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

Responses and functions of dopamine in nucleus accumbens core during social behaviors

Social behaviors are among the most important motivated behaviors. How dopamine (DA), a "reward" signal, releases during social behaviors has been a topic of interest for decades. Here, we use a genetically encoded DA sensor, GRABDA2m, to record DA activity in the nucleus accumbens (NAc) core during various social behaviors in male and female mice. We find that DA releases during approach, investigation and consummation phases of social behaviors signal animals' motivation, familiarity of the social target, and valence of the experience, respectively. Positive and negative social experiences evoke opposite DA patterns. Furthermore, DA releases during mating and fighting are sexually dimorphic with a higher level in males than in females. At the functional level, increasing DA in NAc enhances social interest toward a familiar conspecific and alleviates defeat-induced social avoidance. Altogether, our results reveal complex information encoded by NAc DA activity during social behaviors and their multistage functional roles.

Circuit selectivity in drug versus natural reward seeking behaviors

Substance use disorder (SUD) is characterized, in part by behavior biased toward drug use and away from natural sources of reward (e.g., social interaction, food, sex). The neurobiological underpinnings of SUDs reveal distinct brain regions where neuronal activity is necessary for the manifestation of SUD-characteristic behaviors. Studies that specifically examine how these regions are involved in behaviors motivated by drug versus natural reward allow determinations of which regions are necessary for regulating seeking of both reward types, and appraisals of novel SUD therapies for off-target effects on behaviors motivated by natural reward. Here, we evaluate studies directly comparing regulatory roles for specific brain regions in drug versus natural reward. While it is clear that many regions drive behaviors motivated by all reward types, based on the literature reviewed we propose a set of interconnected regions that become necessary for behaviors motivated by drug, but not natural rewards. The circuitry is selectively necessary for drug seeking includes an Action/Reward subcircuit, comprising nucleus accumbens, ventral pallidum, and ventral tegmental area, a Prefrontal subcircuit comprising prelimbic, infralimbic, and insular cortices, a Stress subcircuit comprising the central nucleus of the amygdala and the bed nucleus of the stria terminalis, and a Diencephalon circuit including lateral hypothalamus. Evidence was mixed for nucleus accumbens shell, insular cortex, and ventral pallidum. Studies for all other brain nuclei reviewed supported a necessary role in regulating both drug and natural reward seeking. Finally, we discuss emerging strategies to further disambiguate the necessity of brain regions in drug- versus natural reward-associated behaviors.

Biparental care in C57BL/6J mice: effects on adolescent behavior and alcohol consumption

RATIONALE

Social attachment plays an important role in offspring development. Different parenting experiences during lactation may shape offspring behavior and later alcohol use.

OBJECTIVES

We tested the hypothesis that differential rearing conditions (single mother, SM or biparental, BP) in the non-monogamous C57BL/6J mice may affect (1) parental behavior during lactation, (2) adolescent behavior, and (3) adolescent initiation of alcohol drinking.

METHODS

Mice were reared in SM or BP (cohabitation of father-mother since copulation) condition until weaning (postnatal day, PND, 21). Litters from both conditions were filmed during PNDs 6, 9, and 12 and an ethogram was made taking into account nest-, pup-, or self-directed behaviors. At PNDs, 28-29 adolescent animals were evaluated in a modified version of the concentric square field for measurement of behavioral patterns. Other groups of adolescents were tested in a 4-h daily, two-bottle choice alcohol consumption test (10% alcohol vs. water) during 3 weeks (4 days per week).

RESULTS

Single mothers spent less time in the nest, left unattended the nest more times, displayed more self-directed and less pup-directed behaviors than BP parents. SM-reared adolescents displayed more anxiogenic-like and less risk-associated behaviors than BP counterparts. The alcohol consumption test indicated a strong effect of rearing condition. Since the fifth day of test, SM adolescents consumed more quantities of alcohol than BP adolescents.

CONCLUSIONS

During single-mother parenting, pups are left unattended more often, and during adolescence, these organisms exhibited increased anxiety responses. This behavioral phenotype may act as a risk factor for alcohol initiation during adolescence.

