Biomedical subjects

S Segovia

Publications and source records attributed to S Segovia.

At least 19 recordsLinked to original sources

PubMed2003

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.

Animals↗

PubMed2001

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.

Aging↗

PubMed2001

[Quality control in Medicine. Position of the Chilean Academy of Medicine].

In the last two decades, important changes in medical training and care have occurred in Chile. The number of medical schools has been doubled, exceeding the national availability of professors and qualified training fields. The quality assessment and accreditation of medical training and care is insufficient in Chile. A National Autonomous Corporation of Certification of Medical Specialties, has certified more than 4,000 physicians in 44 specialties. The Chilean Association of Faculties of Medicine has accredited training centers during the last four decades. The National Commission of Undergraduate Training Accreditation, has developed a voluntary system for medical school accreditation. The Academy supports these strategies and considers that accreditation does not threaten institutions or individuals. It is rather a mechanism that identifies strengths and weaknesses of institutions and programs. This will finally result in better quality in medical training and patient care.

Academies and Institutes↗

PubMed2000

Functional sex differences in the accessory olfactory bulb of the rat.

The aim of this study is to determine whether sex-related differences exist in the biosynthetic activity of the mitral cells within the mitral layer of the AOB. Possible functional changes over the estrus cycle and the potential effects of castration and androgenization are assessed. Biosynthetic activity was measured using silver staining of the argyrophilic proteins associated with the nucleolar organizer regions (Ag-NOR). Assisted by stereological methods, the following parameters were studied: mean number, percentage and mean area of Ag-NOR in estrus and diestrus females, intact males, castrated and androgenizated rats. We detected sex differences in a histochemical marker related to synthetic activity, an estrus cycle effect and changes resulting from the perinatal treatments. We conclude that this structurally dimorphic region is also functionally dimorphic.

Animals↗

PubMed2000

Estradiol masculinizes the posteromedial cortical nucleus of the amygdala in the rat.

It has been demonstrated that the posteromedial cortical amygdaloid nucleus (PMCo), is sexually dimorphic. It is shown (Experiment 1) that male orchidectomy on the day of birth (D1) decreases the volume and number of neurons of the PMCo, while a single injection of propionate testosterone to the female on D1 masculinizes the PMCo in this gender. Since male gonadectomy on D1 (Experiment 2) is counteracted by a single injection of estradiol benzoate in males it has been suggested that the masculinization of the PMCo is due to the aromatization of testosterone to estradiol in this structure. These findings support the hypothesis that the development of sex differences in structures that belong to the vomeronasal system are due to the aromatization of testosterone to estradiol shortly after birth.

Amygdala↗

PubMed1999

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.

Animals↗

PubMed1999

Expression of intracellular progesterone receptors in rat brain during different reproductive states, and involvement in maternal behavior.

Progesterone is one of a complex of hormones which influences the occurrence of maternal behavior in rats. The present study provides information on progesterone's mechanism and possible neural site(s) of action with respect to maternal responsiveness. Progesterone can exert cellular effects by acting on membrane receptors or by acting on intracellular receptors. In the first experiment we show that RU 486 can antagonize progesterone's inhibitory effect on maternal behavior. Since RU 486 acts as an antagonist to progesterone's action at its intracellular receptor, these results support the involvement of that receptor in maternal behavior control. The second experiment employs immunocytochemical techniques to detect the number of cells in various forebrain regions which contain intracellular progesterone receptors during different reproductive states. The number of cells which contained progesterone receptors was higher toward the end of pregnancy (progesterone is presumably exerting its effects on maternal behavior at this time) when compared to either early pregnancy or lactation in the following forebrain regions: anteroventral periventricular nucleus of the preoptic area; medial preoptic area; ventral part of the bed nucleus of stria terminalis; ventrolateral division of the ventromedial nucleus; arcuate nucleus; anterior paraventricular nucleus of the hypothalamus; and medial amygdala. The possible involvement of these regions as a site or sites where progesterone might exert its effects on maternal behavior is discussed.

Analysis of Variance↗

PubMed1998

Sex differences in the posteromedial cortical nucleus of the amygdala in the rat.

It has been hypothesized that the vomeronasal system (VNS), a complex neural network implicated in the control of reproductive behaviors, is sexually dimorphic. The posteromedial cortical amygdaloid nucleus (PMCo) belongs to the group of amygdaloid structures that receive direct olfactory input from the accessory olfactory bulb. In the present study we looked for sex differences in this nucleus in male and female adult rats and we found that the males had larger volumes and more neurons than the females. These results support the hypothesis that the VNS is a sexually dimorphic system.

Amygdala↗

PubMed1998

Development of sex differences in the bed nucleus of the accessory olfactory tract in the rat.

