Long-term cholinergic enhancement of evoked potentials in rat hindlimb somatosensory cortex displays characteristics of long-term potentiation

Pairing a cutaneous electrical stimulus of the hind-paw with stimulation of the basal forebrain produces long-term cholinergic enhancement of the resp onsiveness to a tactile stimulus. A short period of pairing (20 trials) inc reased the area of the two main components of the evoked potential by 37.1/-13.5% (+/-SEM) and 37.9+/-6.8%, respectively. The effects lasted for the duration of the experiment (>2 h). The enhancement could be blocked by eith er MK-801, an NMDA receptor antagonist or by L-NAME, a nitric-oxide-synthas e inhibitor when they were given prior to pairing. Control experiments with Skin stimulation alone and basal forebrain stimulation alone had only smal l long-term effects (similar to 10%) on the size of the evoked potential. T hus, long term cholinergic enhancement, attributable to disinhibition and i ncreased release of acetylcholine in the cortex during neuronal excitation by other sources, and so named because it is blocked by atropine, may be a form of long-term potentiation. The existence of such a mechanism for the c ontrol of cortical neuronal plasticity identifies the basal forebrain as a powerful modulator of long-lasting changes in cortical neuronal excitabilit y.