Stimulation of the Sphenopalatine Ganglion Induces Reperfusion and Blood-Brain Barrier Protection in the Photothrombotic Stroke Model

The treatment of stroke remains a challenge. Animal studies showing that electrical stimulation of the sphenopalatine ganglion (SPG) exerts beneficial effects in the treatment of stroke have led to the initiation of clinical studies. However, the detailed effects of SPG stimulation on the injured brain are not known.The effect of acute SPG stimulation was studied by direct vascular imaging, fluorescent angiography and laser Doppler flowmetry in the sensory motor cortex of the anaesthetized rat. Focal cerebral ischemia was induced by the rose bengal (RB) photothrombosis method. In chronic experiments, SPG stimulation, starting 15 min or 24 h after photothrombosis, was given for 3 h per day on four consecutive days. Structural damage was assessed using histological and immunohistochemical methods. Cortical functions were assessed by quantitative analysis of epidural electro-corticographic (ECoG) activity continuously recorded in behaving animals.Stimulation induced intensity- and duration-dependent vasodilation and increased cerebral blood flow in both healthy and photothrombotic brains. In SPG-stimulated rats both blood brain-barrier (BBB) opening, pathological brain activity and lesion volume were attenuated compared to untreated stroke animals, with no apparent difference in the glial response surrounding the necrotic lesion.SPG-stimulation in rats induces vasodilation of cortical arterioles, partial reperfusion of the ischemic lesion, and normalization of brain functions with reduced BBB dysfunction and stroke volume. These findings support the potential therapeutic effect of SPG stimulation in focal cerebral ischemia even when applied 24 h after stroke onset and thus may extend the therapeutic window of currently administered stroke medications

Conditioned Pain Modulation Is Associated with Common Polymorphisms in the Serotonin Transporter Gene

BACKGROUND: Variation in the serotonin transporter (5-HTT) gene (SLC6A4) has been shown to influence a wide range of affective processes. Low 5-HTT gene-expression has also been suggested to increase the risk of chronic pain. Conditioned pain modulation (CPM)--i.e. 'pain inhibits pain'--is impaired in chronic pain states and, reciprocally, aberrations of CPM may predict the development of chronic pain. Therefore we hypothesized that a common variation in the SLC6A4 is associated with inter-individual variation in CPM. Forty-five healthy subjects recruited on the basis of tri-allelic 5-HTTLPR genotype, with inferred high or low 5-HTT-expression, were included in a double-blind study. A submaximal-effort tourniquet test was used to provide a standardized degree of conditioning ischemic pain. Individualized noxious heat and pressure pain thresholds (PPTs) were used as subjective test-modalities and the nociceptive flexion reflex (NFR) was used to provide an objective neurophysiological window into spinal processing. RESULTS: The low, as compared to the high, 5-HTT-expressing group exhibited significantly reduced CPM-mediated pain inhibition for PPTs (p = 0.02) and heat-pain (p = 0.02). The CPM-mediated inhibition of the NFR, gauged by increases in NFR-threshold, did not differ significantly between groups (p = 0.75). Inhibition of PPTs and heat-pain were correlated (Spearman's rho = 0.35, p = 0.02), whereas the NFR-threshold increase was not significantly correlated with degree of inhibition of these subjectively reported modalities. CONCLUSIONS: Our results demonstrate the involvement of the tri-allelic 5-HTTLPR genotype in explaining clinically relevant inter-individual differences in pain perception and regulation. Our results also illustrate that shifts in NFR-thresholds do not necessarily correlate to the modulation of experienced pain. We discuss various possible mechanisms underlying these findings and suggest a role of regulation of 5-HT receptors along the neuraxis as a function of differential 5-HTT-expression

Diabetic Neuropathy and Axon Reflex-Mediated Neurogenic Vasodilatation in Type 1 Diabetes

