Ciliary ganglion stimulation. II. Neurogenic, intraocular pathway for excitatory effects on aqueous humor production...

Data obtained suggest that preganglionic stimulation of the ciliary ganglion produces an increase of aqueous humor formation and of facility of outflow "C" through the following neurogenic pathway: (1) the preganglionic fibers synapse in the ciliary ganglion as evidenced by depression of the response with nicotine applied topically to the ganglion. (2) The impulse proceeds to the equivalent of an intraocular interneuron which can be blocked by low concentrations of atropine and has been previously identified as being an E-2 receptor site. (3) From the interneuron, activity is ultimately exerted without further synapse on alpha-adrenergic receptors through the release of norepinephrine from the neuronal terminals. The adrenergic mechanism of action is supported by the inhibition of the responses by phenoxybenzamine, bretylium, and guanethidine. Constriction of efferent ciliary process blood vessels by neuron-released norepinephrine seems to be the end effect responsible for the increased production of aqueous humor. The site of the end response to increase "C" is unclear.