Evidence for sexual differentiation of glia in rat brain

It is well established that gonadal steroids mediate sexual differentiation of the brain via direct effects on neurons during a restricted critical period. In addition, estrogen can influence glial morphology in the adult brain, and in vitro studies suggest estrogen induces glial differentiation. However, there is a lack of in vivo evidence for steroid effects on glia during the critical period. We report here a hormone-mediated sexual differentiation of arcuate glia as early as Postnatal Day 1. Using glial fibrillary acidic protein immunoreactivity (GFAP-ir), we compared the responsiveness of astroglia in the rat arcuate nucleus among five hormonally different groups. The results indicate increased GFAP-ir cell surface area 24 hr after hormonal manipulation in castrate males compared to intact males, intact females (ANOVA; P < 0.01), and females injected with testosterone propionate (50 microg; ANOVA; P < 0.05). However, astroglia in intact males extended their processes significantly greater distances from the cell body compared to all other treatment groups (ANOVA; P < 0.01). The GFAP-ir cells were categorized into four distinct classes ranging from a simple bipolar to a fully stellate morphology. The frequency distribution of classes varied between groups with more stellate cells found in intact males. Finally, these sex differences in arcuate glia persisted into adulthood. We hypothesize that during the critical period, testosterone, or its metabolite estrogen, induce sexual differentiation of glia. We further hypothesize that in females glial cells remain partially undifferentiated and this may be important to glial plasticity seen in adult female arcuate.     

Sex differences and androgen-dependent regulation of aromatase (CYP19) mRNA expression in the developing and adult rat brain

Sex differences, androgen dependence and asymmetries of aromatase activity have been reported during ontogeny of the rat. It remains to be elucidated, however, whether the changes in aromatase activity are reflected by similar changes in specific mRNA levels. In addition, very little is known regarding mechanism(s) underlying such differential regulation of aromatase expression. To address these questions, we have employed the in situ hybridization (ISH) technique to examine specific mRNA levels in the brain of both male and female rats at selected stages of development. In prenatal stages of development, at gestational day (GD) 18 and 20, aromatase mRNA was detected in several hypothalamic and limbic brain regions. Semiquantitative analysis of aromatase mRNA did not reveal statistically significant sex differences in any of these regions (except in one experiment at GD20, when a sex difference was found in the medial preoptic nucleus). In contrast, clear sex differences were determined at postnatal day (PN) 2; male animals contained significantly more aromatase mRNA in the bed nucleus of the stria terminalis (BST) and the sexually dimorphic nucleus of the preoptic area (SDN) compared to female rats. Four days later in development, at PN6, sex differences of aromatase mRNA signals were observed in the BST, but were no longer detectable in the SDN. At PN15 and in adult animals, no sex differences could be determined. The effect of flutamide treatment (50 mg/kg/day) was investigated in GD20 fetuses as well as in adult rats. No statistically significant changes in aromatase mRNA expression were found in either case. In summary, our results suggest that differential regulation of aromatase mRNA expression during the critical period of sexual differentiation might, in part, account for the establishment of some of the many sexually dimorphic parameters of the rat brain. The role of androgens in the regulation of the sex-specific and developmental expression of aromatase mRNA in the rat brain remains to be clarified.     

Castration decreases single cell levels of mRNA encoding glutamic acid decarboxylase in the diagonal band of broca and the sexually dimorphic nucleus of the preoptic area

Using quantitative in situ hybridization histochemistry (ISHH), we determined the effect of castration on single cell levels of glutamic acid decarboxylase (GAD) mRNA in discrete hypothalamic regions of the male rat brain associated with the control of gonadotropin secretion. A 48-base oligodeoxynucleotide probe was used to detect with equal affinity the two isoforms of GAD message, GAD65 and GAD67. GAD message also was quantitated in a number of selected areas of the brain to contrast GAD gene expression amongst several populations of GABAergic neurons. Comparison of 11 brain regions demonstrated a 9.3-fold range in the quantity of single cell GAD mRNA with levels being highest in the amygdala and the diagonal band of Broca, moderate in the piriform cortex, caudate nucleus, substantia innominata, globus pallidus, cingulate cortex and medial septal nucleus, and lowest in the lateral septal nucleus and the medial preoptic nucleus (MPN). Castration markedly reduced single cell GAD mRNA levels in the DBB and the MPN, two discrete hypothalamic structures known to contain dendritic fields, cell bodies, and axons of GnRH neurons projecting to the median eminence. A striking finding was a dense core of steroid-sensitive GABAergic neurons within the MPN comprising the sexually dimorphic nucleus of the preoptic area (SDN-POA). Similar to the MPN as a whole, the amount of GAD mRNA expressed by cells in the SDN-POA of sham operated control rats was greater than in castrated animals. GAD mRNA levels were inversely related to serum LH titers, suggesting a role for these neurons in the mechanism controlling gonadal steroid negative feedback on LH secretion. This report provides the basis for future work to determine if GAD65, GAD67 or whether both isoforms are affected by gonadal steroid input.     

