Lack of tone response in retinal arterioles secondary to electrical field stimulation
Abstract
Purpose
The retinal vascular system is devoid of autonomic nervous supply and therefore retinal blood flow is autoregulated. However, it is unknown to what extent electrical activity in the retina during the visual process contributes to this flow regulation. The purpose of the present study was to study changes in vascular tone in retinal arterioles during electrical field stimulation (EFS) simulating neuronal activity around the vessels.
Methods
Porcine ciliary arteries and retinal arterioles were mounted in a myograph system and the tone was measured during: A) Six series of bipolar field stimulations with a frequency of 1 Hz successively doubled to reach 32 Hz. In each series 30 mA pulses with a duration of 0.3 msec were applied during 20 sec, followed by a resting period of 5 min. B) The successive addition of the Na+ channel opener veratridine in the concentrations: 10−6, 3 ×10−6, 10−5 and 3 × 10−5 mM. The experiments were repeated after addition of the Na+ blocker tetrodotoxin (TTX) and after removal of the perivascular retinal tissue.
Results
EFS had no significant effect on the tone of retinal arterioles (p > 0.66), whereas veratridine showed a concentration dependent relaxation of these vessels (p < 0.01). The effect was partially reduced by TTX which depended on the presence of perivascular retinal tissue.
Conclusions
EFS has no effect on the tone of porcine retinal arterioles in vitro, whereas veratridine induces relaxation of these vessels. The findings are in accordance with a lack of autonomic nervous supply in retinal arterioles.
