Age-related deficits in retention of the classically conditioned nictitating membrane response in rabbits.

Young and aged rabbits underwent classical conditioning of the nictitating membrane response (NMR) to a tone conditioned stimulus (CS) and a corneal airpuff unconditioned stimulus (UCS) for 18 consecutive days. Rabbits were then returned to their home cages for a 90-day period in which they received no further conditioning, but they were handled daily. On Day 91 they underwent retention testing during which the CS alone was presented 20 times. This was immediately followed by reacquisition in which the CS and UCS were again paired for 100 trials. Reacquisition was repeated on the following day. As in previous studies, aged rabbits acquired the conditioned response (CR) more slowly than young rabbits; however, by the end of acquisition, both groups reached similar asymptotic levels. Retention of the CR was significantly lower for aged than young rabbits. Reacquisition was also retarded in aged vs. young rabbits. Nonassociative factors, such as sensitivity to the stimuli or general health, could not account for these differences. Data are discussed in terms of using retention of the conditioned eyeblink response as a model system for studying age-related memory deficits.

Frozen RPMI 8402 cells: a reliable source of terminal deoxynucleotidyl transferase positive control material.

A reliable source of positive control material is needed for immunoperoxidase or immunofluorescent terminal deoxynucleotidyl transferase (TdT) assays. The cell line RPMI 8402 was obtained from a patient with acute lymphoblastic leukemia and is positive for nuclear TdT. The kinetics of TdT expression in a series of cultured RPMI 8402 cells and the effect of cryopreservation on TdT expression were evaluated. The highest percentage of TdT+ cells was detected on days 5-8 of RPMI 8402 cell cultures. TdT positivity was preserved for more than 3 years in cells stored in suspension at -70 degrees C, and at least 76 days on slide preparations when fixed with methanol prior to freezing. We conclude that when RPMI 8402 cells with maximum TdT positivity are stored at -70 degrees C, aliquots can be used as a constant source of positive control material thereby eliminating the necessity and expense of a continuing culture system.