The effect of heterotopic noxious conditioning stimulation on Aδ‐, C‐ and Aβ‐fibre brain responses in humans

Human studies have shown that heterotopic nociceptive conditioning stimulation (HNCS) applied to a given body location reduces the percept and brain responses elicited by noxious test stimuli delivered at a remote body location. It remains unclear to what extent this effect of HNCS relies on the spinal–bulbar–spinal loop mediating the effect of diffuse noxious inhibitory controls (DNICs) described in animals, and/or on top‐down cortical mechanisms modulating nociception. Importantly, some studies have examined the effects of HNCS on the brain responses to nociceptive input conveyed by Aδ‐fibres. In contrast, no studies have explored the effects of HNCS on the responses to selective nociceptive C‐fibre input and non‐nociceptive Aβ‐fibre input. In this study, we measured the intensity of perception and event‐related potentials (ERPs) to stimuli activating Aδ‐, C‐ and Aβ‐fibres, before, during and after HNCS, obtained by immersing one foot in painful cold water. We observed that (i) the perceived intensity of nociceptive Aδ‐ and C‐stimuli was reduced during HNCS, and (ii) the ERPs elicited by Aδ‐ and Aβ‐ and C‐stimuli were also reduced during HNCS. Importantly, because Aβ‐ERPs are related to primary afferents that ascend directly through the dorsal columns without being relayed at spinal level, the modulation of these responses may not be explained by an influence of descending projections modulating the transmission of nociceptive input at spinal level. Therefore, our results indicate that, in humans, HNCS should be used with caution as a direct measure of DNIC‐related mechanisms.     

Venlafaxine and oxycodone effects on human spinal and supraspinal pain processing: a randomized cross‐over trial

Severe pain is often treated with opioids. Antidepressants that inhibit serotonin and norepinephrine reuptake (SNRI) have also shown a pain relieving effect, but for both SNRI and opioids, the specific mode of action in humans remains vague. This study investigated how oxycodone and venlafaxine affect spinal and supraspinal pain processing. Twenty volunteers were included in this randomized cross‐over study comparing 5‐day treatment with venlafaxine, oxycodone and placebo. As a proxy of the spinal pain transmission, the nociceptive withdrawal reflex (NWR) to electrical stimulation on the sole of the foot was recorded at the tibialis anterior muscle before and after 5 days of treatment. For the supraspinal activity, 61‐channel electroencephalogram evoked potentials (EPs) to the electrical stimulations were simultaneously recorded. Areas under curve (AUCs) of the EMG signals were analyzed. Latencies and AUCs were computed for the major EP peaks and brain source analysis was done. The NWR was decreased in venlafaxine arm (P = 0.02), but the EP parameters did not change. Oxycodone increased the AUC of the EP response (P = 0.04). Oxycodone also shifted the cingulate activity anteriorly in the mid‐cingulate‐operculum network (P < 0.01), and the cingulate activity was increased while the operculum activity was decreased (P = 0.02). Venlafaxine exerts its effects on the modulation of spinal nociceptive transmission, which may reflect changes in balance between descending inhibition and descending facilitation. Oxycodone, on the other hand, exerts its effects at the cortical level. This study sheds light on how opioids and SNRI drugs modify the human central nervous system and where their effects dominate.     

Involvement of spinal α2‐adrenoceptors in prolonged modulation of hind limb withdrawal reflexes following acute noxious stimulation in the anaesthetized rabbit

