EFFECTS OF CONCOMITANT NICOTINIC AND MUSCARINIC BLOCKADE ON SPATIAL MEMORY DISTURBANCE IN RATS ARE PURELY ADDITIVE - EVIDENCE FROM THE MORRIS WATER TASK

This study reexamined the role played by a concurrent manipulation of nicotinic and muscarinic acetylcholine (ACh) receptors on performance of rats in the Morris water maze. A series of experiments was performe d to test decreasing doses of scopolamine, a muscarinic ACh blocker, g iven concurrently with a fixed dose level of mecamylamine, a nicotinic ACh blocker, down to a subthreshold combination. Both substances were also tested separately. Data were analyzed to distinguish between a s ummative and a greater than additive (synergistic) effect of the two b locking agents. Our results fully support the important role played by ACh systems on cognitive functions and also show the substantial func tional independence of the two ACh receptors in regulating spatial lea rning processes. In fact, data analysis did not reveal any significant interaction between the two ACh receptor blockers other than their ad ditive effect: the hypothesis of a reciprocal modulation between the t wo ACh receptors, raised by some authors, cannot be supported for spat ial learning mechanisms, at least with regard to the Morris water maze paradigm.