According to a currently popular biological hypothesis schizophrenic symptoms are caused by a hyperactivity in dopaminergic neurotransmission. Since cholecystokinin (CCK) is a neuromodulator of dopaminergic neurotransmission, the effects of CCK (0.3 microgram/kg; given in a single dose intravenously) were studied in six chronic paranoid schizophrenic patients. 2. Following 3 baseline assessments on separate days, the effects of CCK treatment were assessed immediately after the injection, daily for one week and weekly thereafter for 5 weeks by the Brief Psychiatric Rating Scale (BPRS) and by the Schizophrenia Subscale of the Present State Examination (SS-PSE). 3. One way analysis of variance revealed statistically significant changes in all BPRS factors as well as in the nuclear syndrome and in the total score of the SS-PSE. Dunnett's tests revealed that the time at which the changes from baseline became statistically significant was as follows: anxiety-depression factor of the BPRS, immediately after the injection; anergia factor of the BPRS, by day 2; thought disturbance factor of the BPRS, immediately after; activation factor of the BPRS, immediately after; hostile-suspiciousness factor of the BPRS, by day 1; total BPRS score, immediately after; nuclear syndrome of the SS-PSE, by day 1; and total score of the SS-PSE, by day 1. 4. It is concluded that further controlled studies of the antipsychotic properties of CCK are warranted.
