The genetic basis of parental care evolution in monogamous mice.

Parental care is essential for the survival of mammals, yet the mechanisms underlying its evolution remain largely unknown. Here we show that two sister species of mice, Peromyscus polionotus and Peromyscus maniculatus, have large and heritable differences in parental behaviour. Using quantitative genetics, we identify 12 genomic regions that affect parental care, 8 of which have sex-specific effects, suggesting that parental care can evolve independently in males and females. Furthermore, some regions affect parental care broadly, whereas others affect specific behaviours, such as nest building. Of the genes linked to differences in nest-building behaviour, vasopressin is differentially expressed in the hypothalamus of the two species, with increased levels associated with less nest building. Using pharmacology in Peromyscus and chemogenetics in Mus, we show that vasopressin inhibits nest building but not other parental behaviours. Together, our results indicate that variation in an ancient neuropeptide contributes to interspecific differences in parental care.

Effects of oxytocin and vasopressin administration on human fathers' sensitive and challenging parenting: A randomized within-subject controlled trial.

This randomized, double-blind, placebo-controlled within-subject study examined the effects of intranasal administration of oxytocin and vasopressin on fathers' sensitive and challenging parenting behaviors. Furthermore, we examined the moderating role of fathers' early childhood experiences. The sample consisted of 70 fathers with their 2- to 12-month-old infants. All fathers were assigned to each of the three experimental sessions (oxytocin, vasopressin, and placebo), on three separate days, with random order and intervening periods of one to two weeks. Sensitive and challenging parenting behaviors (CPB) were observed during a 10-minute free play task. Results showed no effects of vasopressin administration on paternal sensitivity. Fathers in the oxytocin condition were less sensitive than fathers in the placebo condition, and this effect was moderated by fathers' own childhood experiences: Fathers who reported higher levels of experienced parental love withdrawal were less sensitive in the oxytocin condition as compared to the placebo condition, whereas fathers with less experienced parental love withdrawal showed no difference in sensitivity between the oxytocin and placebo condition. No effects were found of oxytocin and vasopressin administration on fathers' CPB. Our results, although partly unexpected, are largely in line with previous literature showing that oxytocin administration can exert negative effects in individuals with adverse childhood experiences.

Do nonapeptides regulate parental care depending on experience in zebra finches?

Recent research suggests that the nonapeptide neurohormones regulate parental behaviors in a diverse array of vertebrates. However, it remains unclear how these neurohormones regulate parental care among birds, especially those which exhibit biparental care, or whether hormonal effects are contingent on a bird's previous experience as a parent. We measured the effects of nonapeptides on parental behaviors by peripherally injecting, over three treatment days, a short-acting nonapeptide receptor antagonist (OTA) or a saline control into breeding pairs of zebra finches (Taeniopygia guttata) that either did or did not have previous parental experience. We then compared how the duration of parental behaviors changed over the five days of observation (including one day before and two days after injections were administered). To compare treatment effects on parental outcomes, we also measured chick growth and mortality rates for each pair. There was a nearly significant interaction between treatment and experience for the amount of time birds spent in the nest, with time in the nest declining across the experiment inexperienced and experienced OTA birds. There was also a significant treatment by trial day interaction for nest guarding and a treatment by experience by trial day interaction for nest maintenance. Chicks reared by parents that received the OTA had significantly lower growth rates than chicks reared by control parents and, among experienced birds, higher mortality relative to control birds. Together, these results provide some support for the hypothesis that nonapeptides play a role in regulating parental outcomes and some parental behaviors in both experienced and inexperienced zebra finches.

Oxytocin increases after affiliative interactions in male Barbary macaques.

Mammals living in stable social groups often mitigate the costs of group living through the formation of social bonds and cooperative relationships. The neuropeptide hormone oxytocin (OT) is proposed to promote both bonding and cooperation although only a limited number of studies have investigated this under natural conditions. Our aim was to assess the role of OT in bonding and cooperation in male Barbary macaques (Macaca sylvanus). First, we tested for an effect of affiliation - grooming and triadic male-infant-male interactions - with bond and non-bond partners on urinary OT levels. Second, we tested whether grooming interactions (and thus increased OT levels) increase a male's general propensity to cooperate in polyadic conflicts. We collected >4000 h of behavioral data on 14 adult males and measured OT levels from 139 urine samples collected after affiliation and non-social control periods. Urinary OT levels were higher after grooming with any partner. By contrast, OT levels after male-infant-male interactions with any partner or with bond partners were not different from controls but were higher after interactions with non-bond partners. Previous grooming did not increase the likelihood of males to support others in conflicts. Collectively, our results support research indicating that OT is involved in the regulation of adult affiliative relationships. However, our male-infant-male interaction results contradict previous studies suggesting that it is affiliation with bond rather than non-bond partners that trigger the release of OT. Alternatively, OT levels were elevated prior to male-infant-male interactions thus facilitating interaction between non-bond partners. The lack of an association of grooming and subsequent support speaks against an OT linked increase in the general propensity to cooperate.

