The distribution of enkephalin in the mediobasal hypothalamus of the mouse brain: effects of neonatal administration of MSG.

The immunocytochemical distribution of the pentapeptides, methionine- and leucine-enkephalin (Enk) were examined in the mediobasal hypothalamus of control mice with a neurotoxic lesion of the arcuate nucleus due to neonatal treatment of monosodium glutamate (MSG). In control mice immunoreactive Enk cells and fibers were present in the arcuate nucleus. Enk fibers were found in the subependymal, internal and external layers of the median eminence. At 60 days of age, mice receiving neonatal injections of MSG displayed symptoms of neuroendocrine deficiencies. Histochemical methods revealed a loss of Enk immunoreactivity from the arcuate nucleus and all layers of the median eminence. These results suggest that the lack of Enk cells and fibers in the mediobasal hypothalamus of MSG-treated animals is partially responsible for the endocrine dysfunctions exhibited by these animals.