Muscarinic agonists block a late-afterhyperpolarization in medial septum/diagonal band neurons in vitro.

Intracellular recordings were made from neurons located in the medial septum (MS), and nucleus of the diagonal band (nDB) from slices of guinea pig brain. These forebrain nuclei contain both cholinergic and noncholinergic neurons that project to the cortex and hippocampus and are involved in many cortical functions. Muscarinic agonists (bethanechol, 2-30 microM) had the specific action to reduce a long-duration afterhyperpolarization (long-AHP) while leaving other shorter duration AHPs intact. Since the long-AHP was observed in both cholinergic and non-cholinergic neurons, muscarinic agonists were not selective for any one cell type. Block of a long-AHP was not associated with a consistent increase in cell excitability and therefore can not fully explain the excitatory actions of acetylcholine (ACh) observed in vivo within the MS/nDB.