Perinatal administration of diazepam alters sexual dimorphism in the rat accessory olfactory bulb

Sexually dimorphic expression of KCC2 and GABA function

GABA(A) receptors have an age-adapted function in the brain. During early development, they mediate depolarizing effects, which result in activation of calcium-sensitive signaling processes that are important for the differentiation of the brain. In more mature stages of development and in adults, GABA(A) receptors acquire their classical hyperpolarizing signaling. The switch from depolarizing to hyperpolarizing GABA(A)-ergic signaling is triggered through the developmental shift in the balance of chloride cotransporters that either increase (i.e. NKCC1) or decrease (i.e. KCC2) intracellular chloride. The maturation of GABA(A) signaling follows sex-specific patterns, which correlate with the developmental expression profiles of chloride cotransporters. This has first been demonstrated in the substantia nigra, where the switch occurs earlier in females than in males. As a result, there are sensitive periods during development when drugs or conditions that activate GABA(A) receptors mediate different transcriptional effects in males and females. Furthermore, neurons with depolarizing or hyperpolarizing GABA(A)-ergic signaling respond differently to neurotrophic factors like estrogens. Consequently, during sensitive developmental periods, GABA(A) receptors may act as broadcasters of sexually differentiating signals, promoting gender-appropriate brain development. This has particular implications in epilepsy, where both the pathophysiology and treatment of epileptic seizures involve GABA(A) receptor activation. It is important therefore to study separately the effects of these factors not only on the course of epilepsy but also design new treatments that may not necessarily disturb the gender-appropriate brain development.

Differential effects of undernourishment and nutritional rehabilitation on serum leptin levels in male and female rats

Leptin, a peptide hormone, is secreted by adipose tissue and is crucial to the regulation of feeding behaviour. The present study has shown that both male and female rats which have been undernourished since day six of gestation, show significantly decreased serum leptin levels on postnatal day 12; but when undernourishment continues into adulthood, only males continue to show decreased leptin levels. If nutritional rehabilitation is implemented early enough in males, serum leptin levels recover and nearly reach levels found in control adult males. Undernutrition also has a long term effect on body weight in both sexes, but nutritional rehabilitation leads to some degree of body weight recovery varying with sex and the age at which rehabilitation was implemented. Undernutrition seems to affect different developmental processes in males than in females, with males being more vulnerable than females in so far as long-term effects on serum leptin levels.

Undernutrition and food rehabilitation effects on the locus coeruleus in the rat

Perinatal nutrition plays a fundamental role on the morphological organization and function of a number of brain stem structures. Because little is known of the effects of perinatal undernutrition upon sexually dimorphic structures underlying reproductive behavior, the locus coeruleus morphology of 60-day-old male and female Wistar rats was analyzed. Perinatal food deprivation until weaning significantly decreased the volume and neuronal number of locus coerulus in male and female rats, while nutritional rehabilitation ameliorated these alterations in males but not in females. Data suggest that perinatal undernutrition interferes with the neuroendocrine mechanisms underlying the establishment of sex differences of the locus coeruleus.

Long-lasting handling affects behavioural reactivity in adult rats of both sexes prenatally exposed to diazepam

Environmental stressors can substantially affect the adaptive response of rats to novelty in a sexually dimorphic manner. Gender-related differences are also observed in neurochemical and behavioural patterns of adult rats following prenatal exposure to diazepam (DZ). In the present study the behavioural reactivity to novelty is investigated in open field (OF) and in acoustic startle reflex (ASR) tests, in non handled (NH), short-lasting handled (SLH) and long-lasting handled (LLH) adult male and female rats prenatally exposed to DZ. A single daily s.c. injection of DZ (1.5 mg/kg) over gestation days 14-20 decreases GABA/BDZ receptor function in both sexes, as shown by the decreased electrographic hippocampal response to DZ and the increased response to picrotoxin, after intra-locus coeruleus injection of the two compounds. In OF NH DZ-exposed males display a lower total distance travelled (TDT), a higher rearing frequency (RF) and a greater number of transitions in the centre of the arena (CNT) compared to NH rats prenatally exposed to vehicle. Conversely, NH DZ-exposed females show slight changes in TDT and RF and a greater reduction in CNT and in the amount of time spent in the centre of the arena (CAT). These effects are associated with an increase in the peak amplitude of the ASR in both sexes. Short-lasting handling slightly influences DZ-evoked effects in animals of both sexes. In DZ-exposed males long-lasting handling attenuates the reduction in TDT and the enhancement in RF, prevents the increase in CNT and reduces the peak amplitude of ASR. In DZ-exposed females, long-lasting handling increases TDT and RF, induces a lower avoidance of the centre of the arena, and does not modify the peak amplitude of ASR, when compared to controls. These findings indicate that prenatal exposure to DZ differently affects behavioural reactivity in adult male and female rats, and suggest that a long-lasting handling is able to attenuate some behavioural deficits induced by prenatal DZ exposure.

