TL neuro

November 19, 2010

Cosgrove et al, 2002: Wheel running suppresses cocaine taking

Filed under: Cocaine, Exercise — mtaffe @ 10:44 am

In 2008 at the Annual Meeting of CPDD, I heard Nora Volkow, Director of NIDA, describe a new interest of NIDA in the role that regular exercise plays in preventing or ameliorating drug use. Some of the rationale was epidemiological, you may think of this as “adolescents who are in sports are less likely to do drugs”. It was backed by a little bit of evidence that adding exercise to a smoking cessation program may have some additional benefit.

K. P. Cosgrove, R. G. Hunter and M. E. Carroll. Wheel-running attenuates intravenous cocaine self-administration in rats: Sex differences. Pharmacology, Biochemistry and Behavior 73 (2002) 663–671

ResearchBlogging.orgThe study used male and female Sprague-Dawley rats which were individually housed in a 12 hr light/dark cycle. Experimental sessions (wheel or drug access) were 6 hours in length and conducted in the light portion of the cycle (i.e., inactive for this nocturnal species). Rats were first were habituated to 24 hr / day access to activity wheels for at least 14 days or until running patterns stabilized. Thereafter they were implanted with intravenous catheters for self-administration testing. The key experimental conditions first provided five days in which animals were permitted to press a lever to receive cocaine infusions. In the next 5 sessions, animals were allowed access to cocaine as well as the activity wheel. The third block of 5 sessions permitted access only to cocaine. In the final block, animals were permitted access to the running wheel only (although only 3 subjects participated in this stage of the experiment).

The key result of this paper is that rats self-administered less cocaine when permitted to run on the wheels compared with the prior conditions in which the wheels were fixed in place. In addition, rats ran less on the wheels when permitted simultaneous access to cocaine then before first experiencing cocaine.

Discussion
There are two reasons why this paper is of such fundamental importance. First, it provided a model system in which it was possible to show that physical exercise could modify the choice to consume drugs of abuse. As will be discussed in future posts, there has been some recent experimental success with the addition of an exercise component to human smoking cessation programs. This has combined with epidemiological data showing that adolescents who are involved with exercise regimens or sporting programs are less likely to use drugs to put a fine point on an experimental question: Is there anything neurobiological about these effects?

It might be the case, for example, that a hour spent jogging is merely an hour in which it is impractical to smoke. For adolescents, it may be that peer pressures associated with self-identification with the sports team are sufficient to discourage the initiation or maintenance of drug use. While these are genuine effects, if present, the argument for exercise as an anti-drug strategy would be strengthened if there was some experimental evidence that the effects may be neurobiologically specific.

The second most important part of the Cosgrove finding points to to the reciprocity in which drug taking suppressed wheel running. This is potentially because wheel running is an effective reinforcer for laboratory rats. That is, they can be trained to press a lever to obtain access to a running wheel- the wheel access maintains the operant response in a manner similar to the delivery of a food pellet or intravenous infusion of cocaine. This taps into the idea that, for example, individuals in impoverished environments with minimal alternative sources of conventional reinforcement (social, vocational, personal) may be liable for drug abuse due simply to a reinforcer deficit. This model also hints at a capacity to model a gradual change in the value of exercise as a reinforcer as drug exposure continues.

Limitations

This model is limited by the choice to pre-train the animals on the wheels and the paper is limited by the failure to describe very cleanly what criteria were used to conclude stable wheel running had been established. When given longer term access to a wheel (possibly 6 hrs is sufficient) per day rats will increase how much they run over an interval of several weeks. There is a possibility that a change in the reinforcing value of the wheel has been induced by the pre-training.

The male rats had a similar trend as the females but this did not reach statistical reliability. Would definitely like to see a slightly larger sample size since the N=9 for the males can be right on the edge of sufficient for drug self-administration studies. Thrown in another factor like the wheel access and the combined variability might recommend a larger sample.
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Literature Cited
Cosgrove KP, Hunter RG, & Carroll ME (2002). Wheel-running attenuates intravenous cocaine self-administration in rats: sex differences. Pharmacology, biochemistry, and behavior, 73 (3), 663-71 PMID: 12151042

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