Neurons In Dorsomedial Hypothalamus Research Articles

Asymmetry in the control of cardiac performance by dorsomedial hypothalamus

Dorsomedial hypothalamus (DMH) plays a key role in integrating cardiovascular responses to stress. We have recently reported greater heart rate responses following disinhibition of the right side of the DMH (R-DMH) in anesthetized rats and greater suppression of stress-induced tachycardia following inhibition of the R-DMH in conscious rats [both compared with similar intervention in the left DMH (L-DMH)], suggesting existence of right/left side asymmetry in controlling cardiac chronotropic responses by the DMH. The aim of the present study was to determine whether similar asymmetry is present for controlling cardiac contractility. In anesthetized rats, microinjections of the GABAA antagonist bicuculline methiodide (BMI; 40 pmol/100 nl) into the DMH-evoked increases in heart rate (HR), left ventricular pressure (LVP), myocardial contractility (LVdP/dt), arterial pressure, and respiratory rate. DMH disinhibition also precipitated multiple ventricular and supraventricular ectopic beats. DMH-induced increases in HR, LVP, LVdP/dt, and in the number of ectopic beats dependent on the side of stimulation, with R-DMH provoking larger responses. In contrast, pressor and respiratory responses did not depend on the side of stimulation. Newly described DMH-induced inotropic responses were rate-, preload- and (largely) afterload-independent; they were mediated by sympathetic cardiac pathway, as revealed by their sensitivity to β-adrenergic blockade. We conclude that recruitment of DMH neurons causes sympathetically mediated positive chronotropic and inotropic effects, and that there is an asymmetry, at the level of the DMH, in the potency to elicit these effects, with R-DMH > L-DMH.

Activity of preoptic area neurons supports thermal effector activation during fever

Prostaglandin E2 (PGE2) in the preoptic area (POA) mimics fever by stimulating thermogenesis in brown adipose tissue (BAT), skeletal muscle via shivering and the heart via tachycardia, as well as by reducing heat loss via skin vasoconstriction. PGE2‐evoked stimulations of BAT, shivering EMGs and heart rate (HR) are postulated to arise from disinhibition of thermogenesis‐promoting neurons in the dorsomedial hypothalamus (DMH), and possibly in the rostral raphe pallidus (rRPa), due to the EP3 receptor (EP3‐R)‐mediated inhibition of GABAergic, warm‐sensitive neurons in the POA that project to inhibit DMH (and possibly rRPa) neurons. We tested the hypothesis that neurons in the medial preoptic (MPO) provide the necessary excitatory drive to downstream, thermogenesis‐promoting neurons for febrile heat production. Bilateral muscimol injection in the MPO completely inhibited the shivering EMGs and reversed the increases in BAT temperature and HR following injection of PGE2 into the POA. We conclude that the MPO contains neurons whose activity is necessary to support thermogenesis during fever. The data are consistent with a model in which a population of MPO neurons provides a tonically‐active, excitatory (glutamatergic) input to DMH (and rRPa?) neurons that drives thermogenesis upon disinhibition of DMH neurons during EP3‐R activation in the POA and potentially during cold exposure. Support NIH grant NS40987.

Glucagon-like peptide-1 of brainstem origin activates dorsomedial hypothalamic neurons in satiated rats

