PSYC62H3 Chapter Notes - Chapter 5: Neurotransmitter, Synaptic Plasticity, Neuromodulation

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24 Apr 2012
Chapter Five Page 1 of 7
Chapter 5: Synaptic Transmission, Drugs, and Chemical Neuroanatomy
Neurotransmitters and Chemical Signaling in the Nervous System
Neurotransmitters are commonly viewed as chemicals that are located In specific regions of
neurons, are released under specific stimulation, act on a specific set of receptors and induce
some type of postsynaptic action such as a change in membrane potentials or metabolic activity
Neurohormone refers to substances that are synthesized and released from neurons, but act as
hormones; these substances include hormones such as corticotrophin releasing factor, which is
released from hypothalamic neurons and act on the anterior pituitary gland, and also includes
oxytocin and vasopressin, which are synthesized in the hypothalamus and released into systemic
circulation in the posterior pituitary
Neuromodulator includes any substance that alters neurotransmission in some way
o Neurotransmission is a specific subclass of neuromodulation
o However, neuromodulation is sometimes used to describe the condition in which a
substance modifies neural transmission but isn’t itself the means of transmission (ie. It
doesn’t show any direct shifts in membrane potential or conductance when tested for
actions on its own
The same substance can meet the definition of a neurohormone, neuromodulator, and
neurotransmitter (eg. DA)
Most substances that are neurotransmitters also act as neuromodulator
Dale’s Law or Dale’s Principal – a given neuron uses the same neurotransmitter at all its
synapses. Thus, a given neuron can be identified in terms of which transmitter it uses (ie. A
GABAergic neuron). This observation was first formulated based upon early studies of classical
studies of classical transmittesr, but it sometimes has been misinterpreted to mean that one
neuron uses only one transmitter. We now know that a given neuron can co-localize multiple
transmitters - often a combo of a classical transmitter and a neuropeptide. It’s not true that any
given neuron can have any combo of transmitters
Neurotransmitter Groups
Monoamines (MA) includes the catecholamines DA, NE, and EPI, as well as the indolamine 5-
o The neurons that utilize MA share biochemical features and this also means that some
drugs act broadly on all MA
o The catecholamines DA, NE, and EPI are structurally related to each other. Also share
common synthesis and enzymatic breakdown pathways. They’re closely related in their
o All catecholamines are siblings and 5-HT neurons are their cousin
o 5-HT indolamine because of structure
Synthetic pathway resembles that of catecholamines, and one of the
metabolizing enzymes (MAO)
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Chapter Five Page 2 of 7
Acetylcholine (Ach) released by electrical stimulation of the vagus nerve because the fluid
surrounding the stimulated nerve terminals was shown to slow the heart rate
o Involved in motor control, sleep, emotional/cognitive processes, and many drugs that
treat Parkinson’s and Alzheimer’s act on ACh
Histamine (H) promotes secretion in tissues
o Drugs that block H receptors are used to treat colds, allergies, ulcers
o Involved in regulating sleep and wakefulness
Amino Acids important compounds for metabolism and are the basic building blocks for
proteins and peptides, but some amino acids also act as neurotransmitters
o GLU and aspartate (ASP) excitatory amino acids
Induce excitation in neurons
GLU most common excitatory transmitter in the NS, and glutamatergic
pathways form much of the basic excitatory wiring of the neural circuitry of the
Excitatory amino acids are important for neural plasticity and the plastic
changes in synaptic function that are regulated by GLU are important for
learning and memory
Long term Potentiation (LTP) widely studied model of synaptic plasticity
studies indicates that GLU is involved in LTP
Overstimulation of excitatory amino acid receptors can cause brain damage
Factor in the secondary brain damage induced by cerebral
strokes/hypoxia, because when GLU neurons die, they dump their GLU
into the extracellular space
Drugs that block excitatory amino acid transmission can act as
neuroprotective agents
GLU, ASP, and GLY (glycine) alpha amino acids
Group of amino acids that are the building block units for peptides and
GABA most common inhibitory neurotransmitter but can be excitatory early in
Induces inhibitory postsynaptic potentials
GABAa subtype very heterogeneous made up of five subunits that
can combine into a wide variety of configurations
o Combination of subunits determine what effects it will have
AN endogenous cannaboid
o Fatty acid derivative that acts as a neural signaling molecule
o Delta 9 THC acts to mimic the effects of AN on its receptors
Adenosine purine neurotransmitter/neuromodulator
o Synthesized from cell energy pathways that use AMP-ADP-ATP
o Widespread through body and brain
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