Foot Shock Analgesia

Abstract

Effects of inescapable foot shock on pain threshold and on levels of immunoreactive β-endorphin (ir-βEP) in anterior pituitary, neuro-intermediate lobe and plasma were determined by hot plate test and radioimmunoassay respectively. Whereas handling and conditioned stress failed to alter baseline pain threshold, 20 min inescapable foot shock produced modest and transient analgesia. Levels of plasma ir-βEP and corticosterone were significantly and concurrently raised by all treatments and remained elevated 40 min after foot shock. Changes in plasma levels of ir-βEP and corticosterone were found to parallel one another but did not correlate with changes in pain threshold. AP content of ir-βEP was significantly reduced 60 min after the cessation of inescapable foot shock, and N-IL content from 20 min after. The findings suggest that (i) plasma levels of ir-βEP and corticosterone do not reflect changes in pain threshold, and (ii) ir-βEP levels in anterior pituitary, neurointermediate lobe and plasma probably are not causally related to foot shock analgesia.

Stress-induced Changes in Plasma Concentrations of Immunoreactive ß-Endorphin and Cortisol in Response to Routine Surgical Procedures in Lambs

“…The degree of stress-induced analgesia (Wolfle and Liebeskind 1983) that might be associated with such increased peripheral plasma {3-EP I -31 levels in the lamb was not assessed in these preliminary experiments. Increased levels of {3-EP may not always be correlated with the degree of induced analgesia, for example, after footshock in rats (Lim et al 1982b) or after acupuncture in horses (Bossut et al 1983), although {3-EP I -31 has been shown to be a potent analgesic by intravenous injection (Tseng et al 1976;Feldberg and Smyth 1977).…”