Efferent and. afferent innervation of primate trabecular meshwork and scleral spur

PURPOSE. TO determine the correlation between nerve terminals and cells or extracellular matrix (ECM) components in different portions of the primate trabecular meshwork (TM) and scleral spur (SS). METHODS. Serial sagittal and tangential sections through the anterior segme nts of 10 cynomolgus monkey eyes and 12 human eyes were investigated immuno histochemically with antibodies against the vesicular acetylcholine transpo rter (VACHT), vasoactive intestinal polypeptide (VIP), tyrosine-hydroxylase (TH), neuropeptide Y (NPY), substance P (SP), calcitonin gene-related pept ide (CGRP), and galanin (GAL) and with a reduced nicotinamide adenine dinuc leotide phosphate-diaphorase (NADPHd) reaction. The distribution of the ter minals was compared with that of alpha-smooth-muscle actin (SMA) staining i n TM and SS. The relationship between terminals and adjacent cells or ECM c omponents was also studied in ultrathin sections through the TM and SS of 1 1 monkey eyes cut in sagittal, tangential, and frontal planes. RESULTS. NADPHd-positive nerve terminals were present, especially in the ou ter portion of both human and monkey TM and in the SS. VACHT-immunoreactive (IR) fibers were found in human but not in monkey SS and TM. The fibers we re most numerous in the elongated SS and posterior TM where most cells also stained for SMA. SP- and CGRP-IR nerve endings were also more numerous in the outer TM and SS than in the inner TM. Ultrastructurally, staining for S P was seen in nerve endings containing mitochondria and dense core vesicles and was in contact with the cribriform elastic network. In the posterior S S of monkey eyes were large terminals similar to those previously described in human eyes. CONCLUSIONS. The results show for the first time that in the primate TM and SS, there are cholinergic and nitrergic nerve terminals that could induce contraction and relaxation of TM and SS cells. Terminals in contact with th e elastic-like network of the TM and containing SP-IR resemble afferent mec hanoreceptor-like terminals in other parts of the body. These findings rais e the possibility that the TM may have some ability to self-regulate aqueou s humor outflow.