Colocalization of neurotransmitters in presynaptic boutons of inhibitory synapses in the lamprey spinal cord.

Electron-microscopic immunocytochemical studies were performed to detect GABA and glycine immunoreactivity in presynaptic axon terminals in the central gray matter of the spinal cord of the lamprey Lampetra fluviatilis. The immunopositive presynaptic terminals contacting identified dendrites of motoneurons and unidentified postsynaptic profiles included terminals immunopositive for GABA only (44%) and glycine only (26%), as well as terminals containing GABA and glycine (30%). Glycine-immunopositive presynaptic terminals contained flattened synaptic vesicles. Large synaptic vesicles with dense cores were present along with classical synaptic vesicles in 74% of GABA-immunopositive boutons.