level. Formosan wood mice, Apodemus semotus, are endemic rodents and are broadly distributed at altitudes between 1400 m and 3700 m in Taiwan. Interestingly, Formosan wood mice show similar locomotor activity in the laboratory as they do in the wild. Hence, we are interested in studying whether exploratory behaviors and central dopaminergic activity are changed in the open field test. We used male C57BL/6J mice as the control, comparing their behavioral responses in the open field, step-down inhibitory avoidance discrimination and novel object recognition tests with those of male Formosan wood mice. We also examined dopamine and its major metabolite 3,4-dihydroxyphenylacetic acid in the medial prefrontal cortex, striatum and nucleus accumbens. In open field tests, Formosan wood mice revealed higher levels of locomotion and exploration than C57BL/6J mice. Learning and memory performance in the novel object recognition test was similar in both Formosan wood mice and C57BL/6J mice, but more agile responses in the inhibitory avoidance discrimination task were found in Formosan wood mice. There was no difference in behavioral responses in the open field test between new second-generation Formosan wood mice and Formosan wood mice that were inbred for more than ten generations. After repeated exposure to the open field test, high levels of locomotion and exploration as well as central dopaminergic activities were markedly persistent in Formosan wood mice, but these activities were significantly reduced in C57BL/6J mice. Diazepam (anxiolytic) treatment reduced the higher exploratory activity and central dopaminergic activities in Formosan wood mice, but this treatment had no effect in C57BL/6J mice. This study provides comparative findings, as two phylogenetically related species showed differences in behavioral responses.

The Value of Comparative Animal Research: Krogh's Principle Facilitates Scientific Discoveries

Biomedical research is dominated by relatively few nonhuman animals to investigate healthy and disease conditions. Research has overrelied on these models due to their well-described genomes, the capability to control specific genes, and the high rate of reproduction. However, recent advances in large-scale molecular sequencing experiments have revealed, in some cases, the limited similarities in experimental outcomes observed in common rodents (i.e., mice) compared with humans. The value of more varied comparative animal models includes examples such as long-term body weight regulation in seasonally breeding hamsters as a means to help understand the obesity epidemic, vocal learning in songbirds to illuminate language acquisition and maintenance, and reproduction in cichlid fish to discover novel genes conserved in humans. Studying brain genes in prairie voles and cichlids advanced knowledge about social behavior. Taken together, experiments on diverse animal species highlight nontraditional systems for advancing our understanding of human health and well-being.

Place preferences associated with pups or cocaine change the expression of D2R, V1aR and OTR in the NAcc and MeA and the levels of plasma AVP, OT, T and E2 in mandarin vole fathers

Drug abuse often has negative impacts on parenting behavior. The dopamine (DA), arginine vasopressin (AVP) and oxytocin (OT) systems are involved in paternal behavior and drug-induced behaviors. Mandarin voles (Microtus mandarinus) are socially monogamous rodents with high levels of paternal behavior. The aims of this study were to examine the protein expression levels of the DA 2-type receptor (D2R), AVP receptor 1A(V1aR) and OT receptor (OTR) in the nucleus accumbens (NAcc) and medial amygdala (MeA) as well as the plasma hormone responses after mandarin vole fathers were conditioned with their pups or cocaine. Our experimental models are based on the conditioned place preference (CPP) paradigm. We observed CPP in response to either pup- or cocaine-associated cues in the mandarin vole fathers. Fathers that were conditioned to either pups or cocaine had a lower expression of D2R and V1aR in the NAcc than did controls. Fathers that were conditioned to pups had higher levels of OTR expression in the MeA and higher plasma levels of AVP, OT, estradiol (E2), and lower plasma levels of testosterone (T) than did controls. Fathers that were conditioned to cocaine exhibited lower levels of plasma AVP and T. These results indicate that the reward effects of pup and cocaine are both mediated by D2R, V1aR and OTR in the NAcc and MeA and that there are subtle differences between the pup and cocaine reward mechanisms that are associated with altered plasma AVP, OT, T and E2.

