AGE-RELATED-CHANGES IN EXCITABILITY AND RECURRENT INHIBITION IN THE RAT CA1 HIPPOCAMPAL REGION

In hippocampal slices from male Wistar rats aged 1-34 months, we recor ded the synaptic field potential responses of the CA1 neurons to stimu lation of Schaffer collaterals. Eight electrophysiological indexes wer e extracted from input/output curves and compared in 11 age groups fro m 1 to 30 months. Neuronal excitability presented a U-shaped curve of development with a minimum at similar to 7-8 months of age. There was a significant continuous increase in neuronal excitability, i.e, a dec rease in excitatory postsynaptic potential (EPSP) producing both the t hreshold and half-maximal population spike from middle age (8-10 month s) to senescence (30 months). Synaptic efficiency also increased in ol d rats to reach a maximum during senescence, i.e, both the current for threshold EPSP and that for half-maximal EPSP reached a minimum in se nescence, although the earlier developmental patterns of these two ind exes were non-linear. The duration of the field EPSP elicited with max imal stimulation presented an abrupt decay after the first month. Aged animals presented a relatively small maximal population spike. Recurr ent inhibition was most prominent on neuronal excitability rather than synaptic strength. Measured as the percentage change in the half-maxi mal EPSP and half-maximal population spike, recurrent inhibition was f ound to decrease during the first 7-10 months of life and remained sma ll in later development.