This article explores a variety of chemosensory strategies – pungent foods, ammonia salts, and essential oils – as potentially useful interventions for clinical states of dissociative shutdown (including functional/dissociative seizures); re-experiencing symptoms of posttraumatic stress disorder; and other states involving changes in arousal and a loss of balance in the neural pathways or networks crucial for the processing and integration of somatic, or body-based, sensations, as a result of stress-system dysregulation or trauma-related experiences. All of these states are common in clinical practice. Patients find them distressing as they interfere with normal daily function, quality of life, and capacity to manage the daily challenges of life. Based on the current literature we, the authors, provide an update pertaining to the current knowledge base about the neurobiology that underlies the therapeutic effects and clinical utility of these chemosensory substances. Whilst the use of chemosensory substances goes back into antiquity, our understanding of underlying neurobiological mechanisms is just beginning to emerge.

Instrumental actions are initially goal-directed but with repeated performance can become habitual. Habitual actions are adaptive, learned behaviours that are automated in order to reduce cognitive load and to allow for efficient interaction with the environment. Goal-directed and habitual actions are mediated by distinct neurocircuits which centre on the dorsal striatum and involve different cortical and limbic inputs. The lateral hypothalamus (LH) has yet to be considered in this neurocircuitry despite its anatomical connections with these neurocircuits and its established role in motivated behaviour. The aim of the current study was to determine whether the LH has a role in the development of habitual actions in rats by knocking down protein expression in the LH with short hairpin RNAs (shRNA). Two shRNAs were utilised, both of which were shown to reduce the expression of two neuropeptides within the LH, orexin and melanin-concentrating hormone, compared to a saline-vehicle control. This was unexpected given that one shRNA was a control vector (i.e, scrambled sequence), and the other shRNA was supposed to selectively target orexin's precursor protein. Given this lack of specificity and that shRNA's are known to be neurotoxic, the current study examined the impact of non-selective dysfunction of the LH on habitual actions. Adult male Long-Evans rats were trained to press a lever for a food outcome and were tested for goal directed and habitual behaviour following devaluation of the food. The shRNA groups displayed goal-directed actions following moderate instrumental training, but did not develop habitual actions following extended training. That is, control rats developed the expected habitual behaviour where lever-response rates were insensitive to outcome value when tested, whilst the shRNA groups reduced rates of responding on the lever under devalued conditioned and hence remained goal-directed. This failure to demonstrate habitual actions was unlikely to be secondary to changes in motivation or arousal as the shRNA groups did not show altered food consumption, body weight, lever response rates, or motor performance on a rota rod or tapered balance beam. However, locomotor activity was reduced in an open field test, consistent with the proposed role of the LH in spontaneous locomotor activity. Therefore, this study implicates the LH in habitual learning, and adds to the emerging evidence that the LH has a role in associative learning processes. This finding has implications for human conditions where there is dysfunction or neurodegeneration in the LH, as well as altered habitual actions, such as in Parkinson's disease and drug addiction.

The neuropeptide orexin-A (OX-A) has diverse functions, including maintaining arousal, autonomic control, motor activity and stress responses. These functions are regulated at different terminal regions where OX-A is released. The current study examined the physiological and behavioural effects of OX-A microinjections into the central amygdala (CeA) under basal and stressed conditions in rats. When OX-A was microinjected into the CeA and the animals returned to the home-cage, heart rate and mean arterial pressure were increased compared to vehicle-injected controls. General activity of the animal was also increased, indicating that OX-A activity in CeA contributes to increased arousal. This outcome is similar to the effects of central intracerebroventricular infusions of OX-A, as well as the cardiovascular effects previously demonstrated at many of OX's efferent hypothalamic and brainstem structures. In a second study, animals were fear-conditioned to a context by delivery of electric footshocks and then animals were re-exposed to the conditioned context at test. When OX-A was microinjected at test, freezing behaviour was reduced and there was a corresponding increase in the animal's activity but no impact on the pressor and cardiac responses (i.e, blood pressure and heart rate were unchanged). This reduction in freezing suggests that OX-A activates amygdala neurons that inhibit freezing, which is similar to the actions of other neuropeptides in the CeA that modulate the appropriate defence response to fearful stimuli. Overall, these data indicate that the CeA is an important site of OX-A modulation of cardiovascular and motor activity, as well as conditioned freezing responses.

