Tail-pinch hyperalgesia and analgesia: Test-specific opioid and nonopioid actions

Empathic behavior according to the state of others in mice

INTRODUCTION

Empathic behavior is essential for social activities in social animals. Therefore, lack of empathy is a feature of several neuropsychiatric disorders. However, the underlying mechanisms of empathy and which animals possess it remain unclear. In this study, we investigated whether mice show empathic behavior.

METHODS

We tested mice for empathy-like behaviors toward conspecifics who were distressed. We investigated behavioral changes in cage-mate or stranger mice.

RESULTS

When the conspecific mice were in a painful state, subject mice showed preferential approach behavior toward them, presumably recognizing the state. Both visual information and olfactory information are indispensable for this empathic behavior.

CONCLUSIONS

These results suggest that the mouse recognizes the emotional state of the conspecific and engages in social interaction. The results of this study are useful for the elucidation of the causal mechanisms involved in neuropsychiatric disorders and may contribute in the development of novel treatment targets.

Arcuate nucleus lesions reduce opioid stress-induced analgesia (SIA) and enhance non-opioid SIA in rats

When rats were tested more than two weeks following surgery, lesions of the medial basal hypothalamus centered on the arcuate nucleus enhanced a form of foot-shock stress-induced analgesia (SIA) that was not blocked by injections of the opiate receptor blocker, naltrexone (6 mg/kg;). These arcuate nucleus lesions reduced the SIA produced by the same stressor when similar rats were tested 3-4 days following surgery. Finally, when similar rats were tested more than 2 weeks following surgery these lesions reduced a different form of SIA that was blocked by naltrexone. There were no effects of the lesions or naltrexone on baseline pain reactivity in any of the experiments. We suggest that arcuate nucleus lesions disrupt a system important for the elaboration of opiate-mediated SIA (Expt. 4), perhaps by damaging the brain's beta-endorphin system. In response to damage to this opioid analgesic system, we hypothesize that the damaged brain initiates time-dependent compensatory changes in an undamaged non-opioid analgesic system, resulting in enhanced non-opiate-mediated SIA.