Oxytocin and CD38 in the paraventricular nucleus play a critical role in paternal aggression in mice.

In mammals, the development of healthy offspring requires maternal care. Behavior by lactating mothers toward other individuals is an important component of maternal aggression. However, it is unclear whether fathers display aggression primed by pups (an external factor), and the protection mechanism is poorly understood. To address this question, we examined paternal aggression in the ICR mouse strain. We found that sires exposed to cues from pups and lactating dams showed stronger aggression toward intruders than did sires that were deprived of family cues or exposed to nonlactating mates. c-Fos immunohistochemistry showed that cells in both the paraventricular and supraoptic nuclei (PVN and SON, respectively) in the hypothalamus of sires exposed to any cues were highly activated. However, c-Fos activation in oxytocinergic neurons was increased only in sires exposed to pup cues and solely in the PVN. In Cd38-knockout sires, the presence of pups induced no or reduced parental aggression; however, this phenotype was recovered, that is, aggression increased to the wild-type level, after intraperitoneal administration of oxytocin (OT). Specific c-Fos activation patterns induced by pup cues were not found in the PVN of knockout sires. These results demonstrate that the PVN is one of the primary hypothalamic areas involved in paternal aggression and suggest that a CD38-dependent OT mechanism in oxytocinergic neurons is critical for part of the behavior associated with the protection of offspring by nurturing male mice.

Functional New World monkey oxytocin forms elicit an altered signaling profile and promotes parental care in rats.

The neurohormone oxytocin is a key player in the modulation of reproductive and social behavioral traits, such as parental care. Recently, a correlation between different forms of oxytocin and behavioral phenotypes has been described in the New World Monkeys (NWMs). Here, we demonstrate that, compared with the Leu8OXT found in most placental mammals, the Cebidae Pro8OXT and Saguinus Val3Pro8OXT taxon-specific variants act as equi-efficacious agonists for the Gq-dependent pathway but are weaker agonists for the ß-arrestin engagement and subsequent endocytosis toward the oxytocin receptor (OXTR). Upon interaction with the AVPR1a, Pro8OXT and the common Leu8OXT yielded similar signaling profiles, being equally efficacious on Gq and ß-arrestin, while Val3Pro8OXT showed reduced relative efficacy toward ß-arrestin. Intranasal treatment with either of the variants increased maternal behavior and also promoted unusual paternal care in rats, as measured by pup-retrieval tests. We therefore suggest that Val3Pro8OXT and Pro8OXT are functional variants, which might have been evolutionarily co-opted as an essential part of the adaptive genetic repertoire that allowed the emergence of taxon-specific complex social behaviors, such as intense parental care in the Cebidae and the genus Saguinus.

Vasopressin, but not oxytocin, modulates responses to infant stimuli in marmosets providing care to dependent infants.

In family-living species, the quality and patterning of caregiving is the product of an individual's role within the family (mother, father, sibling) and parental experience, both of which interact with underlying neurobiological substrates. Among these substrates are the nonapeptides vasopressin and oxytocin, which modulate maternal, paternal, and alloparental care. We used a nonhuman primate model of the "nuclear family," the marmoset (Callithrix jacchus), to investigate relationships between caregiving experience, role within the family, and activation of either the oxytocin or vasopressin systems in shaping responsiveness to offspring. During two phases of offspring development (early infancy, juvenile), mothers, fathers, and older siblings were treated with vasopressin, oxytocin, or saline via intranasal application, and tested for responses to infant distress stimuli in a within-subjects design. Interest in infant stimuli was highest among marmosets that were caring for infants compared to those caring for juveniles, and parentally experienced marmosets were quicker to respond to infant stimuli than first-time caregivers. Moreover, marmosets treated with vasopressin showed enhanced responsiveness to infant stimuli compared to control stimuli only when caring for infants. Thus, in all classes of marmoset caregivers, vasopressin enhances responsiveness to infant-associated stimuli in caregivers during periods in which infant care is most crucial.

