Background & Aims
CPM is one of the endogenous pain suppression mechanisms and is an analgesic mechanism mediated by the lower brainstem, including the medulla dorsal reticular and subnucleus reticularis dorsalis (SRD). The nucleus raphe magnus (RMg) play an important role in endogenous analgesia mechanisms thought to have not been involved 1). However, recent studies of CPM 2-4) have reported that the brain noradrenaline system and the brain serotonin system are involved in CPM.
On the other hand, brain microdialysis enabled to insert a probe directly into the target area in the brain and collect the perfusate containing neurotransmitters present in the synaptic cleft that flows into the probe 5-8). It is possible to quantitatively measure neurochemical substances in perfusate samples with great accuracy.
This study aims to investigate the mechanism of endogenous pain suppression by CPM and the noradrenaline nervous system and serotonin nervous system in the brain using microdialysis.
Methods
1. Animals
Male Wistar rats (275-360g, SLC, Japan) were used.
2. Study design of microdialysis
The coordinates of microdialysis probe were below
PAG; A/P-7.3, L/M +1.5, V/D –6.1 from the lambda and dura, 14° Angled
LC; A/P-3.3, L/M +1.3, V/D –8.3 from the lambda and scalp, 15° angled from vertical
2-1. Monoamine (5-HT, NA, DA) and Amino acid (GABA, Glu)
The neurochemical substances noradrenaline, dopamine, serotonin, GABA and Glutamate in perfusion samples were quantitatively measured simultaneously in two parts of the brain.
2-2 stimulation 9, 10)
First, we measured the changes in monoamines and amino acids using only a pinch stimulus of the tail, once the changes have settled down enough, both tail pinch stimulation (test stimulation) and mechanical stimulation (conditioning stimulation) using von Frey filaments were applied, and changes in monoamines and amino acids were measured.
Results
1. Monoamine (5-HT, NA, DA)
There were no significant differences in the amount of change in 5-HT, NA, and DA in LC and PAG, between when only tail pinch stimulation was given, and when both tail pinch stimulation (test stimulation) and mechanical stimulation (conditioning stimulation) using von Frey filaments.
2. Amino acid (GABA, Glu)
There were no significant differences in the amount of change in GABA, and gulutamate in LC and PAG, between when only tail pinch stimulation was given, and when both tail pinch stimulation (test stimulation) and mechanical stimulation (conditioning stimulation) using von Frey filaments.
Conclusions
We investigated whether the amount of neurotransmitters in the brain induced by tail pinch noxious stimulation (test stimulation) was modified by ectopic noxious stimulation using Von Frey filament (conditioning stimulation).
Changes in neurotransmitters (5-HT, DA, NA, GABA, Glu) in the LC and PAG during tail pinch stimulation (test stimulation) were not affected by the ectopic noxious stimulation using Von Frey filament (conditioning stimulation).
References
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