Asylum-seeking children presenting in the shutdown state have been the subject of much discussion and controversy—on both government and medical system levels—in Australia and in Sweden. In this article, we conceptualize the shutdown state as an evolutionary response to extreme threat. We adopt a neuroscience approach to present five plausible models for explaining this shutdown state, their strengths and shortcomings, and the overlaps between them. Model 1—the sustained autonomic arousal model—draws on polyvagal theory. Model 2—the innate-defence model—draws on research pertaining to animal and human innate defence responses. Model 3—the catatonia model—draws on clinical and research data with patients presenting with catatonia. Model 4—the hypometabolic model—draws on an emerging body of work pertaining to hypometabolic states in animals and humans. Model 5—the defence cascade model of dissociation—draws on clinical research pertaining to human trauma states that present as dissociation. At present, each of the models provides a plausible pathophysiological explanation—or a component of a potential pathophysiological explanation—and none of them, for the moment, has enough evidence to be either accepted or disregarded. We hope that our discussion of the models advances scientific discussion and opens up possibilities for effective treatment.

Background: Orexin is a neuropeptide which can influence a wide range of physiological functions including blood pressure, sympathetic nervous system activity and arousal. Orexinergic signalling is suggested to contribute to the neurogenic hypertension in BPH/2J mice, based on the hypotensive response to the dual orexin receptor (OxR) antagonist, Almorexant, which was not observed in normotensive BPN/3J controls. Orexin is also known to influence the cardiovascular response to certain stressors. Thus, it is possible that orexin may also contribute to the exaggerated pressor response to stress that is reported in BPH/2J mice. Objective: To determine the contribution of orexin to the hypertension and exaggerated stress reactivity in BPH/2J wild type mice by comparing with BPH/2J Orexin homozygous knock out (BPH OxKO) mice. Methods: BPH OxKO (n=9) and BPH wild type (BPH WT) mice (n=6) were implanted with radiotelemetry probes to measure blood pressure (BP), heart rate (HR) and locomotor activity across the 24hr period and in response to restraint and dirty cage swap stressors. The BP responses to ganglion blocker pentolinium (5mg/kg, i.p.), was also measured. Results: There was no difference in average mean arterial pressure (MAP) over the 24hr period in BPH OxKO mice (131±1 vs 133±1mmHg, P =0.351), but there was a modest elevation in systolic AP (+4.5mmHg) exclusively during light period in BPH OxKO compared with BPH WT mice (145±2 vs 141±2mmHg, P <0.032). HR was comparable between strains ( P =0.160) and locomotor activity tended to be lower in BPH OxKO compared with BPH WT mice during the dark period (1.1±0.2 vs 1.7±0.3 units respectively, P =0.051). The pressor response to dirty cage swap stress was lower in BPH OxKO compared with BPH WT mice (22±1 vs 28±1mmHg respectively, P <0.001), as was the response to restraint stress (36±1 vs 40±2mmHg respectively, P <0.05). The depressor response to ganglion blockade was comparable between strains ( P =0.255). Conclusion: The present findings suggest that whilst orexin does not contribute to sympathetically mediated hypertension, it may play a role in the exaggerated cardiovascular response to stress and hyperactivity in BPH/2J mice.

Previously, a sub-population of defeated anesthetized rats (Dlow) was characterized by persistent low blood levels of brain-derived neurotrophic factor (BDNF) at day 29 and autonomic alteration at day 30 after social challenge, while the other population (Dhigh) was similar to non-defeated (ND) animals. The aims of this study were to determine the time-course of autonomic dysfunction in awake animals, and whether Dhigh and/or Dlow were vulnerable to cardiac events. Defeated animals were exposed to four daily episodes of social defeats from day 1 to day 4. At day 30, anesthetized Dlow displayed decreased experimental and spontaneous reflex responses reflecting lower parasympathetic efficiency. In addition, Dlow but not Dhigh were characterized by left ventricular hypertrophy at day 30. Telemetric recordings revealed that Dlow had increased low frequency-to-high frequency ratio (LF/HF) and diastolic (DBP) and systolic (SBP) blood pressure, associated with decreased HF and spontaneous baroreflex responses (BRS) from day 3 to day 29. LF/HF, DBP and SBP recovered at day 5, and HF and BRS recovered at day 15 in Dhigh. Ventricular premature beats (VPBs) occurred in Dlow and Dhigh animals from day 5. Time course of VBP fluctuations in Dhigh mirrored that of HF and BRS, but not that of LF/HF, DBP and SBP. These results suggest that a psychosocial stress associated to low serum BDNF levels can lead to vulnerability to persistent autonomic dysfunction, cardiac hypertrophy and ventricular ectopic beats. The parasympathetic recovery seen in Dhigh may provide protection against cardiac events in this population.

