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Biology 202
2002 Second Paper
On Serendip

Munchies and More: The Effects of Marijuana on the Brain

Kathryn Fong

To many, marijuana is seen as a horrible narcotic that causes many physical and social problems. To others, it's a harmless drug that gives the body a relaxing sensation. Marijuana can be found on many college campuses and high schools. It is estimated that at least 70 million Americans have tried it, and of those people, 10-14% become dependent of the drug (1). Marijuana is often referred to as the "gateway" drug, leading the user to more serious narcotics. Marijuana users experience different sensations, from excessive mellowness, fuzzy memory, to the munchies. Some of the typical effects are impairment of memory, alteration of memory, motor coordination, posture, cognitive ability, and sensory perception. So what is it in marijuana that keeps users wanting more?

The active ingredient in marijuana is delta-9-trans-tetrahydrocannabinol, or THC. The structure of THC is very similar to the endogenous cannabinoids, or endocannabinoids for short, which are naturally occurring chemicals in the body (1).The THC binds to the receptors of the endocannabinoids, and activates the neurons, causing the different sensations experienced during a high. These receptors are spread throughout the brain. THC affects the central nervous system, as well as the peripheral tissue systems. THC can reduce pain, lower body temperature, and enhance appetite. It can also be used for anti-inflammatory, bronchodilatory, and anti-convulsant, which is why THC is used for medicinal purposes. THC is used as a popular treatment for glaucoma by reducing ocular pressure, and for neurological disorders such as multiple sclerosis, Huntington's Disease, and spinal cord injury (4).

The THC acts on the receptors of the endocannabinoids. Two known endocannabinoid receptors are CB1 and CB2, which are found in the nervous system and the periphery nervous system, respectively. The receptors are coupled with G-proteins and mediate the inhibition of adenylyl cyclase activity, which in turn reduce the production of cyclic AMP, cAMP. The reduction of cAMP formation blocks calcium ion flow into the cells, which would disrupt the formation of action potentials. This may attribute to some of the side effects to marijuana use (4). Cyclic AMP and calcium ions regulate several neurotransmitters, including acetylcholine and dopamine (1). This may account for the nice and mellow feeling people experience when smoking pot.

The precise physiopathological responses between the stimulation and inactivation of endocannabinoid receptors are still unclear, however, it is known that the performance of the nervous system and the peripheral processes, such as modulation of neurotransmitters, control of immune, gastrointestinal, reproductive, and cardiovascular systems are impacted. By observing the actions of the CB1 receptor, researchers are able to determine different response pathways. The actions of the CB1 receptors interact with thermoregulatory systems in the body. CB1 receptors also interact with sensory perception such as hearing, color vision, and touch. Motor responses are also affected by CB1 receptors, some motor responses being movement, coordination, posture, and muscle function. THC has a high affinity to CB1 receptors, which may account for the different sensations when one gets "high. Often times, a person under the influence of marijuana feels an increase of body temperature, hallucinates, seeing colors and objects that are not really there, has trouble walking, or staggers around. It is the binding of the THC to the receptors that cause this. The CB1 receptors and their corresponding enzymes and proteins can be found in the thalamus, hippocampus, cortex, striatum, substantia nigra, and cerebellum. This shows that endocannabinoids and their substrates have a role in motor and cognitive response (2).

THC may also affect the endocrine system. The CB1 receptors are found in the hypothalamus of the brain, which regulates the secretion of pituitary hormones. The release of the pituitary hormones can also lead to the secretion of adrenocorticotropic hormones (2).

It is still unknown if marijuana is addictive, or contains any addictive agents. An experiment was done with monkeys, in which every time they hit a lever, they would get injected with THC. After the monkeys figured out how to operate the levers, they hit the lever about 30 times per minute. This however, does not prove whether the monkeys were addicted or whether they just enjoyed the sensation, and felt it was a reward. In humans, about 10-14% of users become dependent. There are many treatment programs that help those addicted to marijuana (3). It may more difficult to diagnose a marijuana addict because the symptoms of marijuana addiction are not as noticeable as symptoms of different dependence, such as alcoholism (1).

One thing that I wanted to find information on, but was not able to was about the "munchies". My friend and I came up with the same question: Do people actually experience the "munchies", or are it because they heard that everyone experiences "munchies" after they smoke marijuana, so they get the "munchies" too. Are the "munchies" a physiological effect of marijuana use, or just a psychological effect? Though I did not get an answer, I think it may be related to THC. This question may require more research for the future.


1) Carrol, Linda, Marijuana Effects: More Than Just Munchies, New York Times, January 29, 2002

2)endogenous signaling system: chemistry, biochemistry, and physiology, from the Internet Journal of Science - Biological Chemistry

3)Hooked on Hash, from New Scientist, 2000

4. 4)The Pharmacology and Biochemistry of Cannabinoid Receptors, May 1997

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