Figure 4. Gamma frequency oscillations support long-lasting synaptic plasticity.
(A) Light micrograph of an example CA3 PC. Insert: The regular firing pattern of this PC in response to a depolarizing current injection. (B) The area of SWR-associated EPSC increases significantly after gamma frequency oscillations (gray and red filled squares for EPSCs and p-EPSC, respectively). Administration of MPEP (50 µM) prevents the increase of p-EPSC (gray and black filled triangles illustrate EPSC and p-EPSC, respectively). Holding PCs in voltage clamp configuration at −70 mV during gamma frequency oscillations leads to a significant decrease in EPSC area (gray and red open squares for EPSC and p-EPSC, respectively). The significance stars compare the pre-gamma data with the marked post-gamma data. Insert: Representative examples of EPSC (gray) and p-EPSC recorded without (left, red) and with MPEP (middle, black), as well as using voltage clamping of cells during gamma rhythms (right, red, gamma-VC). (C) SWR-associated IPSCs exhibit a moderate increase in area in PCs held in both current- (filled gray and blue triangles) and voltage-clamp mode (open gray and black triangles for IPSC and p-IPSC, respectively) during gamma rhythms. Inserts: Representative examples of corresponding IPSC (gray) and p-IPSC (gamma-CC, blue and gamma-VC, black). (D) Contra-directional change in p-EPSC to p-IPSC ratio for PCs held in current- (gamma-CC) vs. voltage-clamp mode (gamma-VC) during gamma rhythms (normalized to pre-gamma values).