Link Between Stress Of Isolation Early In Life And Enhanced Juvenile Response To Cocaine
April 18, 2009
Drug addiction affects millions of people around the world, causing numerous
problems ranging from emotional and psychological difficulties to physical and
health issues. Initial drug use can be motivated by curiosity or peer pressure,
but in some animals, such as rats, it can also be the result of a stressful
early life event, such as social isolation. A new study examines the impact of
social isolation on the animal's response to cocaine.
The study, Social Isolation During Perinatal Development Alters the Behavioral
Response to Cocaine in Juvenile Rats, was conducted by Natasha Lugo-Escobar,
Nicole Carreras and Annabell C. Segarra, University of Puerto Rico, School of
Medicine, Rio Piedras, PR. The team will present its findings at the 122nd
Annual Meeting of the American Physiological Society, which is part of the
Experimental Biology 2009 scientific conference. The meeting will be held April
18-22, 2009 in New Orleans.
The Study
Drugs of abuse act on the reward centers of the brain. These areas are normally
involved in mediating pleasure, and also regulate the psycho-stimulant effects
of drugs such as cocaine. Stress is known to enhance drug seeking behavior, as
well as the psychostimulant effects of cocaine. Since rats are social animals,
isolation was used as a stressor to explore the association between stress
during development and susceptibility to the psychostimulant effects of drugs of
abuse, such as cocaine.
Rats were stressed: (1) as fetuses (by housing the pregnant mother alone), (2)
as neonates (by isolating newborn rats for 1 hr daily during the first 9 days of
life) or as adolescents (by housing each rat separately during days 21-35). Two
additional groups: (4) isolated as fetuses, neonates and adolescents and (5)
controls - not isolated during any developmental period, comprised the 5 groups
studied. When rats reached 21 days of age, they were weaned from their mothers
and tested for the psychostimulant response to cocaine as well as for the
development of sensitization, 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).
This was followed by a 7 day drug free period and an additional cocaine
injection on day 13. Locomotor activity was measured on days 1, 5 and 13
immediately after injection.
Results
The researchers found that:
 | Rats that were isolated during all three developmental periods, showed a
higher locomotor response to cocaine than control rats.|
| The study indicates 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. |
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