ULTRASTRUCTURAL-LOCALIZATION OF NITRIC-OXIDE SYNTHASE IMMUNOREACTIVITY IN THE CAT VENTROBASAL COMPLEX

This study describes the ultrastructural localization of nitric oxide synthase (NOS) immunoreactivity in the cat ventrobasal complex. NOS im munoreactivity was found in the cell bodies and dendrites of local cir cuit neurons and in vesicle-containing profiles. The vesicle-containin g profiles could be divided into two classes, those of dendritic origi n (presynaptic dendrite boutons) and those of axonal origin. The NOS l abelled axon terminals varied in size and packing density and were pri ncipally located in the extra-glomerular neuropil. These boutons prese nted a range of morphologies and it was not possible to determine the probable source based on morphological criteria. The NOS immunoreactiv e presynaptic dendrite boutons were found both within and outside glom eruli and established both pre-and post-synaptic relationships with ot her elements. Post-embedding GABA immunocytochemistry showed that some NOS immunoreactive axonal boutons and presynaptic dendrites were also immunopositive for GABA. This finding suggests that some of the NOS l abelled axonal boutons are of local circuit neuron origin. These resul ts suggest that local circuit neurons in the cat ventrobasal complex m ight be involved in specific, short range interactions using GABA and longer, more global interactions using nitric oxide.