Distribution of estrogen receptor β containing cells in the brains of bacterial artificial chromosome transgenic mice

Angiotensin II slow-pressor hypertension enhances NMDA currents and NOX2-dependent superoxide production in hypothalamic paraventricular neurons

Adaptive changes in glutamatergic signaling within the hypothalamic paraventricular nucleus (PVN) may play a role in the neurohumoral dysfunction underlying the hypertension induced by "slow-pressor" ANG II infusion. We hypothesized that these adaptive changes alter production of gp91phox NADPH oxidase (NOX)-derived reactive oxygen species (ROS) or nitric oxide (NO), resulting in enhanced glutamatergic signaling in the PVN. Electron microscopic immunolabeling showed colocalization of NOX2 and N-methyl-D-aspartate receptor (NMDAR) NR1 subunits in PVN dendrites, an effect enhanced (+48%, P < 0.05 vs. saline) in mice receiving ANG II (600 ng·kg⁻¹·min⁻¹ sc). Isolated PVN cells or spinally projecting PVN neurons from ANG II-infused mice had increased levels of ROS at baseline (+40 ± 5% and +57.6 ± 7.7%, P < 0.01 vs. saline) and after NMDA (+24 ± 7% and +17 ± 5.5%, P < 0.01 and P < 0.05 vs. saline). In contrast, ANG II infusion suppressed NO production in PVN cells at baseline (-29.1 ± 5.2%, P < 0.05 vs. saline) and after NMDA (-18.9 ± 2%, P < 0.01 vs. saline), an effect counteracted by NOX inhibition. In whole cell recording of unlabeled and spinally labeled PVN neurons in slices, NMDA induced a larger inward current in ANG II than in saline groups (+79 ± 24% and +82.9 ± 6.6%, P < 0.01 vs. saline), which was reversed by the ROS scavenger MnTBAP and the NO donor S-nitroso-N-acetylpenicillamine (P > 0.05 vs. control). These findings suggest that slow-pressor ANG II increases the association of NR1 with NOX2 in dendrites of PVN neurons, resulting in enhanced NOX-derived ROS and reduced NO during glutamatergic activity. The resulting enhancement of NMDAR activity may contribute to the neurohumoral dysfunction underlying the development of slow-pressor ANG II hypertension.

Distribution of angiotensin type 1a receptor-containing cells in the brains of bacterial artificial chromosome transgenic mice

In the central nervous system, angiotensin II (AngII) binds to angiotensin type 1 receptors (AT(1)Rs) to affect autonomic and endocrine functions as well as learning and memory. However, understanding the function of cells containing AT(1)Rs has been restricted by limited availability of specific antisera, difficulties discriminating AT(1)R-immunoreactive cells in many brain regions and, the identification of AT(1)R-containing neurons for physiological and molecular studies. Here, we demonstrate that an Agtr1a bacterial artificial chromosome (BAC) transgenic mouse line that expresses type A AT(1)Rs (AT1aRs) identified by enhanced green fluorescent protein (EGFP) overcomes these shortcomings. Throughout the brain, AT1aR-EGFP was detected in the nuclei and cytoplasm of cells, most of which were neurons. EGFP often extended into dendritic processes and could be identified either natively or with immunolabeling of GFP. The distribution of AT1aR-EGFP cells in brain closely corresponded to that reported for AngII binding and AT1aR protein and mRNA. In particular, AT1aR-EGFP cells were in autonomic regions (e.g., hypothalamic paraventricular nucleus, central nucleus of the amygdala, parabrachial nucleus, nuclei of the solitary tract and rostral ventrolateral medulla) and in regions involved in electrolyte and fluid balance (i.e., subfornical organ) and learning and memory (i.e., cerebral cortex and hippocampus). Additionally, dual label electron microscopic studies in select brain areas demonstrate that cells containing AT1aR-EGFP colocalize with AT(1)R-immunoreactivity. Assessment of AngII-induced free radical production in isolated EGFP cells demonstrated feasibility of studies investigating AT1aR signaling ex vivo. These findings support the utility of Agtr1a BAC transgenic reporter mice for future studies understanding the role of AT(1)R-containing cells in brain function.

