Periaqueductal Gray Region Research Articles

Specific regions display altered grey matter volume in μ-opioid receptor knockout mice: MRI voxel-based morphometry.

μ Opioid receptor knockout (MOP-KO) mice display several behavioural differences from wild-type (WT) littermates including differential responses to nociceptive stimuli. Brain structural changes have been tied to behavioural alterations noted in transgenic mice with targeting of different genes. Hence, we assess the brain structure of MOP-KO mice. Magnetic resonance imaging (MRI) voxel-based morphometry (VBM) and histological methods were used to identify structural differences between extensively backcrossed MOP-KO mice and WT mice. MOP-KO mice displayed robust increases in regional grey matter volume in olfactory bulb, several hypothalamic nuclei, periaqueductal grey (PAG) and several cerebellar areas, most confirmed by VBM analysis. The largest increases in grey matter volume were detected in the glomerular layer of the olfactory bulb, arcuate nucleus of hypothalamus, ventrolateral PAG (VLPAG) and cerebellar regions including paramedian and cerebellar lobules. Histological analyses confirm several of these results, with increased VLPAG cell numbers and increased thickness of the olfactory bulb granule cell layer and cerebellar molecular and granular cell layers. MOP deletion causes previously undescribed structural changes in specific brain regions, but not in all regions with high MOP receptor densities (e.g. thalamus, nucleus accumbens) or that exhibit adult neurogenesis (e.g. hippocampus). Volume differences in hypothalamus and PAG may reflect behavioural changes including hyperalgesia. Although the precise relationship between volume change and MOP receptor deletion was not determined from this study alone, these findings suggest that levels of MOP receptor expression may influence a broader range of neural structure and function in humans than previously supposed. This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

Acute serotonergic treatment changes the relation between anxiety and HPA-axis functioning and periaqueductal gray activation

Serotonergic (5-HT) drugs are widely used in the clinical management of mood and anxiety disorders. However, it is reported that acute 5-HT treatment elicits anxiogenic-like behavior. Interestingly, the periaqueductal gray (PAG), a midbrain structure which regulates anxiety behavior – has robust 5-HT fibers and reciprocal connections with the hypothalamic–pituitary–adrenal (HPA) axis. Although the HPA axis and the 5-HT system are well investigated, the relationship between the stress hormones induced by 5-HT drug treatment and the PAG neural correlates of the behavior remain largely unknown. In this study, the effects of acute and chronic treatments with buspirone (BUSP) and escitalopram (ESCIT) on anxiety-related behaviors were tested in an open-field (OF). The treatment effects on PAG c-Fos immunoreactivity (c-Fos-ir) and corticosterone (CORT) concentration were measured in order to determine the neural-endocrine correlates of anxiety-related behaviors and drug treatments. Our results demonstrate that acute BUSP and ESCIT treatments induced anxiogenic behaviors with elevation of CORT compared to the baseline. A decrease of c-Fos-ir was found in the dorsomedial PAG region of both the treatment groups. Correlation analysis showed that the CORT were not associated with the OF anxiogenic behavior and PAG c-Fos-ir. No significant differences were found in behaviors and CORT after chronic treatment. In conclusion, acute BUSP and ESCIT treatments elicited anxiogenic response with activation of the HPA axis and reduction of c-Fos-ir in the dorsomedial PAG. Although no correlation was found between the stress hormone and the PAG c-Fos-ir, this does not imply the lack of cause-and-effect relationship between neuroendocrine effects and PAG function in anxiety responses. These correlation studies suggest that the regulation of 5-HT system was probably disrupted by acute 5-HT treatment.

Blockade of 5-Ht3 receptors in the septal area increases Fos expression in selected brain areas

