Biomedical subjects

S Segovia

Publications and source records attributed to S Segovia.

At least 19 recordsLinked to original sources

PubMed1992

Postnatal administration of dihydrotestosterone to the male rat abolishes sexual dimorphism in the accessory olfactory bulb: a volumetric study.

The regulatory action of the non-aromatizable androgen dihydrotestosterone (DHT) on sexual differentiation of the volume of the rat accessory olfactory bulb (AOB) was studied. Postnatal treatment with DHT (180 micrograms/day) carried out daily between days 6 and 20 produced a drastic reduction in overall AOB size and that of its constituent neural layers in genetic males with respect to intact and control males. The volumetric measures found in DHT-treated males did not differ from those shown by the intact females. These results, which indicate a demasculinization and a feminization of the AOB volume in gonadally intact male rats induced by DHT, are discussed in relation to the presumably regulatory role of DHT on neuron populations during the sexual organizational process of the brain.

Animals↗

PubMed1992

Sexual dimorphism of the dopamine-beta-hydroxylase-immunoreactive neurons in the rat locus ceruleus.

Sex differences in the noradrenaline synthesizing neurons of the locus ceruleus (LC) in rat brain were investigated immunocytochemically using an antibody to dopamine-beta-hydroxylase. Female adult rats contained a greater structural volume and average somatic area in the anterior intermediate region of the nucleus compared with males. Whether this difference is related to the endocrine status of the animals, and consequently a functionally distinct population of neurons, is yet to be determined.

Animals↗

PubMed1992

Maternal behavior induced in male rats by bilateral lesions of the bed nucleus of the accessory olfactory tract.

In the present study, we investigate the effect of bilateral electrolytic lesions of the bed nucleus of the accessory olfactory tract (BAOT) in male Wistar rats that did not have care-pups experience, using a test of induced maternal behavior. Consistent with our previous findings in virgin female rats (10), there was a significantly shorter sensitization (3 days) and retrieval (2 days) latencies in the BAOT-lesioned group than in the sham-lesioned and intact-control male groups (12 days for both). Based on these findings, we propose that BAOT, a sexually dimorphic nucleus of the vomeronasal system, exerts an inhibitory modulation in the expression of parental behavior in male and female virgin rats. It may do so by maintaining an olfactory-based tonic inhibition of maternal behavior, thereby resulting in the adults' tonic avoidance of the pups until this inhibition is abolished by lesion, or reduced or overridden by appropriate hormonal and/or sensory influences.

Amygdala↗

PubMed1992

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 male's 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.

Androgen Antagonists↗

PubMed1992

Female's DHT controls sex differences in the rat bed nucleus of the accessory olfactory tract.

In the present study the regulatory action of the non-aromatic androgen dihydrotestoterone (DHT) on the volume of the sexually dimorphic bed nucleus of the accessory olfactory tract (BAOT) was investigated. Postnatal treatment with DHT (180 micrograms day-1) between days 6 and 20 (D6-D20) induced, in gonadally intact male rats, a drastic reduction in the overall volume to levels typical in control females. Conversely, the postnatal administration of the anti-androgen cyproterone acetate (CA) to the females from D6-D20 produced an increment in the BAOT volume not dissimilar to that found in control males. These findings reveal that sexual organization in this vomeronasal structure is dependent on the presence of DHT in females during postnatal development.

Androgen Antagonists↗

PubMed1991

Bilateral lesions of the bed nucleus of the accessory olfactory tract facilitate maternal behavior in virgin female rats.

In this study the effects of electrolytic lesions of the bed nucleus of the accessory olfactory tract (BAOT) on the induction of maternal behavior in virgin female Wistar rats was investigated. Results demonstrate a functional role of the BOAT in the neural control of maternal behavior in virgin female rats since bilaterally BOAT lesioned (BL) animals showed significantly shorter sensitization latencies (BL = 6 days) than sham lesioned (SH = 12 days) and intact control (C = 12 days) female rats. At the same time, statistically significant differences were observed in retrieval latency between BL (5.5 days) and C (10 days) groups, but not in the SH group (8 days). In physical contact frequency, the BL group reached higher scores than SH or C group. However, bilateral BAOT lesions failed to affect other maternal patterns such as nest building quality. Thus these results indicate that the BOAT, a vomeronasal system structure, is involved in the control of maternal behavior and that BL electrolytic lesions facilitate the onset of this behavior in virgin female Wistar rats.

Amygdala↗

PubMed1991

Sexual dimorphism in accessory olfactory bulb mitral cells: a quantitative Golgi study.

