Sensory and Affective Dimensions of Pain and Anxiety Like Behaviors Are Altered in an Animal Model of Pain Empathy.

Objective: Pain is a unique and subjective experience that has a prominent function in animals' survival. Observation of pain in others leads to alterations in pain sensation and affection, termed "Empathy for pain". The present study aimed to evaluate the effect of empathy on sensory and affective dimensions of pain and its effect on anxiety-like behaviors. Method : In this study, male Wistar rats were used. Two cage mates were selected, one of which underwent administration of a noxious stimuli for 10 days and the other observed the conspecific in pain. Hot plate, tail flick, and conditioned place aversion were used to evaluate sensory and affective dimensions of pain, respectively. Anxiety-like behavior was assayed using elevated plus maze paradigm and time spent in open and close arms and number of entrance into each arm was recorded as the anxiety indicator within a 5-minute framework. Results: Rats observing the cage mate in pain had a lower threshold to noxious stimuli in comparison to controls. They also had an increased aversion from painful stimuli, demonstrating heightened affective response to pain. Anxiety-like behavior was also enhanced in the observers. Conclusion: Results of this study demonstrate that both sensory and affective dimensions of pain are altered following observation of pain in a conspecific. Further studies evaluating the underlying mechanisms are encouraged to elucidate the role of different neurotransmitters in this phenomenon.

Role of anxiety and depression in association with migraine and myofascial pain temporomandibular disorder.

BACKGROUND: Previous studies have demonstrated a strong association between primary headaches (HAs) and temporomandibular disorders (TMDs), specifically the myofascial pain subtype of TMD (MP TMD). The role of anxiety and depression in presentation and maintenance of MP TMD and migraine is previously demonstrated. Therefore, the objective of the current study was to evaluate the modification effect of anxiety and depression on the possible association of MP TMD and migraine. METHODS: In this retrospective case-control study, individuals between 15 and 45 years old who were diagnosed with migraine HA according to the international classification of headache disorder-II (ICHD-II) were selected as case subjects (n = 65). Non-HA control subjects were matched by sex and age (n = 63). Research diagnostic criteria (RDC/TMD) (Axis I) was used to diagnose patients with MP TMD; other subtypes of RDC/TMD Axis I were excluded from the study. Subjects' anxiety and depression were screened using Persian version of Hospital Anxiety and Depression Scale-14. Chi-square and Mantel-Haenszel tests were used to analyze the data. P < 0.05 was considered statistically significant. RESULTS: A significant association was found between migraine and MP TMD so that subjects with MP TMD had a five times chance of developing HA (P < 0.001). Further analysis using stratification method revealed that anxiety and depression have a modification effect in the association of MP TMD and HA and MP TMD patients with anxiety or depression had more chance of developing migraine HA (P = 0.003). CONCLUSION: Association between HA and TMD was observed in this study. Besides, we depicted that anxiety and depression interact in this association so that patients who did not have anxiety or depression did not demonstrate an association between TMD and HA. We suggest further studies to confirm the modifying effects of anxiety and depression.

Evidence of Altered Trigeminal Nociception in an Animal Model of Fibromyalgia.

Objective: Fibromyalgia (FM) is a debilitating chronic condition that significantly affects quality of life. A strong association has been demonstrated between FM and chronic pain in the trigeminal region in clinical studies. This study was performed to evaluate the response to acute and chronic noxious stimuli applied to the facial region. Methods: Adult male Wistar rats (250-270 g, N = 10 for each group) were used in the current study. A subchronic swim stress model was used as the animal model of FM. Anxiety-like behaviors and response to acute and chronic noxious stimuli were assayed using the elevated plus maze, eye wiping test, and orofacial formalin test, respectively. Balance and motor function were evaluated using rotarod and wire grip tests. Results: An increased anxiety-like behavior was observed in swim stress rats in comparison with control and sham subjects. Response to acute and chronic noxious stimuli in the trigeminal region was increased in the stressed rats. Motor and balance function were not altered following stress. Conclusions: Results of the current study demonstrated a hyperalgesic state in the trigeminal region in a possible animal model of FM. This study provides a reliable animal model for further research on the possible mechanisms of orofacial pain in FM.

Migraine patients have a higher prevalence of PTSD symptoms in comparison to chronic tension-type headache and healthy subjects: a case-control study.

