Trace fear conditioning is reduced in the aging rat.
Auditory trace fear conditioning is a hippocampus-dependent learning task that requires animals to associate an auditory conditioned stimulus (CS) and a fear-producing shock-unconditioned stimulus (US) that are separated by an empty 20-s trace interval. Previous studies have shown that aging impairs learning performance on hippocampus-dependent tasks. This study measured heart rate (HR) and freezing fear responses to determine if aging impairs hippocampus-dependent auditory trace fear conditioning in freely moving rats. Aging and Young rats received one long-trace fear conditioning session (10 trials). Each trial consisted of a tone-CS (5 s) and a shock-US separated by an empty 20-s trace interval. The next day rats received CS-alone retention trials. Young rats showed significantly larger HR and freezing responses on the initial CS-alone retention trials compared to the Aging rats. A control group of aging rats received fear conditioning trials with a short 1-s trace interval separating the CS and US. The Aging Short-Trace Group showed HR and freezing responses on the initial CS alone retention trials that were similar to the Young Long-Trace Group, but greater than the Aging Long-Trace Group. A second aging control group received unpaired CSs and USs, and showed no HR or freezing responses on CS-alone retention trials. These data show that HR and freezing are effective measures for detecting aging-related deficits in trace fear conditioning.
McEchron
Matthew D
MD
Pennsylvania State University College of Medicine, Hershey, PA 17033, USA. mdm27@psu.edu
Cheng
Alex Y
AY
Gilmartin
Marieke R
MR
D000161:Acoustic Stimulation; D000375:Aging / Q000502:physiology*; D000818:Animals; D003214:Conditioning, Classical / Q000502:physiology*; D005239:Fear / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006624:Hippocampus / Q000502:physiology*; D051381:Rats; D011916:Rats, Inbred F344; D011930:Reaction Time / Q000502:physiology*