Neonatal manipulation of oxytocin alters oxytocin levels in the pituitary of adult rats.

The neuropeptide oxytocin (OT) and its OT antagonists (OTA) in infant rats affect their behavior as adults. In this study we attempted to determine whether treating rats on the day of birth (postnatal day 1) with OT or OTA would affect brain OT levels of these rats as adults. Rat pups were injected with OT (3 microg), OTA (0.3 microg) or saline vehicle ip on postnatal day 1. As 60-day-old adults, treated rats were killed, and the OT content in their medial preoptic areas (MPOAs), medial hypothalami (MH) and pituitaries were assayed. In females, treatment with OTA on postnatal day 1 significantly decreased pituitary OT levels as adults. In males, by contrast, treatment with OTA on postnatal day 1 resulted in increased pituitary OT levels when they become adults compared to male rats treated with OT on postnatal day 1. There were no significant effects of neonatal treatment on OT levels in either the MH or MPOA. Day 1 postnatal treatment with OT or OTA had a long-term sexually dimorphic effect on OT levels in the pituitary.     

Endogenous oxytocin is necessary for preferential Fos expression to male odors in the bed nucleus of the stria terminalis in female Syrian hamsters

Successful reproduction in mammals depends on proceptive or solicitational behaviors that enhance the probability of encountering potential mates. In female Syrian hamsters, one such behavior is vaginal scent marking. Recent evidence suggests that the neuropeptide oxytocin (OT) may be critical for regulating this behavior. Blockade of OT receptors in the bed nucleus of the stria terminalis (BNST) or the medial preoptic area (MPOA) decreases vaginal marking responses to male odors; lesion data suggest that BNST, rather than MPOA, mediates this effect. However, how OT interacts with sexual odor processing to drive preferential solicitation is not known. To address this issue, intact female Syrian hamsters were exposed to male or female odors and their brains processed for immunohistochemistry for Fos, a marker of recent neuronal activation, and OT. Additional females were injected intracerebroventricularly (ICV) with an oxytocin receptor antagonist (OTA) or vehicle, and then tested for vaginal marking and Fos responses to sexual odors. Colocalization of OT and Fos in the paraventricular nucleus of the hypothalamus was unchanged following exposure to male odors, but decreased following exposure to female odors. Following injections of OTA, Fos expression to male odors was decreased in BNST, but not in MPOA or the medial amygdala (MA). Fos expression in BNST may be functionally relevant for vaginal marking, given that there was a positive correlation between Fos expression and vaginal marking for BNST, but not MPOA or MA. Together, these data suggest that OT facilitation of neuronal activity in BNST underlies the facilitative effects of OT on solicitational responses to male odors.     

Neonatal manipulation of oxytocin influences female reproductive behavior and success

During early neonatal development, oxytocin (OT) may influence the expression of adult behavior and physiology. Here we test the prediction that early postnatal exposure to OT or an oxytocin antagonist (OTA) can affect the subsequent expression of sexual receptivity and reproductive success of females. To test this hypothesis, female prairie voles (Microtus ochrogaster) received one of four treatments within 24 h of birth. Three groups received an intraperitoneal injection of OT, OTA, or isotonic saline. A fourth group was handled, but not injected. Around 75 days of age, females were paired with sexually experienced males for 72 h and sexual activity was recorded. Treatment had no effect on the probability of mating. Injection, regardless of treatment, reduced latency to mate compared with handled controls. OT and OTA treatment decreased mating bout frequency compared to saline and handled controls, while OTA treatment increased reproductive success, probability of successfully producing a litter. The results suggest that neonatally OT, both endogenous and exogenous, can affect the expression of adult female reproductive activity and that blocking the effects of endogenous OT during neonatal development can affect female reproductive success. Finally, the results suggest that a number of aspects of reproduction are regulated by OT during the postnatal period, but that the mechanism of action may differ depending upon the reproductive activity.     

