Chronic intermittent hypoxia enhances glycinergic inhibition in nucleus tractus solitarius.

Chronic intermittent hypoxia (CIH), an animal model of sleep apnea, has been shown to alter the activity of second-order chemoreceptor neurons in the caudal nucleus of the solitary tract (cNTS). Although numerous studies have focused on excitatory plasticity, few studies have explored CIH-induced plasticity impacting inhibitory inputs to NTS neurons, and the roles of GABAergic and glycinergic inputs on heightened cNTS excitability following CIH are unknown. In addition, changes in astrocyte function may play a role in cNTS plasticity responses to CIH. This study tested the effects of a 7-day CIH protocol on miniature inhibitory postsynaptic currents (mIPSCs) in cNTS neurons receiving chemoreceptor afferents. Normoxia-treated rats primarily displayed GABA mIPSCs, whereas CIH-treated rats exhibited a shift toward combined GABA/glycine-mediated mIPSCs. CIH increased glycinergic mIPSC amplitude and area. This shift was not observed in dorsal motor nucleus of the vagus neurons or cNTS cells from females. Immunohistochemistry showed that strengthened glycinergic mIPSCs were associated with increased glycine receptor protein and were dependent on receptor trafficking in CIH-treated rats. In addition, CIH altered astrocyte morphology in the cNTS, and inactivation of astrocytes following CIH reduced glycine receptor-mediated mIPSC frequency and overall mIPSC amplitude. In cNTS, CIH produced changes in glycine signaling that appear to reflect increased trafficking of glycine receptors to the cell membrane. Increased glycine signaling in cNTS associated with CIH also appears to be dependent on astrocytes. Additional studies will be needed to determine how CIH influences glycine receptor expression and astrocyte function in cNTS.NEW & NOTEWORTHY Chronic intermittent hypoxia (CIH) has been used to mimic the hypoxemia associated with sleep apnea and determine how these hypoxemias influence neural function. The nucleus of the solitary tract is the main site for chemoreceptor input to the CNS, but how CIH influences NTS inhibition has not been determined. These studies show that CIH increases glycine-mediated miniature IPSCs through mechanisms that depend on protein trafficking and astrocyte activation.

Odorant Receptor Sensitivity Modulation in Drosophila.

The ability to modulate sensitivity in sensory systems is essential for useful information to be extracted from fluctuating stimuli in a wide range of background conditions. The mechanisms underlying sensitivity regulation in insect primary olfactory neurons are poorly understood. Here we reveal that dephosphorylation of OrcoS289 that occurs upon prolonged odor exposure is a mechanism underlying reduction in odorant sensitivity in Drosophila primary olfactory neurons in both sexes. OrcoS289A mutants, unable to phosphorylate this position, have low intrinsic odorant sensitivity that is independent of altered expression or localization. A phosphomimetic allele, OrcoS289D , has enhanced odorant sensitivity compared with wild-type controls. To explore the functional ramifications of this phosphorylation in vivo, we generated phospho-specific antiserum to OrcoS289 and show that phosphorylation at this residue is dynamically regulated by odorant exposure with concomitant modulation of odorant sensitivity. OrcoS289 is phosphorylated in the sensitized state, and odorant exposure triggers dephosphorylation and desensitization without altering receptor localization. We further show that dephosphorylation of OrcoS289 is triggered by neuronal activity, and not conformational changes in the receptor occurring upon ligand binding. Mutant flies unable to regulate Orco function through phosphorylation at S289 are defective for odor-guided behavior. These findings provide insight into the mechanisms underlying regulation of insect odorant receptors in vivoSIGNIFICANCE STATEMENT We have uncovered a mechanism underlying olfactory receptor sensitivity regulation in Drosophila The phosphorylation state of Orco S289 is altered in an odorant-dependent manner and changes in phosphorylation affect receptor sensitivity without changing subcellular localization. We show that neuronal activity triggers the phosphorylation changes and that this phenomenon is important for odorant-guided behaviors in Drosophila This phosphorylation site is conserved in other insects, including mosquitoes, indicating this mechanism may be a target for manipulation of insect behaviors in the future.

Multiple channels of DEET repellency in Drosophila.

BACKGROUND: N,N-Diethyl-meta-toluamide (DEET) is the prophylactic insect repellent used most widely to inhibit insect bites. Despite its use since 1944, the mechanism of DEET repellency remains controversial. Here, we revisited the role of smell and taste in DEET repellence using Drosophila as a model. RESULTS: Analysis of the responses of individual olfactory receptor neuron (ORN) classes to DEET reveals that 11 ORNs are activated and two are inhibited by this compound. Blocking individual ORN classes in the antenna does not block DEET repellence. This argues against the existence of a single ORN mediating DEET repellence in Drosophila. Activation of all ORCO-expressing neurons using channelrhodopsin favors attraction, not repellence, in behavioral valence. We also demonstrate that gustatory neurons are highly sensitive to DEET. We used RNA interference to screen candidate receptors encoded by gene families involved in the detection of bitter compounds, including 34 gustatory receptors (Grs), 14 ionotropic receptors (Irs), five pick-pocket subunits (PPKs), three transient receptor potential ion channels (TrpA, TrpL, Painless) and one metabotropic glutamate receptors gene (DmXR). We saw striking defects in DEET-mediated oviposition behavior when expression of either Gr32a or Gr33a was inhibited. CONCLUSION: Our findings support a multimodal mechanism for DEET detection in fruit flies and indicate a prominent role for taste detection mediating DEET repellence. © 2019 Society of Chemical Industry.