Lorenzo LE, Godin AG, Ferrini F, Bachand K, Plasencia-Fernandez I, Labrecque S, Girard A, Boudreau D, Kianicka I, Gagnon M, Doyon N, Ribeiro-da-Silva A, De Koninck Y
PMID: 32054836 | DOI: 10.1038/s41467-019-14154-6
Spinal disinhibition has been hypothesized to underlie pain hypersensitivity in neuropathic pain. Apparently contradictory mechanisms have been reported, raising questions on the best target to produce analgesia. Here, we show that nerve injury is associated with a reduction in the number of inhibitory synapses in the spinal dorsal horn. Paradoxically, this is accompanied by a BDNF-TrkB-mediated upregulation of synaptic GABAARs and by an ?1-to-?2GABAAR subunit switch, providing a mechanistic rationale for the analgesic action of the ?2,3GABAAR benzodiazepine-site ligand L838,417 after nerve injury. Yet, we demonstrate that impaired Cl- extrusion underlies the failure of L838,417 to induce analgesia at high doses due to a resulting collapse in Cl- gradient, dramatically limiting the benzodiazepine therapeutic window. In turn, enhancing KCC2 activity not only potentiated L838,417-induced analgesia, it rescued its analgesic potential at high doses, revealing a novel strategy for analgesia in pathological pain, by combined targeting of the appropriate GABAAR-subtypes and restoring Cl- homeostasis
Frezel, N;Ranucci, M;Foster, E;Wende, H;Pelczar, P;Mendes, R;Ganley, RP;Werynska, K;d'Aquin, S;Beccarini, C;Birchmeier, C;Zeilhofer, HU;Wildner, H;
PMID: 36947543 | DOI: 10.1016/j.celrep.2023.112295
Corticospinal tract (CST) neurons innervate the deep spinal dorsal horn to sustain chronic neuropathic pain. The majority of neurons targeted by the CST are interneurons expressing the transcription factor c-Maf. Here, we used intersectional genetics to decipher the function of these neurons in dorsal horn sensory circuits. We find that excitatory c-Maf (c-MafEX) neurons receive sensory input mainly from myelinated fibers and target deep dorsal horn parabrachial projection neurons and superficial dorsal horn neurons, thereby connecting non-nociceptive input to nociceptive output structures. Silencing c-MafEX neurons has little effect in healthy mice but alleviates mechanical hypersensitivity in neuropathic mice. c-MafEX neurons also receive input from inhibitory c-Maf and parvalbumin neurons, and compromising inhibition by these neurons caused mechanical hypersensitivity and spontaneous aversive behaviors reminiscent of c-MafEX neuron activation. Our study identifies c-MafEX neurons as normally silent second-order nociceptors that become engaged in pathological pain signaling upon loss of inhibitory control.
Science translational medicine
Tang, YL;Liu, AL;Lv, SS;Zhou, ZR;Cao, H;Weng, SJ;Zhang, YQ;
PMID: 36475906 | DOI: 10.1126/scitranslmed.abq6474
Green light exposure has been shown to reduce pain in animal models. Here, we report a vision-associated enkephalinergic neural circuit responsible for green light-mediated analgesia. Full-field green light exposure at an intensity of 10 lux produced analgesic effects in healthy mice and in a model of arthrosis. Ablation of cone photoreceptors completely inhibited the analgesic effect, whereas rod ablation only partially reduced pain relief. The analgesic effect was not modulated by the ablation of intrinsically photosensitive retinal ganglion cells (ipRGCs), which are atypical photoreceptors that control various nonvisual effects of light. Inhibition of the retino-ventrolateral geniculate nucleus (vLGN) pathway completely abolished the analgesic effects. Activation of this pathway reduced nociceptive behavioral responses; such activation was blocked by the inhibition of proenkephalin (Penk)-positive neurons in the vLGN (vLGNPenk). Moreover, green light analgesia was prevented by knockdown of Penk in the vLGN or by ablation of vLGNPenk neurons. In addition, activation of the projections from vLGNPenk neurons to the dorsal raphe nucleus (DRN) was sufficient to suppress nociceptive behaviors, whereas its inhibition abolished the green light analgesia. Our findings indicate that cone-dominated retinal inputs mediated green light analgesia through the vLGNPenk-DRN pathway and suggest that this signaling pathway could be exploited for reducing pain.
