Schizophrenia-Like Phenotype Inherited by the F2 Generation of a Gestational Disruption Model of Schizophrenia

Abstract

Both environmental and genetic factors contribute to schizophrenia; however, the exact etiology of this disorder is not known. Animal models are utilized to better understand the mechanisms associated with neuropsychiatric diseases, including schizophrenia. One of these involves gestational administration of methylazoxymethanol acetate (MAM) to induce a developmental disruption, which in turn produces a schizophrenia-like phenotype in post-pubertal rats. The mechanisms by which MAM produces this phenotype are not clear; however, we now demonstrate that MAM induces differential DNA methylation, which may be heritable. Here we demonstrate that a subset of both second (F2) and third (F3) filial generations of MAM-treated rats displays a schizophrenia-like phenotype and hypermethylation of the transcription factor, Sp5. Specifically, ventral tegmental area of dopamine neuron activity was examined using electrophysiology as a correlate for the dopamine hyperfunction thought to underlie psychosis in patients. Interestingly, only a subset of F2 and F3 MAM rats exhibited increases in dopamine neuron population activity, indicating that this may be a unique model with a susceptibility to develop a schizophrenia-like phenotype. An increase in dopamine system function in rodent models has been previously associated with decreases in hippocampal GABAergic transmission. In line with these observations, we found a significant correlation between hippocampal parvalbumin expression and dopamine neuron activity in F2 rats. These data therefore provide evidence that offspring born from MAM-treated rats possess a susceptibility to develop aspects of a schizophrenia-like phenotype and may provide a useful tool to investigate gene-environment interactions.

Figure 1

Methylazoxymethanol acetate (MAM) administration on gestational day (GD) 17 produces alterations in hippocampal DNA promoter methylation in F1 (detected by methylated DNA immunoprecipitation (MeDIP)-chip) and F2 (detected by MeDIP-seq) rats. Computer-assisted pathway analysis demonstrates similar statistically significant associations with specific diseases and disorders (a), as well as molecular and cellular functions (b). Select genes in the F2 population determined by independent pathway analysis as being related to schizophrenia are shown in c. F2 MAM rats display either increased (red) or decreased (green) absolute methylation scores relative to F2 saline controls. It is important to note that the transcription factor, Sp5, was similarly hypermethylated in both F1 and F2 generations.

Figure 2

Offspring born from methylazoxymethanol acetate (MAM)-treated parents exhibit enhanced ventral tegmental area (VTA) dopamine neuron activity. F2 generation rats born from MAM-treated fathers, regardless of the phenotype of the mother, display a significant increase in dopamine neuron population activity (a) when compared with F2 rats born from saline parents. Cross-fostered (c.f., dashed bar) rats born from MAM-treated mothers, but raised by control dams, also demonstrated an increase in dopamine neuron population activity. No significant differences were observed in the firing rate (b) or burst firing (c) of dopamine neurons between any crosses. *represents a significant difference from saline (♂) × saline (♀).

Figure 3

A subset of F2 generation rats displays an augmented dopamine neuron population activity. Examination of the data demonstrated that dopamine population activity followed a bimodal distribution with an R² of 0.93 (a). The percentage of F2 generation rats displaying a population activity ⩾1.5 is presented in (b) and the number of cells/track recorded for each subset is depicted in (c). *represents a significant difference from respective <1.5 cells/track population activity; ^#represents a significant difference from saline (♂) × saline (♀) rats.

Figure 4

A subset of F3 generation rats displays an augmented dopamine neuron population activity. F3 generation rats born from F2 methylazoxymethanol acetate (MAM) fathers display a significant increase in dopamine neuron population activity (a) when compared with F3 rats born from F2 saline parents. Interestingly, this phenotype was observed regardless of whether the F2 MAM father displayed an increase in dopamine neuron population activity (MAM (+)) or no change in activity (MAM (−)) (b). The percentage of F3 generation rats displaying a population activity ⩾1.5 is presented in c. ‡p=0.05 from F3 saline rats.

Figure 5

F2 generation rats display decreased levels of ventral hippocampal (vHipp) parvalbumin (PV). Representative films demonstrating PV levels in the vHipp are depicted in a, whereas the quantification of these data is presented in b. *represents a significant difference from saline (♂) × saline (♀) rats. There is a significant correlation between PV expression in the vHipp and the population activity of dopamine neurons in the ventral tegmental area (VTA; Pearson correlation; R²=0.9908; c).