Both oxytocin and vasopressin may influence alloparental behavior in male prairie voles

Neuropeptides, especially oxytocin (OT) and arginine vasopressin (AVP), have been implicated in several features of monogamy including alloparenting. The purpose of the present study was to examine the role of OT and AVP in alloparental behavior in reproductively na?ve male prairie voles. Males received intracerebroventricular (ICV) injections of artificial cerebrospinal fluid (aCSF), OT, an OT receptor antagonist (OTA), AVP, an AVP receptor antagonist (AVPA), or combinations of OTA and AVPA and were subsequently tested for parental behavior. Approximately 45 min after treatment, animals were tested for behavioral responses to stimulus pups. In a 10-min test, spontaneous alloparental behavior was high in control animals. OT and AVP did not significantly increase the number of males that showed parental behavior, although more subtle behavioral changes were observed. Combined treatment with AVPA and OTA (10 ng each) significantly reduced male parental behavior and increased attacks; following a lower dose (1 ng OTA/1 ng AVPA), males were less likely to display kyphosis and tended to be slower to approach pups than controls. Since treatment with only one antagonist did not interfere with the expression of alloparenting, these results suggest that access to either OT or AVP receptors may be sufficient for the expression of alloparenting.     

Adolescent exposure to oxytocin,but not the selective oxytocin receptor agonist TGOT,increases social behavior and plasma oxytocin in adulthood

There are indications that exposing adolescent rodents to oxytocin (OT) may have positive “trait-changing” effects resulting in increased sociability and decreased anxiety that last well beyond acute drug exposure and into adulthood. Such findings may have relevance to the utility of OT in producing sustained beneficial effects in human psychiatric conditions. The present study further examined these effects using an intermittent regime of OT exposure in adolescence, and using Long Evans rats, that are generally more sensitive to the acute prosocial effects of OT. As OT has substantial affinity for the vasopressin V1a receptor (V1aR) in addition to the oxytocin receptor (OTR), we examined whether a more selective peptidergic OTR agonist – [Thr4, Gly7]-oxytocin (TGOT) – would have similar lasting effects on behavior. Male Long Evans rats received OT or TGOT (0.5–1 mg/kg, intraperitoneal), once every three days, for a total of 10 doses during adolescence (postnatal day (PND) 28–55). Social and anxiety-related behaviors were assessed during acute administration as well as later in adulthood (from PND 70 onwards). OT produced greater acute behavioral effects than TGOT, including an inhibition of social play and reduced rearing, most likely reflecting primary sedative effects. In adulthood, OT but not TGOT pretreated rats displayed lasting increases in social interaction, accompanied by an enduring increase in plasma OT. These findings confirm lasting behavioral and neuroendocrine effects of adolescent OT exposure. However, the absence of such effects with TGOT suggests possible involvement of the V1aR as well as the OTR in this example of developmental neuroplasticity.     

小型田鼠:研究单配制进化与调控的模型

哺乳动物的单配制通常被认为是社会性单配制,它不是单纯地由性行为来决定,而是由诸多因素,包括长期的pair bond、夫妻双方共同抚育后代、免近亲交配以及雌雄两性相似等来决定的。在这篇综述中,我们论述了如何以啮齿类田鼠属(Microtus)为模型,通过比较研究来帮助我们理解社会性单配制的进化以及其神经调控机制。对田鼠属的研究不仅证实了单配制起源于艰苦的生存条件的假说,而且还证实了雌性性选择可能有利于维持单配制。不仅如此,哺乳动物单配制的进化还需要雄性的prosocial行为的不断强化。例如,亲近行为可以促进pairbond的形成并强化雄性对后代的哺育行为,而这种强化则来源于神经多肽催产素(OT)和加压素(AVP)与类固醇类激素的相互作用。催产素和加压素调控pairbond和双亲哺育行为的表达,而单配制和多配制田鼠的催产素和加压素受体在脑内的分布有显的不同。比较研究揭示了小型田鼠单配制的调控机制,而种内差异和行为上的可塑性则有助于我们进一步理解这种机制。比如,在某些条件下,多配制的草原田鼠(Microtus pennsylvanicu)的雄性个体具有哺育后代的行为。尽管草原田鼠的加压素Vla受体在脑内的分布与其他多配制的田鼠相似,但是如果脑室注射加压素,仍可以诱发其哺育后代的行为。同样是单配制的橙腹田鼠(Microtus ochrogaster),生活在：Illnois的显示出高水平的prosocial行为,而生活在Kansas的则表现出较低水平的社会性行为。即使两个种群的催产素或加压素Vla受体在脑内的分布相同,它们的雌激素受体表达水平显不同,这在雄性个体表现尤其明显。与Kansas的雄性个体相比,在终纹床核(bed rucleus of the stria tenninalis)和杏仁核中区(medial amygdala)这两个调控亲近行为和攻击行为的脑区,Illinois的雄性个体的α雌激素受体的水平要低得多。这些研究表明对雌激素的低敏感程度有利于高水平地表达prosocial行为并降低特定类型的攻击行为。     

