A Perioculomotor Nitridergic Population in the Macaque and Cat

Abstract

We determined the distribution of cells containing synthetic enzymes for the unconventional neurotransmitter, nitric oxide, with respect to the known populations within the oculomotor complex. The oculomotor complex was investigated in monkeys and cats by use of histochemistry to demonstrate nicotinamide adenine dinucleotide phosphate diaphorase positive (NADPHd(+)) cells and antibodies to localize neuronal nitric oxide synthase positive (NOS(+)) cells. In some cases, wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) was injected into extraocular muscles to allow comparison of retrogradely labeled and NADPHd(+) cell distributions. The distribution of the NADPHd(+) and NOS(+) neurons did not coincide with that of preganglionic and extraocular motoneurons in the oculomotor complex. However, labeled perioculomotor neurons were observed. Specifically, in monkeys, they lay in an arc that extended from between the oculomotor nuclei into the supraoculomotor area (SOA). Comparison of WGA-HRP-labeled medial and superior rectus motoneurons with NADPHd staining confirmed that the distributions overlapped, but showed that the C- and S-group cells were not NADPHd(+). This suggested that NADPHd(+) cells are part of the centrally projecting Edinger-Westphal population (EWcp). Examination of the NADPHd(+) cell distribution in the cat showed that these cells were indeed found primarily within its well-defined EWcp. Based on their similar distributions, it appears that the peptidergic EWcp neurons, which project widely in the brain, also may be nitridergic. While the preganglionic and C- and S-group motoneuron populations do not use this nonsynaptic neurotransmitter, nitric oxide produced by surrounding NADPHd(+) cells may modulate the activity of these motoneurons.