Figure 2.

Increased temperature leads to reduced axonal recruitment.

[A] Graph derived from Table 1 in Pinto et al (2008), estimating the changes in conduction velocity for Aδ and C-fibers, which exhibit conduction velocities comparable to SPN fibers observed in mice. Using trend line formulas and experimental data collected at 22°C (fast: 0.31-2.2m/s [2-14ms from stim onset]; slow: 0.06-0.23m/s [19-70ms from onset]), predicted changes to conduction velocity ranges were extrapolated for fast (0.58-3.4m/s) [1.3-7.6ms from onset] and slow populations (0.11-0.44 m/s) [10-40ms from onset] at 36°C as shown in temp and frequencies comparison studies summarized in Table 2. [B] Example T° differences in CAP appearance and separation into fast and slow groups. Fast and slow SPNs within conduction velocity ranges above are highlighted with bars and shaded boxes at 36°C (red) and 22°C (blue). [C] Scaling approach shown in another example recording. [C₁] shows difference in responses at 36°C and 22°C with colored bars identifying conduction ranges for fast and slow CAPs as in [B]. [C₂] shows overlaid volleys with 36°C response scaled to 22°C using pre-determined scaling factors (shown). Note preferential loss of slower responses. [D] Evoked responses from 36°C and 22°C were rectified, integrated, scaled, and compared. The percent reduction in magnitude of evoked response was determined for fast and slow-conducting epochs of the CAP. The IGN slower-conducting axons exhibited a substantially higher % reduction in evoked response (48.1 ± 6.4%; p<0.001) compared to that seen in faster-conducting axons (75.3 ± 5.1%; p<0.05) [n=6]. For the splanchnic nerve these values were reduced by 50.0 ± 9.1% (p<0.01) and 63.7 ± 8.0%, (p<0.05), respectively [n=5]. (*, p<0.05; **,p<0.01; ***, p<0.001; paired t-tests).