The 21-aminosteroid antioxidant, U74389F, prevents estradiol-induced depletion of hypothalamic beta-endorphin in adult female rats

Sex differences in cytochrome P450 1B1, an estrogen-metabolizing enzyme, in the rhesus monkey telencephalon

The metabolic enzyme CYP1B1 is a recently cloned member of the cytochrome P450 superfamily, expressed widely throughout primate tissue, including the CNS. Although CYP1B1 protein is known to metabolize estradiol to catecholestrogens in the uterus, its localization and function in brain have not yet been described. To better understand CYP1B1 distribution, we have combined in situ hybridization (ISH) for its mRNA with immunohistochemistry (IHC) for the CYP1B1 protein in selected brain regions of male and female adult rhesus monkeys (Macaca mulatta). Blocks of formalin-fixed tissue obtained from the frontal cortex, hippocampus, thalamus, and amygdala were processed and embedded in paraffin. They were then sectioned and stained as described for human tissue [Muskhelishvili, L., Thompson, P.A., Kusewitt, D.F., Wang, C., Kadlubar, F.F., 2001. In situ hybridization and immunohistochemical analysis of cytochrome P450 1B1 expression in human normal tissues. J. Histochem. Cytochem. 49, 229-236]. Results indicated widespread distribution of CYP1B1 mRNA in both male and female monkey frontal cortex, hippocampus, thalamus, and amygdala. In contrast, although CYP1B1 protein was co-localized with its mRNA in the female brains, it was primarily restricted to hippocampal pyramidal neurons in the male brains. These results suggest that CYP1B1 may subserve widespread metabolic functions in the female primate brain but have more restricted actions within the hippocampal pyramidal neurons of the male.

Brain iron deposition and the free radical-mitochondrial theory of ageing

The central hypothesis of this paper states that oxidative stress, augmented iron deposition, and mitochondrial insufficiency in the ageing and degenerating CNS constitute a single neuropathological 'lesion', and that the advent of one component of this triad obligates the appearance of the others. Evidence in support of this unifying perspective is adduced from human neuropathological studies, experimental paradigms of ageing-associated neurological disorders, and a comprehensive model of astroglial senescence. A pivotal role for the enzyme, heme oxygenase-1 (HO-1) in consolidating this tripartite lesion in the ageing and diseased CNS is emphasized. The data are discussed in the context of a revised 'free radical-mitochondrial-metal' theory of brain ageing, and some scientific and clinical implications of the latter are considered.

Neonatal administration of monosodium glutamate prevents the development of ethanol- but not psychostimulant-induced sensitization: a putative role of the arcuate nucleus

Lesions of the arcuate nucleus by monosodium glutamate, goldthioglucose and oestradiol valerate treatments are known to prevent the acute stimulating effect of ethanol in mice. On the basis of these results, the current study analysed whether a lesion of the arcuate nucleus by monosodium glutamate was able to block ethanol-induced locomotor sensitization. To produce the arcuate nucleus lesions, pups were injected with saline or monosodium glutamate (4 mg/g body weight) subcutaneously on 5 alternate days, starting on postnatal day one. Sensitization treatments began 10 weeks after the initial lesions. Sensitization training consisted of six trials on alternate days, in which groups of mice were treated with ethanol (2 g/kg) or saline, and then tested in an open-field for the induction of locomotor activity. The present study demonstrated that animals with monosodium glutamate-induced lesions did not develop locomotor sensitization to ethanol. Different groups of mice were used to assay blood ethanol levels and to evaluate the effect of arcuate nucleus lesions on psychostimulant-induced locomotor sensitization. Sensitization to cocaine or amphetamine was spared in monosodium glutamate-pre-treated animals, although the lesion of arcuate nucleus reduced the sensitivity of mice to cocaine. Our findings therefore suggest that the arcuate nucleus may be critical for the neuroadaptations that underlie the behavioural sensitization to ethanol, in contrast to those mediating psychostimulant-induced sensitization.

Effects of estradiol treatment on voluntary and forced alcohol consumption in male rats

Estrogens have been related to alcohol as a dependent variable, but scarcely as a causal variable, that affects the alcohol consumption. The scope of the present work was to study the effect of estrogens on both the amount and the pattern of alcohol consumption. Male Wistar rats were individually exposed to forced alcohol consumption (FAC) and voluntary alcohol consumption (VAC) in each of the following four periods: precastration (PreC), postcastration (PosC) or post-sham castration, estradiol (E) treatment (5 microg of estradiol benzoate/day/rat) and postestradiol (PosE). Estrogenic treatment reduced significantly the alcohol consumption with respect to the PreC and PosE periods in castrated (C) males during VAC. E treatment showed the lowest value of alcohol intake in FAC, but differences were significant only with respect to PreC regardless of the male gonadal condition. E treatment decreased food intake regardless of the male gonadal condition in both FAC and VAC. Castration and E treatment modified differentially the patterns of alcohol consumption depending on the volitive characteristics of alcohol intake. Castration reduced the size of the licking rates without affecting the number of drinking bouts in FAC. This pattern was maintained in the E and PosE periods of C males. Castration did not affect the pattern of alcohol consumption in VAC, but estrogen reduced both the bout size and the number of bouts during the day, which gave an additional support to the inhibitory effect of estrogens on VAC. Results are discussed in terms of a possible inhibitory action of estrogens on the opioid system, which possibly reduces the rewarding properties of alcohol.

