INSTRUMENTAL LEARNING WITHIN THE RAT SPINAL CORD: LOCALIZATION OF THE ESSENTIAL NEURAL CIRCUIT. G.T.Liu1; E.R.Crown1; R.C.Miranda2; J.W.Grau1* 1. Dept Psychol, Texas A&M Univ, College Station, TX, USA; 2. Med Anatomy, Texas A&M Univ, College Station, TX, USA
We have previous shown that spinal cord neurons can support a simple form of instrumental learning. Rats are spinally transected at T2 and tested 24 hrs later. Response contingent shock is applied to one hind limb whenever the leg is extended. Over the course of 30 min of training, subjects learn to maintain their leg in a flexed position, minimizing net shock exposure. Rats that receive the same amount of shock independent of leg position fail to learn. The present experiments attempt to isolate the region of the spinal cord that mediates learning. Experiment 1 used histological procedures to trace the fiber pathways that innervate the region of stimulation. The fluorescent tracers Fluoro-Gold and diI were microinjected at the site where shock is normally applied and spinal tissue below T9 was examined for labeling. A diffuse pattern of labeling was observed that extended from L1 to below S1. Experiment 2 used surgical procedures to isolate the essential neural tissue. Surgical transections were made at progressively lower sites, starting at segment L1. Subjects were tested with response contingent shock 24 hrs later. Learning survived transections at L1, L3, and L5. A transection at S1 eliminated learning (p < .05). Learning also survived a dual transection performed at L5 and S3, suggesting that the essential neural circuit lies within this region of the spinal cord. Additional experiments are being conducted to further localize the locus of learning.
Supported by: MH60157 & NS41548 to JWG & RCM.
Citation: G.T.Liu, E.R.Crown, R.C.Miranda, J.W.Grau. INSTRUMENTAL LEARNING WITHIN THE RAT SPINAL CORD: LOCALIZATION OF THE ESSENTIAL NEURAL CIRCUIT. Program No. 167.17. 2002 Abstract Viewer/Itinerary Planner. Washington, DC: Society for Neuroscience, 2002. CD-ROM.