Region-specific regulation of glutamic acid decarboxylase (GAD) mRNA expression in central stress circuits

Neurocircuit inhibition of hypothalamic paraventricular nucleus (PVN) neurons controlling hypothalamo-pituitary-adrenocortical (HPA) activity prominently involves GABAergic cell groups of the hypothalamus and basal forebrain. In the present study, stress responsiveness of GABAergic regions implicated in HPA inhibition was assessed by in situ hybridization, using probes recognizing the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD65 and GAD67 isoforms). Acute restraint preferentially increased GAD67 mRNA expression in several stress-relevant brain regions, including the arcuate nucleus, dorsomedial hypothalamic nucleus, medial preoptic area, bed nucleus of the stria terminalis (BST) and hippocampus (CA1 and dentate gyrus). In all cases GAD67 mRNA peaked at 1 hr after stress and returned to unstimulated levels by 2 hr. GAD65 mRNA upregulation was only observed in the BST and dentate gyrus. In contrast, chronic intermittent stress increased GAD65 mRNA in the anterior hypothalamic area, dorsomedial nucleus, medial preoptic area, suprachiasmatic nucleus, anterior BST, perifornical nucleus, and periparaventricular nucleus region. GAD67 mRNA increases were only observed in the medial preoptic area, anterior BST, and hippocampus. Acute and chronic stress did not affect GAD65 or GAD67 mRNA expression in the caudate nucleus, reticular thalamus, or parietal cortex. Overall, the results indicate preferential upregulation of GAD in central circuitry responsible for direct (hypothalamus, BST) or multisynaptic (hippocampus) control of HPA activity. The distinct patterns of GAD65 and GAD67 by acute versus chronic stress suggest stimulus duration-dependent control of GAD biosynthesis. Chronic stress-induced increases in GAD65 mRNA expression predict enhanced availability of GAD65 apoenzyme after prolonged stimulation, whereas acute stress-specific GAD67 upregulation is consistent with de novo synthesis of active enzyme by discrete stressful stimuli.     

GABAergic neurons in the embryonic olfactory pit/vomeronasal organ: maintenance of functional GABAergic synapses in olfactory explants

In previous work, we showed a robust gamma-aminobutyric acid (GABAergic) synaptic input onto embryonic luteinizing hormone-releasing hormone (LHRH) neurons maintained in olfactory explants. In this study, we identify GABAergic neurons in olfactory pit (OP) of embryonic mice in vivo and study, using patch-pipet whole-cell current and voltage clamp techniques, synaptic interactions of these neurons in explant cultures. In vivo, glutamate decarboxylase (GAD, the enzyme which synthesizes GABA) mRNA was first detected in nasal regions on Embryonic Day (E) 11.5. From E12.5 to E13.5, robust GAD expression was localized to cells primarily in the ventral aspect of the OP. GAD mRNA was not detected over dorsally located cells in olfactory sensory or respiratory epithelium. In addition, GAD mRNA was not observed in cells along olfactory axons. GAD mRNA was dramatically reduced in the OP/vomeronasal organ by E16.5. Using antibodies against both GABA and GAD, immunopositive axonal-like tracts were detected in the nasal septum on E12.5. GABAergic staining decreased by E13.5. To examine synaptic interactions of these GABAergic cells, embryonic olfactory explants were generated and maintained in serum-free media. As explants spread, neuron-like cells migrated into the periphery, sometimes forming ganglion-like clusters. Cells were recorded, marked intracellularly with Lucifer Yellow and post-fixation, immunocytochemically examined. Forty-six cells, typically multipolar, were GABAergic, had resting potentials around -50 mV, and exhibited spontaneous action potentials which were generated by spontaneous depolarizing GABAergic (GABAA) synaptic activity. OP neurons depolarized in response to GABA by increasing Cl- conductance. The biophysical properties of OP-derived GABAergic neurons were distinct from those reported for olfactory receptor neurons but similar to embryonic LHRH neurons. However, unlike LHRH neurons, GABAergic neurons did not migrate large distances in olfactory explants or appear to leave the olfactory pit in vivo.     