The role of spinal α ₂‐adrenoceptors in mediating long‐lasting modulation of hind limb withdrawal reflexes following acute noxious chemical stimulation of distant heterotopic and local homotopic locations has been investigated in pentobarbitone‐anaesthetized rabbits. Reflexes evoked in the ankle extensor muscle medial gastrocnemius (MG) by electrical stimulation of the ipsilateral heel, and reflexes elicited in the ankle flexor tibialis anterior and the knee flexor semitendinosus by stimulation at the base of the ipsilateral toes, could be inhibited for over 1 h after mustard oil (20%) was applied to either the snout or into the contralateral MG. The heel–MG response was also inhibited after applying mustard oil across the plantar metatarsophalangeal joints of the ipsilateral foot, whereas this homotopic stimulus facilitated both flexor responses. Mustard oil also caused a significant pressor effect when applied to any of the three test sites. The selective α₂‐adrenoceptor antagonist, RX 821002 (100–300 μg, intrathecally), had no effect on reflexes per se, but did cause a decrease in mean arterial blood pressure. In the presence of the α₂‐blocker, inhibitory and facilitatory effects of mustard oil on reflexes were completely abolished. These data imply that long‐lasting inhibition of spinal reflexes following acute noxious stimulation of distant locations involves activation of supraspinal noradrenergic pathways, the effects of which are dependent on an intact α₂‐adrenoceptor system at the spinal level. These pathways and receptors also appear to be involved in facilitation (sensitization) as well as inhibition of reflexes following a noxious stimulus applied to the same limb.     

Tumor necrosis factor enhances the sleep‐like state and electrical stimulation induces a wake‐like state in co‐cultures of neurons and glia

We characterise sleep‐like states in cultured neurons and glia during development in vitro as well as after electrical stimulation, the addition of tumor necrosis factor alpha (TNF), and the combination of TNF plus electrical stimulation. We also characterise optogenetic stimulation‐induced ATP release and neuronal interleukin‐1 and TNF expression in vitro demonstrating the activity dependence of these putative sleep‐regulatory substances. Action potential (AP) burstiness, expressed as the burstiness index (BI), synchronization of slow electrical potentials between recording electrodes (SYN), and slow wave (SW) power (0.25–3.75 Hz) determined using fast Fourier analyses emerged as network properties, maturing after 2 weeks in culture. Homologous in vivo measures are used to characterise sleep. Electrical stimulation reduced the BI, SYN and SW power values during and/or after the stimulus period. One day later, homeostasis was evident from rebounds of SYN and SW power values to above baseline levels; the magnitude of the rebound was stimulus pattern‐dependent. The addition of TNF enhanced BI, SYN and SW power values, suggesting the induction of a deeper sleep‐like state. Electrical stimulation reversed these TNF effects, suggesting the network state was more wake‐like. The day after TNF plus electrical stimulation, the changes in SYN and SW power values were dependent upon the stimulus patterns the cells received the day before. We conclude that sleep and wake states in cultured in vitro networks can be controlled and they share molecular regulatory mechanisms with local in vivo networks. Further, sleep is an activity‐dependent emergent local network property.     

Brain‐Derived Neurotrophic Factor and Substrate Utilization Following Acute Aerobic Exercise in Obese Individuals

Brain‐derived neurotrophic factor (BDNF) serves as a vital regulator of neuronal proliferation and survival, and has been shown to regulate energy homeostasis, glucose metabolism and body weight maintenance. Elevated concentrations of plasma BDNF have been associated with obesity and type 2 diabetes mellitus. Acute aerobic exercise transiently increases circulating BDNF, potentially correcting obesity‐related metabolic impairment. The present study aimed to compare acute aerobic exercise elicited BDNF responses in obese and normal‐weight subjects. Furthermore, we aimed to investigate whether acute exercise‐induced plasma BDNF elevations would be associated with improved indices of insulin resistance, as well as substrate utilization [carbohydrate oxidation (CHOoxi) and fat oxidation (FAToxi)]. Twenty‐two healthy, untrained subjects [11 obese (four men and seven women; age = 22.91 ± 4.44 years; body mass index = 35.72 ± 4.17 kg/m²) and 11 normal‐weight (five men and six women; age = 23.27 ± 2.24 years; body mass index = 21.89 ± 1.63 kg/m²)] performed 30 min of continuous submaximal aerobic exercise at 75% maximal oxygen consumption. Our analyses showed that the BDNF response to acute aerobic exercise was similar in obese and normal‐weight subjects across time (time: P = 0.015; group: P = not significant) and was not associated with indices of IR. Although no differences in the rates of CHOoxi and FAToxi were found between both groups, total relative energy expenditure was significantly lower in obese subjects compared to normal‐weight subjects (3.53 ± 0.25 versus 5.59 ± 0.85; P < 0.001). These findings suggest that acute exercise‐elicited BDNF elevation may not be sufficient to modulate indices of IR or the utilization of either carbohydrates or fats in obese individuals.     

