Neonatal monosodium glutamate differentially alters two models of behavioral activity in conjunction with reduced hypothalamic endorphins.

Neurotoxic doses of monosodium glutamate were administered to neonatal male and female Sprague-Dawley rats for five days postpartum. The rats were tested at 6 months for alterations in two forms of activity--initial activity in an open field and overnight activity in a familiar cage. In comparison with age-, sex- and handling-matched littermate controls, experimental subjects exhibited increased open field behaviors and reduced overnight activity. Subsequent histology indicated marked reductions in arcuate and periarcuate cells which included but probably were not limited to beta-endorphin containing neurons. These findings indicate that neonatal MSG has long-term behavioral and neurological consequences, that some changes occur within behaviorally discrete systems, and that they may be associated with functional alterations within endogenous opioid systems, inter alia.