THE LOW-AFFINITY NEUROTROPHIN RECEPTOR P75 REGULATES THE FUNCTION BUTNOT THE SELECTIVE SURVIVAL OF SPECIFIC SUBPOPULATIONS OF SENSORY NEURONS

Mice with a targeted deletion of the low-affinity neurotrophin recepto r p75 (p75-/-) exhibit a 50% loss of large- and small-diameter sensory neurons in the dorsal root ganglion. Using neurophysiological recordi ng techniques, we now show that p75 is not required for the survival o f specific, functionally defined subpopulations of sensory neurons. Ra ther, p75-/- mice exhibit losses of neurons that subserve nociceptive as well as non-nociceptive functions. The receptive properties of larg e myelinated afferent fibers were normal in p75-/- mice. However, the receptive properties of subpopulations of afferent fibers with thin my elinated or unmyelinated axons were strikingly impaired in mice lackin g p75. Furthermore, the presence of p75 is required for normal mechano transduction in C fibers and D-hair receptors and normal heat sensitiv ity in A-fiber nociceptors.