Figure 4: Chem-LTP in vivo causes synchronous bursting activity in the visual cortex.

(a) The upper trace (black) shows the field recording resulting from perfusion with the Chem-LTP solution. Each large response recorded by the field electrode is associated to the synchronous firing of all neurons in the field, as shown by simultaneous two-photon imaging of calcium concentration. The coloured traces show Ca²⁺ activity of the brightest cells in the field. Images on the right show the Ca²⁺ changes occurring during the burst indicated by the red bar over the field recording. The last image shows the field where neurons are stained by Oregon Green Bapta1, whereas one astrocyte and several processes are stained in red by the dye Sulforhodamine 101. Scale bar, 15 μm. (b) Electrophysiological recordings at the peak of the bursting activity in a control mouse (upper trace) and in a mouse treated with ChABC (lower trace). Insets show typical bursts on an enlarged time scale. (c) Activation of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and NMDA receptors during the synchronous bursts. The red trace show that activation of NMDA receptors supports the late phase of the burst, whereas the early phase, not blocked by APV, is supported by AMPA activation. The red and green traces were recorded immediately before and after superfusion with the NMDA blocker APV. (d) Plots showing the time course of burst frequency. The treatment with the Chem-LTP solution lasts 10 min (black horizontal bar) and bursting activity appears towards the end of treatment. The coloured plots show data from four control mice and four mice treated with ChABC. (e) Average time course of the burst frequency for control and treated mice (mean and s.e.m.).