The early postdenervation depolarization of rat diaphragm muscle fibers (8–10 mV within 3 h in vitro) is substantially smaller (3 mV) when muscles are bathed with 1×10−3 M l-glutamate (Glu) or 1×10−3 M N-methyl-d-aspartate (NMDA). The effects of Glu and NMDA are inhibited in a dose-dependent manner by competitive inhibitor 2-amino-5-phosphonovaleric acid (APV) withK i 6.3×10−4 M, by 2×10−7 M MK-801, which acts as an open channel inhibitor, by 2–3×10−4 Zn2+, which reacts with surface-located sites of the NMDA subtype of the glutamate receptor, and also by glycine-free solutions and 7-Cl-kynurenic acid, which inhibits the glycine binding sites on NMDA receptors. It follows that the effect of glutamate on early postdenervation depolarization is mediated by the NMDA subtype of glutamate receptor with similar pharmacological properties to those found in neurons. The only exception found was the glutamate-like action of 1×10−7 M MK-801, which partially prevented the early postdenervation depolarization when present in the muscle bath during the first 3 h after nerve section.
The content and composition of gangliosides were examined in an experimental mouse brain tumor, EPEN, that was grown subcutaneously in the flank of the syngeneic C57BL/6J (B6) host and in the B6 severe combined immunodeficiency (SCID) host. SCID mice lack functional T- and B-lymphocytes, but have a normal complement of macrophages. The content and distribution of the brain tumor gangliosides were similar whether the tumor was grown in the immunocompetent B6 host or in the B6-SCID host. N-acetylneuraminic acid- (NeuAc) containing GM3 was the major ganglioside in the subcutaneous tumors and in the cultured EPEN cells. Significant amounts of N-glycolylneuraminic acid- (NeuGc) containing gangliosides were found in the tumor grown in both mouse hosts. NeuGc-containing gangliosides are not expressed in normal mouse brain, but are present in macrophages and serum. An extremely complex pattern of minor gangliosides was found in the subcutaneous tumors on two-dimensional, high-performance thin-layer chromatograms. Most of the minor gangliosides comigrated with those found in mouse macrophages. The results show that the absence of functional T- and B-lymphocytes does not markedly affect brain tumor ganglioside composition and suggest that NeuGc-containing gangliosides in the EPEN can be derived from tumor infiltrating host cells (mostly macrophages) and from the extracellular milieu (serum).
Excitatory amino acids participate in the generation of seizure activity. Consequently, the effects of GYKI 52466 [1-(4-aminophenyl)-4-methoxy-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride], an antagonist of glutamate-mediated events, on the protective activity of conventional antiepileptic drugs against pentetrazol were studied.
The distributions of constitutive and inducible 70-kDa heatshock proteins (Hsc70 and Hsp70, respectively) and ubiquitin (Ub) were investigated in autopsy specimens from 24 adult human brains. The objectives were to verify that the milder fixation and celloidin embedding applied to those specimens preserved protein immunoreactivity in the tissue sections, even with extended intervals between death and fixation, and to determine the typical pattern of distribution of the proteins in aged human cerebellum and caudate nucleus. To achieve these objectives, the patterns of immunoreactivity in human specimens were compared with those in normal rat brain after three methods of immersion fixation: 1% Formalin; 10% Formalin; Methacarn (a modification of Carnoy’s solution). Additionally, some rats were left refrigerated, but unfixed for up to 24 h to mimic the postmortem interval that commonly occurs prior to fixation of human autopsy material. Tissues were embedded in celloidin, sectioned at 100 μm, and the celloidin dissolved to permit immunostaining Immunoreactivity for all antigens was greatly diminished in the rat brain by fixation in 10% formalin compared to 1% formalin or methacarn. Rat and human brain tissues fixed in the latter two solutions showed similar patterns of low levels of Hsp70 immunostaining in gray matter and other areas where neuronal somata were concentrated, whereas Hsc70 immunostaining was much greater in those same areas. Little Hsc70 or Hsp70 immunoreactivity was detected in the white matter from either source, but immunoblots of human gray and white matter suggested that white matter contained more Hsc70 and Hsp70 than apparent by tissue section immunoreactivity. Ubiquitin immunostaining in rat and human brain showed the same high levels as Hsc70 in gray matter, but unlike Hsc70, was also visible in white matter. These patterns remained the same in rat brains even if fixation was delayed for 24 h. In three human brain specimens, elevated Hsc70 staining, but not Hsp70 or Ub, was found in a ring pattern similar to that described as the ischemic penumbra in experimentally induced brain ischemia. These results indicated that dilute formalin preserved Hsc/Hsp70 and Ub antigenicity well, and that the proteins had similar distributions in human and rat brains, despite the extended postmortem delay in fixation of the former. They also suggested that evidence of premortem, localized cellular metabolic stress may be preserved in the postmortem, human brain by an alteration in the typical distribution of Hsc70.
