Monoaminerge Transmitter in der Zerebrospinalflüssigkeit von Patienten mit akuten, chronischen und episodischen Schmerzen

Central nervous system monoaminergic activity in hip osteoarthritis patients with disabling pain: associations with pain severity and central sensitization

In patients with osteoarthritis undergoing total hip arthroplasty, higher cerebrospinal fluid concentrations of serotonin and dopamine metabolites are associated with increased pain severity and central sensitization.

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Relationship between blood- and cerebrospinal fluid-bound neurotransmitter concentrations and conditioned pain modulation in pain-free and chronic pain subjects

Descending pain inhibition is an endogenous pain control system thought to depend partially on the activation of bulbospinal monoaminergic pathways. Deficits in descending pain inhibition have been reported in numerous human chronic pain conditions, but there is currently no consensus regarding the neurochemical correlates responsible for this deficit. The aims of this study were to 1) assess the efficacy of descending pain inhibition in pain-free and chronic pain subjects, 2) screen for changes in centrally (ie, cerebrospinal fluid) and peripherally (ie, plasma) acting monoamine concentrations, and 3) explore the relationship between descending pain inhibition and monoamine neurotransmitter concentrations. Our results clearly show a deficit in pain inhibition, along with lower plasma norepinephrine and metanephrine concentrations in chronic pain subjects, compared to pain-free subjects. No differences were found in cerebrospinal fluid neurotransmitter concentrations. Finally, our results revealed a positive relationship between blood-bound norepinephrine and metanephrine concentrations and the efficacy of descending pain inhibition. Thus, basal monoamine levels in blood were related to descending pain inhibition. This finding supports the emerging idea that individual differences in descending pain inhibition may be linked to individual differences in peripheral processes, such as monoamines release in blood, which are possibly related to cardiovascular control.

PERSPECTIVES

This article presents psychophysical and neurochemical findings that indicate that the latent potential of descending pain inhibitory responses is associated with differential activity in peripheral processes governed by monoamine neurotransmitter release, bringing insights into the relationship between descending pain inhibition and cardiovascular control in humans.

The interface between inhibition of descending noradrenergic pain control pathways and negative affects in post-traumatic pain patients

BACKGROUND

Animal studies have shown that surgical trauma activates the descending noradrenergic pathway. However, perioperative patients have decreased concentrations of noradrenaline (NA) in the cerebrospinal fluid (CSF). We proposed that the descending monoaminergic pathway is altered in post-traumatic pain patients and that CSF monoamine neurotransmitters may be more closely related to affective symptoms. We investigated the levels of monoamine neurotransmitters and assessed pain in these patients.

METHODS

Patients were divided into a post-traumatic pain group, a pain-free group, a painful labor group, and a pain-free labor group. CSF was collected from all patients, and concentrations of NA, 3-methoxy-4-hydroxyphenylglycol (MHPG), dopamine, homovanillic acid, and 5-hydroxyindoleacetic acid (5-HIAA) were measured by high-performance liquid chromatography.

RESULTS

In the post-traumatic pain group, lumbar CSF concentrations of NA and MHPG were significantly decreased (P < 0.01) compared to the control group. The post-traumatic pain group displayed a significant negative correlation between NA and the respective total value of the short form of the McGill pain questionnaire (SF-MPQ), SF-MPQ (affective), and visual analog scale (r = -0.388, r = -0.433, and r = -0.367; P < 0.05).

CONCLUSIONS

Post-traumatic pain patients demonstrated decreased concentrations of NAin CSF, indicating that descending noradrenergic pain control pathways may be inhibited. NA is more closely related to negative affects in post-traumatic pain patients.

Medullary monoamines and NMDA-receptor regulation of cardiovascular responses during peripheral nociceptive stimuli

We have previously reported that AMPA-receptor blockade within the rostral ventrolateral medulla (RVLM) attenuates cardiovascular responses and extracellular concentrations of glutamate during mechanical, but not during thermal stimulation [Gray, T., Lewis III, E., Maher, T.J., Ally, A., 2001. AMPA-receptor blockade within the RVLM modulates cardiovascular responses via glutamate during peripheral stimuli. Pharmacol. Res. 43, 47-54]. In this study, we examined the role of NMDA-receptor blockade within the RVLM on cardiovascular responses and release of biogenic monoamines (serotonin [5HT], dopamine [DA], and norepinephrine [NE]) during both mechanical and thermal nociception using anesthetized Sprague-Dawley rats. Both mechanical and thermal stimulation have been shown to activate peripheral Adelta and C-fiber polymodal nociceptors. Noxious mechanical stimuli were induced by applying a pinch to alternate hindpaw for 5s while the noxious thermal stimuli involved immersion of the metatarsus of alternate hindpaw in a water bath at a temperature of 52 degrees C for 5 s. Mechanical stimulation increased mean arterial pressure (MAP), heart rate (HR), extracellular fluid 5HT, and DA concentrations (n=10). However, extracellular levels of NE were decreased within the RVLM. Furthermore, NMDA-receptor blockade with a competitive antagonist, AP-7 (200 nM), within the RVLM attenuated the cardiovascular responses and changes in 5HT and DA, but had no effect on NE levels. The thermal stimulation elicited similar increases in MAP and HR, however, extracellular levels of 5HT or DA did not change. Concentrations of NE were decreased during a thermal stimulation similar to the levels observed following mechanical stimuli. In contrast to mechanical stimuli, bilateral administration of AP-7 (200-1 mM) into the RVLM had no effect on cardiovascular responses, 5HT, DA or NE concentrations during a thermal stimulation. These results show that NMDA receptors within the RVLM most likely play a role in modulating cardiovascular responses by altering 5HT and DA concentrations within the RVLM during mechanical but not thermal nociception. Overall, the present study delineates the NMDA-receptor mediated central integrative mechanisms within the RVLM that coordinate processing of sensory impulses arising from peripheral noxious stimulation.