Rostral Raphe Pallidus Research Articles

Mediobasal hypothalamic neurons contribute to the control of brown adipose tissue sympathetic nerve activity and cutaneous vasoconstriction

The mediobasal hypothalamus (MBH) contains heterogeneous neuronal populations that regulate food intake and energy expenditure. However, the role of MBH neurons in the neural control of thermoeffector activity for thermoregulation is not known. This study sought to determine the effects of modulating the activity of MBH neurons on the sympathetic outflow to brown adipose tissue (BAT), BAT thermogenesis, and cutaneous vasomotion. Pharmacological inhibition of MBH neurons by local administration of muscimol, a GABAA receptor agonist, reduced skin cooling-evoked BAT thermogenesis, expired CO2, body temperature, heart rate, and mean arterial pressure, while blockade of GABAA receptors by nanoinjection of bicuculline in the MBH induced large increases in BAT sympathetic nerve activity (SNA), BAT temperature, body temperature, expired CO2, heart rate, and cutaneous vasoconstriction. Neurons in the MBH send projections to neurons in the dorsal hypothalamic area and dorsomedial hypothalamus (DMH), which excite sympathetic premotor neurons in the rostral raphe pallidus area (rRPa) that control sympathetic outflow to BAT. The increases in BAT SNA, BAT temperature, and expired CO2 elicited by blockade of GABAA receptors in the MBH were reversed by blocking excitatory amino acid receptors in the DMH or in the rRPa. Together, our data show that MBH neurons provide a modest contribution to BAT thermogenesis for cold defense, while GABAergic disinhibition of these neurons produces large increases in the sympathetic outflow to BAT, and cutaneous vasoconstriction. Activation of glutamate receptors on BAT thermogenesis-promoting neurons of the DMH and rRPa is necessary for the increased sympathetic outflow to BAT evoked by disinhibition of MBH neurons. These data demonstrate neural mechanisms that contribute to the control of thermoeffector activity, and may have important implications for regulating body temperature and energy expenditure.

Acute deep brain stimulation of the paraventricular nucleus of the hypothalamus increases brown adipose tissue thermogenesis in rats

Brown adipose tissue (BAT) activity is controlled by the sympathetic nervous system. Activation of BAT has shown significant promise in preclinical studies to elicit weight loss. Since the hypothalamic paraventricular nucleus (PVN) contributes to the regulation of BAT thermogenic activity, we sought to determine the effects of electrical stimulation of the PVN as a model of deep brain stimulation (DBS) for increasing BAT sympathetic nerve activity (SNA). The rostral raphe pallidus area (rRPa) was also chosen as a target for DBS since it contains the sympathetic premotor neurons for BAT. Electrical stimulation (100 µA, 100 µs, 100 Hz, for 5 min at a 50 % duty cycle) of the PVN increased BAT SNA and BAT thermogenesis. These effects were prevented by a local nanoinjection of bicuculline, a GABAA receptor antagonist. We suggest that electrical stimulation of the PVN elicited local release of GABA, which inhibited BAT sympathoinhibitory neurons in PVN, thereby releasing a restraint on BAT SNA. Electrical stimulation of the rRPa inhibited BAT thermogenesis and this was prevented by a local nanoinjection of bicuculline, suggesting that local release of GABA suppressed BAT SNA. Electrical stimulation of the PVN activates BAT metabolism via a mechanism that may include activation of local GABAA receptors. These findings contribute to our understanding of the mechanisms underlying the effects of DBS in the regulation of fat metabolism and provide a foundation for further DBS studies targeting hypothalamic circuits regulating BAT thermogenesis as a therapy for obesity.

The neural pathway of the hyperthermic response to antagonists of the transient receptor potential vanilloid-1 channel

ABSTRACT We identified the neural pathway of the hyperthermic response to TRPV1 antagonists. We showed that hyperthermia induced by i.v. AMG0347, AMG 517, or AMG8163 did not occur in rats with abdominal sensory nerves desensitized by pretreatment with a low i.p. dose of resiniferatoxin (RTX, TRPV1 agonist). However, neither bilateral vagotomy nor bilateral transection of the greater splanchnic nerve attenuated AMG0347-induced hyperthermia. Yet, this hyperthermia was attenuated by bilateral high cervical transection of the spinal dorsolateral funiculus (DLF). To explain the extra-splanchnic, spinal mediation of TRPV1 antagonist-induced hyperthermia, we proposed that abdominal signals that drive this hyperthermia originate in skeletal muscles – not viscera. If so, in order to prevent TRPV1 antagonist-induced hyperthermia, the desensitization caused by i.p. RTX should spread into the abdominal-wall muscles. Indeed, we found that the local hypoperfusion response to capsaicin (TRPV1 agonist) in the abdominal-wall muscles was absent in i.p. RTX-desensitized rats. We then showed that the most upstream (lateral parabrachial, LPB) and the most downstream (rostral raphe pallidus) nuclei of the intrabrain pathway that controls autonomic cold defenses are also required for the hyperthermic response to i.v. AMG0347. Injection of muscimol (inhibitor of neuronal activity) into the LPB or injection of glycine (inhibitory neurotransmitter) into the raphe blocked the hyperthermic response to i.v. AMG0347, whereas i.v. AMG0347 increased the number of c-Fos cells in the raphe. We conclude that the neural pathway of TRPV1 antagonist-induced hyperthermia involves TRPV1-expressing sensory nerves in trunk muscles, the DLF, and the same LPB-raphe pathway that controls autonomic cold defenses.

