The normal functioning of a human is largely dependent on the behaviours which relates to the central nervous system; hence behavioral techniques have been used in both animal and human model to further understand the central nervous system. These tests have been widely used to look at the pharmalogical efficacy and the mechanism of depression, anxiety, addiction, memory other mental complications. These techniques are relatively more cost efficient, simple, and easy to conduct, therefore it is widely used. The aim of this paper is to review the advantages, and disadvantages of such techniques and what have been discovered using such techniques.
DEPRESSION
Depression is a growing concern around the world, and anti-depressants available are not always effect for each individual. In addition, the therapeutic effect of all anti-depressant can be only seen only after a few weeks after administration, therefore having a much delayed therapeutic effect (Lopex-Rodriguez et al., 2004). Hence the forced swim test (FST) is used in numerous studies in expectation to help improve the efficacy and development of antidepressants. The FST, also known as the “behavioural despair test”, due to its ease of use, and inter-lab reliability and specificity, it is very common technique to assess depression and assess efficacy of antidepressant in animal models, typically in rodents.
In a FST, a rodent is placed in a pool filled with water which rodents cannot escape from. Data observed are usually scored in three diverse behaviors, immobility, swimming and climbing. Swimming is defined as horizontal movement in both front and hind legs, producing a paddling movement. Climbing is defined as the additional vertical position with hind legs below the surface of the pool water. Swimming and climbing are usually seen during the initial phase of FST (Kulikov et al.,2010). However, after the initial 5 minutes reduction in movement (immobility) is expected. Immobility is defined as there is no, or minimal horizontal movement, floating on the surface of water. These data are then compared between different treatment groups. Treatment group with an effective anti-depressant should show a longer swimming/climbing phase and a reduction in immobility phase (Slattery and Cryan, 2012). The improvement of immobility time evaluation is also important. One of the major contributions was from a FST study was conducted by Detke et al. He has improved the model, and anti-depressant that act on the serotonergic pathway showed an increase in swimming phase and anti-depressant that act on the noradrenergic pathway showed an increase in climbing phase (Detke and Lucki, 1995).
An example of FST that has led to a new anti-depressant is the discovery of 3-ethoxyquinoxalin-2-carboxamides (Mahesh et al., 2011). 3-ethoxyquinoxalin-2-carboxamides, a newly synthesized compound is a 5-HT3 receptor antagonist, which by acting on 5-HT3 it acts as an anti-vomiting agent in therapy such as chemotherapy. When mice treated with 3-ethoxyquinoxalin-2-carboxamides were tested on the FST, a reduction in immobility time was seen, which correlated with the effect of 5-HT3 agonist in depression (Mahesh et al., 2011).
Although FST is very sensitive to antidepressants, the FST is not sensitive to other stimulants such as sedatives or motor-impairing compounds can affect the observed results and produce a false negative or false positive. Therefore, FST is usually paired with the assessment of locomotor activity to provide in-depth detail of behaviour changes seen after treatment to further determine the efficacy of a particular drug (Slattery and Cryan, 2012).
One of the limitations with such behavioral technique such as FST is that data interpreted and be indistinct between spectators, particularly when determining the immobility phase. Hence this detection of the various phases has been automatized, using inverted lighting, silhouette alteration method for the evaluation of animal movement, automated choice of the threshold and the permutation test for drugs’ effect was invented by Kulikov et al., 2010.
Another limitation of FST is the validity of the test. Anti-depressant drugs only show a therapeutic response typically few weeks after administration in depressed humans. However the reduced immobility of a rodent are observed 24 hours after administration in the FST. This does not correlate, and has been questioned.
ANEXIETY
The elevated plus maze (EPM) test is a common test used to study the mechanism of anxiety and avoidance and the efficacy of anxiolytic like drugs (Sziray et al., 2008). This test like the FWT has its own advantages, and similar advantages. EPM are able to be conducted as ease, and equipment aren’t expensive. EPM also does not necessitate any continued training, water/food deficiency, and any use of risky stimulation to the rodent which considered acceptable ethically (Rodgers and Dalvi, 1997).
The EPM was originally in a Y shaped, however the modern EPM typically has four arms in a shape of a plus, and is elevated to 50 cm above ground. Two opposite arms (the close arms) will be close with side walls, whereas the other two (the open arms) will have no side walls at all, or with a raised edge to prevent rodents from falling (Pawlek et al., 2012). When rodent in exposed to an unfamiliar environment, the primary response is to explore to maze. This creates an encounter between the innate curiously to explore and natural dislike to possible threats (open arm) (Sidor et al., 2010). When wild type rodents are forced to stay on open arms, it shows fear related reactions such as freezing and increase plasma corticosteroids (Treit et al., 1993).
