Back-propagating potentials are modulated by extracellular pH and Mg²⁺.

Sample recordings show the responses of CA1 cells from RTT (A) and WT animals (B) as indicated. bAPs were evoked by 8 pulses delivered at 100 Hz. Calcium changes were measured as relative changes in fluorescence of fluo-4 added to pipette solution. Upper traces in each panel show voltage trajectories and the lower traces indicate calcium changes in the apical dendrite (100 μm apart from the cell soma, see the inset, left bottom). In the control ACSF (pH 7.4), stimulation triggered normally several discharges within a minute after bAPs, which were mirrored by the calcium transients (lower violet traces). The responses in RTT CA1 neurons (B) showed marked enhancement. In ACSF with pH 8.4, the post-stimulation activities in WT and RTT were augmented (in RTT to much bigger extent). Lowering external pH to 6.4 and 8 mM Mg²⁺ markedly depressed ‘after-discharges’. Group summaries in the lower part of (A) and (B) represent peak calcium amplitudes during bAPs and the integral during after-discharges. The data was evaluated before and 2 min after the exchange of bathing solutions. The inset in the left bottom corner shows a typical CA1 neuron filled with fluo-4.