Immediate early genes and sensory maps of olfactory and gustatory function

Abstract

Considerable progress has been achieved towards the understanding of molecular and physiological properties of sensory systems, transmission and encoding of sensory stimuli. However, it remains largely mysterious how, in molecular terms, perception of a sensory stimulus is associated and related to internal representations of previous experience and emotions resulting in the meaningful integration of sensory information. Furthermore, how sensory stimulus processing is finally transformed into long lasting cellular changes, and how these enable the formation of memories that affect behavior (e.g. a stimulus becomes familiar, associated with a cue and thus the identical stimulus later results in a different response) remains largely hypothetical. Investigations conducted in recent years have allowed researchers to gain insight into some of the molecular processes underlying synaptic plasticity and to develop concepts considering plasticity as fundamental to the formation of a memory. In this chapter, we will summarize some work using immediate early gene (IEG) expression in the olfactory and gustatory systems for functional mapping. These studies provide new insight about odor and taste coding, processing of novel versus familiar stimuli, and the neuronal networks involved and illustrate that IEGs are not simply markers of neuronal activity but rather indicate information processing and plasticity events. IEG expression identifies neurons undergoing long lasting molecular changes, thus, the study of IEG expression patterns reveals the activation of neuronal circuitry involved in the processing of information.