Frequency potentiation in granule cells in vivo at theta frequency perforant path stimulation

The effect of frequency potentiation on the postsynaptic potential in granule cells was studied stimulating the perforant path in curarized and urethanized rats. At stimulation frequencies between 2.0-5.0 Hz, synaptic efficacy in eliciting an orthodromic action potential increased despite the hyperpolarization of the transmembrane potential. The excitatory postsynaptic potential (EPSP) slope and duration also increased while the inhibitory postsynaptic potential (IPSP) was reduced. Stimulation frequencies greater than 5.0 Hz produced similar changes in the transmembrane potential and EPSP-IPSP sequence, but they did not increase synaptic efficacy. The frequency potentiation at frequencies into the theta band suggest that this potentiation participates in theta rhythm genesis in this structure which, in turn, suggests that the fascia dentata could work as a band-pass filter. In 12.5% of cases postpotentiation was also observed.