A high number of neurons express c-fos in response to unlimited food intake in fasted rats in the ventral subdivision of the hypothalamic dorsomedial nucleus (DMHv). We report here, that in same conditions, limited food consumption failed to induce Fos expression in DMHv neurons suggesting that satiation should be one of the important signals that activate these neurons. The possible origin of fibers conducting satiation signals to the DMHv could be in the lower brainstem, especially glucagon-like peptide-1 (GLP-1)-containing neurons in the nucleus of the solitary tract (NTS). We demonstrate that GLP-1-immunoreactive fibers and fiber terminals topographically overlap with activated Fos-positive neurons in the DMHv in refed rats. Using immunocytochemistry and in situ hybridization histochemistry, we demonstrated GLP-1 receptors in Fos-expressing neurons of the DMH. Unilateral transections of ascending GLP-1-containing fibers from the NTS inside the pons in refed rats (unlimited food consumption) resulted in a dramatic decrease in the density of GLP-1 fibers and in the number of Fos-immunoreactive neurons in the DMHv, but only on the side of the transection. Contralateral to the transection, neither the GLP-1 fiber density nor the number of Fos-positive cells changed significantly. Meanwhile, the density of GLP-1 immunoreactivity was markedly accumulated in transected nerve fibers caudal to the cuts, as a consequence of the interruption of the ascending GLP-1 transport route. These findings suggest that the solitary-hypothalamic projections may represent the neuronal route through GLP-1 neurons of the NTS activate DMHv neurons via GLP-1 receptors by conveying information on satiety.

Acute Stress Increases the Synthesis of 7α-Hydroxypregnenolone, a New Key Neurosteroid Stimulating Locomotor Activity, through Corticosterone Action in Newts

7α-Hydroxypregnenolone (7α-OH PREG) is a newly identified bioactive neurosteroid stimulating locomotor activity in the brain of newt, a wild animal, which serves as an excellent model to investigate the biosynthesis and biological action of neurosteroids. Here, we show that acute stress increases 7α-OH PREG synthesis in the dorsomedial hypothalamus (DMH) through corticosterone (CORT) action in newts. A 30-min restraint stress increased 7α-OH PREG synthesis in the brain tissue concomitant with the increase in plasma CORT concentrations. A 30-min restraint stress also increased the expression of cytochrome P450(7α) (CYP7B), the steroidogenic enzyme of 7α-OH PREG formation, in the DMH. Decreasing plasma CORT concentrations by hypophysectomy or trilostane administration decreased 7α-OH PREG synthesis in the diencephalon, whereas administration of CORT to these animals increased 7α-OH PREG synthesis. Glucocorticoid receptor was present in DMH neurons expressing CYP7B. Thus, CORT appears to act directly on DMH neurons to increase 7α-OH PREG synthesis. We further investigated the biological action of 7α-OH PREG in the brain under stress. A 30-min restraint stress or central administration of 7α-OH PREG increased serotonin concentrations in the diencephalon. Double immunolabeling further showed colocalization of CYP7B and serotonin in the DMH. These results indicate that acute stress increases the synthesis of 7α-OH PREG via CORT action in the DMH, and 7α-OH PREG activates serotonergic neurons in the DMH that may coordinate behavioral responses to stress. This is the first demonstration of neurosteroid biosynthesis regulated by peripheral steroid hormone and of neurosteroid action in the brain under stress in any vertebrate class.

Endocannabinoids Gate State-Dependent Plasticity of Synaptic Inhibition in Feeding Circuits

Changes in food availability alter the output of hypothalamic nuclei that underlie energy homeostasis. Here, we asked whether food deprivation impacts the ability of GABA synapses in the dorsomedial hypothalamus (DMH), an important integrator of satiety signals, to undergo activity-dependent changes. GABA synapses in DMH slices from satiated rats exhibit endocannabinoid-mediated long-term depression (LTD(GABA)) in response to high-frequency stimulation of afferents. When CB1Rs are blocked, however, the same stimulation elicits long-term potentiation (LTP(GABA)), which manifests presynaptically and requires heterosynaptic recruitment of NMDARs and nitric oxide (NO). Interestingly, NO signaling is required for eCB-mediated LTD(GABA). Twenty-four hour food deprivation results in a CORT-mediated loss of CB1R signaling and, consequently, GABA synapses only exhibit LTP(GABA). These observations indicate that CB1R signaling promotes LTD(GABA) and gates LTP(GABA). Furthermore, the satiety state of an animal, through regulation of eCB signaling, determines the polarity of activity-dependent plasticity at GABA synapses in the DMH.

