Glutamate or a parent substance is thought to be the afferent neurotransmitter in the auditory system. In situ hybridization showed that mGluR1 alpha mRNA was expressed by type I and type II spiral ganglion neurons in the cochlea. The glial cells surrounding the type I spiral ganglion neurons lacked such expression. The hybridization signal was low compared to that reported for non-NMDA receptors, suggesting that mGluR1 alpha receptors, as is the case for NMDA receptors, play a minor role in auditory transmission. The uniform expression of mGluR1 alpha mRNAs along the cochlear spiral suggests their co-expression in spiral ganglion neurons with NMDA and non-NMDA receptors and thus functional cooperation.