Parents induced- conditioned place preference and the neuronal expression of oxytocin and tyrosine hydroxylase in preweanling female pups

Parents-offspring bonding is critical for development of offspring in mammals. While it is known that pups stimuli provide rewarding effects on their parents, few studies have assessed whether parental stimuli serve as a reinforcing agent to their pups, and what the neural mechanisms underlying this reward process may be. In addition to maternal care, male ICR mice display pairmate-dependent parental behavior. Using the conditioned place preference (CPP) paradigm, we examined the effects of maternal and paternal conditioning on the postnatal day 17-21 female ICR mice pups, and compared the expression of oxytocin (OT)- and tyrosine hydroxylase (TH)- immunoreactive (IR) neurons. We found that the pups established dam- or sire- induced CPP when using mother conditioning (MC) or father conditioning (FC) alone. However, the pups failed to show any preference when using mother versus father conditioning (MFC). Compared to the control group, the MC and MFC groups displayed more OT-IR neurons in the supraoptic nucleus and more TH-IR neurons in the ventral tegmental area (VTA). The FC group showed more TH-IR neurons in the VTA compared to the control group, but there were no significant differences in OT-IR neurons. These findings indicate that female ICR mice pups may establish mother- or father- induced CPP. The underpinnings of preference for parents are associated with the activity of VTA dopaminergic neurons, and the preference of pups for mother in particular appears to be associated with OT levels.

Ventral Tegmental Area Dopamine Cell Activation during Male Rat Sexual Behavior Regulates Neuroplasticity and d-Amphetamine Cross-Sensitization following Sex Abstinence

Experience with sexual behavior causes cross-sensitization of amphetamine reward, an effect dependent on a period of sexual reward abstinence. We previously showed that ΔFosB in the nucleus accumbens (NAc) is a key mediator of this cross-sensitization, potentially via dopamine receptor activation. However, the role of mesolimbic dopamine for sexual behavior or cross-sensitization between natural and drug reward is unknown. This was tested using inhibitory designer receptors exclusively activated by designer drugs in ventral tegmental area (VTA) dopamine cells. rAAV5/hSvn-DIO-hm4D-mCherry was injected into the VTA of TH::Cre adult male rats. Males received clozapine N-oxide (CNO) or vehicle injections before each of 5 consecutive days of mating or handling. Following an abstinence period of 7 d, males were tested for amphetamine conditioned place preference (CPP). Next, males were injected with CNO or vehicle before mating or handling for analysis of mating-induced cFos, sex experience-induced ΔFosB, and reduction of VTA dopamine soma size. Results showed that CNO did not affect mating behavior. Instead, CNO prevented sexual experience-induced cross-sensitization of amphetamine CPP, ΔFosB in the NAc and medial prefrontal cortex, and decreases in VTA dopamine soma size. Expression of hm4D-mCherry was specific to VTA dopamine cells and CNO blocked excitation and mating-induced cFos expression in VTA dopamine cells. These findings provide direct evidence that VTA dopamine activation is not required for initiation or performance of sexual behavior. Instead, VTA dopamine directly contributes to increased vulnerability for drug use following loss of natural reward by causing neuroplasticity in the mesolimbic pathway during the natural reward experience.

SIGNIFICANCE STATEMENT

Drugs of abuse act on the neural pathways that mediate natural reward learning and memory. Exposure to natural reward behaviors can alter subsequent drug-related reward. Specifically, experience with sexual behavior, followed by a period of abstinence from sexual behavior, causes increased reward for amphetamine in male rats. This study demonstrates that activation of ventral tegmental area dopamine neurons during sexual experience regulates cross-sensitization of amphetamine reward. Finally, ventral tegmental area dopamine cell activation is essential for experience-induced neural adaptations in the nucleus accumbens, prefrontal cortex, and ventral tegmental area. These findings demonstrate a role of mesolimbic dopamine in the interaction between natural and drug rewards, and identify mesolimbic dopamine as a key mediator of changes in vulnerability for drug use after loss of natural reward.

