A. Kirkwood et al., Modulation of long-term synaptic depression in visual cortex by acetylcholine and norepinephrine, J NEUROSC, 19(5), 1999, pp. 1599-1609
In a slice preparation of rat visual cortex, we discovered that paired-puls
e stimulation (PPS) elicits a form of homosynaptic long-term depression (LT
D) in the superficial layers when carbachol (CCh) or norepinephrine (NE) is
applied concurrently. PPS by itself, or CCh and NE in the absence of synap
tic stimulation, produced no lasting change. The LTD induced by PPS in the
presence of NE or CCh is of comparable magnitude with that obtained with pr
olonged low-frequency stimulation (LFS) but requires far fewer stimulation
pulses (40 vs 900). The cholinergic facilitation of LTD was blocked by atro
pine and pirenzepine, suggesting involvement of M-1 receptors. The noradren
ergic facilitation of LTD was blocked by urapidil and was mimicked by metho
xamine, suggesting involvement of alpha 1 receptors. beta receptor agonists
and antagonists were without effect. Induction of LTD by PPS was inhibited
by NMDA receptor blockers (completely in the case of NE; partially in the
case of CCh), suggesting that one action of the modulators is to control th
e gain of NMDA receptor-dependent homosynaptic LTD in visual cortex. We pro
pose that this is a mechanism by which cholinergic and noradrenergic inputs
to the neocortex modulate naturally occurring receptive field plasticity.