4.35 - Regeneration in the Olfactory Bulb

Abstract

Most organisms rely on an olfactory system to detect and analyze chemical cues from the external world in the context of essential behavior. From insects to vertebrates, chemicals are detected by odorant receptors expressed by olfactory sensory neurons, which send an axon to the primary processing center: the olfactory bulb in vertebrates. Within this relay, sensory neurons form excitatory synapses with projection neurons – the mitral/tufted cells – and with local inhibitory interneurons. As a result of complex synaptic interactions, the output of a given projection neuron is determined not only by the sensory input, but also by the activity of local microcircuits. Furthermore, the olfactory bulb both processes sensory information from the odor space and integrates a number of newly formed interneurons. Recent studies have provided clues to how these newcomers incorporate into a preexisting neural network and how basic network functions are maintained when a large percentage of neurons are continually being renewed. Here I describe the adaptation of new interneuron production to experience-induced plasticity. In particular, I will show how the integration of newly generated neurons is highly sensitive to the level of sensory inputs and how, in turn, neurogenesis may adjust the functioning of the neural network to optimize the processing of sensory information. Ongoing neurogenesis in adults, by maintaining a constitutive turnover of bulbar interneurons subject to modulation by environmental cues, is associated with improvements in sensory and cognitive abilities. Finally, this chapter brings together recent descriptions of the properties of interneurons and emerging principles concerning their functions indicating that these cells play a much more complex role than that of simple gatekeepers inhibiting the olfactory bulb network.