The purpose of the present study was to identify the existence of sexual dimorphism in the dendritic field of accessory olfactory bulb mitral cells in rats and to investigate the effects of male orchidectomy and female androgenization on the day of birth upon this dendritic field. The rapid Golgi method was used to conduct a quantitative study of various characteristics of the dendritic field of accessory olfactory bulb mitral cells. The results indicated greater values for males than females for the following characteristics: (i) somatic area; (ii) degree of branching in the dendritic field; (iii) total dendritic length; and (iv) dendritic density around the neuronal soma. Orchidectomy of males, as well as androgenization of females, on the day of birth inverted these differences.

Animals↗

PubMed1991

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.

Aging↗

PubMed1990

Sexual dimorphism in the bed nucleus of the accessory olfactory tract in the rat.

This work investigates the existence of sex differences in the volume and number of neurons and glial cells in the bed nucleus of the accessory olfactory tract (BAOT). Males showed larger volume and number of cells than female rats. Early postnatal (day 1 after birth) orchidectomy in males, and androgenization in females, reversed these differences. No sex differences were found in BAOT glial cells. The sexual dimorphism found in the neuron/glial cell ratio reflects sex differences in neuron number. The existence of sexual dimorphism in the BAOT supports our earlier hypothesis which states that the vomeronasal system (VNS) is sexually dimorphic.

Animals↗

PubMed1990

Sexual dimorphism in the parastrial nucleus of the rat preoptic area.

This work investigates the possible existence of sex differences in the volume of the parastrial nucleus (PSN), a component of the preoptic area in the rat. The effects of postnatal (on day 1 after birth) male orchidectomy and female androgenization on this nucleus were studied. The volume of the PSN was greater in the control females than in the control males and postnatal treatments reversed this sexual dimorphism.

Animals↗

PubMed1990

SBR: a computer program to record and analyse sexual behavior in rodents.

SBR (Sexual Behavior Recorder) is a program designed to record and analyse data from research on the sexual behavior of rats and other animals with similar patterns of sexual behavior. SBR allows the user to record the characteristic events of both the male and female's sexual behavior: mounts, intromissions, ejaculations and lordosis. It also allows the user to record two other types of events, and analyse them in terms of frequency and duration, using two user-defined keys. The program allows the correction of any event erroneously recorded. SBR can simultaneously control observations made by one or two observers, and on one or two experiment boxes. In the case that two observers record from the same experiment box, the program calculates a set of measures of reliability between the observers. At the end of each observation, SBR conducts a descriptive analysis of the recorded events, including the parameters normally used in scientific literature on the subject, and writes this analysis to disk files. As well as the default calculation parameters, it is possible to calculate any other, or to use the program as a record of general purpose events using the file which contains all the recorded events in sequential order and the exact time at which they were recorded. SBR was written using the compiler Turbobasic 1.1 from Borland International Inc. (1987).

Animals↗

PubMed1990

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 male's but not female's rates of response. These results are discussed in regard to the possible interaction between DZ and gonadal hormones during the early sexual differentiation period.

Animals↗

PubMed1989

Learned immobility explains the behavior of rats in the forced swimming test.

The rat forced-swimming test (FST) is widely used for screening substances with a potential antidepressant effect. The rat immobility shown in the FST has been interpreted as "behavioral despair" and has been suggested as an animal model of human depression. In the following series of experiments it is shown that measuring rat mobility by an automatic recording device is more accurate than measuring immobility time by direct observation (Experiment 1 and 5). The automatic recording procedure was tested with imipramine and mianserin showing similar results to those reported in the literature using a direct observation procedure by the researcher (Experiment 2). In Experiment 3 it was demonstrated that: (a) rat mobility decreased with experience, (b) switching water depth on Day 2 of the test increased mobility and (c) anisomycin acts as a false positive. In Experiment 4 the possible state dependent effect of imipramine in the FST was studied. The effect of imipramine on rat behavior in the FST is not state dependent. The imipramine-saline group shows greater mobility than the saline-saline group and does not differentiate from the imipramine-imipramine group. Thus, it was suggested that imipramine could interfere with the acquisition and/or consolidation processes. In Experiment 5, it is shown that a single dose of 25 mg/kg of imipramine, administered before or immediately after training on Day 1, increases rat's mobility on Day 2, thus suggesting that imipramine alters the consolidation process. From these results it is suggested that the behavioral process involved in the FST is "learning to be immobile" instead of "behavioral despair" as previously suggested in the literature.

