Nicotinic Acetylcholine Receptor α9 and α10 Subunits Are Expressed in the Brain of Mice

The alpha 9 and alpha 10 nicotinic acetylcholine receptor (nAChR) subunits are likely to be the evolutionary precursors to the entire cys-loop superfamily of ligand-gated ion channels, which includes acetylcholine, GABA, glycine and serotonin ionotropic receptors. nAChRs containing alpha 9 and alpha 10 subunits are found in the inner ear, dorsal root ganglia and many non-excitable tissues, but their expression in the central nervous system has not been definitely demonstrated. Here we show the presence of both alpha 9 and alpha 10 nAChR subunits in the mouse brain by RT-PCR and immunochemical approaches with a range of nAChR subunit-selective antibodies, which selectivity was demonstrated in the brain preparations of alpha 7-/-, alpha 9-/- and alpha 10-/- mice. The alpha 9 and alpha 10 RNA transcripts were found in medulla oblongata (MO), cerebellum, midbrain (MB), thalamus and putamen (TP), somatosensory cortex (SC), frontal cortex (FC) and hippocampus. High alpha 9-selective signal in ELISA was observed in the FC, SC, MO, TP and hippocampus and alpha 10-selective signal was the highest in MO and FC. The alpha 9 and alpha 10 proteins were found in the brain mitochondria, while their presence on the plasma membrane has not been definitely confirmed The alpha 7-, alpha 9- and alpha 10-selective antibodies stained mainly neurons and hypertrophied astrocytes, but not microglia. The alpha 9- and alpha 10-positive cells formed ordered structures or zones in cerebellum and superior olive (SO) and were randomly distributed among alpha 7-positive cells in the FC; they were found in CA1, CA3 and CA4, but not in CA2 region of the hippocampus. The alpha 9 and alpha 10 subunits were up-regulated in alpha 7-/- mice and both alpha 7 and alpha 9 subunits were down-regulated in alpha 10-/- mice. We conclude that alpha 9 and alpha 10 nAChR subunits are expressed in distinct neurons of the mouse brain and in the brain mitochondria and are compensatory up-regulated in the absence of alpha 7 subunits.