Respiratory modulation of brown adipose tissue sympathetic nerve activity during activation of dorsomedial hypothalamic neurons

Activation of dorsomedial hypothalamic (DMH) neurons contributes to the increases in brown adipose tissue (BAT) sympathetic nerve activity (SNA), BAT thermogenesis and heart rate (HR) induced by skin cooling and during the febrile response mimicked by injection of PGE2 into the medial preoptic area. Neurons in the same DMH region mediate increases in HR, and potentially other autonomic variables, during stress responses. In this study, the relationship between BAT SNA and phrenic nerve activity (PHR) was characterized during activation of localized populations of DMH neurons with nanoinjections of NMDA in urethane/chloralose-anesthetized, vagotomized, artificially-ventilated rats. NMDA in DMH usually elicited increases both in BAT SNA and in PHR amplitude and rate, although the optimal sites for evoking maximal increases in BAT SNA and in PHR were rarely the same. The bursts in evoked BAT SNA displayed a strong respiratory modulation with a phase relationship to the PHR which was not different from that observed during skin cooling-evoked activation of BAT SNA. These data are consistent with the availability of a descending drive to BAT and to respiration from likely separate populations of DMH neurons and with an influence of central respiratory networks on BAT SNA that is mediated at a site caudal to the DMH. Supported by NIH grant NS40987.

GLP-1 fibers of brainstem origin activate dorsomedial hypothalamic neurons in refed rats

GLP-1 fibers of brainstem origin activate dorsomedial hypothalamic neurons in refed rats

Identifying the efferent projections of leptin‐responsive neurons in the dorsomedial hypothalamus using a novel conditional tracing approach

Tracing the axonal projections of selected neurons is labor intensive and inherently limited by currently available neuroanatomical methods. We developed an adeno-associated virus (AAV) that can be used for efficiently tracing identified neuronal populations. The virus encodes a humanized Renilla green fluorescent protein (hrGFP) that is transcriptionally silenced by a neo cassette flanked by LoxH/LoxP sites (AAV-lox-Stop-hrGFP). Thus, hrGFP is expressed only in neurons with Cre recombinase activity. To demonstrate the utility of this approach, the virus was injected unilaterally into the dorsomedial hypothalamus (DMH) of mice that express Cre in neurons expressing the leptin receptor. Animals with DMH injections showed robust hrGFP expression in DMH neurons, as visualized by its endogenous fluorescence or following immunolabeling. We found that hrGFP was expressed in approximately one-third to one-half of Cre-expressing neurons at the site of injection, but not in non-Cre-expressing neurons. The expression of GFP allowed us to identify the projection fields of DMH leptin-responsive neurons. Our results show hrGFP-positive axonal projections and terminals in the paraventricular nucleus of the hypothalamus, arcuate nucleus, preoptic area, bed nucleus of the stria terminalis, paraventricular thalamus, periaqueductal gray, and precoeruleus. The aforementioned pattern of projections was similar to DMH projections determined by injections of biotinylated dextran amine in the mouse DMH. Interestingly, some hrGFP-positive terminals were seen contacting the ependymal layer of the third and fourth ventricles. In summary, this approach is an effective tool for tracing axonal projections of chemically identified neurons, including leptin-responsive neurons.

Expression of the orphan GPR50 protein in rodent and human dorsomedial hypothalamus, tanycytes and median eminence

