Shifting the sociometer: opioid receptor blockade lowers self-esteem.

Given the evolutionary importance of social ties for survival, humans are thought to have evolved psychobiological mechanisms to monitor and safeguard the status of their social bonds. At the psychological level, self-esteem is proposed to function as a gauge-'sociometer'-reflecting one's social belongingness status. At the biological level, endogenous opioids appear to be an important substrate for the hedonic signalling needed to regulate social behaviour.

Anhedonia to music and mu-opioids: Evidence from the administration of naltrexone.

Music's universality and its ability to deeply affect emotions suggest an evolutionary origin. Previous investigators have found that naltrexone (NTX), a μ-opioid antagonist, may induce reversible anhedonia, attenuating both positive and negative emotions. The neurochemical basis of musical experience is not well-understood, and the NTX-induced anhedonia hypothesis has not been tested with music.

Behavioral evidence for photophobia and stress-related ipsilateral head pain in transgenic Cacna1a mutant mice.

Migraine is a highly prevalent, disabling and complex episodic brain disorder whose pathogenesis is poorly understood, due in part to the lack of valid animal models. Here we report behavioral evidence of hallmark migraine features, photophobia and unilateral head pain, in transgenic knock-in mice bearing human familial hemiplegic migraine, type 1 (FHM-1) gain-of-function missense mutations (R192Q or S218L) in the Cacna1a gene encoding the CaV2.1 calcium channel α1 subunit.

The neurochemistry of music.

Music is used to regulate mood and arousal in everyday life and to promote physical and psychological health and well-being in clinical settings. However, scientific inquiry into the neurochemical effects of music is still in its infancy. In this review, we evaluate the evidence that music improves health and well-being through the engagement of neurochemical systems for (i) reward, motivation, and pleasure; (ii) stress and arousal; (iii) immunity; and (iv) social affiliation.

Spinal cord Toll-like receptor 4 mediates inflammatory and neuropathic hypersensitivity in male but not female mice.

The innate immune system is increasingly appreciated to play an important role in the mediation of chronic pain, and one molecule implicated in this process is the Toll-like receptor 4 (TLR4). Here, using pharmacological and genetic manipulations, we found that activating TLR4 in the spinal cord, with the agonist lipopolysaccharide (LPS), causes robust mechanical allodynia but only in male mice. Spinal LPS had no pain-producing effect in female mice.

Pain characteristic differences between subacute and chronic back pain.

Unlabelled: Back pain is commonly classified based on duration. There is currently limited information regarding differences in the clinical features of back pain between these duration-based groupings. Here, we compared the pain characteristics of patients with subacute (SBP; pain 6-16 weeks, n = 40) and chronic back pain (CBP; pain ≥1 year, n = 37) recruited from the general population.

Coding of facial expressions of pain in the laboratory mouse.

Facial expression is widely used as a measure of pain in infants; whether nonhuman animals display such pain expressions has never been systematically assessed. We developed the mouse grimace scale (MGS), a standardized behavioral coding system with high accuracy and reliability; assays involving noxious stimuli of moderate duration are accompanied by facial expressions of pain. This measure of spontaneously emitted pain may provide insight into the subjective pain experience of mice.

Social modulation of pain as evidence for empathy in mice.

Empathy is thought to be unique to higher primates, possibly to humans alone. We report the modulation of pain sensitivity in mice produced solely by exposure to their cagemates, but not to strangers, in pain. Mice tested in dyads and given an identical noxious stimulus displayed increased pain behaviors with statistically greater co-occurrence, effects dependent on visual observation.

Sex differences in the effects of amiloride on formalin test nociception in mice.

Amiloride is a nonspecific blocker of acid-sensing ion channels (ASICs) that have been recently implicated in the mediation of mechanical and chemical/inflammatory nociception. Preliminary data using a transgenic model are suggestive of sex differences in the role of ASICs. We report here that systemic administration of amiloride (10-70 mg/kg ip) produces a robust, dose-dependent blockade of late/tonic phase nociceptive behavior on the mouse formalin test (5%; 20 microl) in female but not male mice, completely abolishing the known sex difference in formalin test response.