Are bilateral nigrostriatal dopaminergic pathways functionally linked in the rat brain? A microdialysis study in conscious rats.

In the present study, we have infused 6 prototypical drugs known to affect nigrostriatal dopaminergic neurons (kainate, baclofen, muscimol (10 mumol/l), picrotoxin (50 mumol/l), tetrodotoxin (TTX) (5 mumol/l) and 1-methyl-4-phenylpyridinium ion (MPP+) (10 mmol/l) via a microdialysis probe unilaterally into the left substantia nigra. During the infusion of these compounds, the extracellular content of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) was recorded simultaneously via microdialysis cannulas in both left and right striatum. Intranigral infusion of TTX, MPP+ and baclofen decreased dopamine release in the ipsilateral striatum, whereas muscimol, picrotoxin and kainate increased dopamine release. No changes were seen in the extracellular content of dopamine in the contralateral striatum. During all experiments, extracellular DOPAC increased in the ipsilateral striatum. No changes were seen in the extracellular content of DOPAC in the contralateral striatum. The present data provide no evidence that the bilateral nigrostriatal dopaminergic pathways are functionally linked in the rat brain.