Inhibition of Cortical Laser‐Evoked Potentials by Transcutaneous Electrical Nerve Stimulation

Objectives. This study attempts to confirm the hypothesis that transcutaneous electrical stimulation (TENS) of peripheral Aβ fibers inhibits nociceptive processing, by quantifying the change of laser‐evoked potential (LEP) components, using a 980‐nm diode laser. Materials and Methods. Cutaneous heat stimuli were delivered to the dorsum of the right hand in 13 volunteers. LEPs and pain intensity ratings were recorded before, during, and after the use of TENS (110 Hz) at the dorsolateral forearm. Area under the curve (AUC), LEP amplitudes (N2P2), and peak latencies (N2, P2) were calculated. The paired samples t‐test was used for statistical analysis. Results. A significant reduction of LEP amplitudes and AUC was found during and after the use of TENS (p < 0.05). After 10 min of TENS this was associated with a clinically relevant decrease of pain intensity. Conclusions. Our data suggest that TENS inhibits nociceptive processing. Ten minutes of TENS exerts a clinically relevant pain reduction.     

Lentivirus‐Mediated α‐Melanocyte‐Stimulating Hormone Overexpression in the Hypothalamus Decreases Diet Induced Obesity in Mice

Melanocyte stimulating hormone (MSH) derived from the pro‐hormone pro‐opiomelanocortin (POMC) has potent effects on metabolism and feeding that lead to reduced body weight in the long‐term. To determine the individual roles of POMC derived peptides and their sites of action, we created a method for the delivery of single MSH peptides using lentiviral vectors and studied the long‐term anti‐obesity effects of hypothalamic α‐MSH overexpression in mice. An α‐MSH lentivirus (LVi‐α‐MSH‐EGFP) vector carrying the N‘‐terminal part of POMC and the α‐MSH sequence was generated and shown to produce bioactive peptide in an in vitro melanin synthesis assay. Stereotaxis was used to deliver the LVi‐α‐MSH‐EGFP or control LVi‐EGFP vector to the arcuate nucleus (ARC) of the hypothalamus of male C57Bl/6N mice fed on a high‐fat diet. The effects of 6‐week‐treatment on body weight, food intake, glucose tolerance and organ weights were determined. Additionally, a 14‐day pairfeeding study was conducted to assess whether the weight decreasing effect of the LVi‐α‐MSH‐EGFP treatment is dependent on decreased food intake. The 6‐week LVi‐α‐MSH‐EGFP treatment reduced weight gain (8.4 ± 0.4 g versus 12.3 ± 0.6 g; P < 0.05), which was statistically significant starting from 1 week after the injections. The weight of mesenteric fat was decreased and glucose tolerance was improved compared to LVi‐EGFP treated mice. Food intake was decreased during the first week in the LVi‐α‐MSH‐EGFP treated mice but subsequently increased to the level of LVi‐EGFP treated mice. The LVi‐EGFP injected control mice gained more weight even when pairfed to the level of food intake by LVi‐α‐MSH‐EGFP treated mice. We demonstrate that gene transfer of α‐MSH, a single peptide product of POMC, into the ARC of the hypothalamus, reduces obesity and improves glucose tolerance, and that factors other than decreased food intake also influence the weight decreasing effects of α‐MSH overexpression in the ARC. Furthermore, viral MSH vectors delivered stereotaxically provide a novel tool for further exploration of chronic site‐specific effects of POMC peptides.     