Obesity is a health problem affecting more than 40% of US adults and 13% of the global population. Anti-obesity treatments including diet, exercise, surgery and pharmacotherapies have so far failed to reverse obesity incidence. Herein, we target obesity with a pharmacotherapeutic approach that decreases caloric efficiency by mitochondrial uncoupling. We show that a recently identified mitochondrial uncoupler BAM15 is orally bioavailable, increases nutrient oxidation, and decreases body fat mass without altering food intake, lean body mass, body temperature, or biochemical and haematological markers of toxicity. BAM15 decreases hepatic fat, decreases inflammatory lipids, and has strong antioxidant effects. Hyperinsulinemic-euglycemic clamp studies show that BAM15 improves insulin sensitivity in multiple tissue types. Collectively, these data demonstrate that pharmacologic mitochondrial uncoupling with BAM15 has powerful anti-obesity and insulin sensitizing effects without compromising lean mass or affecting food intake.

Neurons controlling cardiovascular responses and glucose counter regulation are co‐located within the RVLM, with activated neurons lying almost exclusively caudal to the caudal pole of the facial nucleus (FN). However, it is unclear whether the same neurons are involved in triggering both cardiovascular and metabolic responses. We compared the distributions of RVLM C1 neurons activated by cardiovascular or metabolic stimuli using Fos to identify activated neurons. To conscious male or female rats, we administered insulin (10 U/kg ip) or 2‐deoxyglucose (2DG; 400 mg/kg sc) to induce hypoglycaemia or nitroprusside (NP; 1 mg/ml iv), hydralazine (HDZ; 10 mg/kg iv) or diazoxide (DZX; 50 mg/kg iv) to cause hypotension. Rats were transcardially perfused with formaldehyde 90 or 120 minutes later. Coronal 30‐micrometer thick sections of medulla (1:4 series) from the spinomedullary junction to mid‐FN were immunoperoxidase‐stained to show Fos‐immunoreactivity plus phenylethanolamine N‐methyl transferase (PNMT)‐immunoreactivity to identify C1 neurons. The 6 sections containing the 600 micrometers caudal to the caudal pole of FN (sections FN0 to FN‐5) were each divided into 3 equal segments (medial, middle, lateral) and the total numbers of PNMT neurons with Fos nuclei (Fos+PNMT neurons) were counted. The numbers of Fos+PNMT neurons were greater in the medial and middle thirds than in the lateral third of the C1 cell column in insulin‐ and 2DG‐treated rats. In NP‐, DZX‐or HDZ‐treated rats, the numbers of Fos+PNMT neurons were greater in the middle and lateral two thirds of the C1 cell column. Two‐way ANOVA showed a very strong interaction between stimulus and laterality (p<0.0001), both for number of Fos+PNMT neurons and for percentage of PNMT neurons with Fos nuclei. These results reveal that the extent of Fos expression in PNMT neurons in the medial versus lateral zones depends on the type of stimulus. Post‐hoc analysis confirmed that, in the medial zone, the metabolic stimuli activated more PNMT neurons than cardiovascular stimuli, while it was the opposite in the lateral zone (p<0.0001 in both cases). These results show that hypoglycaemia‐responsive RVLM C1 neurons are concentrated in the medial and middle thirds of the C1 cell column whereas hypotension‐responsive RVLM C1 neurons are concentrated in the middle and lateral two thirds of the column. Hence, within the rat RVLM, C1 neurons are distributed topographically according to their function. Support or Funding Information NHMRC 1025031; NIH HL096787 & HL130577 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Sensory problems such as neuropathic pain are common and debilitating symptoms in multiple sclerosis (MS), an autoimmune inflammatory disorder of the CNS. Regulatory T (Treg) cells are critical for maintaining immune homeostasis, but their role in MS-associated pain remains unknown. Here, we demonstrate that Treg cell ablation is sufficient to trigger experimental autoimmune encephalomyelitis (EAE) and facial allodynia in immunized female mice. In EAE-induced female mice, adoptive transfer of Treg cells and spinal delivery of the Treg cell cytokine interleukin-35 (IL-35) significantly reduced facial stimulus-evoked pain and spontaneous pain independent of disease severity and increased myelination of the facial nociceptive pathway. The effects of intrathecal IL-35 therapy were Treg-cell dependent and associated with upregulated IL-10 expression in CNS-infiltrating lymphocytes and reduced monocyte infiltration in the trigeminal afferent pathway. We present evidence for a beneficial role of Treg cells and IL-35 in attenuating pain associated with EAE independently of motor symptoms by decreasing neuroinflammation and increasing myelination.SIGNIFICANCE STATEMENT Pain is a highly prevalent symptom affecting the majority of multiple sclerosis (MS) patients and dramatically affects overall health-related quality of life; however, this is a research area that has been largely ignored. Here, we identify for the first time a role for regulatory T (Treg) cells and interleukin-35 (IL-35) in suppressing facial allodynia and facial grimacing in animals with experimental autoimmune encephalomyelitis (EAE). We demonstrate that spinal delivery of Treg cells and IL-35 reduces pain associated with EAE by decreasing neuroinflammation and increasing myelination independently of motor symptoms. These findings increase our understanding of the mechanisms underlying pain in EAE and suggest potential treatment strategies for pain relief in MS.

