Abstract
Glomeruli are the functional units of olfactory information processing but little remains known about their individual unit function. This is due to their widespread activation by odor stimuli. We expressed channelrhodopsin-2 in a single olfactory sensory neuron type, and used laser stimulation and simultaneous in vivo calcium imaging to study the responses of a single glomerulus to optogenetic stimulation. Calcium signals in the neuropil of this glomerulus were representative of the sensory input and nearly identical if evoked by intensity-matched odor and laser stimuli. However, significantly fewer glomerular layer interneurons and olfactory bulb output neurons (mitral cells) responded to optogenetic versus odor stimuli, resulting in a small and spatially compact optogenetic glomerular unit response. Temporal features of laser stimuli were represented with high fidelity in the neuropil of the glomerulus and the mitral cells, but not in interneurons. Increases in laser stimulus intensity were encoded by larger signal amplitudes in all compartments of the glomerulus, and by the recruitment of additional interneurons and mitral cells. No spatial expansion of the glomerular unit response was observed in response to stronger input stimuli. Our data are among the first descriptions of input-output transformations in a selectively activated olfactory glomerulus.
Highlights
Mouse olfactory bulbs contain approximately 2000 glomeruli that are each innervated by sensory neurons expressing a single functional odorant receptor type[1,2]
We investigated (1) how glomeruli respond to odor vs. optogenetic activation, (2) how optogenetic stimuli are represented in the glomerular neuropil, interneurons and mitral cells, and (3) how stimulus intensity is encoded in the optogenetically-activated glomerulus
(2) Interneuron signals were treated as ‘modulation’ signals and were obtained from cell bodies located in the glomerular layer. (3) ‘Output’ signals were recorded from mitral cells located 150–200 μm below the olfactory bulb surface
Summary
Mouse olfactory bulbs contain approximately 2000 glomeruli that are each innervated by sensory neurons expressing a single functional odorant receptor type[1,2]. We sought to establish an experimental model of single glomerular activation, and to clarify some aspects of the input-output logic of the mouse olfactory bulb. We investigated (1) how glomeruli respond to odor vs optogenetic activation, (2) how optogenetic stimuli are represented in the glomerular neuropil, interneurons and mitral cells, and (3) how stimulus intensity is encoded in the optogenetically-activated glomerulus. We find (1) a significant reduction in the amplitude(s) and population size(s) of cells responding to laser vs odor stimuli; (2) discrete temporal stimulus representations across different compartments of the glomerulus, and (3) describe a glomerular unit as a very compact population of interneurons and an output compartment that is made up of very few mitral cells
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