Peripherally administered non-peptide oxytocin antagonist, L368,899, accumulates in limbic brain areas: a new pharmacological tool for the study of social motivation in non-human primates

Central administration of oxytocin (OT) antagonists inhibits maternal and sexual behavior in non-primates, providing the strongest experimental evidence that endogenous OT facilitates these behaviors. While there have been a few reports that ICV administration of OT increases social behaviors in monkeys, no studies to date have assessed the effects of OT antagonists. Therefore, we studied in rhesus monkeys whether L368,899, a non-peptide antagonist produced by Merck that selectively blocks the human uterine OT receptor, penetrates the CNS after peripheral administration and alters female maternal and sexual behavior. In two studies in four male monkeys, L368,899 was injected iv (1 mg/kg) after which (1) CSF samples were collected at intervals over 4 h and (2) brains were collected at 60 min. Assay of samples confirmed that iv-administered L368,899 entered CSF and accumulated in the hypothalamus, septum, orbitofrontal cortex, amygdala and hippocampus, but not other areas. An adult female monkey was tested for interest in either an infant or sexual behavior, receiving a different iv treatment prior to each test (1 or 3 mg/kg of L368,899 or saline). OT antagonist treatment reduced or eliminated interest in the infant and sexual behavior. These results, although preliminary, are the first to directly implicate endogenous OT in activation of primate maternal interest and sexual behavior. While it remains to be empirically demonstrated that peripherally administered L368,899 blocks central OT receptors, our behavioral findings suggest that this non-peptide antagonist may facilitate testing OT involvement in a variety of social and other behaviors in primates.     

Central blockade of oxytocin receptors during mid-late gestation reduces amplitude of slow afterhyperpolarization in supraoptic oxytocin neurons

The neurohypophysial hormone oxytocin (OT), synthesized in magnocellular paraventricular (PVN) and supraoptic (SON) nuclei, is well known for its effects in lactation. Our previous studies showed that central OT receptor (OTR) binding is increased during gestation and that blockade of central OTRs, specifically during mid-late gestation, causes a delay in OT release during suckling and reduces weight gain in pups, suggesting decreased milk delivery. In the present study, we tested whether central OTR blockade during late gestation disrupts the gestation-related plasticity in intrinsic membrane properties. Whole cell current-clamp recordings were performed in OT neurons from pregnant rats (19-22 days in gestation) that were infused with an OTR antagonist (OTA) or artificial cerebrospinal fluid (aCSF) and from virgin rats infused with aCSF into the third ventricle via an osmotic minipump beginning on days 12-14 of gestation. The amplitudes of both Ca(2+)-dependent afterhyperpolarizations (AHPs), an apamin-sensitive medium AHP (mAHP) and an apamin-insensitive slow AHP (sAHP), were significantly increased during late gestation in control pregnant animals. However, the amplitude of the sAHP from pregnant rats treated with the OTA was significantly smaller than that of pregnant control rats and similar to that of virgins. These results indicate that the diminished efficiency in lactation due to OTR blockade may be partly a result of an altered sAHP that would shape OT bursting. These findings suggest that central actions of OT during late gestation are necessary for programming the plasticity of at least some of the intrinsic membrane properties in OT neurons during lactation.     

Effects of testosterone metabolites on copulation, medial preoptic dopamine, and NOS-immunoreactivity in castrated male rats