Methamphetamine Consumption Inhibits Pair Bonding and Hypothalamic Oxytocin in Prairie Voles

Methamphetamine (MA) abuse has been linked to violence, risk-taking behaviors, decreased sexual inhibition, and criminal activity. It is important to understand mechanisms underlying these drug effects for prevention and treatment of MA-associated social problems. Previous studies have demonstrated that experimenter-administered amphetamine inhibits pair bonding and increases aggression in monogamous prairie voles. It is not currently known whether similar effects on social behaviors would be obtained under conditions during which the drug is voluntarily (actively) administered. The current study investigated whether MA drinking affects pair bonding and what neurocircuits are engaged. In Experiment 1, we exposed male and female voles to 4 days each of 20 and 40 mg/L MA under a continuous 2-bottle choice (2BC) procedure. Animals were housed either singly or in mesh-divided cages with a social partner. Voles consumed MA in a drinking solution, but MA drinking was not affected by either sex or housing condition. In Experiment 2, we investigated whether MA drinking disrupts social bonding by measuring aggression and partner preference formation following three consecutive days of 18-hour/day access to 100 mg/L MA in a 2BC procedure. Although aggression toward a novel opposite-sex animal was not affected by MA exposure, partner preference was inhibited in MA drinking animals. Experiment 3 examined whether alterations in hypothalamic neuropeptides provide a potential explanation for the inhibition of partner preference observed in Experiment 2. MA drinking led to significant decreases in oxytocin, but not vasopressin, in the paraventricular nucleus of the hypothalamus. These experiments are the first investigation into how voluntary pre-exposure to MA affects the development of social attachment in a socially monogamous species and identify potential neural circuits involved in these effects.

Dopamine and opioid systems interact within the nucleus accumbens to maintain monogamous pair bonds

Prairie vole breeder pairs form monogamous pair bonds, which are maintained through the expression of selective aggression toward novel conspecifics. Here, we utilize behavioral and anatomical techniques to extend the current understanding of neural mechanisms that mediate pair bond maintenance. For both sexes, we show that pair bonding up-regulates mRNA expression for genes encoding D1-like dopamine (DA) receptors and dynorphin as well as enhances stimulated DA release within the nucleus accumbens (NAc). We next show that D1-like receptor regulation of selective aggression is mediated through downstream activation of kappa-opioid receptors (KORs) and that activation of these receptors mediates social avoidance. Finally, we also identified sex-specific alterations in KOR binding density within the NAc shell of paired males and demonstrate that this alteration contributes to the neuroprotective effect of pair bonding against drug reward. Together, these findings suggest motivational and valence processing systems interact to mediate the maintenance of social bonds.

Prairie Voles as a Model to Screen Medications for the Treatment of Alcoholism and Addictions

Most preclinical studies of medications to treat addictions are performed in mice and rats. These two rodent species belong to one phylogenetic subfamily, which narrows the likelihood of identifying potential mechanisms regulating addictions in other species, ie, humans. Expanding the genetic diversity of organisms modeling alcohol and drug abuse enhances our ability to screen for medications to treat addiction. Recently, research laboratories adapted the prairie vole model to study mechanisms of alcohol and drugs of abuse. This development not only expanded the diversity of genotypes used to screen medications, but also enhanced capabilities of such screens. Prairie voles belong to 3-5% of mammalian species exhibiting social monogamy. This unusual trait is reflected in their ability to form lasting long-term affiliations between adult individuals. The prairie vole animal model has high predictive validity for mechanisms regulating human social behaviors. In addition, these animals exhibit high alcohol intake and preference. In laboratory settings, prairie voles are used to model social influences on drug reward and alcohol consumption as well as effects of addictive substances on social bonding. As a result, this species can be adapted to screen medications whose effectiveness could be (a) resistant to social influences promoting excessive drug taking, (b) dependent on the presence of social support, and (c) medications affecting harmful social consequences of alcohol and drug abuse. This report reviews the literature on studies of alcohol and psychostimulants in prairie voles and discusses capabilities of this animal model as a screen for novel medications to treat alcoholism and addictions.

