, 1966 and Suga, 1968). Along the central auditory pathway of rats, such neurons have been observed in the inferior colliculus (Clopton and Winfield, 1974, Selleck HKI-272 Felsheim and Ostwald, 1996 and Rees and Møller, 1983), the medial geniculate body (Lui and Mendelson, 2003), and

the auditory cortex (Ricketts et al., 1998, Ye et al., 2010 and Zhang et al., 2003). Direction selectivity (DS) of cortical neurons is inherited from their excitatory inputs and shaped by cortical inhibition, and its topography is highly correlated with the tonotopic map (Zhang et al., 2003). Because the selectivity for FM direction is not observed in the auditory nerve fibers (Sinex and Geisler, 1981), the inputs to the central auditory system, it is reasonable to assume that direction selectivity and its topography emerges somewhere between the cochlear nuclei and the auditory cortex. Previous studies suggest that the inferior colliculus is the major processing stage at which direction selectivity is constructed, because PLX-4720 order most of the cells in lower auditory nuclei are not direction selective, especially in rats (Moller, 1969 and Poon et al., 1992). Two mechanisms are hypothesized to explain the emergence of direction selectivity (Gittelman et al., 2009 and Suga, 1968). One hypothesis relies on the temporal asymmetry between excitation and

inhibition, in which the preferred direction activates excitatory inputs first, whereas the null direction activates inhibitory inputs first. The second hypothesis depends on the temporal coincidence of the arrival of the synaptic inputs, in which the preferred direction activates more coincident excitatory inputs or less coincident Terminal deoxynucleotidyl transferase inhibitory inputs, whereas the situation is reversed for the null direction. It is worth noting that to prove either hypothesis requires a clear dissection of synaptic inputs to the identified DS neurons. Recently, several studies suggested that inhibition shapes neurons’ direction selectivity, which is inherited from presynaptic neurons at different

processing stages (Gittelman et al., 2009, Ye et al., 2010 and Zhang et al., 2003). However, to understand the synaptic circuitry mechanisms that generate direction-selective responses, we have to target those DS neurons receiving nonselective inputs and directly examine both their excitatory and inhibitory inputs in sufficient detail. In this study, by using multiunit recording techniques, we mapped all the three major subcortical nuclei of the central auditory pathway, including the cochlear nuclei (CN), the inferior colliculus (IC), and the medial geniculate body (MGB) of rats, to search for DS neurons and their topography. With cell-attached (loose-patch) recordings followed by juxtacellular labeling, we identified the morphology of DS neurons in the IC post hoc.