Monday, February 28, 2011

Drugs Alter the Brain's Reward Pathway


“The reward pathway is responsible for driving our feeling of motivation, reward, and behavior.”

Neurons: The tradition definition of a neuron is the following: cells in various shapes and sizes liable for transporting chemical and electrical messages along the pathways of the brain. Their diversity permits the nerve cell to put specialized assignments in action. Examples of individual functions include short and long term memory storage and muscle composure.

The center of the brain acts as the main control headquarters, or reward pathways, rather. This nucleus, so to speak, is responsible for how the exclusive being reacts by dominating feelings of motivation, rewards, and behavior. When we converse, eat, sleep, or complete any task that depends on our survival, it is the central brain’s job to let us know that we have accomplished something, and ultimately makes us feel adept, or even proficient in that particular area. These “good vibes” are then sent off into other sections of the brain that control separate primal functions, such as the five fundamental senses. When a larger percentage of the brain as a whole has a strong understanding of current emotions, it rapidly gains a grip of the outside environment, and triggers memory sensations of previous activity. When the memory bank accounts for the beneficial behavior, it makes sure that that action is repeated a great amount of times, depending on how advantageous the act was. How do other sections of the brain receive this information? Through neurotransmitters, any necessary data is conveyed to different locations. To illustrate my point, take the core of the motor center. It acquires details of the beneficial act, analyzes what motions it takes to perform it, and keeps the connections in the brain running smoothly. Strengthening brain circuits, which is what is really occurring, is significant when dealing with the pathway because it keeps instinctual behavior regulated and is a chief part of survival. The reward pathway is not just a simile for routine scientific activity, but is also the route in which dopamine, a neurotransmitter in the brain that brings about a surge of satisfaction.

Parts of a Neuron

Axon: The long extension from the neuron’s cell body carries outgoing nerve impulses toward other neurons.

Cell Body: Also called the some, this is the largest part of the neuron. It contains the nucleus and the cytoplasm.

Myelin Sheath: This is an insulating membrane that surrounds the axon.

Axon Terminal: This is the end of the axon, where nerve impulses are transmitter to the dendrite of other neurons.

Dendrites: These extensions from the neuron’s cell body receive incoming nerve impulses from other neurons.
Nucleus: The part of the neuron that contains its genetic information.

Send nerve impulse through neurons

How Neurons Talk to Each Other

As you get to familiarize yourself with the reward pathway in the brain, you will find that it is an elaborate matrix of millions of nerve cells. How does anything communicate in such a jumble of crossed wires? Through synapses and neurotransmitters, signals are enabled to circulate in the brain. Although everything seems like it must be so compressed, there are still mini gaps between cells called synaptic clefts. And with all of the chaos, each cell and messenger must follow order and conduct through a process that involves the following: a messenger cell becomes laden with vesicles that are stocked with neurotransmitter molecules. For an example’s sake, let’s say that the vesicles contain dopamine. It would only make sense that the receptor is coated in dopamine as well, so that the receiver will accept the message. The vesicles are then charged with electrical impulses, and off they go into the synaptic cleft. There, they cling for the glazed, similarly molded receptor. Once that is accomplished, and no dopamine particle is left behind, the new sender (which was previously the receptor) generates a second messenger. This messenger is slower than the first, and thus accumulates more cultured results. It also interacts with other molecules to prompt the sensations you can actually feel when it is en route on the reward pathway. The dopamine then ejects from its prior ride, only to snag onto yet another to return to the sending cell. When it gets to this point in time, it will either be “recycled” in the process or decomposed. Back to the second messenger, yet another nerve impulse is commenced and travels down its “spine” to the axon ending. It is here that the remaining contents are released and the process is reiterated. Does the impulse continue on forever and ever? Well, if the impulse’s receiving quantity is lessened, the neuron would not follow through to begin with. Also, an assortment of neurotransmitters are restrained and have strict limits. Of course, hundreds and hundreds of neurons are needed for this whole system to even initiate. That is why the brain’s passageways are so complex.