The biological roles of nitric oxide (NO) and cGMP as inter- and intracellular messengers have been intensively investigated during the last decade. NO and cGMP both mediate physiological effects in the cardiovascular, endocrinological, and immunological systems as well as in central nervous system (CNS). In the CNS, activation of theN-methyl-d-aspartic acid (NMDA) type of glutamatergic receptor induces Ca2+-dependent NOS and NO release, which then activates soluble guanylate cyclase for the synthesis of cGMP.
Oxidative stress in the central nervous system (CNS) may cause oxidation of lipoprotein particles. The oxidized lipoproteins may damage cellular and subcellular membranes, leading to tissue injury and cell death. Human low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL) are oxidized by transition metal ions, such as Cu 2+ . Using PC 12 cells, we tested the cytotoxicity of oxidized LDL and VLDL. Cell death was increased in a dose-dependent manner. Antioxidants added to the incubation medium, such as vitamins E or C, or resveratrol showed some protection. Results indicated that oxidized lipoproteins may serve as an oxidative stressor, which may initiate the neuronal cell death leading to the manifestation of Alzheimer disease (AD).
Effects of tacrine (1,2,3,4-tetrahydro-9-aminoacridine) on memory deficits in rats treated with ethylcholine aziridinium ion (AF64A) were studied using active avoidance test in the two-way shuttle box. Neurotoxin AF64A injected at a dose of 6 nmol (icv, bilaterally) causes nonspecific tissue damage in hippocampal fields CA2 and CA3. Two weeks after treatment with 6 nmol, AF64A active avoidance performance of toxin-treated rats was significantly deteriorated compared to vehicle-treated animals estimated in learning test (68±3.5 and 83±3.2% of correct responses, respectively; p <0.01) and in retention test (53±5 and 76±3.6%, respectively; p <0.01). Under these conditions, chronic treatment with tacrine at a daily dose of 1 mg/kg for 12–14 d reverses the effect of AF64A on the active avoidance performance both in learning (78±3.2%) and retention (72±4%) tests. It is supposed that behavioral effects of tacrine considerably depend on a severity of neurodegeneration in the hippocampus.
Lipid peroxidation has been suggested to be a potential cause of neuronal damage in neurodegenerative diseases. Changes in several parameters of lipid peroxidation, including basal (unstimulated) lipid peroxidation, stimulated lipid peroxidation, tissue iron concentrations, and the concentrations of some oxygen radical scavengers, have been reported in neurodegenerative diseases. However, the in vitro interaction of oxygen radical scavengers and stimulated lipid peroxidation in neurodegenerative disease has been less well-studied. The purpose of the present study was to determine the effects of oxygen radical scavengers on ascorbate-stimulated lipid peroxidation in Alzheimer disease (AD). We have found that some parameters of ascorbate-stimulated lipid peroxidation are altered in AD and that the effects of superoxide dismutase (SOD) on ascorbate-stimulated lipid peroxidation are significantly different in AD as compared to aged.
