Abstract
Choline acetyltransferase (ChAT,E.C.2.3.1.6) catalyzes the synthesis of acetylcholine, and is considered to be a phenotypic marker specific for cholinergic neurons. In situ hybridization using a nonradioactive cRNA probe identified a large number of cell bodies expressing ChAT mRNA in the cortices of wild-type Drosophila melanogaster brain. Strong labeling is remarkable in the cortical regions associated with the lamina and antennal lobe, and also in the median neurosecretory (MNS) cells within pars intercerebralis, suggesting that some of the lamina monopolar neurons, antennal interneurons, and MNS cells are cholinergic. In two temperature-sensitive mutant alleles, Chats1 and Chats2, most hybridization signal disappears after exposure to a restrictive temperature (30 degrees C). Loss of signal is especially evident in the optic lobes. Some centrally located neurons, however, continue to express ChAT mRNA and are thus likely to have expression controlled in a different way than the majority of cholinergic neurons. Immunocytochemistry, using a ChAT specific monoclonal antibody, identified two sets of paired neurons located in the posterior cortex of the brain. These neurons persist in ChAT immunoreactivity even in the Chats mutants exposed to restrictive temperature. ChAT mRNA is also detectable in the corresponding cell bodies when Chats mutants are held at restrictive temperature. Our findings demonstrate some specific cholinergic neurons in Drosophila brain, and indicate that ChAT expression is differentially regulated in particular sets of cholinergic neurons.