Serotonin is widely distributed throughout the brain and is involved in a multiplicity of visceral, cognitive and behavioral responses. It has been previously shown that injections of different doses of ondansetron, a 5-HT3 receptor antagonist, into the medial septum/vertical limb of the diagonal band complex (MS/vDB) induce a hypertensive response in rats. On the other hand, administration of m-CPBG, a 5-HT3 agonist, into the MS/vDB inhibits the increase of blood pressure during restraint stress. However, it is unclear which neuronal circuitry is involved in these responses. The present study investigated Fos immunoreactive nuclei (Fos-IR) in different brain areas following the blockade of 5-HT3 receptors located in the MS/vDB in sham and in sinoaortic denervated (SAD) rats. Ondansetron injection into the MS/vDB increases Fos-IR in different brain areas including the limbic system (central amygdala and ventral part of the bed nucleus of the stria terminalis), hypothalamus (medial parvocellular parts of the paraventricular nucleus, anterodorsal preoptic area, dorsomedial hypothalamic nucleus), mesencephalon (ventrolateral periaqueductal gray region) and rhombencephalon (lateral parabrachial nucleus) in sham rats. Barodenervation results in higher Fos expression at the parvocellular and magnocellular part of the paraventricular nucleus, the lateral parabrachial nucleus, the central nucleus of amygdala, the locus coeruleus, the medial part of the nucleus of the solitary tract, the rostral ventrolateral medulla and the caudal ventrolateral medulla following 5-HT3receptor blockade in the MS/vDB. Based on the present results and previous data showing a hypertensive response to ondansetron injected into the MS/vDB, it is reasonable to suggest that 5-HT3receptors in the MS/vDB exert an inhibitory drive that may oscillate as a functional regulatory part of the complex central neuronal network participating in the control of blood pressure.

The cholinergic agonist carbachol increases the frequency of spontaneous GABAergic synaptic currents in dorsal raphe serotonergic neurons in the mouse

Dorsal raphe nucleus (DRN) serotonin (5-HT) neurons play an important role in feeding, mood control and stress responses. One important feature of their activity across the sleep–wake cycle is their reduced firing during rapid-eye-movement (REM) sleep which stands in stark contrast to the wake/REM-on discharge pattern of brainstem cholinergic neurons. A prominent model of REM sleep control posits a reciprocal interaction between these cell groups. 5-HT inhibits cholinergic neurons, and activation of nicotinic receptors can excite DRN 5-HT neurons but the cholinergic effect on inhibitory inputs is incompletely understood. Here, in vitro, in DRN brain slices prepared from GAD67-GFP knock-in mice, a brief (3min) bath application of carbachol (50μM) increased the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) in GFP-negative, putative 5-HT neurons but did not affect miniature (tetrodotoxin-insensitive) IPSCs. Carbachol had no direct postsynaptic effect. Thus, carbachol likely increases the activity of local GABAergic neurons which synapse on 5-HT neurons. Removal of dorsal regions of the slice including the ventrolateral periaqueductal gray (vlPAG) region where GABAergic neurons projecting to the DRN have been identified, abolished the effect of carbachol on sIPSCs whereas the removal of ventral regions containing the oral region of the pontine reticular nucleus (PnO) did not. In addition, carbachol directly excited GFP-positive, GABAergic vlPAG neurons. Antagonism of both muscarinic and nicotinic receptors completely abolished the effects of carbachol. We suggest cholinergic neurons inhibit DRN 5-HT neurons when acetylcholine levels are lower i.e. during quiet wakefulness and the beginning of REM sleep periods, in part via excitation of muscarinic and nicotinic receptors located on local vlPAG and DRN GABAergic neurons. Higher firing rates or burst firing of cholinergic neurons associated with attentive wakefulness or phasic REM sleep periods leads to excitation of 5-HT neurons via the activation of nicotinic receptors located postsynaptically and presynaptically on excitatory afferents.

Humor processing in children: Influence of temperament, age and IQ

Emerging evidence from fMRI studies suggests that humor processing is a specific social cognitive–affective human function that comprises two stages. The first stage (cognitive humor component) involves the detection and resolution of incongruity, and is associated with activity in temporo-occipito-parietal brain areas. The second stage (emotional humor component) comprises positive feelings related to mirth/reward, and is linked with reward-related activity in mesocorticolimbic circuits.In healthy adults, humor processing was shown to be moderated by temperament traits like intro-/extraversion, neuroticism, or social anxiety, representing risk factors for psychopathology. However, comparable data from early developmental stages is crucially lacking. Here, we report for the first time data from 22 children (ages 6 to 13) revealing an influence of temperament on humor processing. Specifically, we assessed the effects of Emotionality, Shyness, and Sociability, which are analogous to neuroticism, behavioral inhibition/fear and extraversion in adults. We found Emotionality to be positively, but Shyness negatively associated with brain activity linked with both cognitive and emotional humor components. In addition, Shyness and Sociability were positively related to activity in the periaqueductal gray region during humor processing. These findings are of potential clinical relevance regarding the early detection of childhood psychopathology.Previous data on humor processing in both adults and children furthermore suggest that intelligence (IQ) supports incongruity detection and resolution, whereas mirth and associated brain activity diminishes with increasing age. Here, we found that increasing age and IQ were linked with stronger activity to humor in brain areas implicated in the cognitive component of humor. Such data suggest that humor processing undergoes developmental changes and is moderated by higher IQ scores, both factors likely improving incongruity detection and resolution.

