β-endorphin-like immunoreactivity levels in the hypothalamus, the periaqueductal grey and the pituitary of the DBA mouse: Determination by ELISA and relationship to nociception

Abstract The present paper describes the development and application of an enzyme-linked immunosorbent assay (ELISA) for the assessment of β-endorphin-like immunoreactivity (β-ELIR) levels in the hypothalamus, the periaqueductal grey (PAG) and the pituitary of DBA/2 mice that were subjected to mild social stress (aggressive confrontation). After confrontation these subjects showed elevated tail-flick latencies (TFL) when compared to controls, a finding that indicates stress-induced analgesia (SIA). A positive correlation was found between individual TFLs and β-ELIR levels in the PAG but not in the hypothalamus and the pituitary. These results suggest that high individual baseline PAG β-ELIR levels may be taken as a predictor of high degrees of stress-induced analgesia.