neuroscience - chapter 8 Flashcards
Define neurotransmitter systems. (simple definition)
Neurotransmitter systems refer to the networks of neurons and chemical messengers (neurotransmitters) that work together to transmit signals across the brain and nervous system. Each system typically involves a specific neurotransmitter (like dopamine, serotonin, or acetylcholine) and a set of receptors, enzymes, and pathways that influence various mental and physical functions, such as mood, movement, and cognition.
What are the three types of neurotransmitters?
Amino acids, amines and peptides.
What does this chapter focus on?
-Criteria and methods used to identify NTs
-NT life cycle, from synthesis to degradation (for specific NTs & learn where drugs act)
What are the four criteria a molecule must meet to be considered a neurotransmitter?
- Synthesis and localization (the molecule must be synthesized and stored in pre-synaptic neurons)
- Release (the molecule must be released by the presynaptic terminal upon stimulation)
- Response mimicry (when experimentally applied, the molecule must produce a response that mimics the response of a post-synaptic cell to the NT release)
- Inactivation/degradation (the molecule must be actively removed from the synaptic cleft)
- SYNTHESIS AND LOCALIZATION
Enzymes for making the NT should be present for which neurotransmitters?
Amino acids and amines.
NOT peptides.
Name the two different methods for localization.
- Immunohistochemistry
- In situ hybridization
Describe the process of immunohistochemistry (if applied to a tissue).
- Used to anatomically localize an NT or the enzyme that makes it
- Create “tagged” antibodies for the NT or enzyme
process:
(a) The molecule of interest (a neurotransmitter candidate) is injected into an animal, causing an immune response and the generation of antibodies. (b) Blood is withdrawn from the animal, and the antibodies are isolated from the serum. (c) The antibodies are tagged with a visible marker and applied to sections of brain tissue. The antibodies label only those cells that contain the neurotransmitter candidate. (d) A close-up of the complex that includes the neurotransmitter candidates, an antibody, and its visible marker.
What must the neurotransmitter demonstrate to satisfy criterion 1?
To satisfy criterion 1, you must demonstrate that the candidate neurotransmitter AND the enzyme that synthesizes are contained in the same neuron, or better still, the same axon terminal.
Describe the process of in situ hybridization (if applied to a tissue).
- Locates the mRNA for peptide NTs and their synthesizing enzymes
- A radioactively labelled strand of complimentary mRNA
- Only cells with the target mRNA become radioactive
In situ hybridization. Strands of mRNA consist of nucleotides arranged in a specific sequence. Each nucleotide will stick to one other complementary nucleotide.
In the method of in situ hybridization, a synthetic probe is constructed containing a sequence of complementary nucleotides that will allow it to stick to the mRNA. If the probe is labeled, the location of cells containing the mRNA will be revealed.
What must the neurotransmitter demonstrate to satisfy criterion 1?
Same thing. To satisfy criterion 1, you must demonstrate that the candidate neurotransmitter AND the enzyme that synthesizes are contained in the same neuron, or better still, the same axon terminal.
- RELEASE
In order for the neurotransmitters to be released, what needs to happen?
Stimulation!
Describe the release process in the PNS.
*a specific set of cells or axons can be stimulated while taking samples of the fluids bathing their synaptic targets (Loewi’s frog heart study?).
*The biological activity cause by the sample can then be tested to see if it mimics the effect of the intact synapses.
*sample can then be chemically analyzed to reveal the structure of the active molecule.
Describe the release process in the CNS.
*Until recently, it was impossible to stimulate
(electrically) a single population of synapses
containing only a single neurotransmitter, so
many synapses in a region of the brain and Loading…
researchers had to be content with stimulating
collecting and measuring all the chemicals that were released (in brain slices in “in vitro” preparations).
*With the advent of “optogenetics”, it is now possible to activate just one specific type of synapse at a time. Genetic methods are used to induce one particular type of neuron to express light-sensitive ion channels, and then those neurons can be stimulated with brief flashes of light. Any transmitters released are likely to have come from the optogenetically selected type of synapse.
Define optogenetic stimulation.
Optogenetic stimulation is the use of light to activate specific cells, usually neurons, that have been genetically modified to respond to light. This method allows precise control of cell activity to study how these cells affect behaviour, brain function, or other biological processes. (target specific neurons)
- RESPONSE MIMICRY BY IONTOPHORESIS
Describe the process.
Applying the molecule (to a “postsynaptic” neuron) results in a synaptic response that mimics stimulation of the axon
Define micro iontophoresis.
This method enables a researcher to apply drugs or neurotransmitter candidates in very small amounts to the surface of neurons. The responses generated by the drug can be compared to those generated by synaptic stimulation.
Is this criteria alone proof of the candidate being a neurotransmitter?
Notice that molecules other than the NT can also interact with receptors, so this criterion by itself is no “proof” of the candidate molecule being a NT.
- INACTIVATION
Describe the process.
Specific mechanisms remove the molecule (viewed previously).
Define neurotransmitter synthesis.
Neurotransmitter synthesis is the process by which neurons produce neurotransmitters, the chemical messengers used to send signals across the nervous system.
Which type of neurotransmitter is made where?
-peptide NTs made in soma
-amino acid and amine NT made in the axon terminal
Describe the synthesis of peptide neurotransmitters.
(a) Peptides:
1. A precursor peptide is synthesized in the rough endoplasmic reticulum. 2. The precursor peptide is split in the Golgi apparatus to yield the active neurotransmitter.
3. Secretory vesicles containing the peptide bud off from the Golgi apparatus.
4. The secretory granules are transported down the axon to the terminal where the peptide is stored.
Define Dale’s principle.
The convention established by Dale classifies neurons into mutually exclusive groups by neurotransmitter (cholinergic, glutamatergic, GABAergic, and so on).The idea that a neuron has only one neurotransmitter is often called Dale’s principle. (one neuron will only release one neurotransmitter = not true)
