Fig. 4: Cortico-bulbar GABAergic axons induce net inhibition onto GCL neurons and MC/TC populations in vivo.
From: Long-range GABAergic projections contribute to cortical feedback control of sensory processing
a Cortical GABAergic axons were stimulated in the OB of freely moving mice. Top, Optic fiber for cortical GABAergic axon optogenetic stimulation (1 s) and GABAergic interneuron calcium imaging in the ventral GCL. Bottom, GCaMP6f expression across OB layers and ChRimson in AON/APC GABAergic axons. Blue, DAPI. b Stimulation of cortical GABAergic axons decreased GCL interneuron spontaneous population activity. Left, example trial-averaged responses to different light stimulation patterns. CL continuous light. “Light control” is CL illumination in mice lacking ChRimson expression. Right, Mean fluorescence change in response to light stimulation (RM-One-way-ANOVA with Tukey’s post-hoc test, F(2,22) = 21.28, P < 0.0001). Data presented as mean ± sem; gray lines, individual mice. c Stimulation of cortical GABAergic axons decreased GCL interneuron odor-evoked population activity. Left, fluorescence signals during odor presentation only (black) and odor presentation coupled with stimulation of cortical GABAergic axons (orange). Traces are trial-averaged example responses. Mean ± sem are represented. Right, Net impact of light on odor responses across light stimulation protocols (10 Hz, 33 Hz, CL) compared to no light stimulation (“odor only”). The net impact of light was measured as the difference between the mean odor-evoked response in the 1 s window before versus during light stimulation. Population odor response were inhibited by light stimulation of cortical GABAergic axons and inhibition magnitude scaled with the stimulation strength (One-way-ANOVA with Tukey’s post-hoc test, F(3,416) = 62.98, p = 10−3). Violin plots are ks density estimates; black bar, median; circle, individual odor-recording site pair. d MC/TC population responses to cortical GABAergic axon optogenetic stimulation in the OB of freely moving mice utilizing fiber photometry (left). Middle: Representative trial-averaged traces of light-evoked inhibitory responses in MCs/TCs using different stimulation patterns. Right: Stimulation of cortical GABAergic axons produced increasing inhibition with increasing stimulation frequency (RM-One-way ANOVA with Tukey’s post-hoc test, F(3,15) = 12.20, P = 0.0003, n = 6 recording sites in 4 mice). Data presented as mean ± sem; Gray, individual recording sites. Source data are provided as a Source Data file.
