Oxidative stress in Huntington's disease.

It has been five years since the elucidation of the genetic mutation underlying the pathogenesis of Huntington's disease (HD) (97), however the precise mechanism of the selective neuronal death it propagates still remains an enigma. Several different etiological processes may play roles, and strong evidence from studies in both humans and animal models suggests the involvement of energy metabolism dysfunction, excitotoxic processes, and oxidative stress. Importantly, the recent development of transgenic mouse models of HD led to the identification of neuronal intranuclear inclusion bodies in affected brain regions in both mouse models and in HD brain, consisting of protein aggregates containing fragments of mutant huntingtin protein. These observations opened new avenues of investigation into possible huntingtin protein interactions and their putative pathogenetic sequelae. Amongst these studies, findings of elevated levels of oxidative damage products such as malondialdehyde, 8-hydroxydeoxyguanosine, 3-nitrotyrosine and heme oxygenase in areas of degeneration in HD brain, and of increased free radical production in animal models, indicate the involvement of oxidative stress either as a causative event, or as a secondary constituent of the cell death cascade in the disease. Here we review the evidence for oxidative damage and potential mechanisms of neuronal death in HD.

The cerebral metabolic consequences of nitric oxide synthase deficiency: glucose utilization in endothelial and neuronal nitric oxide synthase null mice.

Nitric oxide has multiple physiologic roles in the CNS. Inhibiting nitric oxide synthesis might therefore alter functional activity within the brain. We used [14C]-2-deoxyglucose in vivo autoradiography to measure local CMRglc in "knockout" mice lacking the genes for either the endothelial (eNOS) or neuronal (nNOS) isoforms of nitric oxide synthase, and in the progenitor strains (SV129, C57B1/6). Glucose utilization levels did not significantly differ between nNOS and eNOS knockout mice and C57B1/6 mice in any of the 48 brain regions examined, but were relatively lower in some subcortical regions in SV129 mice.

Familial multisystem degeneration with parkinsonism associated with the 11778 mitochondrial DNA mutation.

OBJECTIVE: To investigate a family with maternally inherited, adult-onset multisystem degeneration including prominent parkinsonism to determine whether clinical features can result from a mitochondrial DNA (mtDNA) mutation. The parkinsonism was levodopa responsive and was associated with the loss of pigmented neurons in the substantia nigra in at least one patient. BACKGROUND: Mitochondrial dysfunction is hypothesized to play a role in late-onset neurodegenerative diseases including PD and AD. Mitochondrial genetic mutations are hypothesized to account for these defects, but attempts to identify specific mtDNA mutations have been inconclusive. METHODS: Clinical examinations, DNA sequencing, and restriction digestion and biochemical analyses were performed. RESULTS: Maternal relatives harbor a G-to-A missense mutation, heteroplasmic in some patients, at nucleotide position 11778 of the mitochondrial ND4 gene of complex I that converts a highly conserved arginine to a histidine. Sequencing of the entire mitochondrial genome in an affected family member reveals no other mutations likely to be pathogenic. This mutation has been identified previously only in families with Leber's hereditary optic neuropathy-a disorder also linked to complex I dysfunction but usually limited clinically to optic atrophy. CONCLUSIONS: These data reveal previously unsuspected clinical heterogeneity of the G11778A mutation, and suggest that an inherited mtDNA mutation can contribute to the development of adult-onset parkinsonism and multisystem degeneration.

AMPA receptor antagonists and local cerebral glucose utilization in the rat.

Local cerebral glucose utilization was examined using [14C]2-deoxyglucose autoradiography following systemic administration of the AMPA antagonists 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX) and 6-(2-(1H-tetrazol-5-yl)ethyl)decahydroisoquinoline-3-carboxy lic acid (LY-293558) in conscious rats. Both NBQX (10, 30 and 100 mg/kg) and LY-293558 (10, 30 and 100 mg/kg) produced marked, anatomically widespread, dose-dependent reductions in glucose utilization throughout the brain. In none of the 50 regions investigated were elevations in glucose use observed at any dose of either agent. The reductions in glucose use were accompanied by sedation, suppression of spontaneous behaviour, and respiratory depression after NBQX (30 and 100 mg/kg) and LY-293558 (30 and 100 mg/kg) administration. The greatest reductions in glucose use after NBQX or LY-293558 occurred in primary auditory regions, limbic structures (particularly hippocampal regions and cingulate cortex), neocortex and some thalamic nuclei. However, a small number of regions were found to be insensitive to either NBQX or LY-293558, most notably the superior colliculus superficial layer which failed to display significant alterations in glucose use following any concentration of either AMPA antagonist. The anatomical pattern of altered glucose use was essentially similar following either agent although the cerebral cortex, thalamus and auditory regions were more sensitive to LY-293558 and subcortical regions more sensitive to NBQX. The anatomical pattern of glucose use alterations after AMPA receptor antagonists differs from that described previously for competitive and non-competitive NMDA receptor antagonists.

