Leg flexion conditioning in the rat: its advantages and disadvantages as a model system of age-related changes in...

Twelve- and 28-month-old Fischer 344 rats of both sexes received five 60-trial sessions of Pavlovian conditioning in which the CS was a 75 dB, 10,000 Hz tone, and the US was a 0.5-mA, 0.5-sec duration footshock. Right foreleg flexion was measured as the conditioned response (CR). Other animals received a random sequence of unpaired tones and footshock and served as pseudoconditioning control groups. Interstimulus intervals (ISIs) of 1.5 and 3.5 sec were studied. The longer ISI resulted in higher rates of responding in both the conditioning and pseudoconditioning groups. However, with the exception of the young males, all animals showed significantly higher levels of responding in the conditioning groups. Females also showed faster acquisition and higher levels of responding than males. A significant sex by age by sessions interaction occurred, suggesting that old males may be somewhat retarded in acquiring the leg flexion CR compared to the other groups of animals. Old males were also slower to reach a criterion of 5 successive CRs than either young males or young or old females.