Infusions of tyrosine hydroxylase antisense oligodeoxynucleotide into substantia nigra of the rat: effects on tyrosine hydroxylase mRNA and protein content, striatal dopamine release and behaviour.

Abstract

Modulation of the transcriptional message of tyrosine hydroxylase was investigated in vivo in the rat nigrostriatal dopamine system with unmodified antisense oligodeoxynucleotide, mismatch oligodeoxynucleotide or vehicle controls. Oligodeoxynucleotide was infused (0.5 microgram/0.5 microliter/h) unilaterally into the substantia nigra by an osmotic minipump system over 14 days. The presence of oligodeoxynucleotide in the brain was verified by in situ hybridization and fluorescence labelling. Animals treated with unmodified antisense oligodeoxynucleotide showed ipsilateral turning behaviour when challenged systemically with the indirect dopamine agonist amphetamine, whereas mismatch- and vehicle-infused rats showed no such behavioural asymmetries. In the substantia nigra, antisense treatment had no effects on tyrosine hydroxylase mRNA, but it led to a reduction in tyrosine hydroxylase protein content. Tissue levels of dopamine, measured in postmortem tissue punches of the neostriatum and substantia nigra, were reduced in the oligodeoxynucleotide-treated hemisphere. Furthermore, basal extracellular levels of dopamine, monitored by in vivo microdialysis, were also lower in the neostriatum ipsilateral to antisense infusion and showed a weaker response to an amphetamine challenge when compared with the contralateral side. These effects were not observed after infusion of mismatch oligodeoxynucleotide or vehicle into the substantia nigra. Finally, the GABAergic enzyme glutamate decarboxylase was not affected in the antisense-treated substantia nigra, indicating that non-specific damage in this area was not caused by this treatment. Our results indicate that antisense oligodeoxynucleotide treatment against tyrosine hydroxylase in the substantia nigra has behavioural and neurochemical effects that are comparable with known actions of dopamine neurotoxins, which are conventional pharmacological tools for the depletion of dopamine. Furthermore, our data show the potential of antisense targetting to reveal new relationships between neurotransmitter-related enzymes and behavioural parameters, because the possibility of selectively and discretely manipulating tyrosine hydroxylase function is likely to produce new insights into the physiological and behavioural functions of the dopaminergic nigrostriatal system.