Nucleus accumbens oxytocin and dopamine interact to regulate pair bond formation in female prairie voles

Reward, motivation, and emotion systems associated with early-stage intense romantic love

Early-stage romantic love can induce euphoria, is a cross-cultural phenomenon, and is possibly a developed form of a mammalian drive to pursue preferred mates. It has an important influence on social behaviors that have reproductive and genetic consequences. To determine which reward and motivation systems may be involved, we used functional magnetic resonance imaging and studied 10 women and 7 men who were intensely "in love" from 1 to 17 mo. Participants alternately viewed a photograph of their beloved and a photograph of a familiar individual, interspersed with a distraction-attention task. Group activation specific to the beloved under the two control conditions occurred in dopamine-rich areas associated with mammalian reward and motivation, namely the right ventral tegmental area and the right postero-dorsal body and medial caudate nucleus. Activation in the left ventral tegmental area was correlated with facial attractiveness scores. Activation in the right anteromedial caudate was correlated with questionnaire scores that quantified intensity of romantic passion. In the left insula-putamen-globus pallidus, activation correlated with trait affect intensity. The results suggest that romantic love uses subcortical reward and motivation systems to focus on a specific individual, that limbic cortical regions process individual emotion factors, and that there is localization heterogeneity for reward functions in the human brain.

Opioid receptor function in social attachment in young domestic fowl

Opioid systems are implicated in social attachment processes. This research sought to determine the functional contribution of each opioid receptor in modulating social attachment/separation distress. Following ICV administration of opiate probes, 7-day-old cockerels were isolated from conspecifics for a 3 min test period under either a mirror or no-mirror condition. Vocalizations served as the measure of separation-stress. Opioid receptor probes included: the mu agonist DAMGO (0.02, 0.19, 1.95 nmol), the mu antagonist CTOP (0.009, 0.09, 0.9 nmol), the delta agonist SNC80 (0.3, 1.0, 3.0 micromol), the delta antagonist naltrindole (0.2, 2.2, 22.2 nmol), the kappa agonist U50, 488 (1, 30, 100 nmol), the kappa antagonist norBNI (1.3, 13.6, 136.1 nmol), the NOP agonist N/OFQ (0.01, 0.1, 1.0 nmol), and the NOP antagonist UFP-101 (0.1, 1.0, 10.0 nmol). DAMGO attenuated separation distress vocalizations. No other drug probe enhanced or attenuated distress vocalizations. Further, the non-selective opiate antagonist naloxone (0.3, 8.3, 27.5 nmol) did not exacerbate distress vocalizations. These results suggest that only the mu receptor modulates social attachment in young domestic fowl.

Neurochemical regulation of pair bonding in male prairie voles

Pair bonding represents social attachment between mates and is common among monogamous animals. The prairie vole (Microtus ochrogaster) is a monogamous rodent in which mating facilitates pair bond formation. In this review, we first discuss how prairie voles have been used as an excellent model for neurobiological studies of pair bonding. We then primarily focus on male prairie voles to summarize recent findings from neuroanatomical, neurochemical, cellular, molecular, and behavioral studies implicating vasopressin (AVP), oxytocin (OT), and dopamine (DA) in the regulation of pair bonding. Possible interactions among these neurochemicals in the regulation of pair bonding, the brain areas important for pair bond formation, and potential sexually dimorphic mechanisms underlying pair bonding are also discussed. As analogous social bonds are formed by humans, investigation of the neurochemical regulation of pair bond formation in prairie voles may be beneficial for our understanding of the mechanisms associated with normal and abnormal social behaviors in humans.

Anatomy and neurochemistry of the pair bond

Studies in monogamous rodents have begun to elucidate the neural circuitry underlying the formation and maintenance of selective pair bonds between mates. This research suggests that at least three distinct, yet interconnected, neural pathways interact in the establishment of the pair bond. These include circuits involved in conveying somatosensory information from the genitalia to the brain during sexual activity, the mesolimbic dopamine circuits of reward and reinforcement, and neuropeptidergic circuits involved specifically in the processing of socially salient cues. Here we present an integrated description of the interaction of these circuits in a model of pair bond formation in rodents with a discussion of the implications of these findings for evolution, individual variation, and human bonding.

Altered social behavior in pituitary adenylate cyclase-activating polypeptide type I receptor-deficient mice

The olfactory bulb plays a critical role in odor discrimination and in processing olfactory cues controlling social behavior in mammals. Given that the pituitary adenylate cyclase-activating polypeptide (PACAP) type 1 receptor (PAC1) is highly expressed in the olfactory bulb, we examined its role in regulating olfaction and social investigation. We found that olfactory detection of nonsocial stimuli was similar in PAC1-deficient mice and wild-type (WT) littermates. In contrast, PAC1-deficient mice displayed markedly abnormal social behaviors. PAC1-deficient mice exhibited a faster decrease in social investigation after repeated exposure to social cues or ovariectomized female urine compared with WT mice. Moreover, PAC1-deficient females exhibited delayed affiliative behavior when housed with novel males, and PAC1-deficient males displayed excessive sexual mounting toward both females and males as well as reduced aggression and increased licking and grooming toward intruder males. In aggregate, these results uncover PAC1 signaling as an important factor in the development and/or functioning of neural pathways associated with pheromone processing and the regulation of social interactions in mice. In turn, these studies raise the potential clinical relevance of PACAP signaling dysfunctions in neuropsychiatric disorders characterized by social reciprocity impairments such as autism spectrum disorders.