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Clemens A Strohmaier, Karolina Motloch, Christian Runge, Andrea Trost, Alexandra Kaser-Eichberger, Jeffrey W Kiel, Herbert Reitsamer; Choroidal blood flow responses to central electrical stimulation in the rat: Effect of nitric oxide synthase inhibition. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4630.
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© ARVO (1962-2015); The Authors (2016-present)
Electrical brain stem stimulation at the coordinates of the nucleus salivatorius superior (SSN) is known to increase choroidal blood flow, but the neurotransmitters involved are not known. In the present study we investigated the effect of NO synthase inhibition on choroidal blood flow responses to SSN stimulation in rats.
Male Sprague-Dawley rats (n= 10) were anesthetized using pentobarbital sodium (50mg/kg ip. initially, supplemented iv. as needed) and paralyzed with gallamine triethiodide (1 mg/kg, iv). The animals were artificially ventilated and the femoral artery and vein were cannulated for blood pressure measurement and drug administration. Choroidal blood flow was measured using Laser Doppler flowmetry. After a craniotomy was performed, a unipolar stainless steel electrode was inserted into the brainstem at the coordinates of the SSN using a stereotactic instrument. Stimulations were performed at 20Hz, 9 µA, 1 ms pulse duration and 200 pulses. After baseline measurements with subsequent SSN stimulations, L-NAME (L-NG-Nitroarginine methyl ester , 10 mg/kg) was applied intravenously and the stimulation protocol was repeated.
Stimulation at the SSN coordinates increased choroidal blood flow from 248.17 ± 46.92arbitrary units (a.u.) to 347.30 ± 60.44 a.u. (p ≤ 0.05). The choroidal resistance index decreased by 33%. After L-NAME application, choroidal blood flow increased from 218.77 ± 41.21 a.u. to 290.66 ± 57.97 a.u. (p ≤ 0.05), corresponding to a resistance decrease by 29%.Mean arterial blood pressure increased from 99.12 ± 4.67 mmHg to 139.30 ± 6.06 mmHg after L-NAME application and was not altered by SSN stimulation.
Electrical stimulation at the SSN coordinates yielded a significant increase in choroidal blood flow, the application of L-NAME did not block the stimulation effect and thus indicates that NO is not the primary neurotransmitter involved in mediating the stimulation effect.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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