Compare and Contrast how Cocaine, Ecstasy, Heroin and Cannabis Work in the Brain
Drugs of abuse, such as cocaine, ecstasy, heroin and cannabis, are of natural or synthetic origin, which can alter the emotional state, perception, body functioning and behaviour of an individual. Drugs are known to work in the brain by activating certain brain circuits via different mechanisms, and stimulate or inhibit different neurons in the pathway. However, due to the effects of each drug being different, a drug will affect either different pathways and neurons in the brain to that of another, or through a different process, i.e. direct or indirect activity. This essay will discuss the different ...view middle of the document...
, Romero, Rice, Carroll, and Partilla, 2001), with users experiencing changes in behaviour patterns concerned with mood, sleep and appetite. Cocaine, on the other hand, has been found to have a profound effect on increased dopamine activity. Kennedy & Hanbauer (1983; cited in Karch, 2007) found a strong correlation between cocaine binding and the inhibition of dopamine uptake, and therefore proposed that dopamine transporters are binding sites for cocaine. Such research, which correlates strong reinforcing properties of cocaine with inhibition of dopamine transporters, suggests that cocaine has a more significant affect upon dopamine, than than it has upon serotonin and noradrenaline. The excessive role of dopamine can explain the high degree of pleasure that users of cocaine experience, as well as depression and cravings, which follow.
In contrast to ecstasy and cocaine, which increase the secretion of natural neurotransmitters by blocking transporters, ‘direct agonists’ imitate natural endogenous neuromediators and bind to their receptors. Heroin and cannabis are both examples of direct agonists.
Many regions of the brain contain cannabinoid receptors, of which anandamide molecules, concerned with regulating mood, appetite and emotions, naturally bind to. Cannabis contains an active ingredient known as ‘delta-9-tetrahydrocannabonic’ (THC), and when smoked or eaten, the THC imitates the activity of anandamide by binding to cannabinoid receptors on nerve cells, and therefore influences their activity (Spinella, 2005).
In a similar action to cannabis, heroin binds to certain receptors in the brain, but to different ones than THC in cannabis. There are believed to be three different types of opioid receptors in the brain; mu, delta, and kappa, and endorphin, enkephalin, and dynorphin neurons naturally bind to these. When heroin enters the body, it is quickly turned to morphine and binds to opiod receptors, imitating the body’s natural endogenous opiods (Klein & Thorne, 2006).
While all drugs have different mechanisms of action, each drug increases the activity of certain neurotransmitters. Like cocaine and ecstasy, heroin and cannabis have been found to have an effect upon increasing dopamine activity. However, unlike cocaine, which increases dopamine activity through direct action at dopamine transporters, heroin and cannabis appear to increase the levels of the neurotransmitter by indirectly stimulating dopamine neurons. This is due to the drugs activating the mesolimbic reward system, which generates a signal in ventral tegmental area (VTA). This, in turn, triggers the release of dopamine in the nucleus accumbens (N-Ac), and therefore causes feelings of pleasure. Research has shown that when heroin binds to opiate receptors, activation of these receptors decreases GABA release within the nucleus accumbems, which normally inhibits dopamine release. Therefore, dopamine activity is increased, affecting the pleasure pathway (Johnson & North,...