Targeting the lateral hypothalamus with short hairpin RNAs reduces habitual behaviour following extended instrumental training in rats.

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.

Behavioural and cardiovascular effects of orexin-A infused into the central amygdala under basal and fear conditions in rats.

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.

Social defeat: Vagal reduction and vulnerability to ventricular arrhythmias.

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.

Mitochondrial uncoupler BAM15 reverses diet-induced obesity and insulin resistance in mice.

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.

Vulnerability to stress consequences induced by repeated social defeat in rats: Contribution of the angiotensin II type 1 receptor in cardiovascular alterations associated to low brain derived neurotrophic factor.

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.

Regulatory T Cells and Their Derived Cytokine, Interleukin-35, Reduce Pain in Experimental Autoimmune Encephalomyelitis.

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.

Adaptation of Respiratory-Related Brain Regions to Long-Term Hypercapnia: Focus on Neuropeptides in the RTN.

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 preBötC and 30% of BötC 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 in children and adolescents: Part I - Diagnostic formulations.

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 in children and adolescents: Part II - explanations to families, treatment, and group outcomes.

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.

A Split-Luciferase Reporter Recognizing GFP and mCherry Tags to Facilitate Studies of Protein-Protein Interactions.

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.

Brief optogenetic inhibition of rat lateral or ventrolateral periaqueductal gray augments the acquisition of Pavlovian fear conditioning.

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. (PsycINFO Database Record

Effects of chemogenetic excitation or inhibition of the ventrolateral periaqueductal gray on the acquisition and extinction of Pavlovian fear conditioning.

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.

The respiratory control of carbon dioxide in children and adolescents referred for treatment of psychogenic non-epileptic seizures.

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 and Central Modulation of Cardiovascular and Respiratory Function.

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.

Orexin, Stress and Central Cardiovascular Control. A Link with Hypertension?

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.

Peripheral and Central Neuroinflammatory Changes and Pain Behaviors in an Animal Model of Multiple Sclerosis.

Pain is a widespread and debilitating symptom of multiple sclerosis (MS), a chronic inflammatory demyelinating disease of the central nervous system. Although central neuroinflammation and demyelination have been implicated in MS-related pain, the contribution of peripheral and central mechanisms during different phases of the disease remains unclear. In this study, we used the animal model experimental autoimmune encephalomyelitis (EAE) to examine both stimulus-evoked and spontaneous pain behaviors, and neuroinflammatory changes, over the course of chronic disease. We found that mechanical allodynia of the hind paw preceded the onset of clinical EAE but was unmeasurable at clinical peak. This mechanical hypersensitivity coincided with increased microglial activation confined to the dorsal horn of the spinal cord. The development of facial mechanical allodynia also emerged in preclinical EAE, persisted at the clinical peak, and corresponded with pathology of the peripheral trigeminal afferent pathway. This included T cell infiltration, which arose prior to overt central lesion formation and specific damage to myelinated neurons during the clinical peak. Measurement of spontaneous pain using the mouse grimace scale, a facial expression-based coding system, showed increased facial grimacing in mice with EAE during clinical disease. This was associated with multiple peripheral and central neuroinflammatory changes including a decrease in myelinating oligodendrocytes, increased T cell infiltration, and macrophage/microglia and astrocyte activation. Overall, these findings suggest that different pathological mechanisms may underlie stimulus-evoked and spontaneous pain in EAE, and that these behaviors predominate in unique stages of the disease.

Olfactory ensheathing cells but not fibroblasts reduce the duration of autonomic dysreflexia in spinal cord injured rats.

