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 paired pulse depression were studied in the dentate gyrus of rats at four 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 sustained potentiation of population spike amplitude and population EPSP slope; in adults a progressive decline was seen in both measures. Inhibitory circuitry as assessed by paired pulse depression was intact at all ages studied. Kindling produced no lasting changes in this measure at 14-22 days; in the older age groups a significant increase in paired pulse depression was seen. Thus immature animals differed from adults in that they manifested persistent facilitation of excitatory transmission as a result of kindling and failed to mount a compensatory inhibitory 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.