Ultrastructural study of nitric oxide synthase-containing striatal neurons and their relationship with...

Single- and double-label electron microscopic immunocytochemistry was used to examine the ultrastructure of striatal neurons containing nitric oxide synthase (NOS+) and evaluate the synaptic relationship of NOS+ striatal neurons with those containing parvalbumin (PV+). In both the single-label and double-label studies, NOS+ perikarya were observed to possess polylobulated nuclei. In the single-label studies, NOS+ terminals were seen forming synaptic contacts with dendritic shafts and dendritic spines that did not contain NOS, but not with NOS+ perikarya or dendrites. In the double-label studies (using diaminobenzidine and silver intensified immunogold as markers), nitric oxide synthase and parvalbumin immunoreactions were found in two different populations of medium-sized aspiny striatal neurons. The PV+ axon terminals were seen forming symmetric synapses on the dendritic spines of neurons devoid of PV or NOS labeling, on PV+ dendrites, and on NOS+ soma and dendrites. In contrast, NOS+ terminals were not observed to form synaptic contacts with the dendrites or soma of either PV+ or NOS+ neurons. These findings suggest that NOS+ striatal interneurons form synaptic contact with the spines and presumably the dendrites of striatal projection neurons, but not with the dendrites or soma of PV+ or NOS+ striatal interneurons. NOS+ neurons do, however, receive synaptic input from PV+ neurons.