Androgen and prolactin manipulation induces changes in aggressive and nurturing behavior in a fish with male parental care.

Parental care can include two general types of behavior: (1) aggressive behavior, which is used to defend offspring from predators; and (2) nurturing behavior, which is used to provide offspring with environmental conditions or resources necessary for survival. Many studies have implicated androgens in promoting aggressive behavior and prolactin in promoting nurturing behavior. We experimentally manipulated these hormones to investigate their effects on parental care behavior in bluegill (Lepomis macrochirus). Parental males, which provide sole care to the developing eggs and larvae, received an implant with an androgen (11-ketotestosterone [11-KT]), an androgen antagonist (flutamide), prolactin, a prolactin-release inhibitor (bromocriptine), or castor oil (placebo). We found that 11-KT implants led to a significant increase in the frequency of aggressive behavior directed towards a simulated brood predator, and were associated with a nearly significant decrease in the frequency of nurturing behavior directed towards the developing eggs. In contrast, prolactin implants were associated with a significant increase in the frequency of nurturing behavior, but also reduced the frequency of aggressive behavior directed towards the simulated brood predator. These results suggest a hormone-mediated mechanistic trade-off between nurturing and aggressive behavior, whereby parental males are unable to be both highly nurturing and highly aggressive.

Effect of testosterone blockers on male aggression, song and parental care in an arctic passerine, the Lapland longspur (Calcarius lapponicus).

In many passerine birds, testosterone stimulates song and aggression but inhibits paternal care, but few studies have explored whether such effects can be reversed with testosterone blockers. We explored the effect of testosterone blockers on song, aggression and paternal care of Lapland longspurs (Calcarius lapponicus), an arctic passerine with a short breeding season. Twenty-one "blocker males" received implants containing an androgen receptor blocker and an aromatase inhibitor, compared to 27 control males with empty or no implants. Song, aggression and other behaviors were evaluated with simulated territorial intrusions (STI) during mate-guarding, and with focal observations (without STI) during mate-guarding and incubation. Nests were monitored and nestlings weighed as an indirect measure of paternal care. During STI, blocker males exhibited similar song rates, significantly lower aggression, and were significantly less likely to be found on territory than control males. Focal observations revealed no differences in spontaneous song, aggression, foraging, preening, or flight activity. Blocker males' nestlings had greater body mass on day 5 after hatching, but this difference disappeared by fledging, and both groups fledged similar numbers of young. Two blocker males exhibited unusual paternal care: incubation and brooding of young, or feeding of nestlings at another male's nest. In sum, testosterone blockers affected aggression but not song, contrasting with results from previously published testosterone implant studies. Effects on paternal care were concordant with testosterone implant studies. These patterns may be related to rapid behavioral changes characteristic of the short breeding season of the Arctic.

Role of oxytocin in the medial preoptic area (MPOA) in the modulation of paternal behavior in mandarin voles.

Parental care plays an important role in individual survival and development in mammals. Many studies have focused on the mechanisms underlying maternal behavior. However, the underlying neural mechanisms of paternal behavior are less understood. Using monogamous mandarin voles (Microtus mandarinus), the present study found that fathers initiated more paternal behavior and the virgin male showed more infanticide. Moreover fathers had shorter latency to approach a pup at the postnatal day (PND) 10 than PND1, PND20 than nonfathers. Fathers had a shorter latency to take care of unfamiliar pups than nonfathers. They had higher levels of paternal behavior at PND 10 than PND1 and PND20 toward the mandarin vole pups. Fathers had a significantly higher serum concentration of oxytocin (OT) than virgin males. Both RT-PCR and Western blot results indicated that the levels of the oxytocin receptor (OTR) in the medial preoptic area (MPOA) of fathers were significantly higher than in virgin males, but the levels of vasopressin 1a receptor (V1AR) mRNA and protein expression in the MPOA did not show significant differences. Microinjection of an oxytocin receptor antagonist into the MPOA significantly reduced the total duration of paternal behavior and increased the latency to approach the pup and initiate paternal behavior. Our results indicated that OT plays a key role in the modulation of paternal behavior via the MPOA.

Synthesis of oxytocin derivatives lipidated via a carbonate or carbamate linkage as a long-acting therapeutic agent for social impairment-like behaviors.