Systemic Interleukin‐1β Elicits Cyclooxygenase‐Independent Fever

Interleukin‐1β (IL‐1β) induces neuroimmune responses that help to fight infections. IL‐1β‐induced fever is not abolished by cyclooxygenase (COX) inhibitors used to treat inflammation and the neural pathways responsible for COX‐independent fever are still unknown. Considering that neurons that reside in the rostral raphe pallidus area (rRPa) and in the dorsomedial hypothalamus (DMH) play a key role in the control of thermoeffectors, we hypothesized that neurons in these areas contribute to COX‐independent fever elicited by intravenous (iv) IL‐1β. Female and male Sprague Dawley rats were anesthetized with urethane and α‐chloralose (ur/ch) or isoflurane (iso) and treated with saline or indomethacin, prior to receiving iv IL‐1β. Systemic IL‐1β increased brown adipose tissue (BAT) sympathetic nerve activity (SNA) (+2852 ± 2020% baseline (BL), p = 0.003), BAT temperature (TBAT; +2.6 ± 1.3°C, p < 0.001), expired CO2 (+1.0 ± 0.4%, p < 0.001), core body temperature (TCORE; +0.6 ± 0.2°C, p < 0.001), heart rate (HR; +102 ± 42 bpm, p < 0.001), mean arterial pressure (MAP; +11 ± 7 mmHg, p = 0.002), and paw temperature (TPAW; ‐6.9 ± 1.2°C, p < 0.001), which is an index of cutaneous vasoconstriction (CVC). Indomethacin did not prevent IL‐1β‐evoked increases in BAT SNA (+2545 ± 756% BL, p < 0.001), TBAT (+2.9 ± 1.3°C, p < 0.001), expired CO2 (+1.2 ± 0.6%, p = 0.003), TCORE (+0.9 ± 0.5°C, p = 0.005), HR (+117 ± 47 bpm, p < 0.001), MAP (+27 ± 20 mmHg, p = 0.01), or TPAW (‐5.9 ± 3.4°C, p = 0.02). Nanoinjection of muscimol in the rRPa prevented IL‐1β‐evoked increases in BAT SNA (p < 0.01), TBAT (p < 0.01), expired CO2 (p < 0.01) and TCORE (p < 0.01), but not in HR (p = 0.08), in comparison to the group that received IL‐1β only. Nanoinjection of muscimol in the rRPa in indomethacin‐pretreated rats prevented IL‐1β‐evoked increases in BAT SNA (p < 0.01), TBAT (p < 0.01), expired CO2 (p < 0.01), TCORE (p < 0.01), and TPAW (p = 0.03), but not in HR (p = 0.12), in comparison to an indomethacin‐pretreated group that received IL‐1β. Nanoinjections of glutamate receptor antagonists in the DMH markedly reduced IL‐1β‐evoked increases in BAT SNA (‐838 ± 542% BL, p = 0.03), TBAT (‐1.1 ± 0.4°C, p = 0.003), expired CO2 (‐0.4 ± 0.1%, p = 0.009) and HR (‐38 ± 20 bpm, p = 0.01), and reduced MAP (‐4 ± ‐2 mmHg, p = 0.02). Plasma PGE2 levels following iv IL‐1β were significantly higher (by ~3 fold) in rats that were not anesthetized when receiving IL‐1b (263.1 ± 136.4 pg/ml) compared to all other groups of rats that were maintained under anesthesia for 2 h (ur/ch anesthetized, saline pretreated: 96.7 ± 30.8 pg/ml, p = 0.007, or indomethacin pretreated: 119.7 ± 51.9 pg/ml, p = 0.02; iso anesthetized, saline pretreated: 82.5 ± 21.2 pg/ml, p = 0.003, or indomethacin‐pretreated: 108.4 ± 39.1 pg/ml, p = 0.01). Therefore, we suggest that the anesthetics used inhibited the systemic production of PGE2. Together, our data suggest that a glutamatergic input to the DMH is necessary for providing the excitatory drive for increasing BAT thermogenesis and tachycardia in response to circulating IL‐1β, likely via rRPa neurons. Additionally, IL‐1β‐evoked CVC requires activation of neurons in the rRPa. These data define critical components of the neural circuit for systemic IL‐1β‐induced fever and provide a foundation for elucidating additional brain mechanisms responsible for COX‐independent fever.

