Lecture13 - BioNB222 Cornell University Spring 2008 Ronald...

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BioNB222 Spring 2008 Cornell University Ronald Harris-Warrick 1 Lecture 13. Just Say “Know”: Effects of Street Drugs on the Brain Reading Assignment Purves et al., Chapter 6, especially the boxes on p. 139 and p. 147. Summary: Psychoactive drugs are a window into how the brain generates consciousness. They do not create any new physiological actions, but act by modifying processes that are always going on. By studying their mechanisms and sites of action, we gain further insights into normal brain function. Most psychoactive drugs act preferentially at synapses, and we will discuss their actions there. Stimulants such as cocaine, amphetamines and ecstasy act pre-synaptically to block the transporters that remove dopamine or serotonin from the synaptic cleft, thus prolonging the monoamines’ actions at their synapses. Ecstasy is neurotoxic at high concentrations, killing the serotonin nerve terminals which only slowly (or not at all) recover. Other drugs, including psychedelics such as LSD and opiates, act post-synaptically, mimicking normal transmitter actions to enhance the activity of serotonergic or endorphinergic pathways. Marijuana mimics the actions of the endogenously released endocannabinoids, and primarily binds to pre-synaptic terminals to block transmitter release. Alcohol acts much less selectively, affecting many transmitter systems to induce confusion, motor incoordination and eventually coma. Learning Objectives 1. To learn about the basic effects of cocaine, methamphetamine, ecstasy, LSD, marijuana and alcohol on normal perception and consciousness. 2. To learn the basic molecular targets of action of these drugs to start to understand how they act on the brain. 3. To begin to learn how these molecular actions result in changes in human consciousness. Lecture Outline A. Stimulants with a pre-synaptic action: Cocaine and the amphetamines Cocaine is typically extracted as a hydrochloride salt from the leaves of Erythroxylon coca . When extracted in ether to obtain the free base, it becomes crack which can be smoked. Amphetamines such as methamphetamine are drugs related to dopamine and also exist as a hydrochloride salt (“speed”) and a smokable form (“Ice”). Both drugs have similar actions to elevate mood, induce euphoria, increase alertness and reduce fatigue; however, a cocaine “high” usually lasts 30-60 minutes, while a methamphetamine trip lasts 12-24 hours.
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2 When smoked or injected, the “rush” is intensely pleasurable for a period of seconds to minutes. This is followed by a longer period of milder euphoria mixed with increased anxiety and a strong desire to obtain more of the drug. During this time, the user is also prone to acts of violence due to paranoia and anxiety. Upon repeated use over short times, a toxic paranoid psychosis can be evoked
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This note was uploaded on 04/30/2008 for the course BIO 2220 taught by Professor Hopkins,c.d. during the Spring '08 term at Cornell University (Engineering School).

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Lecture13 - BioNB222 Cornell University Spring 2008 Ronald...

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