The Psychopharmacology (From Greek Pharmakon "Drug") is defined as the science that studies the effects of drugs on both the nervous system and behavior.
Colloquially it is usually called drugs to certain psychotropic substances (that acts on the central nervous system) that are taken for recreational use, but in the field of psychology and medicine is included within the drugs any external psychotropic substance that significantly alters the Normal functioning of our cells at relatively low doses.
It specifies that the substance must be external (or exogenous) to be considered drugs because our body manufactures its own chemical substances (endogenous substances) that can have effects similar to psychotropic drugs, such as neurotransmitters, neuromodulators or hormones.
It is important to clarify that drugs cause significant changes at low doses since at high doses almost any substance can cause changes in our cells, even water in large quantities can modify our cells.
The effect of drugs depends mainly on their place of action, the place of action is the exact point where the molecules of the drug bind to the molecules of the cells that will modify, biochemically affecting these cells.
The study of psychopharmacology is useful for both psychiatrists and psychologists, it is useful for psychiatrists to develop psychopharmacological therapies to treat psychological disorders, and for psychologists to better understand the functioning of nervous system cells and their relation to behavior .
In this article I will try to describe psychopharmacology in a way that is useful for psychologists, or people with training in the subject, and also for the general public. To do this I will first explain some key concepts of psychopharmacology.
Principles of psychopharmacology
Pharmacokinetics
The Pharmacokinetics Is the study of the process by which drugs are absorbed, distributed, metabolized, and excreted.
Step one: Administration or absorption of drugs
The duration and intensity of the effect of the drug depends largely on the route by which it has been administered, as it varies the rate and amount of drug that reaches the bloodstream.
The main routes of administration of the drugs are:
- Injection. The most common way of administering drugs to laboratory animals is by injecting it, usually a liquid solution of the drug is prepared. There are several places where the drug can be injected:
- Intravenously. This route is the fastest since the drug is injected directly into the veins, so it enters the bloodstream immediately and reaches the brain in a few seconds. Administration through this route can be dangerous since the entire dose reaches the brain at the same time and if the individual or animal is especially sensitive there will be little time to administer another drug that counteracts the effect of the first.
- Intraperitoneal route. This route is also quite rapid, though not as much as the intravenous route. The drug is injected into the abdominal wall, specifically into the intraperitoneal cavity (the space that surrounds the internal abdominal organs, such as the stomach, intestines, liver...). This route of administration is widely used in research with small animals.
- Intramuscular use. The drug is injected directly into a long muscle, such as the muscles of the arm or legs. The drug passes into the bloodstream through the capillary veins that surround the muscles. This route is a good choice if administration is required to be slow because in that case the drug can be mixed with another drug that constricts blood vessels (such as ephedrine) and delays the blood circulation through the muscle.
- Subcutaneous use. In this case the drug is injected into the space that exists just below the skin. This type of administration is only used if a small amount of drug is injected since injecting large amounts can be painful. In cases where slow release of the drug is desired, solid pellets of this drug can be made or introduced into a silicone capsule and implanted in the subcutaneous zone, in this way the drug will slowly be absorbed.
- Intracerebral and intraventricular route . This route is used with drugs that are not able to pass the blood barrier, so they are injected directly into the brain, into the cerebrospinal fluid Or in the cerebrospinal (in the cerebral ventricles). Direct injections into the brain are often used only in research and with very small amounts of drugs. Injections into the ventricles are rarely used and are mainly used to administer antibiotics if there is a serious infection.
- Orally. It is the most usual way to administer psychotropic drugs to humans, it is not usually used with animals because it is difficult to make them eat anything if they do not like their taste. Drugs administered by this route begin to degrade in the mouth and continue to degrade in the stomach, where they are finally absorbed by the veins that supply the stomach. There are some substances that can not be administered orally because they would be destroyed by stomach acid or digestive enzymes (This happens for example with insulin, so it is usually injected).
- Sublingual route. This type of administration consists of depositing the drug under the tongue, the psychoactive drug will be absorbed by the capillary veins of the mouth. For obvious reasons this method is only used with humans, since it would be difficult to co-operate with an animal in this way. The nitroglycerine Is an example of a drug usually given by this route, this drug is vasodilator and is taken to calm the pain of angina, caused by an obstruction in the coronary arteries.
