Genetic analyses in Drosophila have identified peptides that facilitate sensory neuron activity. Short neuropeptide F (sNPF), a homolog of neuropeptide Y, is released by OSNs and increases the activity of other OSNs projecting to the same glomerulus [19**,21]. Increased activity of a glomerulus could make odors that are specifically processed by it salient when information is transmitted to higher processing centers. Interestingly, the receptor for sNPF, sNPFR1, is expressed on sensory neurons only
upon starvation [19**]. This observation indicates that peptide signaling integrates behavioral state information with odorant information directly in sensory neurons. Similar mechanisms might also exist in rodents (Figure 1c). For example, the peptide FMRFamide increases the magnitude of delayed-rectifier potassium currents in the mouse olfactory bulb, as measured by whole cell patch-clamp recordings [22]. The action of such neuropeptides may increase the excitability of OSNs. However, the behavioral relevance of this modulation remains to be established.
Antagonistic peptide signals might act as gain controls for sensory neurons. Presynaptic inhibition increases the ability of these neurons to respond to high odor concentrations, while facilitation may increase neuronal sensitivity to lower odor concentrations. The slow time course of peptide signaling could also extend the time that an OSN remains active and stabilize an odor representation over the second to minute timescales of olfactory-driven behaviors. The conservation across species of mechanisms enabling neuropeptide modulation of OSNs suggests their importance in permitting animals to respond to changing environments and physiological drives.
Genetic analyses in Drosophila have identified peptides that facilitate sensory neuron activity. Short neuropeptide F (sNPF), a homolog of neuropeptide Y, is released by OSNs and increases the activity of other OSNs projecting to the same glomerulus [19**,21]. Increased activity of a glomerulus could make odors that are specifically processed by it salient when information is transmitted to higher processing centers. Interestingly, the receptor for sNPF, sNPFR1, is expressed on sensory neurons onlyupon starvation [19**]. This observation indicates that peptide signaling integrates behavioral state information with odorant information directly in sensory neurons. Similar mechanisms might also exist in rodents (Figure 1c). For example, the peptide FMRFamide increases the magnitude of delayed-rectifier potassium currents in the mouse olfactory bulb, as measured by whole cell patch-clamp recordings [22]. The action of such neuropeptides may increase the excitability of OSNs. However, the behavioral relevance of this modulation remains to be established.Antagonistic peptide signals might act as gain controls for sensory neurons. Presynaptic inhibition increases the ability of these neurons to respond to high odor concentrations, while facilitation may increase neuronal sensitivity to lower odor concentrations. The slow time course of peptide signaling could also extend the time that an OSN remains active and stabilize an odor representation over the second to minute timescales of olfactory-driven behaviors. The conservation across species of mechanisms enabling neuropeptide modulation of OSNs suggests their importance in permitting animals to respond to changing environments and physiological drives.
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