The release of neuromodulators by widely projecting neurons often allows sensory systems to alter how they process information based on the physiological state of an animal. Neuromodulators alter network function by changing the biophysical properties of individual neurons and the synaptic efficacy with which individual neurons communicate. However, most, if not all, sensory networks receive multiple neuromodulatory inputs and the mechanisms by which sensory networks integrate multiple modulatory inputs are not well understood. Here, we characterized the relative glomerular distribution of two extrinsic neuromodulators associated with distinct physiological states, serotonin (5-HT) and dopamine (DA), in the antennal lobe (AL) of the moth Manduca sexta. Using immunocytochemistry and mass dye fills, we characterized the innervation patterns of both 5-HT and tyrosine hydroxylase immunoreactive processes (TH-ir) relative to each other, olfactory receptor neurons (ORNs), projection neurons (PNs) and several subsets of local interneurons (LNs). 5-HT-ir had nearly complete overlap with PNs and LN, yet no overlap with ORNs, suggesting that 5-HT may modulate PNs and LNs directly but not ORNs. TH-ir overlapped with PNs, LNs and ORNs suggesting that dopamine has the potential to modulate all three cell types. Furthermore, the branching density of each neuromodulator differed with 5-HT exhibiting denser arborizations and TH-ir processes being more sparse. Our results suggest that 5-HT and DA extrinsic neurons target partially overlapping glomerular regions, yet DA extends further into the region occupied by ORNs.
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