17beta-Oestradiol stimulation of G-proteins in aged and Alzheimer's human brain: comparison with phytoestrogens.

The neuroprotective action of oestrogens and oestrogen-like compounds is in the focus of basic and clinical research. Although such action has been shown to be associated with neuronal plasma membranes, the implication of G-proteins remains to be elucidated. This study revealed that micromolar concentrations (microM) of 17beta-oestradiol and phytoestrogens, genistein and daidzein, significantly (P < 0.05) stimulate G-proteins ([(35)S]GTP gamma S binding) in the post-mortem hippocampal membranes of age-matched control women with the respective maximum effects of 28, 20 and 15% at 10 microM. In the frontocortical membranes, the stimulation of G-proteins did not differ significantly from that in hippocampal membranes. Although in the hippocampus and frontal cortex of the Alzheimer's disease (AD) women's brain, 10 microM 17beta-oestradiol produced significantly (P < 0.05) lower stimulation of G-proteins than in the control regions, stimulation by phytoestrogens revealed no remarkable decline. 17beta-Oestradiol, genistein and daidzein revealed a selective effect on various G-proteins (G(alphas), G(alpha o), G(alpha i1) or G(alpha 11) plus G(beta 1 gamma 2)) expressed in Sf9 cells. At a concentration of 10 microM, 17beta-oestradiol suppressed the H(2)O(2) and homocysteine stimulated G-proteins in the frontocortical membranes of control women to a greater extent than phytoestrogens. In AD, the suppressing effect of each compound was lower than in the controls. In the cell-free systems, micromolar concentrations of phytoestrogens scavenged OH(*) and the 2.2-diphenyl-1-picrylhydrazyl free radical (DPPH(*)) more than 17beta-oestradiol did. In the frontocortical membranes of control women, the 20 microM 17beta-oestradiol stimulated adenylate cyclase with 20% maximal effect, whereas, in AD, the effect was insignificant. Genistein did not stimulate enzyme either in control or AD frontocortical membranes. Our data confirm that the agents stimulate G-proteins in control and AD women's brains, although 17beta-oestradiol and phytoestrogens have similarities and differences in this respect. We suggest that, besides the ER-dependent one, the ER-independent antioxidant mechanism is responsible for the oestrogen stimulation of G-proteins in the brain membranes. Both of these mechanisms could be involved in the neuroprotective signalling of oestrogens that contributes to their preventive/therapeutic action against postmenopausal neurological disorders.

The distribution and the modulation of tyrosine hydroxylase immunoreactivity in the lateral olivocochlear system of the guinea-pig.

It was previously shown that tyrosine hydroxylase (TH) immunoreactivity in the terminals of the lateral efferents of the cochlea is decreased by acoustic trauma and that sound preconditioning counteracted this decrease [Hear Res 174 (2002) 124]. Here we identify those neurons in the lateral olivocochlear system (LOC) in the brainstem that regulates the peripheral expression of TH in the cochlea. By employing retrograde tracing techniques, dextran-labeled neurons were found predominantly in the ipsilateral LOC system including lateral superior olive (LSO), and the surrounding periolivary regions (dorsal periolivary nucleus [DPO], dorsolateral periolivary nucleus [DLPO], lateral nucleus of trapezoid body [LNTB]). Employing immunocytochemistry, it was found that a control group had 35% of the ipsilateral LOC neurons positively stained with TH. Of the total population of TH neurons, 77% were double-stained (TH and dextran) in the LOC system. Acoustic trauma decreased the number of TH positive neurons in the LSO and the surrounding DLPO, and caused a reduction of TH fiber immunolabeling in these regions. Changes were not found in the DPO or the LNTB after acoustic trauma. Sound conditioning protected against the decrease of TH immunolabeling by acoustic trauma and increased the fiber staining for TH in the LSO and DLPO, but not in the DPO or the LNTB. These results provide evidence that TH positive neurons are present in the LOC system in the guinea-pig. It is now demonstrated that protection against acoustic trauma by sound conditioning has a central component that is governed by TH in the LSO and the surrounding periolivary DLPO region.

The synaptic-vesicle-specific proteins rab3a and synaptophysin are reduced in thalamus and related cortical brain regions in schizophrenic brains.

Two synaptic-vesicle proteins, rab3a and synaptophysin, have been studied on post-mortem brain tissues of schizophrenics and healthy controls. We found significantly reduced levels of rab3a in thalamus (p<0.001); for both proteins in gyrus cinguli and hippocampus (p<0.0001); for rab3a in frontal and parietal cortex (p<0.05); and no differences in temporal cortex or cerebellum in schizophrenics compared with controls. Reduced synaptic density may be a prominent feature of the molecular neuropathology of schizophrenia.

GABA transporters (GAT-1) in Alzheimer's disease.

