EXPOSURE TO A NOCICEPTIVE STIMULUS IMPAIRS RECOVERY AFTER A CONTUSION INJURY. J.W. Grau*, G. Garcia, A.R. Ferguson, E.D. Crown, J. Olson, & R.C. Miranda. Depts. of Psychology and Medical Anatomy, Texas A&M University, College Station, TX 77843.
We have shown that exposure to intermittent tailshock undermines behavioral potential within the spinal cord. Rats were spinally transected and exposed to brief (80 msec) intermittent (2 s apart; range: 0.2-3.8 s) tailshock at an intensity (1.5 mA) that engages nociceptive mechanisms. Exposure to shock for just 6 min undermines the capacity to learn a new response for up to 48 hrs. Here we examine whether exposure to a this nociceptive stimulus affects the recovery of function after a contusion injury. Rats were anesthetized with pentobarbital and the spinal cord was injured using the NYU impactor (12.5 mm. drop) The next day, rats received nothing or shock for 6 or 30 min. Another group received 2 days of shock (30 min/day). The impact of shock treatment was assessed using the BBB scale (Basso et al., 1995, J. Neurotrauma, 12, 1-21). A day after surgery, rats exhibited little hindlimb function (BBB score: 2.82+0.48 (mean+SEM)). Six weeks later the unshocked controls (n=7) had recovered considerable hindlimb function, yielding a BBB score of 13.7+1.3. Shocked rats (n=6) did not recover the same level of hindlimb function (BBB score=8.17+1.48 at Day 42) and were significantly different from the unshocked controls (p < .05). Just 6 min of intermittent shock had a disruptive effect. Six out of 21 shocked rats died 6-26 days after surgery and 2 shocked rats exhibited autotomy behavior. None of the unshocked controls died and none have exhibited autotomy. Shocked rats also exhibited higher vocalization thresholds to a von Frey hair applied to the hind paw (6.41 vs. 5.15, p < .05). We thank J. Bresnahan for her assistance. Supported by MH60157 to JWG & RCM.
Published in Society for Neuroscience Abstracts, 27, 2001, 2039.
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