Effects of diet-induced obesity on motivation and pain behavior in an operant assay.

Obesity has been associated with multiple chronic pain disorders, including migraine. We hypothesized that diet-induced obesity would be associated with a reduced threshold for thermal nociception in the trigeminal system. In this study, we sought to examine the effect of diet-induced obesity on facial pain behavior. Mice of two different strains were fed high-fat or regular diet (RD) and tested using a well-established operant facial pain assay. We found that the effects of diet on behavior in this assay were strain and reward dependent. Obesity-prone C57BL/6J mice fed a high-fat diet (HFD) display lower number of licks of a caloric, palatable reward (33% sweetened condensed milk or 30% sucrose) than control mice. This occurred at all temperatures, in both sexes, and was evident even before the onset of obesity. This diminished reward-seeking behavior was not observed in obesity-resistant SKH1-E (SK) mice. These findings suggest that diet and strain interact to modulate reward-seeking behavior. Furthermore, we observed a difference between diet groups in operant behavior with caloric, palatable rewards, but not with a non-caloric neutral reward (water). Importantly, we found no effect of diet-induced obesity on acute thermal nociception in the absence of inflammation or injury. This indicates that thermal sensation in the face is not affected by obesity-associated peripheral neuropathy as it occurs when studying pain behaviors in the rodent hindpaw. Future studies using this model may reveal whether obesity facilitates the development of chronic pain after injury or inflammation.

Obesity increases nociceptive activation of the trigeminal system.

BACKGROUND: Obesity is a risk factor associated with several pain syndromes. However, the mechanisms underlying the association between obesity and pain are not known. The aim of this study was to test the hypothesis that obesity enhances neuronal responses to nociceptive stimulation within the trigeminal nucleus caudalis (TNC). METHODS: Male and female C57BL/6J mice were fed a high-fat or regular diet from the time of weaning until 20 weeks of age. We then quantified neuronal activation by measuring Fos immunoreactivity within the TNC in response to a facial injection of a low dose of capsaicin (1 µg/10 µL). RESULTS: We found that 0.01% capsaicin did not significantly increase Fos immunoreactivity in control mice fed a regular diet. In contrast, this low dose of capsaicin caused a 3.3-fold increase in Fos in the TNC in obese mice (p < 0.001). CONCLUSIONS: These results support the hypothesis that diet-induced obesity in mice enhances nociceptive processing within the TNC. Diet-induced obesity may be a useful model for mechanistic studies. Future studies will improve our understanding of how obesity may contribute to trigeminal pain by sensitizing the trigeminal nociceptive system.

History of childhood maltreatment is associated with comorbid depression in women with migraine.

BACKGROUND: A bidirectional relationship between migraine and depression suggests a neurobiological link. Adverse experiences, particularly childhood maltreatment, may alter neurobiological systems, and predispose to a multiplicity of adult chronic disorders. Our objective is to determine, within a headache clinic population of women, if depression moderates the abuse-migraine relationship. METHODS: At six headache specialty clinics, women with migraine were diagnosed using ICHD-II criteria, and frequency was recorded. A questionnaire regarding maltreatment history, headache characteristics, current depression, and somatic symptoms was completed. RESULTS: A total of 949 women with migraine completed the survey: 40% had chronic headache (> or =15 headache days/month) and 72% had "very severe" headache-related disability. Major depression was recorded in 18%. Physical or sexual abuse was reported in 38%, and 12% reported both physical and sexual abuse in the past. Migraineurs with current major depression reported physical (p < 0.001) and sexual (p < 0.001) abuse in higher frequencies compared to those without depression. Women with major depression were more likely to report sexual abuse occurring before age 12 years (OR = 2.30, 95% CI: 1.14 to 4.77), and the relationship was stronger when abuse occurred both before and after age 12 years (OR = 5.08, 95% CI: 2.15 to 11.99). Women with major depression were also twice as likely to report multiple types of maltreatment (OR = 2.07, 95% CI: 1.27 to 3.35) compared to those without depression. CONCLUSIONS: Childhood maltreatment was more common in women with migraine and concomitant major depression than in those with migraine alone. The association of childhood sexual abuse with migraine and depression is amplified if abuse also occurs at a later age.

High prevalence of somatic symptoms and depression in women with disabling chronic headache.

OBJECTIVE: To better define, in women with headache, the relationship of depression and somatic symptoms to headache, characterized by diagnoses, frequency, and disability. METHODS: At six headache specialty clinics, women with headache were classified using ICHD-II criteria, and frequency was recorded. A questionnaire addressing demographics, age at onset of headache, headache-related disability, somatic symptom, and depression severity was completed. Logistic regression was performed to measure the associations of headache frequency and headache-related disability with somatic symptom and depression severity. RESULTS: A total of 1,032 women with headache completed the survey, 593 with episodic (96% with migraine) and 439 with chronic headache (87% with migraine). Low education and household income was more common in chronic headache sufferers and in persons with severe headache disability. Somatic symptom prevalence and severity was greater in persons with chronic headache and with severe headache-related disability. Significant correlation was observed between PHQ-9 and PHQ-15 scores (r = 0.62). Chronic headache, severe disability, and high somatic symptom severity were associated with major depressive disorder (OR = 25.1, 95% CI: 10.9 to 57.9), and this relationship was stronger in the subgroup with a diagnosis of migraine (OR = 31.8, 95% CI: 12.9 to 78.5). CONCLUSIONS: High somatic symptom severity is prevalent in women with chronic and severely disabling headaches. Synergistic relationship to major depression exists for high somatic symptom severity, chronic headache, and disabling headache, suggesting a psychobiological underpinning of these associations.