Total acetylcholinesterase (AChE) and the molecular forms of the enzyme from six brain regions were compared in young adult (6 mo) and aged (24 mo) Fischer 344 rats. Total AChE activity was significantly reduced in aged striatum (48.7%), parietal cortex (39%), cerebellum (30.2%), and medulla/pons (23.1%). Forebrain of aged rats showed nonsignificant reduction of AChE (18.4%), but olfactory bulbs exhibited no differences in aged rats. The ratio of G4/G1 molecular forms, as isolated on sucrose density gradients, was unaltered in all aged rat brain tissues examined. These results indicate that aged rats exhibit reduced brain AChE, but there is no evidence for selective effects on individual molecular forms.
The messenger ribonucleic acid (mRNA) of gap junction protein connexin 43 was quantified in the tetanus toxin rat model of focal epilepsy following injection of toxin into the left amygdala. Animals were monitored electrographically at weekly intervals with bilateral amygdala electrodes. Cohorts of 3 rats were sacrificed at weeks 1, 2, 3, 4, 6, 8, and 10, and bilateral regions containing the amygdala and posterior cerebral cortex were sampled, frozen, and later pooled for northern blot analysis. Spike generation was manifest in all animals during the first 4 wk followed by variable attenuation and cessation by 10 wk. Electrode implantation alone was shown by regression analysis to cause significant (p < 0.05) elevation of connexin mRNA in weeks 1-4. Injection of toxin diminished connexin mRNA expression in the amygdala when compared to electrode implantation alone. No trend in connexin mRNA expression was established over time in either amygdala or cerebral cortex in the acute epileptic or chronic postepileptic phase. No association between connexin 43 mRNA expression and the development of epileptogenicity was found in the context of a self-limiting animal model of focal epilepsy.
Twelve 4-urea-5,7-dichlorokynurenic acid derivatives were synthesized by reacting the 4-tosylimino derivative of 5,7-dichlorokynurenate methyl ester first with triphosgene and then with a secondary amine. Compounds were screened in mice for anticonvulsant activity using maximal electroshock (MES), subcutaneous pentylenetetrazole (Met), and threshold tonic extension (TTE) tests. A rotorod test was used to determine neurotoxicity. Seven of the derivatives had anticonvulsant activity in TTE testing at 100 mg/kg. One compound, 2-methyl carboxylate-5,7-dichloro-4-([{diphenylamino}-carbonyl]amino)-quinoline, had an ED 50 value of 134 mg/kg (95% conf. int.: low—78.5, high— 205.7; slope 1.9 SE=0.44) in TTE testing. Two derivatives had MES activity. Only one compound, an N,N -diethylamino derivative, was neurotoxic in the rotorod test. Compounds were screened at a 10-μ M concentration for activity in displacing 5,7-dichlorokynurenic acid from synaptosomal membrane fragments. Since 9 of the 12 compounds synthesized and tested have demonstrated anticonvulsant activity, this class of chemicals offers promise for the production of useful therapeutic agents.
The effect of transient cerebral ischemia on phosphorylation of the microtubule-associated protein (MAP) τ was investigated using the rat four-vessel occlusion model. Phosphorylation of τ is proposed to regulate its binding to microtubules, influencing the dynamics of microtubule assembly necessary for axonal growth and neurite plasticity. In this study, τ was rapidly dephosphorylated during ischemia in the hippocampus, neocortex, and striatum. Dephosphorylation of τ was observed within 5 min of occlusion and increased after 15 min in all three brain regions, regardless of their relative vulnerability to the insult. Thus, dephosphorylation of τ is an early marker of ischemia and precedes the occlusion time required to cause extensive neuronal cell death in this model. On restoration of blood flow for a little as 15 min, τ was phosphorylated at a site(s) that causes a reduction in its electrophoretic mobility. The dephosphorylation/phosphorylation of τ may alter its distribution between axon and cell body, and affect its susceptibility to proteolysis. These changes would be expected to influence microtubule stability, possibly contributing to disruption of axonal transport, but also allowing neurite remodeling in a regenerative response.
