Intro to Neurotransmitters

Amino acids, amines, peptides

3 classes of neurotransmitters

Dale’s Principle

a neuron that has only one neurotransmitter

Co-transmitters

two or more transmitters released from one nerve terminal (ex. amino acid or amine plus a peptide)

Nomenclature

This system classifies psychotropic medications by their mechanism of action and pharmacological activity (-ergic)

By the molecule, synthetic machinery, packaging, reuptake and

degradation, and action

How to define particular transmitter systems?

1. Synthesis and storage in presynaptic neuron

2. released by presynaptic axon terminal

3. mimics postsynaptic cell response produced by release of neurotransmitter from the presynaptic neuron

3 scientific study to establish a neurotransmitter

In situ Hybridization

Detect mRNA that encodes neurotransmitter-synthesizing enzymes or neuropeptides.

Immunocytochemistry

anatomically localize particular molecules to particular cellsusing antibodies that bind to specific antigens.

molecule must evoke same response as a naturally occuring neurotransmitter from the pre-synaptic neuron

How can a neuron qualify as a sufficient neurotransmitter?

Microiontophoresis

technique in which drugs can be ejected in very small amounts to assess postsynaptic actions

microelectrode

measures effects on membrane potential and allows for the recording of electrical activity within a neuron.

Molecular analysis

receptor protein classes that categorize receptors based on their structure and function.

transmitter-gated ion channels

are membrane-spanning proteins consisting of four or five subunits that come together to form a pore between

• GABA_A receptors

• 4-5 subunits, each made w/ various combos of subunit polypeptides

G-protein coupled receptors

can have slow longer lasting, and much more diverse postsynaptic actions

• GABA_B receptors

• 7-transmembrane signaling molecules

Acetylcholine (ACh)

an amine that serves as a neurotransmitter at many synapses in the peripheral and central nervous systems, including the neuromuscular junction

• First identified neurotransmitter

• important for autonomic nervous system

Cholinergic (ACh) neurons

describes neurons or synapses that produce acetylcholine

Choline acetyltransferase (ChAT)

enzyme required for ACh synthesos that transfers acetyl groups from acetyl-CoA to choline, forming acetylcholine.

acetylcholinesterase (AChE)

cleaves the ACh molecule, rendering it inactive at the ACh receptors

Catecholaminergic Neurons

involved in movement, mood, attention, and visceral function

Tyrosine

precursor for three amine neurotransmitters that contain catechol group: dopamine, norepinephrine, and epinephrine.

• Tyrosine hydroxylase (TH)

• Dopa decarboxylase

• Dopamine 𝛃–hydroxylase (DBH)

• Phentolamine N-methyltransferase (PNMT)

Enzymes involved with Catecholaminergic Neurons

Serotonergic (5-HT) Neurons

derived from the amino acid tryptophan and relatively few in number as they play an important role in the brain systems that regulate mood, emotional behavior, and sleep

2-step synthesis from Tryptophan. Enzymes involved are Tryptophan

hydroxylase and 5-HTP decarboxylase

synthesis of serotonin

• glutamate (Glu)

• Glycine (Gly)

• GABA

Amino Acidergic Neurons

Glutamate

major excitatory CNS neurotransmitter that plays a key role in synaptic plasticity and cognitive functions such as learning and memory.

GABA

Major inhibitory CNS neurotransmitter that reduces neuronal excitability and plays a crucial role in regulating muscle tone and anxiety.

Glutamic acid decarboxylase (GAD)

key enzyme in GABA synthesis that serves as a good marker for GABAergic neurons which are major source of synaptic inhibition in the CNS