The medial preoptic area (MPOA) is an important integrative site for male sexual behavior. Dopamine (DA) is released in the MPOA of male rats shortly before and during copulation. In a previous study, we identified 17beta-estradiol (E(2)) as the metabolite of testosterone (T) that maintains MPOA basal extracellular DA levels. However, the presence of dihydrotestosterone (DHT), an androgenic metabolite of T, is required for the female-induced increase in MPOA DA observed during copulation. Recently, we reported that assays of MPOA tissue DA content showed that castrates actually had more stored DA than did gonadally intact males. Therefore, the reduction in extracellular levels in castrates was not due to decreased availability of DA; most likely it was due to decreased release. Furthermore, T upregulates neuronal nitric oxide synthase (nNOS) in the MPOA. NO has been implicated in the regulation of DA release in the MPOA. It is not known, however, which metabolite(s) of T regulate(s) tissue stores of DA and/or nNOS in the MPOA of male rats. The present experiments were designed to test the following: (1) whether E(2), DHT, or the combination of the two influences MPOA DA tissue levels, an indication of stored DA, in male rat castrates; and (2) whether E(2), DHT, or the combination of the two influences NOS-ir in the MPOA of castrated male rats. The results indicate that E(2) up-regulates nNOS-ir in the MPOA and maintains tissue content of DA at levels similar to those in T-treated rats. DHT did not influence nNOS-ir, while attenuating the effect of castration on tissue DA content.     

Vaginocervical stimulation attenuates the sensitization of appetitive sexual behaviors by estradiol benzoate in the ovariectomized rat

The acute administration of estradiol benzoate (EB) to the ovariectomized (OVX) rat induces low levels of lordosis while sexually appetitive behaviors (e.g., hops, darts, solicitations) are absent, yet the repeated administration of EB results in a behavioral sensitization in which lordosis is potentiated and sexually appetitive behaviors are induced. We have shown that repeated copulation attenuates the sensitization of appetitive sexual behaviors. Here, we assessed which component of male stimulation during copulation is involved in the attenuation. On 8 occasions, sexually experienced OVX Long–Evans rats were treated with 10 μg EB and 48 h later assigned to one of six groups that differed in their experience on intermediates tests (2–7). One was given repeated access to a male (EB/Male), and another was placed in the copulation chamber alone (EB/Alone) on intermediate tests. Three groups were given one of three somatosensory stimuli by the experimenter: manual flank stimulation (FLS), clitoral stimulation (CLS), or vaginocervical stimulation (VCS). Finally, the control group was left undisturbed in the animal care facility (ACF). Sexual behaviors were measured on Tests 1 and 8. VCS received from the experimenter (VCS) or from the male during copulation (EB/Male) attenuated the magnitude of the sensitization of appetitive sexual behaviors compared with those that were not brought to the testing rooms (ACF), and the effect was most pronounced on sexual solicitations. These results suggest that VCS received during penile intromission inhibits the sensitization of sexually appetitive behaviors by repeated administration of EB. As such, repeated administration of EB may oppose those mechanisms that induce estrous termination, perhaps by sensitizing inhibitory processes within the ventromedial hypothalamus that typically prevent the display of sexual behaviors (i.e., by facilitating disinhibition).     

Sex differences in oxytocin receptor binding in forebrain regions: Correlations with social interest in brain region- and sex- specific ways

Social interest reflects the motivation to approach a conspecific for the assessment of social cues and is measured in rats by the amount of time spent investigating conspecifics. Virgin female rats show lower social interest towards unfamiliar juvenile conspecifics than virgin male rats. We hypothesized that the neuropeptide oxytocin (OT) may modulate sex differences in social interest because of the involvement of OT in pro-social behaviors. We determined whether there are sex differences in OT system parameters in the brain and whether these parameters would correlate with social interest. We also determined whether estrus phase or maternal experience would alter low social interest and whether this would correlate with changes in OT system parameters. Our results show that regardless of estrus phase, females have significantly lower OT receptor (OTR) binding densities than males in the majority of forebrain regions analyzed, including the nucleus accumbens, caudate putamen, lateral septum, bed nucleus of the stria terminalis, medial amygdala, and ventromedial hypothalamus. Interestingly, male social interest correlated positively with OTR binding densities in the medial amygdala, while female social interest correlated negatively with OTR binding densities in the central amygdala. Proestrus/estrus females showed similar social interest to non-estrus females despite increased OTR binding densities in several forebrain areas. Maternal experience had no immediate or long-lasting effects on social interest or OT brain parameters except for higher OTR binding in the medial amygdala in primiparous females. Together, these findings demonstrate that there are robust sex differences in OTR binding densities in multiple forebrain regions of rats and that OTR binding densities correlate with social interest in brain region- and sex-specific ways.     