A Foundation for the Neural Control of Viral Fever

Fever, an acute‐phase neurally‐regulated increase in body temperature, is thought to be an adaptive response to optimize host defenses against invading pathogens. However, fever can be an unpleasant symptom of infection and excessive fever (>41oC) can cause irreversible protein denaturation and result in tissue damage, seizure, coma and death. Common therapeutic approaches to fever include the use of non‐steroidal anti‐inflammatory drugs and cyclooxygenase inhibitors, however these approaches are ineffective for reducing prostaglandin‐independent fevers, can interfere with adaptive and innate immune defenses and are contraindicated for use in some viral infections, including SARS‐CoV2. Although research over the past couple of decades has defined the fundamental central nervous system (CNS) pathways necessary for the lipopolysaccharide model of bacterial fever, the CNS circuits mediating viral fevers are almost completely unknown. Double‐stranded RNA is an intermediary in viral replication and serves as a pathogen‐associated molecular pattern that elicits the acute phase responses to viral infection. Systemic administration of polyinosinic:polycytidylic acid (poly I:C), a synthetic double stranded RNA, mimics the acute phase responses to viral infection. Neurons in the rostral raphe pallidus area (rRPa) and the dorsomedial hypothalamus play important roles in the control of the sympathetic outflow to thermoeffectors, therefore we hypothesized that neurons in these areas would be essential for fever elicited by a model of viral fever, intravenous (iv) poly I:C. Female and male Sprague Dawley rats anesthetized with urethane and α‐chloralose (for BAT sympathetic nerve recording, n=3) or isoflurane (for cutaneous vasoconstriction experiments, n=3) received iv poly I:C (1mg/kg for experiments with sympathetic nerve recording, or 500μg/kg for experiments for cutaneous vasoconstriction). Systemically administered poly I:C increased BAT SNA (+601 ± 161% baseline), BAT temperature (TBAT; +3.1 ± 0.8°C), and expired CO2 (+0.9 ± 0.2%). Poly I:C also elicited CVC, as observed by reductions in paw or tail skin temperature (TPAW/TTail) (‐2.6 ± 1.2°C). A nanoinjection of the ionotropic glutamate receptor antagonists, AP5 and CNQX in the rRPa reversed poly I:C‐evoked increases in BAT SNA (‐596 ± 128% baseline), TBAT (‐1.3 ± 0.2°C), and expired CO2 (‐0.5 ± 0.1%). Nanoinjection of AP5 and CNQX into the DMH reversed the polyI:C‐evoked reduction in TPAW/TTail (+2.8 ± 1.1°C). These data suggest that the activity of neurons in the rRPa and the DMH are necessary for poly I:C‐induced activation of BAT thermogenesis and cutaneous vasoconstriction. These data define critical components of the neural circuits for poly I:C‐induced fever, highlight differences between the neural circuitry mediating bacterial fever and viral fever, and provide a foundation for elucidating additional brain mechanisms responsible for viral fever.

Neural circuits mediating circulating interleukin-1β-evoked fever in the absence of prostaglandin E2 production

Infectious diseases and inflammatory conditions recruit the immune system to mount an appropriate acute response that includes the production of cytokines. Cytokines evoke neurally-mediated responses to fight pathogens, such as the recruitment of thermoeffectors, thereby increasing body temperature and leading to fever. Studies suggest that the cytokine interleukin-1β (IL-1β) depends upon cyclooxygenase (COX)-mediated prostaglandin E2 production for the induction of neural mechanisms to elicit fever. However, COX inhibitors do not eliminate IL-1β-induced fever, thus suggesting that COX-dependent and COX-independent mechanisms are recruited for increasing body temperature after peripheral administration of IL-1β. In the present study, we aimed to build a foundation for the neural circuit(s) controlling COX-independent, inflammatory fever by determining the involvement of brain areas that are critical for controlling the sympathetic outflow to brown adipose tissue (BAT) and the cutaneous vasculature. In anesthetized rats, pretreatment with indomethacin, a non-selective COX inhibitor, did not prevent BAT thermogenesis or cutaneous vasoconstriction (CVC) induced by intravenous IL-1β (2 µg/kg). BAT and cutaneous vasculature sympathetic premotor neurons in the rostral raphe pallidus area (rRPa) are required for IL-1β-evoked BAT thermogenesis and CVC, with or without pretreatment with indomethacin. Additionally, activation of glutamate receptors in the dorsomedial hypothalamus (DMH) is required for COX-independent, IL-1β-induced BAT thermogenesis. Therefore, our data suggests that COX-independent mechanisms elicit activation of neurons within the DMH and rRPa, which is sufficient to trigger and mount inflammatory fever. These data provide a foundation for elucidating the brain circuits responsible for COX-independent, IL-1β-elicited fevers.

Dopaminergic input from the posterior hypothalamus to the raphe pallidus area inhibits brown adipose tissue thermogenesis.

Systemic administration of dopamine (DA) receptor agonists leads to falls in body temperature. However, the central thermoregulatory pathways modulated by DA have not been fully elucidated. Here we identified a source and site of action contributing to DA's hypothermic action by inhibition of brown adipose tissue (BAT) thermogenesis. Nanoinjection of the type 2 and type 3 DA receptor (D2R/D3R) agonist, 7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT), in the rostral raphe pallidus area (rRPa) inhibits the sympathetic activation of BAT evoked by cold exposure or by direct activation of N-methyl-d-aspartate (NMDA) receptors in the rRPa. Blockade of D2R/D3R in the rRPa with nanoinjection of SB-277011A increases BAT thermogenesis, consistent with a tonic release of DA in the rRPa contributing to inhibition of BAT thermogenesis. Accordingly, D2Rs are expressed in cold-activated and serotonergic neurons in the rRPa, and anatomical tracing studies revealed that neurons in the posterior hypothalamus (PH) are a source of dopaminergic input to the rRPa. Disinhibitory activation of PH neurons with nanoinjection of gabazine inhibits BAT thermogenesis, which is reduced by pretreatment of the rRPa with SB-277011A. In conclusion, the rRPa, the site of sympathetic premotor neurons for BAT, receives a tonically active, dopaminergic input from the PH that suppresses BAT thermogenesis.

