Individual variation in the expression profiles of nicotinic receptors in the olfactory bulb and trigeminal ganglion and identification of alpha2, alpha6, alpha9, and beta3 transcripts.

Nicotine evokes dose-dependent and often variable chemosensory responses in animals and humans. Earlier observations that nicotine binds to some nicotinic acetylcholine receptor (nAChR) subtypes in the olfactory bulb (OB) and trigeminal ganglion (TG) led us to investigate the complete nAChR expression profile in each tissue and to determine whether inter-individual differences exist in male and female rats. Total RNA was extracted from individual samples of dissected OB and TG and analyzed by a sensitive reverse transcription-polymerase chain reaction (RT-PCR) assay to determine the messenger RNA profiles of ten transcripts encoded by the alpha2, alpha3, alpha4, alpha5, alpha6, alpha7, alpha9, beta2, beta3, and beta4 nAChR genes. We found that (a) in the OB, all animals expressed alpha2, alpha3, alpha4, alpha5, alpha7, beta2, and beta4 subunit mRNAs, whereas alpha6, beta3, and alpha9 transcripts were expressed in only 17, 28, and 33% of the animals, respectively, and (b) in the TG, all animals expressed alpha2, alpha3, alpha6, alpha7, beta2, and beta4 subunit mRNAs, whereas alpha9, beta3, alpha4, and alpha5 transcripts were expressed in 4, 38, 88, and 92% of the animals, respectively. These results also identified new subunits that are expressed in each tissue (alpha2, alpha6, alpha9, and beta3) and demonstrated that individual rats may have different tissue-specific expression profiles for alpha4, alpha5, alpha6, alpha9, and beta3 transcripts. Such variations are likely to be reflected in the composition of functional receptor subtypes in the rat OB and TG that have different activation and desensitization characteristics to acetylcholine and nicotine.