GLUTAMATE CONTAINING NEURONS IN THE CAT SUPERIOR COLLICULUS REVEALED BY IMMUNOCYTOCHEMISTRY

Glutamate is the probable neurotransmitter of both retinal and cortica l afferents to the cat superior colliculus (SC). The present study sho ws that glutamate is also contained in many postsynaptic neurons in SC . The distribution, morphology, and ultrastructure of neurons in SC we re examined using glutamate antibody immunocytochemistry. Labeled cell s were widely distributed throughout, but a specific laminar pattern w as evident. Relatively few cells were found in the zonal and upper sup erficial gray layers (SGL). A dense band of intensely labeled neurons was found within the deep superficial gray and upper optic layers. Man y cells were also labeled in the deeper layers. Labeled cells had vari ed sizes and morphologies. Soma diameters ranged from 9-67 mu m, with a mean of 22 mu m Cells with stellate, vertical fusiform, and multipol ar morphologies were labeled. Cells in the deep subdivision all had mo rphologies and sizes typical of projection neurons. To determine if la beled cells in the dense band were also projection neurons, WGA-HRP wa s injected into the lateral posterior nucleus and these sections were double-labeled with the glutamate antibody. Over one-half of cells in the dense band that were labeled by HRP were also obviously labeled by antibody. At the electron-microscope level, both medium- and large-si zed neurons were also labeled by glutamate antibodies. These cells had different but characteristic morphologies.