, 2006; Walter et al., 2007; Kron et al., 2010; Santos et al., 2011; Danzer, 2012). Gli1-CreERT2 expression in the neonatal dentate gyrus is restricted to granule cell progenitors, so PTEN deletion in the present study targets that same population of neurons that is implicated in these traditional models of temporal lobe epilepsy. While small in relative number, however, computational modeling studies predict that only 5% of the granule cell population needs to be abnormal

to support seizures Linsitinib clinical trial ( Morgan and Soltesz, 2008). It is notable, therefore, that abnormal granule cell numbers here were well above this threshold, and epilepsy developed rapidly. PTEN deletion reproduced numerous hippocampal granule cell pathologies associated with temporal lobe epilepsy, including mossy fiber sprouting ( Tauck and Nadler, 1985; Nadler, 2003), ectopic granule cells ( Scharfman et al., 2000), hilar basal dendrites ( Ribak et al., 2000), somatic hypertrophy and increased spine density ( Murphy et al., 2011). Mossy fiber sprouting was only present among

a subset of PTEN KO animals with seizures; however, sprouting was strongly correlated with the percentage of PTEN KO cells within the dentate. Taken together, these observations indicate that sprouting is not required for epilepsy in this model, but that greater numbers of KO cells promote more robust sprouting. Moreover, in animals with robust sprouting, roughly found 75% was derived from GFP-negative (PTEN wild-type) cells ( Figure 8). One plausible

interpretation of these findings is Ruxolitinib that animals with more KO cells develop a more severe or earlier onset epilepsy. Repeated seizures can induce mossy fiber sprouting among wild-type granule cells ( Cavazos et al., 1991), so earlier disease onset or more severe disease would be predicted to promote greater mossy fiber sprouting. Technical limitations in recording 24/7 EEG from very young animals precluded us from determining the age at which seizures first appear in these animals, and analysis of data from older animals did not reveal any significant correlations. Nevertheless, the ability to dissociate mossy fiber sprouting and seizures could make this a useful model for future studies of this particular plasticity. In contrast to mossy fiber sprouting, neuronal hypertrophy, basal dendrites, and increases in spine density were present among almost all PTEN KO granule cells regardless of whether the animals developed epilepsy, indicating that these changes could contribute to disease etiology. Recent work suggests that neuronal hypertrophy and increased spine density observed here likely reflect proexcitatory changes in granule cells ( Luikart et al., 2011). In this prior study, PTEN mRNA was targeted in granule cells using a shRNA-lentiviral approach, reducing PTEN levels by about 80%.