Abstract
Cerebral cortex is widely innervated by noradrenergic (NA) fibers originating from the locus coeruleus. NA is implicated in the control of behaviors, such as attention, arousal level, S/N ratio in the sensory responsiveness, and so on, but underlying mechanism to achieve such controls in synaptic level within the cortical network is largely unknown. To investigate roles of NA in the cortical network, we looked at what effects NA has on synaptic responses. Thalamocortical slices were prepared from GAD67-GFP (δneo) mice (P10-24). Excitatory postsynaptic currents (EPSCs) were recorded in voltage-clamp mode from neurons in layer IV in response to stimulations at either ventrobasal nucleus (VB) of thalamus or neighboring layer IV for activation of thalamic or horizontal inputs, respectively. EPSCs from excitatory as well as inhibitory neurons in response to VB stimulation were significantly suppressed (72% and 65% of control, p<0.05) by NA. The effect was dose-dependent. NA also suppressed horizontal inputs to inhibitory (71%, p<0.05) but not excitatory cells (p=0.24). Analyses of coefficient of variation (CV) of EPSCs suggested that NA reduced the release of transmitters acting on presynaptic terminals. These results indicated that NA largely suppresses synaptic inputs to layer IV cells with possible differential effects depending on target cell type. [J Physiol Sci. 2007;57 Suppl:S164]
