Autonomic nerves containing substance P in the aqueous outflow channels and scleral spur of the guinea pig.

PURPOSE To study the innervation of the aqueous outflow channels and scleral spur by autonomic nerves containing substance P. METHODS The experiments were conducted on guinea pigs. Immunohistochemical techniques and capsaicin-ablation of the sensory nerves were used to investigate nerves containing substance P at the light and electron microscopic level. RESULTS Nerves containing substance P were observed in the aqueous outflow channels and scleral spur regions. The fine structures of these nerves had a similar pattern in those regions, and the labeled elements had abundant small vesicles, a few large vesicles, and numerous neurotubuli. Following capsaicin treatment, these nerves remained intact and no degenerated substance P-like immunoreactive nerves were found. CONCLUSIONS Nerves containing substance P are most likely of autonomic origin in view of their ultrastructural features. These nerves innervate the aqueous outflow channels and scleral spur, and are probably important for neurogenic influences on the intraocular pressure by the autonomic nervous system.