Novelty-seeking behavior and stress-induced locomotion in rats of juvenile period differentially related to morphine place conditioning in their adulthood.

The relationship between motor responses in a novel environment and susceptibility to place conditioning effect of psychostimulants has been reported in adult rats. However, it is in question whether this correlation could be generalized to motor activity in rats of juvenile period and place conditioning effect in their adulthood for narcotic morphine. In the present study, we tested locomotor activity in an arena open-field and the subsequent novelty-seeking behavior after adaptation process in juvenile rats (P42) and morphine (2 mg/kg) place conditioning effect 56 days later in the same rats' adulthood (P98). Our results showed that rats with high response to novelty (HRN) spent more prolonged duration in the drug-paired compartment in the place conditioning test compared with their low response counterparts (LRN), with the latter group no salient change on this measure. Moreover, rats with high response to the open-field test (HRS) expressed equally elevated duration in drug-paired side relative to their low response counterparts (LRS). The present research demonstrated that novelty-seeking behavior and locomotor activity in the open-field in rats of juvenile period differentially related to morphine place conditioning in their adulthood, with slow acquisition of morphine place conditioning effect in LRN animals.