The time in the closed and open arms are primarily used to assess anxiety like behaviours. An example of EPM would be the use of Diazepam in rodents as an anxiolytic drugs. Diazepam, is able to block GABA-ergic receptors in brain, hence able to enhance the GABA activity (Ostrovskaya et al., 1975). When rodents are treated with acute diazepam, studies have shown that it is able to increase the duration, and frequency in the open arms (Treit et al, 1992). However when treated with chronic dosages of diazepam, EPM does not correlate to result obtained from acute dosages, and inhibited the exploration (Ruarte and Alvarez, 1999). Such limitation would also cause an unreliable validity in such test.
Although EPM test is the most common technique used to assess anxiety, technique such as open field, emergence and light dark test, and social interaction are also used to assess anxiety to obtain similar results. These test can possibly use in subjects to increase the reliability of results. For example Ruarte and Alvarez, 1999, also tested mice in a light dark test, which also showed similar response, increased exploration in acute doses and an inhibition of exploration seen in choric dosages (Ruarte and Alvarez, 1999).
ADDICTION
Drug addiction is a growing health problem, and can be considered as a chronic brain disorder characterized by a high rate of relapse following detoxification. This relapse is the primary problem making treatment a challenge. The behaviour of drug craving is observed in addicts who are put into an environmental stimuli related with their drug-taking behaviour, drug itself or stress, even after a long period of no drug treatment. This behaviour in addiction suggests that an alteration in brain and behaviours technique can help further understand the mechanism of such behaviours, and possibly find cure for drug abusers (Aguilar et al., 2009).
Conditioned Place Preference (CPP) is a common technique to assess the potential of addiction for a particular drug, and most drugs are able to elicit CPP (Natarajan et al., 2011). The CPP apparatus typically consist of two main compartments, separated by a small compartment. These compartments are usually in contrast colour (black and white), with different flooring. The duration and frequency to component will be measured, and when a preference is seen with the component associated with drug administration, it is considered to elicit a CPP. When rodent because contextual stimuli and provoke appetitive properties when paired with a primary reinforce, therefore increases the risk of drug abuse. However this was not seen in the ability of nicotine to induce CPP.
Other techniques such as self-administration procedure can also assess the potential of addiction. This procedure was tested with cocaine, has provided to insight that changes in dopamine, norepinephrine, serotonin, glutamate and GABA innervations of the forebrain was observed (Smith et al., 2003.). This technique has also provided greater understanding of addiction by discovering the dopamine (DA) hypothesis of reinforcement (Wise, 2006).
MEMORY
Memory function is a very important part of neuroscience, and the learning task is able to assess the deficits that may be occurring in an individual. These memory functions are categorized into two; declarative memory and procedural memory, and they also refer in the brain parts that are responsible for its respective function.
Declarative memory is the memory of facts and events, such as recalling a list of words, is interrupted in individuals with temporal lobe and hippocampal damage. It is assed with the use of free recall and recognition. This type of memory is seen to decrease with the increase of age and can be paired with amnesic patients. In order to asses this memory; the California Verbal Learning Test (CVLT) can be used (Lengenfelder et al., 2000). This is a list learning test consisting of 16 common shopping list items in several categories presented identically in 5 trials. The individual will be asked to recall the list in an ordered manner and a free call (Gorp et al., 1999).
Procedural memory is a subtype of the nondeclarative memory. It is responsible for the skill and procedural learning. Individuals with interrupted procedural memory are observed to have damaged basal ganglia (Gorp et al., 1999). One of the tests to assess procedural memory is the Pursuit Rotor Motor Learning Test. Tested individual holds a photosensitive baton and they will have to follow and maintain contact with a 2 cm light disk rotating on a variable speed turntable. 4 trails with 15, 30, 45, and 60 revolutions per minuets are used to test the variable (Gorp et al., 1999 and Hatakenaka et al., 2011).
In conclusion the behavioral techniques have provided a greater insight and a better understanding of the central nervous system, especially when dealing with neuropharmacology, and looking at the efficacy of a particular drug. However, these techniques often involve rodents as the test subjects, which may cause variance in the results. Animal behaviours have been suggested to mirror the personality of the animal and like humans; animals do not react identically in a given situation. Therefore to further improve such behavioral techniques, subtypes of characteristic must be included to improve results. This behavioral technique also has a potential for observer bias during result collection. Although animal models are able to provide understanding of drug mechanism, it is still questioned the relativeness to human, and how drug pharmacokinetics and pharmacodynamics might be altered. Behavioral techniques often involve a degree of bias when determining the results. However this limitation has been gradually improved alongside with the improvement of technology. Much has been gained from techniques listed above, however with technology and alteration of methods, more precise and reliable can be possibly to provide results to further understand the mechanism in the CNS, and also provide help to develop treatments for mental disorders.