SELECTIVE REDUCTION OF HIPPOCAMPAL DENTATE FREQUENCY-POTENTIATION IN STRIATALLY LESIONED RATS WITH IMPAIRED PLACE LEARNING

The induction of hippocampal frequency-potentiation (i.e. post-tetanic potentiation (PTP) and long-term potentiation (LTP) was analyzed in r at hippocampal slices obtained from animals showing impaired place lea rning in the Morris water maze as a consequence of bilateral striatal injection of quinolinic acid. Vehicle-injected animals, showing normal performances in the Morris water maze, behaved as controls. After the application of an electrical tetanus (1 s, 100 Hz, 50 mu A) in the st ratum radiatum, no significant differences were found in the percent o f induction of both PTP and LTP in the CA1 area of hippocampal slices obtained from lesioned and sham-operated rats. After the application o f an electrical tetanus (1 s, 100 Hz, 50 mu A) in the stratum molecula re, a significant difference was found in the percent of dentate PTP i nduction in hippocampal slices obtained from lesioned and sham-operate d rats. Specifically, dentate PTP induction was significantly (P < 0.0 1) higher in slices obtained from sham-operated rats with a good perfo rmance in the Morris water maze than in slices obtained from striatall y lesioned rats, which had shown poor performance in the Morris water maze. On the contrary, no significant differences were found in the pe rcent of dentate LTP in hippocampal slices obtained from rats of the t wo groups. The data demonstrate that the impairment of the place learn ing in striatally lesioned rats is associated with a selective reducti on of hippocampal dentate frequency-potentiation.