In the course of our studies of hydrophobic oxytocin (OT) analogues, we newly synthesized lipidated OT (LOT-4a-c and LOT-5a-c), in which a long alkyl chain (C14-C16) is conjugated via a carbonate or carbamate linkage at the Tyr-2 phenolic hydroxy group and a palmitoyl group at the terminal amino group of Cys-1. These LOTs did not activate OT and vasopressin receptors. Among the LOTs, however, LOT-4c, having a C16-chain via a carbonate linkage at the phenolic hydroxyl group of the Tyr-2, showed very long-lasting action for the recovery of impaired social behavior in CD38 knockout mice, a rodent model of autistic phenotypes, whereas the effect of OT itself rapidly diminished. These results indicate that LOT-4c may serve as a potential prodrug in mice.

An increase in estradiol facilitates the onset of paternal behavior in the dwarf hamster (Phodopus campbelli).

In the dwarf hamster (Phodopus campbelli), activational effects of testosterone (T) and estradiol (E2) in the regulation of paternal behavior have been repeatedly rejected because peripheral concentrations of E2 do not change across the reproductive cycle of males. Further, castration no affected paternal behavior despite that both T and E2 concentrations decreased significantly. However, the role of these hormones has not been evaluated in models of castration and hormonal replacement in virgin males. Here, we analysed the effects of E2 and T in paternal behavior in virgin male dwarf hamster (Phodopus campbelli). Thirty paternal (PAT) males were bilaterally castrated; of them, 10 were implanted with T, 10 with E2 and 10 males received no treatment. Other 10 PAT males underwent sham-castration. Seventeen aggressive (AGG) males were also bilaterally castrated; of these, 10 AGG received E2 replacement, 7 were not treated. Other 7 AGG males were submitted to sham-castration. Following treatments, paternal behavior tests were conducted again. T and E2 levels in plasma were quantified by radioimmunoassay (RIA). The results showed that the treatments did not affect the paternal behavior of males that were initially paternal. Neither castration nor sham-castration surgery affected the behavior of AGG males. However, when these males were treated with E2 and the concentrations of this hormone increase significantly they became paternal. Our data suggest that an increase in E2 levels shifted infanticidal behavior to paternal behavior in dwarf hamster.

Intranasal oxytocin, but not vasopressin, augments neural responses to toddlers in human fathers.

This study investigates paternal brain function with the hope of better understanding the neural basis for variation in caregiving involvement among men. The neuropeptides oxytocin (OT) and vasopressin (AVP) are implicated in paternal caregiving in humans and other species. In a double-blind, placebo-controlled, within-subject pharmaco-functional MRI experiment, we randomized 30 fathers of 1-2year old children to receive either 24IU intranasal OT before one scan and placebo before the other scan (n=15) or 20IU intranasal AVP before one scan and placebo before the other scan (n=15). Brain function was measured with fMRI as the fathers viewed pictures of their children, unknown children and unknown adults, and as they listened to unknown infant cry stimuli. Intranasal OT, but not AVP, significantly increased the BOLD fMRI response to viewing pictures of own children within the caudate nucleus, a target of midbrain dopamine projections, as well as the dorsal anterior cingulate (dACC) and visual cortex, suggesting that intranasal oxytocin augments activation in brain regions involved in reward, empathy and attention in human fathers. OT effects also varied as a function of order of administration such that when OT was given before placebo, it increased activation within several reward-related structures (substantia nigra, ventral tegmental area, putamen) more than when it was given after placebo. Neither OT nor AVP had significant main effects on the neural response to cries. Our findings suggest that the hormonal changes associated with the transition to fatherhood are likely to facilitate increased approach motivation and empathy for children, and call for future research that evaluates the potential of OT to normalize deficits in paternal motivation, as might be found among men suffering from post-partum depression.

Estrogen-dependent modifications to hippocampal plasticity in paternal California mice (Peromyscus californicus).

In many biparental species, mothers and fathers experience similar modifications to circulating hormones. With these modifications come alterations in neural structure and function suggesting that neuroendocrine mechanisms may underlie postpartum plasticity in both males and females. In the biparental California mouse (Peromyscus californicus), adult neurogenesis is maintained and anxiety-like behavior is attenuated in fathers during the mid-postpartum period. Given a causal relationship between estrogen and regulation of both adult neurogenesis and anxiety, we aimed to elucidate the role of estrogen-dependent mechanisms in paternal experience-related modifications to hippocampal neuroplasticity in California mice. In Experiment 1, hippocampal estrogen receptor beta (ERß) mRNA expression, along with circulating estradiol concentrations, were determined throughout the postpartum period. An upregulation in ERß expression was observed in postnatal day 16 males compared to virgins. Additionally, a rise in circulating estradiol concentrations was detected on postnatal day 2 compared to virgins; levels began to decline toward virgin levels on postnatal day 16 and postnatal day 30. In Experiment 2, we determined the role of estrogen-dependent mechanisms in adult neurogenesis and anxiety-like behavior by treating virgin and paternal males with saline or the selective estrogen receptor modulator, tamoxifen (TMX), during the time of axon extension (i.e., one week after bromodeoxyuridine injection). While TMX failed to alter elevated plus maze performance, TMX treatment inhibited survival of adult born neurons but only in paternal mice. These findings highlight the potential for estrogen-dependent pathways to mediate hippocampal adult neurogenesis in paternal mice.

