Related Experiment Videos
Neonatal and preweanling rats are able to express short-term behavioral sensitization to cocaine
1Biological Psychology and Pharmacopsychology Unit, University of Liège, Belgium. ezio.tirelli@ulg.ac.be
Insights
Suckling rats show short-term behavioral sensitization to cocaine before weaning. This study demonstrates that even young rats can develop cocaine sensitization with appropriate methods.
Area of Science:
- Neuroscience
- Developmental Psychology
- Pharmacology
Background:
- Early-life exposure to drugs of abuse can have lasting neurodevelopmental consequences.
- Understanding behavioral sensitization to psychostimulants in developing organisms is crucial for assessing potential long-term effects.
Purpose of the Study:
- To assess the capacity of pre-weanling rats to exhibit short-term behavioral sensitization to cocaine.
- To investigate age-dependent behavioral responses to cocaine sensitization in suckling rats.
Main Methods:
- Rat pups aged 3-19 days received daily intraperitoneal injections of cocaine (7.5 or 15 mg/kg) for 2 or 4 consecutive days.
- Behavioral responsiveness to cocaine was tested 24 hours after the last injection in the same drug-associated context.
- Sensitive video recording techniques were employed to measure behavioral changes, including locomotion, horizontal activity, mouth movements, and immobility.
Main Results:
- Locomotor activity was sensitized at all tested ages (7, 14, and 21 days).
- Specific age-dependent behaviors, such as uncoordinated movements, mouth movements, and stereotyped head movements, were observed.
- Neonatal rats (7-day-olds) showed reduced immobility, indicating sensitization.
Conclusions:
- Short-term behavioral sensitization to cocaine's motor effects can be expressed by suckling rats prior to weaning.
- The findings challenge previous assumptions by demonstrating sensitization with appropriate methodologies and relatively short injection regimens.
- This research highlights the sensitivity of the developing brain to psychostimulants.
Abstract:
The present study assessed the ability of suckling rats to express short-term behavioral sensitization to cocaine prior to weaning. Rat pups, aged either 3, 5, 10, 12, 17 or 19 days at the beginning of the experiment, were placed in a chamber after daily injection with cocaine (7.5 or 15 mg/kg. i.p.) for either 2 or 4 consecutive days, and were tested for behavioral responsiveness to cocaine in the same chamber 24 h later (at either 7, 14 or 21 days of age). Such a short post-treatment interval was adopted, along with a consistent pairing of the testing context with the drug effect and a sensitive technique of behavioral measurement (video recording), in order to maximize the possibility of detecting any cocaine sensitization. Locomotion was sensitized at all ages, after both regimens in 14-day-old pups, but solely after 2 injections in 21- and 4 injections in 7-day-old pups. Sensitization was also expressed via behaviors specific to each age. Four cocaine injections augmented cocaine-induced uncoordinated movements of head, paws and body (horizontal activity) in 7-day-old pups, and mouth movements in 14-day-old pups. In 21-day-old pups, sensitization was dose- and regimen-dependently expressed via adult-like stereotyped head movements. In neonatal 7-day-old pups, cocaine sensitization was also visible as reductions in immobility (both injection regimens). Contrary to previous studies, these results indicate that, given the use of an appropriate methodology, short-term sensitization to the motoric effects of cocaine can be expressed by suckling rats prior to weaning, even after relatively short regimens of daily injections.