EFFECTS OF STIMULATION OR BLOCKADE OF CENTRAL NICOTINIC-CHOLINERGIC RECEPTORS ON PERFORMANCE OF A NOVEL VERSION OF THE RAT STIMULUS DISCRIMINATION TASK

This study evaluated the effects of two central nicotinic-cholinergic receptor agonists and an antagonist on performance accuracy of a rat, delayed stimulus discrimination task (DSDT), Rats were trained to disc riminate between an auditory and visual stimulus by pressing a right o r left lever. To diminish the rat's ability to use mediating spatial s trategies to solve the task, computer automated, retractable doors sep arated the animal from the levers during delay intervals, thus reducin g positioning at the lever. After stable baselines were achieved, rats were grouped and administered placebo (saline) and nicotine, lobeline or mecamylamine in a randomized dose series. Each group received two complete series of the selected compound on different occasions. Mecam ylamine impaired DSDT accuracy in a dose-dependent manner while optima l doses of nicotine and lobeline significantly improved accuracy. Nico tine differed from lobeline in regard to its interaction with a dose o f mecamylamine (1.0 mg/kg) that had not impaired DSDT accuracy. Combin ed administration of lobeline and mecamylamine was followed by a signi ficantly increased level of DSDT accuracy that was similar to the impr ovement following administration of lobeline alone. In contrast, combi ned administration of nicotine and mecamylamine did not result in incr eased DSDT accuracy, Furthermore, lobeline administration similarly im proved accuracy of trials associated with both the light and the tone, while nicotine improved accuracy of trials associated with the Light to a much greater degree, These data suggest that the increases in DSD T accuracy associated with lobeline may be expressed through non-nicot inic mechanisms or a nicotinic receptor which is not blocked by mecamy lamine.