Alcohol deters the outgrowth of serotonergic neurons at midgestation

We have previously demonstrated that treatment of pregnant C57BL mice from gestation days 8 to 14 with alcohol with 20% ethanol-derived calories (EDC) reduced the number of serotonin (5-HT) neurons and retarded their migratio n in the fetal brains. In the present study, we obtained similar results wi th the use of 25% EDC and extended our previous findings by demonstrating t hat besides the alteration of the number of 5-HT neurons, prenatal alcohol exposure also affects their projecting fibers in their early development. P regnant C57BL mice were divided into an alcohol-exposed (ALC) group given 2 5% EDC (4.49%, v/v), a pair-fed group to the ethanol-fed group (PF) and a c how-fed group (Chow). The PF and Chow groups served as controls. Our result s showed that in the ALC group, when compared with the control groups, pren atal alcohol exposure with 25% EDC reduced the number of 5-HT-immunoreactiv e neurons in both the median and dorsal raphe, and the amount of 5-HT-immun oreactive fibers in the medial forebrain bundle (MFB). The diameter of the 5-HT-immunoreactive MFB was also reduced as a result of treatment. No signi ficant differences of the above parameters were found between the PF and Ch ow groups. The previous and present work confirmed that alcohol reduces the normal formation and growth of 5-HT neurons in the midbrain, Furthermore, the projection of 5-HT fibers, in density as well as in distribution, is re duced in the major trajectory bundle. This may affect the amount of 5-HT fi bers available to the forebrain. In light of the importance of the 5-HT sys tem in brain development, alcohol may affect the growth of the forebrain th rough its effect on 5-HT signaling. Copyright (C) 2001 National Science Cou ncil, ROC and S. Karger AG, Basel.