Protection by dihydroergocryptine of glutamate-induced neurotoxicity

Glutamate-induced cell death and formation of radicals can be reduced by lisuride in mesencephalic primary cell culture

Oxidative stress evoked by excitotoxicity is considered an important factor for the loss of dopaminergic neurons in Parkinson's disease. In vitro, protective effects of the dopamine agonist lisuride on complex I inhibition in primary dopaminergic cell culture have been reported. However, little is known about the effects of lisuride on glutamate-induced radical formation. Here, effects of lisuride on the formation of nitric oxide (NO) and superoxide radicals following glutamate exposure were studied on primary cell cultures prepared from mouse mesencephala. Glutamate treatment resulted in doubling of NO and superoxide radical formation, increased dopaminergic cell degeneration and extensively altered neuronal appearance. Pretreatment with lisuride significantly lowered the levels of either reactive species and increased the survival of dopaminergic neurons compared to glutamate-treated cultures. Moreover, the beneficial effect of lisuride could be completely inhibited by the D2/D3 receptor antagonist sulpiride when co-treated in cultures.

Redox mechanisms at the glutamate synapse and their significance: a review

This paper reviews what is currently known about the redox state of the glutamate synapse and its possible role in modulating synaptic plasticity and thus learning and neurocomputation. The hypothesis is presented that the growth or pruning of the synaptic spine is controlled in part by the balance in the synapse between neurodestructive pro-oxidants (e.g., nitric acid radical and hydrogen peroxide) and neuroprotective antioxidants (e.g., ascorbate and carnosine). In addition, there may be a role for catecholamines, in particular dopamine, related to its role in reinforcement signalling. Activation of the dopamine D2 receptor induces the synthesis of an antioxidant enzyme, possibly catalase. Dopamine may also affect the redox balance in the glutamate synapse directly by diffusion from the adjacent dopaminergic bouton-en-passage. Catecholamines are powerful antioxidants, scavengers of free radicals and iron chelators. Catecholamine-iron complexes are potent dismuters of superoxide ions. Additional agents participating in spine pruning may be neurotoxic catecholamine o-quinones present in the brain. This system may be at fault in schizophrenia and Parkinson's disease. Experiments to test the hypothesis are suggested.

The neurochemical basis of learning and neurocomputation: the redox theory

This paper presents a new theory of the biochemical basis of learning and neurocomputation. It has now been determined that excitatory synapses on dendritic spines in the brain are continually being formed and removed. This requires a neurochemical mechanism. There is evidence to suggest that the redox state of the glutamate synapse plays an important role in determining the growth or deletion of that synapse. This redox state is controlled by the balance between the pro-oxidants hydrogen peroxide and the nitric acid radical, and the antioxidants ascorbate, carnosine, the nitrosium ion and catecholamines. Key enzymes involved are prostaglandin H synthase and nitric acid synthase. Mediation of signals of reinforcing stimuli by the catecholamines may be mediated in part by their antioxidant effect on glutamate synapses. Some experiments to test the theory are suggested.

The biochemical basis of synaptic plasticity and neurocomputation: a new theory

The recent finding that dendritic spines (on which 90% of all excitatory synapses on pyramidal cells are formed) are not permanent structures but are continually being formed and adsorbed has implications for the present theoretical basis of neurocomputation, which is largely based on the concept of fixed nerve nets. This evidence would tend to support the recent theories of Edelman, Freeman, Globus, Pribram and others that neuronal networks in the brain operate mainly as nonlinear dynamic, chaotic systems. This paper presents a hypothesis of a possible neurochemical mechanism underlying this synaptic plasticity based on reactive oxygen species and toxic 0-semiquinones derived from catecholamines (i) by the enzyme prostaglandin H synthetase induced by glutamatergic NMDA receptor activation and (ii) by reactive nitrogen species derived from nitric oxide in a low ascorbate environment. A key factor in this neuromodulation may be the fact that catecholamines are potent antioxidants and free radical scavengers and are thus able to affect the redox mediated balance at the glutamate receptors between synapse formation and synapse removal that may be a key factor in neurocomputational plasticity. But catecholamines are also easily oxidized to neurotoxic 0-semiquinones and this may be relevant to the pathology of several diseases including schizophrenia. The relationship between dopamine release and positive reinforcement is relevant to this hypothesis.

Dihydroergokryptine vs. placebo in dementia of Alzheimer type: interim results of a randomized multicenter study after a 1-year follow-up

In order to evaluate the efficacy of dihydroergokryptine mesylate (DEK) - a semisynthetic ergot alkaloid having a neuroprotective activity through the activation of antioxidant enzymatic systems - in dementia of Alzheimer type, a long-term, randomized, placebo-controlled, double-blind study was carried out. The interim analysis after 1-year follow-up is here reported. Two-hundred-and-fifteen patients fulfilling the NINCDS-ADRDA criteria for probable Alzheimer's disease were enrolled by 14 geriatric and neurologic Italian centers. The study design included a 1-month pre-treatment phase with placebo; 1-year double-blind treatment with DEK or placebo; a further 1-year open phase of treatment with DEK. The active drug dosage was 5 mg bid orally administered for the first 2 weeks, 10 mg bid for the following 2 weeks, 20 mg bid for the following 11 months. Efficacy was assessed by means of Gottfries-Bråne-Steen (GBS) Rating Scale for dementia and Mental Deterioration Battery. The univariate analysis showed a significant improvement of GBS subscales and factors (with the exception of the Factor III, depression-anxiety). Multivariate analysis showed a significant difference between treatments in GBS scale (P=0.002) without any influence of age and illness duration. These results were confirmed by the end-point analysis carried out on GBS scores using baseline value as covariate. Minor adverse events were observed in 9 out of 108 patients (8.3%) of the DEK group and in 7 out of 107 (6.5%) of the placebo group. No change in blood pressure, heart rate and routine laboratory tests was observed. These preliminary results suggest positive symptomatic effects of DEK on elderly patients with probable Alzheimer's disease indicating a slowing down of the cognitive decline.

Melatonin stimulates brain glutathione peroxidase activity

Exogenously administered melatonin causes a 2-fold rise in glutathione peroxidase activity within 30 min in the brain of the rat. Furthermore, brain glutathione peroxidase activity is higher at night than during the day and is correlated with high night-time tissue melatonin levels. Glutathione peroxidase is thought to be the principal enzyme eliminating peroxides in the brain. This antioxidative enzyme reduces the formation of hydroxyl radicals formed via iron-catalyzed Fenton-type reactions from hydrogen peroxide by reducing this oxidant to water. Since the hydroxyl radical is the most noxious oxygen radical known, induction of brain glutathione peroxidase might be an important mechanism by which melatonin exerts its potent neuroprotective effects.