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Jereld R. Nicholson Library

Subject Area

Psychology

Description

Past research using rat models suggests that uncontrollable stress experienced as an adult enhances morphine’s rewarding properties using place conditioning techniques (Will, Watkins & Maier, 1997; Der-Avakian et al., 2007). Recent work using a new peripubertal stress paradigm indicates that exposure to fear inducing stressors, synthetic fox odor (TMT) and an elevated platform (EP), during postnatal days 28 through 42 (P28-P42) increases aggression in adulthood (Marquez et al., 2013). Few studies have explored whether adolescent stress enhances morphine-induced conditioned place preference (CPP), and the present work adapts a new stress paradigm to explore modulation of opiate reward.

Adolescent Sprague-Dawley rats (n=12) arrived P25 and the stress phase commenced P28. Half of the animals remained in the homecage (No Stress, NS). The remaining animals received two stressors (Stress, S), exposure to fox urine (TMT) and an elevated platform (EP). The S treatment continued 7 days starting P28 (EP only), P29 (EP, TMT), P30 (TMT, EP), P31 (TMT only), P33 (EP only), P34 (EP, TMT) and P35 (EP only). TMT exposure occurred in a cage containing a small cloth saturated with 10 mls of TMT for 25 mins. EP exposure occurred by placing each animal on a 12x12 cm platform atop a 95 cm tall column for 25 mins. Two days after the stress phase, all rats received morphine place conditioning. Subjects received a 15-minute preference test (Pre-test) to determine the initially nonpreferred side of the apparatus followed by 8 conditioning days. On alternating days, each animal received either morphine (15 mg/kg, IP) in the initially nonpreferred side of the apparatus (B/G+ (black/grid) or W/H+ (white/hole)) or saline solution (1 ml/kg, IP) in the non-drug paired side of the apparatus for 15 minutes. After the last day of conditioning, a place preference test (Post-test) was conducted identical to the pre-test. Time on the nonpreferred side of the apparatus served as the primary dependent measure.

A 2 (S v. NS) X 2 (Pre- v. Post-test) mixed ANOVA revealed significant main effects of stress (F(1,10)=6.854, p=.026) and test (F(1,10)=49.47, p=.000). A statistically significant interaction showed a unique effect of stress during post-test indicating that adolescent stress increases morphine CPP (F(1,10)=6.981, p=.025). Similar to uncontrollable stress as an adult, adolescent stress enhances the rewarding properties of opiates.

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Presenters: Chloe Shields and Sarah Becker

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May 15th, 12:15 PM May 15th, 1:30 PM

Adolescent Stress Enhances Morphine Conditioned Place Preference in Rats

Jereld R. Nicholson Library

Past research using rat models suggests that uncontrollable stress experienced as an adult enhances morphine’s rewarding properties using place conditioning techniques (Will, Watkins & Maier, 1997; Der-Avakian et al., 2007). Recent work using a new peripubertal stress paradigm indicates that exposure to fear inducing stressors, synthetic fox odor (TMT) and an elevated platform (EP), during postnatal days 28 through 42 (P28-P42) increases aggression in adulthood (Marquez et al., 2013). Few studies have explored whether adolescent stress enhances morphine-induced conditioned place preference (CPP), and the present work adapts a new stress paradigm to explore modulation of opiate reward.

Adolescent Sprague-Dawley rats (n=12) arrived P25 and the stress phase commenced P28. Half of the animals remained in the homecage (No Stress, NS). The remaining animals received two stressors (Stress, S), exposure to fox urine (TMT) and an elevated platform (EP). The S treatment continued 7 days starting P28 (EP only), P29 (EP, TMT), P30 (TMT, EP), P31 (TMT only), P33 (EP only), P34 (EP, TMT) and P35 (EP only). TMT exposure occurred in a cage containing a small cloth saturated with 10 mls of TMT for 25 mins. EP exposure occurred by placing each animal on a 12x12 cm platform atop a 95 cm tall column for 25 mins. Two days after the stress phase, all rats received morphine place conditioning. Subjects received a 15-minute preference test (Pre-test) to determine the initially nonpreferred side of the apparatus followed by 8 conditioning days. On alternating days, each animal received either morphine (15 mg/kg, IP) in the initially nonpreferred side of the apparatus (B/G+ (black/grid) or W/H+ (white/hole)) or saline solution (1 ml/kg, IP) in the non-drug paired side of the apparatus for 15 minutes. After the last day of conditioning, a place preference test (Post-test) was conducted identical to the pre-test. Time on the nonpreferred side of the apparatus served as the primary dependent measure.

A 2 (S v. NS) X 2 (Pre- v. Post-test) mixed ANOVA revealed significant main effects of stress (F(1,10)=6.854, p=.026) and test (F(1,10)=49.47, p=.000). A statistically significant interaction showed a unique effect of stress during post-test indicating that adolescent stress increases morphine CPP (F(1,10)=6.981, p=.025). Similar to uncontrollable stress as an adult, adolescent stress enhances the rewarding properties of opiates.

 

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