The melatonin receptor family is composed of three members, MT(1) and MT(2) receptors that bind melatonin with high affinity and the orphan GPR50 that does not bind melatonin but shares significant sequence homology with the two other subtypes. In the absence of any known ligand for this orphan receptor, little is still known about its function. We recently reported the development of the first anti-GPR50 antibodies that reliably recognized the recombinant human GPR50. We here used these antibodies to study the expression of GPR50 in mouse, rat and human hypothalamus, a region reported to express GPR50 mRNA. GPR50 immunoreactivity (ir) was observed in dorsomedial hypothalamic (DMH) cells co-stained with the neuronal marker HuC/D. GPR50-ir was also observed in cells of the ependymal layer of the third ventricle that co-stained with vimentin. More specifically, its localization in the lower region of the third ventricle and along the long basal processes contacting portal blood vessels in the median eminence (ME) suggested expression of GPR50 in tanycytes. Consistent staining patterns were observed in all three species with two different antibodies. Taken together, our study validates two GPR50-specific antibodies for the use in rodent and human tissue. Evolutionary conserved expression of GPR50 in DMH neurons and tanycytes, together with previously reported expression of the receptor in the pituitary, support the potentially important role of GPR50 in key hypothalamic functions, including regulation of the hypothalamo-pituitary axes.

Activation of 5-HT receptors in the periaqueductal gray attenuates the tachycardia evoked from dorsomedial hypothalamus

Studies have shown that the dorsomedial hypothalamus (DMH) is a key region in the descending pathways mediating the cardiovascular response to emotional stress. We have recently demonstrated that the lateral/dorsolateral periaqueductal gray (l/dlPAG) is an important synaptic relay in mediating the tachycardic effect produced by activation of DMH neurons. This synaptic relay is mediated via NMDA excitatory amino acid receptors. In this study, our aim was to investigate, in conscious rats, whether activation of 5-Hydroxytriptamine 1A (5-HT1A) receptors in the l/dlPAG can attenuate the increases in heart rate and arterial pressure evoked by a) chemical activation of the DMH, b) air jet stress paradigm and c) chemical activation of l/dlPAG. Microinjections of the 5-HT1A receptor agonist, 8-OH-DPAT (1 nmol/100 nl), into the l/dlPAG reduced (by 62%) the increases in heart rate evoked by chemical activation of DMH neurons with the GABAA antagonist bicuculline methiodide (10 pmol/100 nl). The tachycardic and pressor responses evoked by air jet stress paradigm were also attenuated after treatment with 8-OH-DPAT in the l/dlPAG. The increases in heart rate and arterial pressure produced by microinjection of the excitatory amino acid receptor agonist, NMDA, into the l/dlPAG were largely reduced (by 94% and 73%, respectively) after treatment in the same region with 8-OH-DPAT. Taken together, our findings indicate that 5-HT1A receptors at the lateral dorsolateral PAG play a significant role in modulating the descending cardiovascular pathways from the dorsomedial hypothalamus and consequently the cardiovascular response to emotional stress.

Role of orexin input in the diurnal rhythm of locus coeruleus impulse activity

Activation of noradrenergic locus coeruleus (LC) neurons promotes wakefulness and behavioral arousal. In rats, LC neurons receive circadian inputs via a circuit that originates in the suprachiasmatic nucleus (SCN) and relays through the dorsomedial hypothalamus (DMH) to LC; this circuit input increases LC activity during the active period. DMH neurons expressing the peptide neurotransmitter orexin/hypocretin are ideally situated to act as a relay between SCN and LC due to their synaptic inputs from SCN and innervation of LC. Here, we examined the hypothesis that orexin is involved in transmitting circadian signals to LC using single-unit recordings of LC neurons in anesthetized rats maintained in 12:12 light–dark housing. We replicated earlier findings from this lab that LC neurons fire significantly faster on average during the active compared to rest periods. Local microinjection of an orexin antagonist, SB-334867-A attenuated the impulse activities of the fastest firing population of LC neurons during the active period. We also found that DMH orexin neurons project preferentially to LC and express a diurnal rhythm of activation that correlates with LC neuronal firing frequency. Therefore, we propose that DMH orexin neurons play a role in modulating the day–night differences of LC impulse activity.

