CONDITIONED ANTINOCICEPTION IN SPINAL RATS: ASSOCIATIVE LEARNING VERSUS PROTECTION FROM HABITUATION. R.L. Joynes* & J.W. Grau, Dept. of Psychology, Texas A&M University, College Station, TX 77843.
Conditioned antinociception can be demonstrated in spinalized rats by pairing stimulation (10-s, 1-mA shock) to one hind leg (the conditioned stimulus [CS]) with an intense (2-s, 3-mA) tailshock (the unconditioned stimulus [US]). After 30 CS-US pairings, tail-flick latencies are assessed during the CS. Relative to a CS that was presented in an unpaired fashion (the CS-), rats exhibit longer tail-flick latencies during the paired CS (the CS+) (Grau et al., Behav. Neurosci., 104, 489, 1990). The present study explores the mechanisms that underlie this learning.
Prior work has shown that our CSs elicit some antinociception prior to training and that presenting the CS alone attenuates (habituates) its antinociceptive impact. But when the CS is paired with the US, no habituation is observed. Does the US simply "protect" the CS from habituation, or does it support a simple form of associative learning? These two alternatives can be distiguished by varying the intertrial interval (ITI) and the number of training trials. If associative learning is involved, increasing the ITI and the number of CS-US pairings should strengthen the CS+/CS- difference, while a habituation account anticipates the opposite; increasing the ITI should reduce the CS+/CS- difference by decreasing habituation to the CS-, whereas increasing the number of CS-US pairngs should reduce it by facilitating habituation to the CS+. Our results indicate that protection from habituation underlies learning in our spinal paradigm. Supported by MH48994 to J.W.G.
Published in Society for Neuroscience Abstracts, 22, 1996.