Reduced number of striatal neurons expressing preprosomatostatin mRNA in rats with oral dyskinesias after long-term haloperidol administration.

Neuroleptic-induced oral dyskinesia in rats, a putative analogue to human tardive dyskinesia, may be due to degeneration within the striatum. Using unbiased stereological methods, a decreased number of striatal neurons expressing preprosomatostatin mRNA was observed only in rats that developed pronounced oral dyskinesias after 30 weeks of haloperidol administration. The amount of preprosomatostatin mRNA in each striatal neuron, measured in terms of optical densities of individual neurons, was not affected by haloperidol. A tendency toward a reduction in the number of NADPH-diaphorase positive neurons was observed in rats receiving haloperidol. These results indicate that the mechanism by which neuroleptics induce oral dyskinesias in rats, and perhaps tardive dyskinesia in humans, involves a functional disruption and possibly damage of a subpopulation of interneurons in the striatum.