UPTAKE AND RELEASE OF D-ASPARTATE, GABA, AND GLYCINE IN GUINEA-PIG BRAIN-STEM AUDITORY NUCLEI

This study attempts to determine if the medial (MSO) and lateral super ior olive (LSO), medial nucleus of the trapezoid body (MNTB), Ventral nucleus of the lateral lemniscus (VNLL), and central nucleus of the in ferior colliculus (ICc) contain glutamatergic synaptic endings. Microp unch and microdissection procedures provided fresh samples of these au ditory nuclei for the measurement of the high-affinity uptake and elec trically evoked release of exogenous D-[H-3]ASP. The study also determ ined if the LSO and MSO contain glycinergic synaptic endings by measur ing uptake and release of [C-14]-Gly in these nuclei, and whether the MNTB, VNLL, and ICc contain GABAergic endings by assessing the uptake and release of [C-14]GABA in these structures. Several strategies opti mized the evoked Ca2+-dependent release of the labeled amino acids. Th ese included the enhancement of high-affinity uptake during loading of the markers into the tissues, inhibition of uptake during the subsequ ent measurement of release, and use of an electrical stimulus current that evoked maximal Ca2+-dependent release. Each of these nuclei manif ested the high-affinity uptake and the evoked Ca2+-dependent release o f D-[H-3]Asp, suggesting the presence of synaptic endings that may use Glu or Asp as a transmitter. Similar findings suggest the presence of glycinergic synaptic endings in the LSO and MSG, and of GABAergic syn aptic endings in the MNTB, VNLL, and ICc.