Melanin-concentrating hormone neurons affect adipose tissues and modulate weight gain.

Melanin-concentrating hormone neurons affect adipose tissues and modulate weight gain.

SUN-LB125 Violet Sensitive Preoptic Area Neurons That Express Opsin 5 Regulate Thermogenesis and Energy Metabolism

The thermogenic potential of brown adipose tissue (BAT) is a promising therapeutic target in the treatment of obesity and metabolic disorders. The preoptic area (POA) is a region in the anterior hypothalamus responsible for autonomic thermoregulation by means of modulating BAT activity through sympathetic nerve activity (SNA). Neurons in the POA express opsin-5 (OPN5), an atypical opsin found in various extraretinal tissues and known to respond to violet wavelengths with a lambda-max of 380 nm. OPN5 has previously been shown to regulate seasonal breeding behavior in birds. Loss of OPN5 in mice have been demonstrated to impair circadian photoentrainment. We have also shown OPN5 to be required in retinal ganglion cells for in vivo entrainment of a retina circadian clock independent of the suprachiasmatic nucleus. To date, no other physiological role for mammalian OPN5 has been proposed. The same POA neurons that express OPN5 also engage the central thermoregulatory circuit that modulates BAT activity. We show that POA OPN5 neurons polysynaptically project to the BAT using a retrograde PRV-mRFP1 pseudorabies virus. Also via a genetically targeted glycoprotein-deleted rabies virus injected into the POA, we identified labeled neurons in the rostral raphe pallidus (rRPa), the lateral parabrachial nucleus (LPB), and the dorsomedial hypothalamus (DMH), all nuclei known to participate in central BAT thermoregulation. Opn5-/- mice better defend their core body temperature during acute 4°C challenge. Our results indicate this effect to be due to increased BAT thermogenesis and not heat retention or pyrexia. Furthermore, BAT thermogenesis target gene transcripts (Ucp-1, Prdm16, Pgc-1a) were elevated in these cold stressed Opn5-/- animals. To demonstrate the importance of OPN5’s violet light sensing function in cold defense, C57BL/6J mice reared from E16.5 without 380 nm light largely phenocopy Opn5-/- animals when acutely cold challenged. Furthermore, chemogenetic inhibition of POA OPN5 neurons further augments cold exposure defense and BAT activation. Indirect calorimetry studies reveal Opn5-/- mice to be hypermetabolic, consuming more food and having a higher energy expenditure than controls. Paradoxically, this increased turnover does not translate to weight-gain resistance under high fat challenge. Our results suggest a mechanism where near-UV sensitive hypothalamic OPN5 neurons regulate BAT thermogenesis directly, proposing that the mammalian autonomic thermoregulatory apparatus is light responsive.

Central Circuits Inhibiting Skeletal Muscle Shivering

BackgroundSkeletal muscle shivering is the most important source of thermogenesis in the human cold‐defensive maintenance of core body temperature (Tcore) and the elevated Tcore during fever. We have described the thermoregulatory reflex pathway through which skin and core cooling, or injection of prostaglandin E2 into the preoptic area of the hypothalamus, leads to activation of skeletal muscle shivering (J Physiol 589.14: 3641–3658, 2011). Here we describe brain regions containing neurons that can provide an inhibitory regulation of shivering.ResultsEMG activities in masseter, neck and gastrocnemius muscles were recorded in Inactin‐anesthetized rats during cold exposure or injection of PGE2 into the preoptic hypothalamus. Cold‐evoked and febrile shivering EMGs were eliminated by activation of neurons in the ventral part of the lateral preoptic nucleus (vLPO), or by increasing the discharge of neurons in the paraventricular hypothalamus, in the nucleus of the tractus solitarii, or in the ventrolateral medulla. Inhibiting neuronal discharge or blocking glutamate receptors in the vLPO elicited a sustained increase in shivering EMGs in warm rats.ConclusionThese results indicate the strong, tonic inhibitory influence of neurons in the vLPO on skeletal muscle shivering, likely through a GABAergic input to shivering premotor neurons in the rostral raphe pallidus. The discovery of the vLPO and other neuronal populations capable of inhibiting shivering supports the potential for the therapeutic control of shivering in the settings of neurogenic fever, brain injury, or induction of hypothermia.Support or Funding InformationSupported by NIH grants NS040987 and NS091066This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Dopaminergic Projections to Raphe Pallidus Inhibit Brown Adipose Tissue Thermogenesis

