Biological Aspects of Drug Addiction.

¶ … biological aspects of drug addiction. In order to do this we provide a detailed analysis of two main categories of drugs. These categories include stimulants and depressants. We then compare their mechanisms of addiction and then finally conclude with the possible therapies that can be administered to counter these addictions.

The addiction to drugs a condition also referred to as drug dependence is one of the most serious health problems (Nutt,1996).It causes a massive amount of direct health costs that results due to psychiatric and physical financial burden associated with the condition. The other costs that are associated with this health problem are crime, loss of productivity and earnings as well as social damage. The drugs of our primary concern are stimulants (cocaine and amphetamines), opioids and depressants such as alcohol. The other one which we are not going to focus on is nicotine addiction (smoking), another major cause of health concern. One of the major goals of medicine is to come up with a way of reducing the extent of drug addiction.

The addiction mechanisms in the brain

The process of drug addiction involves the alteration of certain functions of the brain since the abused drugs are neuroactive substances that are involved in a process of altering the brain transmitter functions.There is a lot of research which is currently being undertaken in order to provide further insight into the exact neurochemical as well as the molecular actions of drug use and abuse. This is with the intention of determining the reasons as to why humans misuse drugs and how to rehabilitate the users. There are various interesting new development into the study of the mechanism of drug addiction in the brain. One of these is neuroimaging that entails:

PET (position emission tomography)

SPELT (single photon emission computed tomography),technologies that have been hailed as being the very first to be used in the testing for the mechanisms of drug addiction in humans by means of data derived from various preclinical studies.

The specific processes in the brain that have been noted to be responsible for alcoholism and its various manifestations have been documented to involve the functions of attention, learning, emotion as well as cognition. A normal human brain must first of all orchestrate most of these functions at the same time in order to perceive a given environment. They then access the significance of the environment in relations to survival. This is then followed with an initiation of the behavioral reactions. These processes and activities require a very efficient communication mechanism between the different regions of a person's brain. There is also a multilevel communication within these brain regions. In order to illustrate the mechanism of addiction in the brain of a human being, we consider the case of alcohol addiction. In this paper we presents this process by means of a three level process of communication within the brain of a human being. These are:

1. The synaptic level-involves the transfer of information between the individual neurons

2. The system level that represents the integrated activities of the different regions of the brain

3. The intracellular level-comprises of the various signaling processes that takes place within the neurons.

Information is then effectively transferred by the various chemical messengers (neurotransmitters) which gets released by a neuron then bound effectively by a specialized protein type called receptors. These receptors are embedded in the membrane (outer one) of another neuron. There exists a tiny gap between these communicating neurons. It is referred to as a synapse.

Several neurotransmitters are active during the process of addiction. Each of these transmitters does bind to a certain specific receptor. It is however worth pointing out that a specific receptor may be in existence in multiple subtypes. Each of these subtypes may produce unique responses to the same transmitter. This is what accounts for the multiple effects of a certain neurotransmitter in different parts of the same neuron as pointed out by Weiner et al. (1997).It is worth noting that a given neuron's response to a certain information that is received from other neurons depends largely on the complex interactions that exists between potentially conflicting messages that do arrive simultaneously as indicated by Charness (1990).

One of the most dominant effects of alcohol is the reduction of the pace at which the brain activity takes place through;

1. The reduction of the excitatory mechanisms of glutamate, a neurotransmitter at the NMDA subtype of the glutamate receptor.

The boosting of the various inhibitory actions of a transmitter referred to as gamma-aminobutyric acid (GABA) .This occurs at the GABAA receptor as pointed out by Diamond and Gordon (1997).These actions are just among the reasons as to why alcohol is considered a depressant.

The actions of the NMDA and GABAA re c e p t o r s are effectively linked via ionic channels. These do function through the opening of a special pore at the surface of the membrane that allows for the specific ion (atoms that are electrically charged ) to go into the cell hence affecting the cell's electrolytic balance as postulated by Harris (1999).The other neurotransmitters that affect the process of alcohol addiction are dopamine, opioptides and serotonin (5-HT).These neurotransmitters do interact in specific ways with the various receptors in order to modulate the various activities of the specific neurons in which the reside. The role of dopamine in the encouragement of motivational behavior has been noted. This happens through a complex process of pursing of a certain rewarding stimuli. The administration of alcohol causes the release of dopamine in the brain of an individual. This region is called the nucleus accumbens and is a key member of a special group of structures that are linked and associated with the process of development of addiction to drugs (Rassnick et al. 1992; Bro'd I e and Pesold 1999).

The Opioid peptides are yet another class of neurotransmitters that are active in the production of physiological effects that are very similar to those of heroin and morphine. In the body of a human being however, the opioid peptides do interact with certain other neurotransmitters in order to influence a particularly broad spectrum of physiological functions that include the control of pain in humans.