Animals↗

PubMed1988

Early effects of gonadal steroids on the neuron number in the medial posterior region and the lateral division of the bed nucleus of the stria terminalis in the rat.

This work investigates the possible existence of sex differences in the number of neurons in the medial posterior region (BNSTMp) and the lateral division (BNSTL) of the bed nucleus of the stria terminalis in the rat. These two zones of the bed nucleus of the stria terminalis belong, respectively, to the vomeronasal system (VNS), and to the main olfactory system (MOS). In the BNSTMp, males showed a greater number of neurons than females. Early postnatal (Day 1 after birth) orchidectomy in males, and androgenization in females, eliminated and reversed these differences. In the BNSTL, sexual dimorphism was restricted to its anterior region (BNSTLa). Females showed there a greater number of neurons than males. Male orchidectomy on Day 1 after birth increased the number of neurons, while female androgenization produced the opposite effect. The results obtained in this study support the hypothesis that the VNS is sexodimorphic, and suggest that sex differences exist in MOS, and that these differences are controlled by gonadal steroids during the perinatal period.

Animals↗

PubMed1988

The distribution of glial fibrillary acidic protein in the adult rat brain is influenced by the neonatal levels of sex steroids.

Sex steroids during the perinatal period are able to modify the postnatal development of neurons within steroid-sensitive areas in the rat brain. This study was designed to test the possible influence of the early postnatal levels of sex steroids on the morphology of the astrocytes. The experimental manipulation of the neonatal levels of sex steroids was performed by the androgenization of females with a single injection of testosterone propionate and by the orchidectomy of males on the day of birth. Control females received a single injection of vehicle and control males were sham operated. All the animals were sacrificed at 3 months of age postnatally. The immunohistochemical distribution of the glial fibrillary acidic protein (GFAP), a marker of astrocytic filaments, was studied on coronal sections of the dorsal hippocampus, the globus pallidus and the hypothalamic arcuate nucleus. The number of GFAP immunoreactive cells, the number of GFAP immunoreactive primary processes per cell and the surface density of the GFAP immunoreactive material were evaluated. This morphometric evaluation revealed a decreased surface density of GFAP immunoreactive material in the hippocampus, globus pallidus and the ventral part of the arcuate nucleus of orchidectomized males when compared to control males. Sex differences in the distribution of GFAP immunoreactivity were detected in the hippocampus and globus pallidus. These differences were abolished by the androgenization of females. The number of GFAP immunoreactive cells was similar in all the experimental groups, indicating that the differences in surface density represent an effect of sex steroids on the growth of astrocytic processes rather than on the proliferation of astrocytes.

Animals↗

PubMed1988

Effects of sex steroids on the development of the locus coeruleus in the rat.

The effects of postnatal (on day 1 (D1) after birth) male orchidectomy and female androgenization on the locus coeruleus (LC) are studied. Normal adult female rats show greater LC volume and cell number than males. Testosterone treatment of females on D1 eliminates these differences. However, D1 male orchidectomy does not affect either the volume or the number of cells.

Animals↗

PubMed1988

Effects of early postnatal gonadal steroids on acquisition and extinction of a single alternation response in discrete-trials lever pressing.

The present report studies the effect of sex on the acquisition and extinction of a single alternation schedule of reinforced (R) and nonreinforced (N) trials in a Skinner box. In addition to the investigation of the basic sex differences in Experiment 1, the effects of early gonadal steroids treatment and postpubertal gonadectomy of male and female rats were examined in Experiments 2 and 3, respectively. Both acquisition and extinction performances were evaluated by means of latency. In Experiment 1, males showed higher latencies on N trials and extinguished faster than female rats. In Experiment 2, female androgenization and male orchidectomy on day one after birth reversed the direction of the sex differences found in the previous experiment. However, postpubertal gonadectomy (Experiment 3) does not affect the performance of male and female rats.

Animals↗

PubMed1987

The bed nucleus of the stria terminalis in the rat: regional sex differences controlled by gonadal steroids early after birth.

The effects of postnatal (on day 1 (D1) after birth) male orchidectomy and female androgenization on the bed nucleus of the stria terminalis (BNST) were studied. The volume of the medial posterior region of the BNST was greater in the control males than in the control females. Postnatal treatment reversed these differences. Sex differences were also found in the medial anterior region of the BNST where female rats always showed a greater volume than did the males. Female androgenization on D1 did not affect the volume of the BNST medial anterior region. However, D1 male orchidectomy did increase significantly the volume of this region. No sex differences were found in lateral, ventral or intermediate BNST divisions.

Androgens↗