Neonatal treatment with monosodium glutamate does not alter grooming behavior induced by novelty or adrenocorticotropic hormone

The increased grooming behavior observed in a novel environment has been attributed to release of peptides derived from proopiomelanocortin (POMC), such as ACTH, α-melanocyte-stimulating hormone (α-MSH), or β-endorphin, which themselves can elicit grooming. This is because novelty-induced grooming is attenuated both by hypophysectomy and by antiserum to ACTH injected into the cerebral ventricles. Administration of monosodium glutamate (MSG) to neonatal rats destroys neurons in the arcuate nucleus of the hypothalamus, depleting the brain of POMC peptides, and also hypothalamic dopamine and choline acetyl-transferase activity. Neonatal MSG treatment did not significantly alter the grooming scores of adult rats in either home or novel environments compared to saline-treated animals. There were also no differences between MSG- and saline-treated rats in the grooming scores observed following graded doses of ACTH_1-24 (0.2-1.0 μg) administered intracerebroventricularly. Thus if increased grooming in the novel environment is due to release into the ventricles of ACTH, α-MSH, β-endorphin, these peptides more likely derive from the pituitary rather than from brain cells, although the failure of the MSG treatment to produce quantitative depletions of cerebral POMC peptides, especially in the brain stem, leaves open the latter possibility.