Expression of the P2X1 receptor remains in the type II spiral ganglion neurons in the mature rat cochlea

Our sense of hearing commences in the cochlea, the peripheral sensory organ for hearing. Spiral ganglion neurons (SGN) in the cochlea are primary auditory neurons responsible for auditory neurotransmission. There are two classes of SGNs: type I SGNs, which make up 90-95% of the SGN population, and type II SGNs, which make up the remainder. Previous studies have shown that SGNs express a combination of purinergic (P2X, P2Y and adenosine) receptors at the mRNA and protein levels. In this study, we have focused on the P2X1 receptor to characterise its expression pattern in the Wistar rat cochlea at postnatal day 8 and in adult (6-8-week-old) rats of both genders using immunohistochemistry. Our results show differential expression of P2X1 receptors in 9.4-14.2% of SGNs in the adult cochlea, and 14.2-23.3% in the cochlea of P8 pups. In most of these neurons, P2X1 receptors were co-expressed with peripherin-1, an established type II SGN marker. These results suggest a potential role for the P2X1 receptor as a modulator of auditory neurotransmission in type II spiral ganglion neurons.