Electrophysiological Study of Supraspinal Input and Spinal Output of Cat's Subnucleus Reticularis Dorsalis (SRD) Neurons

This work addressed the study of subnucleus reticularis dorsalis (SRD) neurons in relation to their supraspinal input and the spinal terminating sites of their descending axons. SRD extracellular unitary recordings from anesthetized cats aimed to specifically test, 1) the rostrocaudal segmental level reached by axons of spinally projecting (SPr) neurons collateralizing or not to or through the ipsilateral nucleus reticularis gigantocellularis (NRGc), 2) whether SPr fibers bifurcate to the thalamus, and 3) the effects exerted on SRD cells by electrically stimulating the locus coeruleus, the periaqueductal grey, the nucleus raphe magnus, and the mesencephalic locomotor region. From a total of 191 SPr fibers tested to cervical 2 (Ce2), thoracic 5 (Th5) and lumbar5 (Lu5) stimulation, 81 ended between Ce2 and Th5 with 39 of them branching to or through the NRGc; 21/49 terminating between Th5 and Lu5 collateralized to or through the same nucleus, as did 34/61 reaching Lu5. The mean antidromic conduction velocity of SPr fibers slowed in the more proximal segments and increased with terminating distance along the cord. None of the 110 axons tested sent collaterals to the thalamus; instead thalamic stimulation induced long-latency polysynaptic responses in most cells but also short-latency, presumed monosynaptic, in 7.9% of the tested neurons (18/227). Antidromic and orthodromic spikes were elicited from the locus coeruleus and nucleus raphe magnus, but exclusively orthodromic responses were observed following stimulation of the periaqueductal gray or mesencephalic locomotor region. The results suggest that information from pain-and-motor-related supraspinal structures converge on SRD cells that through SPr axons having conduction velocities tuned to their length may affect rostral and caudal spinal cord neurons at fixed delays, both directly and in parallel through different descending systems. The SRD will thus play a dual functional role by simultaneously regulating dorsal horn ascending noxious information and pain-related motor responses.

Comparison of tolerance to morphine-induced respiratory and analgesic effects in mice

Morphine is responsible for severe poisonings in chronically treated patients. We hypothesize that toxicity could be related to the development of weaker tolerance for morphine-induced deleterious respiratory effects in comparison to analgesic effects. Our objectives were to compare tolerance to both effects in mice and investigate possible mechanisms for such possible differences. Tolerance to morphine-induced analgesia and respiratory effects was assessed using hot plate response latencies and plethysmography, respectively. Mechanisms of tolerance were investigated using binding studies to mu-opioid receptors (MOR) and adenylate cyclase (AC) activity measurement in homogenates of cell membranes from the periaqueductal gray region (PAG) and brainstem. Morphine (2.5mg/kg) was responsible for analgesia with significant increase in inspiratory time. Acute tolerance to analgesia (p<0.01) and effects on respiratory frequency (p<0.05) was observed in mice pre-treated with 100mg/kg morphine in comparison to saline. Following repetitive administration (2.5mg/kg/day during 10 days), we observed a 13-fold increase in the effective dose-50% (ED50) of morphine-induced analgesia in comparison to a 2- or 4-fold increase in the ED50 of its related increase in inspiratory time determined in air and 4% CO2, respectively. No significant alteration in MOR expression was observed in either PAG or brainstem following repeated morphine administration. However, in PAG, in contrast to brainstem, superactivation of AC was observed in morphine-treated mice in comparison to controls (p<0.05). In conclusion, tolerance to morphine-induced respiratory effects is much more limited than tolerance to its analgesic effects in repeatedly morphine-treated mice. The difference in morphine-induced AC activation between the brainstem and the PAG contributes to the observed difference in tolerance between both morphine effects.

