1. Neurotransmitters

2. Monoamines as Neurotransmitters

3. Monoamine Neurotransmitters
Monoamines are regulatory molecules derived from amino acids.
CATECHOLAMINES: these are tyrosine derivatives: dopamine, norepinephrine, epinephrine. Bind to adrenergic receptors.
Norepinephrine is a neurotransmitter and hormone but epinephrine is primarily a hormone
tyrosine
tyrosine
Other monoamines: 2) SEROTONIN (derived from tryptophan)
3) Histamine (derived from histidine)

4. Norepinephrine as a neurotransmitter
Used in both the CNS and PNS
Sympathetic neurons use norepinephrine on smooth muscles, cardiac muscles, and glands.
Used by neurons of the CNS in brain regions associated with arousal
Amphetamines work by stimulating norepinephrine pathways in the brain.

5. Monoamine Action and Inactivation
KNOW THIS PATHWAY

6. Monoamines use G-protein Coupled Channels
THIS IS A SECOND MESSENGER SYSTEM
This is a BETA ADRENERGIC receptor.
Sympathetic neurons of the PNS use norepinephrine as their neurotransmitter.

7. Serotonin as a neurotransmitter
Used by neurons in the raphe nuclei (middle region of brainstem)
Implicated in mood, behavior, appetite, and cerebral circulation
The drug LSD and other hallucinogenic drugs may be agonists.
Serotonin specific reuptake inhibitors (SSRIs) are used to treat depression.
Prozac, Paxil, Zoloft
Over a dozen known receptors allow for diversity of serotonin function.
Different drugs that target specific serotonin receptors could be given for anxiety, appetite control, and migraine headaches.
serotonin

8. Dopamine as a neurotransmitter
Neurons that use dopamine (dopaminergic neurons) are highly concentrated in the midbrain in two main areas:
Nigrostriatal dopamine system: involved in motor control
Mesolimbic dopamine system: involved in emotional reward
Nigrostriatal – axons coming from substantia nigra --> basal ganglia
Mesolimbic – axons coming from vental tegmental area  nucleus accumbens and prefrontal cortex
dopamine

9. Nigrostriatal dopamine system: (motor)
Parkinson disease is caused by degeneration of these neurons.
Patients are treated with L-dopa and monoaminoxidase inhibitors
Activates the substantia nigra brain region.
dopamine

10. Mesolimbic dopamine system
involved in emotional reward.
Schizophrenia is associated with too much dopamine.
Dopamine antagonists are used to treat schizophrenia
Activates the limbic system.
Associated with addictions to nicotine, alcohol, other drugs
dopamine

11. Abused because it elevates energy/mood Crosses the blood-brain barrier
Cocaine
Abused because it elevates energy/mood
Crosses the blood-brain barrier
In mesolimbic reward system, it is a triple-reuptake inhibitor:
Blocks reuptake of dopamine
Blocks reuptake of serotonin
Blocks reuptake of norepinephrine
Danger:
Blocks Na+ ion channels
Raises heart rate/blood pressure
Increase risk of stroke, seizure

12. Other Neurotransmitters

13. Amino acids as NTs Excitatory NT – glutamate and aspartate
Glutamate – major excitatory neurotransmitter
Produces EPSPs in 80% of synapses in cortex
Constitutes major energy use in the brain
Involved in memory
Astrocytes take glutamate from the synaptic cleft to maintain homeostasis
glutamate

14. Inhibitory NTs
Glycine
produces IPSPs
Binding of glycine opens Cl− channels, causing an influx of Cl−.
Makes it harder to reach threshold
Important in the spinal cord for regulating skeletal muscle movement.
This allows antagonistic muscle groups to relax while others are contracting
(e.g. biceps relax while triceps contract).

15. GABA , another inhibitory neurotransmitter
Gamma-aminobutyric acid
most common neurotransmitter in the brain
used by 1/3 of the brain’s neurons.
inhibitory, opens Cl− channels
involved in motor control. Degeneration of GABA-secreting neurons in the cerebellum results in Huntington disease.

16. GABA receptors contain a chloride channel

17. Nitric Oxide
Nitric oxide (not nitrous oxide laughing gas)
A gas produced by some neurons in the CNS and PNS from the amino acid L-arginine
Diffuses across the presynaptic axon plasma membrane (no vesicle)
Diffuses into the target cell and activates the production of cGMP as a second messenger
Causes blood vessel dilation (Viagra works by stimulating the action of nitric oxide) and helps kill bacteria
May also act as a retrograde NT

18. Summation: Spatial
Spatial summation occurs due to convergence of signals onto a single postsynaptic neuron.
All of the EPSPs and IPSPs are added together at the axon hillock.

19. Summation: Temporal
Temporal summation is due to successive waves of neurotransmitter release that add together at the initial segment of the axon.