BackgroundThe observations that patients with Parkinson's disease experience weight loss, while dopamine (DA) replacement therapy causes body weight gain, suggest that suppressing the DA system could stimulate energy expenditure. Peripheral administration of dopaminergic drugs decreases heat production by inhibition of brown adipose tissue (BAT) thermogenesis and by an increase in the threshold for muscular shivering. However, the exact neuroregulatory site through which DA modulates the activity of thermogenic thermoeffectors remains undefined.ResultsIn urethane/chloralose‐anesthetized, artificially‐ventilated rats, activation of type 2 or 3 dopamine receptors in the rostral raphe pallidus (rRPa) inhibits cold‐evoked BAT sympathetic activity, reduced BAT temperature and expired CO2, and produced hypotension and bradycardia. Anatomic evidence shows the co‐localization of TH and CTb immunoreactivities in neurons in the in the periventricular gray zona following injection of the retrograde tracer in the rRPa. These data indicate that this dopaminergic cell group projects to rRPa and is the likely source of the dopaminergic inhibition of BAT sympathetic activity.ConclusionOur data provide the first evidence that a DA input to the rRPa from periventricular gray zona modulates BAT thermogenesis and cardiovascular function. Modulating the dopaminergic input to rRPa could provide a novel therapeutic approach to promote fat oxidation, favor better glycaemic control, and accelerate weight loss.Support or Funding InformationNIH R01‐NS091066This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Neurons in the rat ventral lateral preoptic area are essential for the warm-evoked inhibition of brown adipose tissue and shivering thermogenesis.

To determine the role of neurons in the ventral part of the lateral preoptic area (vLPO) in CNS thermoregulation. In vivo electrophysiological and neuropharmacological were used toevaluate the contribution of neurons in the vLPO to the regulation of brown adipose tissue (BAT) thermogenesis and muscle shivering in urethane/chloralose-anaesthetized rats. Nanoinjections of NMDA targeting the medial preoptic area (MPA) and the vLPO suppressed the cold-evoked BAT sympathetic activity (SNA), reduced the BAT temperature (TBAT ), expired CO2 , mean arterial pressure (MAP), and heart rate. Inhibition of vLPO neurons with muscimol or AP5/CNQX elicited increases in BAT SNA, TBAT , tachycardia, and small elevations in MAP. The BAT thermogenesis evoked by AP5/CNQX in vLPO was inhibited by the activation of MPA neurons. The inhibition of BAT SNA by vLPO neurons does not require a GABAergic input to dorsomedial hypothalamus (DMH), but MPA provides a GABAergic input to DMH. The activation of vLPO neurons inhibits the BAT thermogenesis evoked by NMDA in the rostral raphe pallidus (rRPa), but not that after bicuculline in rRPa. The BAT thermogenesis elicited by vLPO inhibition is dependent on glutamatergic inputs to DMH and rRPa, but these excitatory inputs do not arise from MnPO neurons. The activation of neurons in the vLPO also inhibits cold- and prostaglandin-evoked muscle shivering, and vLPO inhibition is sufficient to evoke shivering. The vLPO contains neurons that are required for the warm ambient-evoked inhibition of muscle shivering and of BAT thermogenesis, mediated through a direct or indirect GABAergic input to rRPa from vLPO.

Dapagliflozin, a Sodium-Glucose Co-transporter-2 Inhibitor, Acutely Reduces Energy Expenditure in Brown Adipose Tissue via Neural Signals in Mice

Selective sodium glucose transporter-2 inhibitor (SGLT2i) treatment promotes urinary glucose excretion, thereby reducing blood glucose as well as body weight. However, only limited body weight reductions are achieved with SGLT2i administration. Hyperphagia is reportedly one of the causes of this limited weight loss. However, the effects of SGLT2i on systemic energy expenditure have not been fully elucidated. We investigated the acute effects of dapagliflozin, an SGLT2i, on systemic energy expenditure in mice. Eighteen hours after dapagliflozin administration, oxygen consumption and brown adipose tissue (BAT) expression of ucp1, a thermogenesis-related gene, were significantly decreased as compared with those after vehicle administration. In addition, dapagliflozin significantly suppressed norepinephrine (NE) turnover in BAT and c-fos expression in the rostral raphe pallidus nucleus (rRPa), which contains the sympathetic premotor neurons responsible for thermogenesis. These findings indicate that the dapagliflozin-mediated acute decrease in energy expenditure involves a reduction in BAT thermogenesis via decreased sympathetic nerve activity from the rRPa. Furthermore, common hepatic branch vagotomy abolished the reductions in ucp1 expression, NE contents in BAT, and c-fos expression in the rRPa. In addition, alterations in hepatic carbohydrate metabolism, such as decreases in glycogen contents and upregulation of phosphoenolpyruvate carboxykinase, occurred prior to the suppression of BAT thermogenesis, e.g., 6 h after dapagliflozin treatment. Collectively, these results suggest that SGLT2i acutely suppresses energy expenditure in BAT via regulation of an interorgan neural network consisting of the common hepatic vagal branch and sympathetic nerves.

