RELATIONSHIP OF HEMATOLOGICAL VARIABLES TO LEARNING-PERFORMANCE IN AGED FISCHER-344 RATS

The relationship between hematological variables and the ability to pe rform behaviorally in two learning tests was evaluated in male F344 ra ts aged 22-24 months. Rats were screened for ability to meet criterion for learning one-way active avoidance in a straight runway task. Rats failing to meet criterion were given no further testing and were assi gned to Group 1 (G1). Rats meeting criterion were tested in a I l-unit T-maze (2 days, 10 trials/day). Failure to negotiate the T-maze withi n 600 s on any three trials resulted in assignment to Group 2 (G2) wit h no further testing. Rats successfully completing both tasks constitu ted Group 3 (G3). Trunk blood was collected following behavioral testi ng and was assayed to determine red blood cell count (RBC), hematocrit (HCT), hemoglobin (HGB), mean corpuscular volume (MCV), mean corpuscu lar hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC) , white blood cell count (WBC), bands (END), polymorphs (POLY), lympho cytes (LYM), monocytes (MON), and eosinophils (EOS). The combined G1/G 2 group had significantly lower RBC, HCT, HGB, and EOS but significant ly higher MCV and MCH than G3 rats. Correlational analysis revealed a positive relationship of group membership (i.e., learning test complet ion) to RBC, HCT, HGB, and EOS, but a negative correlation of group me mbership to MCH. No significant correlation emerged between any hemato logical characteristic and performance in either behavioral task. Thes e results suggest that a simple blood test to determine HCT may be a u seful screen for removal of moribund rats from aging studies attemptin g to control for effects of health on behavioral performance in rodent models.