Nociceptive reflexes are commonly used as indices of nociception in human subjects and in experimental animals. Justification for such an interpretation of segmental reflex responses is provided by evidence that many spinal cord dorsal horn neurons have response characteristics related to both nociception and reflex mechanisms. Much evidence suggest that our understanding of organization of some of the most basic segmental spinal reflexes is far from complete. If such reflexes are to provide insights into organization of more complex sensorimotor functions of the mammalian central nervous system, it is important to focus attention back at the segmental level of the spinal cord. The work of Dr. James McMillan has two goals. The first is to examine some basic aspects of the organization of segmental nociceptive spinal cord reflexes. Such "simple" reflexes are considered as models of more complex sensorimotor integration in the central nervous system. The primary focus of this part of the study is the differential contribution of synergistic muscles to the reflex movement around a single joint. The flexion and crossed extension reflexes will be monitored by recording isometric tension from appropriate muscles in decerebrate cats. effects of body position and other physiological stimuli on excitability of the reflex responses of fast and slow knee and ankle extensors will be examined in detail. The second goal is to evaluate segmental nociceptive reflexes as animal models of pain perception in humans. Such reflexes are commonly used as experimental indices of pain perception, but there is evidence that some procedures known to affect pain perception do not affect these reflexes in the same way. The studies proposed here are part of a long-term effort to examine similarities and differences between these reflexes and pain perception.
