Drugs will automatically interfere with the bodily functions. That is guaranteed. But some drugs do not only alter minor body functions but go a step further in inhibiting the functions of neurotransmitters. Most of the drugs that can mimic or interfere with the functions of the neurotransmitters in any way are mostly hard and are hence illegal in many parts of the world. The brain is the engine that drives all the body functions. Even as you are reading this article you do not see with your eyes but you see with your brain. It has various mechanisms through which it accomplishes all the functions of the body. Before we learn how the drugs can affect the neuron transmitters it is good to know how they work.
Neurotransmitters are very crucial in the system. They are the chemicals that transmit messages from one nerve cell to another. Nerve cells are known as neurons. The nerve impulse travels from the first nerve cell through the axon, a single smooth body arising from the nerve cell to the axon terminal and the synaptic knobs. Each synaptic knob communicates with a dendrite or cell body of another neuron, and the synaptic knobs contain neurovesicles that store and release neurotransmitters. The synapse lies between the synaptic knob and the next cell. For the impulse to continue traveling across the synapse to reach the next cell, the synaptic knobs release the neurotransmitter into that space, and the next nerve cell is stimulated to pick up the impulse and continue it. An interference with the neurotransmitters can adversely affect the flow of message within the nervous system.
A point to note is that there is neurotransmitter compatibility, that is every transmitter is designed to be bound by a specific receptor. Some drugs are structurally similar to neurotransmitters and hence may be bound by the receptors and hence mimic the functions of the neurotransmitters. The drug will therefore disrupt the functions of the neurotransmitters adversely affecting the whole neuron system. Typically, this is like having an intruder into your personal computer- he will definitely interfere with your programs.
Here are some of the ways through which a drug can interfere with the neurotransmitters functions.
- Stop the chemical reactions that create neurotransmitters.
- Empty neurotransmitters from the vesicles where they’re normally stored and protected from breakdown by enzymes.
- Block neurotransmitters from entering or leaving vesicles.
- Bind to receptors in place of neurotransmitters.
- Prevent neurotransmitters from returning to their sending neuron (the reuptake system).
- Interfere with second messengers, the chemical and electrical changes that take place in a receiving neuron.
Marijuana for example has a compound known as THC which is known to mimic the functions of various neurotransmitters. It mimics the activities of a natural neurotransmitter called anandamide. Anandamide is an important neurotransmitter as it is charged with the role of boosting memory and learning, reducing pain, and stimulating the appetite. Anandamide normally works in conjunction with dopamine, and together these neurotransmitters turn on and turn off different chemical pathways as required so as to accomplish certain functions.
The fact THC mimics the Anandamide does not mean that it will work as that natural neural transmitter would. When a person takes marijuana THC binds to cannabinoid CB1 and CB2 receptors, which are located in several parts of the brain namely, the hippocampus, cerebral cortex, cerebellum, and basal ganglia. These brain areas are responsible for short-term memory, coordination, learning, problem solving, and unconscious muscle movements. When THC gets itself bound in the cannabinoid receptors, it blocks natural neurotransmitters like anandamide that need to bind to those sites to achieve all their functions. This therefore makes the functions of these neurotransmitters unaccomplished. When THC prevents anadamide from doing its job, the delicate balance between anadamide and dopamine is thrown off and suddenly a person will feel euphoric, off-balance, hyperactive, senseless to pain and unable to retain information.
The core structures of the brain reward pathway are located in the limbic system. These are a set of primitive structures in the human brain. Typically, the function of the limbic system is to monitor internal homeostasis, mediate memory, mediate learning, and experience emotion. It also enables important aspects of sexual behavior, motivation, and feeding behaviors. The primary parts of the limbic system include the hypothalamus, amygdala, hippocampus, septal nuclei, and anterior cingulate gyrus. Also important in the function of the limbic system is the limbic striatum, which includes the nucleus accumbens, ventral caudate nucleus and the putamen. The nucleus accumbens, often abbreviated as (NA) has been implicated as an especially important structure of the brain reward pathway because it is targeted by drugs of abuse.
When the brain becomes exposed to a certain drug, it begins relying on self stimulation as opposed to the natural neurotransmitter induced stimulation and this is what causes addiction. Several experiments have been done on animal models by use of electrodes that are placed into the nucleus accumbens under conditions of imposed environmental stress. Through these experiments the dependence on drugs for stimulation in brains exposed to these drugs is seen.
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