Behavioral and neuroendocrine effects in rats of postnatal exposure to low dietary levels of maneb.

Several behavioral and neurochemical consequences of neonatal and/or postneonatal exposure to maneb (ethylenebisdithiocarbamate manganese), a popularly used fungicide, were investigated in male rats at dietary levels of 0, .5, 1.0, or 10 ppm. Three different periods of exposure were employed: (1) during the 28-day neonatal period; (2) during the 5 months postweaning; and (3) during both the neonatal and postweaning periods of life. Behaviorally, neonatal exposure to maneb depressed exploratory activity of the 30-day old wealings. As adults, neonatally treated rats demonstrated enhanced learning ability in an operant conditioning procedure. However, no facilitation of learning was found in animals whose exposure to maneb was restricted to only their postweaning period of life. Although unrelated to the behavioral changes, neuroendocrine effects were also found. Regional brain cholinesterase (ChE) activity was reduced in rats exposed to maneb during either the neonatal period alone or during the 5 month postweaning period alone, but continuous exposure to maneb during both the neonatal and postweaning periods did not appreciably affect brain ChE activity. Adult plasma corticosterone levels were elevated by exposure to maneb only postweaning. No such change was found in the neonatally exposed rats.