Response of extrapyramidal and limbic neurotensin systems to phencyclidine treatment

Although phencyclidine (PCP) has several neurochemical effects, the most pharmacologically relevant are thought to be its ability to antagonize the activity of N-methyl- d-aspartate (NMDA)-type glutamate receptors and to increase extracellular dopamine concentrations. In order to elucidate the nature and consequence of PCP actions on glutamatergic and dopaminergic pathways, this study examined the response of extrapyramidal and limbic neurotensin systems to this drug. Multiple, but not single, doses of PCP caused increases in striatal neurotensin-like immunoreactivity content of 150–200% of control. These effects were blocked by the dopamine D 1 receptor antagonist, SCH 23390, suggesting they were caused by PCP-mediated enhanced dopamine activity at dopamine D 1 receptors. In contrast, MK-801 (dizocilpine), a selective NMDA receptor antagonist that acts at the same site as PCP, had no effect on neurotensin-like immunoreactivity content when given alone. In addition, coadministration of MK-801 with PCP did not alter the effect of PCP on striatal neurotensin-like immunoreactivity content. This lack of effect suggests that the actions of PCP on NMDA receptors was not involved in the neurotensin response. The PCP effect on neurotensin striatal pathways also appeared not to be associated with the dopamine D 2 or γ-aminobutyric acid (GABA) systems: a possible role for the sigma receptor in this effect could not be eliminated. Administration of multiple doses of PCP also affected neurotensin-like immunoreactivity content in the nucleus accumbens (160% compared to control) and frontal cortex (40% compared to control), but not the substantia nigra. The neurotensin effects of PCP are compared to those of another psychotomimetic drug of abuse, methamphetamine.