James R. Brawer

Distribution of μ, δ and κ opioid receptors in the hypothalamus of the rat

The radioautographic distribution of mu, delta and kappa opioid binding sites was examined by in vitro radioautography in the rat hypothalamus using the highly selective ligands [125I]-FK 33-824, [125I]azidoDTLET and [125I]DPDYN, respectively. Levels of mu opioid binding sites varied considerably amongst hypothalamic nuclei. mu Opioid labeling was dense in the medial preoptic area, medial preoptic nucleus, suprachiasmatic nucleus and ventromedial nucleus, whilst the supraoptic nucleus, paraventricular nucleus, arcuate nucleus and dorsomedial nucleus were devoid of labeling. Delta opioid labeling was sparse throughout most of the hypothalamus; however, moderate binding densities were detected in the suprachiasmatic and ventromedial nucleus. kappa Opioid labeling was also scant throughout the hypothalamus with the exception of the suprachiasmatic nucleus which was very densely labeled. Our results indicate that the 3 opioid receptors types are differentially distributed within the hypothalamus, although a significant overlap exists. In general, the distribution of hypothalamic opioid receptors correlates well with that of opioid-containing terminal fibers and may represent the anatomical substrate for opioid involvement in the hypothalamic regulation of autonomic, behavioral and neuroendocrine functions.

Astrocyte Mitochondria: A Substrate for Iron Deposition in the Aging Rat Substantia Nigra

Little is currently known concerning the cellular substrates for, and the mechanisms mediating the pathological deposition of, redox-active brain iron in Parkinsons disease. In various subcortical brain regions, populations of astroglia progressively accumulate peroxidase-positive cytoplasmic inclusions derived from effete, iron-laden mitochondria. In the present study, histochemical, ultrastructural, and elemental microanalytical techniques were used to demonstrate the existence of peroxidase-positive astroglia in the substantia nigra of adult rats. At 4 months of age and earlier, few GFAP-positive nigral astroglia contained small, electron-dense cytoplasmic inclusions which exhibited faint endogenous peroxidase activity (diaminobenzidine reaction product) and no detectable iron by microprobe analysis. In contrast, by 14-18 months of age, there was a significant, fourfold increase in numbers of peroxidase-positive astrocyte inclusions in the substantia nigra. The nigral gliosomes in the older animals were heterogeneously electron dense, immunoreactive for ubiquitin and a mitochondrial epitope, and often exhibited X-ray emission peaks for iron. Copper peaks were also detected in a minority of nigral gliosomes. Previous in vitro work indicated that the iron-mediated peroxidase activity in these cells promotes the bioactivation of dopamine and other catechols to neurotoxic free radical intermediates. Thus, mitochondrial sequestration of redox-active iron in aging nigral astroglia may be one factor predisposing the senescent nervous system to parkinsonism and other neurodegenerative disorders.

The effect of estrogens on hypothalamic structure and function.

Data accumulated from studies of several species indicate that sex steroids are metabolized by neuroendocrine tissues in a manner analogous to that of other target tissues. Evidence that androgens or their estrogenic metabolites affect the morphology and function of the nervous system in fetal, newborn, developing, and adult rats is presented. The destruction of neural processes subsequent to the administration of large doses of estrogen to intact rats can now be added to the previously known effects on synaptogenesis, cell morphology, and function. We believe this destruction to be a form of chemical deafferentation and that it may underlie age-related hypothalamic failure and the development of multifollicular ovaries in the rat. Implications for other species are not clear at present.

The origin and composition of peroxidase-positive granules in cysteamine-treated astrocytes in culture.

Gomori astrocytes, which are prominent in periventricular regions of the brain, contain inclusions that stain with Gomori dyes, and exhibit an orange-red autofluorescence and a non-enzymatic peroxidase activity. Recently, such astrocytes have been induced in dispersed glial cultures by exposure to cysteamine. Using these cells, we have shown that the peroxidase-positive inclusions (Gomori bodies) are multicompartmental, that iron co-localizes with the peroxidase activity, and that the iron is often segregated in one of the compartments of the body. The goal of the present study was to determine the origin and process of formation of these bodies. The results indicate that cysteamine induces aberrations in mitochondrial structure associated with the acquisition of iron and the associated peroxidase activity. Mitochondria thus transformed appear to initiate an autophagic process in which they, and adjacent structures, are sequestered. The presence of acid phosphatase activity in a number of mature Gomori bodies attests to the participation of lysosomal elements in this process. These results indicate, therefore, that the Gomori body is a complex autophagosome in which the iron-containing compartments, putatively responsible for the peroxidase activity, represent undegraded transformed mitochondria.

Effects of Estradiol-Induced Lesions of the Arcuate Nucleus on Gonadotropin Release in Response to Preoptic Stimulation in the Rat

Female Wistar rats treated with a single subcutaneous injection of 2 mg estradiol valerate (EV) develop gradually progressive, multifocal lesions of the arcuate nucleus. They also exhibit vaginal estrus and endocrine profiles characteristic of animals sustaining anterior hypothalamic deafferentation. In this study, EV-treated females with the arcuate lesions released significantly less LH 1 h following electrochemical stimulation of the medial preoptic area (MPOA) than did normally cycling controls in proestrus. FSH release in response to MPOA stimulation was the same for both groups. As plasma LH concentrations were not significantly different between EV-treated and control animals 1 h after the injection of a potent LHRH analog, the reduced LH response to MPOA stimulation appears to reflect a primarily hypothalamic defect. However, the EV treatment also affected pituitary responsiveness to long-term stimulation as evidenced by reduced LH responses to the LHRH analog after 2 and 3 h. No such differences were seen in the FSH response.

