Anatomical identification of neurons responsive to nociceptive stimuli

We describe methods for labeling and identifying neurons within the central nervous system involved in the transmission of nociceptive stimuli. The most reliable methods are physiological identification followed by intracellular injection or immunocytochemical detection of stimulus-induced markers such as Fos. These latter strategies are used with appropriate controls to distinguish neurons activated secondarily (e.g., motor response or inhibitory neurons) by the nociceptive stimuli. Other methods include location and morphology as determined by standard cytological and tracing methods and/or the presence of specific neurochemical markers such as substance P determined by immunocytochemistry.