Figure 7.

Perception of thermal, mechanical, and chemical stimuli in naive mGlu4KO mice. A, mGlu4KO mice and their WT littermates display a similar thermal sensitivity, determined by measuring the latency to withdraw the tail immersed in water at temperatures ranging from 4°C to 50°C (n = 10 animals per group). B, mGlu4KO mice display a significantly higher threshold for tail withdrawal after noxious mechanical stimuli evoked by tail compression in the Randall–Selitto (RS) than WT mice (n = 10 animals per group). C, Both mGlu4KO and WT mice displayed the typical biphasic time course of nocifensive behavior (paw licking/biting) after injection of 15 μl of a 5% formalin solution in the right hindpaw. The second phase of the response occurs faster for mGlu4KO mice. Right, Histogram representing the mean time ± SEM of nocifensive behavior during the first phase (0–10 min) and the second phase (15–50 min) of the formalin test. The response in the second phase is significantly higher for mGlu4KO mice than for WT mice (n = 8 animals per group). D, Mechanical sensitivity assessed by measuring the number of paw lifts of five stimulations using von Frey filaments corresponding to innocuous (0.07 g), intermediate (0.6 g), and noxious (1.4 g) bending forces does not differ between mGlu4KO and WT mice (n = 10 animals per group). *p < 0.05. **p < 0.01. ***p < 0.001.