Paternal and infanticidal behavior in the Mongolian gerbil (Meriones unguiculatus): An approach to neuroendocrine regulation.

This study aimed to provide evidence on estrogen and androgen pathways regulating the Mongolian gerbil's paternal and infanticidal behaviors (Meriones unguiculatus). We analyzed estrogen receptor alpha (ERα) and androgen receptor (AR) distribution in the medial preoptic area (mPOA), the bed nucleus of stria terminalis (BNST), as well as the anterior hypothalamic nucleus (AHN), the ventromedial hypothalamus nucleus (VMH), and the periaqueductal gray area (PAG) nuclei activated when males interact paternally or aggressively with the pups, respectively. Twenty aggressive males towards the pups and 10 paternal were selected through a screen paternal behavior test. Three groups of 10 males each were formed: paternal males (PAT), males with testosterone (T)-induced paternal behavior (T-PAT), and aggressive males (AGG). Male gerbils could interact with a pup for a few minutes, and their brains were removed and dissected for ERα and AR immunoreactivity (ir). The results showed that in T-PAT and PAT males, the number of ERα-ir and AR-ir cells in the mPOA/BNST was significantly higher than in AGG males. In AGG males, the number of ERα-ir and AR-ir cells in the AHN/VMH/PAG was significantly higher than PAT and T-PAT males. This difference in the presence of ERα and AR in nuclei activated in paternal interactions in the Mongolian gerbil supports the idea that these receptors participate in regulating paternal behavior. Also, these results suggest, for the first time, that they could be involved in the infanticidal behavior in this rodent.

Neuronal activation associated with paternal and aversive interactions toward pups in the Mongolian gerbils (Meriones unguiculatus).

Approach/avoid model is used to analyze the neural regulation of maternal behavior in the laboratory rat. This model proposes that the medial preoptic area (mPOA) and bed nucleus of stria terminalis (BNST) are brain regions involved in facilitating mechanisms. By contrast, anterior hypothalamic nucleus (AHN), ventromedial hypothalamic nucleus (VMH), and periaqueductal gray participate in the inhibiting mechanisms of neural regulation of maternal behavior. We hypothesized that there are also facilitating and inhibiting mechanisms in the neural regulation of paternal behavior. Here, we determined which neural areas are activated during paternal and aversive interactions with pups in the Mongolian gerbils (Meriones unguiculatus). By testing paternal behavior, we selected 40 males aggressive toward pups and 20 paternal males. These males were organized into six groups of 10 animals in each group: aggressive males that interacted with pups (AGG-pups) or candy (AGG-candy), paternal males that interacted with pups (PAT-pups) or candy (PAT-candy), and males with testosterone (T)-induced paternal behavior that interacted with pups (IPAT-pups) or candy (IPAT-candy). After interacting with pups or candy, the brains were extracted and analyzed for immunoreactivity (ir) with c-fos. Males that interacted with pups had significantly higher c-fos-ir in the mPOA/BNST than males that interacted with candy. Males that displayed aggression had significantly higher c-fos-ir in the AHN, VMH, and periaqueductal gray than aggressive males that interacted with candy. These results suggest that in the neural regulation of paternal behavior in the Mongolian gerbil underlie positive and negative mechanisms as occurs in maternal behavior.

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.

Testosterone induces paternal behavior in sexually inexperienced males of Neotomodon alstoni (Rodentia: Muridae) / La testosterona induce conducta paterna en machos sin experiencia sexual del ratón Mexicano de los volcanes Neotomodon alstoni (Rodentia: Muridae)

Abstract The inhibition of infanticide can be considered a prerequisite for the onset of paternal behavior. Thus, hormones such as testosterone (T) would be expected to mediate the inhibition of aggression toward pups and the onset of paternal care. However, the effect of T in onset of this behaviorseems to depend of sexual experience. The aim of this study was to determine whether T induces paternal behavior in sexually inexperienced males of the Mexican volcano mouse (Neotomodon alstoni). For this, 33 non-paternal males were selected based on paternal behavior tests. These non-paternal mice were organized in three groups: 10 males were castrated, 10 subjected to sham procedure, and 13 underwent castration and T replacement. After of these treatments, the males were again evaluated by a second paternal behavior test, and blood samples were obtained to measure plasma T levels by radioimmunoassay. Castrated males with T replacement changed their behavior; 46.2 % of these males displayed paternal behavior despite 92.3 % of these males having previously displayed aggressive behavior in the selection test. An increase in T facilitates the onset of paternal behavior in sexually inexperienced males of Mexican volcano mouse, as occurs in sexual experience males. These results support the hypothesis that an increase in T levels would be involved in the neuroendocrine mechanisms that suppress infanticide and promote the onset of parental behavior in Mexican volcano mice males. Future studies in this mouse will investigate whether T regulates the onset of paternal behavior via conversion to estradiol or whether both T metabolites are involved in its onset.

