Howdy neuroscientists!

This coming Monday, October 26th, will be the first Brain Bag of the year. Annie Liu from the Urban lab will be presenting her work on the olfactory bulb (abstract below). Join us at 6:00pm in the Mellon Institute Social Room. If you plan to attend, please RSVP https://www.surveymonkey.com/r/D7YFDXR. Note that we're trying something a little different this year by letting you choose which food we'll be having on Monday, so if you have strong feelings RSVP quickly!

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Effects of odorant exposure on the M72 glomerular module

Liu A, Urban NN

The mechanisms regulating organization and wiring patterns of olfactory bulb (OB) circuitry are largely unknown. Olfactory sensory neurons (OSNs) located in the olfactory epithelium project axons to the OB that coalesce into spherical structures called glomeruli. These glomeruli and their post-synaptic targets (including mitral and tufted projection neurons and periglomerular cells) form networks called glomerular modules, which comprise the basic odor-coding units of the OB. The identity of the odorant receptor expressed by OSNs plays a crucial role in reliable targeting of OSN axons to specific locations within the OB, as well as the stabilization of glomerular location during the early postnatal period. Odorant experience accelerates the maturation of glomerular targeting by OSN axons. In addition, early prenatal and postnatal odorant conditioning leads to enlargement of activated glomeruli and alters odorant preference. Our experiments investigate 1) the organization of the glomerular module’s post-synaptic targets following prenatal and early postnatal odorant conditioning, and 2) the stability of anatomical and behavioral changes caused by early odorant conditioning. We focus on the development of one specific, genetically-identified glomerulus, the dorsolateral M72 glomerulus and use an odorant conditioning paradigm involving food odorized with methylsalicylate, a specific M72 odorant ligand. Using in vivo dye electroporation, we find that projection neuron number increases significantly following prenatal and early postnatal odorant conditioning (control vs. conditioned, 6.8 ± 0.33 vs. 10 ± 0.38 mitral cells, 2.9 ± 0.28 vs. 6.63 ± 0.49 tufted cells, n=8 vs. n=11), which suggests that early odorant experience has a profound impact on olfactory bulb circuit structure beyond glomerular level changes. Consistent with

previously published work (Todrank et al, 2007), we show that early prenatal odorant experience causes a significant increase M72 glomerular volume (control vs. conditioned, 110367 ± 14920 µm3 vs.189106 ± 10655 µm3, n=10, p=0.003). Concomitant behavioral changes are also observed, with conditioned mice demonstrating a preference for methysalicylate-scented food over control food. However, our data demonstrate that while the increase in glomerular volume persists well beyond the early postnatal odorant exposure period (glomeruli of conditioned mice weaned onto control vs. methylsalicylate-scented food sacrificed at P63, 248183 ± 20573 µm3 vs. 244611 ± 12167 µm3, n=16, p=0.8833, n.s.), the effect on odorant preference is transient and dependent on continued odorant exposure, suggesting that experience-dependent changes in glomerular volume are irreversible beyond an early critical period, while alternative circuit mechanisms underlie flexible experience-dependent behavioral changes.

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Your Brain Bag Committee,

Sanjeev Khanna and Zach Weinberg