In the present study we in vivo assessed in rats the effects of trigeminal nerve stimulation obtained by mandibular extension (ME) on mean arterial blood pressure (MABP), pial microcirculation and gene expression of endothelial, neuronal and inducible nitric oxide synthase (e-, n-, i-NOS).

Pial microcirculation was visualized by fluorescent microscopy; MABP and vessels diameter were monitored and evaluated by computer-assisted methods. Measurements were carried out in baseline conditions, during 5, 10 or 15 min ME and for 180 min after ME. ME was induced by a specially designed extensor.

In control rats both MABP and pial arterioles diameter did not change throughout the observation period. ME induced a significant time-dependent decrease in MABP compared with the baseline lasting for 150 min after 10-15 min ME. Pial arteriolar diameters decreased during ME and afterwards significantly increased; this vasodilatation lasted for 150 min after 10 or 15 min ME and was abolished by L-NAME, (eNOS inhibitor). Naloxone, a nociceptors inhibitor, prevented the vasoconstriction detected during ME.

Using RT-PCR, the gene expression of eNOS resulted up-regulated by ME up to 120 min after ME, while nNOS reduced up to 60 min after ME and increased after 180 min. ME did not affect the expression of iNOS gene.

Therefore, the trigeminal nerve stimulation triggers specific mechanisms of cerebral circulation regulation sustained by eNOS that could be of interest in vascular diseases.