Whole-cell recordings without GTP uncover T-type Ca²⁺ channel contribution to mature GC excitability and LTP. A, Example first ISIs in response to current injections 5 min after breaking into a mature GC without GTP in the pipette, before (above) and after TTA application (below). Right, Paired t test, t₍₇₎ = 2.6 *p = 0.03. n = 8. B, Example EPSPs in mature GCs in ACSF (top) or TTA (bottom) without GTP in the pipette before and after TBS. Middle, When GTP is excluded from the recording pipette, mature GCs exhibit robust LTP with inhibition intact (n = 7) that is sensitive to TTA (n = 6). Right, Summary of EPSP amplitudes at 25–30 min post-TBS, unpaired t test, t₍₁₁₎ = 2.8, *p = 0.02.