Exposure to quinestrol and levonorgestrel affects maternal behavior and offspring development in midday gerbil (Meriones meridianus)

Quinestrol and levonorgestrel (EP-1, at a ratio of 1:2) are often used as anti-fertility compounds (sterilants) in rodents. As most of the research has focused on the sterility and damage caused in parental reproductive organs, there is little research on the effect of these contraceptive hormones on maternal behavior and offspring's early development. In this study, we examined maternal behavior after treatment with different doses of EP-1 (10 ml/kg) at postnatal days 3 and 10, separately. Various parameters were measured after treatment, including oxytocin expression, serum levels of estradiol and luteinizing hormone (LH), ovary damage after weaning of offspring, as well as the development and ultrasonic vocalizations (USVs) of midday gerbil (Meriones meridianus) offspring. At postnatal days 5 and 12, the EP-1 increased maternal licking, grooming, and retrieving behavior, while reducing contacting behavior. Oxytocin expression in the hypothalamic paraventricular and supraoptic nuclei increased, while the levels of estradiol and LH decreased. The ovaries and the development of follicles were clearly affected by the treatment. The EP-1 significantly reduced the pups' body weight, the amount and pulse duration of USVs, whereas the frequency range variation of USVs was increased. Overall, treatment with EP-1 during lactation significantly affected maternal behavior and impaired offspring early development in the midday gerbil.

Neuroendocrinology and Adaptive Physiology of Maternal Care

Parental care is critical for offspring survival in many species. In mammals, parental care is primarily provided through maternal care, due to obligate pregnancy and lactation constraints, although some species also show paternal and alloparental care. These behaviors are driven by specialized neural circuits that receive sensory, cortical, and hormonal input to generate a coordinated and timely change in behavior, and sustain that behavior through activation of reward pathways. Importantly, the hormonal changes associated with pregnancy and lactation also act to coordinate a broad range of physiological changes to support the mother and enable her to adapt to the demands of these states. This chapter will review the neural pathways that regulate maternal behavior, the hormonal changes that occur during pregnancy and lactation, and how these two facets merge together to promote both young-directed maternal responses (including nursing and grooming) and young-related responses (including maternal aggression and other physiological adaptions to support the development of and caring for young). We conclude by examining how experimental animal work has translated into knowledge of human parenting, particularly in regards to maternal mental health issues.

Effects of paternal deprivation on cocaine-induced behavioral response and hypothalamic oxytocin immunoreactivity and serum oxytocin level in female mandarin voles

Early paternal behavior plays a critical role in behavioral development in monogamous species. The vast majority of laboratory studies investigating the influence of parental behavior on cocaine vulnerability focus on the effects of early maternal separation. However, comparable studies on whether early paternal deprivation influences cocaine-induced behavioral response are substantially lacking. Mandarin vole (Microtus mandarinus) is a monogamous rodent with high levels of paternal care. After mandarin vole pups were subjected to early paternal deprivation, acute cocaine- induced locomotion, anxiety- like behavior and social behavior were examined in 45day old female pups, while hypothalamic oxytocin immunoreactivity and serum oxytocin level were also assessed. We found that cocaine increased locomotion and decreased social investigation, contact behavior and serum oxytocin level regardless of paternal care. Cocaine increased anxiety levels and decreased oxytocin immunoreactive neurons of the paraventricular nuclei and supraoptic nuclei in the bi-parental care group, whilst there were no specific effects in the paternal deprivation group. These results indicate that paternal deprivation results in different behavioral response to acute cocaine exposure in adolescents, which may be in part associated with the alterations in oxytocin immunoreactivity and peripheral OT level.

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.

Behavioral responses to pups in males with different reproductive experiences are associated with changes in central OT, TH and OTR, D1R, D2R mRNA expression in mandarin voles

Male rodents behave differently toward pups because of different sexual and/or paternal experiences; however, the mechanisms underlying these responses are not well understood. Using socially monogamous mandarin voles (Microtus mandarinus) we investigated the behavioral responses of males with different reproductive experiences (virgin males, paired males and new fathers) to new born pups. Central levels of neuropeptide oxytocin (OT), tyrosine hydroxylase (TH), as well as oxytocin receptor (OTR), dopamine 1-type receptor (D1R) and dopamine 2-type receptor (D2R) mRNA expression in the nucleus accumbens and medial amygdala were also measured in these males. Our data showed that new fathers exhibited more approaching behavior and contained more OT-immunoreactive and TH-immunoreactive neurons. In addition to increased OTR mRNA expression in the nucleus accumbens and medial amygdala, new fathers had higher D1R and D2R mRNA expression in the nucleus accumbens, and less D1R and D2R mRNA expression in the medial amygdala than paired males. These results demonstrate that males with different reproductive experiences display different behavioral responses to pups and that these differences are associated with altered OT and dopamine, and their receptors in specific brain regions.

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.