Objective: Axon reflex-mediated neurogenic vasodilatation in response to cutaneous heating may reflect early, pre-clinical small fibre dysfunction. We aimed to evaluate the distribution of the vascular flare area measured by laser doppler imaging (‘‘LDI FLARE area’’) in type 1 diabetes and in healthy volunteers. Research and Methods: Concurrent with clinical and electrophysiological examination to classify diabetic sensorimotor polyneuropathy (DSP), LDIFLARE area (cm 2) was determined in 89 type 1 diabetes subjects matched to 64 healthy volunteers. We examined the association and diagnostic performance of LDI with clinical and subclinical measures of DSP and its severity. Results: Compared to the 64 healthy volunteers, the 56 diabetes controls without DSP had significantly lower LDIFLARE area (p = 0.006). The 33 diabetes cases with DSP had substantially lower LDIFLARE area as compared to controls without DSP (p = 0.002). There was considerable overlap in LDIFLARE area between all groups such that the ROC curve had an AUC of 0.72 and optimal sensitivity of 70 % for the detection of clinical DSP. Use of a subclinical definition for DSP, according to subclinical sural nerve impairment, was associated with improved AUC of 0.75 and sensitivity of 79%. In multivariate analysis higher HbA1c and body mass index had independent associations with smaller LDIFLARE area. Conclusions: Axon reflex-mediated neurogenic vasodilatation in response to cutaneous heating is a biomarker of earl

The effect of acupuncture duration on analgesia and peripheral sensory thresholds

<p>Abstract</p> <p>Background</p> <p>Acupuncture provides a means of peripheral stimulation for pain relief. However, the detailed neuronal mechanisms by which acupuncture relieves pain are still poorly understood and information regarding optimal treatment settings is still inadequate. Previous studies with a short burst of unilateral electroacupuncture (EA) in the Tendinomuscular Meridians (TMM) treatment model for pain demonstrated a transient dermatomally correlated bilateral analgesic effect with corresponding peripheral modality-specific sensory threshold alterations. However, the impact of EA duration on the analgesic effect in this particular treatment model is unknown. To obtain mechanistically and clinically important information regarding EA analgesia, this current prospective cross-over study assesses the effects of EA duration on analgesia and thermal sensory thresholds in the TMM treatment model.</p> <p>Methods</p> <p>Baseline peripheral sensory thresholds were measured at pre-marked testing sites along the medial aspects (liver and spleen meridians) of bilateral lower extremities. A 5-second hot pain stimulation was delivered to the testing sites and the corresponding pain Visual Analog Scale (VAS) scores were recorded. Three different EA (5Hz) stimulation durations (5, 15 and 30 minutes) were randomly tested at least one week apart. At the last 10 seconds of each EA session, 5 seconds of subject specific HP stimulation was delivered to the testing sites. The corresponding pain and EA VAS scores of de qi sensation (tingling) during and after the EA were recorded. The measurements were repeated immediately, 30 and 60 minutes after the EA stimulation. A four-factor repeat measures ANOVA was used to assess the effect of stimulation duration, time, location (thigh vs. calf) and side (ipsilateral vs. contralateral) of EA on sensory thresholds and HP VAS scores.</p> <p>Results</p> <p>A significant (P < 0.01) main effect of time and location with warm, cold and hot pain thresholds at the four testing sites without any significant difference in duration effect was observed. Similar time and location effects were observed with HP VAS with the longer durations (15 and 30 minutes) of stimulation showed a slower onset, but a more sustainable bilateral analgesic benefit than the short stimulation duration (5 minutes). The 15-minute stimulation resulted in an earlier onset of analgesic effect than the 30-minute stimulation paradigm.</p> <p>Conclusion</p> <p>Longer durations of EA stimulation provide a more sustainable analgesic benefit to hot noxious stimulation than a shorter duration of stimulation. The increase of cold threshold with sustained warm threshold temperature elevation as observed in the longer durations of EA suggests that as the duration of EA lengthened, there is a gradual shifting from an initial predominantly spinally mediated analgesic effect to a supraspinally mediated modulatory mechanism of thermal pain. The 15-minute stimulation appeared to be the optimal setting for treating acute pain in the lower extremities.</p