Blocking muscarinic receptors in the olfactory bulb impairs performance on an olfactory short-term memory task

Sasha Devore,Laura C Manella,Christiane Linster

doi:10.3389/fnbeh.2012.00059

Abstract

Cholinergic inputs to cortical processing networks have long been associated with attentional and top-down processing. Experimental and theoretical studies suggest that cholinergic inputs to the main olfactory bulb (OB) can modulate both neural and behavioral odor discrimination. Previous experiments from our laboratory and others demonstrate that blockade of nicotinic receptors directly impairs olfactory discrimination, whereas blockade of muscarinic receptors only measurably impairs olfactory perception when task demands are made more challenging, such as when very low-concentration odors are used or rats are required to maintain sensory memory over long durations. To further investigate the role of muscarinic signaling in the OB, we developed an olfactory delayed match-to-sample task using a digging-based behavioral paradigm. We find that rats are able to maintain robust short-term odor memory for 10–100 s. To investigate the role of muscarinic signaling in task performance, we bilaterally infused scopolamine into the OB. We find that high dosages of scopolamine (38 mM) impair performance on the task across all delays tested, including the baseline condition with no delay, whereas lower dosages (7.6 mM and 22.8 mM) had no measureable effects. These results indicate that general execution of the match-to-sample task, even with no delay, is at least partially dependent on muscarinic signaling in the OB.

Highlights

Cholinergic inputs to cortical processing networks have long been proposed to be associated with attentional and top-down processing (Hasselmo et al, 1992; Sarter and Bruno, 1997; Sarter et al, 2005; Yu and Dayan, 2005; Hasselmo and Giocomo, 2006)
Because of the strong correlations between sensory inputs, neural activity and perception, we and others have investigated the role of cholinergic inputs for task attention and perceptual discrimination in the main olfactory bulb (OB) of rodents (Linster et al, 2001; Cleland et al, 2002; Linster and Cleland, 2002; Cleland and Linster, 2005)
Recent experiments from our laboratory suggest that while the cholinergic inputs to the OB can modulate perceptual discrimination between odorants (Linster and Cleland, 2002; Mandairon et al, 2006; Chaudhury et al, 2009) they do not seem to affect the acquisition of an odor memory or an odorreward association per se (Linster and Cleland, 2002; Mandairon et al, 2006)

Summary

Introduction

Cholinergic inputs to cortical processing networks have long been proposed to be associated with attentional and top-down processing (Hasselmo et al, 1992; Sarter and Bruno, 1997; Sarter et al, 2005; Yu and Dayan, 2005; Hasselmo and Giocomo, 2006). Cholinergic projections originating in the basal forebrain target early sensory processing areas as well as higher-order association and executive processing areas (Mesulam et al, 1983). Recent experiments from our laboratory suggest that while the cholinergic inputs to the OB can modulate perceptual discrimination between odorants (Linster and Cleland, 2002; Mandairon et al, 2006; Chaudhury et al, 2009) they do not seem to affect the acquisition of an odor memory or an odorreward association per se (Linster and Cleland, 2002; Mandairon et al, 2006). When rats were trained to associate an odor with a food reward, the specificity but not the strength of this association was modulated by cholinergic inputs, both when immunotoxic lesions of cholinergic neurons (Linster et al, 2001) or local infusions of cholinergic antagonists were used (Chaudhury et al, 2009)

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Conclusion