Neonatal exposure to amphetamine alters social affiliation and central dopamine activity in adult male prairie voles

The prairie vole (Microtus ochrogaster) is a socially monogamous rodent species that forms pair bonds after mating. Recent data have shown that amphetamine (AMPH) is rewarding to prairie voles as it induces conditioned place preferences. Further, repeated treatment with AMPH impairs social bonding in adult prairie voles through a central dopamine (DA)-dependent mechanism. The present study examined the effects of neonatal exposure to AMPH on behavior and central DA activity in adult male prairie voles. Our data show that neonatal exposure to AMPH makes voles less social in an affiliation test during adulthood, but does not affect animals' locomotor activity and anxiety-like behavior. Neonatal exposure to AMPH also increases the levels of tyrosine hydroxylase (TH) and DA transporter (DAT) mRNA expression in the ventral tegmental area (VTA) in the brain, indicating an increase in central DA activity. As DA has been implicated in AMPH effects on behavioral and cognitive functions, altered DA activity in the vole brain may contribute to the observed changes in social behavior.

Sex differences in the influence of social context, salient social stimulation and amphetamine on ultrasonic vocalizations in prairie voles

Prairie voles (Microtus ochrogaster) are a socially monogamous rodent species and their cooperative behaviors require extensive communication between conspecifics. Rodents use ultrasonic vocalizations (USVs) to communicate and because a prairie vole breeder pair must engage in extensive cooperation for successful reproduction, auditory communication may be critical for this species. Therefore, we sought to characterize USVs in adult male and female prairie voles, and to determine how these calls are influenced by social context, salient social stimuli and the psychostimulant drug of abuse amphetamine (AMPH). Here, we characterize prairie vole USVs by showing the range of frequencies of prairie vole USVs, the proportion of various call types, how these call types compare between males and females, and how they are influenced by social stimulation and AMPH. AMPH caused a robust increase in the number of USVs in both males and females and there was a dramatic sex difference in the complexity of call structures of AMPH-induced USVs, with males emitting more elaborate calls. Moreover, we show that novel (i.e. salient) social cues evoked differential increases in USVs across sex, with males showing a much more robust increase in USV production, both with respect to the frequency and complexity of USV production. Exposure to an estrous female in particular caused an extraordinary increase in USVs in male subjects. These data suggest that USVs may be a useful measure of social motivation in this species, including how social behaviors can be impacted by drugs of abuse.

Drinking alcohol has sex-dependent effects on pair bond formation in prairie voles

Alcohol use and abuse profoundly influences a variety of behaviors, including social interactions. In some cases, it erodes social relationships; in others, it facilitates sociality. Here, we show that voluntary alcohol consumption can inhibit male partner preference (PP) formation (a laboratory proxy for pair bonding) in socially monogamous prairie voles (Microtus ochrogaster). Conversely, female PP is not inhibited, and may be facilitated by alcohol. Behavior and neurochemical analysis suggests that the effects of alcohol on social bonding are mediated by neural mechanisms regulating pair bond formation and not alcohol's effects on mating, locomotor, or aggressive behaviors. Several neuropeptide systems involved in the regulation of social behavior (especially neuropeptide Y and corticotropin-releasing factor) are modulated by alcohol drinking during cohabitation. These findings provide the first evidence to our knowledge that alcohol has a direct impact on the neural systems involved in social bonding in a sex-specific manner, providing an opportunity to explore the mechanisms by which alcohol affects social relationships.

Cocaine withdrawal influences paternal behavior and associated central expression of vasopressin, oxytocin and tyrosine hydroxylase in mandarin voles

Although the disruptive effects of cocaine on the maternal care are well known, little is known about paternal care in the context of cocaine abuse. Vasopressin (AVP), oxytocin (OT) and dopamine (DA) have been found to regulate paternal behavior and are also involved in cocaine abuse. Mandarin voles (Microtus mandarinus) are socially monogamous and display high levels of paternal care. Here, we investigated whether paternal behavior and associated central levels of AVP, OT and DA were altered following 24 h of withdrawal from 4 day administration of 20 mg/kg/day cocaine. Our data shows that vole fathers did not experience altered levels of locomotion during an open field test. However, compared to controls, cocaine attenuated licking/grooming and contact behavior and shortened the latency to crouching, contact and pup retrieval. Last, fewer AVP and OT immunoreactive neurons in the paraventricular nucleus and more tyrosine hydroxylase immunoreactive neurons in the ventral tegmental area were observed in cocaine-treated fathers. These results indicate that cocaine withdrawal disturbs the expression of partial paternal behavior by altering central levels of AVP, OT and DA.

