Olfaction in Olfactory Bulbectomized Rats

Abstract

Experimental rats had their right olfactory bulb removed on postnatal day 2 (P2) and their left olfactory bulb removed on P90. Control rats had one or both olfactory bulbs removed on P90. Before and after their adult-stage surgery, rats were trained using olfactometry and operant conditioning to detect and discriminate odors. Anterograde transport of horseradish peroxidase applied to the olfactory epithelium revealed numerous axons of olfactory sensory neurons in the right hemisphere of 27 experimental rats. These axons terminated in glomerular-like clusters within the frontal neocortex (n ϭ 5) or anterior olfactory nucleus with some axons extending into the subventricular epithelium (n ϭ 22). Seventeen of the experimental rats were able to detect a variety of odors and to discriminate between odors. Performance accuracy was related to the location and density of these anomalous inputs; experimental rats with inputs confined to frontal neocortex and those lacking any inputs to the forebrain were anosmic, as were adult-operated bilaterally bulbectomized rats. Our results provide strong support for the contention that, in the absence of the olfactory bulbs, olfactory connections to novel forebrain sites can support both odor detection and odor discrimination.

High-Frequency Oscillations Are Not Necessary for Simple Olfactory Discriminations in Young Rats

“…The results observed here are reminiscent of the extensive literature on the effects of olfactory bulb lesions on simple odor discrimination by Slotnick and Bisulco (2003) and Slotnick et al (2004). There is clear evidence that odorants evoke unique spatial patterns of glomerular layer activity in the olfactory bulb, but that large lesions within these patterns have no detectable effect on simple discrimination.…”

A new dopaminergic nigro-olfactory projection

“…The ensuing cavity was carefully cauterized and filled with Gelfoam (Upjohn, Kalamazoo, MI) to prevent postoperative bleeding and olfactory regeneration [50]. The lesion extended into the olfactory peduncle and included part of the anterior olfactory nuclei.…”

Olfactory Computations and Network Oscillation

“…It will be interesting to make these population measurements in animals with substantially reduced olfactory processing networks that spare significant olfactory ability (de Belle and Heisenberg, 1994; Slotnick et al, 2004;Komischke et al, 2005).…”

“…The Limax experiment will be even more informative using a newly developed in vitro nose-brain preparation, also using motor neuron activation to index the attractive or repellent nature of the applied odor . Other perturbations used to explore the causal link between olfactory circuit function and odor-guided behavior include lesions of the olfactory bulbs (Slotnick et al, 2004), genetic lesions of specific neurotransmitter receptor subtypes (Nusser et al, 2001) or ionic channel subunits (Fadool et al, 2004) in the olfactory bulb, pharmacological manipulations of the olfactory bulbs during odorguided behavioral tasks (Ravel et al, 1994;Kendrick et al, 1997), and direct electrical stimulation of the olfactory bulb in awake behaving animals to create "electric odors" (Jirsa and Radil, 1997;Mouly and Gervais, 2002;Roman et al, 2004). Creative use of these and other methods for selective perturbation of olfactory networks during their participation in olfactory computations and the readout of the effects of these perturbations in odorguided behavior is critical to fully clarify the computational role of olfactory oscillations and synchronous cellular activity during odor processing.…”