, 2011). This provides an anatomical substrate for synthesis of co-occurring odorant features. In fact, piriform cortical neurons may require coactivation of multiple glomeruli to drive spiking activity. Photo-uncaging of glutamate with precise spatial patterns of photo-stimulation in the olfactory bulb glomerular layer with intracellular recording of piriform cortex pyramidal cells in vivo showed that individual cells were responsive to specific spatial patterns of glomerular activation ( Davison and Ehlers, 2011). Single glomerular activation was ineffective at driving cortical neurons. Similar
results were reported in an in vitro olfactory bulb-piriform cortex slice ( Apicella et al., 2010). Of course cortical association fiber activity contributes to this pyramidal SAR405838 solubility dmso cell activity, but the results strongly suggest convergence of multiple glomerular input onto individual
pyramidal cells. Interestingly, similar convergence of odor feature information onto individual neurons appears to occur in see more the zebrafish dorsal pallium, the homolog of mammalian olfactory cortex ( Yaksi et al., 2009). The efficacy of individual afferent fibers in driving cortical pyramidal cells is also consistent with a convergence requirement. Although afferent fiber glutamatergic synapses onto piriform cortical pyramidal cells are relatively strong, layer II pyramidal cells require coactivation of multiple afferent fibers to reach spike threshold (Franks and Isaacson, 2006, Suzuki and Bekkers, 2006 and Suzuki and Bekkers, 2011). However, subclasses of pyramidal cells show differential sensitivity to afferent input. Semilunar cells, which have apical dendrites with large spines located selectively
within Layer Ia and thus anatomically appear highly sensitive to afferent input, are in fact more strongly depolarized by afferent input than superficial pyramidal cells in Layer II (Suzuki and Bekkers, 2011). In addition, semilunar cells have no basal dendrites (Neville and Haberly, 2004) and thus appear to be primarily tuned to afferent input with only minimal responses to association fiber no input (Suzuki and Bekkers, 2011). Thus, these cells may have unique contributions to the intracortical association fiber system described below. For example, semilunar cells form a major component of the association fiber input to superficial pyramidal cells, forming in essence a second layer of processing in piriform cortex (Suzuki and Bekkers, 2011). Interestingly, semilunar cells are also profoundly affected by loss of afferent input, showing rapid apoptosis following either olfactory bulbectomy (Capurso et al., 1997 and Heimer and Kalil, 1978) or naris occlusion (Leung and Wilson, 2003).