Atropine-sensitive and -insensitive components of the somatosensory evokedpotential

The evoked potential in primary somatosensory cortex changes with time. Sho rt puffs of air administered to the nose of awake, quietly resting adult ra ts elicited potentials that could be altered by one of several treatments ( saline, atropine methyl nitrate or atropine sulfate). The change produced b y blocking muscarinic receptors in the central nervous system with atropine sulfate (100 mg/kg) was the largest, but control substances also altered t he potential, suggesting that the gradual changes observed in the evoked po tential 30 min after intraperitoneal injection may also be affected by fact ors such as the stress associated with injection itself and the blockade of peripheral muscarinic receptors. The changes observed in the evoked potent ial when central cholinergic receptors are blocked include a large shift to wards positivity in the early components (between 18 and 64 ms with maxima at 20 and 47 ms) and a similarly significant shift towards negativity in th e later components (between 90 and 208 ms with maxima at 115 and 157 ms). T he actual changes observed during inactivation of central muscarinic recept ors suggest that the role of acetylcholine during arousal is more than to s imply bias the cortex towards greater excitability. Rather, the muscarinic receptors on inhibitory interneurons or on the dendritic terminals of pyram idal cells in superficial layers of cortex enhance the first intracortical synaptic events but reduce the population response at later times during th e first 250 ms following a tactile stimulus. (C) 2001 Elsevier Science B.V. All rights reserved.