Trigeminal antidromic vasodilatation and plasma extravasation in the rat: effects of acetylcholine antagonists and cholinesterase inhibitors.

Antidromic stimulation of sensory peripheral branches of the trigeminal system (mental nerve) leads to cutaneous vasodilatation and increases vascular permeability in the rat. Antidromic vasodilatation is observed only at high intensity stimulation (10 V, 15 Hz, 0.2 or 5 ms) supporting the participation of afferent C-fibres in cutaneous dilator responses. Both antidromic vasodilatation and neurogenic plasma extravasation are significantly reduced by muscarinic antagonists suggesting that a cholinergic component may be involved in these trigeminal neurogenic responses. Neurogenic plasma extravasation remains unchanged by hexamethonium while antidromic vasodilatation is reduced. This latter effect may be merely a consequence of the dramatic fall in arterial pressure produced by the ganglion blocker. Antidromic vasodilatation is increased or unaffected by acetylcholinesterase inhibitors. On the other hand, the reduction of the plasma extravasation observed with these drugs could be due to their known ability to decrease the amount of acetylcholine released.