Differential patterns of local cerebral glucose utilisation associated with rilmenidine- or B-HT 933-induced hypotension.

The anti-hypertensive drug, rilmenidine, has activity at both imidazoline-preferring receptors (IPRs) and alpha 2-adrenoceptors. However, available evidence suggests that its hypotensive effect is mediated via central IPRs. In the present study, the neuroanatomical regions involved in mediating the hypotensive response to rilmenidine were investigated using the [14C]2-deoxyglucose in vivo autoradiographic technique to map drug-induced changes in glucose utilisation within the CNS of conscious, spontaneously hypertensive rats (SHR). The cerebral metabolic effects of rilmenidine were compared with those of B-HT 933, a selective, alpha 2-adrenoceptor agonist with no selectivity for the IPR. Rilmenidine (1 mg/kg, s.c.) and B-HT 933 (2 mg/kg, s.c.) both elicited a moderate but significant hypotension (-24 +/- 2 and -18 +/- 5 mmHg, resp.) and bradycardia (-62 +/- 19.5 and -69 +/- 14 beats/min, resp.). [14C]2-deoxyglucose autoradiography, initiated after stabilisation of the drug-induced reduction in blood pressure, revealed significant reductions (P < 0.05) in local cerebral glucose utilisation (LCGU) in the intermediolateral cell column of the spinal cord, area postrema, ventrolateral medulla, nucleus tractus solitarius and cuneate nucleus of rilmenidine-treated rats. Rilmenidine did not significantly alter LCGU in a number of structures containing high densities of alpha 2-adrenoceptors such as nucleus accumbens, locus coeruleus, frontal cortex. No significant changes in glucose use were evident in any of the 26 CNS regions examined following B-HT 933 administration. These results provide evidence for the functional involvement of brainstem cardiovascular control centres in the central hypotensive effects of rilmenidine.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological modification of glutamate neurotoxicity in vivo.

The ability of five agents (dizocilpine [MK-801], 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)-quinoxaline [NBQX], enadoline [CI-977], L-nitroarginine methyl ester [L-NAME] and BW 1003c87) with well defined, distinct pharmacological profiles and with established anti-ischemic efficacy, to modify neuronal damage has been examined in a simple in vivo model of glutamate excitotoxicity. Cortical lesions were produced in physiologically-monitored halothane-anesthetised rats by reverse dialysis of glutamate. The volume of the lesion was quantified histologically by image analysis of approximately 20 sections taken at 200 microm intervals throughout the lesion. The AMPA and NMDA receptor antagonists (NBQX and MK-801) and the inhibitor of nitric oxide synthase (L-NAME) significantly reduced the lesion volume by a similar extent (by approximately 30% from vehicle). Two agents (the kappa opioid agonist, CI-977 and the sodium channel blocker, BW 1003c87) which putatively inhibit the release of endogenous glutamate presynaptically, had dissimilar effects on lesion size. CI-977 failed to alter the amount of damage produced by exogenous glutamate, whereas BW 1003c87 reduced the lesion size by approximately 50%. Using this model, the neuroprotective effects of anti-ischemic drugs can be explored in vivo, uncomplicated in contrast to experimental ischemia by reduced oxygen delivery, drug effects on tissue blood flow and compromised energy generation. In consequence, additional mechanistic insight into anti-ischemic drug action in vivo can be obtained.

Oxidative damage to mitochondrial DNA in Huntington's disease parietal cortex.

Oxidative damage to DNA may play a role in both normal aging and in neurodegenerative diseases. Using a sensitive high-performance liquid chromatography (HPLC) assay, we examined concentrations of 8-hydroxy-2-deoxyguanosine (OH8dG) in mitochondrial DNA (mtDNA) isolated from frontal and parietal cerebral cortex and from cerebellum in 22 Huntington's disease (HD) patients and 15 age-matched normal controls. A significant increase in OH8dG in mtDNA of parietal cortex was found in HD patients as compared with controls, while there were no significant changes in frontal cortex or cerebellum. The present findings are consistent with regionally specific oxidative damage in HD, which may be a further evidence of a metabolic defect.

