Differentiation of the substrates for XXXX and vocalizations elicited by midbrain stimulation in rats: refractory period estimates.

@entity2195 @entity1337
Stimulation of periaqueductal gray sites resulted in both increased latencies to escape heated water with a tail-flick and audible vocalizations. To determine whether these two responses were the result of stimulation of the same substrates, refractory periods were estimated by delivering paired-pulse trains of stimulation. Stimulation consisted of 10 or 20 s trains of single pulses or pulse pairs. The pulse pair frequency threshold for both behaviors was determined for intra-pulse ( @entity2195 ) intervals of 0.4-10 ms. The ratio of single to double pulse frequency thresholds provided an indication of relative effectiveness of the paired-pulse stimulation. For @entity1337 , the paired-pulse effectiveness gradually increased between @entity2195 intervals of 2.0 and 5.0 ms, after which asymptotic effectiveness values were obtained. Thus, the estimated refractory period for @entity1337 was 2.0-5.0 ms. The refractory period estimate for vocalizations was shorter. Effectiveness values increased with a @entity2195 interval of 1.2 ms and reached asymptote with a @entity2195 interval of 2.0 ms. These results suggest that different fibers with overlapping spatial distributions contribute to @entity1337 and vocalizations produced by midbrain stimulation.
