ABSTRACT
The traditional, textbook view of the “pain” pathway illustrates an unmyelinated primary afferent C-ber, the nociceptor, contacting a second-order dorsal horn neuron at the origin of the spinothalamic and spinoreticular pathways. Although the ultimate cortical target of these different pathways is unclear, there is no question that a better understanding of the mechanisms through which noxious stimuli produce pain requires a better understanding of these circuits. The limitations of our knowledge, of course, go beyond the need to identify cortical targets. We recognize now that there are neurochemically and physiologically distinct populations of afferents, projection neurons, and diverse central nervous system (CNS) targets.
7.1 Introduction .................................................................................................. 163 7.2 Traditional Anatomical Tracing Approaches ............................................... 165 7.3 Genetic Tracing with Transneuronal Tracers ............................................... 166 7.4 A Genetic Approach to the Anatomical Mapping of Complex Circuits:
