Some Morphological Evidence For Transmission And Modulation Of Noxious Information In The Caudal Spinal Trigeminal Nucleus And Spinal Dorsal Horn Of The Rat

It is well known that the superficial layers of the caudal spinal trigeminal nucleus (Vc) is a relay station transmitting primary nociceptive information from orofacial region to the thalamus and lateral parabrachial nucleus (LPB). The Vc is the main projection region of fibers of the "descending inhibitory system" too. Thus, the Vc seems to be closely related to transmission and modulation of primary nociceptive information. The previous studies have proved that C-fibers transmitting primary nociceptive information terminate in the superficial layers of the Vc, and some neurons in laminae I and III send their axons to the thalamus and LPB. On the other hand, descending serotoninergic axons from the periaqueductal gray and raphe nuclei also terminate in the region, and make direct synaptic contacts with both trigeminothalamic and trigeminoparabrachial tract neurons and local circuit neurons. However, the previous studies exist no direct evidence showing that Vc projection neurons are in synaptic contact with 5-HT-like immuoreactive axon terminals and C-fibers are nociceptive.Substance P (SP) is one of the most important neurotransmitters and/or neur modulators in tr(?)smission of nociceptive information from the periphe(?) to the central nervous system. SP-like immunoreactive fibers and te(?)minals are mainly distributed in the superficial layers of the Vc and spinal dorsal horn, and a few in deep layers and a region around the...