Father absence in the monogamous california mouse impairs social behavior and modifies dopamine and glutamate synapses in the medial prefrontal cortex

The role of the father in psycho-affective development is indispensable. Yet, the neurobehavioral effects of paternal deprivation (PD) are poorly understood. Here, we examined the behavioral consequences of PD in the California mouse, a species displaying monogamous bonding and biparental care, and assessed its impact on dopamine (DA), serotonin (5-HT), and glutamate (GLU) transmission in the medial prefrontal cortex (mPFC). In adult males, deficits in social interaction were observed, when a father-deprived (PD) mouse was matched with a PD partner. In adult females, deficits were observed when matching a PD animal with a non-PD control, and when matching 2 PD animals. PD also increased aggression in females. Behavioral abnormalities in PD females were associated with a sensitized response to the locomotor-activating effect of amphetamine. Following immunocytochemical demonstration of DA, 5-HT, and GLU innervations in the mPFC, we employed in vivo electrophysiology and microiontophoresis, and found that PD attenuated the basal activity of low-spiking pyramidal neurons in females. PD decreased pyramidal responses to DA in females, while enhancing responses to NMDA in both sexes. We thus demonstrate that, during critical neurodevelopmental periods, PD leads to sex-dependent abnormalities in social and reward-related behaviors that are associated with disturbances in cortical DA and GLU neurotransmission.

Reinforcing properties of pups versus cocaine for fathers and associated central expression of Fos and tyrosine hydroxylase in mandarin voles (Microtus mandarinus)

The reciprocal interaction of pups and cocaine on reward effects in rodent mothers is known. However,it remains unclear whether such effects are apparent in father-offspring bonding. The mandarin vole (Microtus mandarinus) is a monogamous rodent with a high level of paternal care. We investigated the reinforcing properties of pups on vole fathers using a conditioned place preference paradigm across the postpartum period and looked for interactions and differences between the reinforcing effects of pups and cocaine. We also measured neuronal Fos and tyrosine hydroxylase (TH) expression underlying the preferences of fathers for pups or cocaine. Our data showed that fathers developed strong preferences for pups at various times (postnatal day 5–9, 13–17 and 19–23) without cocaine conditioning. Fathers showed a reduced preference for pups following simultaneous conditioning with cocaine. Although they preferred cocaine over postnatal day (PND) 5–9 pups, this preference was not detected for PND 13–17 pups. Fathers preferring cocaine exhibited an increase in Fos-immunoreactive neurons in the accumbens,medial nucleus of the amygdala, cingulate cortex, medial preoptic area and ventral tegmental area and had more TH-IR neurons in the ventral tegmental area compared to fathers preferring PND 5–9 pups. These results showed that similar to cocaine, mandarin vole pups elicit significant reward value to their fathers, but that paternal motivation is impaired by cocaine. A preference for cocaine over pups arose from the release of more dopamine and activation of a greater number of neurons within specific reward-associated neuronal subsets.

Differences in titi monkey (Callicebus cupreus) social bonds affect arousal, affiliation, and response to reward

Titi monkeys (Callicebus cupreus) are a monogamous, New World primate. Adult pair-mates form a bidirectional social bond and offspring form a selective unidirectional bond to their father. Some of the neurobiology involved in social bonds and maternal behavior is similar to the neural circuitry involved in nonsocial reward. Due to these overlapping mechanisms, social states may affect responses to external rewarding stimuli. We sought to determine whether having a social attachment, and/or being in the presence of that attachment figure, can affect an individual's response to a rewarding stimulus. In addition, we compared affiliative bonds between pair-mates to those between offspring and fathers. Eighteen adult male titi monkeys were either living alone (Lone), with a female pair-mate (Paired), or with the natal group (Natal; N = 6/condition). Each individual went through eight 30-min preference tests for a sweet substance, Tang. For Paired and Natal males, half of the test sessions were with their attachment figure and half were alone. Lone males were always tested alone. Preference scores for Tang, time spent drinking, affiliative, and arousal behaviors were measured. Paired and Natal males emitted significantly more isolation peeps and locomoted more when tested alone compared to when tested with their attachment figure, and paired males engaged in more affiliative behavior than Natal males. Lone males engaged in significantly more behaviors indicative of behavioral arousal such as locomotion and piloerection compared to Paired and Natal males. Finally, Paired males drank significantly more Tang and had a significantly greater preference for Tang compared to Lone and Natal males. These results indicate that offspring undergo a behavioral separation response upon separation from their father that persists into adulthood, Lone males are more behaviorally reactive, and that living with an attachment figure and the type of attachment relationship result in different responses to a rewarding sweet stimulus.