After social stress, rats become vulnerable to depression, and this state is characterized by persistent low blood levels of brain-derived neurotrophic factor (BDNF). The aim of this study was to determine whether low BDNF levels are associated with long term autonomic changes. Defeated animals were subjected to four daily episodes of social defeats. Twenty five days later, defeated rats with low BDNF levels (Dlow) still displayed elevated sympathetic tone (as indicated by an elevated low frequency to high frequency ratio (LF/HF) in heart rate) and elevated blood pressure, as well as reduced baroreflex sensitivity (BRS). In contrast, those with higher BDNF levels (Dhigh) similar to controls, did not. Dlow animals persistent cardiovascular changes were abolished by acute inhibition of the dorsomedial nucleus of the hypothalamus (DMH). These cardiovascular changes were also prevented by chronic sub-cutaneous osmotic infusion of losartan, an angiotensin II type 1 receptor (AT1) receptor antagonist, started immediately after social defeat. In conclusion, the results show that greater vulnerability to stress consequences following a traumatic event is associated with an elevated LF/HF ratio, a persistent high blood pressure and a low BRS, all due to an AT1 receptor activation.

Long-term hypercapnia is associated with respiratory conditions including obstructive sleep apnea, chronic obstructive pulmonary disease and obesity hypoventilation syndrome. Animal studies have demonstrated an initial (within hours) increase in ventilatory drive followed by a decrease in this response over the long-term (days-weeks) in response hypercapnia. Little is known about whether changes in the central respiratory chemoreflex are involved. Here we investigated whether central respiratory chemoreceptor neurons of the retrotrapezoid nucleus (RTN), which project to the respiratory pattern generator within the ventral respiratory column (VRC) have a role in the mechanism of neuroplasticity associated with long-term hypercapnia. Adult male C57BL/6 mice (n = 5/group) were used. Our aims were (1) to determine if galanin, neuromedin B and gastrin-releasing peptide gene expression is altered in the RTN after long-term hypercapnia. This was achieved using qPCR to measure mRNA expression changes of neuropeptides in the RTN after short-term hypercapnia (6 or 8 h, 5 or 8% CO2) or long-term hypercapnia exposure (10 day, 5 or 8% CO2), (2) in the mouse brainstem, to determine the distribution of preprogalanin in chemoreceptors, and the co-occurrence of the galanin receptor 1 (GalR1:Gi-coupled receptor) with inhibitory GlyT2 ventral respiratory column neurons using in situ hybridization (ISH) to better characterize galaninergic RTN-VRC circuitry, (3) to investigate whether long-term hypercapnia causes changes to recruitment (detected by cFos immunohistochemistry) of respiratory related neural populations including the RTN neurons and their galaninergic subset, in vivo. Collectively, we found that hypercapnia decreases neuropeptide expression in the RTN in the short-term and has the opposite effect over the long-term. Following long term hypercapnia, the number of RTN galanin neurons remains unchanged, and their responsiveness to acute chemoreflex is sustained; in contrast, we identified multiple respiratory related sites that exhibit blunted chemoreflex activation. GalR1 was distributed in 11% of preBotC and 30% of BotC glycinergic neurons. Our working hypothesis is that during long-term hypercapnia, galanin co-release from RTN neurons may counterbalance glutamatergic inputs to respiratory centers to downscale energetically wasteful hyperventilation, thereby having a role in neuroplasticity by contributing to a decrease in ventilation, through the inhibitory effects of galanin.

