Regulation of GAP-43 protein and mRNA in nigrostriatal dopaminergic neurons after the partial destruction of dopaminergic terminals with intrastriatal 6-hydroxydopamine.

Changes in the level of GAP-43 and its mRNA in nigrostriatal dopaminergic neurons in an animal model of the presymptomatic period of Parkinson's disease were measured to find the characteristic features of GAP-43 in nigrostriatal dopaminergic neurons. Since the dopaminergic neurons possess a relatively large amount of GAP-43 protein and mRNA, the dopaminergic neurons must be endowed with specific functions related to those of GAP-43. In this study, dopaminergic axon terminals were partially destroyed by intrastriatal 6-hydroxydopamine (6-OHDA). Rats were decapitated 3, 14, and 56 days following treatment. Levels of GAP-43 and tyrosine hydroxylase (TH) in the striatum were detected by immunoblotting and quantified. The number of GAP-43 mRNA-positive neurons and that of TH mRNA-positive neurons in the substantia nigra pars compacta (SNc) were detected by in situ hybridization using alkaline phosphatase (ALP)-labeled probes. Levels of GAP-43 in the striatum showed no significant alteration during the period of the experiment, although levels of TH were gradually restored. The number of GAP-43 mRNA-positive neurons as well as that of TH mRNA-positive neurons in the SNc decreased. These results suggests that dopaminergic neurons restore their axon terminals with little change in GAP-43, and that transcription and/or stability of GAP-43 mRNA in the dopaminergic neurons are susceptible to the toxin, although the dopaminergic neurons can maintain the translational product in the terminals. This feature may be related with a degeneration of dopaminergic neurons in Parkinson's disease.

Effects of acute or prolonged administration of cabergoline on parkinsonism induced by MPTP in common marmosets.

The effects of a single treatment or chronic administration of cabergoline (1-[(6-allylergolin-8beta-yl)carbonyl]-1-[3-(dimethylamino)p ropyl]-3-ethyl-urea), a potent, long-lasting dopamine receptor agonist, on parkinsonism induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in common marmosets were studied. The administration of 0.2 mg/kg or a higer dose of cabergoline began to reverse parkinsonism-like symptoms 60 min after a subcutaneous injection, and showed steady and constant effects throughout the observation period. For prolonged administration, 0.2 mg/kg cabergoline was injected daily for 22 consecutive days. Locomotor activity in MPTP-treated animals increased until it reached its peak on the third day, then it gradually decreased. Akinesia scores, rating the quality of movements, were also improved, and the improvement was sustained up to the last day of chronic administration. None of the animals developed abnormal behaviors after either acute or chronic administration. These results suggest that cabergoline has long-acting effects in the marmoset model of parkinsonism, and that it will be a useful agent for the treatment of Parkinson's disease, particularly in cases with fluctuating motor disabilities.

Increased dopamine turnover in the putamen after MPTP treatment in common marmosets.

The differences in dopamine turnover rate between the putamen and the caudate nucleus in the striatum lesioned by a neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were studied in the common marmoset, a small New World monkey. Systemic administration of MPTP damaged equally and dose-dependently nigrostriatal dopaminergic neurons projecting both to the caudate nucleus and the putamen. The compensatory increase of dopamine turnover, however, occurred more prominently in the putamen than in the caudate. The neural connection and function of the caudate nucleus and the putamen have been differentiated anatomically or physiologically. The compensatory increase of dopamine turnover rate is another different aspect of functions between the caudate nucleus and the putamen. Dopaminergic neurons projecting to the putamen showed more prominent cell loss than those projecting to the caudate in Parkinson's disease or related disorders. The selective augmented turnover rate of lesioned dopaminergic neurons might be, at least partly, involved with selective degeneration of nigrostriatal neurons projecting to the putamen.

Enhanced dopamine release and phosphorylation of synapsin I and neuromodulin in striatal synaptosomes after repeated amphetamine.

Repeated, intermittent treatment of rats with amphetamine followed by a withdrawal period leads to an enhancement in amphetamine-induced dopamine release. We previously reported an increased stoichiometry of site 3-phospho-synapsin I and increased levels of phospho-Ser41-neuromodulin in striatum after repeated amphetamine. In this study, we examined whether the enhanced amphetamine-induced dopamine release and increased levels of these phosphoproteins would be detected in synaptosomes from rats pretreated and withdrawn from repeated amphetamine. Enhanced amphetamine-induced dopamine release was detected in striatal synaptosomes from rats treated with repeated amphetamine compared with controls. The enhanced dopamine release was Ca++ dependent. State-specific antibodies were used to measure the levels of site 3-phospho-synapsin I, phosphorylated by CaM kinase II, and phospho-Ser41-neuromodulin, phosphorylated by protein kinase C, in incubated striatal S1 fractions and synaptosomes. The levels of site 3-phospho-synapsin I and phospho-Ser41-neuromodulin were increased by 40% and 30%, respectively, in amphetamine-pretreated rats compared with controls. Total neuromodulin and synapsin I was not altered. There was a significant 26% increase in CaM kinase II activity in the synaptosomes from amphetamine-pretreated rats but no change in content. No change in protein kinase C activity or content of the alpha-isozyme was detected after repeated amphetamine. Our results demonstrate that the enhanced amphetamine-induced dopamine release and occurring after repeated amphetamine can be detected in synaptosome preparations. Repeated amphetamine leads to alterations in phosphorylation/dephosphorylation activities that can be detected in the incubated synaptosomes. Because the enhanced amphetamine-induced dopamine release after repeated amphetamine appears to be Ca++ sensitive, it is possible that the altered phosphorylation systems, and perhaps site 3-phospho-synapsin I and phospho-Ser41-neuromodulin, play a role in the enhanced dopamine release.