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Unformatted text preview: Drugs of Abuse Drugs of abuse stimulate the brain mechanisms responsible for positive reinforcement Positive reinforcement Behavior is followed by a positive stimulus which increases the likelihood of the behavior occurring again Ex. Rat presses a lever to receive an injection of heroin Ex. Person injects heroin & feels euphoric Negative reinforcement Behavior is followed by removal of a negative stimulus which increases the likelihood of the behavior occurring again Ex. Rat presses a lever to terminate shock Ex. Taking tylenol to stop a headache Neural Circuits in Reinforcement Olds & Milner in 1954 discovered brain areas that rats would continually self- administer brain stimulation to The animals behavior was reinforced by electrical stimulation of these brain areas Probably more than one reinforcement system Focus on mesolimbic & mesocortical DA systems Mesolimbic system DA cell bodies in the ventral tegmental area (VTA) Project up to the nucleus accumbens (NAC) & amygdala System seems to be particularly important in reinforcing brain stimulation, natural rewards (sex, food, etc.), & drugs of abuse Mesocortical system DA cell bodies in the VTA Project to the PFC, limbic cortex (cingulate cortex), & hippocampus Neural Mechanisms of Drugs of Abuse DA in the NAC is the story people tell to explain the reinforcing effects of drugs Not the whole story DA in the NAC goes up in response to a tail pinch and during restraint stress in rats DA release in the NAC habituates even though a drug can still be reinforcing (i.e. an animal will still perform a behavioral response to obtain the drug) DA in the NAC is not simply a signal for good or pleasure Drugs of Abuse Tolerance- the need to take increasingly higher doses of a drug to achieve a particular effect Different kinds of tolerance Changes in the brain that are in an attempt to compensate for the actions of a drug taking chronically Homeostasis Withdrawal The cessation of drug use can elicit symptoms that are opposite to those produced by the drug Negative reinforcement Psychostimulants Include: Amphetamine (AMP) Methamphetamine Free base (ICE or crystal meth) Methylphenidate (Ritalin) Ephedrine (ma huang) AMP is used for fighting fatigue & to increase performance by troops AMP used by students & truck drivers to maintain wakefulness, increase alertness, & delay sleep AMP & Ephedrine are used as appetite suppressants Therapeutic uses for: AMP- treat narcolepsy Methylphenidate- treat ADHD Acute Effects Increased attention Decreased fatigue Euphoria Decreased appetite Hyperthermia Chronic Effects Stereotyped behaviors Psychosis Paranoia, auditory hallucinations, delusions & mood disturbances Stroke Violent behavior Insomnia Anxiety Weight loss Amphetamine...
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- Fall '06