Neural Circuits: Reduced Inhibition in Fragile X Syndrome Randall M. Golovin, Kendal Broadie  Current Biology  Volume 27, Issue 8, Pages R298-R300 (April 2017) DOI: 10.1016/j.cub.2017.03.011 Copyright © 2017 Elsevier Ltd Terms and Conditions

Figure 1 Reduced inhibition broadens circuit and behavior responses in an FXS model. (A) The four-chamber behavioral arena from [7]. Attractive odorants are loaded in one chamber (air in remaining three) and repellant odorants in three chambers (air in other chamber). Air movement flow via a vacuum port produces a movement response that appears identical between attraction and aversion. Right: a theoretical heat plot of position probability for wild-type and FXS model flies. The mutant animals show both impaired olfactory attraction and aversion. (B) Schematic of wild-type and FXS model antennal lobe with a theoretical calcium response to odorant presentation. Left: wild-type response is narrow, with sharp activation near the strongly activated glomeruli and rapidly decaying signal farther away. Right: mutant response is broader, with weaker activation of the most strongly activated glomeruli and more signal area of spread. (C) Schematic of the antennal lobe circuitry showing how decreased inhibition might arise. Left: wild-type with strongly activated glomeruli (orange) also activate GABAergic local interneurons inhibiting surrounding glomeruli (blue) to sharpen odor representation. Right: FXS model circuit displays less strongly activated glomeruli (yellow), proposed due to decreased lateral excitation (not demonstrated). Mutant circuits have reduced projection neuron (green) inhibition response, such that even strongly activated GABAergic local interneurons provide little effective inhibition. This change acts to broaden the odor response by limiting lateral inhibition between glomeruli. LN, lateral interneurons; PN, projection neurons. Current Biology 2017 27, R298-R300DOI: (10.1016/j.cub.2017.03.011) Copyright © 2017 Elsevier Ltd Terms and Conditions