The psychopharmacology (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 act on the central nervous system) that are taken for recreational use, but in the field of psychology and medicine, any external psychotropic substance that significantly alters the substance is included in the drugs. normal functioning of our cells in 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.
What is Psychopharmacology
It is important to clarify that drugs cause significant changes at low doses because 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 at which the molecules of the drug bind with the molecules of the cells that they will modify, affecting these cells biochemically.
The study of psychopharmacology is useful for both psychiatrists and psychologists, for psychiatrists it is useful for the development of psychopharmacological therapies to treat psychological disorders, and for psychologists to better understand the functioning of nervous system cells and their relationship with 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. For this I will first explain some key concepts of psychopharmacology.
Principles of psychopharmacology
The pharmacokinetics is the study of the process by which drugs are absorbed, distributed, metabolized and excreted.
First step: Administration or absorption of drugs
The duration and intensity of the effect of the drug depends in large part on the route through which it has been administered, since it varies the rhythm and the amount of drug that reaches the bloodstream.
The main routes of administration of drugs are:
- Injection. The most usual way to administer drugs to laboratory animals is by injecting them, 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. The administration by this route can be dangerous since the whole 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 fast, although not as fast 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 route The drug is injected directly into a long muscle, such as the muscles of the arm or legs. The drug enters the bloodstream through the capillary veins that surround the muscles. This route is a good option if the administration is required to be slow since, in that case, the drug can be mixed with another drug that constricts the blood vessels (such as ephedrine) and delays 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 used only if a small amount of drug is injected since injecting large amounts can be painful. In cases in which a slow release of the drug is desirable, solid pills of this drug can be elaborated or introduced in a silicone capsule and implanted in the subcutaneous zone, in this way the drug will be absorbed little by little.
- 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 into the cerebrospinal fluid (into the cerebral ventricles). Direct injections into the brain are often used only in research and with very small amounts of drugs. Injections in 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 its taste. The 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, which is why it is usually injected).
- Sublingual way This type of administration consists of depositing the drug under the tongue, the psychotropic 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 cooperate with an animal in this way. The nitroglycerin is an example of a drug that is usually administered by this route, this drug is vasodilator and taken to ease the pain of angina, caused by a blockage in the coronary arteries.
- Intrarectal route. The 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. In regard to the psychotropic drugs that are usually administered through this route, anesthetics stand out, since they usually appear in the form of gases and the effect appears quite fast because the route that the drug follows between the lungs and the brain is quite short.
- Topical way. This type of route uses the skin as a means to administer the drug. Not all drugs can be absorbed directly by the skin. Hormones and nicotine are usually administered in this way using patches that adhere to the skin. Another topical route is the mucosa found inside the nose, this route is usually used more for the use of recreational drugs such as cocaine since the effect is almost immediate.
Second step: Distribution of the drug by the body
Once the drug is in the bloodstream should reach the place of action that is usually 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 substances from entering the brain (soluble in water) but allows liposoluble molecules (soluble in lipids) to pass through, so that they are rapidly distributed throughout the brain. For example, heroin is more fat soluble than morphine, therefore, the former will reach the brain earlier and will have faster effects.
- Plasma protein binding. Once they have entered into the bloodstream some molecules that make up the drug can bind to plasma proteins forming other compounds, the more molecules join the plasma proteins the less amount of drug will reach the brain.
Third step: Psychopharmaceutical action
This step is the most interesting and the most studied from the field of psychopharmacology. The actions of psychotropic drugs can be included in two major categories: agonists if they facilitate the synaptic transmission of a certain neurotransmitter or antagonist if it hinders it. These effects of drugs occur because the molecules of the psychotropic drugs act on a specific place within the neuron which facilitates or inhibits the synapse. So, 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 is produced and those who want to remember it, I leave the following table.
The main places and times 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 a type of enzyme the neurotransmitter will not be created. For example, parachlorophenylalanine inhibits an enzyme (tryptophan hydroxidase) that is essential for the synthesis of serotonin, therefore, it could be said that parachlorophenylalanine decreases serotonin levels.
