Amygdaloid?Striatal Substrates Underlying Odor Hedonics and Odor-Guided Behaviors

Colleen A Payton,Daniel W Wesson

doi:10.3389/fnana.2011.00061

Abstract

tory tubercle by the amygdala. The olfac-tory tubercle is a striatal structure with a cortical-like organization which displays odor-evoked activity and may be criti-cal for olfactory perception (Wesson and Wilson, 2011). The anatomical findings by Novejarque et al. (2011) along with those of previous groups (Usunoff et al., 2009) suggest the involvement of the olfactory tubercle (and perhaps the tubercle’s strong connections with the basal ganglia) in the emotional regulation of olfactory percep-tion and the strong hedonic responses evoked by odors (e.g., Herz and Cupchick, 1995). Despite this, without data showing the role of the olfactory tubercle to olfactory processing, little can be inferred regarding the amygdala innervation of the olfactory tubercle.Another major contribution of the pre-sent study was the finding that all cortical amygdaloid nuclei (excluding the piri-form cortex) innervate the major island of Calleja. This was especially the case for the posteromedial cortical amygdaloid nucleus. The islands of Calleja are dense granule cell clusters residing mostly within layers II and III of the olfactory tubercle in rodents and largely in the nucleus accum-bens in humans. However, the function of the islands of Calleja is unknown. Thus while this finding by Novejarque et al. (2011) is difficult to interpret in terms of functional consequences, it is almost undoubted that the amygdala’s dense innervation of the major island of Calleja will be found important to the emotional modulation of odor perception (given their positioning within the olfactory tubercle) and to the regulation of socio-sexual behaviors.There are ample future directions to link these anatomical findings by Novejarque et al. (2011) to functional significance. First, and most recently discussed, would elimi-nation or inactivation of the major island of Calleja abolish associative changes in odor hedonics? This of course is based upon the

Highlights

Imagine taking a long sniff of your favorite dinner plate, and the strong sense of pleasure felt as you anticipate eating and eventually filing your hunger
While amygdala innervation of the nucleus accumbens’ core and shell regions has received considerable attention (e.g., Everitt et al, 1999), none were performed with such detail in mice as that performed by Novejarque et al (2011)
Perhaps correlating with the complexity and diversity of these learned behaviors, the authors report that the fiber pathways between the amygdala and ventral striatum vary in density and destination depending upon their origin

Summary

Introduction

Imagine taking a long sniff of your favorite dinner plate, and the strong sense of pleasure felt as you anticipate eating and eventually filing your hunger. The authors employed anterograde and retrograde tract-tracing experiments in mice to examine amygdala connectivity with the olfactory tubercle, the nucleus accumbens, and the islands of Calleja. Novejarque et al (2011) hypothesize that the direct projections may be stimulated through an unconditioned response to odors, possibly pheromones, whereas the indirect projections would likely be stimulated through a learned response to associated stimuli.

Results

Conclusion