Early exposure to urethane anesthesia: Effects on neuronal activity in the piriform cortex of the developing brain

Exposure to urethane anesthesia reportedly produces selective neuronal cell loss in the piriform cortex of young brains; however, resulting functional deficits have not been investigated. The present study found abnormalities in piriform cortex activity of isolated brains in vitro that were harvested from guinea pigs exposed to urethane anesthesia at 14 days of age. Current source density (CSD) analysis and voltage-sensitive dye (VSD) imaging experiments were conducted 48h after urethane injection. We applied paired-pulse stimulation to the lateral olfactory tract (LOT) and assessed short-interval intra-cortical inhibition in the piriform cortex. CSD analysis revealed that a current sink in layer Ib remained active in response to successive stimuli, with an inter-stimulus interval of 30-60 ms, which was typically strongly inhibited. VSD imaging demonstrated stronger and extended neural activity in the urethane-treated piriform cortex, even in response to a second stimulus delivered in short succession. We identified gamma-aminobutyric acid (GABA) ergic neurons in the piriform cortex of sham and urethane-treated animals and found a decrease in GABA-immunoreactive cell density in the urethane group. These results suggest that urethane exposure induces loss of GABAergic interneurons and a subsequent reduction in paired-pulse inhibition in the immature piriform cortex.