3.2. Hippocampal Neuron-Derived Cell Line HN2-5

The parent cell line HN2 was developed by Lee and coworkers through somatic cell fusion of embryonic day 18 (E18) hippocampal cells, N18TG2 neuroblastoma cells [36]. Banerjee and coworkers performed stable transfection of the G-21pBCI vector harboring a genomic clone of the human 5-HT_1A-R gene [37,38] (a generous gift from Drs. Raymond and Lefkowitz). The HN2-5 clone obtained after selection with G418 expressed the functional 5-HT_1A-R that was negatively coupled to adenylyl cyclase [25]. Furthermore, both the parent HN2 cells as well as the HN2-5 cells could be differentiated in the presence of 5 μM retinoic acid in 1% serum-containing DMEM to yield hippocampal neuron-like processes, which showed intense immunoreactivity with the neurofilament protein antibody SMI33 but not with glial fibrillary acidic protein (GFAP) antibody [26,39]. Upon nutrient deprivation stress, the HN2-5 cells displayed induced expression of the 5-HT_1A-R gene as did cultured hippocampal neurons [26]. To the best of our knowledge, there is no other hippocampal neuron-derived cell line that expresses the 5-HT_1A-R. More signaling studies performed on this cell line have been cited in this report. Based on such background, the undifferentiated HN2-5 cells were deemed useful in this project as a model for the 5-HT_1A-R-expressing neuroblasts in the hippocampus.