In complex tissues such as the central nervous system, differentiation and functional activity often require temporally and spatially dynamic epigenetic cues that cannot be reproduced in dissociated cell cultures. Organotypic cultures and, among them, hippocampal slice cultures represent in vitro models that keep the different cell types and retain the complex three-dimensional organization of the nervous tissue. In addition, much of the appropriate synaptic circuitry, physiology, and neurotransmitter receptor distribution of the intact hippocampus is preserved in this type of culture (Bahr, 1995 ; Gahwiler et al., 1997 ). Functional activities of neurons in slice culture were found to be similar to theirin situcounterparts. These cultures can be grown for many weeks without any passages. More mature neurons (until 21–23 d postnatal) can be grown with slice culture, but only embryonic or neonatal neurons can be grown with dissociated cell culture techniques. Finally, if needed, even more complexity can be achieved by co-culturing different brain target areas.