Testosterone regulates the density of dendritic spines in the male preoptic area

Male-typical behavior is dependent on testosterone. Castrated males gradually stop mating and engaging in sexual behaviors. Castrates treated with testosterone regain motivation and sex behaviors over time. Although this effect is well characterized, the specific mechanisms by which testosterone treatment recovers sexual behaviors remain unknown. The medial preoptic area (MPOA) is a likely site for testosterone's action on copulation. The integrity of the area is essential for the expression of male sex behavior; and the MPOA is densely populated with receptors for gonadal steroids. Moreover testosterone appears to regulate synaptic efficacy in the MPOA. Exposure to sexually relevant stimuli stimulates the MPOA but only in the presence of circulating testosterone. Sites afferent to the area respond to similar exposure independent of the hormonal milieu suggesting that testosterone mediates communication between the MPOA and its afferents. The protracted time course suggests that the effects of steroidal manipulation are mediated by structural changes. The present experiment evaluated this hypothesis by comparing dendritic spine density among Syrian hamsters that were castrated, castrated and treated with testosterone, or were left gonadally intact. Brains were sectioned and stained using the rapid Golgi stain protocol (FD Neurotechnologies, Baltimore), and the spine density, dendrite length, and the number of branches were compared among groups. Intact and testosterone replaced animals had more spines and greater spine density but did not differ in dendrite length and branching from castrated animals. These results suggest that existing dendrites increase the number of spines available for synapse formation but do not extend their dendrites in response to testosterone treatment.     

Mating-induced expression of c-fos in the male Syrian hamster brain: Role of experience,pheromones, and ejaculations

This study was designed to investigate the effects of pheromonal cues and specific behaviors within the male copulatory sequence on c-fos expression in the medial nucleus of the amygdala (Me), the bed nucleus of the stria terminalis (BNST), and the medial preoptic area (MPOA) of the Syrian hamster brain. Sexually experienced male hamsters were placed into clean testing arenas and were either: 1) left alone as handled controls; 2) exposed to female hamster vaginal secretion (FHVS) on cotton swabs; or mated to various end points of copulation with a sexually receptive female: 3) five intromissions, 4) one ejaculation, 5) five ejaculations, or 6) long intromissions. A seventh group of sexually naive control males 7) was left alone in the arena. The brains of these males were compared to those of the sexually experienced controls to determine whether exposure to cues associated with prior sexual experience could alter c-fos expression. In males exposed only to FHVS, Fos immunoreactivity (Fos-ir) increased within the posterodorsal Me, the anterodorsal part of the posteromedial BNST, and the magnocellular medial preoptic nucleus (MPNmag). Following one ejaculation, Fos-ir increased within the caudal posterodorsal Me, the dorsolateral MPOA, and the paraventricular nucleus of the hypothalamus. After multiple ejaculations, additional labeling was observed within the posteroventral part of the posteromedial BNST, the medial preoptic nucleus (MPN), the central tegmental field, and in cell clusters of the caudal posterodorsal Me and rostral posteromedial BNST. Fos-ir also increased within the posterodorsal Me, MPN, and MPNmag in sexually experienced control males exposed to the empty test chamber compared to sexually naive males exposed to an identical chamber. These results demonstrate that the mating-induced pattern of neuronal activation in sexually experienced males is dependent upon multiple factors, including prior sexual experience in the testing environment, investigation of FHVS, and the number of ejaculations achieved. © 1997 John Wiley & Sons, Inc. J Neurobiol 32: 481–501, 1997     

Sex-specific activity and function of hypothalamic nonapeptide neurons during nest-building in zebra finches

Vertebrate species from fish to humans engage in a complex set of preparatory behaviors referred to as nesting; yet despite its phylogenetic ubiquity, the physiological and neural mechanisms that underlie nesting are not well known. We here test the hypothesis that nesting behavior is influenced by the vasopressin–oxytocin (VP–OT) peptides, based upon the roles they play in parental behavior in mammals. We quantified nesting behavior in male and female zebra finches following both peripheral and central administrations of OT and V_1a receptor (OTR and V1aR, respectively) antagonists. Peripheral injections of the OTR antagonist profoundly reduce nesting behavior in females, but not males, whereas comparable injections of V1aR antagonist produce relatively modest effects in both sexes. However, central antagonist infusions produce no effects on nesting, and OTR antagonist injections into the breast produce significantly weaker effects than those into the inguinal area, suggesting that antagonist effects are mediated peripherally, likely via the oviduct. Finally, immunocytochemistry was used to quantify nesting-induced Fos activation of nonapeptide neurons in the paraventricular and supraoptic nuclei of the hypothalamus and the medial bed nucleus of the stria terminalis. Nest-building induced Fos expression within paraventricular VP neurons of females but not males. Because the avian forms of OT (Ile⁸-OT; mesotocin) and VP (Ile³-VP; vasotocin) exhibit high affinity for the avian OTR, and because both peptide forms modulate uterine contractility, we hypothesize that nesting-related stimuli induce peptide release from paraventricular vasotocin neurons, which then promote female nesting via peripheral feedback from OTR binding in the oviduct uterus.     

