Fgf15 Neurons of the Dorsomedial Hypothalamus Control Glucagon Secretion and Hepatic Gluconeogenesis.

The counterregulatory response to hypoglycemia is an essential survival function. It is controlled by an integrated network of glucose-responsive neurons, which trigger endogenous glucose production to restore normoglycemia. The complexity of this glucoregulatory network is, however, only partly characterized. In a genetic screen of a panel of recombinant inbred mice we previously identified Fgf15, expressed in neurons of the dorsomedial hypothalamus (DMH), as a negative regulator of glucagon secretion. Here, we report on the generation of Fgf15 <sup>CretdTomato</sup> mice and their use to further characterize these neurons. We show that they were glutamatergic and comprised glucose-inhibited and glucose-excited neurons. When activated by chemogenetics, Fgf15 neurons prevented the increase in vagal nerve firing and the secretion of glucagon normally triggered by insulin-induced hypoglycemia. On the other hand, they increased the activity of the sympathetic nerve in the basal state and prevented its silencing by glucose overload. Higher sympathetic tone increased hepatic Creb1 phosphorylation, Pck1 mRNA expression, and hepatic glucose production leading to glucose intolerance. Thus, Fgf15 neurons of the DMH participate in the counterregulatory response to hypoglycemia by a direct adrenergic stimulation of hepatic glucose production while suppressing vagally induced glucagon secretion. This study provides new insights into the complex neuronal network that prevents the development of hypoglycemia

Sleep-Deprivation Regulates α-2 Adrenergic Responses of Rat Hypocretin/Orexin Neurons

We recently demonstrated, in rat brain slices, that the usual excitation by noradrenaline (NA) of hypocretin/orexin (hcrt/orx) neurons was changed to an inhibition following sleep deprivation (SD). Here we describe that in control condition (CC), i.e. following 2 hours of natural sleep in the morning, the α2-adrenergic receptor (α2-AR) agonist, clonidine, had no effect on hcrt/orx neurons, whereas following 2 hours of SD (SDC), it hyperpolarized the neurons by activating G-protein-gated inwardly rectifying potassium (GIRK) channels. Since concentrations of clonidine up to a thousand times (100 µM) higher than those effective in SDC (100 nM), were completely ineffective in CC, a change in the availability of G-proteins is unlikely to explain the difference between the two conditions. To test whether the absence of effect of clonidine in CC could be due to a down-regulation of GIRK channels, we applied baclofen, a GABAB agonist known to also activate GIRK channels, and found that it hyperpolarized hcrt/orx neurons in that condition. Moreover, baclofen occluded the response to clonidine in SDC, indicating that absence of effect of clonidine in CC could not be attributed to down-regulation of GIRK channels. We finally tested whether α2-ARs were still available at the membrane in CC and found that clonidine could reduce calcium currents, indicating that α2-ARs associated with calcium channels remain available in that condition. Taken together, these results suggest that a pool of α2-ARs associated with GIRK channels is normally down-regulated (or desensitized) in hcrt/orx neurons to only become available for their inhibition following sleep deprivation

RGS2 modulates coupling between GABAB receptors and GIRK channels in dopamine neurons of the ventral tegmental area

Agonists of GABA(B) receptors exert a bi-directional effect on the activity of dopamine (DA) neurons of the ventral tegmental area, which can be explained by the fact that coupling between GABA(B) receptors and G protein-gated inwardly rectifying potassium (GIRK) channels is significantly weaker in DA neurons than in GABA neurons. Thus, low concentrations of agonists preferentially inhibit GABA neurons and thereby disinhibit DA neurons. This disinhibition might confer reinforcing properties on addictive GABA(B) receptor agonists such as gamma-hydroxybutyrate (GHB) and its derivatives. Here we show that, in DA neurons of mice, the low coupling efficiency reflects the selective expression of heteromeric GIRK2/3 channels and is dynamically modulated by a member of the regulator of G protein signaling (RGS) protein family. Moreover, repetitive exposure to GHB increases the GABA(B) receptor-GIRK channel coupling efficiency through downregulation of RGS2. Finally, oral self-administration of GHB at a concentration that is normally rewarding becomes aversive after chronic exposure. On the basis of these results, we propose a mechanism that might underlie tolerance to GHB

The molecular and cellular basis of olfactory-driven behavior in Anopheles gambiae larvae

The mosquito Anopheles gambiae is the principal Afrotropical vector for human malaria. A central component of its vectorial capacity is the ability to maintain sufficient populations of adults. During both adult and preadult (larval) stages, the mosquitoes depend on the ability to recognize and respond to chemical cues that mediate feeding and survival. In this study, we used a behavioral assay to identify a range of odorant-specific responses of An. gambiae larvae that are dependent on the integrity of the larval antennae. Parallel molecular analyses have identified a subset of the An. gambiae odorant receptors (AgOrs) that are localized to discrete neurons within the larval antennae and facilitate odor-evoked responses in Xenopus oocytes that are consistent with the larval behavioral spectrum. These studies shed light on chemosensory-driven behaviors and represent molecular and cellular characterization of olfactory processes in mosquito larvae. These advances may ultimately enhance the development of vector control strategies, targeting olfactory pathways in larval-stage mosquitoes to reduce the catastrophic effects of malaria and other diseases

Gamma-Hydroxybutyrate Increases Resting-State Limbic Perfusion and Body and Emotion Awareness in Humans

Gamma-hydroxybutyrate (GHB) is a GHB-/GABA-B receptor agonist inducing a broad spectrum of subjective effects including euphoria, disinhibition, and enhanced vitality. It is used as treatment for neuropsychiatric disorders including narcolepsy and alcohol withdrawal, but is also a drug of abuse. Non-medical users report enhancement of body and emotion awareness during intoxication. However, the neuronal underpinnings of such awareness alterations under GHB are unknown so far. The assessment of regional cerebral blood flow (rCBF) by pharmacological magnetic resonance imaging (phMRI) enables the elucidation of drug-induced functional brain alterations. Thus, we assessed the effects of GHB (35 mg/kg p.o.) in 17 healthy males on rCBF and subjective drug effects, using a placebo-controlled, double-blind, randomized, cross-over design employing arterial spin labeling phMRI. Compared to placebo, GHB increased subjective ratings for body and emotion awareness, and for dizziness (p<0.01-0.001, Bonferroni-corrected). A whole-brain analysis showed increased rCBF in the bilateral anterior cingulate cortex (ACC) and the right anterior insula under GHB (p<0.05, cluster-corrected). ACC and insula rCBF are correlated with relaxation, and body and emotion awareness (p<0.05-0.001, uncorrected). Interaction analyses revealed that GHB-induced increase of body awareness was accompanied by increased rCBF in ACC, whereas relaxation under GHB was accompanied by elevated rCBF in right anterior insula (p<0.05, uncorrected). In conclusion, enhancement of emotion and body awareness, and increased perfusion of insula and ACC bears implications both for the properties of GHB as a drug of abuse as well as for its putative personalized potential for specific therapeutic indications in affective disorders