Androgen regulation of an antigen expressed in regions of developing brainstem monoaminergic cell groups

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.

Neonatal androgen manipulation differentially affects the development of monoamine systems in rat cerebral cortex, amygdala and hypothalamus

Neural tissue during perinatal life is sufficiently plastic to respond to the presence of testicular androgens. Here we studied the effect of neonatal androgen manipulation (castration of male and androgenization of female rats) on monoamine neurotransmitter systems in the cerebral cortex and sexually dimorphic regions of brain (hypothalamus and amygdala). Norepinephrine (NE) and dopamine (DA) concentrations in cortex, amygdala and hypothalamus of rats were assayed by HPLC at days 25, 60, 120, 180, 240 and 300. Results show that NE levels in all groups of rats at day 25 were higher in the hypothalamus (5-9 ng/mg protein) compared to the amygdala (0.5-3 ng/mg protein) and the cortex (0.5-1 ng/mg protein). Levels of DA at day 25 in the hypothalamus and the amygdala were comparable (up to 3.5 ng/mg) but higher than in the cortex (1.25-1.75 ng/mg protein). NE and DA concentrations in sham-castrated male and androgen-treated females were higher at day 25 compared to castrated male and control females in both amygdala and hypothalamus; however, levels of NE and DA remained unchanged in the cortex. Pattern of NE concentrations started reversing with increase in age, i.e., NE levels in control females and castrated males increased almost 4-fold in amygdala and 2-fold in hypothalamus by day 300, but there was no significant change in the cortex. Compared to that, NE levels decreased in sham-castrated male (2-fold) and androgen-treated females (3-fold) in amygdala as well as in the hypothalamus (2-fold) in both these groups. A similar pattern of reversal of DA levels was found in both amygdala and hypothalamus, however, at day 300 DA levels were comparable in all the four groups. These studies suggest that androgen manipulation (castration or androgen administration) induces age-dependent short- and long-term effects on the development of noradrenergic and dopaminergic systems in the sexually dimorphic regions of brain, amygdala and hypothalamus, without a significant change in the cerebral cortex.

Generating monoclonal antibodies to neuronal antigens

Methods for generating monoclonal antibodies directed to the functional sites of neuronal antigens are reviewed. These methods include optimal antigen preparation and presentation as well as selective targeting and manipulation of the antigenic response. We describe our use of the immunosuppressant drug, cyclophosphamide, to produce a selective immune response to rare, poorly immunogenic, or actively suppressed antigens. These techniques allow us to generate antibodies to the functional sites of neuronal antigens, such as cell surface molecules. Such antibodies are directed to complex carbohydrates, proteins, protein complexes and glycolipids that form the active site of neuronal antigens. We can use these antibodies in the molecular dissection of functional active sites that are inaccessible to genetic manipulation. These techniques favor the generation of antibodies that can be used to understand and manipulate neuronal cellular activity.

Ontogeny of Leu-enkephalin and beta-endorphin innervation of the preoptic area in male and female rats

The distribution of endogenous opioid peptide-containing fibers in the medial preoptic area of developing male and female rats was examined using immunohistochemical methods. In particular, the ontogeny of leucine-enkephalin (leu-enk) and beta-endorphin (beta-endo) innervation was studied using antisera directed against these compounds. The distribution of Leu-enk and beta-endo differed at each age examined from birth to postnatal day 12 (P12). Furthermore, the patterns of fiber innervation differed across development. Leu-enk-like immunoreactivity was initially densest in the lateral preoptic region of both sexes, ultimately expanding into the medial preoptic region to become densest in the lateral portion of the medial preoptic nucleus by P12. This latter pattern was observed only in males, however, as females continued to exhibit diffuse medial preoptic Leu-enk-like immunoreactivity at P12. In contrast, the distribution and developmental pattern of beta-endo-like immunoreactivity was similar in both sexes; diffuse staining was observed in the medial preoptic region at birth, later becoming dense only in the periventricular and parastrial nuclei. The time course of development of Leu-enk and beta-endo innervation of the medial preoptic area suggests that the sexually dimorphic expression of opioid immunoreactivity occurs after preoptic neurons appear in their sexually dimorphic configuration. Therefore, although the development of opioid-containing pathways could be influenced by the perinatal gonadal steroid hormone environment, medial preoptic Leu-enk and beta-endo innervation might not contribute directly to the sexually dimorphic neuronal organization of the preoptic area.

