Involvement of humoral factors in the mechanism of stress-induced analgesia in mice

The role of hypophyseal and adrenal mechanisms in the hypoalgesic response to non-contingent food delivery in the rat

Exposure to non-contingent food delivery has been shown to elicit an increase in nociceptive thresholds in rats. This hypoalgesia has previously been shown to be reversible by the opiate antagonist naloxone. Given that most opioid forms of SIA are found to rely on an intact pituitary-adrenal axis, this research examined the possibility that the hypoalgesic response to non-contingent food delivery is also hormonally mediated. Hypophysectomy (Expt. 1) but not bilateral adrenalectomy (Expt. 2) was found to completely attenuate the hypoalgesic response to non-contingent food delivery. Preliminary data from ongoing research is presented that points to the possible involvement of the hypophyseal peptides beta-endorphin and adrenocorticotropin hormone (ACTH).

Selective breeding of mice for high and low swim analgesia: differential effect on discrete forms of footshock analgesia

Selective breeding of mice displaying high and low swim-induced analgesia led to the development of two animal lines divergent in the magnitude of analgesic response to swimming. In this study, animals belonging to the seventh generation of both lines were exposed to two temporally different forms of footshock, one of which produced opioid and the other non-opioid analgesia. We found that selective breeding for high and low swim-induced analgesia exerted a striking influence on the magnitude of the opioid-mediated type of footshock analgesia, but was ineffective on that of the non-opioid type.