Gene expressions during the development and sexual differentiation of the olfactory bulb in rats

In this study, expressions of cell-cycle-related genes: p53, retinoblastoma (Rb), p21, bcl-2(alpha), bcl-2(beta); protooncogene c-ski; glial cell marker protein gene S100beta; neurotransmitter gene, substance P and sexual-differentiation-related genes, androgen receptor (AR) and estrogen receptor beta (ER(beta)), are studied in the olfactory bulb of groups of both six female and six male rats at the ages of 3, 10, 20 and 40 days. Expressions of housekeeping genes such as beta-actin, cyclophilin and proliferating cell nuclear antigens (PCNA) are determined using reverse transcription polymerase chain reaction (RT-PCR) for the correction of unequal amount of cDNA added into the samples. Using labeled 32P-dCTP and Phosphorimager technology, relative abundance of radioactivities of the PCR products is obtained by dividing the radioactivity of each individual sample by the corresponding radioactivities of different housekeeping genes. Data evaluated by Two-way ANOVA indicate that only the bcl-2(alpha) gene expression is affected significantly by age, sex and their interactions no matter which of the three housekeeping genes is used for correction. When beta-actin was used for corrections, effects of age but not sex were found in the expressions of p53, Rb, p21, AR, ER(beta), substance P and S100beta genes, but not in bcl-2(beta), c-ski, cyclophilin and PCNA genes. While cyclophilin was used for corrections, only the p53, Rb, AR, ER(beta), substance P and S100beta but not the bcl-2(beta), p21, c-ski, PCNA and beta-actin genes are affected by age. They are all not influenced by sex of the animals. Only the AR, ER(beta) and S100beta genes are age-dependent when PCNA was used for the correction. The other gene expressions are not altered by sex, while the interactions of age and sex were found to be significantly affecting the bcl-2(beta) gene expression. Conclusively, developmental changes of the p53, Rb, AR, ER(beta), substance P and S100beta genes expressions are quite evidenced while only the bcl-2(alpha) gene seems to change significantly during the sexual differentiation of olfactory bulb in rats.

The development of brain sex differences: a multisignaling process

In order to account for the development of sex differences in the brain, we took, as an integrative model, the vomeronasal pathway, which is involved in the control of reproductive physiology and behavior. The fact that brain sex differences take place in complex neural networks will help to develop a motivational theory of sex differences in reproductive behaviors. We also address the classic genomic actions in which three agents (the hormone, the intracellular receptor, and the transcription function) play an important role in brain differentiation, but we also point out refinements that such a theory requires if we want to account of the existence of two morphological patterns of sex differences in the brain, one in which males show greater morphological measures (neuron numbers and/or volume) than females and the opposite. Moreover, we also consider very important processes closely related to neuronal afferent input and membrane excitability for the developing of sex differences. Neurotransmission associated to metabotropic and ionotropic receptors, neurotrophic factors, neuroactive steroids that alter membrane excitability, cross-talk (and/or by-pass) phenomena, and second messenger pathways appear to be involved in the development of brain sex differences. The sexual differentiation of the brain and reproductive behavior is regarded as a cellular multisignaling process.

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.

