Nonetheless, any individual cell of a given type can dynamically alter its precise molecular profile and corresponding physical and electrical properties in response to a variety of external cues (Curran and Morgan, 1985 and Greenberg et al., 1985). Hence, although all cells of the same type stably express a common suite of genes, individual Selleckchem RAD001 members of a cell type may vary in the precise profile of genes expressed depending upon context and activity. We argue also that this ground state is determined shortly after cells exit from their last mitotic

cycle and that the execution and stabilization of neuronal gene expression programs require local events that occur in the final stages of maturation during what are commonly referred to as “critical periods” of development. Furthermore, although it is apparent that cell types can be defined molecularly, an understanding of the nervous system cannot be reached without comprehensive data regarding the circuits in which

they are embedded, their connectivity, and their activity patterns in response to appropriate external stimuli. Only then can we begin to achieve CH5424802 datasheet the ultimate goal of providing an understanding of the contributions of discrete cell types to behavior. In a general sense, the number of cell types present within a given substructure of the nervous system reflects the computational complexity of its functions. In simple organisms or in the context of the peripheral

nervous system (Garcia-Campmany Aplaviroc et al., 2010 and Arber, 2012), the contributions of many specific cell types to behavior have been studied in great detail, and, in most cases, the reasons for their specialization are apparent. For example, specific sensory and motor neuronal classes with distinct anatomical and electrophysiological properties make up simple motor circuits that generate fixed action patterns (Schiff et al., 1999). Local neuron types modulate or generate rhythmic behaviors, allowing these cell types to execute discrete functions (Bargmann and Marder, 2013 and Goulding and Pfaff, 2005). This general model may apply for even more complex circuits with a relatively large number of identifiable cell types. It is believed that a nearly complete accounting for all cell types present in the mammalian retina places the number at around 60 discrete types (Masland, 2012). Although the precise functions of each of these cell types are not known, the fact that they are tiled across the retina suggests that each of them contributes to specific aspects of visual perception. A particularly clear recent example of this idea comes from studies of the JamB retinal ganglion cell population in which the anatomy, physiology, receptive fields, and distribution of JamB cells are all tailored for their ability to perceive upward motion (Kim et al., 2008).