Distribution and postnatal development of α7 nicotinic acetylcholine receptors in the rodent lower auditory brainstem

The distribution and quantity of the α7 nicotinic acetylcholine receptor (nAChR) were mapped in the nuclei of the superior olivary complex, lateral lemniscus, and inferior colliculus in the developing and mature rat brain. Radioactive in situ hybridization and ¹²⁵I-α- bungarotoxin receptor binding were used to measure α7 transcript and membrane-bound protein, respectively. The highest transcript and protein levels were found in the external nucleus of the inferior colliculus and paraolivary nucleus. More moderate levels of transcript and protein were measured in the ventral, intermediate, and dorsal nuclei of the lateral lemniscus, lateral and medial ventral posterior olivary nuclei, rostral periolivary region, lateral periolivary nucleus, caudal periolivary region, ventral and dorsal trapezoid nuclei, medial superior olive, and the lateral superior olive. Peak receptor expression generally occurred before the onset of hearing. The significant overlap of transcript and protein in these regions suggests that the α7 nAChR is predominantly localized postynaptically on somata or proximal dendrites. In a separate experiment, α7 transcript was quantified in the superior olivary complex, lateral lemniscus, and inferior colliculus of +/+ and null mutant (-/-) mice for the acetylcholinesterase (AChE) gene. The distribution and quantity of α7 nAChR were not different in +/+ and -/- mice, suggesting that AChE may not induce or regulate α7 transcription during the early postnatal period.