PERFORANT PATH KINDLING ALTERS DENTATE GYRUS FIELD POTENTIALS AND PAIRED-PULSE DEPRESSION IN AN AGE-DEPENDENT MANNER

The effects of rapid perforant path kindling on field potentials and p aired pulse depression were studied in the dentate gyrus of rats at fo ur developmental stages: 14-16 days, 20-22 days, 27-29 days and 40-60 days (adult). In rats 14-29 days kindling was associated with sustaine d potentiation of population spike amplitude and population EPSP slope ; in adults a progressive decline was seen in both measures. Inhibitor y circuitry as assessed by paired pulse depression was intact at all a ges studied. Kindling produced no lasting changes in this measure at 1 4-22 days; in the older age groups a significant increase in paired pu lse depression was seen. Thus immature animals differed from adults in that they manifested persistent facilitation of excitatory transmissi on as a result of kindling and failed to mount a compensatory inhibito ry response. These results suggest that the balance between excitation and inhibition is more readily shifted toward excitation in immature animals in a manner that may contribute to their unique vulnerability to epileptogenesis.