LOCALIZATION AND TRANSPORT OF N-ACETYLASPARTYLGLUTAMATE IN CELLS OF WHOLE MURINE BRAIN IN PRIMARY CULTURE

N-Acetylaspartylglutamate (NAAG) is the most abundant neuropeptide in the mammalian nervous system. Considerable data support the hypothesis that NAAG is synaptically released in a manner consistent with neurot ransmission. Primary murine brain cultures containing neurons and glia expressed 1.2-3.5 nmol of NAAG/mg of protein. In contrast to conclusi ons drawn from immunohistochemistry, pure glial cultures also expresse d high levels of NAAG (0.6-2.11 nmol/mg of protein). These data sugges t that although a subpopulation of neurons contains very high NAAG lev els, micromolar concentrations of the peptide also are present in glia . Both culture types demonstrated robust extracellular peptidase activ ity when incubated with NAAG, as well as peptide transport. Uptake of [H-3]NAAG was both temperature and sodium dependent, yet relatively in sensitive to the presence of extracellular glutamate. These results in dicate that synaptically released NAAG, as well as that which may be r eleased from glia, is removed from the extracellular space by direct u ptake as well as the robust enzymatic degradation of the peptide. A ki netic analysis of this NAAG transport (estimated K(m) = 1.8 muM) sugge sts a high-affinity NAAG transport system. The balance of the two proc esses of direct peptide uptake and peptide hydrolysis would markedly i nfluence the sequence of receptor-mediated events that follow NAAG rel ease.