ABSTRACT
The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes, via its metabolite MPP(+), damages of the nigrostriatal dopaminergic pathway, similar to those observed in Parkinson's disease. An intranigral injection of 10 microg MPP(+) in rat induced a decrease of about 30% of the neuronal dopamine transporter (DAT) activity 21 days after lesion. Based on the hypothesis that MPTP/MPP(+) neurotoxicity involves the nitric oxide (NO) production and/or an activation of poly(ADP-ribose) polymerase (PARP), we investigated the preventive effects of a treatment either with L-Name, a NO synthase (NOS) inhibitor or 3-aminobenzamide, a PARP inhibitor on the reduction of dopamine uptake induced by MPP(+). Rats received a daily injection i.p. of 50 mg/kg L-Name or 10 mg/kg 3-aminobenzamide 3 days before and during 21 days after the MPP(+) lesion. The results showed that inhibitors of NOS and PARP did not prevent the alteration of DAT activity induced by 10 microg MPP(+), indicating that NO and PARP were not involved in the biochemical cascade leading to the inhibition of rat DAT activity by MPP(+) in our experimental conditions.
Subject(s)
Enzyme Inhibitors/pharmacology , Membrane Glycoproteins , Membrane Transport Modulators , Membrane Transport Proteins/antagonists & inhibitors , Nerve Tissue Proteins , Neurons/drug effects , Nitric Oxide Synthase/antagonists & inhibitors , Parkinsonian Disorders/drug therapy , Poly Adenosine Diphosphate Ribose/antagonists & inhibitors , Substantia Nigra/drug effects , 1-Methyl-4-phenylpyridinium/pharmacology , Animals , Dopamine/metabolism , Dopamine/pharmacokinetics , Dopamine Plasma Membrane Transport Proteins , Drug Interactions/physiology , Male , Membrane Transport Proteins/metabolism , Neurons/enzymology , Neuroprotective Agents/pharmacology , Nitric Oxide/metabolism , Nitric Oxide Synthase/metabolism , Parkinsonian Disorders/enzymology , Parkinsonian Disorders/physiopathology , Poly Adenosine Diphosphate Ribose/metabolism , Presynaptic Terminals/drug effects , Presynaptic Terminals/metabolism , Radioligand Assay , Rats , Rats, Wistar , Substantia Nigra/enzymology , Substantia Nigra/physiopathology , Synaptosomes/drug effects , Synaptosomes/metabolism , TritiumABSTRACT
Previous studies have shown that dopamine (DA) uptake was decreased after preincubation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 1-methyl-4-phenylpyridinium (MPP(+)) in in vitro slice and synaptosome models. The present study, conducted with and without preincubation, attempted to determine whether inhibition results from a direct effect of neurotoxins on neuronal DA transporter or from an alteration of the transporter secondary to other toxic events. DA uptake was inhibited about 50% in the presence of MPTP+O(2) or MPP(+) (0.1, 1 and 5 mM) in rat striatal slices and synaptosomes. Such inhibition was obtained in synaptosomes preincubated for 150 min with MPP(+) and then washed. Inhibition of DA uptake was lower in slices preincubated with MPTP (5 mM)+O(2) and then washed (30%). Experiments in synaptosomes prepared from slices preincubated with MPTP or MPP(+) showed greater inhibition of DA uptake with MPTP. The results suggest that the inhibition of DA uptake in vitro by MPTP or MPP(+) results initially from a direct effect on the transporter during its penetration in nerve endings and subsequently from a transporter alteration related to toxic events. Thus, the preincubation of striatal slices followed by DA uptake measurement in synaptosomes would appear to be a good in vitro model for studying the dopaminergic toxicity of MPTP.