Repetitive noxious neonatal stimuli increases dentate gyrus cell proliferation and hippocampal brain‐derived neurotrophic factor levels

Neonatal noxious stimulation has been proposed to model pain triggered by diagnostic/therapeutic invasive procedures in premature infants. Previous studies have shown that hippocampal neurogenesis rate and the behavioral repertoire of adult rats may be altered by neonatal noxious stimuli. The purpose of this study was to evaluate whether noxious stimulation during neonatal period alters the nociceptive response and dentate gyrus neurogenesis when compared to rats subjected to a single noxious stimulus in late infancy. Plasma corticosterone and hippocampal brain‐derived neurotrophic factor (BDNF) levels were measured. Neurogenesis in the dentate gyrus was evaluated in adolescent rats (postnatal day 40; P40) exposed twice to intra‐plantar injections of Complete Freund's adjuvant (CFA) on P1 and P21 (group P1P21) or P8 and P21 (P8P21) or exposed once on P21 (pubertal). On P21, one subset of animals received 5‐bromo‐2′‐deoxyuridine (BrdU) and was euthanized on P40 for identification of proliferating cells in the dentate gyrus. Another subset was sampled for thermal response or plasma corticosterone measurement and hippocampal BDNF levels. Proliferative cell rate in dentate gyrus was the highest in all re‐exposed groups (P < 0.001), except for P8 females (P8P21F), revealing also a sex difference, where P8P21 males showed higher rate than females (P < 0.001). Stimulated groups took longer than CTL animals to lick the paws (P < 0.001), regardless of the age when the noxious stimulus was applied. Re‐exposed groups had lower corticosterone plasma level (P1P21 M and F, P8P21M) than controls. On the contrary, hippocampal BDNF was increased in males from both re‐exposed groups. These results show that infant noxious stimulation in neonatally previously stimulated rats is related to high proliferation in the DG and this association seems to be modified by the animal's sex. The new generated dentate granule cells in the hippocampus may have a role in the long‐term behavioral responses to neonatal nociceptive stimulation. Noxious stimulation in the neonatal period results in sex‐dependent neurogenic response. © 2013 Wiley Periodicals, Inc.     

Neurones in the Preoptic Area of the Male Goldfish are Activated by a Sex Pheromone 17α,20β‐Dihydroxy‐4‐Pregnen‐3‐One

Pheromones are interesting molecules given their ability to evoke changes in the endocrine state and behaviours of animals. In goldfish, a sex pheromone, 17α,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20β‐P), which is released by preovulatory females, is known to trigger the elevation of luteinising hormone (LH) levels, as well as reproductive behaviour in males. Interestingly, when 11‐ketotestosterone (11‐KT) is implanted into adult female fish, LH levels increase in response to the pheromone at any time of the day, which is normally a male‐specific response. However, the neural mechanisms underlying the male‐specific information processing of 17,20β‐P and its androgen dependence are yet unknown. In the present study, we focused on the preoptic area (POA), which plays important roles in the regulation of reproduction and reproductive behaviours. We mapped activity in the POA evoked by 17,20β‐P exposure using the immediate‐early gene c‐fos. We found that a population of ventral POA neurones close to kisspeptin2 (kiss2) neurones that appear to have important roles in reproduction was activated by 17,20β‐P exposure, suggesting that these activated neurones are important for the 17,20β‐P response. Next, we investigated the distribution of androgen receptor (ar) in the POA and its relationship with 17,20β‐P‐responsive and kiss2 neurones. We found that ar is widely expressed in the ventral POA, whereas it is only expressed in approximately 10% of 17,20β‐P‐activated neurones. On the other hand, it is expressed in almost 90% of the kiss2 neurones. Taken together, it is possible that ar expressing neurones in the ventral POA, most of which were not labelled by c‐fos in the present study, may at least partly account for androgen effects on responses to primer pheromones; the ar‐positive kiss2 neurones in the ventral POA may be a candidate. These results offer a novel insight into the mechanisms underlying male‐specific information processing of 17,20β‐P in goldfish.     

