Abstract
Insulin is an important peptide hormone that regulates food intake and olfactory function. While a multitude of studies investigated the effect of insulin in the olfactory bulb and olfactory epithelium, research on how it modulates higher olfactory centers is lacking. Here we investigate how insulin modulates neural activity of pyramidal neurons in the anterior piriform cortex, a key olfactory signal processing center that plays important roles in odor perception, preference learning, and odor pattern separation. In vitro we find from brain slice recordings that insulin increases the excitation of pyramidal neurons, and excitatory synaptic transmission while it decreases inhibitory synaptic transmission. In vivo local field potential (LFP) recordings indicate that insulin decreases both ongoing gamma oscillations and odor evoked beta responses. Moreover, recordings of calcium activity from pyramidal neurons reveal that insulin modulates the odor-evoked responses by an inhibitory effect. These results indicate that insulin alters olfactory signal processing in the anterior piriform cortex.
Highlights
The sense of smell and status of satiety influence each other
We sought to confirm this finding in mice and asked whether the insulin receptors are expressed by pyramidal neurons
In layer 2 of anterior piriform cortex (APC), where the soma of pyramidal neurons are located, we found that a large proportion of the DAPI-positive cells were insulin-receptor immunopositive (Figure 1, 67.4% ± 5.3, counted in 9 regions of interest (ROIs) of 5 sections from 5 mice, total number of cells = 531)
Summary
While the cue from the olfactory system modulates the eating behavior (Rolls, 2005; Yeomans, 2006; Soria-Gomez et al, 2014; Lushchak et al, 2015), the status of satiety dramatically affects the ability of the olfactory system to detect and discriminate odors in both humans and rodents (Pager, 1978; Julliard et al, 2007; Albrecht et al, 2009; Marks et al, 2009; Stafford and Welbeck, 2011; Rolls, 2015) Several peptide hormones, such as insulin, leptin and orexins are key factors that mediate the interplay between olfaction and food intake (Julliard et al, 2007; Prud’homme et al, 2009; Palouzier-Paulignan et al, 2012; Brunner et al, 2013; Chelminski et al, 2017). Since the OB contains one of the highest concentrations of insulin and insulin receptors within the central nervous system
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