Pathophysiology of Migraine

Mainero C, Boshyan J, Hadjikhani N. Altered functional magnetic resonance imaging resting-state connectivity in periaqueductal gray networks in migraine. Annals of Neurology 2011;70:838-845. Objective: The periaqueductal gray matter (PAG), a known modulator of somatic pain transmission, shows evidence of interictal functional and structural abnormalities in migraineurs, which may contribute to hyperexcitability along spinal and trigeminal nociceptive pathways, and lead to the migraine attack. The aim of this study was to examine functional connectivity of the PAG in migraine. Methods: Using resting-state functional MRI, we compared functional connectivity between PAG and a subset of brain areas involved in nociceptive/somatosensory processing and pain modulation in 17 subjects with migraine, during a pain-free state, versus 17 genderand age-matched controls. We also assessed the relation between intrinsic resting-state correlations within PAG networks and the average monthly frequency of migraine attacks, as well as allodynia. Results: Our findings show stronger connectivity between the PAG and several brain areas within nociceptive and somatosensory processing pathways in migraineurs versus controls. In addition, as the monthly frequency of migraine attacks worsens, the strength of the connectivity in some areas within these pathways increases, whereas a significant decrease in functional resting-state connectivity between the PAG and brain regions with a predominant role in pain modulation (prefrontal cortex, anterior cingulate, amygdala) can be evidenced. Finally, migraineurs with a history of allodynia exhibit significantly reduced connectivity between PAG, prefrontal regions, and anterior cingulate compared to migraineurs without allodynia. Interpretation: These data reveal interictal dysfunctional dynamics within pain pathways in migraine manifested as an impairment of the descending pain modulatory circuits, likely leading to loss of pain inhibition, and hyperexcitability primarily in nociceptive areas. Comments: Functional neuroimaging techniques have helped elucidate the underlying physiology of migraines. Unlike traditional functional magnetic resonance imaging scans done during a task, resting state functional connectivity is a relatively new neuroimaging technique in which participants are scanned at rest, and the lowfrequency spontaneous fluctuations found to be highly correlated are thought to represent brain areas that are functionally connected at baseline. Mainero et al recently conducted this study to assess the functional connectivity of the periaqueductal gray (PAG) (a region previously implicated in the pathogenesis of migraine) to other brain regions in 17 migraineurs interictally compared with 17 age-/gendermatched controls. They found that compared with the controls, the migraineurs had increased resting state functional connectivity between the PAG, and somatosensory and nociceptive processing pathways. The connections between the PAG and the supramarginal gyrus, anterior insula, and hypothalamus were increased in migraineurs with more frequent attacks, while the connections between PAG and the prefrontal cortex, anterior cingulate, amygdala, and medial thalamus were decreased in migraineurs with more frequent attacks. The 5 migraineurs with allodynia also had significantly reduced connectivity between the PAG and the anterior insula, anterior cingulate, and prefrontal cortex vs genderand age-matched migraineurs without allodynia. This study is one of the first to use resting state functional connectivity analyses to compare the intrinsic neural connections in migraineurs vs controls. As expected, many of the connections between the PAG, and nociceptive and sensory processing pathways were increased in the migraineurs, and some of those connections were stronger in those with more frequent attacks. However, unexpectedly, those with more frequent migraines and those with allodynia had decreased connections between the PAG and areas involved in the cognitive modulation of pain. This suggests that From the Graham Headache Center, Faulkner/Brigham and Women’s Hospital, Boston, MA,

Elevated gamma band power in humans receiving naloxone suggests dorsal periaqueductal and periventricular gray deep brain stimulation produced analgesia is opioid mediated

