DEVELOPMENT OF INHIBITORY AND EXCITATORY SYNAPTIC TRANSMISSION IN THERAT DENTATE GYRUS

We studied the ontogeny of inhibitory and excitatory processes in the rat dentate gyrus by examining paired-pulse plasticity in the hippocam pal slice preparation. The mature dentate gyrus produces characteristi c paired-pulse responses across a wide range of interpulse intervals ( IPI). Paired-pulse effects on population excitatory postsynaptic poten tial (EPSP) slope and population spike (PS) amplitude were analyzed at postnatal day 6 (PN6), PN7/8, PN9/10, PN15/16, and PN>60. The synapti c paired-pulse profile (10-5,000 ms IPI) matured by PN7/8. The triphas ic pattern of short-latency depression, a relative facilitation at int ermediate intervals, and long-latency depression was present at all ag es tested. Paired-pulse effects on granule cell discharge indicated th e presence of weak short-latency (20 ms IPI) inhibition at PN6, the ea rliest day that a population spike could be evoked. By PN7/8, short-la tency inhibition was statistically equivalent to the mature dentate gy rus. Long-latency (500-2,000 ms IPI) PS inhibition was present, and eq ual to the mature dentate gyrus by PN6. The most consistent difference between the mature and developing dentate gyrus occurred at intermedi ate IPIs (40-120 ms) where spike facilitation was significantly depres sed in the developmental groups. The studies indicate that short-term plasticity matures rapidly in the dentate gyrus and suggest that the i nhibitory circuitry can function at a surprisingly early age. (C) 1994 Wiley-Liss, Inc.