The content and nature of the preprotachykinin (PPT; i.e., substance P/neurokinin A-encoding) messenger RNAs (mRNAs) present in rat brain striatum and limbic tissues were determined by RNA protection experiments. The rank order of PPT mRNA concentration was striatum greater than nucleus accumbens much greater than bed nucleus of the stria terminalis greater than hypothalamus, amygdala and septum. The proportion of beta-(full length) to gamma-(minus exon 4) PPT mRNA was invariant (40/60) among the tissues tested. Because these brain regions receive prominent dopaminergic innervations, the effects of repeated treatment with dopamine antagonists (antipsychotic drugs) on PPT gene expression were assessed. The prototypical dopamine antagonists haloperidol and chlorpromazine decreased striatal PPT mRNA, had no effect on PPT mRNA in the nucleus accumbens or bed nucleus of the stria terminalis, and increased septal PPT mRNA levels. In contrast, the atypical antipsychotic drugs clozapine and l-sulpiride did not alter striatal or septal PPT mRNA, but increased PPT mRNA content in the nucleus accumbens and bed nucleus. The correlation between the effects of typical and atypical antipsychotic drugs on rat striatal and limbic PPT gene expression and their clinical side effects and therapeutic efficacy is discussed.