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Herwig Brandtner, Christian Runge, Clemens Strohmaier, Barbara Bogner, Andrea Trost, Falk Schrödl, Günther Grabner, Herbert Reitsamer; The Relationship between Choroidal Blood Flow Response and Facial Nerve Stimulation Frequency is altered by L-NAME. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6041.
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To investigate the frequency-dependent effect of facial nerve stimulation on choroidal blood flow. In contrast to our previous stimulation protocols we put the focus on different frequencies as the resulting stimulation-response curve seems to be a powerful instrument for further investigations on the neurovascular coupling in the eye. In addition, the effect of L-NAME on the frequency dependence of the effect of facial nerve stimulation on choroidal blood flow was investigated in the present study.
Mean arterial pressure (MAP), intraocular pressure (IOP) and choroidal blood flow (ChorBF) were measured in anesthetized new Zealand white rabbits (n = 4). MAP and IOP were measured invasively and Laser Doppler Flowmetry was used to measure choroidal blood flow. The facial nerve, which carries parasympathetic fibers to the ciliary ganglion, was exposed in the middle ear cavity using an approach through the tympanic membrane. A platinum electrode was used to apply pulse trains between 2 and 20 Hz (200µs, 2.5 mA, total duration of 20 s) before and after application of the non selective NOS inhibitor, L-NAME (N-ω-Nitro-L-Arginine-methylester, 128mg/kg, i.v. bolus).
There is a direct correlation between frequency and response. With increasing frequency the IOP and the ChorBF increase. The use of the L-NAME shifts the stimulation-response curve for ChorBF as well as for IOP downwards (see plot 1 and 2), but as previously shown it cannot block the stimulation response completely, on the contrary, the effect is smaller than expected from other reports in the scientific literature.
As the stimulation-response curves illustrates the effect of L-NAME it seems to be a useful tool to investigate the effect of antagonists of other players in neurovascular coupling of the eye like vasoactive intestinal peptide (VIP) or pituitary adenylate cyclase-activating polypeptide (PACAP).
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