Neonatal monosodium glutamate. Effects upon analgesic responsivity and immunocytochemical ACTH/beta-lipotropin.
Neonatal administration of monosodium glutamate (MSG) produces neurotoxic degeneration of the retina and medial-basal hypothalamus, including the arcuate nucleus. Since this hypothalamic area contains the only neuronal cell bodies in brain which contain adrenocorticotrophic hormone (ACTH) and beta-lipotropin (beta-LPH) and beta-endorphin, destruction of these cells by MSG may interfere with pain responses mediated by nerve fibers arising from these perikarya. The present study examined whether MSG-treated rats, as compared to littermate controls, exhibited concomitant changes in the immunocytochemical distribution of ACTH and beta-LPH, and their reactivity to several analgesia-inducing manipulations. Although MSG-treated rats did not differ from control rats in their baseline reactivity to electric shock, they displayed an inability to exhibit analgesia following acute exposure to cold-water swim stress. In addition, MSG-treated rats showed an attenuated analgesic response following morphine administration. However, the analgesia elicited by either abrupt food deprivation, or the glucoprivic stress of 2-deoxy-D-glucose, was unaffected by neonatal MSG treatment. Concomitant with these selective analgesic deficits, MSG-treated rats displayed a marked immunocytochemical reduction in ACTH/beta-LPH perikarya and terminals in brain, but not pituitary. These data indicate that multiple pain-inhibitory systems exist, and that some rely upon an intact medial-basal hypothalamus to produce analgesia.
D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000698:Analgesia; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D005971:Glutamates / Q000494:pharmacology*; D006651:Histocytochemistry; D007031:Hypothalamus / Q000378:metabolism; D007124:Immunoenzyme Techniques; D008297:Male; D008636:Mesencephalon / Q000378:metabolism; D009020:Morphine / Q000494:pharmacology*; D051381:Rats; D012970:Sodium Glutamate / Q000494:pharmacology*; D008083:beta-Lipotropin / Q000378:metabolism*
D005971:Glutamates; D009020:Morphine; D000324:Adrenocorticotropic Hormone; D008083:beta-Lipotropin; D012970:Sodium Glutamate