The effect of muscarinic and nicotinic ACh antagonist on the facilitation of rat visual cortical responses

Effects of mecamylamine on flash-evoked potentials, body temperature, and behavior in Long-Evans rats

This experiment examined the effects of mecamylamine, a nicotinic acetylcholine receptor antagonist, on flash-evoked potentials (FEPs) recorded from the visual cortex (VC) and superior colliculus (SC) of chronically implanted male Long-Evans rats, and on body temperature and open field behavior. FEPs were recorded at 20 and 35 min following intraperitoneal injections of saline, and of 0.3, 3.0, and 10.0 mg/kg mecamylamine on separate days. The 0.3 mg/kg dose did not produce significant effects. The amplitude of VC components N₃₀, P₄₈, and P₈₇ increased, N₁₅₀ and P₂₃₁ decreased, and P₂₃, N₄₀, N₅₈, and N₆₈ were unchanged following administration of the 10.0 mg/kg dose. In the SC, component P₂₈ was unaffected, P₃₉ was reduced, and N₄₉ was augmented by the 10.0 mg/kg dose. All component peak latencies were increased by the 3.0 and 10.0 mg/kg doses. Significant hypothermia was also produced by the 3.0 and 10.0 mg/kg doses, suggesting that this was the basis for the increased latencies. The 10.0 mg/kg dose produced a significant decrease in movement during the recording sessions. In subsequent open field observations, both line crossings and rearings were reduced by the 3.0 and 10.0 mg/kg doses. The results suggest that endogenous acetylcholine acting on nicotinic acetylcholine receptors plays at most a modest role in producing FEPs recorded from the VC and SC.

The effect of brainstem stimulation on the evoked potentials in the intergeniculate leaflet

We have investigated the effect of the laterodorsal tegmental (LDTg) stimulation on evoked potentials in the intergeniculate leaflet (IGL) of the rat, in order to characterize how non-specific systems of the brain, whose activity indicates the influence of non-photic information, impact the activity of the IGL. IGL responses were evoked by electrical stimulation of contralateral suprachiasmatic nuclei (SCN). The amplitude of the evoked potentials was, in all experiments, significantly reduced after the LDTg stimulation. This effect indicated strong neuronal integration between the brainstem reticular formation and the IGL. These results are discussed in relation to the putative role of GABAergic projection.