Mónica Rodríguez-Zafra

The development of sex differences in the locus coeruleus of the rat

Development of sex differences in the locus coeruleus (LC) is investigated. The LC is a sexually dimorphic structure in which the female manifests a larger volume and greater number of neurons than do males. Male and female Wistar rats were sacrificed on prenatal days (E) 16 and 20 and postnatally (P) on days 1, 3, 7, 15, 35, 45, 60, and 90. Male and female rats show a continuous increase in the number of neurons after birth that stops in the males by P45 and in females by P60. These findings point out the existence of different patterns of development in male and female rats and may suggest that sex differences could be established because of the existence of a differential period of neurogenesis in both sexes in the postpubertal period.

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.

Early postnatal diazepam exposure alters sex differences in the rat brain

The volume and neuron number of the sexually dimorphic accessory olfactory bulb and locus coeruleus are altered by early postnatal exposure (from the day of birth to postnatal day 16) to diazepam. After diazepam treatment, both volume and neuron number were decreased in the male accessory olfactory bulb and in the female locus coeruleus. These results indicate that early postnatal diazepam administration can bear gender-dependent teratogenic effects upon sexually dimorphic nuclei and suggest that endogenous benzodiazepines may be involved in the sexual differentiation of the brain.

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

The present study examines the effects of pre and/or early postnatal administration of diazepam on the mitral cell and on the light and dark granule cell populations in the sexually dimorphic accessory olfactory bulb of the rat. Quantitative differences related to sex were observed in the numbers of the three types of neurons, with vehicle males showing greater numbers of cells than vehicle females. The number of mitral cells in males decreased to the levels shown by female rats following prenatal and pre-postnatal diazepam treatments, whereas the DZ treatments did not affect the females. In addition, the diazepam administration during the prenatal, postnatal and pre-postnatal periods decreased the numbers of both light and dark granule cells in males, while these two granule cell subpopulations were not affected in diazepam treated females. These results indicate that perinatal administration of diazepam can alter the sexual dimorphism in the accessory olfactory bulb and that the GABAA/benzodiazepine receptor complex is involved in the sexual differentiation this part 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.

Effects of perinatal diazepam exposure on the sexually dimorphic rat locus coeruleus

Diazepam (DZ) administration over prenatal, postnatal, and pre plus postnatal periods altered the normal expression of the morphological sex differences of the LC. Males were affected only by the prenatal exposure and the effect of this exposure produced an increase in the volume and neuron number of males LC. By contrast, females were affected by both pre and postnatal treatments and the effect of this exposure resulted in a decrease in the volume and neuron number of females LC. However, pre plus postnatal treatment did not affect females LC.

Effects of estradiol on the development of sexual dimorphism in the bed nucleus of the accessory olfactory tract in the rat

Orchidectomized males injected with a single dose of estradiol benzoate (EB) on the day of birth (D1) showed a volume and neuron number in the nucleus of the accessory olfactory tract (BAOT) similar to that of control males. However, orchidectomized males and those orchidectomized and given a single dose of DHT on D1 showed a decrease in BAOT volume and neuron number with respect to control males. These results support the notion that estradiol induces the morphological masculinization of this structure. The inability of DHT in counteracting the effect of orchidectomy is addressed taking into account the inhibitory action of androgens.

Effects of perinatal diazepam administration on two sexually dimorphic nonreproductive behaviors

The effects of prenatal and/or early postnatal diazepam (DZ) administration on open field activity and continuously reinforced lever-pressing response were studied. Rat pups of both sexes were prenatally (during the last week of pregnancy) and/or postnatally (from the day of birth to day 16) daily exposed to a 2.5 mg/kg dose of DZ. At the age of 60 days all groups were tested in the open field for 5 consecutive days and thirty days later they were studied in a continuously reinforced lever-pressing situation during four consecutive days. In the open field test, females showed greater activity than males and prenatal and/or early postnatal DZ treatments did not alter this sexual dimorphism, although all treatments decreased the open field activity in both male and female 60-day-old rats. In the Skinner box, 90-day-old males presented higher rates of lever-pressing response than females, and only the early postnatal DZ treatment was effective in altering this sexual dimorphism, by decreasing the males but not females rates of response. These results are discussed in regard to the possible interaction between DZ and gonadal hormones during the early sexual differentiation period.

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.

Effects of early postnatal sex steroids on acquisition and extinction of a continuously reinforced lever-pressing response

The effects of early postnatal dihydrotestosterone (DHT) and estradiol on the sexually dimorphic continuously reinforced lever-pressing response were investigated. 90-day-old male rats postnatally treated (during the first eight days of postnatal life) with cyproterone acetate (CA), tamoxifen (TX) or vehicle, and 90-day-old females treated with estradiol benzoate (EB), DHT or vehicle in the same postnatal period, were studied during the acquisition and extinction of the continuously reinforced lever-pressing response using a free-operant procedure. During acquisition, the control males made more responses per minute than the control females, and also reached the extinction criterion significantly sooner than the females. CA treatment impaired the males performance at the levels of that shown by females, whereas TX treatment affected neither acquisition nor extinction. Inversely, in both experimental phases females treated with DHT performed like control females, whereas the acquisition and extinction performances of the EB-females were similar to those obtained in the control or TX male groups.