Psychogenic non-epileptic seizures (PNES) are a nonspecific, umbrella category that is used to collect together a range of atypical neurophysiological responses to emotional distress, physiological stressors and danger. Because PNES mimic epileptic seizures, children and adolescents with PNES usually present to neurologists or to epilepsy monitoring units. After a comprehensive neurological evaluation and a diagnosis of PNES, the patient is referred to mental health services for treatment. This study documents the diagnostic formulations – the clinical formulations about the probable neurophysiological mechanisms – that were constructed for 60 consecutive children and adolescents with PNES who were referred to our Mind-Body Rehabilitation Programme for treatment. As a heuristic framework, we used a contemporary reworking of Janet’s dissociation model: PNES occur in the context of a destabilized neural system and reflect a release of prewired motor programmes following a functional failure in cognitive-emotional executive control circuitry. Using this framework, we clustered the 60 patients into six different subgroups: (1) dissociative PNES (23/60; 38%), (2) dissociative PNES triggered by hyperventilation (32/60; 53%), (3) innate defence responses presenting as PNES (6/60; 10%), (4) PNES triggered by vocal cord adduction (1/60; 2%), (5) PNES triggered by activation of the valsalva manoeuvre (1/60; 1.5%) and (6) PNES triggered by reflex activation of the vagus (2/60; 3%). As described in the companion article, these diagnostic formulations were used, in turn, both to inform the explanations of PNES that we gave to families and to design clinical interventions for helping the children and adolescents gain control of their PNES.

Psychogenic non-epileptic seizures (PNES) - time-limited disturbances of consciousness and motor-sensory control, not accompanied by ictal activity on electroencephalogram (EEG) - are best conceptualized as atypical neurophysiological responses to emotional distress, physiological stressors and danger. Patients and families find the diagnosis of PNES difficult to understand; the transition from neurology (where the diagnosis is made) to mental health services (to which patients are referred for treatment) can be a bumpy one. This study reports how diagnostic formulations constructed for 60 consecutive children and adolescents with PNES were used to inform both the explanations about PNES that were given to them and their families and the clinical interventions that were used to help patients gain control over PNES. Families were able to accept the diagnosis of PNES and engage in treatment when it was explained how emotional distress, illness and states of high arousal could activate atypical defence responses in the body and brain - with PNES being an unwanted by-product of this process. Patients and their families made good use of therapeutic interventions. A total of 75% of children/adolescents (45/60) regained normal function and attained full-time return to school. Global Assessment of Functioning scores increased from 41 to 67 (t(54)=10.09; p<.001). Outcomes were less favourable in children/adolescents who presented with chronic PNES and in those with a chronic, comorbid mental health disorder that failed to resolve with treatment. The study highlights that prompt diagnosis, followed by prompt multidisciplinary assessment, engagement, and treatment, achieves improved outcomes in children/adolescents with PNES.

