ANTISENSE OLIGONUCLEOTIDES TO THE GLUR2 AMPA RECEPTOR SUBUNIT MODIFY EXCITATORY SYNAPTIC TRANSMISSION IN-VIVO

In the brain, fast excitatory synaptic transmission is mostly mediated by the alpha-amino-3-hydroxy-5-methyl-isoxazole-propionic acid (AMPA) subtype of the glutamate receptors. Molecular cloning has revealed th at four subunits, GluR1, GluR2, GluR3, and GluR4 form heteromeric rece ptors with high affinity for AMPA. Because antagonists and agonists do not discriminate between individual AMPA receptor subunits, we decide d to use antisense oligonucleotides to block the expression of the Glu R2 subunit within the receptor complex in adult animals. In the presen t study, we exploited several advantages afforded by the guinea pig co chlea to determine whether an antisense oligonucleotide directed to th e mRNA of the GluR2 subunit could modify primary auditory neurotransmi ssion. While a random probe with the same base composition had no effe ct, a GluR2 antisense oligonucleotide, continuously delivered into the cochlea, transiently reduced the compound action potential and dimini shed spontaneous activity of single auditory nerve fibers. Although an tisense oligonucleotides penetrated a variety of cells, their effect c ould be physiologically localized to a single site of GluR2 antisense probe action, the primary auditory neuron. Subunit specificity of this effect was confirmed by a significant reduction in GluR2/3, but not G luR4 immunoreactivity in primary auditory neurons. Besides being the f irst demonstration that transient knockout of GluR2 subunit in adult a nimal modifies excitatory synaptic transmission in vivo, these results support the use of the antisense strategy as a powerful tool for bloc king expression of any gene in the cochlea. (C) 1998 Elsevier Science B.V.