Evaluation of the heart rate changes evoked by air jet stress after inhibition of the right or left sides of dorsomedial hypothalamus

Neurons in the dorsomedial hypothalamus (DMH) play a key role in mediating tachycardia resulting from stressful stimuli. We investigated a possible hemispheric difference in DMH neurons on tachycardia evoked by experimental stress. Changes in heart rate (HR) produced by air jet stress after right (R) or left (L) inhibition of the DMH were evaluated in two separated groups (G1, G2). Under tribromoethanol anesthesia (250 mg/Kg) rats received guide cannulas into DMH and a femoral artery catheter. Air jet stress (1.5 litres/min in a 10 min period) was repeated in 2 consecutive days in conscious rats. G1 (n=5) received injections of GABAA agonist, muscimol, (1nmol / 100nL) into LDMH at the 1st day and into the RDMH at the second day. In the G2 (n=5) the sequence of muscimol injections into the DMH was inverse, i.e. R before L. Strikingly, in both groups the tachycardia evoked by air stress was greatly reduced after RDMH inhibition (G1: L=143±17 bpm, R=58±20 bpm; G2: R=56±13 bpm, L=124±12 bpm P<0.05). In additional control experiments we found that after vehicle (NaCl 0.9%) injections into DMH, the tachycardia evoked by air stress averaged 119±17 bpm (n=10). We conclude that activation of the right DMH is critical to the full cardiac response observed during stress. Support: CNPq, FAPEMIG, CAPES.

Functional topography of the dorsomedial hypothalamus

The dorsomedial hypothalamus (DMH) has been proposed to play key roles in both the defense reaction to acute stress and in the thermoregulatory response to cold. We reasoned that the autonomic/respiratory motor patterns of these responses would be mediated by at least partly distinct DMH neuron populations. To test this, we made simultaneous recordings of phrenic nerve and plantar cutaneous vasoconstrictor (CVC) activity in 14 vagotomized, ventilated, urethane-anesthetized rats. Microinjections of d,l-homocysteic acid (DLH; 15 nl, 50 mM) were used to cause localized, short-lasting (<1 min) activation of DMH neuron clusters. Cooling the rat's trunk skin by perfusing cold water through a water jacket-activated plantar CVC activity but depressed phrenic burst rate (cold-response pattern). The expected "stress/defense response" pattern would be phrenic activation, with increased blood pressure, heart rate, and possibly CVC activity. DLH microinjections into 76 sites within the DMH region never reduced phrenic activity. They frequently increased phrenic rate and/or plantar CVC activity, but the magnitudes of those two responses were not significantly correlated. Plantar CVC responses were evoked most strongly from the dorsal hypothalamic area and most dorsal part of the dorsomedial nucleus, whereas peak phrenic rate responses were evoked from more caudal sites; their relative magnitudes varied systematically with rostrocaudal position. Tachycardia correlated with plantar CVC responses but not phrenic rate. These findings indicate that localized activation of DMH neurons does not evoke full "cold-response" or stress/defense response patterns, but they demonstrate the existence of significant functional topography within the DMH region.

Effects of disinhibition of neurons in the dorsomedial hypothalamus on central respiratory drive

Neurons within the dorsomedial hypothalamus (DMH) play a critical role in subserving the cardiovascular and neuroendocrine response to psychological stress. An increase in respiratory activity is also a characteristic feature of the physiological response to psychological stress, but there have been few studies of the role of DMH neurons in regulating respiratory activity. In this study we determined the effects of activation of DMH neurons on respiratory activity (assessed by measuring phrenic nerve activity, PNA) and the relationship between evoked changes in respiratory activity and changes in sympathetic vasomotor activity in spontaneously breathing urethane-anesthetized rats. Microinjections of bicuculline (4-40 pmol in 20 nl) into the DMH evoked dose-dependent increases in PNA burst frequency and amplitude. These were accompanied by dose-dependent decreases in mean tracheal CO(2) levels, indicative of hyperventilation. In control experiments, microinjections of bicuculline into sites adjacent to the DMH evoked much smaller or no changes in PNA. In experiments where renal sympathetic nerve activity (RSNA) was also measured, cycle-triggered averaging revealed that RSNA under resting conditions was partly correlated with the PNA, but in response to DMH disinhibition there was no consistent change in the amplitude of the respiratory-related variations in RSNA. The results indicate that DMH neurons can exert a powerful stimulatory effect on respiratory activity, causing hyperventilation. This is not associated with an increase in the degree of coupling between PNA and RSNA, indicating that the DMH-evoked increase in RSNA is not a consequence of increased central respiratory drive.

