Alpha7 nicotinic XXXX receptors occur at postsynaptic densities of @entity140 receptor-positive and -negative excitatory synapses in @entity35 sensory cortex.

@entity227 @entity4860 @entity139 @entity18858 @entity140 @entity143 @entity35 @entity934
@entity143 receptor (NMDAR) activation requires concurrent membrane depolarization, and glutamatergic synapses lacking @entity140 receptors (AMPARs) are often considered "silent" in the absence of another source of membrane depolarization. During the second postnatal week, @entity143 currents can be enhanced in @entity35 auditory cortex through activation of the alpha7 nicotinic @entity934 receptor (alpha7nAChR). Electrophysiological results support a mainly presynaptic role for alpha7nAChR at these synapses. However, immunocytochemical evidence that alpha7nAChR is prevalent at postsynaptic sites of glutamatergic synapses in hippocampus and neocortex, along with emerging electrophysiological evidence for postsynaptic nicotinic currents in neocortex and hippocampus, has prompted speculation that alpha7nAChR allows for activation of NMDAR postsynaptically at synapses lacking AMPAR. Here we used dual immunolabeling and electron microscopy to examine the distribution of alpha7nAChR relative to AMPAR ( @entity4860 , @entity139 , and @entity18858 subunits combined) at excitatory synapses in somatosensory cortex of adult and 1-week-old @entity35 . alpha7nAChR occurred discretely over most of the thick postsynaptic densities in all cortical layers of both age groups. AMPAR immunoreactivity was also detectable at most synapses; its distribution was independent of that of alpha7nAChR. In both age groups, approximately one-quarter of asymmetrical synapses were alpha7nAChR positive and AMPAR negative. The variability of postsynaptic alpha7nAChR labeling density was greater at @entity227 ( @entity227 ) 7 than in adulthood, and @entity227 7 neuropil contained a subset of small @entity140 receptor-negative synapses with a high density of alpha7nAChR immunoreactivity. These observations support the idea that @entity934 receptors can aid in activating glutamatergic synapses and work together with @entity140 receptors to mediate postsynaptic excitation throughout life.
