||Aggression and the Three Opioid Families (Endorphins, Enkephalins, and Dynorphins) in Mice.
The main objective of the current study was to examine the possible genetic relationship between intermale aggression and brain levels of enkephalins, endorphins, and dynorphins in 11 inbred strains of mice. Pursuit, rattling, and attack behaviors were observed in a dyadic encounter with a standard opponent. The findings indicate that brain Met-sup-5 -enkephalin levels were significantly and highly positively correlated with attack latency. Brain adrenocorticotrophic hormone (ACTH) and β-endorphin levels were significantly and negatively correlated with the number of rattlings, which is consistent with the hypothesis that rattling is a stress-related behavior. In contrast with Met-sup-5-enkephalin, ACTH and β-endorphin, the correlations between dynorphin A and aggression scores were nonsignificant and very low. These preliminary results suggest that common genetic sources of variation contribute to differences between the 11 inbred strains in both endogenous opioidergic systems and intermale aggression. Further studies are required to confirm the genetic relationship between offensive aggression and brain enkephalins and endorphins and to better understand the mechanisms underlying the role of endogenous opioids in offensive aggression with regard to opioid receptor activity. (PsycINFO Database Record (c) 2007 APA, all rights reserved)