Have you ever thought why a tablet of Paracetamol can make your headache go away and how a hot mug of coffee can keep you up late in the night until you really want to fall asleep? It is all because of various chemical compositions of substances or drugs we use, which act on different parts of our body and alter bodily mechanisms in several distinct ways.
The human brain is the most complex organ in our body which regulates thousands of functions including coordination of vision, hearing, perception, vibration, pain, shaping individual behavior and insight, controlling emotions, feelings, and thoughts, etc. Different parts of the brain such as brain stem, cerebral cortex, and limbic system work as a whole by maintaining several inter-relationships and communications. Therefore, they make up the fundamental structure, behavior, and attitudes of an individual. This communication mainly occurs from neuron to neuron, neurotransmitters (chemicals which carry brain messages to and fro), receptors and transporters (brain chemical recycling substances).
Brain stem: This part controls the basic critical aspects of life including heart rate, breathing, and sleeping patterns.
Cerebral cortex: Foremost part of the cortex is known as the regulation center of thinking which controls the ability of planning, problem-solving and decision-making. Other parts of the cortex are responsible for the regulation of specific functions such as vision, hearing, vibration and proprioception.
Limbic system: This is the part of the brain which acts as the reward circuit of the entire body, linking several structures together by carrying the responsibility of perception, control, and regulation of feelings, thoughts, and emotions. It usually gets activated by life-sustaining activities like eating and socializing as well as with drug abuse.
How Do Drugs Affect the Brain
What are Drugs and How do they Act on the Brain
Drugs are chemicals which affect the brain by involving in its communication system and interfering with neurons, especially in the aspects of message sending, receiving and processing. Certain drugs like marijuana and heroin are known to activate the neurons as a result of their chemical structure which is quite similar to that of inherent neurotransmitters. However, this similarity may not be completely similar to that of natural ones, which will result in sending abnormal messages all over the brain as well as to other parts of the body.
Moreover, drugs like Amphetamine or Cocaine are known to result in a huge and sudden release of neurotransmitters or prevent the normal recycling pattern of intrinsic brain chemicals. This ultimate alteration will result in an abnormal linking between communication channels, giving rise to several unusual behavioral patterns, thoughts, emotions, etc.
Routes of Administration
For a certain drug to act on the human body, first it should enter into the blood stream and eventually reach the person’s brain which will result in the alteration of necessary functions. This way, drugs which enter blood faster will have a rapid action along with intense effects. There are several forms of drugs administration including direct intravenous injection to blood, subcutaneous injection, intramuscular injections, intrathecal injections, inhalation, swallowing and per-rectal. It is important for a drug to be able to cross the blood-brain barrier to give out the expected action on the brain.
How does a Synapse Work
Even though neurons communicate in different aspects by maintaining interconnections between axons and dendrites, it is important to identify that there is no physical contact between the terminal end of a neuron and dendrites of the other. The gap between an axon and dendrites is known as ‘synapse’, and once the chemical, electric signal of an activated neuron reaches the terminal end, the electrical message will be halted, and chemical messengers known as ‘neurotransmitters’ (Dopamine, Adrenaline, Noradrenaline, Serotonin, Acetylcholine, Glutamate, Endorphins) will be released into the synapse which will bridge its gap. These neurotransmitters will cross the synaptic space and join proteins known as ‘receptors,’ located in the dendritic wall and result in either the excitation or inhibition of the post-synaptic neurons.
After few cycles, the neurotransmitters which have been released will be taken back into the terminal button by a process known as ‘re-uptake’ which will help in re-circuiting.
The Action of Drugs on Brain
Drugs which enhance the activity of neurotransmitters are known as Agonists whereas those which inhibit neurotransmitters are known as Antagonists.
Agonists
- Can increase the production of particular neurotransmitters
- Can sometimes interfere with the re-uptake of neurotransmitters and enforce them to remain in the synapse, maintaining the interaction with receptors longer than the usual duration
- Can completely bypass the neurotransmitter and cross the synapse and result in the activation of the inherent neurotransmitter’s receptors
- Can usually enhance the natural effect of neurotransmitters
Eg: Cocaine effects the Norepinephrine and Dopamine neurotransmitter systems
Antagonists
- Can interfere with the release of neurotransmitters into the synapse
- Can compete with the neurotransmitter in binding to the inherent receptor
- Some drugs bind to the receptor but does not activate it; instead, of activating, they block receptors from being activated by the neurotransmitter.
Eg: Naloxone blocks opioids by attaching to the opioid receptors without activating them
Major Types of Drugs Affecting the Brain
- Depressants – Alcohol, Benzodiazepines, Barbiturates——Act on GABA receptors
- Stimulants – Amphetamines, Cocaine—–act on Dopamine receptors
- Opioids – Naloxone, Naltrexone——- act on special endorphin receptors in the brain responsible for pain
- Cannabinoids – Marijuana—— acts on the neurotransmitters Serotonin, Dopamine, Acetylcholine and Anandamide
- Hallucinogens – LSD—— antagonize Serotonin by blocking the release.
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