Peripheral Nerve Stimulation Inhibits Nociceptive Processing: An Electrophysiological Study in Healthy Volunteers

Objectives. Electric peripheral nerve stimulation (PNS) is a neuromodulatory therapy in pain patients. The efficacy of this neurosurgical pain treatment is controversial because its antinociceptive effect in humans has not been objectively proven so far. Materials and Methods. Noxious infrared laser stimulation of the left hand dorsum evoked cortical potentials (LEP) by selective excitation of Aδ‐fiber nociceptors in 15 healthy volunteers under control and PNS conditions. LEP were recorded before, during, and after electric Aβ‐fiber stimulation (PNS) of the left superficial radial nerve. In the control session LEP were recorded without PNS. Laser stimulus intensity ratings, LEP latencies, and amplitudes were statistically analyzed (anova ). Results. During PNS, LEP amplitudes (p < 0.001) and laser intensity ratings (p < 0.05) significantly decreased, and LEP latencies significantly increased (p < 0.05). Under control conditions LEP and intensity ratings remained unchanged. Conclusions. The electrophysiologic data provide evidence that electric stimulation of peripheral Aβ‐fibers reliably suppresses Aδ‐fiber nociceptive processing in human volunteers.     

Differential activation of the human trigeminal nuclear complex by noxious and non‐noxious orofacial stimulation

There is good evidence from animal studies for segregation in the processing of non‐nociceptive and nociceptive information within the trigeminal brainstem sensory nuclear complex. However, it remains unknown whether a similar segregation occurs in humans, and a recent tract tracing study suggests that this segregation may not exist. We used functional magnetic resonance imaging (fMRI) to define and compare activity patterns of the trigeminal brainstem nuclear complex during non‐noxious and noxious cutaneous and non‐noxious and noxious muscle orofacial stimulation in humans. We found that during cutaneous pain, signal intensity increased within the entire rostrocaudal extent of the spinal trigeminal nucleus (SpV), encompassing the ipsilateral oralis (SpVo), interpolaris (SpVi) and caudalis (SpVc) subdivisions. In contrast, muscle pain did not activate SpVi, but instead activated a discrete region of the ipsilateral SpVo and SpVc. Further, muscle noxious stimulation activated a region of the ipsilateral lateral pons in the region of the trigeminal principal sensory nucleus (Vp). Innocuous orofacial stimulation (lip brushing) also evoked a significant increase in signal intensity in the ipsilateral Vp; however, non‐noxious muscle stimulation showed no increase in signal in this area. The data reveal that orofacial cutaneous and muscle nociceptive information and innocuous cutaneous stimulation are differentially represented within the trigeminal nuclear complex. It is well established that cutaneous and muscle noxious stimuli evoke different perceptual, behavioural and cardiovascular changes. We speculate that the differential activation evoked by cutaneous and muscle noxious stimuli within the trigeminal sensory complex may contribute to the neural basis for these differences. Hum Brain Mapp, 2009. © 2009 Wiley‐Liss, Inc.     

Efficacy,safety, and tolerability of perampanel in Asian and non‐Asian patients with epilepsy

People of different ethnic or racial backgrounds may experience variations in pharmacokinetic and pharmacodynamic responses to drug therapies. Our post hoc analysis evaluated the efficacy, safety, and tolerability of perampanel in Asian and non‐Asian populations with refractory focal seizures with or without focal to bilateral tonic‐clonic (FBTC) seizures. This analysis pooled data from 4 randomized, placebo‐controlled, phase‐3 studies involving patients aged ≥12 years who have focal seizures with or without FBTC seizures. Patients were receiving 2, 4, 8, or 12 mg perampanel (or placebo) by the end of a 6‐week titration period and for a further 13 weeks during the maintenance phase. Efficacy endpoints included median percent change in seizure frequency per 28 days, and 50% and seizure‐freedom responder rates relative to baseline. The median percent change in seizure frequency per 28 days from baseline was significantly greater than placebo for perampanel 8 and 12 mg (?31.1% and ?38.1% change, respectively; each P < 0.0001) in the Asian population, and for perampanel 4, 8, and 12 mg (?21.1% [P = 0.0001], ?26.3% [P < 0.0001], and ?27.7% [P = 0.0001] change, respectively) in the non‐Asian population. The 50% responder rate relative to baseline was significantly greater than placebo for perampanel 8 and 12 mg (40.1% and 43.8%, respectively; each P < 0.0001) in the Asian population, and for perampanel 4, 8, and 12 mg (29.4% [P = 0.0002], 32.8% [P < 0.0001] and 34.5% [P = 0.0001]), respectively, in the non‐Asian population. Seizure‐freedom rate among all patients was 4.9%‐11.7% for perampanel 2, 4, 8, and 12 mg. The most frequently reported treatment‐emergent adverse events (TEAEs) across both populations were dizziness, somnolence, irritability, headache, and fatigue. The most common psychiatric TEAEs were aggression and irritability. Perampanel demonstrated a favorable and similar risk‐benefit profile in both Asian and non‐Asian populations with refractory focal seizures.     