DIFFERENTIAL CONTROL OF CARDIAC AND SYMPATHETIC VASOMOTOR ACTIVITY FROM THE DORSOMEDIAL HYPOTHALAMUS

1. The dorsomedial hypothalamus (DMH) plays a crucial role in mediating the cardiovascular responses to different stressors, including acute psychological stress and cold stress. Activation of neurons in the DMH evokes increases in arterial pressure and in the activity of sympathetic nerves innervating the heart, blood vessels and brown adipose tissue. The descending pathways from the DMH to the spinal sympathetic outflow include synapses with neurons in medullary nuclei and possibly other brain stem regions. 2. Recent studies from our and other laboratories have indicated that neurons in the rostral ventrolateral medulla (RVLM) and in the region of the raphe pallidus (RP) in the medulla are important components of the descending pathways that mediate the cardiovascular response to activation of the DMH. Neurons in the RP primarily mediate the sympathetic cardiac components of the DMH-evoked response, whereas the RVLM neurons primarily mediate the sympathetic vasomotor component. 3. Activation of DMH neurons not only increases heart rate and sympathetic vasomotor activity, but also resets the baroreceptor reflex such that it remains effective, without any decrease in sensitivity, over a higher operating range of arterial pressure. 4. Activation of 5-hydroxytryptamine 5-HT(1A) receptors in the medulla oblongata leads to a selective suppression of cardiac and sympathetic vasomotor components of the DMH-evoked response, but does not affect sympathetic reflex responses evoked from baroreceptors or chemoreceptors. Thus, central 5-HT(1A) receptors modulate cardiovascular responses evoked from the DMH in a highly potent but selective fashion.

Panic-Prone State Induced in Rats with GABA Dysfunction in the Dorsomedial Hypothalamus Is Mediated by NMDA Receptors

Rats with chronic inhibition of GABA synthesis and consequently enhanced glutamatergic excitation in the dorsomedial hypothalamus (DMH) develop panic-like responses, defined as tachycardia, tachypnea, hypertension, and increased anxiety as measured by a social interaction (SI) test, after intravenous sodium lactate infusions, a phenomenon similar to patients with panic disorder. Therefore, the present studies tested the role of the postsynaptic NMDA and AMPA type glutamatergic receptors in the lactate-induced panic-like responses in these rats. Rats were fit with femoral arterial and venous catheters and Alzet pumps [filled with the GABA synthesis inhibitor L-allylglycine (L-AG; 3.5 nmol/0.5 microl per hour) or its inactive isomer D-AG] into the DMH. After 4-5 d of recovery only those rats with L-AG pumps exhibited panic-like responses to lactate infusions. Using double immunocytochemistry, we found that rats exhibiting panic-like responses (e.g., L-AG plus lactate) had increased c-Fos immunoreactivity in DMH neurons expressing the NMDA receptor 1 (NR1) subunit, but not those expressing the glutamate receptor 2 and 3 subunits of the AMPA receptors. To confirm this pharmacologically, we tested another group of rats implanted with l-AG pumps with intravenous lactate infusions preceded by injections of either NMDA [aminophosphonopentanoic acid (AP-5) or (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d]cyclohepten-5,10-imine maleate (MK-801)] or non-NMDA [CNQX or 4-(8-methyl-9H-1,3-dioxolo[4,5-h][2,3]benzodazepin-5-yl)-benzenamine dihydrochloride (GYKI52466)] antagonists into the DMH. Injections of NMDA, but not non-NMDA, antagonists into the DMH resulted in dose-dependent blockade of the tachycardia, tachypnea, hypertension, and SI responses after lactate infusions. These results suggest that NMDA, and not non-NMDA, type glutamate receptors regulate lactate-induced panic-like responses in rats with GABA dysfunction in the DMH.

