Elevated Striatal Dopamine Function in Immigrants and Their Children: A Risk Mechanism for Psychosis

Abstract

Migration is a major risk factor for schizophrenia but the neurochemical processes involved are unknown. One candidate mechanism is through elevations in striatal dopamine synthesis and release. The objective of this research was to determine whether striatal dopamine function is elevated in immigrants compared to nonimmigrants and the relationship with psychosis. Two complementary case-control studies of in vivo dopamine function (stress-induced dopamine release and dopamine synthesis capacity) in immigrants compared to nonimmigrants were performed in Canada and the United Kingdom. The Canadian dopamine release study included 25 immigrant and 31 nonmigrant Canadians. These groups included 23 clinical high risk (CHR) subjects, 9 antipsychotic naïve patients with schizophrenia, and 24 healthy volunteers. The UK dopamine synthesis study included 32 immigrants and 44 nonimmigrant British. These groups included 50 CHR subjects and 26 healthy volunteers. Both striatal stress-induced dopamine release and dopamine synthesis capacity were significantly elevated in immigrants compared to nonimmigrants, independent of clinical status. These data provide the first evidence that the effect of migration on the risk of developing psychosis may be mediated by an elevation in brain dopamine function.

Keywords: positron emission tomography; schizophrenia; stress.

Fig. 1.

(A) Significant effect of immigration on stress induced DA release in the whole striatum and in striatal subdivisions, including AST, LST, and SMST. WS (F = 8.08; df = 1, 52; P = .006), AST (F = 8.05; df = 1, 52; P = .006), LST (F = 5.22; df = 1, 52; P = .03), and SMST (F = 4.17; df = 1, 52; P = .05). (B) Effects of immigration on stress-induced dopamine release in the whole striatum by clinical vulnerability (mean and standard error of the mean, SEM).

Fig. 2.

(A) Significant effect of immigration on DA synthesis capacity in the whole striatum and SMST, with similar trends in the AST. WS (F = 4.95; df = 1, 73; P = .03), SMST (F = 9.24; df = 1, 73; P = .003), and AST (F = 3.28; df = 1, 73; P = .07). (B) Effects of immigration on DA synthesis capacity in the whole striatum by clinical vulnerability (mean and standard error of the mean, SEM).