The involvement of acetylcholine (ACh) in the induction of neuronal sensory plasticity is well documented.
Recently we demonstrated in the somatosensory cortex of the anesthetized rat that ACh is also involved
in the expression of neuronal plasticity. Pairing stimulation of the principal whisker at a fixed
temporal frequency with ACh iontophoresis induced potentiations of response that required
re-application of ACh to be expressed. Here we fully characterize this phenomenon and extend it
to stimulation of adjacent whiskers. We show that these ACh-dependent potentiations are cumulative
and reversible. When several sensori-cholinergic pairings were applied consecutively with stimulation
of the principal whisker, the response at the paired frequency was further increased, demonstrating a cumulative
process that could reach saturation levels. The potentiations were specific to the stimulus frequency:
if the successive pairings were done at different frequencies, then the potentiation caused by the first pairing
was depotentiated, whereas the response to the newly paired frequency was potentiated.
During testing, the potentiation of response did not develop immediately on the presentation of the
paired frequency during application of ACh: the analysis of the kinetics of the effect indicates that
this process requires the sequential presentation of several trains of stimulation at the paired frequency
to be expressed. We present evidence that a plasticity with similar characteristics can be induced
for responses to stimulation of an adjacent whisker, suggesting that this potentiation could participate
in receptive field spatial reorganizations. The spatial and temporal properties of the ACh-dependent
plasticity presented here impose specific constraints on the underlying cellular and molecular mechanisms.