Opposite effects of nonapeptide antagonists on paternal behavior in the teleost fish Amphiprion ocellaris.

The nonapeptides isotocin (IT) and arginine vasotocin (AVT), along with their mammalian homologs oxytocin and arginine vasopressin, are well known regulators of social behaviors across vertebrate taxa. However, little is known about their involvement in paternal care. Here, we measured the effect of an IT and an AVT V1a receptor antagonist on paternal behaviors in the primarily paternal teleost Amphiprion ocellaris. We also measured the effect of the IT receptor antagonist on aggression in dyadic contests between two non-reproductive fish to assess specificity of the effect on paternal behaviors. Individual differences in levels of paternal behaviors (nips, fanning the eggs, and proportion of the time in the nest) were consistent across spawning cycles when no treatments were administered. The IT receptor antagonist severely reduced paternal behaviors but had no effect on aggression, whereas the AVT V1a receptor antagonist increased paternal behaviors. These results support the idea that IT signaling is crucial for the expression of paternal behavior in A. ocellaris. Based on a previous study showing that the AVT V1a antagonist decreases aggression in dyadic contests, we hypothesize that the antagonist enhances paternal behavior indirectly by reducing vigilance and aggression, thereby alleviating effort directed towards other competing behaviors and allowing for the increased expression of paternal behaviors.

Changes in Glutathione S-Transferase Activity and Parental Care Patterns in a Catfish (Pisces, Ariidae) as a Biomarker of Anthropogenic Impact in a Brazilian Harbor.

Catfish have been used as a model system for studying biochemical mechanisms of biotransformation. The main goal of this study was to identify alterations in hepatic glutathione S-transferase (GST) activity and changes in the parental care pattern of a mouth-brooding catfish, Sciades herzbergii, as a biomarker of anthropogenic impact in a port area on the northeastern coast of Brazil. The fish were sampled from a natural reserve (A1 = reference site) and from an industrialized port area (A2 = impacted site). Two analyses were carried out: hepatic GST activity and mouth-brooding behavior of males. Catfish collected from the A1 site displayed all stages of gonadal maturation, and some of the adult males were mouth brooding 12-30 embryos. Not all gonadal maturation stages of the catfish were represented at the A2 site, and no mouth-brooding males were observed. GST activity in the liver of S. herzbergii was significantly higher in fish from the impacted site compared with fish from the reference site. Values for the enzymatic activity increased progressively in fish sampled from the reserve area as they became more reproductively mature (immature ≤ maturing ≤ mature ≤ spent). However, the greatest values for GST activity (2.84 ± 0.31 µmol min-1 mg protein-1) among fish sampled from the impacted area were found in (immature) juveniles. These data suggest that changes in hepatic GST activity and mouth-brooding behavior of S. herzbergii can be used as biomarkers of anthropogenic impact.

Hormonal stimulation and paternal experience influence responsiveness to infant distress vocalizations by adult male common marmosets, Callithrix jacchus.

Parental experience and hormones play a large role in the common marmoset (Callithrix jacchus) father's care of their offspring. We tested the effect of exogenous estradiol or testosterone on the responsiveness of common marmosets to respond to infant distress vocalizations and whether males who haven't become fathers yet (paired males) would have increased responsiveness to infant distress calls with either steroid or whether parental experience is the most important component for the onset of paternal care. Sixteen male marmosets (8 fathers, 8 paired males) received a vehicle, low dose or high dose of estradiol and additional 16 males were tested with testosterone at three doses for their response either to a vocal control or a recording of an infant distress call for 10min. Without steroid stimulation fathers were significantly more likely to respond to the infant distress stimulus than paired males. Low dose estradiol stimulation resulted in a significant increase in fathers' behavioral response towards the infant distress stimulus but not in paired males. Fathers also showed a significant increase in infant responsiveness from the vehicle dose to the estradiol low dose treatment, but not to the estradiol high dose treatment. Testosterone treatment did not show significant differences between infant responsiveness at either dose and between fathers and paired males. We suggest that neither steroid is involved in the onset of paternal care behaviors in the marmoset but that estradiol may be involved in facilitating paternal motivation in experienced fathers.