Glutamate receptors in the raphe pallidus mediate brown adipose tissue thermogenesis evoked by activation of dorsomedial hypothalamic neurons

Disinhibition of DMH neurons with the GABA A receptor antagonist, bicuculline, increases heart rate (HR) and augments both brown adipose tissue sympathetic nerve activity (BAT SNA) and renal SNA (RSNA) contributing to the evoked increases in BAT thermogenesis and arterial pressure (AP). We determined the role of glutamate receptor activation in the rostral raphe pallidus (RPa) in mediating the sympathoexcitatory responses in HR, BAT SNA and RSNA following disinhibition of DMH neurons in urethane/chloralose anesthetized, artificially ventilated rats. Microinjections of either the selective NMDA receptor agonist, NMDA, or the selective non-NMDA receptor agonist, kainic acid (KA), into the RPa produced increases in BAT SNA (peak: +502% and +408% of control, respectively) and BAT temperature (peak: +0.6 °C and +1.0 °C) accompanied by rises in HR (peak: +38 and +63 bpm), RSNA (peak: +57% and +58% of control) and MAP (peak: +12 and 15 mmHg). These responses were reversed by subsequent microinjection into RPa of the respective selective glutamate receptor antagonists, AP5 and CNQX. Microinjections of the non-selective glutamate receptor antagonist, kynurenic acid (Kyn), the NMDA receptor antagonist, AP5, or the non-NMDA receptor antagonist, CNQX, were effective in reversing the increases in BAT SNA (for Kyn, from peak of +419% of control to +9% of control) and BAT temperature, but not those in HR, MAP or RSNA (for Kyn, from peak of +143% of control to +124% of control) evoked by unilateral microinjection of bicuculline into the DMH. These results indicate that both NMDA and non-NMDA glutamate receptors in the RPa play a significant role in mediating the excitatory synaptic transmission producing the activation of BAT thermogenesis following disinhibition of DMH neurons. Glutamate receptors in the RPa may not be important for transmitting cardiovascular responses induced by activation of the DMH neurons.

Neurons in the dorsomedial hypothalamus (DMH) are required for leptin‐induced activation of brown adipose tissue (BAT) thermogenesis

The increased sympathetic nerve activity (SNA) to BAT stimulated by intravenous (iv) administration of leptin was inhibited by microinjection of the 5-HT1A receptor agonist, 8-OH-DPAT, into the raphe pallidus (RPa), indicating that neurons in RPa, presumably BAT sympathetic premotor neurons, are required for leptin-induced activation of BAT thermogenesis. In present study, we tested the hypothesis that DMH neurons comprised a requisite synaptic link in the central neural pathway for leptin-induced BAT thermogenesis. In six anesthetized rats maintained at a core temperature of 35.5°C, iv administration of leptin (1.0 mg/kg) increased BAT SNA by +4635% of control, BAT temperature by +3.0°C as well as RSNA by +164% of control. Subsequent inhibition of DMH neurons by microinjection of glycine (0.5 M/60 nl) reversed the leptin-induced BAT thermogenesis, but had no effect on the leptin-induced increase in RSNA. Similarly, intracerebroventricular (icv) administration of leptin (10μg/10μl) increased BAT SNA by 3516% of control, BAT temperature by +2.3°C and RSNA by +154% of control at a core temperature of 36.1°C. Icv leptin-induced increases in BAT SNA and BAT thermogenesis, but not those in RSNA, were reversed by subsequent bilaterally microinjection of muscimol (2 mM/60 nl) into the DMH. These results indicate that the increased energy expenditure in BAT by stimulation of central leptin receptors requires activation of neurons in the DMH and that the leptin-evoked stimulation of renovascular function uses a sympathoexcitatory pathway that does not include DMH neurons. Supported by NIH DK57838 and DK20378.

