Modification of the Analgetic Effect in Relation to the Development Stage in Rats

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Abstract
Changes in the sensitivity to analgesic action after morphine application of ultrasonic algic stimulus were investigated in postnatal developing rats. In 14- and 17-day-old animals a high sensitivity was observed; on the contrary a significant decrease in analgetic action (2 mg/kg of morphine) was observed in 32-day-old animals. In 60-, 90- and 120-day-old animals an increasing intensity of analgetic action was established. But in 120-day-old animals the analgetic action was only 60% of that observed in 17-day-old animals.