Objective: Assessment of stress-induced immobility response in mice subjected to repeated forced swimming using a modified Porsolt procedure to evaluate behavioral responses to stress and effects on drug reward sensitivity
Materials & Equipment Checklist
5 items3 from ConductScience
Gather these items before starting the experiment. Check off items as you prepare.
Equipment3
Not specified • Not specified • Not specified • Not specified
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Protocol Steps
View Abstract
Previous studies have demonstrated that stress may increase prodynorphin gene expression, and kappa opioid agonists suppress drug reward. Therefore, we tested the hypothesis that stress-induced release of endogenous dynorphin may mediate behavioral responses to stress and oppose the rewarding effects of cocaine. C57Bl/6 mice subjected to repeated forced swim testing (FST) using a modified Porsolt procedure at 30 degrees C showed a characteristic stress-induced immobility response and a stress-induced analgesia observed with a tail withdrawal latency assay. Pretreatment with the kappa opioid receptor antagonist nor-binaltorphimine (nor-BNI; 10 mg/kg, i.p.) blocked the stress-induced analgesia and significantly reduced the stress-induced immobility. The nor-BNI sensitivity of the behavioral responses suggests an activation of the kappa opioid receptor by a stress-induced release of dynorphin peptides. Supporting this hypothesis, transgenic mice possessing a disrupted prodynorphin gene showed no increase in immobility or stress-induced analgesia after exposure to repeated FST. Because both stress and the kappa opioid system can modulate the response to drugs of abuse, we tested the effects of forced swim stress on cocaine-conditioned place preference (CPP). FST-exposed mice conditioned with cocaine (15 mg/kg, s.c.) showed significant potentiation of place preference for the drug-paired chamber over the responses of unstressed mice. Surprisingly, nor-BNI pretreatment blocked stress-induced potentiation of cocaine CPP. Consistent with this result, mice lacking the prodynorphin gene did not show a stress-induced potentiation of cocaine CPP, whereas wild-type littermates did. The findings suggest that chronic swim stress may activate the kappa opioid system to produce analgesia, immobility, and potentiation of the acute rewarding properties of cocaine in C57Bl/6 mice.
1
Repeated Forced Swim Testing
Subject C57Bl/6 mice to repeated forced swim testing using a modified Porsolt procedure
Note: Intraperitoneal injection at 10 mg/kg dose. This treatment blocks stress-induced analgesia and reduces stress-induced immobility
View evidence from paper
“Pretreatment with the κ opioid receptor antagonist nor-binaltorphimine (nor-BNI; 10 mg/kg, i.p.) blocked the stress-induced analgesia and significantly reduced the stress-induced immobility”
5
Cocaine Conditioning
Condition FST-exposed mice with cocaine in conditioned place preference paradigm
Not specifiedNot specified
Conditioned Place Preference - Mouse (Custom Order)
Matches: Conditioned place preference (CPP) apparatus
Note: Measure preference for cocaine-paired chamber. Stressed mice show potentiated preference compared to unstressed controls
View evidence from paper
“FST-exposed mice conditioned with cocaine showed significant potentiation of place preference for the drug-paired chamber over the responses of unstressed mice”
7
Test nor-BNI Effects on Cocaine CPP
Administer nor-BNI pretreatment and assess effects on stress-induced potentiation of cocaine CPP
Not specifiedNot specified
Note: nor-BNI pretreatment blocks the stress-induced potentiation of cocaine CPP
View evidence from paper
“nor-BNI pretreatment blocked stress-induced potentiation of cocaine CPP”
8
Compare Transgenic and Wild-Type Responses
Compare behavioral responses between prodynorphin gene-disrupted transgenic mice and wild-type littermates
Not specifiedNot specified
Note: Transgenic mice lacking prodynorphin gene show no stress-induced immobility increase, no stress-induced analgesia, and no stress-induced potentiation of cocaine CPP
View evidence from paper
“transgenic mice possessing a disrupted prodynorphin gene showed no increase in immobility or stress-induced analgesia after exposure to repeated FST”
Subjects / Specimens
Species
mouse
Strain
C57Bl/6
Age
Not specified
Sex
unknown
Weight
Not specified
Transgenic mice with disrupted prodynorphin gene and wild-type littermates were also used as comparison groups