Other Brain Cells

The structures within the brain are made up of support cells called glia. Neurons may triumph over their opponents, but it is a group effort when managing bodily functions. Sometimes they need a little help from neighboring cells. For example, astrocytes are supporting cells in the brain are star-shaped glia cells in the central nervous system. The three main glia cells in the brain include oligodendrocytes, microglia, and astrocytes. All of the above are absolutely vital in order for the brain to function and access its potential. The first bead-like types that are discussed are oligodendrocytes, those that envelop axons and fundamentally fabricate myelin sheaths. Their main focus is to quicken action potential, or the electrical signals that permeate through axons, approximately thirty times faster than originally planned. The second genre of nerve cells are microglia. They are basically the healing remedies that detect impaired accomplices, in addition to consume foreign bacteria to prevent other cells from receiving the virus, and eventually signaling for help from fellow brain cells. And last but not least, the stars of the glias, are the astrocytes. They are actually star-shaped, and have recently been in the spotlight. Previous knowledge only enclosed that they held neurons in their rightful position, fed them their nutrition, and even devoured bits of deceased neurons. Nonetheless, they do not provoke action potential. Only in recent years have scientists uncovered the truth about these glia cells.

They can, in fact, intercept and modify already sent messages on their journey to receptors. Powered by the intensifying calcium ion quantity inside the shell, they have the ability to establish their own territory, and amend how a neuron is constructed by directing the production of synapses or dendritic spines. They can even interact with thousands of neurons and synapses to get their chemical message across by utilizing gliotransmitters. The future of gliotransmission is vague, but optimistic, nonetheless. And with the information that scientists have so far, there is no knowing where it will take them.

Drug Abuse

“All Additive drugs affect brain pathways involving reward.”

Every drug activates a dopamine neurotransmitter in the brain. This makes you feel good about yourself or your actions. Without dopamine, all thoughts would turn to the end result of suicide. This is why many take drugs, whether through injection or smoking. Dopamine is a natural chemical, but with the help of drugs such as Meth or Heroin, the cells are tricked into releasing more of the chemical. When someone takes a drug, their brain becomes more tolerant to it because their brain reduces the levels of dopamine receptors in synapses, thus increasing the amount of intake needed to get high because each time. It has been proven that drugs that travel faster through the pathways into the brain are more addicting opposed to those that require a certain amount of time. This habitual behavior is known as becoming “hard-wired”, and is responsible for turning a normal human being into a drug abuser.

Many think that if they quit getting high off of drugs, the effects will just disappear. This is not true. Changes in the brain, especially reward pathways, are majorly distorted after the use is discontinued. And the reward pathways are not the only area affected. Examples of the warped physical aspect are neurons in the reward pathway with extended, bulky dendrites. Judgement, learning, and memory become hard-wired because the drugs continue to infect parts of the brain in which these necessary activities are controlled. If one doesn’t learn how to stop this routine, and ups their intake each time, they can overdose (OD), and eventually kill themselves.

When scientists deal with ranking a drug, based on how addicting they are, they take into consideration their mode of transportation, and how fast they travel to the brain's pathways. As mentioned above, the faster the drug enters the brain, the more addicting it proven to be. The fastest route to the brain is through smoking, or inhalation. To illustrate my point, nicotine in tobacco seeps into lung fluid and the lung itself, thus allowing a quick and easy trip to the body's main control center: the brain. Direct injection is the second chosen method for fast access. This functions through blood vessel transportation. The following ways of getting drugs to destroy the brain, by rank of fastest to slowest is: snorting/sniffing, then ingestion. The difference between the slowest and fastest method is by entire minutes, altering gene expression and altering gene expression and neural circuitry.

In yet another recent search for drug-related answers, those who saw that the time difference has a significant impact also noticed that the drug's mode of delivery also influences separate pieces of the brain. For example, smoking has shown direct correlation with the distortion of brain regions that expedite addiction. However, this sad event has brought about a bitter sweet ending. Those who have aided in the research have also opened up doors for addiction therapies.

Brain Pathways

Nigrostriatal pathway
Substantia Nigra to Striatum
. Motor control
. Death of neurons in
this pathway can result in
Parkinson's Disease

Mesolimbic and Mesocortical pathways
Ventral Tegmental Area to Nucleus
Accumbens, Amygdala & Hippocampus,
and Prefrontal Cortex
. Memory
. Motivation and emotional response
. Reward and desire
. Addiction
. Can cause hallucinations and schizophrenia if not functioning properly

Tuberoinfundibular pathway
Hypothalamus to Pituitary gland
. Hormonal regulation
. Maternal behavior (nurturing)
. Pregnancy
. Sensory processes