Ontogeny of sex differences in the mammalian hypothalamus and preoptic area

1. There are numerous sites in the nervous system where steroid hormones dramatically influence development. Increasing interest in mechanisms in neural development is providing avenues for understanding how gonadal steroids alter the ontogeny of these regions during sexual differentiation. 2. An increasing number of researchers are examining effects of gonadal steroids on neurite outgrowth, cell differentiation, cell death, cell migration, and synaptogenesis. The interrelated timing of these events may be a key aspect influenced by gonadal steroids throughout development. 3. The preoptic area and hypothalamus are characteristically heterogeneous in terms of cell type (e.g., different neuropeptides) and cell derivation. Perhaps a major reason for the ontogeny of sexual differences in the preoptic area and hypothalamus lies in the convergence of many different cell types from diverse sources (i.e., proliferative zones surrounding the lateral and third ventricles, and the olfactory placodes) that can be influenced in an interactive manner by gonadal steroid mechanisms. 4. The characterization of multiple mechanisms (e.g., trophic, migratory, apoptotic, fate, etc.,) that contribute to permanent changes in brain structure and ultimately function is essential for unraveling the process of sexual differentiation.

Sex differences in the vomeronasal system

In the early eighties we found sex differences in the vomeronasal organ (VNO) and hypothesized that the vomeronasal system (VNS), a complex neural network involved in the control of reproductive behavior, might be sexually dimorphic. At that time sex differences had already been described for some structures that receive VNO input, such as the medial amygdala, the medial preoptic area, the ventromedial hypothalamic nucleus, and the ventral region of the premammillary nucleus. Since then, we have shown sex differences in the accessory olfactory bulb (AOB), the bed nucleus of the accessory olfactory tract (BAOT), and the bed nucleus of the stria terminalis (BST). When new VNS connections were found, all of them ended in nuclei that present sex differences. In general, sex differences in the olfactory system show two morphological patterns: one in which males present greater morphological measures than females, and just the opposite. To explain the morphometric measures of males in the latter, it has been hypothesized that androgens serve as inhibitors. Our work on the involvement of the GABA(A) receptor in the development of AOB and maternal behavior sex differences also suggests that neonatal changes in neuronal membrane permeability to the ion Cl- differences. This might be the first animal model to help us to understand the situation in which human genetic and gonadal sex do not agree with brain and behavioral sex. Finally, we stress that sex differences in the VNS constitute a neurofunctional model for understanding sex differences in reproductive behaviors.

Excitatory neurotransmission and sexual differentiation of the brain

During normal development there is a perinatal sensitive period during which the male brain is exposed to high levels of gonadal steroids, resulting in permanent differentiation of neural substrates. The cellular mechanisms mediating hormonally induced sexual differentiation remain largely unknown. In the adult brain, steroids exert profound influences on the amino acid transmitters, GABA, and glutamate. We have found steroid regulation of amino acid neurotransmission during the perinatal sensitive period and propose this may be functionally related to sexual differentiation of the brain. Specifically, the mRNA coding for the rate-limiting enzyme in GABA synthesis, glutamic acid decarboxylase (GAD), is up to twice as high in some steroid-concentrating regions of the neonatal male brain compared to females, including the arcuate nucleus, dorsomedial nucleus, and the CA1 region of hippocampus. Sex differences in GABA tissue concentrations positively correlate with GAD mRNA differences in several brain regions. There are also sex differences in protein levels of GABA(A) receptor subunits. In parallel with these findings are significantly higher levels of binding to the non-NMDA glutamate receptor in steroid-concentrating regions of male brain. Given that GABA is an inhibitory transmitter and glutamate is an excitatory amino acid, these results initially appear paradoxical. However, in contrast to its inhibitory action in the adult brain, early in development GABA is actually excitatory and acts in a manner analogous to glutamate. Therefore, the combination of increased excitatory GABAergic and glutamatergic activity should result in substantially higher levels of neuronal excitation in the male brain. We speculate that an increased level of neuronal excitation is a potential mechanism mediating the permanent masculinization of the brain.

Estradiol masculinizes the number of accessory olfactory bulb mitral cells in the rat

Orchidectomized males injected with a single dose of estradiol benzoate on the day of birth (D1) showed mitral cell numbers in the accessory olfactory bulb similar to those of control males. However, orchidectomized males that received no additional estradiol benzoate treatment and those orchidectomized and given a single dose of dihydrotestosterone on D1 showed decreases in the number of accessory olfactory bulb mitral cells compared with control males. These results support the notion that the presence of estradiol immediately after birth induces the masculinization of mitral cells number in the accessory olfactory bulb.

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.