Figure 4.

Ondansetron antagonism of spinal 5-HT₃ receptors has age-dependent effects on dorsal horn neuron activity. The 5-HT₃R antagonist ondansetron was applied to the surface of the lumbar dorsal horn prior to electrophysiological recordings from WDR neurons at P21 and P40. At P21, 2 μg and 50 μg, but not 10 μg, ondansetron reduced brush-evoked dorsal horn firing activity (A), but not receptive field areas (B). In adult rats, 50 μg ondansetron reduced brush receptive field area (D), but not brush-evoked firing activity (C). Pinch-evoked firing activity was reduced in P21 rats following 10 μg or 50 μg ondansetron treatment (E). Pinch receptive field areas were not changed (F). In adults, 50 μg ondansetron had no effect on pinch evoked firing activity (G) or receptive field areas (H). 50 μg ondansetron also reduced lower and higher force von Frey hair (vFh)-evoked firing activity in P21 rats (I), but not in adults (J). Brush (K) and pinch (L) dorsal horn neuron receptive field heat maps from adult control and ondansetron rats. A typical brush receptive field from an ondansetron-treated adult dorsal horn neuron is shown in (K). Bars indicate mean ± SEM. *^,**^,***P < 0.05, 0.01, 0.001.