- Intrarectal route. Drugs are administered by introducing them into the anus in the form of suppositories, once introduced into the bloodstream through the veins that irrigate the anal musculature. This route is not usually used with animals because they can defecate if they get nervous and would not allow time for the drug to be absorbed. This type of administration is indicated for drugs that could damage the stomach.
- Inhalation. There are many recreational drugs that are administered by inhaling them, such as nicotine, marijuana or cocaine, as the psychotropic drugs that are usually administered through this route emphasize anesthetics, since these are usually presented as gases and the effect appears fairly fast Because the route that follows the drug between the lungs and the brain is quite short.
- Topical route. This type of route uses the skin as a means to administer the drug. Not all drugs can be absorbed directly into the skin. Hormones and nicotine are usually given in this way using patches that adhere to the skin. Another topical route is the mucosa that is inside the nose, this route is usually used more for the use of recreational drugs like cocaine since the effect is almost immediate.
Second step: Distribution of the drug by the body
Once the drug is in the bloodstream it must reach the place of action that is usually found in the brain, the speed with which the drug reaches this place depends on several factors:
- Solubility of the drug . The Blood brain barrier Prevents water-soluble (water-soluble) substances from entering the brain but passes lipid-soluble (lipid-soluble) molecules so that they are rapidly distributed through the brain. For example, heroin Is more fat soluble than morphine , Therefore, the first will arrive before To the brain And will have faster effects.
- Plasma protein binding. Once they have entered the bloodstream, some molecules that make up the drug can bind to plasma proteins forming other compounds, the more molecules that bind to plasma proteins, the less the amount of the drug will reach the brain.
Third step: Action of the psychoactive drug
This step is the most interesting and the most studied from the field of psychopharmacology. The actions of psychotropic drugs can be divided into two broad categories: Agonists If they facilitate the synaptic transmission of a certain neurotransmitter or antagonist If it hinders it. These drug effects occur because the molecules of psychotropic drugs act on a particular site within the neuron which facilitates or inhibits The synapse . So, in order to understand its action, it is necessary to know what the synapse is and how it is produced, for people who do not know how the synapse occurs and those who want to remember it, I leave the following picture.
The main places and moments in which the psychotropic drugs can act are:
- In the synthesis of neurotransmitters. The synthesis of neurotransmitters is controlled by enzymes, so that if a drug inactivates one type of enzymes the neurotransmitter will not be created. For example, parachlorophenylalanine inhibits an enzyme (tryptophan hydroxidase) which is indispensable for the synthesis of Serotonin , Therefore, it could be said that parachlorophenylalanine decreases serotonin levels.
- In transporting the structures necessary to perform synapses up to the axon . The elements that are used in the synapse usually occur in organelles near the nucleus and have to be transported to the axons where the synapse will be realized, if the structures in charge of transporting them deteriorate, the synapse can not be realized and the drug will act like antagonist. For example, Colchicine (Used to prevent gout crises) joins the Tubulin Which is essential for creating the microtubules that carry the transport within the neurons, preventing the microtubules from developing effectively and deteriorating the synapse.
- In the reception and conduction of action potentials . In order to activate a neuron it is necessary that it receives some stimulus (it can be electrical or chemical), to receive the chemical stimulus must have the presynaptic receptors of the dendrites (place where the neurotransmitters join) but there are some drugs that block these receptors Presynaptic and prevent the potential for action. For example, Tetrodotoxin (Present in the balloon fish) blocks the presynaptic channels of sodium (ion channels) so it prevents its activation and cuts the nerve conduction.
- In the storage of neurotransmitters in the vesicles . Neurotransmitters are stored and transported to the axon in synaptic vesicles, some compounds of psychoactive drugs can modify the structure of the vesicles and modify their functioning. For example, Reserpine (a Antipsychotic And antihypertensive) modifies the vesicles causing them to develop pores that"escape"the neurotransmitters and therefore can not perform the synapse.
- In the process of releasing the neurotransmitters to the synaptic cleft . In order to release the neurotransmitters, the vesicles must attach to the presynaptic membrane close to the axons and open a hole through which the neurotransmitters can exit. Some drugs act by facilitating the binding of the vesicle to the presynaptic membrane and others making it difficult. For example, him Verapamil (To treat the hypertension ) Blocks calcium channels and prevents the release of neurotransmitters while amphetamines facilitate the release of catecholamine neurotransmitters such as adrenalin and the Dopamine . A curious example is the mechanism of action of the poison of the black widow (which contains latrotoxins), this compound causes an excess of the release of Acetylcholine , Releasing more acetylcholine from the one that is produced, which exhausts our reserves and causes and state of exhaustion and finally muscular paralysis.