Effects of postnatal estrogen manipulations on juvenile alloparental behavior.

Sex- and species-specific patterns of estrogen receptor (ER)-α expression are established early in development, which may contribute to sexual differentiation of behavior and determine male social organization. The current study investigated the effects of ERα and ERß activation during the second postnatal week on subsequent alloparental behavior and ERα expression in juvenile prairie voles. Male and female pups were treated daily with 17ß-estradiol (E2, ERα/ERß agonist), PPT (selective ERα agonist), DPN (selective ERß agonist), or the oil vehicle on postnatal days (PD) 8-14. Alloparental behavior and ERα expression were examined at PD21. PPT treatment inhibited prosocial motivation in males and increased pup-directed aggression in both sexes. E2 and DPN had no apparent effect on behavior in either sex. PPT-treated males had increased ERα expression in the medial preoptic area (MPN), medial amygdala (MEApd) and bed nucleus of the stria terminalis (BSTpr). DPN treatment also increased ERα expression in males, but only in the BSTpr. Female ERα expression was unaffected by treatment. These results support the hypothesis that ERα activation in early life is associated with less prosocial patterns of central ERα expression and alloparental behavior in males. The lack of an effect of E2 on behavior suggests that ERß may antagonize the effects of ERα on alloparental behavior. The results in DPN-treated males suggest that ERα in the MEApd, and not the BSTpr, may be a primary determinant of alloparental behavior in males.

Oxytocin and vasopressin enhance responsiveness to infant stimuli in adult marmosets.

The neuropeptides oxytocin (OT) and arginine-vasopressin (AVP) have been implicated in modulating sex-specific responses to offspring in a variety of uniparental and biparental rodent species. Despite the large body of research in rodents, the effects of these hormones in biparental primates are less understood. Marmoset monkeys (Callithrix jacchus) belong to a clade of primates with a high incidence of biparental care and also synthesize a structurally distinct variant of OT (proline instead of leucine at the 8th amino acid position; Pro(8)-OT). We examined the roles of the OT and AVP systems in the control of responses to infant stimuli in marmoset monkeys. We administered neuropeptide receptor agonists and antagonists to male and female marmosets, and then exposed them to visual and auditory infant-related and control stimuli. Intranasal Pro(8)-OT decreased latencies to respond to infant stimuli in males, and intranasal AVP decreased latencies to respond to infant stimuli in females. Our study is the first to demonstrate that Pro(8)-OT and AVP alter responsiveness to infant stimuli in a biparental New World monkey. Across species, the effects of OT and AVP on parental behavior appear to vary by species-typical caregiving responsibilities in males and females.

A mechanism for rapid neurosteroidal regulation of parenting behaviour.

While systemic steroid hormones are known to regulate reproductive behaviour, the actual mechanisms of steroidal regulation remain largely unknown. Steroidogenic enzyme activity can rapidly modulate social behaviour by influencing neurosteroid production. In fish, the enzyme 11ß-hydroxysteroid dehydrogenase (11ß-HSD) synthesizes 11-ketotestosterone (KT, a potent teleost androgen) and deactivates cortisol (the primary teleost glucocorticoid), and both of these steroid hormones can regulate behaviour. Here, we investigated the role of neurosteroidogenesis in regulating parenting in a haremic bidirectionally hermaphroditic fish, Lythrypnus dalli, where males provide all requisite parental care. Using an in vitro assay, we found that an 11ß-HSD inhibitor, carbenoxolone (CBX), reduced brain and testicular KT synthesis by 90% or more. We modulated neurosteroid levels in parenting males via intracerebroventricular injection of CBX. Within only 20 min, CBX transiently eliminated parenting behaviour, but not other social behaviour, suggesting an enzymatic mechanism for rapid neurosteroidal regulation of parenting. Consistent with our proposed mechanism, elevating KT levels rescued parenting when paired with CBX, while cortisol alone did not affect parenting. Females paired with the experimental males opportunistically consumed unattended eggs, which reduced male reproductive success by 15%, but some females also exhibited parenting behaviour and these females had elevated brain KT. Brain KT levels appear to regulate the expression of parenting behaviour as a result of changes in neural 11ß-HSD activity.