Expression and function of two nicotinic subunits in insect neurons

Nicotinic acetylcholine receptors (nAChRs) in insects are neuron-specific oligomeric proteins essential for the central transmission of sensorv information. Little is known about their subunit composition because it is difficult to express functional insect nAChRs in heterologous systems. As an alternative approach we have examined the native expression of two subunits in neurons of the nicotinic-resistant, tobacco-feeding insect Manduca sexta. Both the alpha-subunit MARA1 and the beta-subunit MARB can be detected by in situ hybridization in the majority of cultured neurons with an overlapping, but not identical, distribution. Changes in intracellular Ca2+ evoked by nicotinic stim. ulation are more strongly correlated to the expression of MARA1 than MARB and are independent of cell Size. Unlike the previously reported critical role of MARA1 in mediating nicotinic Ca2+ responses. down-regulation of MARE by RNA interference (RNAi) did not reduce the number of responding neurons or the size of evoked responses. suggesting that additional subunits remain to be identified in Manduca. (C) 2004 Wiley Periodocals Inc.