Neural Circuitry Underlying Thermal Afferent Influences During Thermoregulatory Inversion

To maintain body core temperature (TCORE) in mammals, the central nervous system thermoregulatory networks respond to skin cooling by increasing brown adipose tissue (BAT) and shivering thermogenesis, and by reducing heat loss via cutaneous vasoconstriction. However, there are several conditions (e.g., hibernation, torpor, REM sleep) in which these “standard” thermoregulatory responses to protect TCORE appear to be superseded by a “thermoregulatory inversion (TI)” in which, in contrast to normal thermoregulation, cold exposure (skin cooling) causes inhibition of thermogenesis whereas skin warming activates thermogenesis. We hypothesize that blockade or exclusion of the preoptic area (POA) thermoregulatory function is required for the initiation of thermoregulatory inversion, and that such paradoxical thermoregulation is governed by a new central thermoregulatory pathway.We used a pre‐dorsomedial hypothalamus (pre‐DMH) brain transection or inhibition of POA (muscimol nanoinjections) to induce TI in anesthetized rats that had received an injection of the retrograde tracer, CTb, in the DMH. Warm exposure (90 min) of pre‐DMH transected rats increased BAT thermogenesis and increased Fos in DMH and in the external lateral parabrachial nucleus (elPBN) neurons projecting to DMH. In anesthetized rats after a pre‐DMH transection, inhibition of neurons in either the DMH or the elPBN blocked the warm‐evoked activation of BAT thermogenesis characteristic of TI. These results are consistent with elPBN neurons relaying warm thermal information to the DMH, resulting in activation of DMH neurons and BAT sympathetic premotor neurons in the rostral raphe pallidus (rRPa), and eliciting a warm‐evoked activation of BAT during TI.Furthermore, we found that the cold‐evoked inhibition characteristic of TI is mediated by a population of dynorphinergic neurons in the dorsolateral PBN (dlPBN) projecting to DMH. In fact, injection of the k‐receptor antagonist, NOR‐BNI, in the DMH of pre‐DMH transected rats completely prevented the cold‐evoked BAT inhibition during TI.Our data demonstrate that inhibition of POA is sufficient to induce TI and that a novel, short‐loop thermoregulatory pathway (skin thermoreceptors → PBN → DMH → rRPa) mediates the inverted control of BAT thermogenesis during TI. Moreover, we demonstrated that a dynorphinergic input to DMH plays a role in the cold‐evoked inhibition of BAT thermogenesis during TI.We conclude that this line of study opens a new field of research in thermoregulation and will help to elucidate a novel mechanism for a rapid, controllable, stable and reversible induction of hypothermia, which can be beneficial for the treatment of ischemic stroke, brain trauma, and to block persistent high neurogenic fever.Support or Funding InformationTupone: NIH R01 NS099234, Montalcini; Morrison: NIH R01 NS091066; Cano: NIH 5P40OD010996, NIH R01 NS099234.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Neurons in the Ventral Lateral Preoptic (vLPO) Area Inhibit Brown Adipose Tissue (BAT) Thermogenesis

Neurons in the preoptic area of the hypothalamus play important roles in thermoregulation. However, the subregions of the preoptic hypothalamus are heterogeneous, such that neuronal activation at some sites elicits hyperthermia, while others evoke hypothermia. Here we show that in urethane/chloralose‐anesthetized, artificially‐ventilated rats, neurons in the vLPO (0.0 to −1.44 mm caudal to bregma, 0.8 to 1.5 mm lateral to the midline, and −8.0 to 9.8 mm below the dura surface, incisor bar in flat skull position) have a hypothermic effect mediated by inhibition of sympathetic nerve activity (SNA) and BAT thermogenesis. The activation of cvLPO neurons with nanoinjections of NMDA (0.2 mM, 60 nl) evoked a complete inhibition of cold‐evoked BAT thermogenesis: BAT SNA (−97 %, p = 0.01), BAT temperature (TBAT, −0.4 °C, p = 0.01), expired CO2, (Exp CO2, −0.4 %, p = 0.0004), mean arterial pressure (MAP, −9 mmHg, p = 0.01) and heart rate (HR, −53 bpm, p = 0.0005). Similar BAT sympathoinhibitory responses were obtained with nanoinjections of bicuculline (BIC, 1.0 mM, 60 nl) in the vLPO. Under thermoneutral conditions, the inhibition of cvLPO neurons by activation of local GABAA receptors (muscimol, 1.2 mM, 60 nl) increased BAT SNA (+99 % p = 0.0001), TBAT (+2.2 °C, p = 0.0001), Exp CO2 (+1.0 %, p = 0.00003), and HR (+58 bpm, p = 0.007), with no change in MAP (p = 0.5). Nanoinjections of muscimol, or the glutamate receptor antagonists, AP5/CNQX, in the dorsomedial hypothalamus (DMH), or in the rostral raphe pallidus (rRPa), reversed the activation of BAT thermogenesis evoked by inhibition of vLPO neurons. Activation of neurons in vLPO inhibited the BAT thermogenesis evoked by BIC nanoinjections in the DMH, but not the increase in BAT SNA evoked by BIC nanoinjections in the rRPa. We conclude that vLPO contains BAT sympathoinhibitory neurons that mediate the warm ambient‐evoked inhibition of BAT thermogenesis through a direct or indirect GABAergic input to rRPa. Similarly to the cold‐evoked activation of BAT thermogenesis, that following inhibition of vLPO neurons requires the glutamatergic, BAT sympathoexcitatory pathway from DMH to BAT sympathetic premotor neurons in rRPa. These novel findings a key population of BAT sympathoinhibitory neurons in the central pathway mediating the skin warming‐evoked inhibition of BAT thermogenesis, requiring the addition of a BAT sympathoinhibitory pathway between vLPO and rRPa to the current model of central autonomic thermoregulation.Support or Funding InformationThis work was supported by NIH R01‐NS091066 (S.F.M.).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Ventral Lateral Preoptic (vLPO) Neurons Inhibit Brown Adipose Tissue Thermogenesis during Warming of the Preoptic Area