Considerable evidence suggests that oxidative stress plays an important role in tissue damage associated with hypoglycemia and other metabolic disorders. The altered brain neurotransmitters metabolism, cerebral electrolyte contents, and impaired blood-brain barrier function may contribute to CNS dysfunction in hypoglycemia. The present study elucidates the effect of starvation and insulin-induced hypoglycemia on the free radical scavanger system—reduced glutathione (GSH) content, glutathioneS-transferase (GST), glutathione peroxidase (GPx), glutathione reductase (GR), γ-glutamyl transpeptidase (γ-GTP), γ-glutamyl cystein synthetase (γ-GCS), catalase and superoxide dismutase (SOD), and mitochondrial electron transport chain (ETC) complexes I–IV from three different regions of rat brain, namely cerebral hemispheres (CH), cerebellum (CB), and brainstem (BS). Peripheral organs, such as liver and kidney, were also studied. Significant changes in these enzymic activities were observed. The analysis of such alterations is important in ultimately determining the basis of neuronal dysfunction during metabolic stress conditions, such as hypoglycemia, and also defining the nature of these changes may help to develop therapeutic means to cure metabolically stressed tissues.
Membrane-mediated excessive intracellular calcium accumulation (EICA) and diminished cellular energy production are the hallmarks of dystrophic pathobiology in Duchenne and Becker muscular dystrophies. We reported reversal of respiratory damage and Ca 2+ -overloading in the in vitro cardiac mitochondria from CHF-146 dystrophic hamsters (DH) with hereditary muscular dystrophy (Bhattacharya et al., 1993). Here we studied respiratory dysfunctions in the skeletal muscle mitochondria from young and old DH, and whether these abnormalities can be reversed by reducing [Ca 2+ ] in the isolation medium, thereby lowering intramitochondrial Ca 2+ -overloading. Age- and sex-matched CHF-148 albino normal hamsters (NH) served as controls. As an index of EICA and cellular degeneration, Ca and Mg levels were assayed in the skeletal muscle and mitochondria. Mitochondria from young and old DH, isolated without EDTA (B o medium), revealed poor coupling of oxidative phosphorylation, diminished stimulated oxygen consumption rate, and lower respiratory control ratio and ADP/O ratios, compared to NH. Incorporation of 10 m M EDTA (B E medium) in the isolation medium restored mitochondrial functions of the dystrophic organelles to a near-normal level, and reduced Ca 2+ -overloading. The mitochondrial Ca level in DH was significantly higher than in NH, irrespective of the medium. However, compared to B o medium, the dystrophic organelles isolated in B E medium had lower Ca levels and markedly improved oxidative phosphorylation as seen in NH. Muscle Ca contents in the young and old DH were elevated relative to NH, showing a positive correlation with the increased mitochondrial Ca 2+ -sequestration. Dystrophic muscle also revealed Ca deposition with an abundance of Ca 2+ -positive and necrotic myofibers by light microscopy, and intramitochondrial Ca 2+ -overloading by electron microscopy, respectively. However, Mg levels in the muscle and mitochondria did not alter with age or dystrophy. These data parallel our observations in the heart, and suggest that functional impairments and Ca 2+ -overloading also occur in the skeletal muscle mitochondria of DH, and are indeed reversible if EICA is regulated by slow Ca 2+ -channel blocker therapy (Johnson and Bhattacharya, 1993).
The major central norepinephrinergic nucleus, locus ceruleus (LC), is thought to participate in modulation of such brain areas as cerebral cortex, septum, hippocampus, thalamus, hypothalamus, and cerebellum in animals facing various physiological challenges, including stress. Exposure of experimental animals to different stressors causes an increase in LC activity and gene expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. The aim of this work was to investigate the effect of a single and repeated (7 times) or long-term repeated (42 times) daily immobilization stress (IMMO) on TH mRNA levels in LC of laboratory rats by in situ hybridization method. A single IMMO caused significant elevation of LC TH mRNA levels in comparison to unstressed controls. This was found immediately and at 3 and 6 h after IMMO, and progressively increased up to 24 h after the first IMMO terminated. Further exposure to IMMO did not cause additional increases in LC TH mRNA levels, which stayed significantly elevated in comparison to unstressed rats. In animals that underwent IMMO for 42 times, the LC TH gene expression, 24 h after the last stress exposure, was significantly lower when compared to that of singly or seven times stressed rats. Thus, our results indicate a possible adaptation of catecholamine-synthesizing system at the level of TH gene expression in LC of rats exposed to long-term repeated IMMO.