Social bonding decreases the rewarding properties of amphetamine through a dopamine D1 receptor-mediated mechanism

Although the protective effects of social bonds on drug use/abuse have been well documented, we know little about the underlying neural mechanisms. Using the prairie vole (Microtus ochrogaster)--a socially monogamous rodent that forms long-term pair bonds after mating--we demonstrate that amphetamine (AMPH) conditioning induced a conditioned place preference (CPP) in sexually naive (SN), but not pair-bonded (PB), males. Although AMPH treatment induced a similar magnitude of dopamine release in the nucleus accumbens (NAcc) of SN and PB males, it had differential effects on NAcc D1 receptor (D1R) binding. Specifically, AMPH treatment increased D1R binding in SN, but decreased D1R binding in PB males. NAcc D1R, but not D2 receptor, antagonism blocked AMPH-induced CPP in SN males and NAcc D1R activation before AMPH conditioning enabled AMPH-induced CPP in PB males. Together, our data demonstrate that pair-bonding experience decreases the rewarding properties of AMPH through a D1R-mediated mechanism.

Amphetamine alters behavior and mesocorticolimbic dopamine receptor expression in the monogamous female prairie vole

We have recently established the socially monogamous prairie vole (Microtus ochrogaster) as an animal model with which to investigate the involvement of mesocorticolimbic dopamine (DA) in the amphetamine (AMPH)-induced impairment of social behavior. As the majority of our work, to date, has focused on males, and sex differences are commonly reported in the behavioral and neurobiological responses to AMPH, the current study was designed to examine the behavioral and neurobiological effects of AMPH treatment in female prairie voles. We used a conditioned place preference (CPP) paradigm to determine a dose-response curve for the behavioral effects of AMPH in female prairie voles, and found that conditioning with low to intermediate (0.2 and 1.0 mg/kg), but not very low (0.1 mg/kg), doses of AMPH induced a CPP. We also found that exposure to a behaviorally relevant dose of AMPH (1.0 mg/kg) induced an increase in DA concentration in the nucleus accumbens (NAcc) and caudate putamen but not the medial prefrontal cortex or ventral tegmental area (VTA). Finally, repeated AMPH exposure (1.0 mg/kg once per day for 3 consecutive days; an injection paradigm that has been recently shown to alter DA receptor expression and impair social bonding in male prairie voles) increased D1, but not D2, receptor mRNA in the NAcc, and decreased D2 receptor mRNA and D2-like receptor binding in the VTA. Together, these data indicate that AMPH alters mesocorticolimbic DA neurotransmission in a region- and receptor-specific manner, which, in turn, could have profound consequences on social behavior in female prairie voles.

The role of mesocorticolimbic dopamine in regulating interactions between drugs of abuse and social behavior

The use of addictive drugs can have profound short- and long-term consequences on social behaviors. Similarly, social experiences and the presence or absence of social attachments during early development and throughout life can greatly influence drug intake and the susceptibility to drug abuse. The following review details this reciprocal interaction, focusing on common drugs of abuse (e.g., psychostimulants, opiates, alcohol and nicotine) and social behaviors (e.g., maternal, sexual, play, aggressive and bonding behaviors). The neural mechanisms underlying this interaction are discussed, with a particular emphasis on the involvement of the mesocorticolimbic dopamine system.