Chen, Z;Chen, G;Zhong, J;Jiang, S;Lai, S;Xu, H;Deng, X;Li, F;Lu, S;Zhou, K;Li, C;Liu, Z;Zhang, X;Zhu, Y;
PMID: 36028570 | DOI: 10.1038/s41380-022-01742-0
Feeding behavior is regulated by both the homeostatic needs of the body and hedonic values of the food. Easy access to palatable energy-dense foods and the consequent obesity epidemic stress the urgent need for a better understanding of neural circuits that regulate hedonic feeding. Here, we report that neurotensin-positive neurons in the lateral septum (LSNts) play a crucial role in regulating hedonic feeding. Silencing LSNts specifically promotes feeding of palatable food, whereas activation of LSNts suppresses overall feeding. LSNts neurons project to the tuberal nucleus (TU) via GABA signaling to regulate hedonic feeding, while the neurotensin signal from LSNts→the supramammillary nucleus (SUM) is sufficient to suppress overall feeding. In vivo calcium imaging and optogenetic manipulation reveal two populations of LSNts neurons that are activated and inhibited during feeding, which contribute to food seeking and consumption, respectively. Chronic activation of LSNts or LSNts→TU is sufficient to reduce high-fat diet-induced obesity. Our findings suggest that LSNts→TU is a key pathway in regulating hedonic feeding.
A distinct parabrachial-to-lateral hypothalamus circuit for motivational suppression of feeding by nociception
Phua, SC;Tan, YL;Kok, AMY;Senol, E;Chiam, CJH;Lee, CY;Peng, Y;Lim, ATJ;Mohammad, H;Lim, JX;Fu, Y;
PMID: 33962958 | DOI: 10.1126/sciadv.abe4323
The motivation to eat is not only shaped by nutrition but also competed by external stimuli including pain. How the mouse hypothalamus, the feeding regulation center, integrates nociceptive inputs to modulate feeding is unclear. Within the key nociception relay center parabrachial nucleus (PBN), we demonstrated that neurons projecting to the lateral hypothalamus (LHPBN) are nociceptive yet distinct from danger-encoding central amygdala-projecting (CeAPBN) neurons. Activation of LHPBN strongly suppressed feeding by limiting eating frequency and also reduced motivation to work for food reward. Refined approach-avoidance paradigm revealed that suppression of LHPBN, but not CeAPBN, sustained motivation to obtain food. The effect of LHPBN neurons on feeding was reversed by suppressing downstream LHVGluT2 neurons. Thus, distinct from a circuit for fear and escape responses, LHPBN neurons channel nociceptive signals to LHVGluT2 neurons to suppress motivational drive for feeding. Our study provides a new perspective in understanding feeding regulation by external competing stimuli.
Brain Struct Funct. 2018 Oct 20.
Gasparini S, Resch JM, Narayan SV, Peltekian L, Iverson GN, Karthik S, Geerling JC.
PMID: 30343334 | DOI: 10.1007/s00429-018-1778-y
Sodium deficiency elevates aldosterone, which in addition to epithelial tissues acts on the brain to promote dysphoric symptoms and salt intake. Aldosterone boosts the activity of neurons that express 11-beta-hydroxysteroid dehydrogenase type 2 (HSD2), a hallmark of aldosterone-sensitive cells. To better characterize these neurons, we combine immunolabeling and in situ hybridization with fate mapping and Cre-conditional axon tracing in mice. Many cells throughout the brain have a developmental history of Hsd11b2 expression, but in the adult brain one small brainstem region with a leaky blood-brain barrier contains HSD2 neurons. These neurons express Hsd11b2, Nr3c2 (mineralocorticoid receptor), Agtr1a (angiotensin receptor), Slc17a6 (vesicular glutamate transporter 2), Phox2b, and Nxph4; many also express Cartpt or Lmx1b. No HSD2 neurons express cholinergic, monoaminergic, or several other neuropeptidergic markers. Their axons project to the parabrachial complex (PB), where they intermingle with AgRP-immunoreactive axons to form dense terminal fields overlapping FoxP2 neurons in the central lateral subnucleus (PBcL) and pre-locus coeruleus (pLC). Their axons also extend to the forebrain, intermingling with AgRP- and CGRP-immunoreactive axons to form dense terminals surrounding GABAergic neurons in the ventrolateral bed nucleus of the stria terminalis (BSTvL). Sparse axons target the periaqueductal gray, ventral tegmental area, lateral hypothalamic area, paraventricular hypothalamic nucleus, and central nucleus of the amygdala. Dual retrograde tracing revealed that largely separate HSD2 neurons project to pLC/PB or BSTvL. This projection pattern raises the possibility that a subset of HSD2 neurons promotes the dysphoric, anorexic, and anhedonic symptoms of hyperaldosteronism via AgRP-inhibited relay neurons in PB.
