UNASSIGNED: Although the gustatory system provides animals with sensory cues important for food choice and other @entity146 , little is known about neural circuitry immediately following gustatory sensory neurons (GSNs). Here, we identify and characterize a bilateral pair of gustatory second-order neurons (G2Ns) in @entity238 . Previous studies identified GSNs that relay taste information to distinct subregions of the primary gustatory center (PGC) in the gnathal ganglia (GNG). To identify candidate G2Ns, we screened    5,000 GAL4 driver strains for lines that label neural fibers innervating the PGC. We then combined GRASP (GFP reconstitution across synaptic partners) with presynaptic labeling to visualize potential synaptic contacts between the dendrites of the candidate G2Ns and the axonal terminals of @entity69628 -expressing GSNs, which are known to respond to @entity969 . Results of the GRASP analysis, followed by a single-cell analysis by FLP-out recombination, revealed a pair of neurons that contact @entity69628 axon terminals in both brain hemispheres and send axonal arborizations to a distinct region outside the PGC but within the GNG. To characterize the input and output branches, respectively, we expressed fluorescence-tagged @entity934 receptor subunit ( @entity39990 ) and active-zone marker (Brp) in the G2Ns. We found that G2N input sites overlaid GRASP-labeled synaptic contacts to @entity69628 neurons, while presynaptic sites were broadly distributed throughout the neurons' arborizations. GRASP analysis and further tests with the Syb-GRASP method suggested that the identified G2Ns receive synaptic inputs from @entity69628 -expressing GSNs, but not @entity53023 -expressing GSNs, which respond to @entity5834 . The identified G2Ns relay information from @entity69628 -expressing GSNs to distinct regions in the GNG, and are distinct from other, recently identified gustatory projection neurons, which relay information about @entity3363 to a brain region called the antennal mechanosensory and motor center (AMMC). Our findings suggest unexpected complexity for taste information processing in the first relay of the gustatory system.

A gustatory second-order neuron that connects @entity969 -sensitive primary neurons and a distinct region of the gnathal ganglion in the XXXX brain.

@entity3363 :: ('MESH:D002241', 'Chemical') :: ['sugars'] @entity146 :: ('MESH:D001523', 'Disease') :: ['critical behaviors'] @entity69628 :: ('44873(Tax:7227)', 'Gene') :: ['Gr5a'] @entity5834 :: ('MESH:D002110', 'Chemical') :: ['caffeine'] @entity969 :: ('MESH:D013395', 'Chemical') :: ['sucrose'] @entity39990 :: ('32928(Tax:7227)', 'Gene') :: ['Da7'] @entity53023 :: ('38935(Tax:7227)', 'Gene') :: ['Gr66a'] @entity238 :: ('7227', 'Species') :: ['Drosophila'] @entity934 :: ('MESH:D000109', 'Chemical') :: ['acetylcholine']
@entity238 :: (7227,Species) :: ['Drosophila']
