EFFECTS OF VAGAL-STIMULATION ON SWIMBLADDER BLOOD-FLOW IN THE EUROPEAN EEL ANGUILLA-ANGUILLA

The influence of the vagus nerve on swimbladder blood flow in the Euro pean eel (Anguilla anguilla) was characterized by recording the change s in blood flow rate and blood pressure following stimulation of the v agus nerve. After electrical stimulation, blood flow in the swimbladde r artery increased from 0.9 ml min(-1) to 2.1 ml min(-1). Video record ings of small vessels on the caudal side of the rete mirabile revealed an increase in erythrocyte velocity combined with a small vasodilatio n. This effect could not be blocked by injection of the alpha-adrenerg ic antagonist phentolamine, the beta-adrenergic antagonist propranolol or the muscarinic cholinoceptlor antagonist atropine. In all preparat ions with a high initial flow rate (>1.9 ml min(-1)), vagotomy resulte d in a marked decrease in blood flow (by approximately 80 %). This eff ect was not observed in preparations with a low initial swimbladder bl ood flow, Stimulation of the vagus nerve produced a decrease, and vago tomy produced an increase, in perfusion pressure in blood-perfused swi mbladder preparations. Histological studies revealed the presence of a ganglion in the vagus nerve located on the anterior part of the resor bing section of the swimbladder close to the origin of the ductus pneu maticus, which is probably associated with swimbladder function. These results suggest that swimbladder blood flow, at least to some extent, is under vagal tonic control. The effects do not, however, appear to involve the classical alpha- and beta-adrenergic or muscarinic cholino ceptor functions.