Neurotrophic effects of steroids on lesion-induced growth in the hippocampus. I. The asteroidal condition

Effects of Ficus umbellata (Moraceae) Aqueous Extract and 7-Methoxycoumarin on Scopolamine-Induced Spatial Memory Impairment in Ovariectomized Wistar Rats

The present work was undertaken to evaluate the ability of F. umbellata aqueous extract and its major component 7-methoxycoumarin (MC) to improve scopolamine-induced spatial memory impairment in ovariectomized Wistar rats. For this to be done, 10 sham-operated and 30 postmenopausal-like rats were randomly distributed in eight groups (n = 5) and treated with distilled water (2 mL/250 g), estradiol valerate (1 mg/kg BW), piracetam (1.5 mg/kg BW), F. umbellata aqueous extract (50 and 200 mg/kg BW), or MC (1 mg/kg BW) for 21 consecutive days. Before and after the memory impairment with scopolamine (2 mg/kg BW), animals underwent behavioral evaluations on Y- and radial mazes. As results, age and ovariectomy did not induce significant changes in the reference memory errors. While age decreased working memory errors, ovariectomy increased it. The MC as well as F. umbellata extract significantly increased (p < 0.01) the percentage of spontaneous alternation and decreased (p < 0.001) working and spatial reference memory errors and anxiety parameters (rearing and grooming) in ovariectomized rats. MC significantly reduced (p < 0.05) the MDA level, but resulted in an increase in GSH level in brain homogenates. These results suggest that MC is endowed with neuroprotective effects and could account for the neuroprotective effects of F. umbellata in rats.

Testosterone treatment attenuates the effects of facial nerve transection on glial fibrillary acidic protein (GFAP) levels in the hamster facial motor nucleus

Testosterone propionate (TP) administration coincident with facial nerve injury accelerates the recovery rate from facial muscle paralysis in the hamster. One mechanism by which TP could augment peripheral nerve regeneration is through glial fibrillary acidic protein (GFAP) regulation in the facial motor nucleus. In a previous study, axotomy alone induces increases in GFAP mRNA. with TP significantly attenuating the axotomy-induced increases in GFAP mRNA. In the present study, immunoblotting techniques were used to extend our previous GFAP mRNA studies to the protein level. Castrated male hamsters were subjected to a right facial nerve transection, with half of the animals receiving subcutaneous implants of 100% crystalline TP. The left facial motor nucleus of each animal served as an internal control. Postoperative survival times include Days 4, 7, and 14. In non-TP-treated animals, facial nerve transections alone increased GFAP levels at all time points, relative to internal controls. As previously observed at the mRNA level, TP treatment attenuated but did not eliminate the axotomy-induced increase in GFAP levels at all time points tested. These results suggest that the regulatory actions of gonadal steroids on GFAP expression manifested in parallel at the mRNA/protein levels.

Effects of age on gene expression during estrogen-induced synaptic sprouting in the female rat

Age and estrogen treatment influenced fiber outgrowth and compensatory neuronal sprouting after unilateral entorhinal cortex lesions (ECL) which model Alzheimer disease-like deafferentation in the dentate gyrus of the hippocampus. In young F344 rats (3 months old), ovariectomy (OVX) decreased reactive fiber outgrowth by 60%. Sprouting in middle-aged rats (18 months old) was reduced in intact females; no further reduction was caused by OVX. Several astrocyte mRNAs were measured in the dentate gyrus of young and middle-aged female rats in three different estrogen states (sham OVX, OVX, or OVX + estradiol) 1 week after ECL. Glial fibrillary acidic protein (GFAP) mRNA was twofold greater in middle-aged rats than young, although both ages showed threefold increases in response to ECL. In prior studies GFAP was found to be decreased by estradiol treatment 3-4 days after ECL; in this study GFAP mRNA had returned to sham OVX levels in young rats by 7 days post-ECL. Surprisingly, estradiol treatment increased GFAP mRNA levels by 25% above OVX in middle-aged rats. Apolipoprotein E (apoE) mRNA was decreased 20% by age in the dentate, although both age groups showed a 25% increase in apoE mRNA in response to ECL. Apolipoprotein J (apoJ) mRNA was increased 20% in the dentate gyrus of middle-aged rats, and both age groups responded to ECL with a 65% increase in apoJ mRNA. The estrogen state did not alter levels of either apolipoprotein mRNA in the deafferented dentate. The data suggest that the estrogen-induced decrease of GFAP in response to lesions does not persist at 7 days post-ECL during sprouting. Overall effects of age on the dentate gyrus include elevated GFAP mRNA and decreased apoE mRNA. The cortical wound site showed consistent enhancement of GFAP mRNA in both age groups by estradiol above sham OVX and greater responses in middle-aged rats.