Chronic high‐caloric diet modifies sleep homeostasis in mice

Obesity prevalence and sleep habit changes are commonplace nowadays, due to modern lifestyle. A bidirectional relationship likely exists between sleep quality and metabolic disruptions, which could impact quality of life. In our study, we investigated the effects of a chronic high‐caloric diet on sleep architecture and sleep regulation in mice. We studied the effect of 3 months high‐caloric diet (HCD, 45% fat) on sleep and the sleep electroencephalogram (EEG) in C57BL/6J mice during 24‐hr baseline (BL) recordings, and after 6‐hr sleep deprivation (SD). We examined the effect of HCD on sleep homeostasis, by performing parameter estimation analysis and simulations of the sleep homeostatic Process S, a measure of sleep pressure, which is reflected in the non‐rapid‐eye‐movement (NREM) sleep slow‐wave‐activity (SWA, EEG power density between 0.5 and 4.0 Hz). Compared to controls (n = 11, 30.7 ± 0.8 g), mice fed with HCD (n = 9, 47.6 ± 0.8 g) showed an increased likelihood of consecutive NREM‐REM sleep cycles, increased REM sleep and decreased NREM sleep EEG SWA. After SD, these effects were more pronounced. The simulation resulted in a close fit between the time course of SWA and Process S in both groups. HCD fed mice had a slower time constant (T_i = 15.98 hr) for the increase in homeostatic sleep pressure compared with controls (5.95 hr) indicating a reduced effect of waking on the increase in sleep pressure. Our results suggest that chronic HCD consumption impacts sleep regulation.     

Supraspinal influences on nociceptive flexion reflex and pain sensation in man

The sensation of pain and the nociceptive flexion reflex of the biceps femoris muscle (RIII, Bi) elicited by electrical stimulation of the ipsilateral sural nerve were studied in human during 4 conditions: (1) a mental task; (2) a stress; (3) during noxious stimulation of the contralateral ulnar nerve; (4) after an intense noxious stimulation of the sural nerve itself. An inhibition of both pain sensation and RIII, Bi was observed in (1), while a facilitation of these parameters was noted in (2). In contrast, no change in RIII, Bi occurred in (3) while the pain sensation was inhibited. In (4), just after the noxious stimulation, there was a marked facilitation of RIII, Bi associated with increased pain sensation. However, 10--12 sec later, the pain sensation returned to its control values, while the RIII, Bi reflex was still facilitated. The latter recovered to its control values 28--30 sec later. These results show the possibility of a dissociation between afferent ascending nociceptive messages and nociceptive motor activity (in 3 and 4). They suggest that supraspinal descending influences can act differently on spinal dorsal horn neurons in the case of pain ascending volleys, and in the case of spinal nociceptive motor activity.     

Long‐term progressive motor skill training enhances corticospinal excitability for the ipsilateral hemisphere and motor performance of the untrained hand

It is well established that unilateral motor practice can lead to increased performance in the opposite non‐trained hand. Here, we test the hypothesis that progressively increasing task difficulty during long‐term skill training with the dominant right hand increase performance and corticomotor excitability of the left non‐trained hand. Subjects practiced a visuomotor tracking task engaging right digit V for 6 weeks with either progressively increasing task difficulty (PT) or no progression (NPT). Corticospinal excitability (CSE) was evaluated from the resting motor threshold (rMT) and recruitment curve parameters following application of transcranial magnetic stimulation (TMS) to the ipsilateral primary motor cortex (iM1) hotspot of the left abductor digiti minimi muscle (ADM). PT led to significant improvements in left‐hand motor performance immediately after 6 weeks of training (63 ± 18%, P < 0.001) and 8 days later (76 ± 14%, P < 0.001). In addition, PT led to better task performance compared to NPT (19 ± 15%, P = 0.024 and 27 ± 15%, P = 0.016). Following the initial training session, CSE increased across all subjects. After 6 weeks of training and 8 days later, only PT was accompanied by increased CSE demonstrated by a left and upwards shift in the recruitment curves, e.g. indicated by increased MEP_max (P = 0.012). Eight days after training similar effects were observed, but 14 months later motor performance and CSE were similar between groups. We suggest that progressively adjusting demands for timing and accuracy to individual proficiency promotes motor skill learning and drives the iM1‐CSE resulting in enhanced performance of the non‐trained hand. The results underline the importance of increasing task difficulty progressively and individually in skill learning and rehabilitation training.     