BackgroundThe midbrain periaqueductal and periventricular gray (PAVG) region is important for pain and autonomic modulation. We have previously described changes in blood pressure dependent upon dorsal or ventral electrode positioning with PAVG deep brain stimulation (DBS), yet controversy exists about whether DBS acts via endogenous opioid release. Method and resultsWe combined local field potential (LFP) recording from PAVG DBS electrodes in humans with naloxone and saline infusions to determine whether dorsal and ventral PAVG DBS act through opioidergic or other mechanisms. Four awake human subjects were investigated. DBS were implanted contralateral to the painful body part. Electrode contact positions were mapped using MRI and brain atlas information. Naloxone then saline were randomly administered to the blinded subjects and pain rated using a numeric pain rating scale at 30s intervals for 3min. Two subjects received dorsal DBS electrodes and two had ventral placements. Significantly elevated gamma frequency band (30–90Hz) power concomitant with pain exacerbation was found with naloxone versus both saline and rest in dorsal not ventral PAVG LFPs (p<0.005). Significantly elevated delta frequency band (0–4Hz) power (p=0.001) was seen in one ventral PAVG subject with both naloxone and saline infusions. ConclusionsDorsal PAVG DBS may reduce pain by augmenting endogenous opioid release. Elevated gamma oscillations enhance awareness of worsening pain with opioid blockade. Ventral PAVG DBS may act by separate possibly autonomic mechanisms. Increased delta oscillations indicate a survival rhythm involved in the initiation of passive coping responses to homeostatic changes.

Spumiform basement membrane aberrations in the microvasculature of the midbrain periaqueductal gray region in hamster: Rostro-caudal pathogenesis?

Spumiform basement membrane degeneration (sbmd) is a specific kind of aberration present in the capillaries of the midbrain periaqueductal gray (PAG) region of the senescent hamster. These capillaries, separated by the ependymal cell layer, are bordering the Sylvian cerebral aqueduct. The aqueduct, connecting the 3rd and 4th ventricle, may be crucial for local homeostatic as well as general autonomic functions of the PAG. Local pressure effects of the flowing and pulsating cerebrospinal fluid on the PAG-vasculature are probably different for the rostral ‘entrance’ and the caudal ‘exit’ of the aqueduct.In view of the different functions of the various divisions of the PAG, the frequency and extent of the aberrations in the rostral, intermediate and caudal dl/vlPAG-microvasculature could shed some light on the causal factors involved in the regional distribution of the particular microvascular aberrations found in the PAG during aging. In the present study we investigated the ultrastructure of capillaries in dorsal and ventral subdivisions of anterior and posterior regions of the PAG of young and old female Syrian hamsters. Sbmds were classified into four stages of spumiform severity and for each stage the frequency was determined in the rostral PAG, at two levels in the intermediate PAG and in a dorsal and a ventral part of the caudal PAG.Results of our quantitative studies showed that in aged hamster PAG various stages of sbmd were present in 91.6±0.6% of all capillaries. No clear evidence was found for regional differentiation between rostral, intermediate and caudal parts of the PAG. Next to sbmd, capillary split basement membrane (sbm) and vacuolization were common features at all five PAG locations. 84.3±2.3% of all screened PAG capillaries displayed sbm. In agreement with our previous findings, several other types of microvascular aberrations were observed in addition to general aspects of aging and some ependymal structural peculiarities.We conclude that the presence of various forms of sbmds in the PAG of senescent hamsters is a phenomenon that appears to be specific to the PAG region, but causal factors for this type of capillary degeneration remain unclear. Sbmds in the PAG may have serious consequences not only for blood–brain barrier functioning, but also for vascular perfusion and blood supply with eventually serious consequences for adequate regulation of the autonomic and motor control functions of the PAG region.

Midbrain response to milkshake correlates with ad libitum milkshake intake in the absence of hunger

There is now widespread agreement that individual variation in the neural circuits representing the reinforcing properties of foods may be associated with risk for overeating and obesity. What is currently unknown is how and whether brain response to a food is related to immediate subsequent intake of that food. Here we used functional magnetic resonance imaging (fMRI) to test whether response to a palatable milkshake is associated with subsequent ad libitum milkshake consumption. We predicted that enhanced responses in key reward regions (insula, striatum, midbrain, medial orbitofrontal cortex) and decreased responses in regions implicated in self-control (lateral prefrontal and lateral orbitofrontal cortex) would be associated with greater intake. We found a significant positive association between response to milkshake in the periaqueductal gray region of the midbrain and ad libitum milkshake intake. Although strong bilateral insular responses were observed during consumption of the milkshake this response did not correlate with subsequent intake. The associations observed in the midbrain and orbitofrontal cortex were uninfluenced by ratings of hunger, which were near neutral. We conclude that midbrain response to a palatable food is related to eating in the absence of hunger.