Induction of Fos Immunoreactivity in Oxytocin Neurons in the Paraventricular Nucleus After Female Odor Exposure in Male Rats: Effects of Sexual Experience

1. We examined whether oxytocin (OT) neurons in the paraventricular nucleus of the hypothalamus (PVN) were activated by estrus female odor and sexual contact in sexually naïve and experienced Long-Evans rats. 2. Male rats were not presented to anesthetized estrus females (control) or presented to the females without (exposure to the female odor without sexual contact) or with direct contact (exposure to the female odor with sexual contact). 3. Exposure to the female odor with sexual contact significantly increased OT neurons with Fos-ir in both males. Exposure to the female odor without contact increased OT neurons with Fos-immunoreactive cells (Fos-ir) in sexually experienced males but not in naïve males, suggesting that the female odor without sexual contact activated the oxytocinergic neuronal system in the PVN in the experienced males. 4. Therefore, exposure to the estrus female odor itself may exert different effects on sexually naïve and experienced males.     

Hybrid peptide-small molecule oxytocin analogs are potent and selective agonists of the oxytocin receptor

Oxytocin (OT) is a peptide hormone agonist of the oxytocin receptor (OTR) that has been proposed as a therapeutic to treat a number of social and emotional disorders in addition to its current clinical use to induce labor and treat postpartum bleeding. OT is administered intravenously and intranasally rather than orally, in part because its low passive permeability causes low oral bioavailability. Non-peptidic OTR agonists have also been reported, but none with the exquisite potency of the peptide based agonists. In this report, we describe the OTR agonist activity and exposed polarity of a set of truncated OT analogs as well as hybrid peptide-small molecule analogs of OT. Examples of both truncated analogs and peptide-small molecule hybrid analogs are potent and selective OTR agonists. Hybrid agonist 13, which is 232?Da smaller than OT, still retains subnanomolar potency, full agonist activity, and selectivity over V1a. While these compounds were designed to address the low permeability of OT and other full length analogs, we found that reduction in molecular weight and the removal or replacement of the three amino acid tail of OT did not have a significant effect on passive permeability.     

Neonatal oxytocin treatment modulates oxytocin receptor, atrial natriuretic peptide, nitric oxide synthase and estrogen receptor mRNAs expression in rat heart

Oxytocin (OT) has been implicated in reproductive functions, induction of maternal behavior as well as endocrine and neuroendocrine regulation of the cardiovascular system. Here we demonstrate that neonatal manipulation of OT can modulate the mRNAs expression for OT receptor (OTR), atrial natriuretic peptide (ANP), endothelial nitric oxide synthase (eNOS) and estrogen receptor alpha (ERalpha) in the heart. On the first day of postnatal life, female and male rats were randomly assigned to receive one of the following treatments: (a) 50microl i.p. injection of 7microg OT; (b) 0.7microg of OT antagonist (OTA); or (c) isotonic saline (SAL). Hearts were collected either on postnatal day 1 or day 21 (D1 or D21) and the mRNAs expression of OTR, ANP, inducible NOS (iNOS), eNOS, ERalpha and estrogen receptor beta (ERbeta) were compared by age, treatment, and sex utilizing real time PCR. OT treatment significantly increased heart OTR, ANP and eNOS mRNAs expression on D1 in both males and females, ERalpha increased only in females. While there were significant changes in the relative expression of all types of mRNA between D1 and D21, there were no significant treatment effects observed in D21 animals. OTA treatment significantly decreased basal ANP and eNOS mRNAs expression on D1 in both sexes. The results indicate that during the early postnatal period OT can have an immediate effect on the expression OTR, ANP, eNOS, and ERalpha mRNAs and that these effects are mitigated by D21. Also with the exception of ERalpha mRNA, the effects are the same in both sexes.     

