A region of the mammalian brain called the hippocampus is crucial for memory formation. However, how the hippocampus plays a key role in encoding time-varying information is not fully understood. The hippocampus is unique because it is one of only two brain regions in mice that generate new neurons throughout life in a process known as adult neurogenesis. This peculiar anatomical feature has been hypothesized to be central to the ability of the hippocampus to make fine distinctions between similar experiences in a process known as pattern separation. New hippocampal neurons, known as newborn dentate granule cells (DGCs), are believed to play a vital role in the brain’s ability to perform pattern separation. However, DGCs rarely fire action potentials, so traditional electrophysiological techniques that depend on data collected from highly active neurons are not optimal and cannot reliably identify the rarely-firing DGCs. As a result, there are significant gaps in knowledge about how newborn DGCs contribute to the ability of the hippocampus to perform pattern separation, particularly on time-varying information. Central to this study is the optimization of a behavioral paradigm in which head-fixed mice perform a novel temporal pattern separation task that is amenable to study with two-photon calcium imaging. This study establishes a novel training protocol to allow for in-depth study of the temporal aspects of pattern separation in vivo.

Mesial temporal lobe epilepsy (mTLE) is the most common form of temporal lobe epilepsy in adults, and is characterized by seizure activities and pathological changes in the limbic region, including the hippocampal formation. The dentate gyrus (DG) is thought to be a critical node in the hippocampus, with its unique properties, to prevent hippocampus from overexcitation. DG is also one of the only two places in mammalian brain that has new neurons born during adulthood. In both human and animal mTLE models, dramatic changes in migration and wiring of immature new-born dentate granule cells cause them to form pathological excitatory connections with neighboring DGCs. This has been considered as a major contributor to hippocampal hyperexcitability and epileptogenisis in mTLE. Studies have shown that grafting GABAergic inhibitory interneurons into epileptic mTLE mouse model can significantly reduce seizure activity. However, isolating safe, effective and ethical source of inhibitory precursor cells could be challenging for human patients. Hence, we hypothesize that using retrovirus in vivo to overexpress complement inhibitory transcription factors in aberrant DGCs can reprogram them into GABAergic inhibitory interneurons. In order to reach that goal, we first identified Sox2 transcription factor as a way to maintain or reverse the development of adult-born immature DGCs into a multipotent state. However, in the process, we have noticed substantial fluorescent signals in the hilus region, which should not contain any dividing cells. With multiple staining, we have discovered that the extensive fluorescent signals largely mossy cells that appeared to be infected with retrovirus. With further experiments, we found that red fluorescent gene mScarlet was the root cause. We later replaced mScarlet with another red fluorescent reporter gene dTomato and did not see any red fluorescent signal in the hilus region. Future work would involve making a retrovirus construct that contains Sox2 and alternative red fluorescent proteins such as dTomato as well as an inducible Sox2 construct that will give us temporal control. Moreover, we will investigate the possible combination of inhibitory GABAergic and proneural transcription factors Lhx6, Dlx5, Ascl2 and Ngn2, and co-inject with Sox2 construct.

Glioblastoma multiforme (GBM) is one of the most lethal and common forms of brain tumors. There are currently no effective treatment strategies against GBM. In this study, we demonstrate a new treatment strategy of killing cancer stem cells (CSCs) within a GBM tumor using virotherapy with the widely used recombinant adeno-associated virus (rAAV). We show that there is dose-dependent toxicity of rAAV on adult GBM CSCs. Further experiments will demonstrate that the inverted palindromic repeats (ITRs) sequences from rAAV kill GBM CSCs in a dose-dependent manner as well. AAV-mediated toxicity on GBM CSCs and other neural progenitor cells (NPCs) can be explained by overactivation of poly(ADP-ribose) polymerase 1 (PARP-1). Virotherapy against CSCs can be an effective treatment strategy against pediatric GBM or other tumors that involve CSCs.

The most common form of focal epilepsy in adults is mesial temporal lobe epilepsy (mTLE). Evidence points to the hippocampal formation as a key site of epileptogenesis of mTLE, but its mechanisms remain unknown. The dentate gate hypothesis has been a major mechanistic concept in epilepsy for over 20 years which posits that the sparse firing of the dentate gyrus acts as a ‘gate’ that prevents overexcitation of hippocampal circuits that lead to epilepsy. Using in vivo two-photon microscopy and surgical implantation of a chronic cranial imaging window, we were able to study the network activity within the hippocampus in awake mice. Consistent with the dentate gate hypothesis, we found increased hyperexcitability in the dentate gyrus of epileptic mice using a status epilepticus (SE) model in which SE was induced at 6 weeks of age or older. Surprisingly, mice induced with SE at 3 weeks of age did not develop hyperexcitability. The results of this study will be used to further study the pathophysiological and electrophysiological differences between younger and older mice induced with SE.