Social Network Plasticity of Mice Parental Behavior.

Neural plasticity occurs during developmental stages and is essential for sexual differentiation of the brain and the ensuing sex-dependent behavioral changes in adults. Maternal behavior is primarily affected by sex-related differences in the brain; however, chronic social isolation even in mature male mice can induce maternal retrieving and crouching behavior when they are first exposed to pups. Social milieus influence the inherent behavior of adults and alter the molecular architecture in the brain, thereby allowing higher levels of associated gene expression and molecular activity.

Neural Contributions of the Hypothalamus to Parental Behaviour.

Parental behaviour is a comprehensive set of neural responses to social cues. The neural circuits that govern parental behaviour reside in several putative nuclei in the brain. Melanin concentrating hormone (MCH), a neuromodulator that integrates physiological functions, has been confirmed to be involved in parental behaviour, particularly in crouching behaviour during nursing.

Involvement of MCH-oxytocin neural relay within the hypothalamus in murine nursing behavior.

Multiple sequential actions, performed during parental behaviors, are essential elements of reproduction in mammalian species. We showed that neurons expressing melanin concentrating hormone (MCH) in the lateral hypothalamic area (LHA) are more active in rodents of both sexes when exhibiting parental nursing behavior. Genetic ablation of the LHA-MCH neurons impaired maternal nursing.

Oxytocin is indispensable for conspecific-odor preference and controls the initiation of female, but not male, sexual behavior in mice.

Oxytocin (OT) has been demonstrated to be involved in various social behaviors in mammals. However, OT gene knockout (OTKO) mice can conceive and deliver successfully, though females cannot rear their pups because of lack of lactation. Here, we investigated the sociosexual behavior of both sexes in two experimental setups: olfactory preference for sexual partner's odor and direct social interaction in an enriched condition.

Vomeronasal signal deficiency enhances parental behavior in socially isolated male mice.

We previously reported that social isolation promotes parental care in sexually naïve male mice. This effect was blocked by exposure to chemosensory and auditory social signals derived from males in an adjacent compartment. In the present study, we examined whether the chemosensory signals detected in the vomeronasal organ (VNO) are involved in parental behavior by using mice deficient for a VNO-specific ion channel (Trpc2) and thus impaired in VNO-input signaling.

Social isolation prompts maternal behavior in sexually naïve male ddN mice.

Maternal behavior in mice is considered to be sexually dimorphic; that is, females show maternal care for their offspring, whereas this behavior is rarely shown in males. Here, we examined how social isolation affects the interaction of adult male mice with pups. Three weeks of isolation during puberty (5-8 weeks old) induced retrieving and crouching when exposed to pups, while males with 1 week isolation (7-8 weeks old) also showed such maternal care, but were less responsive to pups.

Estrogen configures sexual dimorphism in the preoptic area of C57BL/6J and ddN strains of mice.

Immunohistochemistry using a calbindin D28k antibody revealed a marked sex difference in neuronal distribution in the central portion of the medial preoptic area in C57BL/6J and ddN strains of mice when the animals were sacrificed on D65 (D1 = the day of birth). Male mice had a distinct ellipsoidal cell aggregate, whereas females lacked such a structure. This sex difference was not observed in Nissl-stained sections.

Similar numbers of neurons are generated in the male and female rat preoptic area in utero.

The birth date of neurons comprising the sexually dimorphic nucleus of the rat preoptic area (SDN-POA) was determined by bromodeoxyuridine (BrdU) injections at a prescribed time during the embryonic period. Calbindin immunostaining was used as a marker to identity the SDN-POA. The animals were bred from dams injected with BrdU on days 14, 16 or 18 of pregnancy (fertilization defined as day 1).

Transient transcription of the somatostatin gene at the time of estrogen-dependent organization of the sexually dimorphic nucleus of the rat preoptic area.

In situ hybridization detected a transient, sex-specific transcription of somatostatin gene in the central part of the rat medial preoptic nucleus, which coincides with the sexually dimorphic nucleus of the preoptic area (SDN-POA), during, but not after, the establishment of sex difference. On postnatal d 1 (day of birth), somatostatin mRNA was detected in the SDN-POA of both sexes. On d 8 through 35, the area of somatostatin mRNA-positive cells was significantly larger in males than in females.

Sex difference in the expression and regulation of nitric oxide synthase gene in the rat preoptic area.

Neuronal nitric oxide synthase (nNOS) mRNA-positive cells were visualized by non-isotopic in situ hybridization histochemistry in the organum vasculosum of the lamina terminalis (OVLT) and the preoptic area (POA) in gonadectomized juvenile female and male rats. In the rostral POA (rPOA) at the level of the anteroventral periventricular nucleus, nNOS mRNA-positive cells were distributed in an inverted V-shaped area over the third ventricle and were in close proximity to cell bodies of gonadotropin-releasing hormone (GnRH)-immunoreactive neurons. In the caudal POA (cPOA) at the level of the medial preoptic nucleus, no topological association existed between GnRH and nNOS.

Sexually dimorphic expression of estrogen receptor beta in the anteroventral periventricular nucleus of the rat preoptic area: implication in luteinizing hormone surge.

Striking sex difference was detected in the expression of estrogen receptor (ER) beta mRNA and protein by nonisotopic in situ hybridization and immunohistochemistry in the anteroventral periventricular nucleus (AVPV) of the rat preoptic area. In females more than in males, a significantly larger number of ERbeta mRNA-positive cells were visualized in the medial-most portion of the AVPV within 50 microm from the ependymal lining of the third ventricle. Rats of 7, 14, 21, 35, and 60 days of age (d 1 = day of birth) showed the sex difference.