To determine the function of cerebrovascular parasympathetic nerves, the calibre of rat pial arteries was continuously measured when the nerves (the postganglionic fibres originating from the sphenopalatine ganglion) were electrically stimulated in vivo. The pial arteries (72.3 ± 2.8 μm) dilated immediately after electrical stimulation (5 V, 10 Hz, 0.5 ms, 1 min duration). Their diameter increased 4.7 ± 0.1% (p < 0.01), 6.3 ± 1.7%, 5.1 ± 0.3% (p < 0.05), 6.3 ± 1.4%, at 15, 30, 45 and 60 s after initiation of stimulation, respectively. No significant change was observed in systemic arterial blood pressure or the expiratory carbon dioxide content during stimulation. This is the first direct demonstration of in vivo cerebrovascular neurogenic vasodilatation in the rat.
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