Contribution of acid sphingomyelinase in the periaqueductal gray region to morphine-induced analgesia in mice

Opioids are the most widely used drugs for long-term pain management, but their use is limited by the development of antinociceptive tolerance. The present study investigated the role of ceramide production through acid sphingomyelinase (ASM) activation in the periaqueductal gray region, a brain region implicated in opioid analgesia and tolerance. Morphine treatment was found, using immunohistochemistry, to increase ASM expression and intracellular ceramide in the periaqueductal gray 30 min after an acute injection (10 mg/kg). The effects of acute morphine treatment on ASM expression and ceramide generation in the periaqueductal gray region were completely blocked by pretreatment with naloxone and by silencing the ASM gene by plasmid-mediated transfection of ASM shRNA. In chronic morphine pellet-implanted mice, ASM expression and ceramide generation in the periaqueductal gray region were also significantly increased. Functionally, selective silencing of the ASM gene by local ASM shRNA transfection reduced the analgesic response to acute morphine, but the data on the effect of ASM shRNA on the development of antinociceptive tolerance were inconclusive. These data provide evidence that ASM activation and ceramide generation in the periaqueductal gray region play a major role in the antinociceptive mechanism of morphine.

Changes in Midbrain Pain Receptor Expression, Gait and Behavioral Sensitivity in a Rat Model of Radiculopathy

Intervertebral disc herniation may contribute to inflammatory processes that associate with radicular pain and motor deficits. Molecular changes at the affected dorsal root ganglion (DRG), spinal cord, and even midbrain, have been documented in rat models of radiculopathy or nerve injury. The objective of this study was to evaluate gait and the expression of key pain receptors in the midbrain in a rodent model of radiculopathy. Radiculopathy was induced by harvesting tail nucleus pulposus (NP) and placing upon the right L5 DRG in rats (NP-treated, n=12). Tail NP was discarded in sham-operated animals (n=12). Mechanical allodynia, weight-bearing, and gait were evaluated in all animals over time. At 1 and 4 weeks after surgery, astrocyte and microglial activation was tested in DRG sections. Midbrain sections were similarly evaluated for immunoreactivity to serotonin (5HT2B), mu-opioid (µ-OR), and metabotropic glutamate (mGluR4 and 5) receptor antibodies. NP-treated animals placed less weight on the affected limb 1 week after surgery and experienced mechanical hypersensitivity over the duration of the study. Astroctye activation was observed at DRGs only at 4 weeks after surgery. Findings for pain receptors in the midbrain of NP-treated rats included an increased expression of 5HT2B at 1, but not 4 weeks; increased expression of µ-OR and mGluR5 at 1 and 4 weeks (periaqueductal gray region only); and no changes in expression of mGluR4 at any point in this study. These observations provide support for the hypothesis that the midbrain responds to DRG injury with a transient change in receptors regulating pain responses.

Functional properties of dopamine neurons and co‐expression of vasoactive intestinal polypeptide in the dorsal raphe nucleus and ventro‐lateral periaqueductal grey

The dorsal raphe nucleus (DRN) and ventrolateral periaqueductal grey (vlPAG) regions contain populations of dopamine neurons, often considered to be a dorsal caudal extension of the A10 group [mostly found in the ventral tegmental area (VTA)]. Recent studies suggest they are involved in promoting wakefulness and mediate some of the antinociceptive and rewarding properties of opiates. However, little is known about their electrophysiological properties. To address this, we used Pitx3-GFP and tyrosine hydroxylase (TH)-GFP mice to carry out targeted whole-cell recordings from this population in acute brain slices. We found that DRN/vlPAG dopamine neurons have characteristics similar to most VTA dopamine neurons, but distinct from dorsal raphe serotonin neurons. They fire broad action potentials at a relatively slow, regular rate, exhibit a hyperpolarization-activated inward current and delayed repolarization, and show spike-frequency adaptation in response to prolonged depolarization. In addition, they receive fast excitatory and inhibitory synaptic inputs. Moreover, we found co-expression of vasoactive intestinal polypeptide in small, periaqueductal dopamine neurons, but generally not in larger, more ventral dopamine neurons.

