Experiments on rats conducted by researchers at the University of Puerto Rico have shown that isolation during early development alters the brain sensitivity to cocaine.
Researchers Natasha Lugo-Escobar, Nicole Carreras, and Annabell C. Segarra say that they wanted to study the impact of stressful early life events like social isolation on rats' response to cocaine.
The researchers said that the subject rats were weaned from their mothers when they reached 21 days of age, and tested for the psychostimulant response to cocaine as well as for the development of sensitisation, a phenomenon characterized by an increase response to the same amount of a drug over time.
For 5 days, half of the rats from all groups were injected with saline and the other half with cocaine (15 mg/kg).
That was followed by a 7-day drug free period, and an additional cocaine injection on day 13.
The researchers measured locomotor activity on days 1, 5 and 13 immediately after injection.
They observed that the rats that were isolated during all three developmental periods, showed a higher locomotor response to cocaine than control rats.
Based on their observations, the researchers came to the conclusion that the developmental period most susceptible to isolation stress, particularly in males, is the neonatal period, since males isolated as neonates show an increase in the locomotor, and sensitized response to cocaine, compared to male control and to female rats.
According to the research team, their finding suggest that isolation during early development alters the brain sensitivity to cocaine.
The researchers say when the animal reaches adolescence and is exposed to cocaine, it is more sensitive to the psychostimulant effects of the drug.
These studies contribute to understanding the mechanisms that may lead to greater abuse of drugs during adolescence.