Biphasic response of spinal GABAergic neurons after a lumbar rhizotomy in the adult rat

The expression of gamma-aminobutyric acid (GABA) and of the isoforms of the enzyme involved in its synthesis, glutamic acid decarboxylase (GAD), is modified in several rat brain structures in different injury models. The aim of the present work was to determine whether such plasticity of the GABAergic system also occurred in the deafferented adult rat spinal cord, a model where a major reorganization of neural circuits takes place. GABAergic expression following unilateral dorsal rhizotomy was studied by means of non-radioactive in situ hybridization to detect GAD67 mRNA and by immunohistochemistry to detect GAD67 protein and GABA. Three days following rhizotomy the number of GAD67 mRNA-expressing neurons was decreased in the superficial layers of the deafferented horn, while GABA immunostaining of axonal fibres located in this region was highly increased. Seven days after lesion, on the other hand, many GAD67 mRNA-expression neurons were bilaterally detected in deep dorsal and ventral layers, this expression being correlated with the increased detection of GAD67 immunostained somata and with the reduction of GABA immunostaining of axons. GABA immunostaining was frequently found to be associated with reactive astrocytes that exhibited intense immunostaining for glial fibrillary acidic protein (GFAP) but remained GAD67 negative. These results indicate that degeneration of afferent terminals induces a biphasic response of GABAergic spinal neurons located in the dorsal horn and show that many spinal neurons located in deeper regions re-express GAD67, suggesting a possible participation of the local GABAergic system in the reorganization of disturbed spinal networks.     

Sex differences in the activity of gamma-aminobutyric acidergic neurons in the rat hypothalamus

The rate of GABA turnover was determined in nine microdissected brain regions in adult male and female rats. In the medial preoptic nucleus (central aspect) and ventromedial nucleus (ventrolateral aspect) of the hypothalamus, areas involved in the regulation of gonadotropin secretion and sex behavior, GABAergic neuronal activity was about 2-fold greater in males than females. These results demonstrate a striking sexual dimorphism in the activity of specific populations of hypothalamic GABAergic neurons.     

Expression of two forms of glutamic acid decarboxylase (GAD67 and GAD65) during postnatal development of the cat visual cortex

The postnatal development of GAD67 and GAD65 protein expression and of GAD67 positive neurons and GAD65 containing axon terminals in cat visual cortex was studied. Western blot analysis showed that the expression of both GAD67 and GAD65 increased to approximately two-thirds of the adult level during the first 5 postnatal weeks and gradually increased thereafter. In adult cats, immunohistochemistry showed that GABA and GAD67 containing neurons were found in all cortical layers. Faint cell body staining was seen with the antibody to GAD65, but it densely labeled puncta. In neonates, GABA and GAD67 immunoreactivity was most intense in two distinct bands, one superficial (Layer 1/Marginal zone), another deep (Layer VI/Subplate). Unlike in adults, GAD65 positive cell bodies were clearly evident in neonates and distributed similarly to, but less frequently than, GABA and GAD67. These GAD65 positive cells frequently had morphologies suggestive of embryonic cells and largely disappeared in older animals. During postnatal development, the neurochemical differentiation of GAD67 positive neurons and GAD65 positive axon terminals across visual cortical laminae followed an inside-outside developmental pattern, which reached adult levels after 10 weeks of age. These results suggest that postnatal development of the visual cortical GABA system involves three distinct processes: (A) a dying off of embryonic GABA cells which could play a role in formation of the cortical plate; (B) a period of relative quiescence of the VC GABA system in the first 5 postnatal weeks which could maximize excitatory NMDA effects during the rising phase of the critical period; (C) the prolonged postnatal maturation of the adult GABA system which could be involved in the crystallization of adult physiological properties and the disappearance of neural plasticity.     

