Case 9- depression Flashcards
Amino acid neurotransmitters
1) Acetylcholine (excitatory or inhibitory)
2) Glutamate (excitatory)
3) GABA (inhibitory)
Biogenic amines neurotransmitters
1) Dopamine (excitatory via D1 receptors and inhibitory via D2 receptors)
2) Norepinephrine (excitatory)- hormone and neurotransmitter
3) Epinephrine (excitatory)
4) Serotonin (excitatory or inhibitory)
Neuropeptides neurotransmitters
1) Substance P (excitatory)
2) Opioids (inhibitory)
Catecholamines
A subtype of the biogenic amines containing Dopamine, Norepinephrine and Epinephrine
Indoleamine
A subtype of the biogenic amines. Includes Serotonin and Imedazoleamine
The neurotransmitters linked to depression
Histamine, serotonine, dopamine and norepinephrine
Movement of Serotonin in the brain
Serotonin originates in the raphe nuclei within the brainstem. The axon then moves to the Cerebellum and up to the middle of the brain in the striatum and through the rest of the brain in the cortex.
Serotoninergic pathway
How Serotonin moves through the brain. Goes through the Cerebellum, Cerebral cortex, Hippocampus and the Striatum. The striatum is in the centre of the brain.
What does Serotonin control
Serotonin controls the arousal/sleep wake cycle. It is implicated in mood and behaviours. Linked to appetitive emotions (drive to do things) and emotions.
The three Dopaminergic pathway
Mesolimbic, Mesocorticol and Nigrostriatal
The Mesolimbic dopamine pathway
Start= Ventral tegmental area (VTA)
Finish= Limbic system- nucleus accumbens, hippocampus, amygdala
Reward pathway so can lead to addiction
The Mesocortical dopamine pathway
Start= Ventral tegmental area (VTA)
Finish= Cortex (mostly frontal aspect)
Involved in mood control, can cause depression
The Nigrostriatal dopamine pathway
Start= Substantia Nigra
Finish= Striatum- caudate and putamen nuclei of the basal ganglia
Involved in movement and control, when damaged it causes Parkinson’s disease
Neurotransmitter
A chemical that is specifically released at synapses to communicate between neurones.
Norepinephrine (neurotransmitter)
Used as a neurotransmitter for the Cerebellum, Cerebral cortex, Thalamus and limbic system. The cell bodies originate from the locus ceruleus. It influences arousal/wakefulness. It is implicated in mood and behaviour like appetitive (the desire to do something) and sexual behaviour
Monoamine theory of depression
The main biological theory of the cause of depression. States that depression is due to a reduction in the levels and/or effectiveness of the monoamines (biogenic amines, catacholamines). The main neurotransmitters involved are serotonin, dopamine and Noradrenaline
Arguments in support of the monoamine theory of depression
Tricyclic antidepressants (TCA’s)
Monoamine oxidase inhibitors (MAOI’s)
Reserpine
Arguments in support of the monoamine theory of depression- TCA’s
A drug which treats depression by inhibiting 5-HT (serotoninin) and NA (noradrenaline) reuptakes. This increases neurotransmitter levels in the synapse
Arguments in support of the monoamine theory of depression- MAOI’s
An antidepressant that inhibits the action of Monoamine, which is an enzyme that breaks down neurotransmitters. Increases concentration of 5-HT and NA.
Arguments in support of the monoamine theory of depression- Reserpine
Reserpine is a drug that treats high blood pressure by reducing 5-HT and NA. In patients taking this drug there is a sudden increase in the suicide rate
Arguments against the monoamine theory of depression
- TCAs and MAOIs take time to work. If the problem was simply low levels of neurotransmitters then the effect of these drugs increasing neurotransmitter levels should happen within minutes.
- Cocaine increases the levels of these monoamines in the brain but is not an antidepressant.
- Limited evidence of lowered 5-HT/NA levels or their metabolites in the blood/ CSF/ urine/ brain of people with depression.
- 1/3 of depressed patients do not respond to usual antidepressant drugs.
Triggers for mental disorders
- Stress can lead to depression/anxiety by affecting 5-HT function. Stress can also affect neurogenesis (making new neurons) and neuromorphology (repairing neurons and changing their function).
- Genetics- some people have a genetic predisposition, there is a high concordance in monozygotic twins.
The link between Stress and the Hypothalamic-pituitary-adrenal axis
When you are stressed the Amygdala releases CRH causing the Hypothalamus to release more CRH which acts on the pituitary gland. The anterior pituitary gland releases ACTH into the blood stream. ACTH acts on the adrenal gland to release cortisol, the stress hormone. You get a negative feedback so it’s a short term response. This pathway also feedbacks on the Hippocampus and the Prefrontal cortex, so that you remember the stressful situation.