Effects of the unilateral striatal lesion on neurotransmitter markers in the contralateral striatum and both substantia nigrae of the rat.

We investigated quantitative changes in possible neurotransmitters and their biosynthetic enzymes in the contralateral striatum and both substantia nigrae following unilateral electrothermic lesions of the striatum in the rat. Two types of changes were observed: (1) the first ones were long-lasting (up to 56 post-operative days) effects and consisted in a decrease of GABA content and tyrosine hydroxylase activity in the ipsilateral substantia nigra due to the anterograde and retrograde degeneration of striatal efferent and afferent fibres, respectively, and in a marked increase of glutamate and GABA contents in the contralateral striatum resulting possibly from a modified activity of the collaterals of the glutamatergic corticostriatal fibres and a subsequent secondary increase of GABA. The latter interpretation was supported by the finding that the changes observed were abolished by an additional callosal transection; (2) the second series of changes were transient (only found at 3-7 post-operative days) effects represented by an increase in GABA content, a decrease of tyrosine hydroxylase activity, and a decrease of dopamine content, which mostly appeared in the contralateral substantia nigra. The decrease of dopamine markers may be a subsequent secondary effect of the increase of GABA in the substantia nigra. These results suggest that the contralateral increase of the amino acid transmitters in the striatum and the increase followed by decrease of transmitter markers in the contralateral substantia nigra could be a "plastic" or "compensatory" biochemical response to the unilateral striatal lesions.