The aim of the present study was to examine the influence of a unilateral
6-hydroxydopamine (6-OHDA)-induced partial lesion of both the substantia nigra pars compacta (SNc, A9) and retrorubral field (RRF, A8) on the
tremor evoked by
harmaline.
6-OHDA (8μg/2μl) was injected unilaterally into the region of the posterior part of the SNc and RRF.
Harmaline was administered in a dose of 7.5mg/kg ip on the eighth day after the operation and
tremor of forelimbs, head and trunk was measured. We found that the lesion increased intensity of the
tremor induced by
harmaline but did not influence its character. Stereological examination of the lesion extent revealed losses of dopaminergic (
tyrosine hydroxylase-immunoreactive) neurons in the anterior (30%) and posterior (72%) SNc, as well as in RRF (72% on the average). Levels of
dopamine and all its metabolites, as well as
noradrenaline concentrations, were ipsilaterally moderately decreased in the caudate-putamen in the lesioned animals, however,
dopamine and
DOPAC in the anterior cerebellum were increased. In the caudate-putamen, the ipsi/contra ratio of
dopamine level correlated negatively, while that of
dopamine turnover positively with the
tremor intensity. However, in the anterior cerebellum an inverse relationship was found. Moreover, this symptom correlated positively with the
serotonin level and negatively with the 5-HIAA/
serotonin ratio on the contralateral side of the posterior cerebellum. The present results seem to indicate that the modulation of dopaminergic and serotonergic transmissions by the lesion modelling early stages of
Parkinson's disease may influence
tremor triggered in the cerebellum.