PAIN SENSITIVITY IN CARIOCA HIGH- AND LOW-CONDITIONED FREEZING RATS.

Anxiety disorders (AD) comprise a broad range of psychiatric conditions, including general anxiety (GAD) and specific phobias. Several studies have shown that anxiety disorders have a comorbidity with chronic pain. Here, we investigate whether Carioca high- and low-conditioned freezing rats (CHF and CLF, respectively), a GAD animal model of anxiety, differ in their response to pain stimuli.Adult male and female CHF, CLF and normal age-matched Wistar rats (control) were tested for nociceptive thresholds using the Von Frey test and tail flick test.The Tail Flick test revealed a significant effect of strain on all variables [withdrawal time: F (2,156) = 12.557, p < 0.001; maximum temperature: F (2,156) = 14.825, p < 0.001; temperature delta: F (2,156) = 8.864, p < 0.001].Although sex did not show significant effects on any variables [withdrawal time: F (1,78) = 2.826, p = 0.1; maximum temperature: F (1,78) = 1.126, p = 0.29; temperature delta: F (1,78) = 0.580, p = 0.45], there were significant interactions between strain and sex for withdrawal time [F (2,156) = 4.714, p < 0.05] and maximum temperature [F (2,156) = 3.839, p < 0.05]. Regarding the nociceptive response to mechanical stimulation on the hind paw using Von Frey filaments of different lengths, there were significant effects of filament length [F (4,436) = 343.359, p < 0.001], filament length x strain interaction [F (8,872) = 3.158, p < 0.01], and filament length x sex interaction [F (4,436) = 3.375, p < 0.01. Our findings indicate that CHF rats have a higher nociceptive threshold in response to thermal stimulation compared to CLF and control groups. This difference is primarily observed in CHF males. Interestingly, both male and female CLF rats exhibit nociceptive responses similar to the control groups. Additionally, CHF rats display a lower nociceptive threshold in response to mechanical paw stimulation, contrasting the findings of the tail flick test.