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Studies established that for animals, human beings included, to get electrically stimulated in different regions of the brain, they have to work. This electrical stimulation that occurs in distinct areas of the brain, specifically the septal region generates extinction and acquisition curves which are similar to those generated by conventional primary reward. This observable fact is known as brain-stimulation reward (BSR). Other terms used to refer to it is intracranial stimulation (ICS) or intracranial self-stimulation (Kornetsky & Porrino, 1992).
Researches indicate that many of the abused substances amplify response rate (lever pressing) for rewarding intracranial stimulation. This circumstance is translated to signify an increase in value of reward of the ICS (Olds & Milner, 2007). This is for the reason that alliterations in the response rates may also be a function of impacts if abused drugs and substances on motor performance. Many procedures that have been used to establish effects of a number of drugs on the brain have demonstrated that many of the most common abused substances and drugs elevate the sensitivity of human beings to the rewarding action as a result of electrical stimulation. This happening is however does not depend on any substances’ motor effects.
Kornetsky & Porrino (1992) observe that as a functional unit, human brain is composed of numerous neurons (nerve cells) that through chemical and electrical signals, communicate with each other. Different parts of the brain are responsible for different specific functions. Neurons travel from one point of the brain to another to send and integrate information along pathways which are activated upon an individual receiving positive reinforcement due to some behaviors (reward).
According to Olds & Milner (2007), individuals who use drugs have a tendency of persisting with administering the drugs whenever they are available because they make the feel good. If cocaine or heroine enters into particular areas of their brain or blood stream, they will keep on either snorting or injecting themselves with these drugs. This action is referred to as reward or positive reinforcement as observe above. People normally carry on exhibiting a rewarding behavior, an event that only stops whenever the reward is absent. In the brain, there is a section known as the reward system, which gets activated by both natural rewards (food, sex, etc) and artificial rewards such as drugs.
If someone snorts or smokes cocaine, it runs quickly to the brain. Even though the cocaine will go to all parts of the brain, its areas of concentration are specific. These parts are the caudate nucleus and the accumbens (VTA) to activate pathways. The result of this is accumulation of cocaine in some areas like caudate nucleus as already discussed and the impacts of this on a person will be an increase in stereotypic behaviors such as nail-biting, pacing, scratching among others (Kornetsky & Porrino, 1992). These kinds of stereotypical behaviors are also observed in people who are addicted to use of heroine.
Similarly when one injects themselves with heroin, it makes a quick movement to the brain. It also concentrates in the nucleus accumbens, the VTA and the caudate nucleus just like in the case of cocaine. However, it should be noted more importantly that in addition to the aforementioned parts of the brain, heroin also concentrates in the thalamus. Heroin will also attach to opiate receptors which are highly concentrated in the parts in the reward system (Olds & Milner, 2007). In the same manner like in cocaine, production of dopamine will also increase on addition to other types of neurons. Additionally, the action of heroin in the thalamus will enhance their capacity to generate analgesia. This happens differently in the case of cocaine as it will be observed below.
The presence of cocaine in the synapse will bind the to the uptake pumps. As a result, it will prevent the uptake pumps from getting rid of dopamine from the synapse. Consequently, more dopamine will accumulate in the synapse hence activating more dopamine receptors. This occurrence hampers the work of the cell because whenever there is an increase in the activation of dopamine receptors, there will be an increase in the manufacture of cAMP within the post-synaptic cell. The end result is a lot of alliterations in the cell leading to anomalous firing patterns.
Just like in the case of cocaine, heroin will reward system by use of nucleus accumbens. This process is however more complex than what happens in the case of cocaine. This is as a result of involvement of more than two neurons in the process. It takes three different types of neurons to take part in opiate action (Wise, 2006). They include the dopamine terminal, one more terminal the right side of the brain, which might be containing a different kind of neurotransmitter, possibly GABA and finally, post-synaptic cell having dopamine receptors. When heroin binds to opiate receptors, a signal will be send to the dopamine signal hence triggering the discharge of additional dopamine. One reason that has been availed to explain this phenomenon is that the activation of opiate receptors diminishes the release of GABA, that usually hinder release of dopamine, therefore dopamine production is enhanced.
Another similarity between the effect of cocaine and heroin is how they affect that cAMP. Due to more dopamine being produced as observed above, the rate at which dopamine receptors are activated is increased just like in the case of cocaine. There is an increased release of cAMP within the post-synaptic cell. At this point the normal functioning of the neuron is greatly altered (Wise, 2006).