Figure 7.

Pharmacological and sensory manipulations disrupt functional adaptation of sensory processing in the nociceptive withdrawal reflex. a, Normal developmental functional adaptation of tail withdrawal reflexes in the horizontal plane in three litters. Error rate denotes the proportion of erroneous reflex movements, i.e., toward instead of away from the nociceptive stimulus [modified from Waldenstrom et al. (2003)]. b, MK-801-treated animals (▴; n = 12) displayed significantly higher tail reflex error rates than vehicle-treated pups (■; n = 10; p = 0.029; Mann–Whitney). c, The mean number of action potentials and the corresponding SD for 16 standard sites are plotted for PL [vibrated (gray; n = 7), vehicle (cyan; n = 4), and MK-801 (purple; n = 6)]. The average spontaneous activity recorded before stimulation has been subtracted from poststimulus values; as a consequence, inhibition results in a negative number of action potentials. It can be seen that the vibration-treated pups displayed large interindividual response variability close to the receptive field periphery (encircled values). Note also the expansion of the excitatory receptive fields into skin areas normally producing inhibition, in vibrated and MK-801-treated animals. d, Examples of quantified NWR receptive fields of PL and EDL obtained during the fourth postnatal week. MK-801-treated and vibrated animals exhibited inappropriate and flattened receptive fields, respectively. Vehicle-treated animals displayed normal adult-like receptive fields [in agreement with previous results (Holmberg and Schouenborg, 1996)]. Illustrated receptive fields were constructed from quantified EMG responses (mean of 10 mappings) by stimulation of 16 standardized skin sites; values from intermediate sites were interpolated by spatial low-pass filtering.