Neurotransmitters, Mood and Behaviour

What You Should Know Endorphins are neurotransmitters that stimulate neurones involved in reducing the intensity of pain. Increased levels are also connected with euphoric feelings, appetite modulation and release of sex hormones. Endorphin production increases in response to severe injury, prolonged and continuous exercise, stress and certain foods. The reward pathway involves neurones which secrete or respond to the neurotransmitter dopamine. The reward pathway is activated on engagement of beneficial behaviours, e.g. eating when hungry. Dopamine induces the feeling of pleasure and reinforces particular behaviour in the reward pathway. Many drugs used to treat neurotransmitter related disorders are similar to neurotransmitters Agonists bind to and stimulate receptors mimicking the neurotransmitter. Antagonists bind to specific receptors blocking the action of the neurotransmitter. Other drugs inhibit the enzymes which degrade neurotransmitters or inhibit re-uptake.

Endorphins Are chemicals that function like neurotransmitters Act as natural painkillers by combining with receptors at synapses and blocking the transmission of pain signals

Action of Endorphins

Increased Endorphin release: Endorphin production increases in response to: Physical and emotional stress Severe injury prolonged and continuous exercise Certain foods e.g. chocolate

Other Ways to Increase Endorphin Production sunlight exercise Listen to music meditation laugh

Effect of Increased levels of Endorphins Regulate appetite Release sex hormones Feelings of euphoria

Dopamine Dopamine is a neurotransmitter produced in several areas of the brain, 2 of those centres called ‘V’ and ‘N’ When a survival related urge e.g. hunger is being satisfied by current behaviour, neurons in centre ‘V’ secrete Dopamine This dopamine travels to centre ‘N’ which also secretes & responds to it by inducing a pleasurable feeling Therefore ‘V’ and ‘N’ are referred to as the pleasure centres of the brain The route from ‘V’ to ‘N’ is called the brain’s reward pathway

Treatment of Neurotransmitter Related Disorders Many of the drugs used to treat neurotransmitter related disorders are similar in chemical structure to neurotransmitters Disorders include Alzheimer’s disease Parkinson’s disease Schizophrenia Generalised anxiety disorders Depression

Agonists An agonist is a chemical that binds to and stimulates a specific receptor on the post synaptic membrane They mimic naturally occurring neurotransmitters Trigger a normal cellular response

Antagonists An antagonist is a chemical that binds to specific receptors on the post synaptic membrane blocking the action of the normal neurotransmitter This reduces or stops normal transmission of nerve impulses

Other Drugs Used in Treatment Inhibit the enzymes which degrade neurotransmitters e.g. cholinesterase from degrading acetylcholine OR Inhibit re-uptake e.g. norepinephrine

Mode of Action Recreational Drugs

What You Should Know Mode of action of recreational drugs. Can mimic neurotransmitters, may stimulate the release of neurotransmitters, imitate their action (agonists), block their binding (antagonists), inhibit their re-uptake/enzymatic degradation Changes in neurochemistry alter mood, cognition, perception, behaviour. Many recreational drugs affect neurotransmission in the reward circuit of the brain. Drug addiction/tolerance. Sensitisation is an increase in the number and sensitivity of neurotransmitter receptors as a result of exposure to drugs that are antagonists and leads to addiction. Desensitisation is a decrease in the number and sensitivity of receptors as a result of exposure to drugs that are agonists and leads to drug tolerance.

Recreational Drugs Some people choose to alter their state of consciousness by using recreational drugs Recreational drugs affect the transmission of nerve impulses in the reward circuit of the brain Total drugs market attributed to specific drugs

How Recreational Drugs Work They interact with neurotransmitters in different ways by stimulating the release of neurotransmitters (nicotine, alcohol) imitating their action (agonists)-(morphine, heroin) blocking their binding (antagonists) inhibiting the re-uptake of neurotransmitters (cocaine, ecstasy) Inhibiting the breakdown of neurotransmitters by enzymes

Effect of Recreational Drugs on Neurochemistry An alteration in a person’s neurochemistry can lead to changes in mood (e.g. happier, more confident, more aggressive) cognition (e.g. poorer at complex mental tasks such as problem solving and decision making) perception (e.g. misinterpretation of environmental stimuli- sounds, colours, sense of time) Behaviour (e.g. stays awake for longer and talks about him/herself endlessly)

Drug Addiction and Tolerance

Drug Addiction and Tolerance Drug addiction- is defined as a chronic, relapsing brain disease that is characterised by compulsive drug seeking and use, despite harmful consequences It is considered a brain disease because drugs change the brain; they change its structure and how it works These brain changes can be long lasting and can lead to many harmful, often self-destructive, behaviours

Drug Tolerance Tolerance occurs when the person no longer responds to the drug in the way that person initially responded. E.g. It takes a higher dose of the drug to achieve the same level of response achieved initially. This illustration shows dopamine levels in a monkey's brain after two identical doses of cocaine. The second dose, taken after the effects of the first dose wore off, produced lower levels of dopamine

Drug Desensitisation Repeated use of agonistic drugs results in certain neuroreceptors (eg those that promote dopamine release) being repeatedly stimulated The nervous system responds to this overstimulation by reducing the number and sensitivity of these receptors to the agonist drug This leads to drug tolerance/desensitisation as a larger dose of the drug is needed to stimulate the reduced number of less sensitive

Drug Sensitisation Repeated use of a drug that acts as an antagonist (blocking certain neuroreceptors) prevents the normal neurotransmitter from acting on the receptors The nervous system compensates for the reduced stimulation of the receptors by increasing their number The receptors themselves also become more sensitive to the antagonist drug This leads to addiction