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.

The significance and impact of a faculty teaching award: disparate perceptions of department chairs and award recipients.

Teaching awards are commonly regarded as an incentive to encourage pedagogic excellence. Inasmuch as their effectiveness depends on how they are perceived by faculty, the authors investigated the impact of a teaching award in the Faculty of Medicine (Faculty Honor List for Educational Excellence) on the attitudes of award recipients and departmental chairs. A questionnaire was designed to sample opinion on the extent to which the Honor List program was publicized, whether the award contributed to recognition and/or stature in the academic unit, and whether it was personally valued by recipients. The questionnaire was sent to all 23 departmental chairs and to all 43 faculty members who had received the award between 1998 and 2002; 78% of the chairs and 77% of the recipients responded. The results revealed marked discrepancies between the perceptions of chairs and recipients. Chairs, although uncertain of the effect on quality of teaching, largely regarded the award as prestigious and well publicized within their departments. A notably smaller percentage of award recipients shared these views. Nonetheless, 93% of recipients valued the award highly, and 45% of recipients indicated that the award inspired them to enhance the quality of their teaching. Practice points•Teaching awards are assumed to be an incentive for educational excellence.•The impact of a teaching award on recipients and department chairs was assessed.•Perceptions of recipients and chairs regarding the award differed considerably.•The award was valued highly by most recipients.•The award inspired 45% of the recipients to enhance the quality of their teaching.

Pattern of human chorionic gonadotropin binding in the polycystic ovary

The histologic evolution of polycystic ovaries in the estradiol valerate-treated rat coincides with the development of a unique plasma pattern of luteinizing hormone. To assess the role of luteinizing hormone in polycystic ovaries, it is necessary to evaluate the luteinizing hormone sensitivity of the specific tissues in the polycystic ovary. Therefore, we examined the pattern of luteinizing hormone binding sites in polycystic ovaries. Rats at 4 or 8 weeks after estradiol valerate treatment each received an intrajugular injection of iodine 125-labeled human chorionic gonadotropin. Some rats also received a 1000-fold excess of unlabeled human chorionic gonadotropin in the same injection. Ovaries were prepared for autoradiography. Dense accumulations of grains occurred over the theca of normal and atretic secondary follicles in all ovaries and over clusters of secondary interstitial cells. The iodine label was variable over the typically hypertrophied theca of precystic follicles. The theca of definitive cysts showed little or no label. These results indicate that cyst formation coincides with the loss of luteinizing hormone/human chorionic gonadotropin binding to the affected follicles.

Monosodium glutamate-induced reductions in hypothalamic beta-endorphin content result in mu-opioid receptor upregulation in the medial preoptic area.

Estradiol valerate (EV) treatment in the rat induces a lesion of the hypothalamic arcuate nucleus, resulting in significant decreases in hypothalamic beta-endorphin. In addition, the EV treatment causes a selective increase in mu-opioid binding in the medial preoptic area (MPOA). Since beta-endorphin neurons located in the arcuate nucleus project extensively to the MPOA, we have hypothesized that the EV-induced loss of these afferents induces a compensatory upregulation of mu-opioid receptors in opioid target neurons. In order to test this hypothesis, we have utilized monosodium glutamate (MSG) treated animals as a model of beta-endorphin cell loss and hence of beta-endorphin deafferentation of the MPOA. Neonatal MSG treatment has been shown to result in the destruction of 80-90% of arcuate neurons accompanied by pronounced decreases in beta-endorphin concentrations in both arcuate nucleus and MPOA. mu-Opioid binding sites were radioautographically labeled in sections from the MPOA of sham- and MSG-injected animals using the methionine enkephalin analogue 125I-FK 33-824 and quantitated by computer-assisted densitometry. The remainder of the hypothalamus of these same animals was utilized for the determination of the beta-endorphin concentration. The hypothalami of rats treated with MSG exhibited 62% (p < 0.01) less beta-endorphin than saline-injected controls. In addition, the mean mu-opioid-binding densities in the MPOA were 24% (p < 0.05) above controls in the MSG-treated group.(ABSTRACT TRUNCATED AT 250 WORDS)

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

A single intramuscular injection of 2 mg estradiol valerate (EV) results in neuronal degeneration and beta-endorphin depletion in the hypothalamic arcuate nucleus of adult female rats. We have hypothesized that peroxidase-positive astrocytes in this brain region oxidize estrogens and catecholestrogens to semiquinone radicals which mediate oxidative neuronal injury. In the present study, dietary administration of the potent antioxidant 21-aminosteroid, U-74389F, completely blocked EV-induced beta-endorphin depletion in the hypothalami of adult female rats. Neither EV nor 21-aminosteroid treatment had any effect on hypothalamic concentrations of neuropeptide Y and Met-enkephalin, confirming that the estradiol lesion is fairly selective for the beta-endorphin cell population. The present findings support the hypothesis that the toxic effect of estradiol on hypothalamic beta-endorphin neurons is mediated by free radicals.