Effect of Δ9-Tetrahydrocannabinol on Intraocular Pressure After Removal of Autonomic Input

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Abstract
Sympathetic input to the anterior segment of the eyes of cats was unilaterally removed by either superior cervical ganglionectomy or treatment with 6-hydroxydopamine. Parasympathetic input was unilaterally removed by extirpation of the ciliary ganglion. Δ9-tetrahydrocannabinol ( Δ9-THC; 20 μg/hr) was delivered unilaterally to the denervated eyes and to eyes of surgically intact control cats via osmotic minipumps and connecting extraocular cannulas over a total period of nine days. The results indicated that the degree of reduction of intraocular pressure by Δ9-THC was not affected by removal of input from either branch of the autonomic nervous system. Outflow facility during chronic administration of THC showed a two-to-three fold increase. Ciliary ganglionectomy alone produced a moderate decrease in intraocular pressure that endured for one week. These findings indicate that neither adrenergic nor cholinergic input to the cat eye is apparently required for the mediation of the tension lowering effect of THC. They additionally suggest that cholinergic input may normally play a role in the regulation of steady-state intraocular pressure levels, presumably by modulating aqueous humor formation.