Laminar distribution of cholinergic- and serotonergic-dependent plasticitywithin kitten visual cortex

Both cholinergic and serotonergic modulatory projections to mammalian stria te cortex have been demonstrated to be involved in the regulation of postna tal plasticity, and a striking alteration in the number and intracortical d istribution of cholinergic and serotonergic receptors takes place during th e critical period for cortical plasticity. As well, agonists of cholinergic and serotonergic receptors have been demonstrated to facilitate induction of long-term synaptic plasticity in visual cortical slices supporting their involvement in the control of activity-dependent plasticity. We recorded f ield potentials from layers 4 and 2/3 in Visual cortex slices of 60-80 day old kittens after white matter stimulation, before and after a period of hi gh frequency stimulation (HFS), in the absence or presence of either cholin ergic or serotonergic agonists. At these ages, the HFS protocol alone almos t never induced long-term changes of synaptic plasticity in either layers 2 /3 or 4. In layer 2/3, agonist stimulation of mi receptors facilitated indu ction of long-term potentiation (LTP) with HFS stimulation, while the activ ation of serotonergic receptors had only a modest effect. By contrast, a st rong serotonin-dependent LTP facilitation and insignificant muscarinic effe cts were observed after HFS within layer 4. The results show that receptor- dependent laminar stratification of synaptic modifiability occurs in the co rtex at these ages. This plasticity may underly a control system gating the experience-dependent changes of synaptic organization within developing vi sual cortex. (C) 2001 Elsevier Science B.V. All rights reserved.