Orexin, the arousal peptide, originates from neurons located in an area of the dorsal hypothalamus well known for integrating defense responses and their cardiovascular component. Orexin neurons, which are driven in large part by the limbic forebrain, send projections to many regions in the brain, including regions involved in cardiovascular control, as far down as sympathetic preganglionic neurons in the spinal cord. Central injections of orexin evoke sympathetically mediated cardiovascular responses. Conversely, blockade of orexin receptors reduce the cardiovascular responses to acute stressors, preferentially of a psychological nature. More importantly, lasting upregulation of orexin signaling can lead to a hypertensive state. This can be observed in rats exposed to chronic stress as well as in strains known to display spontaneous hypertension such as the spontaneously hypertensive rat (SHR) or the hypertensive BPH/2J Schlager mouse. Thus, there is a link between orexin, stress and hypertension, and orexin upregulation could be a factor in the development of essential hypertension. Orexin receptor antagonists have anti-hypertensive effects that could be of clinical use. (C) 2016 Elsevier Ltd. All rights reserved.

The use of fluorescently-tagged proteins in microscopy has become routine, and anti-GFP (Green fluorescent protein) affinity matrices are increasingly used in proteomics protocols. However, some protein–protein interactions assays, such as protein complementation assays (PCA), require recloning of each protein as a fusion with the different parts of the complementation system. Here we describe a generic system where the complementation is separated from the proteins and can be directly used with fluorescently-tagged proteins. By using nanobodies and performing tests in cell-free expression systems, we accelerated the development of multiple reporters, detecting heterodimers and homodimers or oligomers tagged with GFP or mCherry. We demonstrate that the system can detect interactions at a broad range of concentrations, from low nanomolar up to micromolar.

The midbrain periaqueductal gray (PAG) coordinates the expression and topography of defensive behaviors to threat and also plays an important role in Pavlovian fear learning itself. Whereas the role of PAG in the expression of defensive behavior is well understood, the relationship between the activity of PAG neurons and fear learning, the exact timing of PAG contributions to learning during the conditioning trial, and the contributions of different PAG columns to fear learning are poorly understood. We assessed the effects of optogenetic inhibition of lateral (LPAG) and ventrolateral PAG (VLPAG) neurons on fear learning. Using adenoassociated viral vectors expressing halorhodopsin, we show that brief optogenetic inhibition of LPAG or VLPAG during delivery of the shock unconditioned stimulus (US) augments acquisition of contextual or cued fear conditioning, and we also show that this inhibition augments postencounter defensive responses to a nonnoxious threat. Taken together, these results show that LPAG and VLPAG serve a key role in the regulation of Pavlovian fear learning at the time of US delivery. These findings provide strong support for existing models that state that LPAG and VLPAG contribute to a fear prediction error signal determining variations in the effectiveness of the aversive US in supporting learning.

The midbrain periaqueductal gray (PAG) has been implicated in the generation and transmission of a prediction error signal that instructs amygdala-based fear and extinction learning. However, the PAG also plays a key role in the expression of conditioned fear responses. The evidence for a role of the PAG in fear learning and extinction learning has been obtained almost exclusively using PAG-dependent fear responses. It is less clear whether the PAG regulates fear learning when other measures of learned fear are used. Here we combined a chemogenetic approach, permitting excitation or inhibition of neurons in the ventrolateral PAG (VLPAG), with conditioned suppression as the measure of learned fear to assess the role of VLPAG in the acquisition and extinction of fear learning. We show that chemogenetic excitation of VLPAG (with some encroachment on lateral PAG [LPAG]) impairs acquisition of fear and, conversely, chemogenetic inhibition impairs extinction of fear. These effects on fear and extinction learning were specific to the combination of DREADD expression and injection of CNO because they were observed relative to both eYFP controls injected with CNO as well as DREADD expressing controls injected with vehicle. Taken together, these results show that activity of L/VLPAG neurons regulates both the acquisition and extinction of Pavlovian fear learning.

