Functional and molecular characterization of neuronal nicotinic ACh receptors in rat CA1 hippocampal neurons

1. The molecular and functional properties of neuronal nicotinic acetylcholine receptors (nAChRs) were characterized from CA1 neurons in rat hippocampal slices using single-cell reverse-transcription polymerase chain reaction (RT-PCR) in conjunction with with hole-cell patch-clamp recordings. 2. We analysed the presence of the neuronal nAChR subunit mRNAs alpha 2-7 and beta 2-4, along with the mRNA for the GABAergic markers GAD (glutamic acid decarboxylase) 65 and 67 isoforms, and VGAT (vesicular GABA transporter) in interneurons from the stratum radiatum and stratum oriens, and in CA1 pyramidal neurons. Functional nAChR-mediated currents were detected in both interneuron populations, but not in pyramidal neurons. 3. The neuronal nAChR subunit mRNAs detected in > 20% of the populations examined were alpha 4, alpha 5, alpha 7 and beta 2-4 in stratum radiatum interneurons; alpha 2, alpha 3, alpha 4, alpha 7, beta 2 and beta 3 subunits in stratum oriens interneurons; and beta 2-4 in pyramidal neurons. High levels of GABAergic marker mRNAs were detected in both interneuron populations, but not in pyramidal neurons. 4. Significant co-expression of nAChR subunits within individual neurons was detected for alpha 3 + alpha 5, alpha 4 + beta 2, alpha 4 + beta 3, alpha 7 + beta 2, beta 2 + beta 3 and beta 3 + beta 4. 5. The kinetics of the nAChR-mediated currents in response to the application of 100 mu M ACh were significantly correlated with the expression of particular nAChR subunits. The alpha 3, alpha 7 and beta 2 nAChR subunits were individually correlated with a fast rise time, the alpha 2 nAChR subunit was correlated with a medium rise time, and the alpha 4 nAChR subunit was correlated with a slow rise time. The alpha 2 and alpha 4 nAChR subunits were also significantly correlated with slow desensitization kinetics.