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Group differences in substance abuse and environments

March 4, 2010

It has been noted that certain groups are more prone to substance abuse than others. Why is this?

Inherent differences in IQ may be a contributing factor, as may environmental differences. A few studies on rats attempt to provide answers:

Rats with different behavioral histories, defined by rearing and housing in either an enriched condition (EC) or an isolation condition (IC), were trained in a two-lever operant procedure to discriminate 5.0 mg/kg cocaine from saline. In cocaine dose-generalization tests, the IC rats exhibited an ED50 (1.01 mg/kg) significantly lower than the EC rats (ED50:1.55 mg/kg). The cocaine-appropriate responding was emitted when the rats were treated with d-amphetamine, and for the d-amphetamine test doses the ED50 (0.19 mg/kg) was again significantly lower for the IC rats compared to the ECs (ED50:0.33 mg/kg). These data suggest that IC rats are more sensitive to the stimulus properties of indirect dopaminergic agonists than EC rats and highlight the importance of environmental variables in governing an organism’s response to the stimulus properties of abused drugs.

[Fowler, SC, Johnson, JS, Kallman MJ. In a drug discrimination procedure isolation-reared rats generalize to lower doses of cocaine and amphetamine than rats reared in an enriched environment. Psychopharmacology 1993;110:115-8.]

If only my parents had beat me, maybe the Adderall would last longer.

A Chinese study also drew the same conclusions with an opiate (EE-Enriched Environment; SE-Standard Environment):

We examined whether manipulations of the enriched environment affected behavioral response to morphine-induced reward in adulthood. Male mice were exposed to the EE, or SE condition for 2 months. When they reached adulthood, we examined their locomotor responses to an acute and repeated injection of morphine. The increase of locomotor activity observed in the EE mice was significantly less pronounced than that in the SE mice treated with morphine at 10 mg/kg. These animals then received six additional daily injections of morphine, and the ability of these treatments to produce behavioral sensitization was assessed by a challenge injection of morphine (10 mg/kg) following a 5-day drug-free interval. Mice exposed to the EE condition showed a significantly less robust behavioral response to the drug-induced reward than the SE mice did. We conclude that early EE condition affected the ability of morphine to induce behavioral sensitization. The rewarding and reinforcing effects of drugs were further studied in the place preference paradigm. The procedure has been found to be sensitive to the rewarding effects of drugs. We observed in experiments that morphine at the dose of 5 mg/kg induced place conditioning in mice. This dose has been previously shown to induce intense rewarding effects in conditioned place preference, which does not increase when using higher doses of morphine (Zachariou et al., 2001). Interestingly, the dose of morphine (5 mg/kg) that established robust place preferences in SE mice failed to establish place preferences in EE mice. Thus, the EE mice are less sensitive to the reinforcing effects of morphine and showed less prolonged morphine conditioning.

[Xu Z, Hou B, Gao Y, et al. Effects of enriched environment on morphine-induced reward in mice. Exp Neurol. 2007 ;204:714-9.]

How significant were these differences? Here’s how much time individual rats from the different environmental groups spent in the “morphine-conditioned” box:

**(p<0.01)

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