Growth, endocrinological and behavioral deficits after monosodium l-glutamate in the neonatal rat: possible involvement of arcuate dopamine neuron damage

Abstract

(1) The syndrome induced by the systemic administration of monosodium l-glutamate (MSG) to neonatal rats was investigated. (2) Animals receiving five injections of 4 mg/g of MSG (MSG V) in the first 10 days of life showed, as adults, growth, endocrinological, and behavioral abnormalities, whereas those receiving one injection (MSG I) showed few of the characteristic symptoms associated with neonatal MSG treatment. (3) MSG V females were markedly hypoactive ten weeks after weaning as measured in circular photocell activity cages in the dark part of the rats' day-night cycle. (4) MSG V rats were extremely stunted and obese (as determined by the Lee index) but appeared normophagic. (5) A previously unreported aspect of MSG toxicity, tail automutilation, occurred in a large proportion of MSG I and MSG V animals, with the highest incidence in MSG V females. (6) MSG V animals were hypothyroid as measured by radioimmunological determinations of serum triiodothyronine (T 3) and free thyroxine index (FTI). In addition, MSG V females had smaller ovaries, uteri, and pituitaries when compared with saline-treated controls. (7) Histochemical examination of the hypothalamic arcuate area revealed a marked loss of dopaminergic perikarya in MSG V, but not MSG I animals; other catecholamine systems appeared intact. This raises the possibility that damage to the tubero-infundibular dopamine system may contribute to endocrinological and other deficits observed after neonatal MSG treatment.