Abstract
The inter-regional connectivity of sensory structures in the brain allows for the modulation of sensory processing in manners important for perception. In the olfactory system, odor representations in the olfactory bulb (OB) are modulated by feedback centrifugal innervation from several olfactory cortices, including the piriform cortex and anterior olfactory nucleus. Previous studies reported that an additional olfactory cortex, the olfactory tubercle, also centrifugally innervates the OB and may even shape the activity of OB output neurons. In an attempt to identify the cell-types of this centrifugal innervation, we performed retrograde tracing experiments in mice utilizing three unique strategies, including retrobeads, retrograde adeno-associated virus (AAV) driving a fluorescent reporter, and retrograde AAV driving Cre-expression in the Ai9 floxed transgenic reporter line. Our results replicated the standing literature and uncovered robustly labeled neurons in the ipsilateral piriform cortex, anterior olfactory nucleus, and numerous other structures known to innervate the OB. Surprisingly, consistent throughout all of our approaches, no labeled soma were observed in the olfactory tubercle. These findings indicate that the olfactory tubercle is unique among other olfactory cortices in that it does not innervate the OB, which refines our understanding of the centrifugal modulation of the OB.
Significance statement The perception of our environment relies upon the distribution of sensory information throughout brain regions. This is true in the olfactory system wherein projections between olfactory centers, including feedback centrifugal input to the olfactory bulb, provide the basis for olfactory perception. Here, we show that one olfactory cortical structure, the olfactory tubercle, is unique among olfactory cortices in that it lacks feedback projections to the olfactory bulb. This ‘negative result’ is important in that it refines current models for the circuitry of our olfactory system and challenges previous literature reporting such a pathway in fact exists.
Footnotes
The authors state no conflict of interest.
Funding sources: This work was supported by NIH NIDCD R01DC014443 and R01DC016519 to D.W. E.Z. was supported by an undergraduate award from the University of Florida Center for Smell and Taste.
E.E.Z. and H.L.C. Equally contributing first authors
E.Z., H.C., and D.W. designed research, analyzed data, and wrote the paper. E.Z., H.C. and H.D. performed research.
This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
Jump to comment: