Effects of iontophoretic application of trimethyltin on spontaneous neuronal activity in mouse hippocampal slices.

Changes in spontaneous activity in various regions of mouse hippocampal slices were observed following iontophoretic application of trimethyltin (TMT). TMT (0.5 mM) dissolved in 0.15 M NaCl and ejected in 30 sec periods from four barrel micropipettes using anodal ejection currents (3-28 nA) produced dose dependent increases in the spontaneous activity of 67.6% of the 34 dentate gyrus cells tested. Seventy percent of the 25 CA3 cells tested displayed prolonged (30-200 sec) decreases in activity. The majority of CA1 and CA2 cells examined also displayed a decrease in firing rate. Repeated applications of TMT produced increased variability in spontaneous firing rates in all regions tested. When slices were maintained in a low Ca++, high Co++ perfusion fluid to inhibit synaptic activity, the TMT induced increase of dentate gyrus cell firing rate was not observed. The results demonstrate that direct application of TMT produces immediate changes in hippocampal cell activity that is specific for certain regions. Significant increases in firing rate were only observed in the dentate gyrus and these effects were calcium dependent.