The Effect of Maternal Methyl-Enriched Diet on the Number of Dopaminergic Neurons in the Ventral Tegmental Area in Adult Offspring of WAG/Rij Rats

Abstract

WAG/Rij rats are genetic model of absence epilepsy with comorbid depression. Pathologic phenotype in WAG/Rij rats was shown to be associated with reduced dopamine (DA) tone within the mesolimbic DAergic brain system. Previously, it was found that maternal methyl-enriched diet (MED) in the perinatal period increases DA content in the mesolimbic DAergic brain system and reduces absence seizures and comorbid depression in adult offspring of WAG/Rij rats. Ventral tegmental area (VTA), containing DA cells bodies, is a main source of the mesolimbic DA synthesis. The aim of this study was to test the hypothesis that increases in the mesolimbic DAergic tone induced by maternal MED in offspring may be due to an increase in the number of DA-synthesizing neurons in the VTA. Immunohistochemistry for thyrosine hydroxylase (TH) was used to assess the number of TH-immunopositive cells in adult offspring of WAG/Rij rats born to mothers fed control diet or MED and subjected or not subjected to behavioral testing for 2 consecutive days in the light-dark choice, open field, elevated plus maze and forced swimming tests. One hour after the forced swimming test animals were anesthetized. Brains were fixed using transcardial perfusion. The number of DAergic neurons was determined by the number of TH-immunopositive cells on brain slices at the level of VTA. The number of TH-immunopositive cells was counted in left and right hemispheres separately. A significant effect of maternal MED on the number of cells in the VTA expressing TH has been established. Adult WAG/Rij offspring born to mothers fed MED had an increased number of TH-immunopositive cells as compared with the offspring born to mothers fed control diet. Moreover, in WAG/Rij offspring born to mothers fed MED, the number of TH-immunopositive cells was greater in animals subjected to behavioral testing compared with animals not subjected to behavioral testing. The effects of maternal MED and behavioral testing on the number of TH-immunopositive cells in the VTA were equally expressed in the left and right hemispheres of the brain. Results suggest that maternal MED in the perinatal period can affect the developing mesolimbic DAergic brain system, promoting the generation and/or maintenance of DA neurons in the VTA, and thereby prevent the occurrence of genetic absence epilepsy and comorbid depression in the offspring of WAG/Rij rats.