The effect of various anaesthetics on the spatial tuning of two major wave peaks in the transient pattern electroretinogram of the cat: Evidence for pattern and luminance components

The main PERG component of the transient contrast reversal pattern electroretinogram (PERG) in cats was a negative wave (3.5 μV average, SD 1.7 μV) peaking at about 130 msec (N 130) with a spatial resolution above 5.5c/deg, close to behavioural estimates. The early positivity (P 35) was more variable, smaller and had lower spatial resolution. Different anaesthetic protocols affected both the waveform and the amplitude by spatial frequency functions. Responses of urethane anaesthetised cats were like those reported previously for decerebrate cats or cats paralysed and ventilated with N 2O/O 2/CO 2 (75%/24%/1%). P 35 was evoked only by coarse stimuli and N 130 amplitude decreased linearly as spatial frequency increased. When the luminance response amplitude, predicted from the optical transfer function of the eye, was subtracted, spatial tuning appeared. An anaesthetic mixture of ketamine hydrochloride and xylazine depressed both P 35 and N 130 at low spatial frequencies while enhancing them at high frequencies. In paralysed animals ventilated with N 2O/O 2 (67%/33%) P 35 was larger and recordable to 1.6 c/deg. Peak times were reduced and the inter-peak time halved. Other anaesthetics depressed the ERGs. These effects suggest that cats are a good model for studying N 130 in isolation or its interaction with P 35 and that both PERG peaks include luminance and pattern components.