Perception Of Thermal Stimuli Research Articles

Quantitative sensory testing in a magnetic resonance environment: considerations for thermal sensitivity and patient safety.

Quantitative sensory testing (QST) is often used to understand the perceptual basis of acute and chronic conditions, including pain. As the need grows for developing a mechanistic understanding of neurological pathways underlying perception in the basic and clinical sciences, there is a greater need to adapt techniques such as QST to the magnetic resonance (MR) environment. No studies have yet evaluated the impact of the MR environment on the perception of thermal stimuli. This study aimed to evaluate the differences in temperature sensitivity outside an MR environment and during an MRI scanning session. We hypothesized that there would be a difference in how participants reported their pain sensitivity between the two environments. Healthy participants underwent thermal QST outside the MR scanning environment, where they were asked to rate the temperature of a noxious stimulus at which they perceived their pain to be 7/10, using a Likert scale ranging from 0 to 10. Participants repeated this procedure inside a 3.0 T MRI approximately 30 min later. We repeated our investigation in a clinical cohort of participants with a chronic pain condition. There were statistically significant changes of 1.1°C in thermal sensitivity between environments. This increase in pain threshold was found in healthy participants and replicated in the clinical cohort. Findings can be applied toward improving MR safety, the resolution of brain pathways underlying pain mechanisms, and to more broadly comment on the impact of the MR environment on investigations that integrate perception-influenced processes.

654 Stimulation and Protection of Cutaneous Sensory Neuron System induced by Forest Honey from Ikaria Island

Sensory innervation involves nerve endings which are located in dermis and epidermis, reaching the uppermost viable layer of skin. Cutaneous innervation is closely linked with major skin functions and contributes to skin homeostasis. Wound-healing, repair process, sense of touch, perception of thermal stimuli as well as intra-epidermal nerve fibre density on face decrease with aging and are associated with changes in neuronal functions and structures. For centuries, honey has been utilized for wound healing purposes but recently, information regarding honey’s mechanisms of action on wound healing and as a therapeutic agent for skin disorders has accumulated at a rapid pace. However, each honey is very specific especially due to the surrounding flora and bee strains associated. Our previous studies have shown that all honeys were not equivalent and consequently, they did not induce the same biological activities. For counteracting the alteration of sensory innervation system, we studied the activities of a forest honey from Ikaria Island (FHII) on a new human sensory neurons 2D model. Human sensory neurons derived from human induced pluripotent cells were co-cultured with human keratinocytes. After treatment by FHII for 10 days; the numbers of neurons, the growth of neurites and the expression of TrkA (NGF receptor) and mu-opioid receptors (MOR), which are four key parameters for sensory neuron homeostasis, were studied by immunocytofluorescence. We have observed that treatment by FHII did not induce neurone proliferation but significantly stimulated by 30% the growth of neurites and the increase of TrkA and MOR expressions by +38% and +45% respectively. These results indicate that FHII stimulates the development of neuronal network, protects its functionalities and suggest a beta-endorphin-like activity of this natural compound making this forest honey from Ikaria island a good candidate for maintaining homeostasis of human cutaneous sensory neuron system and skin.

A Nociceptive Signaling Role for Neuromedin B

Here we used an array-based differential screen to uncover the expression of the neuropeptide neuromedin B (NMB) in the trigeminal ganglia of mice. Double-labeling experiments reveal NMB is expressed in a subset of sensory neurons that colabel with calcitonin gene-related peptide and TRPV1 suggestive of a role for NMB in nociception. Indeed, administration of NMB antagonist greatly attenuates edema and nerve sensitization following stimulation of peripheral nerves with mustard oil, demonstrating that NMB contributes to neurogenic inflammation. Moreover, direct injection of NMB causes local swelling and nociceptive sensitization. Interestingly, we also find that the receptor for NMB is expressed in interneurons in the superficial layers of the dorsal horn. We used NMB-saporin to specifically eliminate NMBR-expressing neurons and determined they are required in responses to noxious heat, but not for reaction to mechanical and pruritic stimuli. Thus, NMB may be a neurotransmitter that is selectively involved in the perception of thermal stimuli.

Graded cutaneous electrical vs thermal stimulation in humans shows different insular and cingulate cortex activation

Pain can result from various sensory input modalities. To elucidate the differences of cortical responses to graded electrical and thermal stimulation, functional magnetic resonance imaging (fMRI) results of two studies using the same stimulation paradigms but different modalities with 15 healthy subjects each are compared. During painful electrical stimulation contralateral dorsal posterior insula and ventral posterior anterior cingulate cortex (ACC) activated more. During thermal stimulation, there was more activation in ipsilateral primary motor area (MI)/primary sensory area (SI) complex and premotor areas as well as dorsal posterior ACC. Thus electrostimulation preferably activates structures of the lateral pain projection system resulting in contralateral dorsal posterior insula and ventral posterior ACC activation. During thermal stimulation, more dorsal areas of the posterior ACC activated. The activation of ipsilateral MI/SI complex and premotor areas may be attributed to the slower perception of thermal stimuli and resulting re-evaluation. This has to be taken into account in the interpretation of other cross-modality studies as well.

Improved analgesia with clonidine when added to local anesthetic during combined spinal‐epidural anesthesia for hip arthroplasty: a double‐blind, randomized and placebo‐controlled study

The perioperative effects of intrathecal and epidural clonidine combined with local anesthetic were evaluated in 60 patients undergoing hip arthroplasty. This was a double-blinded study and the patients were randomized into three groups, with 20 patients in each group. All patients received spinal anesthesia with 17.5 mg of plain bupivacaine with 15 microg of clonidine (Group BC-RC) or without clonidine (Groups B-R and B-RC). Postoperatively, epidural infusion was administered in the following way: Group B-R-ropivacaine 4 mg h(-1); Groups B-RC and BC-RC: ropivacaine 4 mg h(-1) and clonidine 40 microg h(-1). Sensory block was assessed with light touch, pinprick, transcutaneous electrical stimulation at T12 and L2 dermatomes, and perception of thermal stimuli. The maximal upper level of sensory block measured by pin-prick (T6-T7) did not differ between the groups while the partial sensory block for cold and warmth were increased two dermatomes above pin-prick level in the group with intrathecal clonidine compared to the other two groups (P < 0.05). Duration of anesthesia, analgesia and motor block were longer in Group BC-RC compared to Groups B-R and B-RC (P < 0.02). Postoperatively, both VAS score on movement and PCA-morphine consumption were higher in Group B-R than in Groups B-RC and BC-RC (P < 0.01). The arterial pressure and heart rate in Groups B-RC and BC-RC were significantly lower than in Group B-R at 10-24 and 15-24 h, respectively, after spinal injection. Low-dose intrathecal clonidine provided a better quality of anesthesia and longer-lasting analgesia. Epidural clonidine-ropivacaine infusion resulted in improved postoperative analgesia but was associated with a moderate decrease in blood pressure.