Correlation of AMPA receptor subunit composition with synaptic input in the mammalian cochlear nuclei

The composition of AMPA receptors in patches excised from somata and dendri tes of six cell types In the mammalian cochlear nuclei was probed and compa red electrophysiologically and pharmacologically with the rapid application of glutamate. Cells excited predominantly by auditory nerve fibers had AMP A receptors with exceptionally rapid gating (submillisecond deactivation an d desensitization time constants). The nonlinear current-voltage relationsh ip In the presence of spermine showed that few of these receptors had GluR2 subunits, and the insensitivity of desensitization to cyclothiazide indica ted that they contained mostly flop splice variants. At synapses made by pa rallel fibers, AMPA receptors were slowly gating (time constants of deactiv ation and desensitization > 1 msec) and contained higher levels of GluR2 an d flip isoforms. However, receptors at auditory nerve synapses on cells tha t also receive parallel fiber input, the fusiform cells, had intermediate p roperties with respect to kinetics and contained GluR2 and flip isoforms. G iven the diverse biophysical properties, patterns of innervation, patterns of electrical activity, and targets of each cell type in vivo, these data i ndicate that the kinetics and permeation properties of AMPA receptors are l inked to factors associated with synaptic connectivity.