Decreasing GAD neonatally attenuates steroid-induced sexual differentiation of the rat brain.

During development, exposure to gonadal steroids results in brain sexual differentiation. Postnatally, hypothalamic gamma-aminobutyric acid (GABA) levels are almost double in males versus females. We hypothesized that increased GABA neonatally results in masculinization. Males, females, and androgenized females were infused intrahypothalamically with antisense oligonucleotides against glutamic acid decarboxylase (GAD) mRNA at birth to reduce GABA synthesis. GAD protein and GABA levels were reduced 24 hr later without obvious toxic effects, as determined by histological examination. As adults, neonatally antisense-treated, androgenized females showed reduced intromission-like behavior and lordosis quotients compared with vehicle and scrambled controls. Lordosis quotients were reduced about 50% in nonandrogenized females versus vehicle and scrambled controls. These data suggest that GABA is involved in mediating brain sex differentiation and may act in both males and females. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An analysis of automatic teller machine usage by older adults: a structured interview approach

Sex differences in the activity of aromatase cytochrome P450 (CYP19) in the rat brain have been reported during pre- and postnatal development. It is unclear, however, whether these differences are reflected by corresponding differences in specific mRNA levels. To address this question, we have examined aromatase mRNA levels in specific regions of male and female rat brains by means of in situ hybridization (ISH). At prenatal stages of development, i.e. at gestational day 18 (GD18) and GD20, aromatase mRNA was detected in several preoptic, hypothalamic and limbic brain regions. Semiquantitative analysis of aromatase mRNA did not reveal sex differences in any of these regions. In contrast, clear-cut sex differences were determined at postnatal day (PN) 2; male animals expressed significantly more aromatase mRNA in the bed nucleus of stria terminalis (BST) and the sexually dimorphic nucleus of the preoptic area (SDN). Smaller but still significant differences (females > males) were obtained in the medial preoptic area (MPO). At PN6, sex differences of aromatase mRNA signals (males > females) were still present in the BST, but were no longer detectable in the SDN and the MPO. At PN15 and in adult animals, aromatase mRNA levels were similar in BST and medical amygdaloid nucleus of male and female rats. Since aromatase mRNA expression decreases during postnatal development, no ISH signals could be detected anymore in MPO, SDN and ventromedial hypothalamic nucleus. Our results are consistent with the concept that differential regulation of aromatase mRNA expression might be important for the establishment of different neuronal circuitry in male and female animals.     

Pre-embedding staining for GAD67 versus postembedding staining for GABA as markers for central GABAergic terminals

Pre-embedding immunocytochemistry for the active form of glutamate decarboxylase (GAD67) and postembedding staining for gamma-aminobutyric acid (GABA) were compared as markers for central GABAergic terminals in the phrenic motor nucleus, in which phrenic motor neurons had been retrogradely labeled with cholera toxin B-horseradish peroxidase. Nerve terminals with or without GAD67 immunoreactivity were identified in one ultrathin section. GABA was localized with immunogold in an adjacent section after etching and bleaching. GABA labeling density was assessed over 519 GAD67-positive and GAD67-negative nerve terminals in the phrenic motor nucleus. Frequency histograms showed that statistically higher densities of gold particles occurred over most GAD67-positive terminals. However, some GAD67-negative terminals also showed high densities of gold particles, and some GAD67-positive terminals showed low densities. Preabsorption of the anti-GABA antibody with a GABA-protein conjugate, but not with other amino acid-protein conjugates, significantly reduced gold labeling over both GAD67-positive and GAD67-negative terminals. These results show that the presence of GAD67 immunoreactivity correlates strongly with high densities of immunogold labeling for GABA in nerve terminals in the phrenic motor nucleus. Preabsorption controls indicate that authentic GABA was localized in the postembedding labeling procedure. Only a small proportion of intensely GABA-immunoreactive terminals lack GAD67, suggesting that both GAD67 and GABA are reliable markers of GABAergic nerve terminals.     