Szlaga, A;Sambak, P;Gugula, A;Trenk, A;Gundlach, AL;Blasiak, A;
PMID: 35973599 | DOI: 10.1016/j.neuropharm.2022.109216
Nucleus incertus (NI) is a brainstem structure involved in the control of arousal, stress responses and locomotor activity. It was reported recently that NI neurons express the dopamine type 2 (D2) receptor that belongs to the D2-like receptor (D2R) family, and that D2R activation in the NI decreased locomotor activity. In this study, using multiplex in situ hybridization, we observed that GABAergic and glutamatergic NI neurons express D2 receptor mRNA, and that D2 receptor mRNA-positive neurons belong to partially overlapping relaxin-3- and cholecystokinin-positive NI neuronal populations. Our immunohistochemical and viral-based retrograde tract-tracing studies revealed a dense innervation of the NI area by fibers containing the catecholaminergic biosynthesis enzymes, tyrosine hydroxylase (TH) and dopamine β-hydroxylase (DBH), and indicated the major sources of the catecholaminergic innervation of the NI as the Darkschewitsch, raphe and hypothalamic A13 nuclei. Furthermore, using whole-cell patch clamp recordings, we demonstrated that D2R activation by quinpirole produced excitatory and inhibitory influences on neuronal activity in the NI, and that both effects were postsynaptic in nature. Moreover, the observed effects were cell-type specific, as type I NI neurons were either excited or inhibited, whereas type II NI neurons were mainly excited by D2R activation. Our results reveal that rat NI receives a strong catecholaminergic innervation and suggest that catecholamines acting within the NI are involved in the control of diverse processes, including locomotor activity, social interaction and nociceptive signaling. Our data also strengthen the hypothesis that the NI acts as a hub integrating arousal-related neuronal information.
Shi Y, Stornetta RL, Stornetta DS, Onengut-Gumuscu S, Farber EA, Turner SD, Guyenet PG, Bayliss DA.
PMID: 29066557 | DOI: 10.1523/JNEUROSCI.2055-17.2017
The retrotrapezoid nucleus (RTN) consists, by definition, of Phox2b-expressing, glutamatergic, non-catecholaminergic, non-cholinergic neurons located in the parafacial region of the medulla oblongata. An unknown proportion of RTN neurons are central respiratory chemoreceptors and there is mounting evidence for biochemical diversity among these cells. Here, we used multiplexed in situ hybridization and single-cell RNA-Seq in male and female mice to provide a more comprehensive view of the phenotypic diversity of RTN neurons. We now demonstrate that the RTN of mice can be identified with a single and specific marker, Nmb mRNA. Most (∼75%) RTN neurons express low-to-moderate levels of Nmb and display chemoreceptor properties. Namely they are activated by hypercapnia, but not by hypoxia, and express proton sensors, Kcnk5 and Gpr4 These Nmb-low RTN neurons also express varying levels of transcripts for Gal, Penk and Adcyap1,and receptors for substance P, orexin, serotonin and ATP. A subset of RTN neurons (∼20-25%), typically larger than average, express very high levels of Nmb mRNA. These Nmb-high RTN neurons do not express Fos after hypercapnia, have low-to-undetectable levels of Kcnk5 or Gpr4 transcripts; they also express Adcyap1, but are essentially devoid of Penk and Gal transcripts. In male rats, Nmb is also a marker of the RTN but, unlike in mice, this gene is expressed by other types of nearby neurons located within the ventromedial medulla. In sum, Nmb is a selective marker of the RTN in rodents; Nmb-low neurons, the vast majority, are central respiratory chemoreceptors whereas Nmb-high neurons likely have other functions.SIGNIFICANCE STATEMENTCentral respiratory chemoreceptors regulate arterial PCO2 by adjusting lung ventilation. Such cells have recently been identified within the retrotrapezoid nucleus (RTN), a brainstem nucleus defined by genetic lineage and a cumbersome combination of markers. Using single-cell RNA-Seq and multiplexed in situ hybridization, we show here that a single marker, Neuromedin B mRNA (Nmb), identifies RTN neurons in rodents. We also suggest that >75% of these Nmb neurons are chemoreceptors because they are strongly activated by hypercapnia and express high levels of proton sensors (Kcnk5 and Gpr4). The other RTN neurons express very high levels of Nmb, but low levels of Kcnk5/Gpr4/pre-pro-galanin/pre-pro-enkephalin, and do not respond to hypercapnia. Their function is unknown.