An investigation of the involvement of GABA in certain pharmacological effects of delta-9-tetrahydrocannabinol.

Experiments were performed with mice to determine whether doses of the benzodiazepine, flurazepam, or the GABA uptake inhibitor, NO-328, known to potentiate catalepsy induced by delta-9-tetrahydrocannabinol (THC), would also interact synergistically with THC in the production of certain other effects. No synergism was detected either in the production of antinociception (tail flick test) or in a test in which the ability of flurazepam to delay onset of clonic convulsions induced by intravenous infusion of pentylenetetrazole was compared in the presence and absence of THC or cannabidiol. The hypothermic effect of THC was unaffected by NO-328 but enhanced by flurazepam, albeit only at doses higher than those needed to potentiate THC-induced catalepsy. In vitro experiments with guinea pig ileum showed that the ability of THC to inhibit electrically evoked contractions was unaffected by delta-amino-n-valeric acid, a GABA(B) receptor antagonist, and that preparations rendered tolerant to GABA responded normally to THC. Contractions induced by GABA in unstimulated ileal longitudinal muscle were attenuated by THC. We conclude that there is little evidence from our data that any of the THC effects studied were GABA mediated.

Neurodegenerative disease.

This report from the Society of Neuroscience meeting in Los Angeles is limited to a small cohort of presentations which reflect this reporter's research interests, namely mechanisms of cell death in neurodegenerative disease, and in particular Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), and Parkinson's disease (PD).

High risk pregnancy in the workplace. Influencing positive outcomes.

Childbearing employees are well served by the occupational health nurse who promotes optimal preconceptual and pregnancy health practices, uses community resources, and maintains current knowledge about high risk pregnancy prevention and care. These broad goals of care can lead to decreased absenteeism, healthier and happier employees, and more positive outcomes of pregnancy. For employees with high risk pregnancies, the role of the occupational health nurse includes, but is not limited to, facilitating awareness with the employer, making suggestions for adjusting working conditions, making frequent assessments of the employee's needs, and communicating with prenatal health care providers. Occupational health nurses should never underestimate their role and potential influence on the mother, and on her significant other, for a positive outcome of her pregnancy.

Brain structures involved in the hypotensive effects of rilmenidine: evaluation by [14C]2-deoxyglucose autoradiography.

The centrally acting, antihypertensive drug rilmenidine has activity at both imidazoline-preferring receptors (IPRs) and alpha 2-adrenoceptors: the IPR has been proposed to be the predominant receptor responsible for the hypotensive effects of rilmenidine. In the present study, the neuroanatomic regions of the brain involved in mediating the hypotensive response to rilmenidine were investigated in spontaneously hypertensive rats with the use of [14C]2-deoxyglucose autoradiography. The selective alpha 2-adrenoceptor agonist B-HT 933 was also studied for comparison. Rilmenidine (1 mg/kg s.c.) and B-HT 933 (2 mg/kg s.c.) induced significant and similar reductions in mean arterial pressure (-24 +/- 2 and -18 +/- 5 mm Hg. respectively) and in heart rate (-62 +/- 29 and -69 +/- 14 beats/min. respectively), whereas the vehicle had no significant hemodynamic effects. [14C]2-Deoxyglucose autoradiography revealed significant reductions in glucose use in the following structures of rilmenidine-treated rats: intermediolateral cell column of the thoracic spinal cord, area postrema, ventrolateral medulla, nucleus tractus solitarius, and cuneate nucleus, B-HT 933 did not significantly influence glucose use in any neuroanatomic structure examined. These results provide support for the functional involvement of brainstem cardiovascular control centres and the involvement of IPRs in the hypotensive response to rilmenidine.

Selective antibody-induced cholinergic cell and synapse loss produce sustained hippocampal and cortical hypometabolism with correlated cognitive deficits.

