Chapter 1: Chemical Neurotransmission
Dendrite
Anatomical versus Chemical Basis of Neurotransmission s
Anatomical basis of neurotransmission
o Neurons and the connections between them Cell
Dendritic
body
(synapses) (Soma) spines
o Synapses
Asymmetric: communication is in one direction
(axon dendrite, soma, another axon)
Presynaptic and postsynaptic elements
that differ
Neurons are designed to send information to En
other neurons via an axon that passes by passant
presynapt
Axo
(en passant) or ends (presynaptic axon n
c axon
terminals
terminal)
Principles of Chemical Neurotransmission
Neurotransmitters
o Six neurotransmitters are targeted by psychotropic drugs Presynapti
Serotonin c axon
terminals
Norepinephrine
Dopamine
Acetylcholine
Glutamate
GABA
o To effectively treat psychiatric disorders it may be necessary to target neurons in
specific circuits
Necessary to treat with multiple drugs because monotherapy is not effective
at relieving symptoms
Especially if more than one neurotransmitter defect is present in the
illness
Neurotransmission: Classic, Retrograde and Volume
Classic Neurotransmission
o Electrical process by which
neurons send electrical signals
from one part of the cell to
another part of the same cell
via their axons
One neuron is sending
neurotransmitters
towards the receptor of a
second neuron
Excitation-
secretion
coupling:
Electrical signal is
converted to a
chemical signal at
the synapse
o First stage of chemical neurotransmission
, o From the presynaptic axon terminal to the second postsynaptic
neuron
Retrograde Neurotransmission
o Postsynaptic neurons can “talk back” to their presynaptic elements
o Endocannabinoids
Produced specifically as retrograde neurotransmitters
Synthesized in the
postsynaptic neuron
and then released and
diffuse to presynaptic
receptors
o Nitric Oxide (NO)
Synthesized by
postsynaptic neuron
and then released to
interact with
presynaptic cGMP
sensitive targets
o Nerve Growth Factor (NGF)
Diffuses to presynaptic neuron where it is taken up by vesicles
Transported back to the cell nucleus via retrograde transport systems
Volume Neurotransmission
o Transmission that does NOT require a synapse
Non-synaptic diffusion neurotransmission
Neurotransmission can occur at any
compatible receptor within the diffusion
radius of the neurotransmitter
Modifying volume transmission may
be a way in which several
psychotropics work in the brain
Dopamine action in the prefrontal cortex
There are very few dopamine transporters (DATs) to terminate the
action of dopamine during neurotransmission
o Dopamine is free to spill over to neighboring dopamine receptor
sites and activate them
Dopamine in the striatum
Presence of multiple dopamine reuptake pumps
Autoreceptors
Inhibit the release of
neurotransmitters from the axonal
end of the neuron
Somatodendritic autoreceptors
o Receive neurotransmitters
from dendritic release
o No synaptic vessels
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