Estrogen improves working but not reference memory and prevents amnestic effects of scopolamine of a radial-arm maze

This study investigated the effect of estrogen treatment on working memory and reference memory of female rats. In addition, the impact of estrogen on the sensitivity of these two types of memory to the cholinergic antagonist scopolamine was investigated. At 35 days of ages, rats were ovariectomized and implanted chronically with Silastic capsules containing either 25% crystalline estradiol or 100% cholesterol. Thirty days after surgery, animals were trained on an eight-arm radial maze with four arms baited to assess both working and reference memory performance. Following training, females were given scopolamine hydrobromide (0.2 mg/kg i.p.) prior to retesting on the task. Results indicated that estrogen treatment improved working memory performance during maze acquisition but did not affect reference memory performance. Scopolamine treatment impaired performance on the working memory component, but not the reference memory component, while estrogen prevented the impairment of working memory by scopolamine. Results support previous evidence that estrogen selectively enhances performance on tasks that depend on working memory.

The effect of age and testosterone on the expression of glial fibrillary acidic protein in the rat cerebellum

Testosterone reversed the age-related increase in glial fibrillary acidic protein (GFAP) in the male rat cerebellum, a brain region not generally associated with gonadal steroid hormone sensitivity. This supports the hypothesis that a decrease in circulating testosterone contributes to age-related increase in GFAP. These data also suggest that reductions in circulating gonadal steroids during aging could render the brain more susceptible to neurodegeneration and that hormone replacement therapy might have value in neurodegenerative disease intervention.

Comparison of the expression of a T alpha 1:nlacZ transgene and T alpha 1 alpha-tubulin mRNA in the mature central nervous system

We have previously demonstrated that one member of the alpha-tubulin multigene family, termed T alpha 1 in rats, is a panneuronal gene that is regulated as a function of neuronal growth and regeneration. Moreover, 1.1 kb of the 5' upstream region from this gene is sufficient to direct expression of a marker gene to growing neurons in transgenic mice. In this report, we have characterized the distribution of the T alpha 1:nlacZ transgene in the mature central nervous system in two lines of transgenic mice and have compared its expression to that of the endogenous T alpha 1 alpha-tubulin mRNA. These results demonstrate that the pattern of expression of the T alpha 1:nlacZ transgene is similar to that of T alpha 1 mRNA, with a few notable differences. Furthermore, expression of the transgene and the mRNA within the mature brain is panneuronal and, in many cases, is highest in those populations of neurons that show some capacity for morphological growth. These results, together with our previous studies on mature regenerating neurons (Gloster et al. [1994] J. Neurosci. 14:7319-7330; Wu et al. [1994] Soc. Neurosci. Abstr. 20:542) suggest that the T alpha 1:nlacZ transgene will provide a useful marker of growth-associated gene expression in the mature nervous system.

Sex differentiation of rat hippocampal GABAergic neurons

In order to analyse mechanisms of sex differentiation of the hippocampus at the cellular level, the differentiation of hippocampal GABAergic neurons was studied in vitro. Serum-supplemented and serum-free dissociated cell cultures were raised from the hippocampus of embryonic day 17 male and female rat embryos for up to 14 days in vitro. This time period roughly corresponds to the critical phase for sex differentiation of the rat brain as determined in vivo. Serum-free cultures were treated with testosterone and/or 17 beta-oestradiol for the entire culture period. Control cultures from male donors contained twice as many GABA-immunoreactive neurons as those from female donors, while there was no sex difference in overall counts of neurons stained for microtubule-associated protein 5. Measurements of high-affinity uptake of [3H]GABA essentially confirmed this sex difference. The development of the sex difference could not be influenced by long-term treatment with androgen or oestrogen. It is concluded that sex differentiation of a specific subpopulation of hippocampal neurons may take place independently of the environment provided by gonadal steroids and in the absence of extrinsic connections with the hypothalamus or other relays of the limbic circuit.

Androgenic enhancement of motor neuron regeneration

In conclusion, the available evidence to date suggests that many of the aspects of neuronal functioning affected by gonadal steroids under steady state conditions are also significantly affected by steroids under stress conditions such as axon disconnection. This argues toward a therapeutic usefulness of gonadal steroids in activating and/or accelerating the reparative response of neurons to injury, a concept that will be exciting to test in future clinical studies.

Glial fibrillary acidic protein: regulation by hormones, cytokines, and growth factors

Levels of glial fibrillary acidic protein (GFAP), an astrocyte-specific intermediate filament protein, are altered during development and aging, GFAP also responds dynamically to neurodegenerative lesions. Changes in GFAP expression can occur at both transcriptional and translational levels. Modulators of GFAP expression include steroids, cytokines, and growth factors. GFAP expression also shows brain region-specific responses to sex steroids and of astrocyte-neuronal interactions. The 5'-upstream sequences of rat, mouse, and human are compared for the presence of response elements that are candidates for transcriptional regulation of GFAP. We propose that the regulation of the GFAP gene has evolved a system of controls that allow integrated responses to neuroendocrine and inflammatory modulators.

