Altered paired pulse facilitation in the fragile X hippocampus Paired pulse stimulation at inter-stimulus intervals (ISI) of 100 ms and up to 300 ms consistently yielded facilitation as determined by the increase of the second EPSP (p2) compared to the first (p1). In Fmrp1-KO slices, stimulation of the hippocampal slices from Fmr1-KO resulted in a consistent depression of the second evoked response at all ISI used. Application of taurine (10µM) resulted in a paired pulse depression of WT responses but not Fmr1-KO. Each data point represents mean ± SEM of EPSP obtained following the paired pulse stimulation and expressed as [(p2-p1)/p1*100]. Data were obtained from 3 brains in each group and at least 5 slices per brain.