Expression of the Raf-1 protein in rat brain during development and its hormonal regulation in hypothalamus

To study mechanisms involved in the sexual differentiation of the rat brain, the expression of the protein product of the proto-oncogene c-raf-1 (Raf-1) was examined. Biochemical and immunocytochemical analyses localized Raf-1 in embryonic rat brain regions and demonstrated hormonally induced changes in Raf-1 expression. For this study an affinity-purified anti-peptide antiserum specific for Raf-1 (NH-44) was used. Western blots revealed an approximately 77 kD polypeptide isolated in the cytosol of developing rat brains. Raf-1 levels were highest in the embryonic (E) day 22 female hypothalamus (HYP), and approximately twofold higher than levels detected in male HYP at E22 as determined by quantitative protein dot blot and semiquantitative Western blot analyses. Raf-1 levels in HYP were greater than those in either brain stem (BS) or cortex. Immunocytochemical analysis revealed high levels of Raf-1 in selective brain regions (e.g., the ventromedial nucleus in the HYP, the mitral cell layers in the main and accessory olfactory bulbs (OB), and the locus coeruleus) at E22 and postnatal (P) day 1. Lower levels of immunoreactivity were observed in many areas of the perinatal neuraxis. To test hormonal regulation of Raf-1, testosterone propionate (TP) was administered to pregnant rats on E17; male and female fetuses were examined on E22. This treatment significantly decreased Raf-1 levels in female HYP, but not in male HYP, as determined by Western blot analysis. No significant sex difference or response to prenatal hormone treatments were observed in either brain stem or cortex. No significant sex difference was noted postnatally, and administration of TP 3 h after birth did not change Raf-1 levels examined 24 h later. In summary, Raf-1 was localized within selective regions of the rat brain, and its expression was altered by exogenous prenatal hormonal stimulation. One role for Raf-1 in signal transduction may be to delimit hormonal critical periods in sexual differentiation of the brain.

Differential hormonal modulation of brain antigens recognized by the AB-2 monoclonal antibody

The expression of monoclonal antibody AB-2 immunoreactivity is age- and sex-dependent in radial glia of developing rat hypothalamus and is regulated by prenatal exposure to gonadal steroids. In the present study, several proteins were recognized by AB-2 and were distributed selectively in subcellular fractions from neonatal hypothalamus (HYP), remaining forebrain (FB), and brainstem regions. Immunoblots revealed polypeptide bands in 3 major molecular weight classes: one at approximately 195 kDa in the cytosolic compartment; and two doublets at 220 kDa and 340 kDa in both microsomal and crude mitochondrial membrane fractions. The 220 kDa and 340 kDa doublets were also Triton-insoluble, suggesting a cytoskeletal association. The 195 kDa-AB-2-immunoreactive band was present in both Triton-soluble and insoluble fractions. AB-2 also recognized several acidic glycolipids extracted from postnatal rat brain regions on immunoblots following high performance thin layer chromatography. One of the bands from postnatal rat brain extracts migrated similarly to purified bovine brain sulfatide, which was also immunoreactive with AB-2. AB-2 immunoreactivity with proteins, polar lipids, and sulfatide suggests that the epitope is a carbohydrate present in multiple cellular compartments. AB-2 recognized the same molecular bands in males and females. Testosterone treatment selectively decreased the level of the 195 kDa AB-2-immunoreactive polypeptide. The 195 kDa AB-2-immunoreactive polypeptide possibly acts in radial glia in the determination of sexually dimorphic neurons in the preoptic area/hypothalamus.

Neonatal exposure to gonadal hormones affects the development of monoamine systems in rat cortex

Abstract The effects of neonatal gonadectomy of male, and testosterone propionate treatment of female rat pups on levels of monoamines and metabolites in the cerebral cortex were assessed using high-performance liquid chromatography with electrochemical detection. In Experiment 1, pups were killed at 0, 4, 10 and 21 days of age and the anterior and posterior portions of cortex in each hemisphere were removed. At 21 days of age the levels of dopamine in anterior cortex were higher in males and testosterone propionate-treated females than in females and gonadectomized males. However, dopaminergic activity developed earlier in females than in males and the gonadal hormone manipulations shifted the pattern of development to that of the other sex. In Experiment 2, the effects of these same gonadal hormone manipulations on the uptake, metabolism and storage capacity of catecholamine neurons in the cingulate, agranular insular, parietal and occipital cortex were estimated at 4 and 10 days of age by considering the difference between measured catecholamines in animals pretreated with vehicle or 2.5 mg/kg reserpine and then given 100 mg/kg L-DOPA. Again, the data indicated earlier development of catecholamine neurons in females, especially in the agranular insular cortex. Dopamine was found to account for group differences; for when dopamine levels alone were considered it was found that, at 4 days of age, females had the highest levels in every area with the exception of the occipital cortex where gonadectomized males had equally high levels. These data suggest a mechanism that might account for sex differences in the development of specific cortical regions.