Excitatory amino acid receptors in the periaqueductal gray mediate the cardiovascular response evoked by activation of dorsomedial hypothalamic neurons

Neurons in the region of dorsomedial hypothalamus are involved in the organization of the physiological responses to emotional stress. We have recently shown that the cardiovascular response evoked by activation of dorsomedial hypothalamus neurons is largely dependent on a synaptic relay with the lateral/dorsolateral periaqueductal gray region. In this study, we aimed to investigate whether excitatory amino acid receptors at the lateral/dorsolateral periaqueductal gray region are involved in mediating the response evoked by activation of dorsomedial hypothalamus neurons. In conscious rats, the cardiovascular effects produced by microinjection of GABA A receptor antagonist, bicuculline methiodide into the dorsomedial hypothalamus were evaluated before and after injection of different excitatory amino acid antagonists into lateral/dorsolateral periaqueductal gray region. Pretreatment of lateral/dorsolateral periaqueductal gray region with the non-selective ionotropic excitatory amino acid receptor antagonist kynurenic acid or with the N-methyl- d-aspartate receptor-selective antagonist, MK-801, largely reduced the tachycardic and pressor effects evoked by activation of dorsomedial hypothalamus neurons by bicuculline methiodide microinjection (heart rate 90 and 74%; blood pressure 81 and 84%, respectively). The non- N-methyl- d-aspartate receptor-selective antagonist 6-cyano-7-nitroquinoxaline-2,3-dione, did not alter the cardiovascular response evoked by dorsomedial hypothalamus activation. In an additional series of experiments, microinjection of the N-methyl- d-aspartate receptor agonist, N-methyl- d-aspartate, into the lateral/dorsolateral periaqueductal gray region, evoked an increase in heart rate and a pressor response that was accompanied by an increase in locomotor activity. These effects were not altered by pretreatment of lateral/dorsolateral periaqueductal gray region neurons with 6-cyano-7-nitroquinoxaline-2,3-dione but were completely abolished by MK-801. Altogether, these findings indicate that the cardiovascular response evoked by dorsomedial hypothalamus activation involves a synaptic relay at the lateral/dorsolateral periaqueductal gray region that is mediated at least in large part by excitatory amino acid receptors, possibly N-methyl- d-aspartate receptors.

Lack of the Central Nervous System- and Neural Crest-Expressed Forkhead Gene Foxs1 Affects Motor Function and Body Weight

To gain insight into the expression pattern and functional importance of the forkhead transcription factor Foxs1, we constructed a Foxs1-beta-galactosidase reporter gene "knock-in" (Foxs1beta-gal/beta-gal) mouse, in which the wild-type (wt) Foxs1 allele has been inactivated and replaced by a beta-galactosidase reporter gene. Staining for beta-galactosidase activity reveals an expression pattern encompassing neural crest-derived cells, e.g., cranial and dorsal root ganglia as well as several other cell populations in the central nervous system (CNS), most prominently the internal granule layer of cerebellum. Other sites of expression include the lachrymal gland, outer nuclear layer of retina, enteric ganglion neurons, and a subset of thalamic and hypothalamic nuclei. In the CNS, blood vessel-associated smooth muscle cells and pericytes stain positive for Foxs1. Foxs1beta-gal/beta-gal mice perform significantly better (P < 0.01) on a rotating rod than do wt littermates. We have also noted a lower body weight gain (P < 0.05) in Foxs1beta-gal/lbeta-gal males on a high-fat diet, and we speculate that dorsomedial hypothalamic neurons, expressing Foxs1, could play a role in regulating body weight via regulation of sympathetic outflow. In support of this, we observed increased levels of uncoupling protein 1 mRNA in Foxs1beta-gal/beta-gal mice. This points toward a role for Foxs1 in the integration and processing of neuronal signals of importance for energy turnover and motor function.