The presynaptically located gamma-aminobutyric acid (GABA) transporter (GAT-1) was studied in a group of patients with Alzheimer's disease (AD) and in a control group using the GAT-1 selective radioligand [3H]tiagabine. Post mortem brain tissue from frontal cortex, temporal cortex, and caudate nucleus from 18 AD patients and 23 age-matched controls were studied. The binding was saturable (Kd 26 nM) and region specific. There were no significant differences between the groups with respect to the binding capacity (Bmax) and binding affinity (Kd). The unaltered [3H]tiagabine binding to GAT-1 protein indicates that intrinsic GABA neurons are spared in Alzheimer's disease.

Modulating calbindin and parvalbumin immunoreactivity in the cochlear nucleus by moderate noise exposure in mice. . A quantitative study on the dorsal and posteroventral cochlear nucleus.

The number of calbindin D-28k and parvalbumin immunoreactive (IR) neurons were characterized on sections from the cochlear nucleus, dorsal cochlear nucleus (DCN) and posteroventral cochlear nucleus (PVCN) using two-dimensional quantification. After noise exposure (6-12 kHz, 2 h, at either 80 dB SPL or 103 dB SPL), the number of calbindin and parvalbumin immunoreactive neurons increased in CBA/CBA mice. Quantitative analysis of calbindin-IR in the PVCN did not show a statistically significant difference between any of the groups, whereas statistically significant differences in calbindin-IR were found in the DCN for the 103 dB and 80 dB group compared to the control group, and 103 dB compared to the 80 dB group, respectively. A statistically significant increase in the number of parvalbumin-IR neurons in the PVCN and the DCN was evident in the 103 dB and 80 dB group compared to the control group, and in the 103 dB compared to the 80 dB group. The data indicate that increasing sound stimulation causes a graded increase in the expression of calcium-binding protein immunoreactivity in the DCN and PVCN neurons and neuropil. This increase of protein expression is due to increased positive immunoreactivity in 'silent' neurons. These findings implicate that these neurons have the possibility to react against trauma and display calbindin or parvalbumin as a rescue event. The ability to map sound-induced calcium-binding protein changes in auditory neurons may be useful in future studies designed for detecting early patterns of neurodegeneration and neuroprotection in the central auditory pathway.

Localization of M1 muscarinic receptors in rat brain using selective muscarinic toxin-1.

Mambas, African snakes of the genus Dendroaspis, produce several types of toxins that are of pharmacological interest. The novel muscarinic toxin-1 (MT-1), from the green mamba Dendroaspis angusticeps, binds specifically to muscarinic M1 receptors in homogenates of rat cerebral cortex. Iodination of the toxin, 125I-muscarinic toxin-1 (125I-MT-1), renders the toxin selective for M1 muscarinic receptors. Quantitative measurement of 125I-MT-1 autoradiography in rat brain sections indicated highest labeling in the nucleus accumbens, striatum, and dentate gyrus. High densities of 125I-MT-1 binding sites were located in the CA1 region of the hippocampus, frontal, and parietal cortices. Moderate densities of binding sites were seen in temporal cortex, and hippocampal subregions CA2, CA3, and CA4, whereas low labeling was observed in the cerebellum and spinal cord.

Effects of nucleus basalis lesion on muscarinic receptor subtypes.

The cholinergic system in the central nervous system is an important component of the neural circuitry of learning, memory and cognition. A decline of cholinergic innervation in the human brain is a characteristic feature of dementia of Alzheimer's type. In this study, changes in cholinergic markers were studied after a unilateral lesion of the nucleus basalis magnocellularis (nbM). Acetylcholinesterase (AChE) histochemistry showed a loss of cortical AChE-containing neurons, and choline acetyltransferase (ChAT) immunohistochemistry demonstrated a loss of cholinergic cells in nbM. The localizations of muscarinic M1 and M2 receptors using [3H]pirenzepine ([3H]PZ) and [3H]AF-DX 384, respectively, were studied by quantitative autoradiography 1, 2, 4 and 6 weeks following unilateral ibotenic acid lesion of nbM. A significant decrease in [3H]PZ binding sites was observed at postlesion week 1 in the parietal and temporal cortices. The decrease in [3H]AF-DX 384 binding sites on the lesioned side was observed throughout frontal, parietal and temporal cortices after postlesion week 1, with a significant increase after 6 weeks, possibly as result of loss of presynaptic receptors and upregulation of postsynaptic ones. Moreover, laminar distribution after nbM lesion shows that M1 and M2 receptor binding sites are more affected in superficial layers (I,II,III) than in the deep layers (IV,V,VI), depending on ligand, postlesion period and cortical region. Furthermore, nbM lesion causes a higher deficit of M2 receptors than of M1 receptors. These data suggest the existence of a presynaptic population as well as a postsynaptic population of M1 and M2 receptors which are differently affected after unilateral nbM lesion.