The effect of parenteral glutamate treatment on the localization of neurotransmitters in the mediobasal hypothalamus.
The localization of cholinergic, aminergic and amino acid-ergic neurones in the mediobasal hypothalamus has been studied in normal rat brain and in brains where neurones in nucleus arcuatus were destroyed by repeated administration of 2 mg/g body weight monosodium glutamate to newborn animals. In normal animals acetylcholinesterase staining, choline acetyltransferase and aromatic L-amino acid decarboxylase were concentrated in the median eminence and the arcuate nucleus. Glutamate decarboxylase was concentrated at the boundary between the ventromedial and the arcuate nuclei, with lower activity in the arcuate nucleus and very low activity in the median eminence. Nucleus arcuatus contained an intermediate level of high affinity glutamate uptake. In the lesioned animals, there were significant decreases in choline acetyltransferase, acetylcholinesterase staining and glutamate decarboxylase in the median eminence, whereas choline acetyltransferase activity and acetylcholinesterase staining, but not glutamate decarboxylase activity, were decreased in nucleus arcuatus. Aromatic L-amino acid decarboxylase was unchanged in all regions studied. The high affinity uptakes of glutamate, dopamine and noradrenaline, and the endogenous amino acid levels were also unchanged in the treated animals. The results indicate the existence of acetylcholine- and GABA-containing elements in the tuberoinfundibular tract. They further indicate that the dopamine cells in the arcuate nucleus are less sensitive to the toxic effect of glutamate than other cell types, possibly because they contain less glutamate receptors.