An investigation of stress and pain perception during manual therapy in asymptomatic subjects.

Stress perceived by the patient during the application of a manual therapy treatment technique may account for the reported findings of sympathoexcitation and hypoalgesia immediately after its application. This study investigated whether there was a difference in the level of perceived stress and pain before, during and after the application of a treatment condition (treatment, placebo or control technique), or whether the difference related to the time course of subject involvement in the study.Twenty-four asymptomatic subjects participated in a double-blind, placebo-controlled, within-subjects study in which stress was measured with a stress rating scale and a stress visual analogue scale. Pain experienced by the subject during the application of the treatment technique was measured with a visual analogue scale and modified McGill pain questionnaire. There was no effect of the treatment condition on perceived stress, but there was a reduction in stress levels over the time course of involvement in the experiment, as demonstrated by pre-application levels of stress. Pain was not produced by the treatment technique.This study demonstrated that stress and pain were not features of the lateral glide manipulation of the cervical spine in asymptomatic subjects. If the dorsal periaqueductal grey region is responsible for the initial effects of manual therapy, as has been previously suggested, then stress and pain do not appear to play a role in activating this system during the application of a manual therapy treatment technique in asymptomatic subjects. Copyright 1999 European Federation of Chapters of the International Association for the Study of Pain.

WEBINO and the Return of the King's Speech

We present a 69year-old man with hypertension who developed the sudden onset of horizontal binocular diplopia and stuttering of speech. On examination, bilateral exotropia (i.e. ‘wall-eyed’) was observed in the primary position. Attempted horizontal saccades revealed bilateral internuclear ophthalmoplegia; all consistent with the wall-eyed bilateral internuclear ophthalmoplegia (WEBINO) syndrome. Convergence, vertical saccades and vestibular ocular reflexes were likewise impaired. Pupillary and levator palpebrae superioris functions were intact. Mild left-sided dysmetria, intention tremor and dysdiadochokinesia were elicited. Conspicuously, further characterization of the patient's history revealed that he had stuttered as a child, but it had resolved in adolescence. Brain MRI revealed an acute infarction of the mesencephalic and upper pontine tegmentum involving the periaqueductal gray region and the medial longitudinal fasciculus bilaterally with greater involvement of the left. Like the WEBINO syndrome, re-emergent developmental stuttering is a rare neurologic phenomenon. To our knowledge, this is the first case report of a mesencephalic and upper pontine infarction causing both syndromes. We discuss the pathobiological underpinnings of the WEBINO syndrome and neurogenic stuttering and in relationship to this unusual case.

Effect of dexmedetomidine on norepinephrine release in midbrain periaqueductal gray in a rat model of incisional pain

Objective To investigate the effect of dexmedetomidine on norepinephrine(NE)release in midbrain periaqueductal gray(PAG)in a rat model of incisional pain.Methods Twenty-four male Wistar rats in which microdialvsis catheter was successfully placed in the ventrolateral region of PAG without complications were randomly divided into 4 groups(n=6 each):group control(group C);group incisional pain(group IP);group dexmetomidine(group D)and group dexmedetomidine+yohimbine(group DY).Incisional pain was induced by an incision made into the plantar surface of left hindpaw in IP,D,DY groups.Dexmedetomidine 30 μg/kg and dexmedetomidine 30 μg/kg+yohimbine 0.5 mg/kg were given intraperitoneally at 15 min before plantar incision in group D and group DY respectively.Mechanical paw withdrawal threshold(MWT)to von Frey filament stimulation was measured at 30 min before(baseline)and 1,2,3,4 h after operation in C,IP,D groups,and at 30 min before(baseline),and 1 h after operation in group DY.Dialysate samples were collected at 30 min before(baseline)and at evcry 30 min after operation for 4 h via cerebral microdialysis catheter for determination of the NE concentration in C,IP,D groups,and at 30 min before(baseline),30,60 min after operation in group DY.Results Incisional pain significantly decreased MWT and increased the NE concentration in dialysate in group IP.Dexmedetomidine premedication significantly inhibited mechanical hyperalgesia and attenuated incisional pain-induced increase in the NE concentration in dialysate in group D.Yohimbine counteracted effects of dexmedetomidine.Conclusion Dexmedetomidine has analgesic effect though inhibition of NE release from PAG. Key words: Dexmedetomidine; Pain; Mesencephalon; Cerebral aqueduct; Norepinephrine

