Intoxicants - Plant Products and Human Affairs - Lecture Slides, Slides of Biology

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Intoxicants

Outline

• Psychoactive and recreational drugs

• Tobacco

• opium

• Cocaine

• Marijuana

Nerves

• The nervous system works by having

individual nerve cells (neurons) transmit

messages to each other.

• Signals in the nervous system travel as

electrical waves down the bodies (the

axons) of nerve cells.

• The signals from different cells are

combined with each other at synapses.

• A synapse is the connecting point between an input cell (or more than one input cell) and an output cell.
• When the input cells stimulate the output cell sufficiently, it fires, sending an electrical wave on to the next synapse.

Synapses

• Each nerve cell releases a specific neurotransmitter chemical, which crosses a small gap (the synapse) and binds to a receptor molecule on the surface of the receiving cell (the “post-synaptic neuron”). - After transmitting the signal , the neurotransmitter chemicals are taken back into the transmitting cell, for re-use.
• Most psychoactive drugs work by affecting the transmission process of a specific neurotransmitter: mimicking its action, or blocking its action, or preventing re-uptake by the transmitting cell.
• Different types of neurotransmitter have different functions in the body and the brain.

The Reward Circuit

• A common feature: recreational drugs affect the reward circuit (mesolimbic system) in specific areas of the brain by increasing or prolonging the release of the neurotransmitter dopamine. You feel good when the nerve cells release a lot of dopamine. This can be caused by drugs, or by other pleasurable or positive experiences. - This is the cause of euphoria, common to all addictive drugs. - It causes you to want to repeat the actions that stimulated the euphoria. - Why an increase in dopamine in certain nerve cells of your brain causes “me” to “feel good” seems to reach the interface between biology and philosophy. - Medical psychoactive drugs, as opposed to recreational psychoactive drugs, avoid stimulating the mesolimbic system.
• Morphine and endorphin work by disabling neurons that inhibit the release of dopamine in the reward system.
• Stimulants like cocaine and amphetamine stimulate the release of dopamine or prolong its action by preventing its removal (re-uptake) from the synapse.
• Other drugs use other mechanisms.

Tolerance

• Addiction is a complicated phenomenon. One

important feature for most addictive drugs is that

tolerance for the drugs develops. It takes a

higher dose of the drug to achieve the same

effect, and the effects aren’t as rewarding as they

initially were.

• Also, previously pleasurable activities aren’t as rewarding as they used to be.
• Tolerance is the brain trying to stay in balance.

The brain cells respond to the flood of dopamine

by “down-regulating”: decreasing the number of

dopamine receptors in the receiving cell. This

makes the nerve cells harder to stimulate.

• Most psychoactive drugs also affect other brain

systems in addition to the reward circuit, which

gives them their specific effects, including the

negative effects. Docsity.com

Drug Risks

• All cultures regulate drug use: which drugs are allowed and forbidden, who can take them, and under what conditions. Why?
• Partly cultural tradition and history.
  • Some drugs are reserved for religious leaders.
  • Conversely, some drugs are seen as immoral: unearned pleasure.
  • In the US, specific drugs have been banned because they are perceived to cause harm to individuals and society. Current political categories aside, we are a generally conservative society: laws tend to stay on the books even if their original rationale is gone.
• Two main problems:
  • Many banned drugs have a high potential for addiction.
  • Many banned drugs have a high risk of causing harm to the user.
• An important aspect of high risk: the ratio between effective dose and lethal dose.
  • The dose of opiates (such as heroin) needed to get high is s only a few times greater than the lethal dose for respiratory failure. This makes overdosing very easy.
  • The effective dose for marijuana is so much less than the lethal dose that it is almost impossible to overdose on marijuana.

Drugs Classified by Addictive Potential

and Effective Dose/Lethal Dose Ratio

European Discovery of Tobacco

• Columbus first saw tobacco at his very first encounter with native Americans on October 12, 1492: they offered him some dried leaves, but Columbus had no idea what they were used for.
• The Spanish first saw it being smoked on the island of Cuba a few weeks later. The natives rolled the dried leaves in palm or maize leaves “in the manner of a musket formed of paper”. They lit one end and “drank” the smoke from the other end.
• Rodrigo de Jerez, one of Columbus’s crewmen on the Santa Maria was apparently the first European smoker. When he got back to Spain, the Inquisition imprisoned him for he sinful and infernal habit. He was release 7 years later, after the habit had caught on.
• It caught on throughout the Old World very quickly: used in Turkey, China, and Japan by 1600.

