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Leading to Drug Abuse.

Exposure to lead during childhood poses many risks, such as anemia, behavioral problems, and neurologic consequences. Heavier cocaine use among drug users might be added to the roster, according to according to
1. As stated or indicated by; on the authority of: according to historians.

2. In keeping with: according to instructions.

 a research team led by psychologist Jack R. Nation at Texas A&M University in College Station. He posits that childhood lead exposure reduces the release of dopamine dopamine (dōp`əmēn), one of the intermediate substances in the biosynthesis of epinephrine and norepinephrine. See catecholamine.

One of the catecholamines, widely distributed in the central nervous system.
 in the brain, requiring higher drug doses to experience euphoric effects. The team reports in the September 2000 issue of Pharmacology, Biochemistry, and Behavior that rat pups exposed to lead in the womb and during lactation lactation

Production of milk by female mammals after giving birth. The milk is discharged by the mammary glands in the breasts. Hormones triggered by delivery of the placenta and by nursing stimulate milk production.
 required larger doses of cocaine to achieve a high. "Lead may induce a sort of tolerance or may alter sensitivity to drug abuse," Nation says.

Nation and colleagues administered 8- and 16-milligram (mg) doses of lead by gavage gavage /ga·vage/ (gah-vahzh´) [Fr.]
1. forced feeding, especially through a tube passed into the stomach.

2. superalimentation.

 to adult female rats starting 30 days before breeding them. Dosing continued through pregnancy and the birth and nursing of pups, ending at weaning weaning,
n the period of transition from breast feeding to eating solid foods.


the act of separating the young from the dam that it has been sucking, or receiving a milk diet provided by the dam or from artificial sources.
. A control group received no lead. The 8-mg dose yielded a blood lead concentration in the mothers of some 20 micrograms per deciliter deciliter /dec·i·li·ter/ (dL) (des´i-le?ter) one tenth (10minus;1) of a liter; 100 milliliters.
Deciliter (dL)
100 cubic centimeters (cc).

Mentioned in: Hypercholesterolemia
, comparable to the level often found in urban human populations.

At 30 and 90 dasts after birth, the researchers gave the pups cocaine doses of 1.25, 2.5, or 5.0 mg per kilogram of body weight. Unexposed rats responded to the drug at all doses, but rats whose mothers received the higher lead dose needed the highest cocaine dose to show a response. In the rats, the observed changes in sensitivity lasted more than a year--a period analogous to 20-30 years in humans, Nation says. And the neurologic effects lasted even after lead residues cleared the soft tissues, indicating that changes may be permanent. The pups' blood lead concentrations at the times of cocaine dosing were comparable to those common in urban children, who by socioeconomic circumstance may also be at greater risk of drug use.

Nation hypothesizes that lead may reduce production of the neuro-transmitter dopamine and thereby change sensitivity in exposed people, though he acknowledges that other mechanisms are possible. For one, lead may simply damage the central nervous system outright, explains Michael T. Bardo Bardo

blind antiquarian wrapped up in his scholarly annotations of the classics. [Br. Lit.: George Eliot Romola]

See : Scholarliness
, director of graduate studies in psychology at the University of Kentucky Coordinates:  The University of Kentucky, also referred to as UK, is a public, co-educational university located in Lexington, Kentucky.  in Lexington. The mechanism is readily testable by measuring dopamine release in the brain's "reward" center, or nucleus accumbens, while rats are performing a behavioral task, he says.

Nation observed a similar effect in previous studies of exposure to cadmium--prevalent in tobacco smoke--in unborn rats, though the mechanism of action is likely wholly different, since cadmium may not penetrate the blood-brain barrier blood-brain barrier
n. Abbr. BBB
A physiological mechanism that alters the permeability of brain capillaries so that some substances, such as certain drugs, are prevented from entering brain tissue, while other substances are allowed to
. "If these contaminants are promoting drug use," Nation says, "then you have a relatively high public health risk."

But other researchers say the jury is still out on how--and whether--lead or other environmental agents may affect drug use. Although reasonably good evidence supports the notion that lowered dopamine concentrations may prompt an individual to use more of a drug to get high, other studies suggest that reduced dopamine concentrations may actually decrease the likelihood of drug abuse. Stephen M. Lasley, a neurotoxicologist at the University of Illinois College of Medicine The University of Illinois College of Medicine, part of the University of Illinois system, is the largest medical school in the United States, with over 2,600 students and trainees. The college provides scientific and clinical training.  at Peoria says it is just as likely that lead exposure may actually hamper a habit from forming because a first-time user may not experience a high. "It may take greater intake initially to establish a habit," he says.

The idea that lead is involved in drug use dates to morphine studies in the 1970s, according to Deborah Cory-Slechta, head of environmental medicine at the University of Rochester The University of Rochester (UR) is a private, coeducational and nonsectarian research university located in Rochester, New York. The university is one of 62 elected members of the Association of American Universities.  School of Medicine and Dentistry. Although she says "there's good evidence that the dopamine system is clearly targeted by lead," she says she'd like to see more proof, preferably drug self-administration studies--the gold standard of behavioral work--to be convinced there's a clear association with drug use. It's unlikely that exposure to lead would automatically lead to taking drugs because various sociocultural so·ci·o·cul·tur·al  
Of or involving both social and cultural factors.

 and psychologic factors are involved in the initiation of drug use, Bardo says. However, he adds, if exposure to lead increases the subsequent drug intake in an individual prone to substance abuse, then one would expect that the risk of dangers associated with overdose, such as heart attack and cocaine-induced psychosis, would be increased.
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Author:Wakefield, Julie
Publication:Environmental Health Perspectives
Date:Feb 1, 2001
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