Social conflict-induced changes in nociception and beta-endorphin-like immunoreactivity in pituitary and discrete brain areas of C57BL/6 and DBA/2 mice.
The present study characterizes the time course of social conflict analgesia and its reversibility by opioid antagonist drugs in the C57BL/6 and DBA/2 inbred strains of mice and examines the relationship between alterations in brain and pituitary levels of beta-endorphin-like immunoreactivity (beta-ELIR) and the antinociception elicited by social stress. Data revealed statistically significant strain differences in regard to beta-ELIR in control animals. The pituitary content of beta-ELIR was higher in DBA/2, while the values in the periaqueductal grey (PAG) and in the amygdala were higher in C57BL/6 mice. No interstrain differences were found in the hypothalamus. Exposure to 50 attack bites resulted in a 6-fold higher analgesia in DBA/2 mice and in a strain-independent fall of beta-ELIR in pituitary (approximately 27%) and PAG (23%). PAG but not pituitary beta-ELIR levels in C57BL/6 mice correlated positively with the increase in tail-flick latency after attack. Mere confrontation with a non-aggressive opponent failed to induce analgesia and was associated in C57BL/6 mice with a significant reduction in the beta-ELIR content of both the pituitary and the PAG. The data are discussed in terms of genotype-dependent sensitivity of the beta-endorphin system to stress and its relation to analgesia.
Külling
P
P
Institute of Pharmacology, University of Zurich, Switzerland.
Frischknecht
H R
HR
Pasi
A
A
Waser
P G
PG
Siegfried
B
B
D000374:Aggression / Q000502:physiology*; D000698:Analgesia; D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000503:physiopathology; D004723:Endorphins / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D010146:Pain / Q000378:metabolism / Q000503:physiopathology*; D010902:Pituitary Gland / Q000378:metabolism* / Q000503:physiopathology; D012931:Social Environment; D013045:Species Specificity
D004723:Endorphins