Parasympathetic nerves from the pterygopalatine ganglia may participate in development of cluster headaches, in vascular responses to hypertension and in modulation of damage due to stroke. Stimulation of the nerves elicits cerebral vasodilatation, but it is not known if the nerves tonically influence cerebrovascular tone. We hypothesized that parasympathetics provide a tonic vasodilator influence and tested that hypothesis by measuring cerebral blood flow in anesthetized rats before and after removal of a pterygopalatine ganglion. Ganglion removal led to reduced cerebral blood flow without changing blood pressure. Thus, parasympathetic nerves provide tonic vasodilatory input to cerebral blood vessels.
KeywordsCerebral blood flow; Parasympathetic; Vasodilatation Cerebral blood vessels are richly innervated both by central pathways (Reis, 1984;Vaucher & Hamel, 1995) and by sympathetic and parasympathetic nerves (Wahl & Schilling, 1993) and are further influenced by metabolic activity of local CNS neurons (Dirnagl et al., 1994;Harder et al., 2002). We have focused on the parasympathetic innervation derived from neurons of the pterygopalatine ganglion (PPG), also referred to as the "sphenopalatine ganglion". We, like others (Morita-Tsuzuki et al., 1993), have shown that electrical stimulation of the PPG causes cerebral vasodilatation . Furthermore, we have shown that the PPG is critical for expression of cerebral vasodilatation mediated by hypertension (Talman & Nitschke Dragon, 2000), that the dilatation is dependent on arterial baroreflexes (Talman et al., 1994), and that those dilatory influences are themselves mediated by nitric oxide synthesized by local neurons (Talman & Nitschke Dragon, 2004;Talman & Nitschke Dragon, 2007). One published study directly tested whether parasympathetic input to cerebral arteries may contribute tonic vasodilatory influences to the tone in those vessels and another tested that possibility in ophthalmic arteries . In both studies, however, cerebral blood flow (CBF) and cerebral vascular resistance were assessed by measuring pial arterial diameter and concomitant blood pressure and not by a direct measurement of flow. Furthermore, the study of cerebral vessels after removal of the PPG was performed in dogs . In contrast, some studies in which influences on cerebrovascular tone were assessed after interruption of parasympathetic input to the vessels reported no change in CBF. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. al., 1995b;Branston et al., 1995). In that varying influences on CBF also have been appreciated in different s...