- At postsynaptic receptors . Once released, neurotransmitters must bind to postsynaptic receptors to activate the next neuron. There are some drugs that affect this process, either by modifying the number of postsynaptic receptors or by joining them. Alcohol is an example of the first type, it increases the number of receptors in GABAergic inhibitory neurons which produces a state of obnubilation (although this effect is lost if alcohol is continued for a prolonged period). An example of drugs that block postsynaptic receptors is nicotine, this drug blocks Acetylcholine Preventing its action.
- In the modulation of neurotransmitters . The neurons have presynaptic autoreceptors in the dendrites, these receptors are united with the same neurotransmitter that the neuron has expelled in the synapse and its function is to control the levels of said neurotransmitter: if many neurotransmitters are united to the receivers will be cut the production of this one While if they join few will continue to occur. Some drugs block these receptors and can either facilitate or inhibit the production of neurotransmitters, since there are drugs that activate these receptors as if they were the same neurotransmitter (which would inhibit its production), while others block them by activating them The release of neurotransmitters). An example of this effect is what happens with caffeine, caffeine molecules block the Adenosine , An endogenous compound (produced by ourselves), which does not release this compound more and prevents its inhibitory and sedative function.
- In the reuptake of neurotransmitters . Once they are used in the synapse to activate the next neuron, neurotransmitters are recapted by the presynaptic neuron to deactivate and degrade them. There are drugs that bind to receptors responsible for reuptake the neurotransmitters and inhibit reuptake, for example, amphetamines and cocaine produce this effect in dopaminergic neurons so that dopamine remains free in the synaptic cleft and continues activating other neurons until That the entire reserve of dopamine is exhausted and the feeling of weariness arrives. There are also antidepressants that act in this way, are called Serotonin reuptake inhibitors (SSRIs), which help maintain or increase levels of this neurotransmitter.
- In the inactivation of neurotransmitters . Once they are recaptados the neurotransmitters are metabolized, that is to say, they are degraded in subcompuestos to deactivate them and to restart the process creating new neurotransmitters. This metabolization is carried out by certain enzymes and there are drugs that bind to these enzymes and inhibit their action, eg another type of Antidepressants , the IMAO (Monoamine oxidase inhibitors), as its name implies, inhibit the enzyme monoamine oxidase that is involved in the deactivation of some neurotransmitters, therefore MAOIs make the neurotransmitters more active.
As can be verified the actions of psychotropic drugs are complex because they depend on multiple factors, the place and moment of action, the previous state of the place of action, etc. Therefore, they should not be taken under any consideration without a prescription, as it can have unexpected and even adverse effects on our health.
Step 4: Inactivation and excretion
Once they have performed their function the psychotropic drugs are inactivated and excreted. Most drugs are metabolized by enzymes located in the kidneys or liver, although enzymes can also be found in the blood and even in the brain itself.
These enzymes normally degrade the drugs, making them inactive compounds that will eventually be secreted through urine, sweat or feces. But there are some enzymes that transform psychoactive drugs into other compounds that remain active, and even compounds with more intense effects than the original psychoactive drug.
References
- Carlson, N. R. (2010). Phychopharmacology. In N. R. Carlson, Physiology of Behavior (Pp. 102-133). Boston: Pearson.
- Castillo, A. (1998). Psychopharmacology. In A. Perales, Manual of psychiatry"Humberto Rotondo". Lime. Retrieved from http://sisbib.unmsm.edu.pe/bibvirtual/
- Nestler, E.J., & Duman, R. S. (2002). Neurotransmitters and signal transduction. In K. L. Davis, D. Charney, J. T. Coyle, & C. Nemeroff, Neuropsychopharmacology - 5th Generation of Progress. Philadelphia: Lippincott, Williams, & Wilkins. Retrieved from http://www.acnp.org/
- Stahl, S. M. (2012). Circuits in psychopharmacology. In S. M. Stahl, Stahl's Essential Psychopharmacology (Pages 195-222). Cambridge: Cambridge University Press.