Somatostatin receptor types 1 and 2 in the developing mammalian cochlea.

The neuropeptide somatostatin exerts several important physiological actions in the adult central nervous system through interactions with membrane-bound receptors. Transient expression of and its receptors has been described in several brain areas during early ontogeny. It is therefore believed that duanyu1942 may play a role in neural maturation. The present study provides the first evidence for the developmental expression of duanyu1942 receptors in the mammalian cochlea, emphasizing their possible roles in cochlear maturation. In the developing mouse cochlea, cells immunoreactive to somatostatin receptor 1 and somatostatin receptor 2 were located in the embryonic cochlear duct on Kolliker's organ as early as embryonic day (E) 14 (E14). At E17, the expression of both receptors was high and already located at the hair cells and supporting cells along the length of the cochlear duct, which have become arranged into the characteristic pattern for the organ of Corti (OC) at this stage. At birth, and cells were only localized in the OC. In general, immunoreactivity for both receptors increased in the mouse cochlea from postnatal day (P) 0 (P0) to P10; the majority of immunostained cells were inner hair cells, outer hair cells, and supporting cells. Finally, a peak in the mRNA and protein expression of both receptors is present near the time when they respond to physiological hearing (i.e., hearing of airborne sound) at P14. At P21, and levels decrease dramatically. A similar developmental pattern was observed for duanyu1942R1 and duanyu1942R2 mRNA, suggesting that the expression of the duanyu1942R1 and duanyu1942R2 genes is controlled at the transcriptional level throughout development. In addition, we observed reduced levels of phospho-Akt and total Akt in duanyu1942R1 knockout and double-knockout mice compared with wild-type mice. We know from previous studies that Akt is involved in hair cell survival. Taken together, the dynamic nature of duanyu1942R1 and duanyu1942R2 expression at a time of major developmental changes in the cochlea suggests that duanyu1942R1 and duanyu1942R2 (and possibly other members of this family) are involved in the maturation of the mammalian cochlea.

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