Autonomic dysreflexia is a common complication after high level spinal cord injury and can be life-threatening. We have previously shown that the acute transplantation of olfactory ensheathing cells into the lesion site of rats transected at the fourth thoracic spinal cord level reduced autonomic dysreflexia up to 8weeks after spinal cord injury. This beneficial effect was correlated with changes in the morphology of sympathetic preganglionic neurons despite the olfactory cells surviving no longer than 3weeks. Thus the transitory presence of olfactory ensheathing cells at the injury site initiated long-term functional as well as morphological changes in the sympathetic preganglionic neurons. The primary aim of the present study was to evaluate whether olfactory ensheathing cells survive after transplantation within the parenchyma close to sympathetic preganglionic neurons and whether, in this position, they still reduce the duration of autonomic dysreflexia and modulate sympathetic preganglionic neuron morphology. The second aim was to quantify the density of synapses on the somata of sympathetic preganglionic neurons with the hypothesis that the reduction of autonomic dysreflexia requires synaptic changes. As a third aim, we evaluated the cell type-specificity of olfactory ensheathing cells by comparing their effects with a control group transplanted with fibroblasts. Animals transplanted with OECs had a faster recovery from hypertension induced by colorectal distension at 6 and 7weeks but not at 8weeks after T4 spinal cord transection. Olfactory ensheathing cells survived for at least 8weeks and were observed adjacent to sympathetic preganglionic neurons whose overall number of primary dendrites was reduced and the synaptic density on the somata increased, both caudal to the lesion site. Our results showed a long term cell type-specific effects of olfactory ensheathing cells on sympathetic preganglionic neurons morphology and on the synaptic density on their somata, and a transient cell type-specific reduction of autonomic dysreflexia.

The organization of defensive behavior elicited by optogenetic excitation of rat lateral or ventrolateral periaqueductal gray.

Rodents display characteristic defense responses to predators that are influenced by predatory imminence. The midbrain periaqueductal gray (PAG) serves an important role controlling these responses. The most influential model states that variations in defensive topography are due to distinct PAG regions: ventrolateral PAG (VLPAG) controls postencounter defense, such as freezing and immobility, whereas lateral PAG (LPAG) controls circa-strike defense, such as escape and flight. Here we used channel rhodopsin (ChR2) stimulation to probe the structure of defensive behavior controlled by LPAG and VLPAG. Suprathreshold LPAG stimulation evoked circa-strike defense that was replaced by freezing at stimulation offset. Suprathreshold VLPAG stimulation evoked postencounter--freezing and immobility--but never circa-strike defense. More interestingly, the topography of defensive behavior evoked from LPAG scaled with variations in 465 nm light power. As light power increased, LPAG animals expressed the full defensive syntax of freezing then activity then flight characteristic of increasing predatory imminence. In contrast, the frequency, not topography, of defensive behavior evoked from VLPAG scaled with variations in light power. These findings suggest that LPAG and VLPAG can control variations in defense with increasing predatory imminence in 2 ways. First, consistent with past models, topographical variation can be assembled from different defensive responses controlled by the LPAG (circa-strike) and VLPAG (postencounter). Second, topographical variation can be assembled from variations in LPAG activity itself. (PsycINFO Database Record

Long-lasting bradypnea induced by repeated social defeat.

Repeated social defeat in the rat induces long-lasting cardiovascular changes associated with anxiety. In this study, we investigated the effects of repeated social defeat on breathing. Respiratory rate was extracted from the respiratory sinus arrhythmia (RSA) peak frequency of the ECG in rats subjected to social defeat for 4 consecutive days. Respiratory rate was recorded under anesthesia 6 days (D+10) or 26 days (D+30) after social defeat. At D+10, defeated (D) rats spent less time in the open arms of the elevated plus maze test, had heavier adrenal glands, and displayed bradypnea, unlike nondefeated animals. At D+30, all signs of anxiety had disappeared. However, one-half of the rats still displayed bradypnea (DL rats, for low respiratory rate indicated by a lower RSA frequency), whereas those with higher respiratory rate (DH rats) had recovered. Acute blockade of the dorsomedial hypothalamus (DMH) or nucleus tractus solitarii (NTS) 5-HT3 receptors reversed bradypnea in all D rats at D+10 and in DL rats at D+30. Respiratory rate was also recorded in conscious animals implanted with radiotelemetric ECG probes. DH rats recovered between D+10 and D+18, whereas DL rats remained bradypneic until D+30. In conclusion, social stress induces sustained chronic bradypnea mediated by DMH neurons and NTS 5-HT3 receptors. These changes are associated with an anxiety-like state that persists until D+10, followed by recovery. However, bradypnea may persist in one-half of the population up until D+30, despite apparent recovery of the anxiety-like state.

Contribution of Orexin to the Neurogenic Hypertension in BPH/2J Mice.

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.