Purpose: To determine the presence and distribution of CB1 cannabinoid receptors within the human eye.
Methods: A subtype-specific affinity-purified polyclonal antibody to the cannabinoid CB1 receptor was used to determine CB1 localization. Postmortem human eyes were fixed in methacarn and embedded in paraffin. Sagittal sections were mounted on slides and immunostained using antibodies to the CB1 receptor. Antibody binding was detected either by using peroxidase conjugated secondary antibodies and developing with diaminobenzidine or by using fluorescent secondary antibodies.
Results: Strong CB1 receptor labeling was detected in the ciliary epithelium, the corneal epithelium, and endothelium of the anterior human eye. Strong-to-moderate levels of CB1 staining were found in the trabecular meshwork and Schlemm's canal. Moderate labeling was detected in the ciliary muscle and in the blood vessels of the ciliary body. Moderate-to-light labeling also was detected in the sphincter papillae of the anterior human eye. Staining for CB1 receptors also was detected in human retina. The two synaptic layers of the retina and the inner and outer plexiform layers, were both moderately stained for CB1. In addition, moderate labeling was detected in the inner nuclear layer, and the ganglion cell layer. Strong labeling was detected in the outer segments of photoreceptors. No staining was observed in the corneal stroma or in the choroid.
Conclusions: The wide distribution of cannabinoid CB1 receptors in both the anterior eye and the retina of humans suggests that cannabinoids influence several different physiological functions in the human eye.