Genetics of aggression in voles

Prairie voles (Microtus ochrogaster) are socially monogamous rodents that form pair bonds-a behavior composed of several social interactions including attachment with a familiar mate and aggression toward conspecific strangers. Therefore, this species has provided an excellent opportunity for the study of pair bonding behavior and its underlying neural mechanisms. In this chapter, we discuss the utility of this unique animal model in the study of aggression and review recent findings illustrating the neurochemical mechanisms underlying pair bonding-induced aggression. Implications of this research for our understanding of the neurobiology of human violence are also discussed.

Chronic metals ingestion by prairie voles produces sex-specific deficits in social behavior: an animal model of autism

We examined the effects of chronic metals ingestion on social behavior in the normally highly social prairie vole to test the hypothesis that metals may interact with central dopamine systems to produce the social withdrawal characteristic of autism. Relative to water-treated controls, 10 weeks of chronic ingestion of either Hg(++) or Cd(++) via drinking water significantly reduced social contact by male voles when they were given a choice between isolation or contact with an unfamiliar same-sex conspecific. The effects of metals ingestion were specific to males: no effects of metals exposure were seen in females. Metals ingestion did not alter behavior of males allowed to choose between isolation or their familiar cage-mates, rather than strangers. We also examined the possibility that metals ingestion affects central dopamine functioning by testing the voles' locomotor responses to peripheral administration of amphetamine. As with the social behavior, we found a sex-specific effect of metals on amphetamine responses. Males that consumed Hg(++) did not increase their locomotor activity in response to amphetamine, whereas similarly treated females and males that ingested only water significantly increased their locomotor activities. Thus, an ecologically relevant stimulus, metals ingestion, produced two of the hallmark characteristics of autism - social avoidance and a male-oriented bias. These results suggest that metals exposure may contribute to the development of autism, possibly by interacting with central dopamine function, and support the use of prairie voles as a model organism in which to study autism.

Neuroplasticity in the mesolimbic system induced by natural reward and subsequent reward abstinence

BACKGROUND

Natural reward and drugs of abuse converge on the mesolimbic system, where drugs of abuse induce neuronal alterations. Here, we tested plasticity in this system after natural reward and the subsequent impact on drug responses.

METHODS

Effects of sexual experience in male rats on behavioral sensitization and conditioned place preference associated with d-amphetamine (AMPH) and Golgi-impregnated dendrites and spines of nucleus accumbens (NAc) cells were determined. Moreover, the impact of abstinence from sexual behavior in experienced males on these parameters was tested.

RESULTS

First, repeated sexual behavior induced a sensitized locomotor response to AMPH compared with sexually naive control subjects observed 1, 7, and 28 days after last mating session. Second, sexually experienced animals formed a conditioned place preference for lower doses of AMPH than sexually naive males, indicative of enhanced reward value of AMPH. Finally, Golgi-Cox analysis demonstrated increased numbers of dendrites and spines in the NAc core and shell with sexual experience. The latter two alterations were dependent on a period of abstinence of 7-10 days.

CONCLUSIONS

Sexual experience induces functional and morphological alterations in the mesolimbic system similar to repeated exposure to psychostimulants. Moreover, abstinence from sexual behavior after repeated mating was essential for increased reward for drugs and dendritic arbors of NAc neurons, suggesting that the loss of sexual reward might also contribute to neuroplasticity of the mesolimbic system. These results suggest that some alterations in the mesolimbic system are common for natural and drug reward and might play a role in general reinforcement.

Biological contribution to social influences on alcohol drinking: evidence from animal models

