Neurotransmitter sign and source-column errors in Drosophila connectome simulation pipelines: an audit of MaleCNS v1.0

Spiking simulations of the Drosophila connectome routinely assign each synapse an excitatory or inhibitory sign by mapping the neurotransmitter (NT) predicted for the presynaptic body to a polarity. Using the recently released MaleCNS v1.0 whole-central-nervous-system connectome (166,700 neurons; 25,582,938 intra-dataset edges), we audited this mapping and found four systematic error classes. First, the per-body predicted_nt column mislabels all 4,064 Kenyon cells as dopaminergic, whereas the curated consensus_nt calls them cholinergic; a naive three-class mapping on predicted_nt would reclassify 884,631 of the 885,611 Kenyon-cell output edges as modulatory, inflating the modulatory count from 435,541 to 1,531,095. Second, histamine—the inhibitory photoreceptor transmitter acting through chloride channels—is treated as excitatory, mis-signing 89,723 edges, a 3.7-fold undercount of the histaminergic pool in predicted_nt (2,126 vs 7,891 neurons). Third, dopamine, serotonin and octopamine (541 neurons; 435,541 edges, including 110,450 PAM→Kenyon-cell contacts) fall through to a default excitatory value, so G-protein-coupled neuromodulation is delivered as fast synaptic drive. Fourth, propagated annotation errors affect gustatory receptor neurons and a recurring claim that PEN/PEG compass neurons are GABAergic. We provide a corrected source column, a three-class (excitatory/inhibitory/modulatory) mapping, and a reproducible audit, and show that the reclassification is exact and bit-for-bit reversible.