Presentation on theme: "LECTURE 5 DRUGS AND ALTERED CONSCIOUSNESS (this material is covered in Drugs and Behaviour section of chapter 4, Martin et al) David Pearson Room T10,"— Presentation transcript:
LECTURE 5 DRUGS AND ALTERED CONSCIOUSNESS (this material is covered in Drugs and Behaviour section of chapter 4, Martin et al) David Pearson Room T10, William Guild Building
The brain is protected by a tightly packed lining of cells called the blood-brain barrier. However, some drugs are able to pass through and influence the operation of the brain. These drugs alter consciousness by facilitating or inhibiting synaptic transmission.
Basic Steps in Synaptic Transmission 1.Neurotransmitters are synthesized in the presynaptic (sending) neuron and stored in vesicles. 2.Neurotransmitters are released into the synapse, where they stimulate receptor sites on the postsynaptic (receiving) neuron. 3.Neurotransmitters are deactivated by enzymes or by reuptake.
Drugs that affect synaptic transmission can be divided into two main categories: Agonist drugs Antagonist drugs
Agonist Drugs Agonist drugs work by increasing the activity of a neurotransmitter. This can be done by: Enhancing a neurons ability to synthesize, store, or release neurotransmitters. Binding with and stimulating postsynaptic receptor sites (or increasing sensitivity of these sites) Prolonging activity of neurotransmitters (e.g., by inhibiting reuptake)
Example of Agonist Action The brain produces natural pain-killing chemicals called endorphins. Drugs known as opiates (e.g., morphine, codeine) have a molecular structure similar to that of endorphins. Opiates can therefore bind to and activate receptor sites that normally receive endorphins, and duplicate their effects.
Antagonist Drugs Antagonist drugs work by inhibiting or decreasing the action of neurotransmitters. This can be done by: Reducing a neurons ability to synthesize, store, or release neurotransmitters Preventing a neurotransmitter from binding with the postsynaptic neuron (e.g., by blocking the receptor sites)
Example of Antagonist Action Symptoms of schizophrenia (hallucinations, delusions etc.) are often associated with abnormal overactivity of the neurotransmitter dopamine. Antipsychotic drugs have a molecular structure similar enough to dopamine to block the receptor sites, but not similar enough to activate them.
Depressants Depressants work by decreasing nervous system activity. In moderate doses depressants reduce feelings of tension and anxiety, and produce a state of relaxed euphoria. In high doses depressants can slow down vital life processes to the point of death.
Alcohol increases the activity of gamma- aminobutyric acid (GABA), a major inhibitory neurotransmitter. Alcohol also decreases the activity of glutamate, which is a major excitatory neurotransmitter. Together these effects produce a substantial reduction in neural firing within the brain.
Neural slowdown reduces activity in the inhibitory control centres in the cerebral cortex. This leads to disinhibition and feelings of euphoria. At higher dosage disruption of cerebral control centres produces disorganised thinking and physical coordination, fatigue, and psychological depression.
Alcohol also produces an effect known as alcohol myopia (Steel & Josephs, 1990). Neural slowdown produces an increased inability to attend to and process new information. Drinkers begin to pay attention only to those aspects of a situation (cues) that stand out, and ignore other relevant information. This produces an increase in risk-taking behaviour and a failure to attend to long-term consequences of actions (MacDonald et al., 2000).
Stimulants Amphetamines Amphetamines can reduce appetite and fatigue, decrease the need for sleep, and in some cases reduce feelings of depression. Amphetamines increase the activity of the neurotransmitters dopamine and norepinephrine. This is done by (a) causing the neuron to release greater amounts of these neurotransmitters, and (b) inhibiting reuptake.
Adverse effects of amphetamines include increased blood pressure, heart failure, cerebral hemorrhage. Repeated high doses can result in long-term brain damage (Diaz, 1997). Continuous heavy amphetamine use can result in amphetamine psychosis (Lynn, 1971). Heavy amphetamine use is linked to severe withdrawal symptoms (crash) due to depletion of dopamine and norepinephrine reserves.
Cocaine Cocaine is a natural stimulant derived from the coca plant (also synthetic version novocain). It produces excitation, sense of increased muscular strength, and euphoria. Works by blocking reuptake of dopamine and norepinephrine. In large doses produces fever, vomiting, convulsions, hallucinations, and paranoid delusions.
Historically cocaine was hailed as a wonder drug and widely used as a local anaesthetic and general stimulant. In 1885 John Pemberton developed a mixture of cocaine, syrup, and kola nut extract and marketed it as health tonic.
By 1891 there was a growing national debate in the USA about the negative aspects of cocaine. By 1902 Coca-cola contained only 1/400 of a grain of cocaine per ounce of syrup. Cocaine not completely removed until 1929.
Hallucinogens In 1943 Swiss chemist Albert Hofmann accidentally absorbed a new chemical that he was synthesising: The dizziness…became so strong at times that I…had to lie down on a sofa…Everything in the room spun around and the familiar objects and pieces of furniture assumed grotesque, mostly threatening forms. Hoffman had synthesised lysergic acid diethylamide (LSD).
We were somewhere around Barstow on the edge of the desert when the drugs began to take hold. I remember saying something like I feel a bit lightheaded; maybe you should drive… And suddenly there was a terrible roar all around us and the sky was full of what looked like huge bats, all swooping and screeching and diving around the car, which was going about a hundred miles an hour with the top down to Las Vegas. Hunter S. Thompson Fear and Loathing in Las Vegas
Hallucinogens are powerful consciousness-altering drugs that produce substantial hallucinations. Natural Hallucinogens Mescaline (peyote cactus extract) Psilocybin (magic mushrooms) Synthetic LSD Phencyclidine (Angel Dust)
Hallucinogenic effects include distorted or intensified sensory experience, synaesthesia, mystical experiences and insights, exhilaration. Adverse effects can include violent outbursts, paranoia, panic, and flashbacks long after the drugs effects have apparently ended.
Molecular structure of LSD is very similar to the neurotransmitter serotonin. Overall LSD decreases serotonin activity. During normal sleep decreased serotonin levels are linked to the onset of REM sleep. Some argue that LSDs inhibition of serotonin allows dreamlike altered perceptions and hallucinations to emerge while we are still awake (Trulson & Jacobs, 1979).
Summary Drugs can alter consciousness by facilitating or inhibiting synaptic transmission in the brain. Agonist drugs increase the activity of neurotransmitters. Antagonist drugs inhibit or decrease the activity of neurotransmitters.