High Cortisol Response to Adrenocorticotrophic Hormone Identifies Ewes with Reduced Melanocortin Signalling and Increased Propensity to Obesity

We have identified female sheep that have either high (HR) or low (LR) cortisol responses to adrenocorticotrophin. On a high‐energy diet, HR have greater propensity to weight gain and obesity, although the underlying mechanisms remain to be determined. Hypothalamic appetite‐regulating peptides (ARP) exert reciprocal effects on food intake and energy expenditure. We aimed to quantify the expression and function of ARP in LR and HR ewes (n = 4 per group). Gene expression for neuropeptide Y (NPY), agouti‐related peptide (AgRP) pro‐opiomelanocortin (POMC), melanin‐concentrating hormone (MCH), orexin and the melanocortin receptors (MC3R and MC4R) was measured by in situ hybridisation. Expression of NPY, AgRP and POMC was similar in HR and LR, although expression of orexin, MCH, MC3R and MC4R was higher (P < 0.05) in LR. Intracerebroventricular infusions of a low dose (50 μg/h) of NPY, α‐melanocyte‐stimulating hormone (αMSH), orexin and MCH were performed between 10.00 h and 16.00 h in meal‐fed ewes (n = 6–7 per group). Skeletal muscle and retroperitoneal (RP) fat temperatures were recorded using dataloggers. Post‐prandial thermogenesis in muscle was higher (P < 0.05) in LR. There was little effect of ARP infusion on muscle or fat temperature in either group. Infusion of these doses of NPY, MCH or orexin did not stimulate food intake in meal‐fed ewes, although αMSH reduced (P < 0.01) food intake in LR only. Using 24‐h ARP infusions with ad lib. feeding, NPY increased (P < 0.001) food intake in both groups but αMSH was only effective in LR (P < 0.05). In summary, we show that HR are resistant to the satiety effects of αMSH and this coincides with a reduced expression of both the MC3R and MC4R in the paraventricular nucleus of the hypothalamus. We conclude that an increased propensity to obesity in HR female sheep is associated with reduced melanocortin signalling.     

The effects of subthalamic deep brain stimulation on mechanical and thermal thresholds in 6OHDA‐lesioned rats

Chronic pain is a major complaint for up to 85% of Parkinson's disease patients; however, it often not identified as a symptom of Parkinson's disease. Adequate treatment of motor symptoms often provides analgesic effects in Parkinson's patients but how this occurs remains unclear. Studies have shown both Parkinson's patients and 6‐hydroxydopamine‐lesioned rats exhibit decreased sensory thresholds. In humans, some show improvements in these deficits after subthalamic deep brain stimulation, while others report no change. Differing methods of testing and response criteria may explain these varying results. We examined this effect in 6‐hydroxydopamine‐lesioned rats. Sprague–Dawley rats were unilaterally implanted with subthalamic stimulating electrodes in the lesioned right hemisphere and sensory thresholds were tested using von Frey, tail‐flick and hot‐plate tests. Tests were done during and off subthalamic stimulation at 50 and 150 Hz to assess its effects on sensory thresholds. The 6‐hydroxydopamine‐lesioned animals exhibited lower mechanical (left paw, P < 0.01) and thermal thresholds than shams (hot plate, P < 0.05). Both 50 and 150 Hz increased mechanical (left paw; P < 0.01) and thermal thresholds in 6‐hydroxydopamine‐lesioned rats (hot‐plate test: 150 Hz, P < 0.05, 50 Hz, P < 0.01). Interestingly, during von Frey testing, low‐frequency stimulation provided a more robust improvement in some 6OHDA lesioned rats, while in others, the magnitude of improvement on high‐frequency stimulation was greater. This study shows that subthalamic deep brain stimulation improves mechanical allodynia and thermal hyperalgesia in 6‐hydroxydopamine‐lesioned animals at both high and low frequencies. Furthermore, we suggest considering using low‐frequency stimulation when treating Parkinson's patients where pain remains the predominant complaint.     

