Central and peripheral cholinergic involvement in the habituation of investigatory head poking in rats.

The effects of some centrally and peripherally acting cholinergic agonists and antagonists on locomotor exploration and investigatory head poking were studied in rats. An apparent disruption of within-trials habituation of locomotion and head-poke frequency was demonstrated for arecoline, nicotine, carbachol, scopolamine, and methylscopolamine. It is suggested that the effect may be a consequence of a drug-induced depression of initial activity. When this factor was eliminated, both scopolamine and methylscopolamine showed some slight attenuation of habituation. The increase in head-poke duration over time in controls was blocked by scopolamine; although peripheral factors were involved, the scopolamine effect had a singinficant central component. The results are discussed in relation to hypothetical links between the cholinergic system and habituation.