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Behavioral effects of morphine on free-operant avoidance under hyperbaric pressure
Abstract:
Morphine sulfate was tested under hyperbaric pressure to assess its effects on behavior. Four male hooded rats were trained to avoid brief electric shocks under a free-operant unsignalled avoidance procedure. Using an individual organism design, we injected each rat subcutaneously with morphine sulfate (2.0, 4.0, 6.0, 8.0 mg/kg body wt.) or saline (0.1 ml/100 g body wt.). Rats were tested at 1.0 and 7.1 atmospheres absolute (ATA) in a dry hyperbaric chamber while breathing a mixture of helium and oxygen. Each session lasted 60 min. Overall, the analgesic effects of morphine at 1.0 and 7.1 ATA were found to be similar. Shock avoidance by a rat was found to be a monotonic function of the drug dose; the fewest shocks were associated with the 2.0 mg/kg dose. Increased pressure did not significantly affect the number of shocks received by a rat across doses. Total responding remained stable throughout the study, but the temporal pattern of responding was differentially influenced by drug dose.
Insights
Morphine sulfate
Area of Science:
- Pharmacology
- Behavioral Neuroscience
- Hyperbaric Medicine
Background:
- Morphine is a potent analgesic.
- Hyperbaric conditions can alter physiological responses.
- Understanding drug effects under pressure is crucial for safety.
Purpose of the Study:
- To investigate the behavioral effects of morphine sulfate under hyperbaric conditions.
- To determine if hyperbaric pressure (7.1 ATA) modifies morphine's analgesic efficacy.
- To assess dose-dependent effects of morphine on shock avoidance behavior.
Main Methods:
- Four male hooded rats were trained in a free-operant unsignalled avoidance task.
- Rats received subcutaneous injections of morphine sulfate (2.0-8.0 mg/kg) or saline.
- Behavioral testing occurred at 1.0 and 7.1 atmospheres absolute (ATA) using a helium-oxygen mixture.
Main Results:
- Morphine's analgesic effects were comparable at 1.0 and 7.1 ATA.
- Shock avoidance improved with increasing morphine dose, peaking at 2.0 mg/kg.
- Hyperbaric pressure did not significantly alter the number of shocks received.
- Total responding was stable, but the timing of responses varied with morphine dose.
Conclusions:
- Hyperbaric pressure does not significantly alter morphine's analgesic efficacy or shock avoidance behavior.
- Morphine's behavioral effects are dose-dependent, with optimal avoidance at 2.0 mg/kg.
- While overall activity is maintained, hyperbaric pressure may influence the temporal patterns of morphine-affected behavior.