- In transporting the necessary structures to perform synapses 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 is performed, if the structures responsible for transporting them deteriorate, the synapse can not be performed and the drug will function as an antagonist. For example, colchicine (used to prevent gout attacks) binds to the tubulin that is essential to create the microtubules that transport within neurons, preventing microtubules from developing efficiently and damaging the synapse.
- In the reception and driving of action potentials . For a neuron to be activated it is necessary to receive some stimulus (it can be electrical or chemical), to receive the chemical stimulus the presynaptic receptors of the dendrites must be operative (place where the neurotransmitters join) but there are some drugs that block these receptors presynaptic and prevent action potentials from being conducted. For example, tetrodotoxin (present in the puffer fish) blocks the presynaptic sodium channels (ion channels) by preventing their activation and cutting the nerve conduction.
- In the storage of neurotransmitters in the vesicles . The neurotransmitters are stored and transported to the axon in synaptic vesicles, some compounds of the psychotropic drugs can modify the structure of the vesicles and modify their functioning. For example, reserpine (an antipsychotic and antihypertensive) modifies the vesicles causing them to develop pores through which neurotransmitters “escape” and therefore can not perform the synapse.
- In the process of release of neurotransmitters to the synaptic cleft . In order to release the neurotransmitters, the vesicles must bind to the presynaptic membrane near the axons and open a hole through which neurotransmitters can exit. Some drugs act by facilitating the union of the vesicle to the presynaptic membrane and others making it difficult. For example, verapamil (to treat hypertension ) blocks calcium channels and prevents the release of neurotransmitters while amphetamines facilitate the release of catecholamine neurotransmitters such as adrenaline and 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, getting to release more acetylcholine than it is produced, which depletes our reserves and causes and state of exhaustion and finally muscle paralysis.
- In 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 the state of obtundation (although this effect is lost if alcohol continues to be taken for a prolonged period). An example of drugs that block postsynaptic receptors is nicotine, this drug blocks acetylcholine receptors, preventing their action.
- In the modulation of neurotransmitters. The neurons have presynaptic autoreceptors in the dendrites, these receptors are joined 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 bind to the receptors, the production of this neurotransmitter will be cut off while if they are united few will continue to be produced. Some drugs block these receptors and can both facilitate and inhibit the production of neurotransmitters, since there are drugs that activate these receptors as if they were the same neurotransmitter (which would inhibit the production of it), while others block them preventing their activation (facilitating the release of neurotransmitters). An example of this effect is what happens with caffeine, caffeine molecules block autoreceptors from adenosine , an endogenous compound (produced by ourselves), which means that this compound is no longer released and prevents its inhibitory and sedative function.
- In the reuptake of neurotransmitters . Once they are used in the synapse to activate the next neuron, the neurotransmitters are recaptured by the presynaptic neuron to deactivate and degrade them. There are drugs that bind to receptors responsible for the reuptake of neurotransmitters and inhibit reuptake. For example, amphetamines and cocaine produce this effect in dopaminergic neurons, so dopamine remains free in the synaptic cleft and continues to activate other neurons. that the entire supply of dopamine is exhausted and the feeling of tiredness arrives. There are also antidepressants that act in this way, are the so-called serotonin reuptake inhibitors (SSRIs), which help maintain or increase the levels of this neurotransmitter.
- In the inactivation of neurotransmitters . Once they are recaptured, the neurotransmitters are metabolized, that is, they are degraded into subcompounds to deactivate them and start the process again creating new neurotransmitters. This metabolization is carried out by certain enzymes and there are drugs that bind to these enzymes and inhibit their action, for example, another type of antidepressant, MAOIs (monoamine oxidase inhibitors), as the name suggests, inhibit the monoamine oxidase enzyme that is involved in the deactivation of some neurotransmitters, therefore, the MAOIs make the neurotransmitters more active.
As you can see, the actions of the psychotropic drugs are complex since they depend on multiple factors, the place and time of action, the previous state of the place of action, etc. Therefore, should not be taken under any consideration without medical prescription, as it can have unexpected and even adverse effects on our health.
Fourth step: 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, but we can also find enzymes in the blood and even in the brain itself.
These enzymes normally degrade the drugs, turning them into inactive compounds that will eventually be secreted through urine, sweat or feces. But there are some enzymes that transform psychotropic drugs into other compounds that are still active, and even into compounds with more intense effects than the original psychoactive drug.