THE EFFECT OF MERCURY-VAPOR ON CHOLINERGIC NEURONS IN THE FETAL BRAIN- STUDIES ON THE EXPRESSION OF NERVE GROWTH-FACTOR AND ITS LOW-AFFINITY AND HIGH-AFFINITY RECEPTORS

The effects of mercury vapour on the production of nerve growth factor during development have been examined. Pregnant rats were exposed to two different concentrations of mercury vapour during either embryonic days E6-E11 (early) or E13-E18 (late) in pregnancy, increasing the po stnatal concentration of mercury in the brain from 1 ng/g tissue to 4 ng/g tissue (low-dose group) or 11 ng/g (high-dose group). The effect of this exposure in offspring was determined by looking at the NGF con centration at postnatal days 21 and 60 and comparing these levels to a ge-matched controls from sham-treated mothers. Changes in the expressi on of mRNA encoding NGF, the low- and high-affinity receptors for NGF (p75 and p140 trk, respectively) and choline acetyltransferase (ChAT) were also determined. When rats were exposed to high levels of mercury vapour during early embryonic development there was a significant (62 %) increase in hippocampal NGF levels at P21 accompanied by a 50% decr ease of NGF in the basal forebrain. The expression of NGF mRNA was fou nd to be unaltered in the dentate gyrus. The expression of p75 mRNA wa s significantly decreased to 39% of control levels in the diagonal ban d of Broca (DB) and to approximately 50% in the medial septal nucleus (MS) whereas no alterations in the level of trk mRNA expression were d etectable in the basal forebrain. ChAT mRNA was slightly decreased in the DB and MS, significantly in the striatum. These findings suggest t hat low levels of prenatal mercury vapour exposure can alter the level s of the NGF and its receptors, indicating neuronal damage and disturb ed trophic regulations during development.