AGE AND STRAIN DIFFERENCES IN RAT PLACE LEARNING AND HIPPOCAMPAL DENTATE GYRUS FREQUENCY-POTENTIATION

Induction of post-tetanic potentiation (PTP) and long-term potentiatio n (LTP) was analyzed in hippocampal slices obtained from (i) young (6 months old) rats of different strains (Sprague-Dawley, SD; spontaneous ly hypertensive rats, SHR; and Wistar-Kyoto, WKY), and (ii) from aged (20-24 months old) SD and Fischer 344 (F 344) rats, each group showing a different performance in the Morris maze test. After the applicatio n of an electrical tetanus (1 s, 100 Hz, 50 mu A) in the stratum molec ulare, a significant difference was found in the percent of induction of the dentate PTP in hippocampal slices obtained from rats of differe nt strains and ages. In particular, the induction of the dentate PTP w as signficantly (P < 0.01) higher in slices obtained from young SD or spontaneously SHR rats, having the better performance in the Morris ma ze than in slices obtained from old SD or F 344 rats or young WKY rats which had poorer performances in the Morris maze. On the contrary, no significant differences were found in the percent of induction of the LTP in the dentate area of hippocampal slices obtained from rats of d ifferent strains and ages. Moreover, after the application of an elect rical tetanus (1 s, 100 Hz, 50 mu A) in the stratum radiatum, no signi ficant differences were found in the percent of induction of both PTP and LTP in the CA1 area of hippocampal slices obtained from rats of di fferent strains and ages. The data show that the induction of hippocam pal dentate high-frequency PTP is reduced not only in old rats but als o in some peculiar strains of rats with impaired behavioural capabilit y in the Morris maze.