Estrogen effects on the brain: actions beyond the hypothalamus via novel mechanisms

From its origins in how the brain controls the endocrine system via the hypothalamus and pituitary gland, neuroendocrinology has evolved into a science that now includes hormone action on many aspects of brain function. These actions involve the whole central nervous system and not just the hypothalamus. Advances in our understanding of cellular and molecular actions of steroid hormones have gone beyond the important cell nuclear actions of steroid hormone receptors to include signaling pathways that intersect with other mediators such as neurotransmitters and neuromodulators. This has, in turn, broadened the search for and identification of steroid receptors to include nonnuclear sites in synapses, dendrites, mitochondria, and glial cells, as well as cell nuclei. The study of estrogen receptors and estrogen actions on processes related to cognition, mood, autonomic regulation, pain, and neuroprotection, among other functions, has led the way in this new view of hormone actions on the brain. In this review, we summarize past and current work in our laboratory on this topic. This exciting and growing field involving many laboratories continues to reshape our ideas and approaches to neuroendocrinology both at the bench and the bedside.

Central cardiovascular circuits contribute to the neurovascular dysfunction in angiotensin II hypertension

Hypertension, a powerful risk factor for stroke and dementia, has damaging effects on the brain and its vessels. In particular, hypertension alters vital cerebrovascular control mechanisms linking neural activity to cerebral perfusion. In experimental models of slow-developing hypertension, free radical signaling in the subfornical organ (SFO), one of the forebrain circumventricular organs, is critical for the hormonal release and sympathetic activation driving the elevation in arterial pressure. However, the contribution of this central mechanism to the cerebrovascular alterations induced by hypertension remains uncertain. We tested the hypothesis that free radical production in the SFO is involved in the alterations in cerebrovascular regulation produced by hypertension. In a mouse model of gradual hypertension induced by chronic administration of subpressor doses of angiotensin II (AngII), suppression of free radicals in the SFO by overexpression of CuZn-superoxide dismutase (CuZnSOD) prevented the alteration in neurovascular coupling and endothelium-dependent responses in somatosensory cortex induced by hypertension. The SFO mediates the dysfunction via two signaling pathways. One involves SFO-dependent activation of the paraventricular hypothalamic nucleus, elevations in plasma vasopressin, upregulation of endothelin-1 in cerebral resistance arterioles and activation of endothelin type A receptors. The other pathway depends on activation of cerebrovascular AngII type 1 (AT1) receptors by AngII. Both pathways mediate vasomotor dysfunction by inducing vascular oxidative stress. The findings implicate for the first time the SFO and its efferent hypothalamic pathways in the cerebrovascular alterations induced by AngII, and identify vasopressin and endothelin-1 as potential therapeutic targets to counteract the devastating effects of hypertension on the brain.

Changes in oestrogen receptor-β mRNA expression in male rat brain with age

Oestrogen has important roles not only in the regulation of reproductive function, but also with respect to other functions, such as cognition, emotion and cardiovascular regulation. Oestrogen acts mainly via its oestrogen receptor (ER), namely, ERα and ERβ in target tissues, including the brain. During ageing, the actions of oestrogen are altered in both females and males, raising the possibility that the expression level of ER may be altered with age. Age-related changes in ER expression in female rat brain have been well demonstrated with regard to reproductive ageing, whereas very little is known about the effects of age on the expression of ERs, especially ERβ, in males. In the present study, which aimed to elucidate the effects of ageing on ERβ expression in the male brain at the transcriptional level, we performed in situ hybridisation using young (10weeks), middle-aged (12months) and old (24 months) gonadally-intact male rats. We revealed a wide distribution of ERβ mRNA-positive cells throughout the brain, and found that the number of ERβ mRNA-positive cells was reduced in several brain regions in males with ageing. ERβ mRNA-positive cells were decreased with age in layer 6 of the cerebral cortex, hippocampal CA1/CA3 regions, the dorsal endopiriform nucleus, the medial septal nucleus, various subregions of the amygdala (central, lateral, anterior cortical and posterolateral cortical subnuclei), the anteroventral periventricular nucleus, the substantia nigra pars compacta, the raphe magnus nucleus and the locus coeruleus. These results suggest that ERβ expression in male rat brain decreases with age at the transcriptional level and that these ageing effects are region-specific.

