MBR: a computer program to record and analyze parental behavior in rodents

Environmental prenatal stress eliminates brain and maternal behavioral sex differences and alters hormone levels in female rats

Environmental prenatal stress (EPS) has effects on fetuses that are long-lasting, altering their hormone levels, brain morphology and behavior when they reach maturity. In previous research, we demonstrated that EPS affects the expression of induced maternal behavior (MB), the neuroendocrine system, and morphology of the sexually dimorphic accessory olfactory bulb (AOB) involved in reproductive behavior patterns. The bed nucleus of the accessory olfactory tract (BAOT) is another vomeronasal (VN) structure that plays an inhibitory role in rats in the expression of induced maternal behavior in female and male virgins. In the present study, we have ascertained whether the behavioral, neuroendocrine, and neuromorphological alterations of the AOB found after EPS also appear in the BAOT. After applying EPS to pregnant rats during the late gestational period, in their female offspring at maturity we tested induced maternal behavior, BAOT morphology and plasma levels of testosterone (T), estradiol (E2), progesterone (P), adrenocorticotropic hormone (ACTH) and corticosterone (Cpd B). EPS: a) affected the induction of MB, showed a male-like pattern of care for pups, b) elevated plasma levels of Cpd B and reduced E2 in comparison with the controls, and c) significantly increased the number of BAOT neurons compared to the control females and comparable to the control male group. These findings provide further evidence that stress applied to pregnant rats produces long-lasting behavioral, endocrine and neuroanatomical alterations in the female offspring that are evident when they become mature.

Maternal care interacts with prenatal stress in altering sexual dimorphism in male rats

The present study analyzes the interaction between prenatal stress and mother's behavior on brain, hormonal, and behavioral development of male offspring in rats. It extends to males our previous findings, in females, that maternal care can alter behavioral dimorphism that becomes evident in the neonates when they mature. Experiment 1 compares the maternal behavior of foster mothers toward cross-fostered pups versus mothers rearing their own litters. Experiment 2 ascertains the induced "maternal" behavior of the male pups, derived from Experiment 1 when they reached maturity. The most striking effect was that the males non-exposed to the stress as fetuses and raised by stressed foster mothers showed the highest levels of "maternal" behavior of all the groups (i.e., induction of maternal behavior and retrieving behavior), not differing from the control, unstressed, female groups. Furthermore, those males showed significantly fewer olfactory bulb mitral cells than the control males that were non-stressed as fetuses and raised by their own non-stressed mothers. They also presented the lowest levels of plasma testosterone of all the male groups. The present findings provide evidence that prenatal environmental stress can "demasculinize" the behavior, brain anatomy and hormone secretion in the male fetuses expressed when they reach maturity. Moreover, the nature of the maternal care received by neonates can affect the behavior and physiology that they express at maturity.

Reproductive toxicity and pharmacokinetics of di-n-butyl phthalate (DBP) following dietary exposure of pregnant rats

Most rodent developmental toxicity studies of dibutylphthalate (DBP) have relied on bolus gavage dosing. This study characterized the developmental toxicity of dietary DBP. Pregnant CD rats were given nominal doses of 0, 100, or 500 mg DBP/kg/day in diet (actual intake 0, 112, and 582 mg/kg/day) from gestational day (GD) 12 through the morning of GD 19. Rats were killed 4 or 24 hr thereafter. DBP dietary exposure resulted in significant dose-dependent reductions in testicular mRNA concentration of scavenger receptor class B, member 1; steroidogenic acute regulatory protein; cytochrome P450, family 11, subfamily a, polypeptide 1; and cytochrome P450 family 17, subfamily a, polypeptide 1. These effects were most pronounced 4 hr after the end of exposure. Testicular testosterone was reduced 24 hr post-exposure in both DBP dose groups and 4 hr after termination of the 500-mg DBP/kg/day exposure. Maternal exposure to 500 mg DBP/kg/day induced a significant reduction in male offspring's anogenital distance indicating in utero disruption of androgen function. Leydig cell aggregates, increased cord diameters, and multinucleated gonocytes were present in DBP-treated rats. Monobutyl phthalate, the developmentally toxic metabolite of DBP, and its glucuronide conjugate were found in maternal and fetal plasma, amniotic fluid, and maternal urine. Our results, when compared to previously conducted gavage studies, indicate that approximately equal doses of oral DBP exposure of pregnant rats, from diet or gavage, result in similar responses in male offspring.

Bicuculline infusion into the accessory olfactory bulb facilitates the induction of maternal behavior in rats

The GABAA antagonist bicuculline, intracranially infused into the accessory olfactory bulb (AOB), facilitated the expression of maternal behavior (MB) in virgin Wistar female rats. Behavioral effects were observed 24 hours after infusion and were injection dependent. Pheromonal stimuli, generated by the pups, are thought to exert an inhibitory effect on vomeronasal nuclei involved in MB in virgin rats. The present study investigated the possibility that a decrement in AOB output, resulting from long-term compensatory synaptic changes to chronic bicuculline infusion, would facilitate the expression of MB. The implications of our findings for the mechanisms involved in the induction of MB and the maternal experience effect are discussed.

Role of the vomeronasal input in maternal behavior

This article reviews the role of the vomeronasal system in the induction of parental behavior in female and male rats, using, primarily, the sensitization model. The following questions are addressed: (1) Is the vomeronasal system sexually dimorphic? (2) Do the sex differences found in the VNS underlie those seen in behavior? (3) Do mechanisms, other than the classical 'organizational' effects of perinatal gonadal steroids, play a role in the organization of behavioral phenotypes in parental behavior? and (4) Does vomeronasal input play a role in the formation of the mother infant bond in humans? The first question has been answered throughout the 1980's in various studies of the organizational actions of postnatal exposure to gonadal steroids. The second aim has been addressed in a functional approach by lesion and neural activation studies. The experiments which lead us to consider the hypothesis that nonsteroidal factors in development, and specifically GABA, could account for the expression of parental care are reviewed. Finally, research relevant to the existence of a vomeronasal organ in humans and a possible pheromonal input in the formation of mother-infant bonds in humans is reviewed.

Early postnatal diazepam exposure facilitates maternal behavior in virgin female rats

Virgin female rats do not display maternal behavior if they are not exposed to the pups during several days. This exposure is called induction. In this work we have studied the effects of early postnatal (PO-P16) diazepam (DZ) administration (1 and 2.5 mg/kg, SC) on the display of maternal behavior of virgin female rats when adults. Although we did not find statistically significant differences between P0-P16 DZ treated and control females with respect to the latency of retrieval, P0-P16 DZ administration resulted in a statistically significant increase of the percentage of female rats that became maternal, showing retrieval behavior. This early postnatal treatment with DZ also increased other variables that are currently measured in maternal behavior tests, such as: time of physical contacts, grooming, crouching, and nest building quality. No statistically significant differences were found in the body weight of treated versus control animals during development, nor during adulthood. Our results provide further evidence that the GABAA-BDZ-Cl- receptor complex is implicated in the development of maternal behavior in female rats.