Opposite effects of monosodium glutamate on the dopaminergic and GABAergic innervations of the median eminence and the intermediate lobe in the mouse.

In the mouse, monosodium glutamate (MSG) administered neonatally provokes the necrosis of most dopaminergic perikarya in the arcuate nucleus, as classically described, but also stimulates surviving neurons as shown by their increase in both size and immunoreactivity for tyrosine hydroxylase (TH). In the treated animals, TH-immunoreactive axons rarefy in the median eminence (ME) external zone, but postnatal dopaminergic innervation of the intermediate lobe (IL) normally develops and even, due to enlarged axonal varicosities, is more conspicuous than in the control littermate IL at same stages. gamma-Aminobutyric acid-ergic (GABAergic) projections in the ME and the IL, revealed with a glutamic acid decarboxylase antiserum, have the same distribution as TH-immunoreactive axons and present the same modifications in the MSG-treated animals. No clearcut differences in dopaminergic and GABAergic innervation patterns can be observed in the IL in treated and control adult mice.