Małgorzata Zapała

Effect of 1,2,3,4,-tetrahydroisoquinoline administration under conditions of CYP2D inhibition on dopamine metabolism, level of tyrosine hydroxylase protein and the binding of [3H]GBR 12,935 to dopamine transporter in the rat nigrostriatal, dopaminergic system

Current concepts of Parkinsons disease (PD) postulate that interaction between neurotoxins and specific genetic background may play an important role in pathogenesis of PD. Therefore, the effect of multiple administration of 1,2,3,4-tetrahydroisoquinoline (TIQ) under conditions of CYP2D blockade on the expression of key markers of PD was studied in the rat striatum (STR) and substantia nigra (SN). TIQ administered alone (50 mg/kg i.p. twice daily for 14 days) markedly decreased the level of tyrosine hydroxylase protein (TH) in the STR; however, this effect was not accompanied by reduction of dopamine (DA) concentration and [(3)H]GBR 12,935 binding to dopamine transporter (DAT). Administration of CYP2D inhibitor, quinine, jointly with TIQ lowered the levels of TH and DA in that structure, but slightly increased DAT binding. In the SN, treatment with TIQ alone did not change TH level although it enhanced DA content and decreased [(3)H]GBR 12,935 binding to DAT in the substantia nigra pars compacta (SNc). Neither the TH level nor DA concentration was affected by the combined treatment, although DAT binding was still reduced in the SN. TIQ did not change the total DA catabolism in the STR, but caused its inhibition in the SN. It strongly depressed the levels of intraneuronal DA metabolite DOPAC and enhanced that of extraneuronal 3-MT in either structure. TIQ more weakly affected the levels of both DA metabolites in the presence of quinine. Our results suggest that endogenous TIQ may act rather as neuromodulator but not as parkinsonism-inducing neurotoxin in the rat brain.

Time course of changes in rotational behavior and DA metabolism in rats lesioned unilaterally with the selective proteasome inhibitor lactacystin

A growing body of evidence suggests that proteasomal dysfunction may play an important role in the pathogenesis of PD. The aim of our study was to examine the effect of unilateral administration of lactacystin, a selective proteasome inhibitor, on rotational behavior and striatal and nigral metabolism of dopamine (DA). Male Wistar rats were used for the study. The animals were injected unilaterally with a single dose of lactacystin (2.5 μg/2 μl) into the substantia nigra (SN) pars compacta. After injection, the rats were examined for spontaneous and apomorphine (0.25 mg/kg)induced rotational behavior in rotameter bowls throughout 60 min. All the testing was done on days 1, 4, 7, 14 and 21 after lactacystin administration. The animals were killed by decapitation on post-lesional days 1, 4, 7 and 21. The levels of DA and its metabolites were assayed in striatal and nigral homogenates using an HPLC method. Behavioral studies showed that the lactacystin-lesioned rats, but not the shamoperated animals, displayed a strong spontaneous circling behavior contralateral to the lesioned side on the 1 and 4 day after lactacystin treatment. This effect disappeared 1 week after the lesion. After apomorfine treatment on day 7, 14 and 21 days after surgery, no contralateral turning was observed in the lesioned rats. Biochemical studies demonstrated that lactacystin evoked a progressive loss in DA and its metabolites in the ipsilateral striatum and SN compared to the ipsilateral striatum of the sham-operated rats. The decreases started on the 7 day after lesion except for the drop in the nigral DA level which began already on the 4 day after surgery. After 21 days, the decline in DA level exceed 90% both in the striatum and SN. As regards DA catabolism, lactacystin evoked a progressive acceleration of MAO-dependent oxidative DA catabolism (DOPAC/DA), COMT-dependent Omethylation (3-MT/DA) and total DA catabolism (HVA/DA), both in the ipsilateral striatum and SN. The present study shows that lactacystin produces biochemical changes characteristic of degeneration of the DA system, namely a robust progressive decrease in DA level and an increase in DA catabolism. However, the presence of spontaneous contralateral rotations on the first few days after lesion indicates that other, probably non-DA mechanisms may play a role in this phenomenon. On the other hand, the lack of contralateral rotations after apomorphine up to three weeks after surgery suggests that the lactacystin-induced dramatic loss of striatal DA does not lead to supersensitivity of the striatal postsynaptic DA receptors.