Cells in the brain communicate with one another by releasing chemical messengers, called neurotransmitters, which activate specific receptors on the next cell. Understanding the brain thus requires a knowledge of the identity and function of these neurotransmitters. Yet, despite thirty years of research on the mammalian visual pathway, the neurotransmitters used by the cells remain largely unknown. Receptors for the excitatory amino acids are involved in this neurotransmission, but evidence suggests that neither of the obvious candidates, aspartate or glutamate is the neurotransmitter. N-acetylaspartylglutamate (NAAG) is an endogenous brain peptide that acts at an excitatory amino acid receptor. Evidence is mounting that NAAG may be a neurotransmitter for retinal ganglion cells. Dr. Tieman's experiments are directed at this question. The lateral geniculate nucleus (LGN) is one of the areas of the brain that receives input from the eye. Dr. Tieman will examine the responses of LGN neurons to stimulation of the input from the eye and to direct application of NAAG. If NAAG is the neurotransmitter, then these responses should be the same. Immunocytochemistry is a technique that uses antibodies to localize specific chemical compounds in brain. Dr. Tieman will use this technique for NAAG combined with a variety of other techniques, such as electron microscopy, to better characterize both the cells that contain NAAG and NAAG's distribution within these neurons. For example, if NAAG is the neurotransmitter for retinal ganglion cells, then it should be localized at the synapse, which is part of the cell that is specialized for communicating with the next cell. Results obtained from these experiments should help to clarify NAAG's role in the visual system and provide a better understanding of intercellular communication in the brain.***//
