The role of sensory experience in intrinsic biophysical diversity of glomerular interneurons of the olfactory bulb

Investigating the adaptive properties of neuronal circuits is central to understanding the operations of the brain. The mouse olfactory bulb is a structure well suited for studying these processes, since it is composed of relatively simple excitatory and inhibitory networks. Recently, it has been shown that principal neurons (mitral cells) of the olfactory bulb that participate in the same glomerular circuit exhibit similar biophysical properties based on their Ih-mediated membrane potential sag. In many cell types, including mitral cells, Ih is known to profoundly influence excitability and thus impact the input/output function of individual neurons and networks. Like principal cells, inhibitory neurons are known to exhibit Ih that influences their integrative properties. In the olfactory bulb, interneurons of the glomerular layer can receive input from one or more glomerular networks and are thought to mediate lateral or centre-surround inhibition. The regulation of Ih in these cells could thus be used as a gain-control mechanism to facilitate contrast enhancement. During my project, I therefore investigated the diversity of Ih in GAD65+ and TH+ juxtaglomerular cells belonging to the same or different glomeruli to determine the diversity of Ih-mediated membrane potential sag within and across different inhibitory circuits. I found that the two juxtaglomerular populations differed substantially in their levels of membrane potential sag. Contrary to TH+ juxtaglomerular cells, the similarity in the amount of sag recorded in GAD65+ juxtaglomerular cells was high when two neurons were found to participate in the same glomerular circuit. Furthermore, the sag amplitude of interneurons affiliated to a specific glomerular circuit was upregulated when mice were exposed to odour stimuli. This indicates that, at least for GAD65+ juxtaglomerular cells, the amount of Ih membrane sag reflects local network processing of odour information