Endogenous opiates and behavior: 2005

Bodnar, Richard J.; Klein, Gad

doi:10.1016/j.peptides.2006.07.011

Cited by 75 publications

(52 citation statements)

References 1,339 publications

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“…In this experiment, 10 females and six males were tested in five groups of 3-4 individuals in a within-subject design with each subject acting as their own control (each group was tested twice, first in the control condition and then in the experimental condition). In experiment 3, three males and two females (mean age ¼ 23.2 years, range [22][23][24] formed the experimental group, and eight males and three females (mean age ¼ 24.6 years, range ¼ 20-32) the control group.…”

Section: Methodsmentioning

confidence: 99%

Social laughter is correlated with an elevated pain threshold

Dunbar

Baron²,

Frangou³

et al. 2011

Proc. R. Soc. B.

175

165

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Although laughter forms an important part of human non-verbal communication, it has received rather less attention than it deserves in both the experimental and the observational literatures. Relaxed social (Duchenne) laughter is associated with feelings of wellbeing and heightened affect, a proximate explanation for which might be the release of endorphins. We tested this hypothesis in a series of six experimental studies in both the laboratory (watching videos) and naturalistic contexts (watching stage performances), using change in pain threshold as an assay for endorphin release. The results show that pain thresholds are significantly higher after laughter than in the control condition. This pain-tolerance effect is due to laughter itself and not simply due to a change in positive affect. We suggest that laughter, through an endorphin-mediated opiate effect, may play a crucial role in social bonding.

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Section: Methodsmentioning

confidence: 99%

Social laughter is correlated with an elevated pain threshold

Dunbar

Baron²,

Frangou³

et al. 2011

Proc. R. Soc. B.

175

165

View full text Add to dashboard Cite

show abstract

“…Moreover, the interrelationship between the above-mentioned brain sites and morphine-induced behavioral sensitization has been well established [18] . On the other hand, previous studies have clearly shown an interaction between the glutaminergic system and dopamine [19,20] or morphine [18] .…”

Section: Introductionmentioning

confidence: 99%

Morphine-Induced Behavioral Sensitization Increased the mRNA Expression of NMDA Receptor Subunits in the Rat Amygdala

et al. 2008

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This study was designed to evaluate the effect of repeated morphine treatment on rat behavioral responses. In the genetic section, the mRNA expression of NMDA receptor subunits (NR1 and NR2A) was measured in certain areas of the male rat brain (striatum, prefrontal cortex, hippocampus, hypothalamus and amygdala). In the behavioral section, the effect of repeated morphine treatment on animal models such as locomotion, oral stereotypy, and state-dependent memory in a passive avoidance test was evaluated in the presence or absence of MK801 (NMDA receptor antagonist). Our results showed that chronic morphine treatment, followed by a 7-day (but not 24-hour) washout period, potentiated the effect of test doses of morphine, which is referred to as behavioral sensitization. Meanwhile, pretreatment of animals with MK801 (0.1 and 0.25 mg/kg), 30 min before a test dose of morphine (5 mg/kg), failed to attenuate the locomotion and oral stereotypy in the behavioral sensitization state. Interestingly, a higher dose of MK801 (0.25 mg/kg) decreased memory retrieval induced by morphine (2.5 mg/kg) in state-dependent memory. This effect may be due to the intrinsic motor enhancer property of higher doses of MK801, rather than the blockade of NMDA receptors. It can be concluded that MK801 does not affect morphine-induced behavioral sensitization in the expression phase. In the genetic section of the study, results of quantitative real-time RT-PCR clearly indicated that morphine sensitization increased the expression of NMDA receptor subunits mRNA in the amygdala (NR1 by 104% and NR2A by 85%), while the other areas of the brain were unaffected. Maenwhile, no change in the mRNA levels was observed in non-sensitized animals (chronic morphine treatment followed by a 24-hour washout period). In summary, the present study indicates that repeated morphine treatment followed by long-term (7-day washout) induces behavioral sensitization and causes a delayed increase in mRNA levels of NMDA receptor subunits in the rat amygdala. Meanwhile, it has previously been reported that the amygdala is involved in behavioral sensitization. Thus, it can be concluded that the increase in NMDA receptor expression is associated with morphine-induced behavioral sensitization.

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“…Anatomical evidence for this concept derives from the observation that hypothalamic POMC neurons project to a broad array of cerebral structures [6]. …”

Section: Discussionmentioning

confidence: 99%

“…The endogenous opioid system has been implicated in a number of CNS functions and may be altered in various pathological states [6]. It appears to modulate responsesto stress, learning and memory acquisition [7].…”

Section: Introductionmentioning

confidence: 99%

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Sex Differences in Brain and Plasma β-Endorphin Content following Testosterone, Dihydrotestosterone and Estradiol Administration to Gonadectomized Rats

et al. 2009

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Aims: The present study aims at evaluating the effect of a 2-week treatment with testosterone (T), dihydrotestosterone (DHT) and estradiol valerate (E₂V) on brain and plasma β-endorphin (β-END) concentrations in gonadectomized rats of both sexes. Methods: Eight groups of female and 8 groups of male Wistar rats were included. For each sex, 1 group of gonad-intact and 1 group of gonadectomized rats were employed as controls (placebo). The other groups received subcutaneous T at the doses of 10 and 100 μg/kg/day (female rats) or 1 and 5 mg/kg/day (male rats). Subcutaneous DHT was administered at the doses of 1, 10, 100 μg/kg/day (female rats) or 0.1, 1 and 5 mg/kg/day (male rats). E₂V was administered subcutaneously at 0.05 mg/kg/day. β-END levels were measured in different brain areas and plasma. Results: Ovariectomy (OVX) induced a significant decrease in β-END in all brain areas analyzed as well as in plasma. Orchidectomy (OCX) reduced opioid concentration in the hypothalamus, anterior pituitary and neurointermediate lobe. In OVX rats, T replacement as well as E₂V significantly increased β-END concentration in all brain areas and in plasma. In the OCX group, T and E₂V did not influence β-END concentrations in different hypothalamic areas. However, they produced a significant rise in β-END levels in the hypothalamus, neurointermediate lobe, anterior pituitary and plasma. Conversely, DHT replacement did not affect β-END levels at any dose administered, either in males or females. Conclusions: The sensitivity of the endogenous opiatergic system to T administration seems to be sex-related. This effect is particularly evident in the brains of female animals where this endogenous endorphin elicits a much greater response than it does in males that have undergone gonadal steroid depletion and subsequent T replacement.

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Endogenous opiates and behavior: 2005

Cited by 75 publications

References 1,339 publications

Social laughter is correlated with an elevated pain threshold

Social laughter is correlated with an elevated pain threshold

Morphine-Induced Behavioral Sensitization Increased the mRNA Expression of NMDA Receptor Subunits in the Rat Amygdala

Sex Differences in Brain and Plasma β-Endorphin Content following Testosterone, Dihydrotestosterone and Estradiol Administration to Gonadectomized Rats

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