OBJECTIVE: Headache is one of the most common disorders and has a heavy socioeconomic burden on both patients and society. Previous studies have demonstrated a high prevalence of psychological issues (e.g. depression and anxiety) in headache and especially migraine patients. The current study was designed to evaluate the prevalence of post-traumatic stress disorder (PTSD) symptomatology in chronic migraine (CM), chronic tension-type headache (CTTH) and healthy subjects. MATERIAL AND METHODS: CM and CTTH subjects were selected consecutively from patients referring to the department of neurology clinic at Shafa Hospital, Kerman University of Medical Sciences, Kerman, Iran. PTSD symptomatology was assessed using PTSD checklist civilian version-Persian edition (PCL-C). Control subjects were enrolled from the family members of headache patients who did not have any history of headache. Chi-square test was used to analyse data and p < .05 was considered statistically significant. RESULTS: Of the 60 control subjects, 5 had a PTSD symptomatology (8.3%); this prevalence was 13.3% for CTTH and 40% for CM groups. CM patients had a significantly higher prevalence of PTSD symptomatology in comparison to CTTH and control subjects (p < .05). With reference to gender, most of the subjects with PTSD symptomatology were female. CONCLUSION: Results of the current study demonstrated that CM patients have a higher prevalence of PTSD symptomatology compared to another chronic headache condition (CTTH) and healthy subjects, which should be considered while treating CM patients. Further studies in larger populations are demanded.

Simultaneous impairment of passive avoidance learning and nociception in rats following chronic swim stress.

BACKGROUND: Stress can alter response to nociception. Under certain circumstances stress enhances nociception, a phenomenon which is called stress-induced hyperalgesia (SIH). While nociception has been studied in this paradigm, possible alterations occurring in passive avoidance (PA) learning after exposing rats to this type of stress has not been studied before. MATERIALS AND METHODS: In the current study, we evaluated the effect of chronic swim stress (FS) or sham swim (SS) on nociception in both spinal (tail-flick) and supraspinal (53.5°C hot-pate) levels. Furthermore, PA task was performed to see whether chronic swim stress changes PA learning or not. Mobility of rats and anxiety-like behavior were assessed using open-field test (OFT). RESULTS: Supraspinal pain response was altered by swim stress (hot-plate test). PA learning was impaired by swim stress, rats in SS group did not show such impairments. Rats in the FS group showed increased mobility (rearing, velocity, total distant moved (TDM) and decreased anxiety-like behavior (time spent in center and grooming) compared to SS rats. CONCLUSIONS: This study demonstrated the simultaneous impairment of PA and nociception under chronic swim stress, whether this is simply a co-occurrence or not is of special interest. This finding may implicate a possible role for limbic structures, though this hypothesis should be studied by experimental lesions in different areas of rat brain to assess their possible role in the pathophysiology of SIH.

Role of nitric oxide in altered nociception and memory following chronic stress.

INTRODUCTION: Chronic stress alters sensory and cognitive function of mankind and animals. Sub-chronic swim stress is known to induce a prolonged hyperalgesia which is mediated through the NMDA and opioid systems. Nitric oxide is a soluble gas which acts as a retrograde messenger that modulates the release of the mentioned neurotransmitters. It is also involved in nociception and memory. The objective of the current study was to evaluate the role of NO pathway in nociception and memory impairments induced by sub-chronic swim stress. METHODS AND MATERIALS: A three session forced swimming stress protocol was administered to the rats. Pretreatment with l-NAME (10mg/kg, i.p.), l-Arginine (10mg/kg, i.p.) or saline was made before each swimming session. Anxiety-like behavior, nociception and passive avoidance (PA) learning were evaluated 24h after the last swim stress session. RESULTS: Swim stress altered locomotion and anxiety-like behaviors in the open field test. Reduced thermal threshold was observed in the nociceptive measurement after swim stress. Pretreatment with l-NAME could reverse the reduced threshold. A decreased step through latency was observed in the PA paradigm after swim stress, which could be inhibited by pretreatment with l-NAME. CONCLUSION: The results of this study indicate that sub-chronic swim stress impairs nociception and PA learning. NO pathway seems to have a modulatory role in these alterations. Further studies are suggested to examine the protective effect of NOS inhibitors on stress-induced impairments in sensory and cognitive function.

Walnut consumption protects rats against cisplatin-induced neurotoxicity.

Walnut is extensively used in traditional medicine for treatment of various ailments. It is described as an anticancer, anti-inflammatory, blood purifier and antioxidant agent. In this study, we investigated whether or not Walnut could protect neurons against cisplatin-induced neurotoxicity in rats. Dietary walnut (6%) was assessed for its neuroprotective effects through the alteration in performance of hippocampus- and cerebellum-related behaviors following chronic cisplatin treatment (5 mg/kg/week for 5 consecutive weeks) in male rats. We also evaluated the effect of cisplatin and walnut administration on nociception. We showed that exposure of adolescent rats to cisplatin resulted in significant decrease in explorative behaviors and memory retention. Walnut consumption improved memory and motor abilities in cisplatin treated rats, while walnut alone did not show any significant changes in these abilities compared to saline. Cisplatin increased latency of response to nociception, and walnut reversed this effect of cisplatin. We conclude that walnuts in the diet following anticancer drugs such as cisplatin might have a protective effect against cisplatin-induced disruptions in motor and cognitive function. However, further studies are needed to elucidate the exact mechanisms of this protective effect of walnut and to explore underlying mechanisms.