Nitric oxide synthase (NOS) in the trigeminal vascular system and other brain structures related to pain in rats

Nitric oxide (NO) is considered to be a key mediator in the pathophysiology of migraine but the localisation of NO synthesizing enzymes (NOS) throughout the pain pathways involved in migraine has not yet been fully investigated. We have used quantitative real-time PCR and Western blotting to measure the respective levels of mRNA and protein for nNOS and eNOS in peripheral and central tissues involved in migraine pain: dura mater, pial arteries, trigeminal ganglion (TG) trigeminal nucleus caudalis (TNC), periaqueductal grey (PAG), thalamus, hypothalamus, cortex, pituitary gland, hippocampus and cerebellum. iNOS was excluded from the present study because it was not induced. In the trigeminal vascular system we found the highest expression of nNOS mRNA in pial arteries. However, protein expression of nNOS was maximum in TNC. Among other brain structures, nNOS mRNA and protein expression was remarkably higher in the cerebellum than in any other tissues. Regarding eNOS in the trigeminovascular system, the highest mRNA expression was found in pial arteries. In the other brain structures, eNOS mRNA expression was similar but with lowest mRNA concentration in the pituitary gland and the highest concentration in cortex. The same pattern of expression was also observed with the eNOS protein. In conclusion, we found both nNOS and eNOS located to areas relevant to migraine supporting the involvement of NO in migraine mechanisms.