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Nicotinic acetylcholine receptors are ligand-gated ion channels expressed in many insect structures, such as mushroom bodies, in which they play a central role. We have recently demonstrated using electrophysiological recordings that different native nicotinic receptors are expressed in cockroach mushroom bodies Kenyon cells. In the present study, we demonstrated that eight genes coding for cockroach nicotinic acetylcholine receptor subunits are expressed in the mushroom bodies. Quantitative real-time polymerase chain reaction (PCR) experiments demonstrated that β1 subunit was the most expressed in the mushroom bodies. Moreover, antisense oligonucleotides performed against β1 subunit revealed that inhibition of β1 expression strongly decreases nicotine-induced currents amplitudes. Moreover, co-application with 0.5 μM α-bungarotoxin completely inhibited nicotine currents whereas 10 μM d-tubocurarine had a partial effect demonstrating that β1-containing neuronal nicotinic acetylcholine receptor subtypes could be sensitive to the nicotinic acetylcholine receptor antagonist α-bungarotoxin.

The present study was conducted to determine whether imidacloprid can impair the avoidance behaviour of the mosquito Stegomyia aegypti. Laboratory investigations using a T-maze apparatus showed that St. aegypti mosquitoes present long term avoidance behaviour when they are exposed to repetitive trials with lemon oil and DEET. The present study tested the effect of a sublethal dose of imidacloprid on the avoidance behaviour of St. aegypti mosquitoes over a 48 h period. Data suggest that 0.5 ng of imidacloprid/mosquito reduces the avoidance behaviour of mosquitoes exposed to lemon oil, on the first day of exposure, after the second trial; whereas imidacloprid affected DEET repellency only the first day of exposure, after the second trial. Imidacloprid was toxic against St. aegypti mosquitoes, and at sublethal doses was able to impair the repellency induced by lemon oil and DEET. The present data were consistent with the finding that St. aegypti mosquitoes exhibit long term avoidance behaviour, and treatment of mosquitoes with a sublethal dose of imidacloprid under DEET application can affect the repellency of DEET against St. aegypti.

Calcium/calmodulin-dependent protein kinase II (CaMKII) is a key kinase that transduces Ca²⁺ signals into downstream effects acting on a range of cellular processes in nervous system and muscular tissues. In insects, different CaMKII isoforms have been reported in Drosophila melanogaster, Apis florae, Bombus terrestris, and Bombus impatiens but little is known on the organization and tissue-specific expression of these isoforms with the exception of Drosophila. The present study reports the cloning of five CaMKII splice variants issued from a single gene and their tissue-specific expression in the cockroach Periplaneta americana. Each CaMKII isoform shared 82-90% identity with Drosophila CaMKII isoforms and accordingly were named PaCaMKII-A, PaCaMKII-B,PaCaMKII-C,PaCaMKII-D, and PaCaMKII-E. PaCaMKII-A and PaCaMKII-D isoforms are ubiquitously expressed in all tissues, but some such as PaCaMKII-B andPaCaMKII-C are preferentially expressed in the nerve cord and muscle. In addition, using single-cell reverse transcriptase-polymerase chain reaction (RT-PCR), we found a tissue-specific expression of PaCaMKII-E in the dorsal unpaired median neurons. Alternative splicing of PaCaMKII transcripts is likely a common mechanism in insects to control the pattern of isoform expression in the different tissues.