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Neuroscience. 1995 Feb;64(4):847-50.

The immunocytochemical localization of N-acetylaspartyl glutamate, its hydrolysing enzyme NAALADase, and the NMDAR-1 receptor at a vertebrate neuromuscular junction.

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Laboratory of Molecular and Developmental Neuroscience, Massachusetts General Hospital East, Charlestown 02129, USA.


Although glutamate is thought to be the neurotransmitter at the invertebrate neuromuscular junction, acetylcholine is accepted as the primary neurotransmitter of the vertebrate motoneurons. N-acetylaspartylglutamate, a dipeptide localized in putative glutamatergic neurons in brain, is also found in high concentrations (> mM) in mammalian motoneurons and the ventral roots of spinal cord. N-acetylaspartylglutamate, which is released from neurons by depolarization in a Ca(2+)-dependent fashion, is implicated in glutamatergic transmission in two ways: it is a partial agonist at NMDA receptors, and it is cleaved to yield extracellular glutamate and N-acetylasparate by the specific peptidase N-acetylated alpha-linked acidic dipeptidase. Given the localization of N-acetylaspartylglutamate in motor neuronal perikarya and axons, we wondered whether N-acetylaspartylglutamate or glutamate cleaved from N-acetylaspartylglutamate by N-acetylated alpha-linked acidic dipeptidase may also play a role in neuromuscular transmission. Here we describe the immunocytochemical detection at the rat neuromuscular junction of N-acetylaspartylglutamate in terminals of motoneurons, of N-acetylated alpha-linked acidic dipeptidase in perisynaptic Schwann cells, and of the NMDAR-1 glutamate receptor subunit on postsynaptic muscle membranes. These results point to a potential role for N-acetylaspartylglutamate at the rat neuromuscular junction. Further, this is the first demonstration of a glutamate receptor protein at vertebrate neuromuscular synapses. Together with other recent findings, our results suggest that glutamate-like molecules are involved in neuromuscular transmission not only in invertebrates but also in veretebrates where they may modulate signaling by acetylcholine.

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