Gonadal steroids modulate the growth-associated protein GAP-43 (neuromodulin) mRNA in postnatal rat brain

Gonadal steroid hormone action during early postnatal life determines the growth and connectivity of certain neuronal populations in the hypothalamus. The results of recent studies indicate that steroid hormones modulate the growth-associated protein GAP-43 mRNA in the adult rodent hypothalamus. Since GAP-43 is concentrated in axonal growth cones and has been implicated in axonal elongation and synaptogenesis, the present study investigated the effect of various gonadal hormonal conditions on GAP-43 mRNA levels in postnatal rat brain. On postnatal day 1, male rats were castrated or sham-operated and injected with sesame oil. Additional intact female rats were also injected with oil, while a group of female pups were injected with testosterone propionate. On postnatal day 6, brains were frozen and 16-microns cryostat sections processed and hybridized with a 35S-labeled antisense riboprobe complimentary to GAP-43 mRNA. Slide-mounted sections were stringently washed, apposed to X-ray film and then dipped in liquid emulsion. Evaluation of slide and film autoradiograms revealed an extensive presence of GAP-43 mRNA in the medial preoptic nucleus, bed nucleus of the stria terminalis and cerebral cortex, while the intensity of hybridization signal in other brain regions including the striatum was low. Quantitative assessment of GAP-43 mRNA in the medial preoptic area revealed that the level of GAP-43 mRNA was highest in the sham-operated male, attenuated after male castration, low in the intact female and markedly augmented in the testosterone-treated female. The pattern of change in the bed nucleus of the stria terminalis and laminae II and III of the frontal cortex was similar to that observed in the preoptic area. The changes in hybridization signal were positively correlated with changes in serum testosterone levels as determined by RIA. The results of these studies indicate that GAP-43 mRNA levels in the medial preoptic area, bed nucleus of the stria terminalis and cerebral cortex are sexually dimorphic and modulated by changes in gonadal steroid hormone levels. The results further suggest that the differential regulation of GAP-43 mRNA by sex steroids in the male and female postnatal brain may influence the phenotype of forebrain neuronal circuitry and thereby determine the phenotype of adult neuronal function.     

Ultrastructural evidence for intra- and extranuclear projections of GABAergic neurons of the suprachiasmatic nucleus

GABAergic projections of the suprachiasmatic nucleus (SCN) were demonstrated in a double-labelling ultrastructural study which visualised the efferents of the SCN by PHA-L tracing, diaminobenzidine (DAB) immunocytochemistry, and GABA with immunogold postembedding staining. The results show a strong contralateral projection of the SCN that is partly GABA-containing. In addition, ipsilateral SCN projections to the dorsomedial hypothalamus and periventricular part of the paraventricular nucleus and sub-paraventricular nucleus were shown to contain GABA. The present results indicate that the SCN may utilize this inhibitory neurotransmitter to regulate and organize its own circadian rhythm as well as using GABA to transmit its diurnal information to other regions of the brain.     

A powerful GABA(B) receptor-mediated inhibition of GABAergic neurons in the arcuate nucleus

We combined histofluorescence with in situ hybridization to identify GABAergic neurons in the arcuate nucleus (ARC) following electrophysiological recordings, using GAD65 as a marker. Intracellular recordings were made in hypothalamic slices prepared from ovariectomized guinea pigs. Over 90% of ARC neurons tested with the GABA(B) receptor agonist baclofen responded with a membrane hyperpolarization or an outward current. The hyperpolarization was dose-dependent, and the GABA(B) receptor antagonist CGP 35,348 produced a rightward shift in the agonist dose-response curve. Agonist potency was lower, and the efficacy greater, in GAD-positive neurons. The use of this novel technique for identifying GABAergic neurons thus reveals differences in the pharmacodynamics of GABA(B) receptor activation GABAergic and non-GABAergic ARC neurons.     

