DIFFERENT EFFECTS OF CHOLINERGIC AGENTS ON RESPONSES RECORDED FROM THE CAT VISUAL-CORTEX AND LATERAL GENICULATE-NUCLEUS DORSALIS

We investigated the effect of cholinergic agents on the cat visual evo ked potentials (VEPs) recorded from the primary visual cortex (V1) and lateral geniculate nucleus dorsalis (LGNd) to determine on which leve l of the visual pathway the cholinergic system acts. VEPs to the alter nation of 0.1 cycles per degree sinusoidal gratings at 1 and 4 Hz were recorded from N2O-anesthetized cats directly from the surface of V1 a nd LGNd The depth of recording in LGNd was determined by the site wher e the maximal response was obtained by 1 Hz stimulation, VEPs to 4 Hz stimulation, which showed sinusoidal waveforms and were analyzed by fa st Fourier transforms, were used as indicators for modulation by choli nergic agents, Physostigmine, an acetylcholinesterase inhibitor, 0.7 m g/kg i.v., suppressed the amplitude of the responses more at V1 (suppr ession ratio: mean +/- SD, 85.4 +/- 9.3%) than at LGNd (32.4 +/- 30.7% ) (P < 0.05). Conversely, scopolamine, a muscarinic receptor blocker, 0.7 mg/kg i.v., increased the amplitude of the responses more at V1 (e nhancement ratio: mean +/- SD, 60.3 +/- 22.3%) than at LGNd (-22.2 +/- 22.5%) (P < 0.05). These results indicate that the V1 changes reflect a direct cortical cholinergic effect, probably by modulating the chol inergic projection from the nucleus basalis of Meynert to V1. (C) 1997 Elsevier Science Ireland Ltd.