NO participate in the communication between the first‐ and second‐order neurons in the trigeminal sensory tract in the dog

Histochemical, immunocytochemical and radioassay study was performed to detect the occurrence of NOS‐immunoreactive primary trigeminal sensory somata in the trigeminal ganglion, including their fiber components. Spinal trigeminal tract and sensory trigeminal nuclei were studied using the same methods. It was found that more than 30% of all somata in the trigeminal ganglion are NOS immunoreactive. Corresponding fibers were detected in the spinal trigeminal tract. NOS immunoreactive fibers of three different categories could be followed to terminate in the sensory trigeminal nuclei. Data presented here confirm that trigeminal sensory system is richly endowed with NOS and that NO is used to communicate between the first and second‐order trigeminal sensory neurons. Acknowledgements: Supported by VEGA Grant no. 2/3217/23PS9, STAA Grant no. 51‐013002 and by NIH grants NS 32794 and NS 40386 to M.M.