Naltrexone-reversible pain suppression in the isolated attacking mouse

Fighting pairs of isolated DBA/2 mice showed a significant increase in tail-flick response latencies independent of whether opponents were losing or winning the combat. The effect lasted less than 10 min in both animals. Elevated pain thresholds were also found in isolates that attacked a nonaggressive conspecific, and were prevented by naltrexone (0.2 mg/kg), while a larger dose (1.0 mg/kg) inhibited the attack behavior. A small increase in pain threshold was observed after exposure of isolates to the test box alone, while isolation per se had no effect on baseline tail-flick latencies. The data demonstrate that endogenous pain suppressing systems are activated during attack and suggest that this opioid-mediated antinociception is a correlate of the isolation syndrome, reflecting enhanced arousal of the attacking animal.     

Incongruent Names: A Theme in the History of Chinese Philosophy

This essay is meant to shed light on a discourse that spans centuries and includes different voices. To be aware of such trans-textual resonances can add a level of historical understanding to the reading of philosophical texts. Specifically, we intend to demonstrate how the notion of the ineffable Dao 道, prominently expressed in the Daodejing 道德經, informs a long discourse on incongruent names (ming 名) in distinction to a mainstream paradigm that demands congruity between names and what they designate. Thereby, we trace the development of the idea of the ineffable Dao quite differently from modern mystical interpretations. We show how, in an early Chinese context, it first gives rise to a sociopolitical critique of the incongruity underlying socially constructed names in the Zhuangzi 莊子, then to a discourse on the incongruity between moral virtues and names in Xuanxue 玄學 philosophy, and eventually to Sengzhao’s 僧肇 claim that a perceived congruence of names with things does not entail actual congruence between names and reality.     

Postaggression footshock inhibits aggressive behavior in dominant but not in isolated mice

Aggressive behavior of dominant and isolated mice was assessed in intermale encounters with nonaggressive intruder mice. After an attack period of 90 s, the aggressor was exposed to a footshock punishment and retested the next day. The shock treatment, independent of the intensity and duration, failed to inhibit spontaneous aggression in isolated DBA/2 mice, while it significantly suppressed spontaneous aggression in dominant C57BL/6 mice. The different effects of post-trial shock punishment were not due to a different shock sensitivity and did not depend on the type of opponent used. Strain differences have been ruled out by the use of dominant and isolated ICR mice. Again, shock punishment was ineffective in isolates, while it reduced aggression in dominant animals. The findings were discussed with reference to the impaired learning performance reported for isolated animals, and suggest a difference between the aggression of isolated and that of dominant mice.     

Place avoidance learning and stress-induced analgesia in the attacked mouse: role of endogenous opioids

In this study, mechanisms of pain inhibition (tail-flick test) and memory (place avoidance paradigm) were investigated in attacked, DBA/2 and C57BL/6, mice. During training, exposure of test animals to 10 or 30 bites by an aggressive, isolated ICR mouse situated in the dark half of a bright/dark conditioning box induced a significantly higher social conflict analgesia in DBA than in C57 mice. Naltrexone (0.5 and 2.0 mg/kg) reduced this response in DBA mice that received 30, but not 10, bites and was ineffective in C57 mice. This points to different, opioid versus naltrexone-insensitive nonopioid, analgesic mechanisms. During place choice testing in the same box 24 h later, DBA mice that had received 30, but not 10, bites showed a significant, naltrexone-reversible, avoidance of the attack place. No place avoidance learning was observed in C57 mice. The data provided unequivocal evidence that place avoidance learning was a result of associative conditioning, in that neither pairing nor social conflict per se significantly changed the preference for the dark side seen in experimentally naive DBA mice. Antagonism of place avoidance conditioning was observed regardless of whether testing was carried out in the drugged or undrugged state, excluding possible state-dependent effects as an explanation for the naltrexone-induced impairment. Individual correlational analysis in saline-injected, attacked DBA mice revealed a negative relationship between the analgesic state immediately after training and the avoidance of attack place during testing. In summary, the results suggest strain-dependent analgesic and learning mechanisms and indicate that endogenous opioids released in attacked DBA mice support pain inhibition and modulate the memorization of attack place by their analgesic effects, as well as by mechanisms independent of pain inhibitory systems.