Changes in beta-endorphin and stress-induced analgesia in mice after exposure to forced walking stress.
In this study, we attempted to clarify the correlation between changes in the level of beta-endorphin (beta-EP) in the mouse brain and the stress-induced analgesia (SIA) after exposing animals to forced walking stress. The immunohistochemical distribution of beta-EP after stress was first analyzed quantitatively in mice and then more specifically using a microphotometry system with results showing that the fluorescence intensity of beta-EP in the peri-aqueductal gray matter (PAG) and arcuate nucleus of the medial basal hypothalamus (ARC) was increased 6 h after exposure to forced walking stress. Further, SIA was examined after exposing animals to the forced walking stress and the formalin test. At 6 h after forced walking stress, significant SIA was observed in the second phase (from 10 to 30 min after formalin injection) of the formalin-induced paw licking behavior, but not in the first phase (from 0 to 10 min after formalin injection). This SIA was antagonized by beta-EP-(1-27), an opioid epsilon receptor antagonist. In nonstressed mice, the injection of beta-EP produced a reduction in formalin-induced paw-licking in the second phase. A significant antinociceptive effect by beta-EP was well antagonized by beta-EP-(1-27). Thus, the present results suggest that the increase in beta-EP levels in PAG and/or ARC may be involved in SIA after exposure of mice to the forced walking stress.
Nakagawasai
O
O
Department of Pharmacology, Tohoku Pharmaceutical University, Sendai, Japan. osamun@tohoku-pharm.ac.jp
Tadano
T
T
Tan No
K
K
Niijima
F
F
Sakurada
S
S
Endo
Y
Y
Kisara
K
K
D000698:Analgesia; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D001921:Brain / Q000378:metabolism*; D005557:Formaldehyde; D006801:Humans; D008297:Male; D051379:Mice; D010146:Pain / Q000378:metabolism; D010147:Pain Measurement; D005082:Physical Exertion; D013312:Stress, Physiological / Q000378:metabolism*; D016138:Walking; D001615:beta-Endorphin / Q000378:metabolism*
D005557:Formaldehyde; D001615:beta-Endorphin