Brain sexual differentiation and gonadotropins secretion in the rat

1. The present work deals with sexual differences in gonadotropin regulation in the rat and the role of sexual organization of the hypothalamus in determining such differences. 2. Sex differences between male and female rats, with regard to their control of gonadotropin secretion, go beyond whether or not gonadotropins are released cyclically. Rats show additional sex differences (a) in the response of gonadotropins to removal and imposition of negative feedback signals and (b) in the ontogeny of gonadotropin regulation from birth to puberty. 3. There is a sensitive developmental period during which sexual differentiation of neural substrates proceeds irreversibly under the influence of gonadal hormones. In the rat this period starts a few days before birth and ends approximately 10 days after birth. Female rats treated during this sensitive period with androgens or estrogens will permanently lose the capacity to release GnRH in response to estrogenic stimulation. 4. Nevertheless although sexual differentiation is dramatically affected by events during the neonatal period, recent data question the "critical" nature of this period, as it has been shown that testosterone can still act on neural substrates well beyond (15 to 30 days of age) the neonatal period to defeminize and masculinize endocrine and behavioral functions. 5. Furthermore, the capacity for the normal display of female sexual behavior and for the cyclic release of gonadotropins is not, as has been assumed, inherent to central nervous tissue but depends on active hormonal estrogenic induction during a sensitive period of development. 6. Besides, during differentiation of male sexual brain function estrogens may be supportive, rather than directive, to the primary action of androgens. 7. Serotonergic, noradrenergic, and opioid systems participate in the sexual dimorphism in gonadotropin control in adult rats. 8. The sex difference in the postcastration LH rise is dependent on the early sexual organization of the hypothalamus, even though in adulthood it can also be influenced by a variety of factors such as the stage of the estrous cycle, age of the animal, estradiol pretreatment, and history of release from feedback inhibition. 9. The characteristic pattern of gonadotropin secretion in the female infantile rat, which is sexually differentiated, can be related to an increase in hypophyseal receptors coupled to an increase in the intracellular calcium response to GnRH. Such events depend on the sexual organization of the hypothalamus. In males the greater sensitivity to GnRH at 30 days is reflected in an increase in pituitary GnRH receptors but not in an increase in the magnitude of Ca2+ mobilization induced by GnRH, therefore it is probable that in this situation alternative second messengers may modulate high sensitivity. Neonatal androgenization of the hypothalamus may decrease the hypophyseal response to GnRH by an alteration in receptor concentration and signal transduction during the infantile period. 10. Finally, serotonergic, dopaminergic, opioid, and noradrenergic regulation of GnRH varies with increasing age, and the sexual organization of the hypothalamus by testosterone or estrogens is a determinant in such regulation.     

Parasolitary nucleus: a source of GABAergic vestibular information to the inferior olive of rat and rabbit

At least two subnuclei of the inferior olive, the beta-nucleus, and the dorsomedial cell column (dmcc), contain vestibularly responsive neurons that receive a dense descending projection that uses gamma-aminobutyric acid (GABA) as the transmitter. In contrast to the GABAergic innervation of other olivary subnuclei, the terminal boutons that terminate on neurons in the beta-nucleus and the dorsomedial cell column remain intact after cerebellectomy, ruling out both the cerebellum and the cerebellar nuclei as afferent sources. By using both immunohistochemical as well as orthograde and retrograde tracer methods, we have identified the source of the GABAergic pathway to the beta-nucleus and dmcc in both rat and rabbit. Under physiologic recording of single olivary neurons to guide electrode placement, we injected the bidirectional tracer, wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the beta-nucleus and dmcc of the inferior olive. These injections retrogradely labeled neurons in the parasolitary nucleus (Psol) near the vestibular complex. Psol neurons were identified as GABAergic with an antibody to glutamic acid decarboxylase (GAD). In the rat, Psol neurons are small (5-7 microm in diameter) and number approximately 1,800. In the rabbit, they are slightly larger (6-9 microm in diameter) and number approximately 2,200. WGA-HRP injections in conjunction with GAD immunohistochemistry double labeled a high percentage of neurons in both the rat and rabbit Psol. Injection of the orthograde tracer Phaseolus vulgaris-leucoagglutinin into the area of the Psol revealed a projection from this region to both the beta-nucleus and dmcc. Subtotal electrolytic lesions of this division of the Psol caused a substantial reduction in GAD-positive synaptic terminals in both the ipsilateral beta-nucleus and dmcc. The location of these GABAergic neurons, bordering both the nucleus solitarius and caudal vestibular complex, emphasizes the importance of the Psol in the processing of both vestibular and autonomic information pertinent to postural control.     