Psychogenic non-epileptic seizures (PNES) are a common problem in paediatric neurology and psychiatry that can best be understood as atypical responses to threat. Threats activate the body for action by mediating increases in arousal, respiration, and motor readiness. In previous studies, a range of cardiac, endocrine, brain-based, attention-bias, and behavioral measures have been used to demonstrate increases in arousal, vigilance, and motor readiness in patients with PNES. The current study uses respiratory measures to assess both the motor readiness of the respiratory system and the respiratory regulation of CO2. Baseline respiratory rates during clinical assessment and arterial CO2 levels during the hyperventilation component of routine video electroencephalogram were documented in 60 children and adolescents referred for treatment of PNES and in 50 controls. Patients showed elevated baseline respiratory rates [t(78) = 3.34, p = .001], with 36/52 (69%) of patients [vs. 11/28 (39%) controls] falling above the 75th percentile (χ 2 = 6.7343; df = 1; p = .009). Twenty-eight (47%) of patients [vs. 4/50 (8%) controls] showed a skewed hyperventilation-challenge profile—baseline PCO2 <36 mmHg, a trough PCO2 ≤ 20 mmHg, or a final PCO2 <36 mmHg after 15 min of recovery—signaling difficulties with CO2 regulation (χ 2 = 19.77; df = 1; p < .001). Children and adolescents with PNES present in a state of readiness-for-action characterized by high arousal coupled with activation of the respiratory motor system, increases in ventilation, and a hyperventilation-challenge profile shifted downward from homeostatic range. Breathing interventions that target arousal, decrease respiratory rate, and normalize ventilation and arterial CO2 may help patients shift brain–body state and avert PNES episodes.

Orexin makes an important contribution to the regulation of cardiorespiratory function. When injected centrally under anesthesia, orexin increases blood pressure, heart rate, sympathetic nerve activity, and the amplitude and frequency of respiration. This is consistent with the location of orexin neurons in the hypothalamus and the distribution of orexin terminals at all levels of the central autonomic and respiratory network. These cardiorespiratory responses are components of arousal and are necessary to allow the expression of motivated behaviors. Thus, orexin contributes to the cardiorespiratory response to acute stressors, especially those of a psychogenic nature. Consequently, upregulation of orexin signaling, whether it is spontaneous or environmentally induced, can increase blood pressure and lead to hypertension, as is the case for the spontaneously hypertensive rat and the hypertensive BPH/2J Schlager mouse. Blockade of orexin receptors will reduce blood pressure in these animals, which could be a new pharmacological approach for the treatment of some forms of hypertension. Orexin can also magnify the respiratory reflex to hypercapnia in order to maintain respiratory homeostasis, and this may be in part why it is upregulated during obstructive sleep apnea. In this pathological condition, blockade of orexin receptors would make the apnea worse. To summarize, orexin is an important modulator of cardiorespiratory function. Acting on orexin signaling may help in the treatment of some cardiovascular and respiratory disorders.

BPH/2J mice are a genetic model of hypertension associated with an overactive sympathetic nervous system. Orexin is a neuropeptide which influences sympathetic activity and blood pressure. Orexin precursor mRNA expression is greater in hypothalamic tissue of BPH/2J compared with normotensive BPN/3J mice. To determine whether enhanced orexinergic signaling contributes to the hypertension, BPH/2J and BPN/3J mice were preimplanted with radiotelemetry probes to compare blood pressure 1 hour before and 5 hours after administration of almorexant, an orexin receptor antagonist. Mid frequency mean arterial pressure power and the depressor response to ganglion blockade were also used as indicators of sympathetic nervous system activity. Administration of almorexant at 100 (IP) and 300 mg/kg (oral) in BPH/2J mice during the dark-active period (2 hours after lights off) markedly reduced blood pressure (−16.1±1.6 and −11.0±1.1 mm Hg, respectively; P <0.001 compared with vehicle). However, when almorexant (100 mg/kg, IP) was administered during the light-inactive period (5 hours before lights off) no reduction from baseline was observed ( P =0.64). The same dose of almorexant in BPN/3J mice had no effect on blood pressure during the dark ( P =0.79) or light periods ( P =0.24). Almorexant attenuated the depressor response to ganglion blockade ( P =0.018) and reduced the mid frequency mean arterial pressure power in BPH/2J mice ( P <0.001), but not BPN/3J mice ( P =0.70). Immunohistochemical labeling revealed that BPH/2J mice have 29% more orexin neurons than BPN/3J mice which are preferentially located in the lateral hypothalamus. The results suggest that enhanced orexinergic signaling contributes to sympathetic overactivity and hypertension during the dark period in BPH/2J mice.