The action of of GTN on meningeal vessels in open cranial window preparation.

<p><b>A</b>, examples of meningeal vessels before (upper image) and after GTN administration (lower image). <b>B</b>, the normalized diameter of meningeal arterioles after injection of the GTN (filled circles) or vehicle (empty circles), real diameter before application 17.4±2 µm for meningeal arterioles and 22.8±4 µm for meningeal venules. <b>C</b>, comparison of changes in the area under curve in GTN vs vehicle in meningeal arterioles (n = 6 and n = 4, respectively, ***  =  P<0.001), <b>D</b> and <b>E</b>, the same for meningeal venules (n = 5 and n = 4, respectively). Note that GTN changed the diameter of arterioles but not venules. Scale bar 40 µm.</p

The action of L-NAME (filled circles) and vehicle (open circles) on the diameter of cortical and meningeal vessels in open cranial window preparation.

<p>A, the time of changes in cortical arterioles (real diameter 38.1±6 µm), B, cortical venules (real diameter 46.4±13 µm), D, meningeal arterioles (real diameter 20.7±5 µm) and E, meningeal venules (real diameter 24.1±7 µm), respectively. C and F, quantification of results (n = 9, 4, 8, 8 for meningeal arterioles, meningeal venules, cortical arterioles and cortical venules, respectively, *** = P<0.001, ** = P<0.01). Notice constriction of cortical but not of meningeal vessels.</p

Schematic presentation of potential mechanisms for opposite modulation of dura mater and pial/cortical vessels by GTN.

<p>In <i>dura mater</i> occupied by mast cells and densely innervated by trigeminal and autonomous nerves GTN can induce vasoconstriction of small vessels either directly, or via release of vasoconstrictory agents from mast cells or through the neuronal control. The functional outcome depends on the combination of vasodilatatory versus vasoconstrictory agents and on the receptor profile. The dilatatory effect of GTN in pial/cortical vessels could be due to the direct action of this agent on the vessel wall or mediated via astrocytes releasing NO.</p

Effects of GTN on cortical vessels in the open cranial window preparation.

<p>A, examples of cortical vessels before (upper image) and after GTN administration (lower image). B, the normalized diameter of cortical arterioles after injection of the GTN (filled circles) or vehicle (empty circles), real diameter before application 36.1±6 µm for cortical arterioles and 38±8 µm for cortical venules. C, comparison of changes in the area under curve (AUC) in GTN versus vehicle in cortical arterioles (n = 6 and n = 3, respectively). D and E, the same for cortical venules (n = 8 and n = 4, respectively). Note that GTN significantly changed the diameter of arterioles (*  =  P<0.05) but not venules (P = 0.09). Scale bar 25 µm.</p