Brown adipose tissue (BAT) and shivering thermogenesis and cutaneous vasoconstriction are inhibited in warm climatic conditions to reduce heat production and increase heat dissipation, thereby maintaining core body temperature homeostasis. We tested the hypothesis that the hypothalamic preoptic area (POA) contains warm sensitive neurons (WSNs) that are activated by local warming to produce inhibition of BAT activity. In urethane/α‐chloralose‐anesthetized, artificially‐ventilated rats, warming the POA bilaterally with a thermode (two silver rods connected to a peltier device) increased POA temperature from 35 to 40°C and promptly inhibited skin cooling (35–36°C)‐evoked BAT sympathetic nerve activity (SNA) (from 1061±2.7 to 102±0.1 that corresponds to 100% reduction, p<0.001) and reduced BAT temperature (1.7±0.2, p<0.001), core temperature (0.3±0.1, p<0.05), expired CO2 (0.7±0.1%, p<0.001), heart rate (61±10, p<0.001) and mean arterial pressure (14±6, p<0.05). Bilateral nanoinjections of the GABAA‐agonist, muscimol (500 mM, 100 nl), into the ventral lateral preoptic area (vLPO) prevented (p<0.001) the local POA warming‐induced inhibition of BAT SNA and the reductions in BAT and core temperatures. Blockade of ionotropic glutamate receptors in vLPO with nanoinjections of AP5/CNQX also prevented (p<0.001) the local POA warming‐induced inhibitions of BAT thermogenesis. POA warming failed (p>0.05) to inhibit the elevated BAT SNA following blockade of local GABAA receptors with nanoinjections of bicuculline (BIC) in the rostral raphe pallidus (rRPa), but still effectively inhibited the elevated BAT SNA following BIC nanoinjections in the dorsomedial hypothalamus (DMH). Our results demonstrate that the POA warming‐evoked inhibition of BAT thermogenesis requires activation of GABAA receptors in rRPa, but not those in DMH. In addition, the finding that glutamate receptor blockade in vLPO prevents the POA warming‐induced inhibition of BAT activity, is consistent with WSNs glutamatergically exciting BAT sympathoinhibitory neurons in vLPO to produce the POA warming‐induced inhibition of BAT thermogenesis. These novel findings elucidate the central pathway mediating POA warming‐evoked inhibition of BAT thermogenesis and require the addition of a BAT sympathoinhibitory pathway between vLPO and rRPa to the current model of central autonomic thermoregulation.Support or Funding InformationSupported by NIH R01091066 (SFM).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Chapter 17 - Efferent neural pathways for the control of brown adipose tissue thermogenesis and shivering

The fundamental central neural circuits for thermoregulation orchestrate behavioral and autonomic repertoires that maintain body core temperature during thermal challenges that arise from either the ambient or the internal environment. This review summarizes our understanding of the neural pathways within the fundamental thermoregulatory reflex circuitry that comprise the efferent (i.e., beyond thermosensory) control of brown adipose tissue (BAT) and shivering thermogenesis: the motor neuron systems consisting of the BAT sympathetic preganglionic neurons and BAT sympathetic ganglion cells, and the alpha- and gamma-motoneurons; the premotor neurons in the region of the rostral raphe pallidus, and the thermogenesis-promoting neurons in the dorsomedial hypothalamus/dorsal hypothalamic area. Also included are inputs to, and neurochemical modulators of, these efferent neuronal populations that could influence their activity during thermoregulatory responses. Signals of metabolic status can be particularly significant for the energy-hungry thermoeffectors for heat production.

Tonic inhibition of brown adipose tissue sympathetic nerve activity via muscarinic acetylcholine receptors in the rostral raphe pallidus.

