Schizophrenia: do all roads lead to dopamine or is this where they start? Evidence from two epidemiologically informed developmental rodent models

Abstract

The idea that there is some sort of abnormality in dopamine (DA) signalling is one of the more enduring hypotheses inschizophrenia research. Opinion leaders have published recent perspectives on the aetiology of this disorder with provocativetitles such as ‘Risk factors for schizophrenia—all roads lead to dopamine’ or ‘The dopamine hypothesis of schizophrenia—thefinal common pathway’. Perhaps, the other most enduring idea about schizophrenia is that it is a neurodevelopmental disorder.Those of us that model schizophrenia developmental risk-factor epidemiology in animals in an attempt to understand how thismay translate to abnormal brain function have consistently shown that as adults these animals display behavioural, cognitiveand pharmacological abnormalities consistent with aberrant DA signalling. The burning question remains how canin uteroexposure to specific (environmental) insults induce persistent abnormalities in DA signalling in the adult? In this review, wesummarize convergent evidence from two well-described developmental animal models, namely maternal immune activation anddevelopmental vitamin D deficiency that begin to address this question. The adult offspring resulting from these two modelsconsistently reveal locomotor abnormalities in response to DA-releasing or -blocking drugs. Additionally, as adults theseanimals have DA-related attentional and/or sensorimotor gating deficits. These findings are consistent with many otherdevelopmental animal models. However, the authors of this perspective have recently refocused their attention on very earlyaspects of DA ontogeny and describe reductions in genes that induce or specify dopaminergic phenotype in the embryonic brainand early changes in DA turnover suggesting that the origins of these behavioural abnormalities in adults may be traced to earlyalterations in DA ontogeny. Whether the convergent findings from these two models can be extended to other developmentalanimal models for this disease is at present unknown as such early brain alterations are rarely examined. Although it ispremature to conclude that such mechanisms could be operating in other developmental animal models for schizophrenia, ourconvergent data have led us to propose that rather than all roads leading to DA, perhaps, this may be where they start.