Morphological and behavioral consequences of recurrent seizures in neonatal rats are associated with glucocorticoid levels

Adult Neurogenesis in Epileptogenesis: An Update for Preclinical Finding and Potential Clinical Translation

Epileptogenesis refers to the process in which a normal brain becomes epileptic, and is characterized by hypersynchronous spontaneous recurrent seizures involving a complex epileptogenic network. Current available pharmacological treatment of epilepsy is generally symptomatic in controlling seizures but is not disease-modifying in epileptogenesis. Cumulative evidence suggests that adult neurogenesis, specifically in the subgranular zone of the hippocampal dentate gyrus, is crucial in epileptogenesis. In this review, we describe the pathological changes that occur in adult neurogenesis in the epileptic brain and how adult neurogenesis is involved in epileptogenesis through different interventions. This is followed by a discussion of some of the molecular signaling pathways involved in regulating adult neurogenesis, which could be potential druggable targets for epileptogenesis. Finally, we provide perspectives on some possible research directions for future studies.

Down-regulation of APLP1 mRNA expression in hippocampus of pilocarpine-induced epileptic rats

OBJECTIVE

To investigate the expression of amyloid beta precursor-like protein 1(APLP1) gene on the transcription level in hippocampus of pilocarpine-induced epileptic rats.

METHODS

Epileptic rats were developed by LiC1 (3 mmol/kg, i.p.) approximately 20 h prior to pilocarpine (30 mg/kg, i.p.) administration. The 3' end partial sequence of rat APLP1 gene was cloned, and the expression levels of APLP1 mRNA in hippocampus of epileptic rats at 6 h, 30 h, 7 d and 15 d were determined by semi-quantitative RT-PCR.

RESULTS

The 3'end partial sequence of rat APLP1 gene shared a 97% homology with that of mice, and 90% with that of human. The APLP1 amino acid sequence of rat was identical with that of mouse, but was different from that of human in 3 residues. Moreover, pilocarpine induced a significant down-regulation of APLP1 mRNA expression at 6 h after epilepsy initiation (P< 0.05), and at 30 h, this down-regulation became more dramatic (P< 0.01), which lasted till day 15 (P< 0.01).

CONCLUSION

The 3' end of APLP1 gene is highly conserved, and APLP1 mRNA expression is kept at low level in hippocampus of pilocarpine-induced epileptic rats.

Fragile X syndrome and epilepsy

Fragile X syndrome (FXS) is one of the most prevalent mental retardations. It is mainly caused by the loss of fragile X mental retardation protein (FMRP). FMRP is an RNA binding protein and can regulate the translation of its binding RNA, thus regulate several signaling pathways. Many FXS patients show high susceptibility to epilepsy. Epilepsy is a chronic neurological disorder which is characterized by the recurrent appearance of spontaneous seizures due to neuronal hyperactivity in the brain. Both the abnormal activation of several signaling pathway and morphological abnormality that are caused by the loss of FMRP can lead to a high susceptibility to epilepsy. Combining with the research progresses on both FXS and epilepsy, we outlined the possible mechanisms of high susceptibility to epilepsy in FXS and tried to give a prospect on the future research on the mechanism of epilepsy that happened in other mental retardations.

Postnatal and adult neurogenesis in the development of human disease

The mammalian brain contains a population of neurons that are continuously generated from late embryogenesis through adulthood-after the generation of almost all other neuronal types. This brain region-the hippocampal dentate gyrus-is in a sense, therefore, persistently immature. Postnatal and adult neurogenesis is likely an essential feature of the dentate, which is critical for learning and memory. Protracted neurogenesis after birth would allow the new cells to develop in conjunction with external events-but it may come with a price: while neurogenesis in utero occurs in a protected environment, children and adults are exposed to any number of hazards, such as toxins and infectious agents. Mature neurons might be resistant to such exposures, but new neurons may be vulnerable. Consistent with this prediction, in adult rodents seizures disrupt the integration of newly generated granule cells, whereas mature granule cells are comparatively unaffected. Significantly, abnormally interconnected cells may contribute to epileptogenesis and/or associated cognitive and memory deficits. Finally, studies increasingly indicate that new granule cells are extremely sensitive to a host of endogenous and exogenous factors, raising the possibility that disrupted granule cell integration may be a common feature of many neurological diseases.