Social factors have a tremendous influence on instances of heavy drinking and in turn impact public health. However, it is extremely difficult to assess whether this influence is only a cultural phenomenon or has biological underpinnings. Research in non-human primates demonstrates that the way individuals are brought up during early development affects their future predisposition for heavy drinking, and research in rats demonstrates that social isolation, crowding or low social ranking can lead to increased alcohol intake, while social defeat can decrease drinking. Neurotransmitter mechanisms contributing to these effects (i.e., serotonin, GABA, dopamine) have begun to be elucidated. However, these studies do not exclude the possibility that social effects on drinking occur through generalized stress responses to negative social environments. Alcohol intake can also be elevated in positive social situations, for example, in rats following an interaction with an intoxicated peer. Recent studies have also begun to adapt a new rodent species, the prairie vole, to study the role of social environment in alcohol drinking. Prairie voles demonstrate a high degree of social affiliation between individuals, and many of the neurochemical mechanisms involved in regulation of these social behaviors (for example, dopamine, central vasopressin and the corticotropin releasing factor system) are also known to be involved in regulation of alcohol intake. Naltrexone, an opioid receptor antagonist approved as a pharmacotherapy for alcoholic patients, has recently been shown to decrease both partner preference and alcohol preference in voles. These findings strongly suggest that mechanisms by which social factors influence drinking have biological roots, and can be studied using rapidly developing new animal models.

Nucleus accumbens dopamine mediates amphetamine-induced impairment of social bonding in a monogamous rodent species

The prairie vole (Microtus ochrogaster) is a socially monogamous rodent species that forms pair bonds after mating, a behavior in which central dopamine (DA) has been implicated. Here, we used male prairie voles to examine the effects of drug exposure on pair bonding and related neural circuitry. In our first experiment, amphetamine (AMPH) motivated behavior was examined using a conditioned place preference (CPP) paradigm and was shown to be mediated by activation of D1-like DA receptors. Next, we examined the effects of repeated AMPH exposure on pair bonding. Intact and saline pretreated control males displayed mating-induced partner preferences, whereas males pretreated with AMPH at the doses effective to induce CPP failed to show mating-induced partner preferences. Such AMPH treatment also enhanced D1, but not D2, DA receptor expression in the nucleus accumbens (NAcc). Furthermore, pharmacological blockade of D1-like DA receptors in the NAcc rescued mating-induced partner preferences in AMPH-treated males. Together, our data indicate that repeated AMPH exposure may narrow the behavioral repertoire of male prairie voles via a DA receptor-specific mechanism in the NAcc, resulting in the impairment of pair bond formation.

The prairie vole: an emerging model organism for understanding the social brain

Unlike most mammalian species, the prairie vole is highly affiliative, forms enduring social bonds between mates and displays biparental behavior. Over two decades of research on this species has enhanced our understanding of the neurobiological basis not only of monogamy, social attachment and nurturing behaviors but also other aspects of social cognition. Because social cognitive deficits are hallmarks of many psychiatric disorders, discoveries made in prairie voles can direct novel treatment strategies for disorders such as autism spectrum disorder and schizophrenia. With the ongoing development of molecular, genetic and genomic tools for this species, prairie voles will likely maintain their current trajectory becoming an unprecedented model organism for basic and translational research focusing on the biology of the social brain.

Anterior hypothalamic vasopressin regulates pair-bonding and drug-induced aggression in a monogamous rodent

After pair-bonding, male prairie voles (Microtus ochrogaster) display aggression toward novel females but not toward their female partner. Here we show that this selective aggression in pair-bonded male prairie voles is associated with increased release of vasopressin (AVP) in the anterior hypothalamus (AH). Pharmacological activation of AVP-V1a receptors (V1aR) in the AH induced selective aggression in sexually naive males, whereas V1aR blockade diminished selective aggression in pair-bonded males. Pair-bonded males also showed an increased density in V1aR binding in the AH compared to their sexually naive counterparts and overexpression of V1aR in the AH, by viral vector-mediated gene transfer, facilitated aggression toward novel females. These data demonstrate that AH-AVP is both necessary and sufficient in the regulation of selective aggression associated with pair-bonding. In the second part of this study, we examined the effects of amphetamine (AMPH) exposure on female-directed aggression and revealed the potential role of AH-AVP underlying this behavior. Repeated AMPH administration in sexually naive male prairie voles enhanced V1aR expression in the AH and induced aggression toward a familiar or unfamiliar female. In addition, this AMPH-induced aggression was blocked by intra-AH administration of a V1aR antagonist. Together, our data reveal a socioneurobiological mechanism, highlighting a critical role of AH-AVP in the regulation of aggression induced by pair-bonding or drug experience in socially monogamous male prairie voles.