The effect of estradiol-induced hypothalamic pathology on sulfated glycoprotein-2 (clusterin) expression in the hypothalamus

Sulfated glycoprotein-2 (SGP-2 or clusterin) is a complex multifunctional molecule that has been recently been implicated in neuronal degeneration and remodeling. We have shown that estradiol treatment results in a selective destruction of beta-endorphin neurons in the hypothalamic arcuate nucleus. We have used immunocytochemistry to determine the distribution of SGP-2 immunoreactivity in the rat hypothalamus and to assess the effects of the estradiol-induced destruction of beta-endorphin neurons on SGP-2 expression. We have found that SGP-2-immunopositive neurons normally occur in the medial preoptic area (MPOA), supraoptic nucleus (SON), paraventricular nucleus (PVN), dorsomedial nucleus (DM), and the lateral hypothalamic area (LHA) in both males and females. The neuropil appears free of label. Treatment with estradiol valerate results in the appearance of immunopositive punctate deposits in the neuropil in the MPOA, PVN and DM. The number and distribution of SGP-2-positive neurons are unaffected by estradiol treatment except in the MPOA, where there are twice as many SGP-2-positive neurons as in controls. These effects are precluded by treatment with vitamin E, with blocks the cytotoxic action of estradiol on beta-endorphin neurons. Thus, we interpret these changes as responses to the loss of beta-endorphin afferents.

Estrogen induction of glial heat shock proteins: implications for hypothalamic aging

In the aging mammalian hypothalamus, a unique subpopulation of glial cells accumulates peroxidase-positive cytoplasmic inclusions distinct from lipofuscin. In adult rodents, this senescence-dependent glial granulation is accelerated by administration of estradiol valerate. In the present study, brain sections derived from male rats given 3 monthly intramuscular injections of estradiol valerate (0.2 mg or 2.0 mg) were immunostained for heat shock proteins and glial fibrillary acidic protein to determine whether a glial stress response is implicated in estrogen-induced granulation. Our findings indicate that estrogen elicits a heat shock response and subsequent granulation in astrocytes residing in estradiol receptor-rich brain regions including the arcuate nucleus and the wall surrounding the third ventricle but not in estradiol receptor-deficient regions such as the striatum and corpus callosum. The heat shock proteins induced by estrogen, namely, the 27, 72, and 90 kDa stress proteins, are upregulated in astrocytes in response to oxidative challenge supporting our hypothesis that estrogen mediates senescent changes in the rodent hypothalamus through oxidative mechanisms.

Estrogen-induced hypothalamic beta-endorphin neuron loss: a possible model of hypothalamic aging

Over the course of normal aging, all female mammals with regular cycles display an irreversible arrest of cyclicity at mid-life. Males, in contrast, exhibit gametogenesis until death. Although it is widely accepted that exposure to estradiol throughout life contributes to reproductive aging, a unified hypothesis of the role of estradiol in reproductive senescence has yet to emerge. Recent evidence derived from a rodent model of chronic estradiol-mediated accelerated reproductive senescence now suggests such a hypothesis. It has been shown that chronic estradiol exposure results in the destruction of greater than 60% of all beta-endorphin neurons in the arcuate nucleus while leaving other neuronal populations spared. This loss of opioid neurons is prevented by treatment with antioxidants indicating that it results from estradiol-induced formation of free radicals. Furthermore, we have shown that this beta-endorphin cell loss is followed by a compensatory upregulation of mu opioid receptors in the vicinity of LHRH cell bodies. The increment in mu opioid receptors presumably renders the opioid target cells supersensitive to either residual beta-endorphin or other endogenous mu ligands, such as met-enkephalin, thus resulting in chronic opioid suppression of the pattern of LHRH release, and subsequently that of LH. Indeed, prevention of the neuroendocrine effects of estradiol by antioxidant treatment also prevents the cascade of neuroendocrine aberrations resulting in anovulatory acyclicity. The loss of beta-endorphin neurons along with the paradoxical opioid supersensitivity which ensues, provides a unifying framework in which to interpret the diverse features that characterize the reproductively senescent female.