Hypothalamic KISS1 Expression,Gonadotrophin‐Releasing Hormone and Neurotransmitter Innervation Vary with Stress and Sensitivity in Macaques

The present study examined the effect of short‐term psychosocial and metabolic stress in a monkey model of stress‐induced amenorrhaea on the hypothalamic‐pituitary‐gonadal axis. KISS1 expression was determined by in situ hybridisation in the infundibular arcuate nucleus. Downstream of KISS1, gonadotrophin‐releasing hormone (GnRH) axons in lateral areas rostral to the infundibular recess, serum luteinising hormone (LH) and serum oestradiol were measured by immunohistochemistry and radioimmunoassay. Upstream of KISS1, norepinephrine axons in the rostral arcuate nucleus and serotonin axons in the anterior hypothalamus and periaqueductal grey were measured by immunohistochemistry. Female cynomolgus macaques (Macaca fascicularis) characterised as highly stress resilient (HSR) or stress sensitive (SS) were examined. After characterisation of stress sensitivity, monkeys were either not stressed, or mildly stressed for 5 days before euthanasia in the early follicular phase. Stress consisted of 5 days of 20% food reduction in a novel room with unfamiliar conspecifics. There was a significant increase in KISS1 expression in HSR and SS animals in the presence versus absence of stress (P = 0.005). GnRH axon density increased with stress in HSR and SS animals (P = 0.015), whereas LH showed a gradual but nonsignificant increase with stress. Oestradiol trended higher in HSR animals and there was no effect of stress (P = 0.83). Norepinephrine axon density (marked with dopamine β‐hydroxylase) increased with stress in both HSR and SS groups (P ≤ 0.002), whereas serotonin axon density was higher in HSR compared to SS animals and there was no effect of stress (P = 0.03). The ratio of dopamine β‐hydroxylase/oestradiol correlated with KISS1 (P = 0.052) and GnRH correlated with serum LH (P = 0.039). In conclusion, oestradiol inhibited KISS1 in the absence of stress, although stress increased norepinephrine, which may over‐ride oestradiol inhibition of KISS1 expression. We speculate that neural pathways transduce stress to KISS1 neurones, which changes their sensitivity to oestradiol.     

Heterogeneous neuronal activity in the lateral habenula after short‐ and long‐term cocaine self‐administration in rats

Cocaine addiction is thought to be the result of drug‐induced functional changes in a neural network implicated in emotions, learning and cognitive control. Recent studies have implicated the lateral habenula (LHb) in drug‐directed behavior, especially its aversive aspects. Limited cocaine exposure has been shown to alter neuronal activity in the LHb, but the impact of long‐term drug exposure on habenula function has not been determined. Therefore, using c‐fos as a marker, we here examined neuronal activity in LHb in rats that self‐administered cocaine for either 10 or 60 days. Both the density of labeled cells and the cellular labeling intensity were measured in the lateral (LHbL) and medial (LHbM) parts of LHb. After 10 days of cocaine self‐administration, both the density and intensity of c‐fos‐positive cells were significantly increased in LHbL, but not LHbM, while after 60 days, an increased density (but not intensity) of labeled neurons in both LHbL and LHbM was observed. Most c‐fos‐labeled neurons were glutamatergic. In addition, we found increased GAD65 expression after 10 but not 60 days of cocaine self‐administration in the rostral mesencephalic tegmental nucleus. These data shed light on the complex temporal dynamics by which cocaine self‐administration alters activity in LHb circuitry, which may play an important role in the descent to compulsive drug use as a result of prolonged cocaine‐taking experience.