A very high level of certain types of opioid peptides does have an effect in the encouragement of euphoria. The consumption of alcohol does affect the activity of the opioid peptide transmitter which responds by increasing the effects of alcohol as pointed out by Roberts et al. (2000).There is a medication referred to as naloxone which is active in the inhibition of the various functions of the receptors, opiod peptides. It blocks the release of the receptor dopamine which resides in the nucleus accumbens which has also been noted to suppress the consumption of alcohol through a laboratory test carried on animals as indicated by the work of Benjamin et al. (1993).Serotonin is also actively involved in the process of regulating mood, appetite, body temperature and a host of other humanly physiological functions. There have been certain experiments involving the mice that involved the genetic altering of the mice to lack serotonin receptor subtypes. These have suggested that there is role of serotonin in the regulation of the drinking levels.

It is worth pointing out that alcohol can lead to induced activation of certain specific serotonin receptor subtypes can lead to a stimulation of the dopaminergic activity in an individual's nucleus accumbens.This potentially contributes to the rewarding effects of alcohol. There are however other serotonin receptors have been shown to have effects and roles in the process of drug intoxication and withdrawal (Venezula,1997).

Symptomology

Addiction to depressants such as alcohols leads the user to exhibit the following symptoms of addiction:

Craving -- the user experiences a very strong desire and compulsion to drink

Physical dependence: the user experiences withdrawal symptoms whenever they stop drinking after an extended period of drinking. These include anxiety, nausea and shaking

Tolerance: The person undergoes a continuous need to take more and more quantities of alcohol in order to get drunk

Loss of control: The user experiences the inability to limit their drinking over a period of time

Alcohol's neuronal circuit

The 1980s discovery that alcohol at certain concentration can cause or rather produce intoxication in human beings which can inhibit the various excitatory effects of the special NMDA receptor thereby enhancing the inhibitory functions of the other special GABA receptor. A lot of research on alcohol has been dedicated towards the identification of the specific ions channels and receptors that get affected by alcohol. Alcohol has a unique characteristic that is absent in the other illicit drugs since it does not have a specific and special transmitter bind site in an individual's brain. It is worth noting that there is a complex behavior that is associated with the use of alcohol. These behaviors cannot be attributed to a certain limited number of special chemical interactions. This form of realization has given rise to an intimate look at the various effects of alcohol on the neuronal communication which can effectively integrate the various activities of a many brain regions.

The process of neuroadaptation

There are two main processes that do contribute to the development of addiction as well as the reinforcement and the process of neuroadaptation. The process of reinforcement occurs when a rewarding stimulus such as alcohol or other drugs such as AOD causes induced euphoria. This could also be a relief from an unpleasant condition or state such as anxiety which usually increases the chances of a behavioral response such as the use of AOD. Neuroadaptation refers to the various compensatory moves and adjustments in which the brain makes deliberate attempts to continue with its normal function irrespective of the fact that it is under the influence of alcohol. The process of neuroadaptation and reinforcement which occurs simultaneously does appear to underline the initial acute response (short-term) to the drug under use as well as the establishment of chronic (long-term) craving that is often characteristic of addiction. It is worth pointing out that certain behaviors that are neuroadaptive makes changes could be permanent thus producing a continuous sense of discomfort that usually causes a relapse some time later after an individual stops to drink (Koob et al. 1993).A more common manifestation of the process of neuroadaptation is the experience of an acute syndrome that is consistent with withdraw which follows the abrupt stop to a heavy bout of drinking. As a reaction to the continued alcoholic content in the brain, a compensatory mechanism is initiated in an attempt to overcome the inhibition of alcohol by NMDA receptors. This is through the increase of the functions of NMDA through a process of up-regulation. At the time which the alcohol leaves the synapse, there is a combination of the up-regulated transmissions which are excitatory as well as the down regulation of the inhibitory transmission which results in the brain being hyper excited. A characteristic which is part of the withdraw syndrome as outlined by (Littleton,1998).The process of withdraw triggers the body to respond to the stress created. This leads to the elevated levels of stress hormone, cortisol in the blood stream. An excessive level of cortisol leads to the death of neurons in the hippocampus which leads to an increased risk to infection, alteration of energy metabolism and the promotion of disorders associated with mood and intellect as pointed out by intellect (Adinoff et al. 1998). The process of neuroadaptation can be thought of using the theories of counteradaptation which includes processes like tolerance that are started by the brain in order to oppose the particularly acute effects of alcohol. Neuroadaptation however includes and refers to sensitization which is referred to as an increase in the response to the effects of a drug as a result of repeated administration. Should the process of sensitization lead to an increased AOD consumption then addiction is likely to occur. The process of sensitization is more likely to result as a result of intermittent and repeated exposure to the AOD's.Tolerance however is likely to occur as a result ot continue exposure as pointed out by exposure (Robinson and Berridge, 1993). Should an addict withdraw within a short time (acute), then motivational effects are likely to occur as pointed out by (Koob and LeMo et,1997).there are various neurological structures that have an association with the reinforcing action of alcohol as well as other drugs.They may involve certain common neural circuits that form separate entity at the base of the forebrain. This is the extended amygdala as pointed out by (Alheid and Heimer,1988).Amygdala refers to a complex structure that is made up of several smaller structures and is situated near the base of a human's frontal area of the brain. The amygdale system has an extensive arrangement of connections to various brain regions that play an integral role on the reinforcement as well as the reward as pointed out by ( Diamond and Gordon, 1997).