Sir Walter Raleigh

• Walter Raleigh learned to smoke from Sir Francis Drake. Raleigh then taught Queen Elizabeth I how to smoke, and introduced the smoking pipe to England.
• Raleigh was an adventurer who became close to Queen Elizabeth (who was known as “the Virgin Queen: Virginia was named after her).
• Elizabeth liked having Raleigh at court. However, he secretly married one of her attendants, which annoyed Elizabeth, and she imprisoned him.
• After they reconciled, Elizabeth funded Raleigh’s colony (Roanoke) in America, which was the first English settlement in the New World.
• The colony failed and all inhabitants vanished. The big problem: no resupply from England due to a war with Spain (Spanish Armada).
• After Elizabeth died in 1601, James I took the throne. James didn’t like Raleigh, and imprisoned him for 13 years, then executed him for treason.

Tobacco in the American Colonies

• The first successful English colony in what is now the US was at Jamestown, Virginia, stared in 1607.
• The Jamestown colony had many problems: bad water supply, disease, no knowledge of how to grow crops under existing conditions, and especially, very bad relations with the natives, who resented having their land taken away from them. Also, it wasn't profitable: the backers in England wanted them to find gold or something else valuable, the way the Spanish had done further south.
• John Rolfe started growing tobacco at Jamestown in 1612 It became the cash crop that made up for the lack of gold, and by 1640 Virginia was economically successful. - John Rolfe also married Pocahantas.
• African slaves first came to Jamestown in 1619, to work in the tobacco fields.
• Between 1617 and 1793, tobacco was the most valuable export from the American colonies.

Nicotine

• Nicotine is the active ingredient in tobacco. It is an alkaloid: bitter, nitrogen- containing compounds that are “secondary metabolites”. - Secondary metabolites are not part of the common macromolecules: proteins, carbohydrates, lipids, and nucleic acids that are found in all cells. - Secondary metabolites vary greatly between species, and are thought to mostly protect the plants from predators.
• Nicotine can be sprayed on plants as a natural insecticide.
• Nicotine is quite poisonous: the LD50 (dose needed to kill 50% of humans) is 40- 60 milligrams. Smoking a typical cigarette delivers about 1 mg. - however, a cigarette contains about 9 mg of nicotine: most of it is destroyed by burning the tobacco.
• It is absorbed easily through the lungs and skin, but not by eating it: it is mostly destroyed by stomach acids. Most cases of nicotine poisoning come from nicotine insecticides.
• It is metabolized quickly, with a half-life of about 2 hours. This contributes to the need to keep smoking.
• Nicotine addiction is considered one of the hardest to break, comparable to opium.

The Tobacco Plant

• Nicotiana tabacum is the cultivated tobacco plant: all

commercial tobacco products use this species.

• Other members of the genus Nicotiana also produce nicotine and are smoked in various parts of the world.
• A species native to Australia, N. suaveolens was independently domesticated. They chewed it, mixed with wood ash to release the alkaloid flavor. It
• Nicotiana is a member of the Solanaceae (nightshade)

family, which also contains potato, tomato, chili

peppers, petunia, and belladonna.

• Many of the Solanaceae produce useful and/or poisonous alkaloids.
• Nicotine is formed in the roots, then transported to

the leaves and other parts of the plant through the

phloem.

• The flowers have long tubes, making them best suited

for hummingbirds as pollinators.

Growing Tobacco

• Tobacco likes a warm moist environment. It is an annual,

so it can be grown in temperate regions, even in Alaska

and Canada.

• Tobacco is grown from seed. It is self-fertilizing and

highly inbred, so good varieties breed true.

• The seeds are very tiny. They are sown directly on the soil

of greenhouse seedbeds, because germination is activated

by light. After the plants have reached a certain height,

they are transplanted into the fields.

• They are often fertilized with the mineral apatite, which partly starves them for nitrogen and improves the taste.
• The plants need a lot of nutrients: this used to deplete soil

very quickly, but modern fertilizer works very well.

• The top buds and side branches are removed, so the upper

leaves get larger.