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GABAA receptor
Gamma-
aminobutyric
acid type B
receptor
N-type calcium
channel
Adenylate
cyclase type 2
G protein-
activated
inward
rectifier
potassium
channel 1
Substance-P
receptor
Kappa-type
opioid receptor
Gβ
Guanine
nucleotide-
binding protein
G(i) subunit
alpha-1
Gγ
γ-Aminobutyric acid
Substance P
Meperidine
cAMP
Ca
+
Ca
+
Na
+
Na
+
γ-Aminobutyric acid
Meperidine
Meperidine
ATP
PP
i
GTP
Pain
Magnesium
Less GABA leads to
disinhibition of dopamine
cell firing in the spinal
chord pain transmission
neurons. This leads to less
pain signalling and
analgesia
Decreased calcium levels
lead to decreased
neurotransmitter release.
Less GABA is released for
synaptic vesicles.
Meperidine activates
presynaptic kappa opioid
type receptors in the dorsal
root ganglion
The Gi subunit of the Kappa
opioid receptor activates
the inwardly rectifying
potassium channel increasing
K+ conductance. This causes
membrane hyperpolarization
decreasing the chances of
neuronal firing/action
potential.
Post-Synaptic Neuron
Pre-Synaptic Neuron
Synapse
Cytosol
Synaptic Vesicle
The kappa opioid receptor
through the gamma subunit
inhibits voltage gated
N-type calcium channels
stopping the influx of
calcium into the neuron.
Meperidine acts at A delta
and C pain fibres in the
dorsal horn of the spinal
chord. By decreasing
neurotransmitter action
there is less pain
transmittance into the
spinal chord. This leads to
less pain perception.
C Pain Fibres
Substance P as well as
acetylcholine and
noradrenaline have a direct
effect on nociceptor firing.
Therefore less of these
neurotransmitters leads to
less firing of the neuron
which leads to less pain
signalling.
The inhibition of adenylate
cyclase prevents the
production of cAMP which
further prevents
depolarization and pain
signalling
GABRG2
GABBR1
CACNA1B
ADCY2
KCNJ3
TACR1
OPRK1
GNB1
GNAI1
GNG2
γ-Aminobutyric
acid
Substance P
Meperidine
cAMP
Calcium
Calcium
Sodium
Sodium
γ-Aminobutyric
acid
Meperidine
Meperidine
Adenosine
triphosphate
Pyrophosphate
Guanosine
triphosphate
Pain
GABRG2
GABBR1
CACNA1B
ADCY2
KCNJ3
TACR1