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

1. The molecular and functional properties of neuronal nicotinic acetylchol ine receptors (nAChRs) were characterized from CA1 neurons in rat hippocamp al 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 a nd beta 2-4, along with the mRNA for the GABAergic markers GAD (glutamic ac id decarboxylase) 65 and 67 isoforms, and VGAT (vesicular GABA transporter) in interneurons from the stratum radiatum and stratum oriens, and in CA1 p yramidal 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 ex amined were alpha 4, alpha 5, alpha 7 and beta 2-4 in stratum radiatum inte rneurons; 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 level s 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 wa s 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 applicati on of 100 mu M ACh were significantly correlated with the expression of par ticular 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 w as correlated with a medium rise time, and the alpha 4 nAChR subunit was co rrelated with a slow rise time. The alpha 2 and alpha 4 nAChR subunits were also significantly correlated with slow desensitization kinetics.