Nitric Oxide Synthase Immunoreactivity in the Rat Spinal Trigeminal Nucleus

The spinal trigeminal nucleus (SpV) is involved in the transmission of nociceptive information from the orofacial region. This study investigates nitric oxide synthase (NOS) immunohistochemical staining and conducts statistical data analysis within the three subnuclei of the SpV in rats. Our immunohistochemistry study revealed that the SpV has a high expression of nNOS, with immunostaining mostly seen in the perikarya and nerve processes of some neurons. Furthermore, we found that glial cells in the nucleus surrounding blood vessels display a significant nNOS immunohistochemical staining. NOS-immunopositive neurons had small cell bodies. Strong staining is also evident in their processes. NOS-immunoreactive neuronal processes encircled a significant amount of blood vessels. There were statistically significant variations in the nNOS expression between the SpV subnuclei. In particular, the caudal subnucleus exhibited the greatest expression, followed by the interpolar subnucleus, and the oral subnucleus showed the lowest expression. Remarkably, there was no discernible variation in the expression of nNOS in the interpolar and oral regions of the SpV. We suggest that NO can act as a neurotransmitter in increasing nociceptive stimuli in the SpV.