Neuronal cholecystokinin and schizophrenia: pathogenic and therapeutic studies.

Neuroleptic-free schizophrenic patients received caerulein, a potent analogue of cholecystokinin octapeptide, in a fixed- and rising-dose schedule. In addition, neuroleptic-treated patients received a single dose of the peptide with a 4-week follow-up. No significant change in mental status was observed after any of these administration schedules. Peak plasma levels of caerulein were noted at 20-30 min after IM administration; at this time no changes in cortical evoked potential were demonstrated. Furthermore, levels of cholecystokinin were not found to be reduced, but were in fact elevated in lumbar cerebrospinal fluid of schizophrenic patients. These data argue against the antipsychotic efficacy of systemic caerulein administration and, because evidence of CNS response to CCK is lacking, suggest that other pharmacologic strategies may be necessary to effectively modify central peptide systems with systemically administered drugs.