Aim: How do drugs affect the brain? The blood brain barrier is both a physical barrier and a system of cellular transport mechanisms. It maintains homeostasis by restricting the entrances of potentially harmful chemicals from the blood, and by allowing the entrance of essential nutrients.

Blood Brain Barrier The BBB is semi-permeable; that is, it allows some materials to cross, but prevents others from crossing. In most parts of the body, the smallest blood vessels, called capillaries, are lined with endothelial cells. Endothelial tissue has small spaces between each individual cell so substances can move readily between the inside and the outside of the vessel. However, in the brain, the endothelial cells fit tightly together and substances cannot pass out of the bloodstream. (Some molecules, such as glucose, are transported out of the blood by special methods.)

General Properties of the BBB Large molecules do not pass through the BBB easily. Low lipid (fat) soluble molecules do not penetrate into the brain. However, lipid soluble molecules, such as barbiturate drugs, rapidly cross through into the brain. Molecules that have a high electrical charge to them are slowed. Functions of the BBB The BBB has several important functions: Protects the brain from "foreign substances" in the blood that may injure the brain. Protects the brain from hormones and neurotransmitters in the rest of the body. Maintains a constant environment for the brain.

The BBB can be broken down by: Hypertension (high blood pressure): high blood pressure opens the BBB Development: the BBB is not fully formed at birth. Hyperosmolity: a high concentration of a substance in the blood can open the BBB. Microwaves: exposure to microwaves can open the BBB. Radiation: exposure to radiation can open the BBB. Infection: exposure to infectious agents can open the BBB. Trauma, Ischemia, Inflammation, Pressure: injury to the brain can open the BBB.

Adolescent brain development takes place in the frontal lobes Reasoning, Planning, Emotions, Problem-solving Adolescents should be educated about their developing brain. We believe three themes should be emphasized: how the “judgment” part of the brain (pre-frontal cortex) is slow to mature, drugs can “hijack” the brain to create addiction, and the adolescent brain is particularly vulnerable to the effects of substances. The adolescent brain about age 12 begins pruning Maintain useful synapses and connections and begins to get rid of unused connections. Pruning seems to be associated with efficient thinking. Some nerves connecting areas of the brain that regulate emotion, judgment, and impulse control myelinate during adolescence Myelination occurs earlier in girls than boys, why teenage girls seem more emotionally mature than boys. http://images.google.com/imgres?imgurl=http://bionoid.net/images/research/lobes.jpg&imgrefurl=http://bionoid.net/index.php%3Fc%3Dblog%26f%3Ditemview%26i%3D3&h=322&w=473&sz=31&hl=en&start=30&tbnid=fk08DjsICE1wBM:&tbnh=88&tbnw=129&prev=/images%3Fq%3Dfrontal%2Blobe%2Bof%2Bthe%2Bhuman%2Bbrain%26start%3D18%26ndsp%3D18%26svnum%3D10%26hl%3Den%26rls%3DGGLJ,GGLJ:2006-10,GGLJ:en%26sa%3DN http://www.sfn.org/index.cfm?pagename=brainBriefings_main&section=publications

RESEARCHERS FOUND THAT, OVERALL, GRAY MATTER VOLUME INCREASED AT EARLIER AGES, FOLLOWED BY SUSTAINED LOSS AND THINNING STARTING AROUND PUBERTY, WHICH CORRELATES WITH ADVANCING COGNITIVE ABILITIES.

Drugs can get into the brain when… Hyperosmolity: a high concentration of a substance in the blood can open the BBB. The drugs cause neurotransmitters (dopamine, serotonin and nor-epinephrine) to increase in the synapse producing an exaggerated effect (euphoria or depression) Each of the major categories of drugs affects the brain ay acting on a distinct set of receptors located on neurons, except alcohol. Amphetamines, Caffeine, Cannabis, Cocaine, Hallucinogens, Inhalants, Nicotine, Opioids, sedatives, hypnotics and others.

Cocaine Addiction Effects Cocaine acts on the brain and is a highly addictive drug. Because crack is smoked, and allows high doses to reach the brain rapidly, crack is even more addictive. Both forms of the drug trap a chemical called dopamine in the spaces between the brain's nerve cells in a part of the brain called the reward system. Dopamine stimulates and re-stimulates these nerve cells, making the user feel intense pleasure. The brain responds to the overabundance of dopamine by destroying some of it, making less of it, and shutting down the cells' receptors so they can no longer receive dopamine's messages As a result - the person consumes more cocaine more often in an effort to re-experience the pleasure felt at first use, gradually losing control over his or her cocaine-taking behavior and becoming addicted.

Most drugs of abuse directly or indirectly target the brain's reward system by flooding the circuit with dopamine. Dopamine is a neurotransmitter present in regions of the brain that regulate movement, emotion, cognition, motivation, and feelings of pleasure. The overstimulation of this system, which rewards our natural behaviors, produces the euphoric effects sought by people who abuse drugs and teaches them to repeat the behavior.