A tonically active, muscarinic cholinergic inhibition of rostral raphe pallidus (rRPa) neurons influences thermogenesis of brown adipose tissue (BAT) independent of ambient temperature conditions. The tonically active cholinergic input to rRPa originates caudal to the hypothalamus. Muscarinic acetylcholine receptor (mAChR) activation in rRPa contributes to the inhibition of BAT sympathetic nerve activity (SNA) evoked by activation of neurons in the rostral ventrolateral medulla (RVLM). The RVLM is not the sole source of the muscarinic cholinergic input to rRPa. Activation of GABA receptors in rRPa does not mediate the cholinergic inhibition of BAT SNA. We sought to determine if body temperature and energy expenditure are influenced by a cholinergic input to neurons in the rostral raphe pallidus (rRPa), the site of sympathetic premotor neurons controlling thermogenesis of brown adipose tissue (BAT). Nanoinjections of the muscarinic acetylcholine receptor (mAChR) agonist, oxotremorine, or the cholinesterase inhibitor, neostigmine (NEOS), in the rRPa of anaesthetized rats decreased cold-evoked BAT sympathetic nerve activity (SNA, nadirs: -72 and -95%), BAT temperature (Tbat, -0.5 and -0.6°C), expired CO2 (Exp. CO2 , -0.3 and -0.5%) and heart rate (HR, -22 and -41bpm). NEOS into rRPa reversed the increase in BAT SNA evoked by blockade of GABA receptors in rRPa. Nanoinjections of the mAChR antagonist, scopolamine (SCOP), in the rRPa of warm rats increased BAT SNA (peak: +1087%), Tbat (+1.8°C), Exp. CO2 (+0.7%), core temperature (Tcore, +0.5°C) and HR (+54bpm). SCOP nanoinjections in rRPa produced similar activations of BAT during cold exposure, following a brain transection caudal to the hypothalamus, and during the blockade of glutamate receptors in rRPa. We conclude that a tonically active cholinergic input to the rRPa inhibits BAT SNA via activation of local mAChR. The inhibition of BAT SNA mediated by mAChR in rRPa does not depend on activation of GABA receptors in rRPa. The increase in BAT SNA following mAChR blockade in rRPa does not depend on the activity of neurons in the hypothalamus or on glutamate receptor activation in rRPa.

Activity-based anorexia activates nesfatin-1 immunoreactive neurons in distinct brain nuclei of female rats

Activity-based anorexia (ABA) is an established animal model for the eating disorder anorexia nervosa (AN). The pathophysiology of AN and the involvement of food intake-regulatory peptides is still poorly understood. Nesfatin-1, an anorexigenic peptide also involved in the mediation of stress, anxiety and depression might be a likely candidate involved in the pathogenesis of AN. Therefore, activation of nesfatin-1 immunoreactive (ir) brain nuclei was investigated under conditions of ABA. Female Sprague-Dawley rats were used and divided into four groups (n=6/group): activity-based anorexia (ABA), restricted feeding (RF), activity (AC) and ad libitum fed (AL). After the 21-day experimental period and development of ABA, brains were processed for c-Fos/nesfatin-1 double labeling immunohistochemistry. ABA increased the number of nesfatin-1 immunopositive neurons in the paraventricular nucleus, arcuate nucleus, dorsomedial hypothalamic nucleus, locus coeruleus and in the rostral part of the nucleus of the solitary tract compared to AL and AC groups (p<0.05) but not to RF rats (p>0.05). Moreover, we observed significantly more c-Fos and nesfatin-1 ir double-labeled cells in ABA rats compared to RF, AL and AC in the supraoptic nucleus (p<0.05) and compared to AL and AC in the paraventricular nucleus, arcuate nucleus, dorsomedial hypothalamic nucleus, dorsal raphe nucleus and the rostral raphe pallidus (p<0.05). Since nesfatin-1 plays a role in the inhibition of food intake and the response to stress, we hypothesize that the observed changes of brain nesfatin-1 might play a role in the pathophysiology and symptomatology under conditions of ABA and potentially also in patients with AN.

Glycinergic inhibition of BAT sympathetic premotor neurons in rostral raphe pallidus.

The rostral raphe pallidus (rRPa) contains sympathetic premotor neurons controlling thermogenesis in brown adipose tissue (BAT). We sought to determine whether a tonic activation of glycineA receptors (GlyAR) in the rRPa contributes to the inhibitory regulation of BAT sympathetic nerve activity (SNA) and of cardiovascular parameters in anesthetized rats. Nanoinjection of the GlyAR antagonist, strychnine (STR), into the rRPa of intact rats increased BAT SNA (peak: +495%), BAT temperature (TBAT, +1.1°C), expired CO2, (+0.4%), core body temperature (TCORE, +0.2°C), mean arterial pressure (MAP, +4 mmHg), and heart rate (HR, +57 beats/min). STR into rRPa in rats with a postdorsomedial hypothalamus transection produced similar increases in BAT thermogenic and cardiovascular parameters. Glycine nanoinjection into the rRPa evoked a potent inhibition of the cooling-evoked increases in BAT SNA (nadir: -74%), TBAT (-0.2°C), TCORE (-0.2°C), expired CO2 (-0.2%), MAP (-8 mmHg), and HR (-22 beats/min) but had no effect on the increases in these variables evoked by STR nanoinjection into rRPa. Nanoinjection of GABA into the rRPa inhibited the STR-evoked BAT SNA (nadir: -86%) and reduced the expired CO2 (-0.4%). Blockade of glutamate receptors in rRPa reduced the STR-evoked increases in BAT SNA (nadir: -61%), TBAT (-0.5°C), expired CO2 (-0.3%), MAP (-9 mmHg), and HR (-33 beats/min). We conclude that a tonically active glycinergic input to the rRPa contributes to the inhibitory regulation of the discharge of BAT sympathetic premotor neurons and of BAT thermogenesis and energy expenditure.