Overactivation of Notch1 Signaling Induces Ectopic Hair Cells in the Mouse Inner Ear in an Age-Dependent Manner

Background: During mouse inner ear development, Notch1 signaling first specifies sensory progenitors, and subsequently controls progenitors to further differentiate into either hair cells (HCs) or supporting cells (SCs). Overactivation of NICD (Notch1 intracellular domain) at early embryonic stages leads to ectopic HC formation. However, it remains unclear whether such an effect can be elicited at later embryonic or postnatal stages, which has important implications in mouse HC regeneration by reactivation of Notch1 signaling. Methodology/Principal Findings: We performed comprehensive in vivo inducible overactivation of NICD at various developmental stages. In CAG CreER+; Rosa26-NICD loxp/+ mice, tamoxifen treatment at embryonic day 10.5 (E10.5) generated ectopic HCs in the non-sensory regions in both utricle and cochlea, whereas ectopic HCs only appeared in the utricle when tamoxifen was given at E13. When tamoxifen was injected at postnatal day 0 (P0) and P1, no ectopic HCs were observed in either utricle or cochlea. Interestingly, Notch1 signaling induced new HCs in a non-cell-autonomous manner, because the new HCs did not express NICD. Adjacent to the new HCs were cells expressing the SC marker Sox10 (either NICD+ or NICDnegative). Conclusions/Significance: Our data demonstrate that the developmental stage determines responsiveness of embryonic otic precursors and neonatal non-sensory epithelial cells to NICD overactivation, and that Notch 1 signaling in the wild type, postnatal inner ear is not sufficient for generating new HCs. Thus, our genetic mouse model is suitable to test additiona

The pilocarpine model of epilepsy in mice

Purpose: To characterize the acute and chronic behavioral, electrographic and histologic effects of sustained seizures induced by pilocarpine in mice.Methods: After status epilepticus, the surviving animals were continuously monitored for 24 h/day for less than or equal to 120 days. the brains were processed by using neo-Timm and Nissl stains.Results: the first spontaneous seizures occurred between 4 and 42 days after status epilepticus. the mean ''seizure-silent period'' lasted for 14.4 +/- 11.9 days. During the chronic phase, recurrent spontaneous seizures were observed 1-5 times per animal per week and were associated with sprouting in the supragranular layer of the dentate gyrus.Conclusions: Structural brain damage promoted by pilocarpine-induced status epilepticus may underlie or be associated with recurrent spontaneous seizures in mice.UNIFESP, EPM, RUA BOTUCATU 862, BR-04023900 São Paulo, BRAZILUNIFESP, EPM, RUA BOTUCATU 862, BR-04023900 São Paulo, BRAZILWeb of Scienc