Continued support is requested for a multifaceted project studying functional and chemical characteristics of somatic primary afferent fibers of fine diameter and the organization of the superficial spinal dorsal horn, a locus for many terminations from these fibers. The emphasis will be upon the part such features and this organization have in the neural processes associated with pain. The work proposed for the next project period concentrates on the relationship between chemical and functional features of primary afferent neurons and upon interrelations in the neuronal activity of the superficial dorsal horn. Identification of chemical mediators utilized by nociceptive primary afferent fibers centrally and the possible influence of peripheral chemical agents upon the responsiveness of cutaneous nociceptors are among the goals. Five sets of experiments are proposed, all based upon a combination of electrophysiological recordings and histochemical or pharmacological probes. Functionally characterized dorsal root ganglion cells, marked intracellularly by iontophoresis with a label (lucifer yellow, HRP) from recording micropipettes, would be tested for reactivity with monoclonal and polyclonal antibodies directed at a) specific surface antigens, b) putative neurotransmitters or c) enzymes specifically associated with the neurotransmitter candidates. The effects of putative neurotransmitters would be tested upon neuronal activity in an in vitro slice preparation of the spinal dorsal horn and dorsal roots from the spinal cord of young rodents. The same in vitro spinal slice preparation would be employed to test the activity (evoked intracellularly) in one neuron of the substantia gelatinosa upon another neuron of that region or of the marginal zone. The effects of putative transmitters would also be tested upon previously established categories of feline spinal neurons in vivo to further evaluate the in vitro observations. A set of experiments is directed at the possible role of substance P, histamine, serotonin and prostaglandins in the process of enhanced responsiveness and in the ongoing activity commonly seen in cutaneous nociceptors after tissue damage; the possibility that different chemical agents or other mechanisms operate in the ongoing and evoked aspects of such "sensitization" and in the different types of nociceptors will be examined in an in vitro rabbit ear preparation. The long term goal is to provide better insight into the underlying neural mechanisms for pain and to provide a better basis for effective pharmacological therapies.