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.
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