Expression of a GABA(B )- Receptor in Olfactory Sensory Neurons of Sensilla trichodea on the Male Antenna of the Moth Heliothis virescens

In the olfactory pathway of Drosophila, a GABA(B) receptor mediated presynaptic gain control mechanism at the first synapse between olfactory sensory neurons (OSNs) and projection neurons has been suggested to play a critical role in setting the sensitivity and detection range of the sensory system. To approach the question if such a mechanism may be realized in the pheromone recognition system of male moths in this study attempts were made to explore if moth's pheromone-responsive cells express a GABA(B)- receptor. Employing a combination of genome analysis, RT-PCR experiments and screening of an antennal cDNA library we have identified a cDNA which encodes the GABA(B)-R1 receptor of Heliothis virescens. Moreover, based on the HvirGABA(B)-R1 sequence we could predict a GABA(B)-R1 protein from genome sequences of the silkmoth Bombyx mori. To assess whether HvirGABA(B)-R1 is expressed in OSNs of male antenna we performed whole-mount in situ hybridization (WM-ISH) experiments. Several HvirGABA(B)-R1 positive cells were visualized under long sensilla trichodea, known to contain pheromone-responsive OSNs. In parallel it was shown that cells under long trichoid hairs were labelled with pheromone receptor specific probes. In addition, the HvirGABA(B)-R1 specific probe also labelled several cells under shorter olfactory sensilla, but never stained cells under mechanosensory/gustatory sensilla chaetica. Together, the results indicate that a GABA(B) receptor is expressed in pheromone-responsive OSNs of H. virescens and suggest a presynaptic gain control mechanism in the axon terminals of these cells.