The distribution of the metabotropic glutamate receptor mGluR1a was studied in the normal and kainate-lesioned rat hippocampus using a monoclonal (MAb) and a polyclonal antibody to mGluR1a. Many labeled nonpyramidal neurons were observed in the stratum oriens of CA1 in sections incubated with MAb. In comparison, fewer labeled neurons were observed in this layer in sections incubated with polyclonal antibody. Many nonpyramidal neurons were observed in the stratum lucidum of CA3 and the hilus of the dentate gyrus, with both antibodies. The cell bodies of pyramidal neurons were unlabeled. A dense network of labeled processes was observed in the neuropil of the CA fields at electron microscopy. Some dendrites were very densely labeled and did not contain dendritic spines. These were identified as dendrites of nonpyramidal neurons. Other dendrites contained lightly labeled dendritic shafts, but densely labeled dendritic spines, and were identified as dendrites of pyramidal neurons. Intravenous kainate injections resulted in destruction of pyramidal neurons and a massive decrease in mGluR1a immunoreactivity in the CA fields. This decrease was obvious even at 1-5 d postinjection, when the nonpyramidal neurons in the stratum oriens remained densely labeled, suggesting that pyramidal neurons contributed significantly to mGluR1a staining in the CA fields. We conclude that the dendritic spines of hippocampal pyramidal neurons contain mGluR1a, even though little staining is observed in their parent dendritic shafts or cell bodies.
Atrial natriuretic peptide receptor (ANP) subtypes and their signal transduction response were characterized in choroid plexus of spontaneously hypertensive (SHR) and normotensive (WKY) rats. We found two ANP receptor subtypes, guanylate cyclase coupled and uncoupled, in both rat strains. Binding of ANP was lower in SHR choroid plexus when compared to WKY. The lower ANP binding in SHR was the result of a decrease of binding to the guanylate cyclasecoupled receptor subtype A, a decrease that correlated well with the decreased ANP-induced cGMP formation in SHR. Forskolin stimulated cGMP production to the same extent in both strains. In WKY rats, ANP increased basal and forskolin-stimulated cAMP production; conversely, in SHR, ANP did not affect the basal level of cAMP and inhibited the forskolin-stimulated cAMP production. These results demonstrate differences in ANP receptor subtype expression, and ANP signal transduction in choroid plexus of hypertensive and normotensive rats, which is of possible significance to the central mechanisms of blood pressure control.
Administration of l -DOPA to Parkinson patients has been suggested to exacerbate “functional denervation” of the nigrostriatal system. Therefore, experiments were conducted to determine if l -DOPA combined with the DOPA decarboxylase inhibitor, Ro4-4602 (benserazide hydrochloride) would potentiate amphetamine-induced neurotoxicity. Mice received two injections of saline or benserazide + l -DOPA (25.0 or 100.0 mg/kg) interspersed with four injections of amphetamine (15.0 mg/kg) at 2-h intervals. Significant depletion of striatal dopamine, DOPAC, and HVA was evident 1 wk following amphetamine administered with or without 25.0 mg/kg l -DOPA+benserazide, whereas 100.0 mg/kg l -DOPA+benserazide potentiated amphetamine-induced depletion of striatal dopamine (17 vs 28% of control values). This enhanced toxicity may be consequent to increased dopamine turnover following l -DOPA (360 vs 231%), a situation akin to that observed in compromised dopaminergic nigrostriatal systems of parkinsonian patients. Furthermore, striatal 5-HT was not altered by amphetamine alone, whereas concurrent administration of l -DOPA/benserazide depleted 5-HT to 82% of control values. No changes were evident in the frontal cortex following amphetamine with or without concurrent l -DOPA/benserazide; however, l -DOPA/benserazide administered alone reduced 5-HT and 5-HT turnover to 58% of control values.
