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Chapter 12

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PSYC 3600
Hernan Humana

Chapter 6 Neurotransmitter SystemsIntroductionThree major classes of neurotransmitters amino acids amines and peptides First molecule identified as a neurotransmitter was acetylcholine AchCholinergic cells that produce and release AchNoradrenergic neurons that use the amine neurotransmitter norepinephrine NEGlutamatergic synapses that use glutamate GABAergic synapses that use GABAPeptidergic synapses that use peptides Ach and all the molecular machinery associated with it are collectively called cholinergic system Studying Neurotransmitter SystemsCertain criteria must be met to distinguish a molecule as a neurotransmitteroThe molecule must be synthesized and stored in the presynaptic neuronoThe molecule must be released by the presynaptic axon terminal upon stimulation oThe molecule must produce a response in the postsynaptic cell Localization of Transmitters and TransmitterSynthesizing EnzymesHints that a particular molecule may be a neurotransmitteroMolecule is concentrated in the brain tissueoApplication of the molecule to certain neurons alters their action potential firing rateTo confirm the molecule is a neurotransmitter the molecule must be localized in and synthesized by particular neurons Two techniques used are immunocytochemistry and in situ hybridizationImmunocytochemistryImmunocytochemistry a method used to anatomically localize particular molecules to particular cells oOnce the neurotransmitter candidate has been chemically purified it is injected into the bloodstream of an animal where it stimulates an immune response oThe response is the generation of large proteins called antibodiesAntibodies can bind tightly to specific sites on the foreign molecule such as the transmitter candidate Best antibodies for this method bind very tightly to the transmitter of interest and bind very little or not at all to other chemicals in the brain oThis method can be used to localize any molecule for which a specific antibody can be generatedIn Situ HybridizationIs also useful for confirming that a cell synthesizes a particular protein or peptide Recall proteins are assembled by the ribosomes according to instructions from specific mRNA molecules A unique mRNA molecule for every polypeptide is synthesized by a neuron If the sequence of nucleic acids in a strand of mRNA is known it is possible to construct in the lab a complementary strand that will stick to the mRNA moleculeoComplementary strand is called a probeoProcess by which the probe bonds to the mRNA molecule is called hybridizationIn order to see if the mRNA for a particular peptide is localized in a neuron we chemically label the appropriate probe so it can be detected apply it to a section of brain tissue allow time for the probes to stick to any complementary mRNA strands then wash away all the extra probes that have not stuck finally we search for neurons that contain the label In situ hybridization probes are usually labelled by making them radioactive oSince we cannot see radioactivity hybridized probes are detected by laying the brain tissue on a sheet of special film that is sensitive to radioactive emissions oAfter exposure to the tissue the film is developed like a photograph and negative images of the radioactive cells are visible as clusters of small dots This technique for viewing the distribution of radioactivity is called autoradiography
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