Increased and decreased choroidal blood flow elicited by cervical sympathetic nerve stimulation in the cat

The effect of electrical stimulation of the cervical sympathetic nerve on choroidal blood flow in the cat was investigated. Flow at various sites in 30 pentobarbital-anesthetized cats was continuously measured trans-sclerally using a laser Doppler flowmeter. Changes in either direction, increases and decreases, occurred in response to electrical stimulation of the peripheral cut end of the cervical sympathetic nerve. These changes in flow appeared to depend on the site of choroidal blood flow measurement, as decreases were seen at sites with a high baseline blood flow and increases at sites with a low baseline level. Both types of response were reduced when the cats were treated with the alpha-adrenoreceptor antagonist phentolamine, but not by treatment with the beta-adrenoceptor antagonist propranolol. The decrease in choroidal blood flow elicited by cervical sympathetic nerve stimulation appears to be mediated via the vasoconstrictor fibers in that nerve. A choroidal blood flow increase may occur as a secondary effect following vasoconstriction of the arterioles elicited by cervical sympathetic nerve stimulation, producing a passive net increase in choroidal blood flow.