Vulnerability and plasticity of the GABA system in the pilocarpine model of spontaneous recurrent seizures

Several similarities exist between the alterations observed in the chronic pilocarpine model of recurrent seizures in the rat and those found in human temporal lobe epilepsy. The present studies are focused on changes in the GABA system in this model. Following the initial pilocarpine-induced seizures, a substantial loss of glutamic acid decarboxylase (GAD) mRNA-containing neurons has been found in the hilus of the dentate gyrus (Obenaus et al., J. Neurosci., 13 (1993) 4470-4485), and, recently, a loss of GAD mRNA-labeled neurons has also been found in stratum oriens of CA1. Yet numerous other GABA neurons remain within the hippocampal formation, and there appear to be multiple compensatory changes in these neurons. Labeling for GAD65 mRNA and associated protein is substantially increased in the remaining GABA neurons at 2-4 months after the initial seizure episode. Such increased labeling suggests that the remaining GABA neurons are part of a functional circuit and may be responding to the need for increased activity. Alterations also occur in at least one subunit of the GABA-A receptor. Labeling for the alpha(5) subunit mRNA is substantially decreased in CA1 and CA2 of pilocarpine-treated rats during the chronic, seizure-prone period. These findings emphasize the complexity of changes in the GABA system and indicate a need for evaluating the functional consequences of each of the changes. The initial loss of specific groups of GABA neurons could be a critical first step in the gradual development of epileptiform activity. While many of the subsequent changes in the GABA system may be considered to be compensatory, significant deficits of GABAergic function could remain.     

Prenatal !b-endorphin can modulate some aspects of sexual differentiation in rats.

Sexually dimorphic traits were studied in offspring of rats injected with 33 μg rat β-endorphin (β-END) 3 times daily from Day 14 to Day 21 of pregnancy. β-END males had shorter neonatal anogenital distances than did controls and were more likely to show the female lordosis pattern as adults, but they did not differ in male copulatory behavior. When given a choice between spending time with an estrous female or a male, β-END males showed a lower preference for the female than did control males. The number and somal size of neurons in the bulbocavernosus and dorsolateral nucleus of the lumbar spinal cord were unaffected by drug exposure. Elevated β-END during fetal ontogeny apparently alters the differentiation of some, but not all, sexually dimorphic traits. The data suggest that endogenous opioids may contribute to the etiology of the prenatal stress syndrome. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual differentiation of the zebra finch song system: positive evidence, negative evidence, null hypotheses, and a paradigm shift

Permanent sex differences in the brain are found in many vertebrates, and are thought to be induced by sex differences in secretion of gonadal steroid hormones during critical periods of early development. This theory has received support primarily from many experiments conducted on mammals, but also from studies on other vertebrate classes, including birds. The only avian neural dimorphism that has allowed extensive tests of this hypothesis is the neural circuit for song in passerine birds, which is much larger in males than in females. Experiments in zebra finches have yielded contradictory results. Although it is relatively easy to induce masculine patterns of development in genetic females with estrogen, it has not been possible to induce feminine patterns of development in males with any treatments, including antiestrogens and inhibitors of estrogen synthesis. Moreover, genetic females that develop with large amounts of functional testicular tissue but with virtually no ovarian tissue nevertheless have a feminine song circuit. The latter studies fail to support the idea of steroid induction of sexual differentiation. An alternative to the steroidal control hypothesis is that nonhormonal gene products expressed in the brain early in development trigger sexually dimorphic patterns of development. Although current evidence in several neural and nonneural systems indicates that sexual differentiation of some somatic phenotypes cannot be explained by the actions of gonadal steroids, the idea of direct genetic (nonhormonal) induction of sexual differentiation has yet to be proved.     

Evidence of proceptive without receptive defeminization in male ferrets.

The latencies of 71 gonadectomized male and female ferrets to approach and interact with a sexually active stimulus male were measured after subcutaneous (sc) administration of estradiol benzoate ([EB] 0, 5, 10, or 15 μg/kg) in adulthood. Receptive responsiveness to stud males was also assessed during additional tests. Control females gonadectomized on Postnatal Day 35 displayed a dose-dependent reduction in approach latencies to the stud male that did not occur in control males castrated on Day 35. The approach latencies of males castrated on Day 20 or Day 5 were intermediate between these 2 extremes. Equivalent dose-dependent reductions in approach latencies were observed in Ss ovariectomized on Day 5 and implanted sc with silastic capsules containing either no hormone or different doses of testosterone over Days 5–20 or 20–35. Equivalent dose-dependent increments in acceptance quotients were obtained in all groups following EB treatment. Results suggest that the capacity to display the proceptive, or appetitive, components of feminine sexual behavior is normally reduced in male ferrets as a consequence of the perinatal action of testicular hormones, whereas receptive behavioral capacity is retained in males of this species. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)