Resumen La inhibición del infanticidio es necesaria en el inicio de la conducta paterna, así hormonas como la testosterona (T) pueden mediar la transición de machos agresivos a paternales. Sin embargo, el efecto de la T en el inicio de la conducta paterna parece depender de la experiencia sexual. El objetivo de este estudio fue determinar si T induce la conducta paterna en machos sin experiencia sexual del ratón Neotomodon alstoni. A través de pruebas de conducta paterna fueron seleccionados 33 machos no paternales; 23 fueron castrados bilateralmente, de los cuales a 13 se les colocó implante de T y 10 no recibieron ningún tratamiento. Otros 10 machos fueron sometidos a simulación del procedimiento. Después de los tratamientos, se realizaron nuevamente pruebas de conducta paterna para determinar cambios en la conducta de los machos hacia las crías. Enseguida se extrajeron muestras sanguíneas, para cuantificar los niveles de T en plasma, por radioinmuensayo. El 46.2 % de los machos castrados que recibieron implantes de T exhibieron conducta paterna, a pesar de que antes de la administración de esta hormona, el 92.3 % fueron agresivos con las crías. Los machos que transitaron a paternales tuvieron concentraciones de T significativamente más altas que los machos con castración simulada. Un incremento en T facilita el inicio de la conducta paterna en machos sexualmente inexpertos del ratón Neotomodon alstoni.Estos resultados apoyan la hipótesis que un incremento en T está involucrado en los mecanismos neuroendócrinos que inhiben la agresión hacia las crías y facilitan el inicio de la conducta paterna. Investigaciones futuras deben enfocarse a establecer la función de ambos metabolitos de la T en la regulación de la conducta paterna de este ratón.

Paternal behavior in the Mongolian gerbil (Meriones unguiculatus): Estrogenic and androgenic regulation.

Here, we analyzed the effects of testosterone (T) and its metabolites, estradiol (E2) and dihydrotestosterone (DHT), on the onset of paternal behavior in virgin male Mongolian gerbils (Meriones unguiculatus). We hypothesized that T and E2, but not DHT, would facilitate the onset of paternal behavior. Seventy males displaying aggression toward pups were selected through a paternal behavior screening test. Forty males were bilaterally castrated. Of them, 10 were implanted with T, 10 with E2, and 10 with DHT, and 10 received no treatment. Another 30 males underwent a sham procedure. In these gerbils, T, E2 and DHT were measured to obtain the basal levels of these hormones. After treatment, the paternal behavior test was conducted again. Blood samples were obtained immediately after the administration of the test for the quantification of T, E2 and DHT by radioimmunoassay. Surprisingly, 100% of the males that received T, E2 and DHT implants stopped being aggressive and became paternal. Castrated and sham-operated males displayed no changes in their aggressive behaviors. This is the first report that T and its metabolites are involved in neuroendocrine mechanisms that inhibit aggression toward pups and facilitate paternal behavior in virgin male Mongolian gerbils. In addition, this is the first report of regulation of paternal behavior in a rodent by estrogenic and androgenic pathways.

Paternal behavior and testosterone plasma levels in the Volcano Mouse Neotomodon alstoni (Rodentia: Muridae)

Paternal behavior and testosterone plasma levels in the Volcano Mouse Neotomodon alstoni (Rodentia: Muridae). Although initially it was thought that testosterone inhibited the display of paternal behavior in males of rodents, it has been shown that in some species high testosterone levels are needed for exhibition of paternal care. In captivity, males of volcano Mouse (Neotomodon alstoni) provide pups the same care provided by the mother, with the exception of suckling. Here we measured plasmatic testosterone concentrations 10 days after mating, five and 20 days postpartum, and 10 days after males were isolated from their families in order to determine possible changes in this hormone, associated to the presence and age of pups. Males of volcano Mouse exhibited paternal behavior when their testosterone levels were relatively high. Although levels of this hormone did not change with the presence or pups age, males that invested more time in huddling showed higher testosterone levels. It is possible that in the volcano Mouse testosterone modulates paternal behavior indirectly, as in the California mouse. Rev. Biol. Trop. 57 (1-2): 433-439. Epub 2009 June 30.

Aunque inicialmente se pensaba que la testosterona inhibía el despliegue de conducta paterna en los machos de roedores, en algunas especies se ha demostrado que son necesarios niveles altos de testosterona para la exhibición de cuidados paternos. En cautiverio, los machos del ratón mexicano de los volcanes (Neotomodon alstoni), proporcionan a sus crías los mismos cuidados que la madre, con la excepción del amamantamiento. En este estudio se midieron los niveles plasmáticos de testosterona: en el día 10 del apareamiento, 5 y 20 días postparto, y 10 días después de aislar a los machos de sus familias, para establecer si los niveles de esta hormona cambian con relación a la presencia y edad de las crías. El ratón de los volcanes exhibió cuidados paternos cuando sus niveles de testosterona fueron relativamente altos, aunque los niveles de esta hormona no variaron significativamente con relación a la edad y presencia de las crías. Sin embargo, los machos que invirtieron más tiempo en abrigar a las crías, presentaron concentraciones relativamente más altas de testosterona. Es posible que en el ratón de los volcanes la testosterona regule la conducta paterna de manera indirecta, como ocurre con el ratón de California.

Comportamiento agresivo del macho del ratón de los volcanes Neotomodon alstoni (Rodentia: Cricetidae) / Aggressive behavior of the male volcano mouse Neotomodon alstoni (Rodentia: Cricetidae)

A study was carried out on the agonistic behavior of the male volcano mouse, Neotomodon alstoni, with 50 pairs of males which were classified as possible dominants (D) and subordinates (S), utilizing Melzack-Thompson's Method. The aggressiveness levels exhibited by this mouse were recording in the Cmbinations: D vs. D and S vs. S. Two groups were formed: Group I with 12 pairs of D males and 13 of S males, and Group II with 11 pairs of D males and 14 of S males. In Group I the aggressiveness level was quantified after one week of mating and after another week of isolation, and in Group II the sequence of observation was inverted. The aggressiveness level was measured by the number of attacks per hour, an attack being defined as the aggressive physical contac of an animal (aggressor) with another (attacked). The kinds of behavior registered, including offense, defense, and submission patterns, revealed hierarchic relationships. Dominance was correlated significatively (p < 0.05) with a higher level of aggressiveness