Nitrous oxide modifies visual responses in the cat retina, striate cortex and superior colliculus

Extracellular records from 54 single cells in cat optic tract (14), visual cortex (18) and superior colliculus (22), have shown that ventilation of acute animals with a 70%: 30% mixture of N₂O/O₂ can modify unit responses to visual stimuli. Results indicate that, under nitrous oxide, (a) responses to flashed or moving stimuli may be severely reduced, and frequently abolished. This may be accompanied by either a sharp decrease; or, conversely, by a dramatic increase, in the resting discharge rate; (b) the degree of directional preference of a given unit, in response to a moving visual stimulus, may be substantially modified; (c) the temporal distribution of unit firing may be modified. While about half (57%) of the units in the optic tract were affected by N₂O, only 28% of cortical cells showed any N₂O-related response modification. The largest effect was observed in the superior colliculus, where 86% of cells were influenced by the anaesthetic. It is suggested that these results might be explained by a selective interference of N₂O with serotonergic transmitter mechanisms.