Rapid differential conditioning of the somatosensory evoked potential by changed patterns of brief innocuous tactile stimuli in waking rats is altered by atropine sulfate
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Abstract
Air puffs delivered to the nose of an awake, lightly restrained rat every 15 s produced
evoked potentials that changed gradually over time so that the averaged response to
the last 40 stimuli was measurably different from the first 40. This habituation-like
paradigm increased the size of an early component of the potential in several places.
When measured with respect to the time of stimulus onset (there was a 21.6 ms delay
in the time of arrival of the stimulus maximum at the nose), one of the largest increases
occurred 46 ms later (39 ms latency to onset, and 55 ms latency to offset). As well,
a late component of the waveform became more positive, showing a maximum between 156
and 185 ms (133 ms latency to onset, and more than 250 ms latency to offset). Changing
the pattern but not the number of stimuli accelerated the rate of this positive shift
with a maximum at 37 ms (21 ms latency to onset, and 42 ms latency to offset), but
did not affect the rate of change in the late component. This effect of altering the
temporal pattern of the stimuli was blocked by systemic injections of atropine sulfate,
a blocker of central muscarinic receptors, whereas, neither saline injections nor
atropine methyl nitrate injections (an atropine analog that does not cross the blood-brain
barrier) could produce these changes. These observations suggest that the adaptive
changes of the somatosensory evoked potential induced by novel patterns intercalated
in otherwise monotonous repetitive somatic stimuli depend upon central muscarinic
mechanisms.