2003 Volume 18 Issue 3 Pages 127-136
Neurons in the reticular formation of the brainstem are thought to participate in transmission of nociceptive information. However, the role of the reticular formation for the pain mechanism remained to be disclosed. In the present study, extracellular single-unit activities were recorded from the nucleus reticularis magnocellularis and adjacent areas (RF) elicited by electrical, mechanical and thermal noxious stimuli of the rat sciatic nerve.
Multiple-spikes responding to single electrical stimulation were recorded in the single neuron in RF, which responded to pinch. They were grouped into three types: 1) The latency of Fast type was not over 30 msec, although the intensity of electrical stimulation increased, 2) the latency of Slow type was over 200 msec, although the intensity was low, and 3) Mixed type had components of both Fast type and Slow type. Considering the latency and intensity, Fast type, Slow type and Mixed type received information carried via Aδ-fibers, C-fiber and Aδ- and C-fibers, respectively. In Fast type, Aδ-fibers terminated to the single neuron of lamina V, which axon terminated to the single neuron of RF.Since the diameter of Aδ-fibers was different,multiple spikes were obtained with the gradually increased intensity. In Slow type, the neuron of lamina I received C-fibers and sent information via the several interneurons in laminae III-IV to the neuron of lamina V, which axon terminated to the single neuron of RF. Since the diameter of C-fibers was different, multiple spikes were obtained with the gradually increased intensity. As the above-mentioned manner, in Mixed type, the neuron of lamina V received information from both Aδ- and C-fibers and projected to the single neuron of RF. Neurons with the spontaneous spikes had tendency to be reacted by pinch but not by thermal stimulation. Neurons without the spontaneous spikes were reacted by both pinch and thermal stimulation.
It seems that the single neuron of RF receiving various information from the peripheral nerve activates the ascending reticular activating system and/or descending pain inhibitory system.