In the present study, we investigate the development of sex differences in the bed nucleus of the accessory olfactory tract (BAOT), a sexually dimorphic structure in which masculinization of male rats depends on the level of postnatal estradiol. Male and female Wistar rats were sacrificed postnatally when they were 1, 3, 7, 15, 45 and 60 days old, and stereological methods were used to estimate the volume and number of neurons in the BAOT of the subjects. With respect to volume, sex differences were established from P15. In relation to the number of neurons, the males acquire their adult morphological parameter by P15, while females show a decrease (P3), increase (from P3 to P15) and later decrease (from P15 to P45). Sex differences from P3 to P7 might be related to greater cell death in the BAOT of the females. These results support the hypothesis that both male and female rats reach their adult morphological pattern within this sexually dimorphic nucleus in an active manner.

Animals↗

PubMed1997

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.

Animals↗

PubMed1997

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.

Animals↗

PubMed1996

Role of GABAA receptors in the organization of brain and behavioural sex differences.

Sex differences in GABA neurotransmitter have been described. We have studied the involvement of the GABAA receptor in sex differences in the brain and reproductive behaviour. Neonatal administration of the GABAA agonist diazepam to male rats facilitated the induction of maternal behaviour in adults, while the antagonist picrotoxin disrupted it in females. Sex differences in the accessory olfactory bulb were also reversed, but gonadal function remained unaltered in both sexes. This suggests that neonatal changes in neuronal membrane permeability to Cl- ions may play a role in the organization of sex differences. Our study constitutes a new model for understanding the early neurobiological organization of sex differences.

Animals↗

PubMed1996

Searching for sex differences in the vomeronasal pathway.

The sexual differentiation of brain and behavior is reviewed from the findings of sex differences in the vomeronasal pathway. A motivational approach to sex differences in reproductive behavior is stressed by taking into account that sex differences are present in neural networks: from the receptor organ (the vomeronasal organ) to effector nuclei. Sex differences in the brain appear in two morphological patterns. In one, the male presents greater morphological measurements than the female; in the other, the opposite occurs. These two morphological patterns are actively differentiated by gonadal steroids. The functional significance of these two morphological patterns is addressed. Moreover, since the GABA(A) receptor is involved in the organization of sex differences in vomeronasal structures such as the accessory olfactory bulb and in maternal behavior, the role of membrane mechanisms, 5alpha reduced hormones, and neurosteroids in the sexual differentiation process is discussed.

Animals↗

PubMed1995

Lesions in the medial posterior region of the BST impair sexual behavior in sexually experienced and inexperienced male rats.

Previous studies have showed that lesions in the bed nucleus of the stria terminalis of experienced male rats impair some parameters of sexual behavior. The aim of this study was to examine the contribution of the medial posterior region of the bed nucleus of the stria terminalis (BSTMP), a sexually dimorphic region of this nucleus that pertains to the vomeronasal system, to the modulation of sexual behavior of the male rat. Small electrolytic bilateral lesions in the BSTMP were made in male heterosexual experienced and inexperienced rats. Sham lesioned animals were also tested as a control of the effects of the general surgical procedures. Behavioral tests were then performed to obtain standard measures of masculine sexual behavior. Our results indicate that the sexually experienced male rats with lesioned BSTMPs showed increases in the number of mounts and the number of intromissions and, consequently, in ejaculation latency. In contrast, the sexually naive male rats showed increases in first mount and intromission latencies and in ejaculation latency, but the latter occurred due to increases in the interintromission intervals. This group also showed low correlations between olfactory investigation of the anogenital area of the female and initiation and maintenance of copulatory behavior. The results suggest that sexual experience obtained in the very artificial conditions of laboratory tests could supply some of the cues provided by the BSTMP in the process of sensorial integration, which we hypothesize modulates the initiation and pacing of copulation. However, sexual experience does not apparently supply any other kinds of cues provided or processed in the BSTMP that are involved in modulating the elicitation of intromissions and ejaculations.

Animals↗

PubMed1995

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.

Analysis of Variance↗

PubMed1994

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.

Animals↗

PubMed1994

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

The Maternal Behavior Recorder (MBR) is a microcomputer program designed to record and analyze data from research on parental behavior of rats and other rodents. It is used to record the specific, characteristic patterns of maternal care in rodents: nest building, grooming, licking, crouching, and retrieval of pups. Moreover, it analyzes these events in terms of frequency and duration, allowing any events erroneously recorded to be corrected. The MBR can also simultaneously control observations made by one or two experimenters, and it calculates a set of reliability measures between them.

Animals↗

PubMed1993

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.

Animals↗