Development of mRNAs for glucocorticoid and mineralocorticoid receptors in rat hippocampus

The hippocampus plays an important role in mediating glucocorticoid effects on the brain. Glucocorticoids are also implicated in neurogenesis and age-related neuronal death in the hippocampus. The effects of glucocorticoids in the hippocampus are elicited through two receptors with high-affinity for corticosterone, the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). In this study, we used a sensitive RNase protection assay to quantify the ontogeny of GR mRNA and MR mRNA in hippocampus from embryonic day 18 (E18) to postnatal day 60 (P60). GR mRNA and MR mRNA are expressed at approximately equal levels in the E18 hippocampus. However, by birth, the level of MR mRNA is three-fold that of GR mRNA and remains elevated up to P60. The levels of both mRNAs increase gradually during the period of postnatal neurogenesis after which they markedly increase to adult levels. In addition, the levels of hippocampal MR mRNA are the same in male and female rats, whereas the levels of GR mRNA are significantly higher in the P60 female rat hippocampus, but not in younger female rats. Our data on the development of mRNA levels do not parallel the levels of glucocorticoid and mineralocorticoid receptors as reported in a number of binding studies. Therefore, our studies, when considered together with previous reports, suggest that posttranscriptional mechanisms play a major role in regulating the levels of glucocorticoid-binding sites in the hippocampus.

Gonadal steroids regulate the expression of glial fibrillary acidic protein in the adult male rat hippocampus

This study demonstrates that gonadal steroids (estradiol, testosterone, dihydrotestosterone) can regulate the expression of glial fibrillary acidic protein in the adult male rat brain. Previously, we showed that castration of adult male rats increased glial fibrillary acidic protein messenger RNA in the hippocampus and that this increase was additive with the increase induced by deafferenting entorhinal cortex lesions [Day et al. (1990) Molec. Endocr. 4, 1995-2002 . We extended these effects of castration and entorhinal cortex lesion to glial fibrillary acidic protein, using immunoassays. Furthermore, we found regional differences in responses to castration and inhibited by sex steroids. In contrast, hypothalamic glial fibrillary acidic protein expression was inhibited by castration. Similar regional differences were also shown for astrocyte glial fibrillary acidic protein distribution by immunocytochemistry. The regional specificity of glial fibrillary acidic protein expression after castration and sex steroid replacement is pertinent to the role of astrocytes in synaptic plasticity in unlesioned adults as well as in responses to lesions where the steroid milieu has been shown to influence sprouting.

Sulfated glycoprotein 2: new relationships of this multifunctional protein to neurodegeneration

Sulfated glycoprotein 2 (SGP-2) from rat, and similar molecules from cow, dog, human, pig, ram and quail are known by 11 or more acronyms. SGP-2 is associated with the responses of brain and other tissues to injury; it and related molecules are also normally secreted by the adrenal gland, the liver and the testes. The mRNA of this protein is found in increased levels in Alzheimer's disease. In rats, after perforant path or excitotoxin lesions, levels of the protein or mRNA are elevated in astrocytes, and also in neurons. In rats, brain SGP-2 is regulated by gonadal and adrenal steroids. However, these increases after brain lesions may relate to a function that is associated with the human protein, namely that of inhibiting complement-mediated cell lysis. Other activities suggested for SGP-2 are lipid transport and cell-cell interactions, which are consistent with sequence data that predict binding of dinucleotides, heparin and lipids. The emerging neurobiology of SGP-2 encompasses the subjects of cell death, synaptic remodelling, neuroendocrinology and neurodegenerative diseases.

Neurotrophic effects of steroids on lesion-induced growth in the hippocampus. II. Hormone replacement

The mediation of lesion-induced sprouting in the nervous system is a complex interaction of local membrane factors and circulating hormones. This series of studies examines the reactivity of the sprouting response of both male and female subjects under different hormonal conditions. Young adult male and female Sprague-Dawley rats which were gonadectomized (GDX) and adrenalectomized (ADX) underwent a unilateral entorhinal cortex lesion, which partially denervates the molecular layer of the ipsilateral hippocampal denate gyrus. At the time of the lesion, each animal received hormonal therapy. Fifteen days post-ERC-ablation the brains were analyzed for changes in reactive fiber outgrowth in the hippocampal commissural/associational afferents. Fiber outgrowth in females in the "asteroidal" (GDX/ADX) condition was unaffected. Asteroidal males demonstrated a decreased response. Gonadal steroid replacement, estrogen or testosterone, enhanced outgrowth in both asteroidal males and females. Glucocorticoid replacement suppressed outgrowth in both asteroidal males and females. Gonadal steroids clearly have neurotrophic activity which is interactive with glucocorticoid activity. Glucocorticoids under the GDX/ADX conditions in vivo have a negative impact on fiber outgrowth in both sexes. The effect of glucocorticoids is most dramatic when compared to the outgrowth of asteroidal animals without additional hormonal supplementation.