Substantial evidence demonstrates that schizophrenia involves a dysregulated dopamine system, potentially driven by overactivity in the hippocampus. Postmortem studies of schizophrenia brains show a substantial loss of parvalbumin GABAergic interneurons in the hippocampus; loss of this neuron likely drives hippocampal hyperactivity and dysrhythmic activity, leading to an over-responsive dopamine system. Our studies suggest that when the hippocampus is hyperactive and dysrhythmic, the dopamine system is hyper-responsive to stimuli, which can underlie the resultant hallucinations and delusions. A major question is why there is interneuron loss in the hippocampus. Parvalbumin interneurons early in life are susceptible to damage due to stress. In a developmental disruption model of schizophrenia in the rat, we found that prepubertally these rats are more anxious, are hyper-responsive to stress, and show hyperactivity in the amygdala; furthermore relieving the stress early in life prevents the transition to “psychosis” in these rats. This suggests that schizophrenia susceptibility may be due to heightened sensitivity to the deleterious effects of stress. Indeed, multiple stressors given during this sensitive period to normal rats can lead to the schizophrenia phenotype. Moreover, elimination of the ability of the medial prefrontal cortex to regulate stress causes minor stressors to yield the schizophrenia phenotype.  In contrast, multiple stressors given to adult rats result in a phenotype resembling models of depression.  However, if the critical developmental period is first re-opened in the adult rat via histone decarboxylase inhibition, the same stressors now yield a schizophrenia phenotype.This leads to the intriguing possibility that genetic predisposition does not cause schizophrenia, but instead like the developmental disruption model causes the individual to be hypersensitive to the deleterious effects of stress. Moreover, stress susceptibility may be a common link in familial risk for schizophrenia and depression. Therefore, controlling stress early in life in susceptible individuals may be an effective means to prevent transition to schizophrenia later in life.

Learning Objectives: 

1. To understand how stress during adolescence can lead to pathological changes in the brain and the emergence of psychosis in the adult
2. To understand how alterations in different regions of the dopamine system can underlie pathophysiological changes in schizophrenia and depression
3. To understand why parvalbumin interneurons are particularly sensitive to the deleterious impact of stress during adolescence but not adulthood