Multireceptive neurons (Ms) of the spinal cord are nonselective in that they respond, differentially, to innocuous and noxious stimulation of the periphery. The following experiments are designed to gain a better understanding of Ms, in particular those from lamina V (L5Ms) of the cat, in the role of processing of sensory, including noxious, input. Project 1 -- Interval Analyses. The discharge timing of L5Ms will be investigated utilizing interval analyses to determine if there is a unique interval code in response to any type of stimulation of the periphery, in particular to noxious stimulation. A main question being asked is: under what conditions can specific information regarding the stimulus (location, intensity and submodality) be transmitted up the spinal cord by L5Ms? Project 2 -- Somatotopy. The somatotopic organization of L5Ms, including low-threshold and high-threshold components will be determined to see if L5Ms conform to the same rules of somatotopy as low-threshold neurons. Project 3 -- Antidromic Stimulation. The projection patterns of L5Ms, which are not fully known, will be determined with antidromic stimulation techniques. Project 4 -- Intracellular Staining. Structural features of L5Ms from lumbosacral and thoracic segments will be ascertained with intracellular recording and staining techniques. These features will be compared with the features reported for sacrocaudal L5Ms. Project 5 -- Single-Spike Input. Studies will be performed to determine the effects of single action potentials, from single, identified input channels on L5Ms. Of most interest are the effects of stimulation of individual cells with C fibers or high-threshold mechanoreceptors in the dorsal root ganglion. Our long term goal is to understand the role of dorsal horn Ms in the processing of light tactile, noxious and thermal input from the periphery. These 5 projects are expected to greatly increase our understanding of the functioning of L5Ms.