Deep Brain Stimulation of the Periaqueductal Grey Induces Vasodilation in Humans

To the Editor: Surgical implantation of electrodes into deep brain structures for the management of conditions such as chronic pain provides an opportunity for assessment of the physiological impact of stimulation of focal brain nuclei in humans.1 Recent studies in humans have suggested that stimulation of the periventricular (PVG)/periaqueductal grey (PAG) regions can result in changes in systemic blood pressure (BP).2,3 In the present case, we examined the physiological impact of such stimulation in humans by obtaining continuous measures of limb blood flow, peripheral resistance, stroke volume, and heart rate (HR) during deep brain stimulation (DBS) of the PVG/PAG. The patient, a 55-year–old woman, was referred for management of recalcitrant chronic neuropathic, phantom limb pain (affecting both lower limbs) in 2004, subsequently leading to PVG/PAG DBS surgery in 2005 at the Radcliffe Infirmary in Oxford. Assessments and procedures were approved by the Oxford Ethics Committee and performed in a quiet thermostatically controlled room (26°C). The patient was placed in a semirecumbent position, at which point the stimulator was turned off for an initial 20-minute rest period. After a baseline BP assessment using a Finometer PRO (Finapres Medical Systems, Amsterdam, Netherlands), the stimulator was turned on, and BP, stroke volume, total peripheral resistance, and brachial artery diameter and blood flow velocity (Terason T3000, Teratech …

Serotonin neurons of the caudal raphe nuclei contribute to sympathetic recovery following hypotensive hemorrhage

Serotonin is thought to contribute to the syncopal-like response that develops during severe blood loss by inhibiting presympathetic neurons of the rostroventrolateral medulla (RVLM). Here, we tested whether serotonin cells activated during hypotensive hemorrhage, i.e., express the protein product of the immediate early gene c-Fos, are critical for the normal sympathetic response to blood loss in unanesthetized rats. Serotonin-immunoreactive cells of the raphe obscurus and raphe magnus, parapyramidal cells of the B3 region, subependymal cells of the ventral parapyramidal region, and cells of the ventrolateral periaqueductal gray region were activated by hypotensive hemorrhage, but not by hypotension alone. In contrast to findings in anesthetized animals, lesion of hindbrain serotonergic cells sufficient to produce >80% loss of serotonin nerve terminal immunoreactivity in the RVLM accelerated the sympatholytic response to blood loss, attenuated recovery of sympathetic activity after termination of hemorrhage, and exaggerated metabolic acidosis. Hindbrain serotonin lesion also attenuated ventilatory and sympathetic responses to stimulation of central chemoreceptors but increased spontaneous arterial baroreflex sensitivity and decreased blood pressure variability. A more global neurotoxic lesion that also eliminated tryptophan hydroxylase-immunoreactive cells of the ventrolateral periaqueductal gray region had no further effect on the sympatholytic response to blood loss. Together, the data indicate that serotonin cells of the caudal hindbrain contribute to compensatory responses following blood loss that help maintain oxygenation of peripheral tissue in the unanesthetized rat. This effect may be related to facilitation of chemoreflex responses to acidosis.

Neural responses of rats in the forced swimming test: [F-18]FDG micro PET study

The forced swimming test (FST) is a widely used tool in the assessment of behavioral despair and prediction of response to antidepressants. However, the neural mechanisms underlying behavioral changes between pretest and test sessions of the FST remain unclear. In this study, we investigated changes in rat brain activity during the FST using [F-18]Fluorodeoxyglucose micro PET. In both pretest and test sessions, the activity of the cerebellum and striatum increased, whereas significant deactivation was observed in the hippocampus, inferior colliculus, orbital cortex, and insula. The periaqueductal gray (PAG) region activated markedly in the pretest session, but did not activate in the test session. There was a significant increase in immobility and a decrease in climbing during the behavioral analysis test session. These results suggest that the PAG region may play an important role in the modulation of FST coping strategies subsequent to failure of the escape response during the pretest session.