Oxytocin receptor binding in the hypothalamus during gestation in rats

Central oxytocin receptors (OTR) may be involved in adaptations of the brain oxytocin (OT) system during gestation, which are critical for systemic release of OT during parturition and lactation. We used quantitative autoradiography to determine changes in OTR binding in numerous brain sites during the course of gestation in the rat. Furthermore, to evaluate the importance of ovarian steroids in mediating pregnancy-related changes in OTR binding, we measured binding in ovariectomized animals treated with progesterone and/or estrogen, and in pregnant animals treated with exogenous progesterone during late gestation. We found that OTR binding was significantly increased in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) by midgestation (day 15) compared with control. In addition, there was a further significant increase in OTR binding in these nuclei by late gestation (day 20). The bed nucleus of the stria terminalis (BNST) and the medial preoptic area (MPOA) also showed significant gestation-associated increases in OTR binding, which were similar during mid- and late pregnancy. Treatment with exogenous progesterone throughout pregnancy did not alter the increase in OTR binding characteristic of late gestation in any of these brain sites. Finally, estrogen treatment in ovariectomized animals resulted in increased OTR binding in the SON, BNST, and MPOA, but not the PVN. These data demonstrate that OTR binding in the hypothalamus is increased during mid- and late-gestation, compared with ovariectomized control animals, which may be mediated by increased estradiol.     

Effects of testosterone metabolites on copulation and medial preoptic dopamine release in castrated male rats

The medial preoptic area (MPOA) is an important integrative site for male sexual behavior. Dopamine (DA) is released in the MPOA of male rats shortly before and during copulation. The recent presence of testosterone (T) may be necessary for this precopulatory increase in release. Previously, the postcastration loss of copulatory ability mirrored the loss of the DA response to an estrous female, and the restoration of copulation with exogenous T was concurrent with the reemergence of this DA response. The present study investigated the effectiveness of the two major metabolites of T in maintaining copulation and basal and female-stimulated DA levels. Adult male rats were castrated and received daily injections of estradiol benzoate (EB), dihydrotestosterone benzoate (DHTB), EB + DHTB, testosterone propionate (TP), or oil vehicle for 3 weeks. Microdialysis samples were collected from the MPOA during baseline conditions, exposure to an estrous female behind a barrier, and copulation testing. EB + DHTB- and TP-treated animals had normal basal DA levels and showed a precopulatory DA response, and most copulated normally. EB-treated castrates had high basal DA levels, but failed to show a female-stimulated increase; most intromitted, but none ejaculated. DHTB- and oil-treated groups had low basal levels of extracellular DA that did not increase during copulation testing; most failed to mount and none ejaculated. These results suggest that E maintains normal basal levels of extracellular DA in the MPOA, which are sufficient for suboptimal copulation, but that androgen is required for the female-stimulated increase in DA release and for facilitation of ejaculation.     

Fibroblast growth factor 2 alters the oxytocin receptor in a developmental model of anxiety-like behavior in male rat pups

We aimed to determine the short-term effects of early-life stress in the form of maternal separation (MS) on anxiety-like behavior in male rat pups. In order to assess anxiety, we measured 40 kHz separation-induced ultrasonic vocalizations (USV) on postnatal day (PND) 11. We further aimed to evaluate the potential involvement of two neurochemical systems known to regulate social and anxiety-like behaviors throughout life: oxytocin (OT) and fibroblast growth factor 2 (FGF2). For these purposes, we tested the effects of neonatal administration (on PND1) of an acute dose of FGF2 on USV and its potential interaction with MS. In addition, we validated the anxiolytic effects of OT and measured oxytocin receptor (OTR) gene expression, binding and epigenetic regulation via histone acetylation. Our results show that MS potentiated USV while acute administration of OT and FGF2 attenuated them. Further, we found that both FGF2 and MS increased OTR gene expression and the association of acH3K14 with the OTR promoter in the bed nucleus of the stria terminalis (BNST). Comparable changes, though not as pronounced, were also found for the central amygdala (CeA). Our findings suggest that FGF2 may exert its anxiolytic effects in male MS rats by a compensatory increase in the acetylation of the OTR promoter to overcome reduced OT levels in the BNST.