| Several reports indicate that 48 hours of post-injury light-deprivation (LD) produces an acute recovery in symmetrical orienting behavior in rats with unilateral injury to the medial agranular cortex (AGm; e.g., Crowne, 1983; Corwin and Vargo, 1993). Some research indicates that LD rats demonstrate a bilateral reduction in reactivity that is not seen in shams or spontaneously recovering AGm operates (Heinrich, Sparkman and Barth, 2000), but may be similar to a bilaterally injured rat. The current studies were designed to ascertain whether or not cortically injured rats that have recovered following post-injury LD have distinctive behavioral recovery patterns from rats that have spontaneously recovered from identical cortical injury. In experiment 1, three groups of rats experienced normal post-injury cyclical lighting (12/12 light/dark): a unilateral AGm-injury group, a bilateral AGm injury group, and a sham group. A fourth group received the unilateral AGm injury, but was exposed to 48 hours of post-injury light-deprivation (LD). For three weeks, the rats were tested for ability to orient toward unilaterally presented stimuli, and for paw preference in removing adhesive patches from the forelimbs. LD increased responding toward contralesional stimuli but did not affect recovery on the adhesive patch removal task. Rats with bilateral AGm (BAGm) injury failed to show asymmetry on any test. BAGm subjects only differed from shams in that they demonstrated longer latencies to contact either adhesive patch. In experiment 2 rats received either unilateral AGm injury, or sham injury. Half of the AGm injured group and half of the sham operates experienced 48 hours of post-operative LD, while the other half experienced normal lighting cycles. On post-surgical day 6 and 22 the all rats received sub-cutaneous injections of SCH-23390 (3.5, 7.0 or 14 μg) or vehicle. LD rats with AGm injury showed bilateral reductions in orienting behavior after receiving the high dose of the drug on day 6. On day 22, spontaneously recovered AGm-injured rats showed only a contralesional decrement in responding after receiving the high dose of the drug. The results suggest that LD may produce bilateral behavioral anomalies, but these do not minor the behavior of the bilaterally injured animal. |
