Distribution and postnatal development of alpha 7 nicotinic acetylcholine receptors in the rodent lower auditory brainstem.

The distribution and quantity of the alpha 7 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 (125)I-alpha-bungarotoxin receptor binding were used to measure alpha 7 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 alpha 7 nAChR is predominantly localized postynaptically on somata or proximal dendrites. In a separate experiment, alpha 7 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 alpha 7 nAChR were not different in +/+ and -/- mice, suggesting that AChE may not induce or regulate alpha 7 transcription during the early postnatal period.