Changes in thermonociceptive thresholds and the role of enkephalinase A in homeostasis in morphine-tolerant rat offspring

The dynamics of thermonociceptive thresholds as a marker of the state of the endogenous opioid system was studied in the offspring of morphine-tolerant rats. Significant, age-dependent increase in thermonociceptive thresholds and higher levels of enkephalinase A in structures of the endogenous antinociceptive system were observed in the offspring compared with the control. These findings attest to disturbances of the opioid system in the progeny of morphine-tolerant rats and confirm the key role of enkephalinase A in the maintenance of homeostasis disturbed by chronic prenatal morphine treatment.