The physiological interrelationships between cognitive impairments, neurotransmitter loss, amyloid processing and energy metabolism changes in AD, cholinergic dementia and Down's syndrome are largely unknown to date. This report contains novel studies into the association between cognitive function and cerebral metabolism after long-term selective CNS cholinergic neuronal and synaptic loss in a rodent model. We measured local cerebral rates of glucose utilization ((14)C-2-deoxyglucose) throughout the brains of awake rats 4.5 months after bilateral intraventricular injections of a cholinotoxic antibody directed against the low-affinity NGF receptor (p75 NGF) associated with cholinergic neurons (192 IgG-saporin). Permanent cholinergic synapse loss was demonstrated by [(3)H]-vesamicol in vitro autoradiography defining presynaptic vesicular acetylcholine (ACh) transport sites. While other metabolic studies have defined acute and transient glucose use changes after relatively nonspecific lesions of anatomical regions containing cholinergic neurons, our results show sustained reductions in glucose utilization in brain regions impacted by cholinergic synapse loss, including frontal cortical and hippocampal regions, relative to glucose use levels in control rats. In the same animals, impaired cognitive spatial performance in a Morris water maze was correlated with reduced glucose use rates in the cortex and hippocampus at this time point, which is consistent with increased postmortem cortical and hippocampal amyloid precursor protein (APP) levels (45, 46). These results are consistent with the view of cholinergic influence over metabolism, APP processing, and cognition in the cortex and hippocampus.

Increased 3-nitrotyrosine in both sporadic and familial amyotrophic lateral sclerosis.

The pathogenesis of neuronal degeneration in both sporadic and familial amyotrophic lateral sclerosis (ALS) associated with mutations in superoxide dismutase may involve oxidative stress. A leading candidate as a mediator of oxidative stress is peroxynitrite, which is formed by the reaction of superoxide with nitric oxide. 3-Nitrotyrosine is a relatively specific marker for oxidative damage mediated by peroxynitrite. In the present study, biochemical measurements showed increased concentrations of 3-nitrotyrosine and 3-nitro-4-hydroxyphenylacetic acid in the lumbar and thoracic spinal cord of ALS patients. Increased 3-nitrotyrosine immunoreactivity was observed in motor neurons of both sporadic and familial ALS patients. Neurologic control patients with cerebral ischemia also showed increased 3-nitrotyrosine immunoreactivity. These findings suggest that peroxynitrite-mediated oxidative damage may play a role in the pathogenesis of both sporadic and familial ALS.

Metabolic dysfunction in familial, but not sporadic, amyotrophic lateral sclerosis.

Autosomal dominant familial amyotrophic lateral sclerosis (FALS) is associated with mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1). Previous studies have implicated the involvement of metabolic dysfunction in ALS pathogenesis. To further investigate the biochemical features of FALS and sporadic ALS (SALS), we examined SOD activity and mitochondrial oxidative phosphorylation enzyme activities in motor cortex (Brodmann area 4), parietal cortex (Brodmann area 40), and cerebellum from control subjects, FALS patients with and without known SOD mutations, SALS patients, and disease controls (Pick's disease, progressive supranuclear palsy, diffuse Lewy body disease). Cytosolic SOD activity, predominantly Cu/Zn SOD, was decreased approximately 50% in all regions in FALS patients with SOD mutations but was not significantly altered in other patient groups. Marked increases in complex I and II-III activities were seen in FALS patients with SOD mutations but not in SALS patients. We also measured electron transport chain enzyme activities in a transgenic mouse model of FALS. Complex I activity was significantly increased in the forebrain of 60-day-old G93A transgenic mice overexpressing human mutant SOD1, relative to levels in transgenic wild-type animals, supporting the hypothesis that the motor neuron disorder associated with SOD1 mutations involves a defect in mitochondrial energy metabolism.

Inhibition of neuronal nitric oxide synthase by 7-nitroindazole protects against MPTP-induced neurotoxicity in mice.

Several studies suggest that nitric oxide (NO.) contributes to cell death following activation of NMDA receptors in cultured cortical, hippocampal, and striatal neurons. In the present study we investigated whether 7-nitroindazole (7-NI), a specific neuronal nitric oxide synthase inhibitor, can block dopaminergic neurotoxicity seen in mice after systemic administration of MPTP. 7-NI dose-dependently protected against MPTP-induced dopamine depletions using two different dosing regimens of MPTP that produced varying degrees of dopamine depletion. At 50 mg/kg of 7-NI there was almost complete protection in both paradigms. Similar effects were seen with MPTP-induced depletions of both homovanillic acid and 3,4-dihydroxyphenylacetic acid. 7-NI had no significant effect on dopamine transport in vitro and on monoamine oxidase B activity both in vitro and in vivo. One mechanism by which NO. is thought to mediate its toxicity is by interacting with superoxide radical to form peroxynitrite (ONOO-), which then may nitrate tyrosine residues. Consistent with this hypothesis, MPTP neurotoxicity in mice resulted in a significant increase in the concentration of 3-nitrotyrosine, which was attenuated by treatment with 7 NI. Our results suggest that NO. plays a role in MPTP neurotoxicity as well as novel therapeutic strategies for Parkinson's disease.