Reprogramming axonal behavior by axon-specific viral transduction

The treatment of axonal disorders, such as diseases associated with axonal injury and degeneration, is limited by the inability to directly target therapeutic protein expression to injured axons. Current gene therapy approaches rely on infection and transcription of viral genes in the cell body. Here, we describe an approach to target gene expression selectively to axons. Using a genetically engineered mouse containing epitope-labeled ribosomes, we find that neurons in adult animals contain ribosomes in distal axons. To use axonal ribosomes to alter local protein expression, we utilized a Sindbis virus containing an RNA genome that has been modified so that it can be directly used as a template for translation. Selective application of this virus to axons leads to local translation of heterologous proteins. Furthermore, we demonstrate that selective axonal protein expression can be used to modify axonal signaling in cultured neurons, enabling axons to grow over inhibitory substrates typically encountered following axonal injury. We also show that this viral approach also can be used to achieve heterologous expression in axons of living animals, indicating that this approach can be used to alter the axonal proteome in vivo. Together, these data identify a novel strategy to manipulate protein expression in axons, and provides a novel approach for using gene therapies for disorders of axonal function.

The mouse primary visual cortex is a site of production and sensitivity to estrogens

The classic female estrogen, 17β-estradiol (E2), has been repeatedly shown to affect the perceptual processing of visual cues. Although gonadal E2 has often been thought to influence these processes, the possibility that central visual processing may be modulated by brain-generated hormone has not been explored. Here we show that estrogen-associated circuits are highly prevalent in the mouse primary visual cortex (V1). Specifically, we cloned aromatase, a marker for estrogen-producing neurons, and the classic estrogen receptors (ERs) ERα and ERβ, as markers for estrogen-responsive neurons, and conducted a detailed expression analysis via in-situ hybridization. We found that both monocular and binocular V1 are highly enriched in aromatase- and ER-positive neurons, indicating that V1 is a site of production and sensitivity to estrogens. Using double-fluorescence in-situ hybridization, we reveal the neurochemical identity of estrogen-producing and -sensitive cells in V1, and demonstrate that they constitute a heterogeneous neuronal population. We further show that visual experience engages a large population of aromatase-positive neurons and, to a lesser extent, ER-expressing neurons, suggesting that E2 levels may be locally regulated by visual input in V1. Interestingly, acute episodes of visual experience do not affect the density or distribution of estrogen-associated circuits. Finally, we show that adult mice dark-reared from birth also exhibit normal distribution of aromatase and ERs throughout V1, suggesting that the implementation and maintenance of estrogen-associated circuits is independent of visual experience. Our findings demonstrate that the adult V1 is a site of production and sensitivity to estrogens, and suggest that locally-produced E2 may shape visual cortical processing.

Anti-anxiety, cognitive, and steroid biosynthetic effects of an isoflavone-based dietary supplement are gonad and sex-dependent in rats

Isoflavone-rich diets are associated with reduced menopausal symptoms and lowered risk of cancers of reproductive tissues. Isoflavones may mimic some effects of estrogen by binding to estrogen receptors, and/or altering steroid availability. Despite their potential health benefits, neither the effects, nor mechanisms, of isoflavones are well understood. We hypothesized that isoflavones would alter behavior and physiology of rats in sex and/or gonad-dependent manner. An isoflavone-based, commercially-available, dietary supplement was administered via subcutaneous implantation to female and male, intact and gonadectomized Long-Evans rats. Affective (elevated plus-maze), cognitive (water-maze), and reproductive (sexual) behavior was examined. Weights of reproductive structures were measured, as an index of trophic effects. Steroid levels in circulation and brain regions associated with behavioral measures were evaluated by radioimmunoassay. The supplement increased anti-anxiety behavior of intact, but not gonadectomized, rats. The supplement enhanced visual-spatial performance of all rats, but this effect was most evident among proestrous female rats, which had the poorest spatial performance. There were neither effects of the supplement on sexual behavior, mass of reproductive tissues, nor plasma steroid levels. The supplement increased levels of 5α-androstane,17ß-diol-3α-diol (3α-diol) in the hippocampus (but not other brain regions) of gonadectomized females. Thus, the supplement altered anxiety and cognitive behavior and brain production of steroids; however, the anti-anxiety effects were limited to rats with an intact reproductive axis and effects on cognitive performance and neurosteriodogenesis were most evident among intact and gonadectomized, female rats respectively.