This document discusses neurotransmitter systems and how they are studied. It provides 3 criteria for classifying a molecule as a neurotransmitter and describes methods for localizing transmitters like immunocytochemistry and in situ hybridization. It also discusses studying transmitter release using brain slices and examining receptors through ligand binding and identifying receptor subtypes. Finally, it outlines the chemistry of several major neurotransmitter systems like acetylcholine, catecholamines, serotonin, and amino acids.

1. NEUROTRANSMITTER SYSTEMS

2. NEUROTRANSMITTER
Basic criteria:
1. The molecule must be synthetized and stored in the presynaptic neuron
2. The molecule must be released by the presynaptic axon terminal upon
stimulation
3. The molecule, when experimentally applied, must produce a response in the
postsynaptic cell that mimics the response generated by the release of the
neurotransmitter by the presynaptic cell

3. HOW TO STUDY NEUROTRASMITTERS
Localization of Transmitters and Transmitter-synthesizing enzyme
Immunocytochemistry
Anatomically localize particular molecules to particular cells

4. HOW TO STUDY NEUROTRASMITTERS
Studying Transmitter Localization
In situ hybridization
mRNA strands can be detected by complementary probe
Probe can be radioactively labeled - autoradiography

5. HOW TO STUDY NEUROTRASMITTERS
Studying Transmitter Release
Loewi and Dale identified Ach as a transmitter
CNS contains a diverse mixture of synapses that use different
neurotransmitters
impossible to stimulate a single population of synapses
Brain slice as a model (ex vivo, brain in a dish)
Kept alive in vitro  Stimulate synapses, collect and measure
released chemicals (mixture)
Often stimulated by high K+ solution to cause massive synaptic release
Ca2+ dependency of the release has to be confirmed

6. HOW TO STUDY NEUROTRASMITTERS
Studying Receptors
No two transmitters bind to the same receptor; however one neurotransmitter
can bind to many different receptors
Receptor subtypes
Neuropharmacology
Subtype specific agonists and antagonists
ACh receptors
Skeletal muscle Heart

7. HOW TO STUDY NEUROTRASMITTERS
Studying Receptors

8. HOW TO STUDY NEUROTRASMITTERS
Studying Receptors
Ligand-binding methods
Drugs that interact selectively with neurotransmitter receptors were used
to analyze natural receptors
Solomon Snyder and opiates
Identified receptors in brain
Subsequently found endogenous opiates
Endorphins, dynorphins, enkephalins
Enormously important for mapping the anatomical distribution of different
neurotransmitter receptors in brain

9. NEUROTRASMITTER CHEMISTRY
Cholinergic (ACh) Neurons
good marker for cholinergic neurons
Rate-limiting step of
Ach synthesis
Secreted from the axon
terminal and associated with
axon terminal membrane

10. NEUROTRASMITTER CHEMISTRY
Cholinergic (ACh) Neurons
Synthesis
Degradation

11. NEUROTRASMITTER CHEMISTRY
Catecholaminergic Neurons
Involved in movement, mood, attention,
and visceral function
Tyrosine: Precursor for three amine
neurotransmitters that contain catechol
group
Dopamine (DA)
Norepinephrine (NE, noradrenaline)
Epinephrine (E, adrenaline)

12. NEUROTRASMITTER CHEMISTRY
Marker for catecholaminergic neurons
Rate limiting, regulated by
physiological signals
•Low-rate release - increased
catecholamine conc. - inhibit TH activity
•High-rate release - increased Ca2+ influx
- boost TH activity
Present in the synaptic vesicles
Present in the cytosol
Released from the adrenal gland as well

13. NEUROTRASMITTER CHEMISTRY
• Serotonergic Neurons
– Serotonin (5-HT,5-
hydroxytryptamine) is derived
from tryptophan
– Regulates mood, emotional
behavior, sleep
– Synthesis of serotonin
• Limited by the availability of
blood tryptophan (diet)
– Selective serotonin reuptake
inhibitors (SSRIs):
Antidepressants

14. NEUROTRASMITTER CHEMISTRY
• Amino Acidergic Neurons
– Amino acid neurotransmitters:
Glutamate, glycine, gamma-
aminobutyric acid (GABA)
– Glutamate and glycine
• Present in all cells - Differences
among neurons are quantitative
NOT qualitative
• Vesicular transporters are specific
to these neurons
– Glutamic acid decarboxylase (GAD)
• Key enzyme in GABA synthesis
• Good marker for GABAergic
neurons
• One chemical step difference
between major excitatory
transmitter and major
inhibitory transmitter