Neurotransmission and the experience of low back pain; no association between CSF monoamine metabolites and pain

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

BACKGROUND AND STUDY PURPOSE

Pain and depression share similar neurobiological characteristics, and it is a common clinical observation that pain and depression may coincide in the same patient. They also appear to influence each other in the process of chronification. Furthermore, there is a complex coupling of pain and depression by monoaminergic transmitter system.

PATIENTS AND METHODS

On the basis of these findings, norepinephrine (NE), epinephrine (E), dopamine (DOP), 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), and vanillylmandelic acid (VMA) concentrations were determined in the cerebrospinal fluid (CSF) in patients with acute (20), chronic (27), and episodic pain syndrome (44) in a prospective study. The biochemical parameters were correlated to self-assessment pain and depression scores. The control group consisted of 13 pain-free patients with diseases affecting the muscular system.

RESULTS

Patients with chronic and episodic pain syndromes had significantly more depressive and psychovegetative symptoms compared to patients with acute pain. In patients with acute pain, DOP was significantly higher than in controls and chronic and episodic pain patients. In addition DOP was positively correlated to self-assessment pain score (p*<0.05). In patients with chronic and episodic pain, NE and 5-HIAA were positively correlated to the duration of disease and were significantly lower than in the control group. In neither of these two groups could significant correlations be established between these parameters and pain or depression self-assessment scores. In all groups, positive correlations were seen between the neurotransmitter and their metabolites.

CONCLUSION

The pathological decrease of NE and 5-HIAA in the CSF points to the crucial role of noradrenergic and serotonergic transmitter systems in the generation, modulation, and perpetuation of chronic and episodic pain syndromes. It indicates that antidepressants are effective drugs in these diseases. However, a discriminative neurochemical pattern between pain and depression could not be established. The demonstration of polyvalent correlations between different neurotransmitters is indicative of complex neurobiological coupling between cortical, limbic, and hypothalamic neuronal networks on the one hand and the nociceptive descending system on the other hand in the genesis of pain and depression.

Difficulties in establishing reference intervals for special fluids: the example of 5-hydroxyindoleacetic acid and homovanillic acid in cerebrospinal fluids

Biochemical measurements in “special fluids” are complicated with the problem of reference intervals. Reference intervals are difficult to establish for these types of samples since they are usually only collected in patients with clinical suspicion of disease. Determination of neurotransmitter metabolites in cerebrospinal fluid illustrates this difficulty. This paper will review the factors and circumstances that have been identified or are suspected to modifythe concentration of 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) in cerebrospinal fluid. In addition to obvious parameters such as age-related variation that can affect the concentration of 5-HIAA and HVA in cerebrospinal fluid, a varietyof other factors can explain the wide range of “control” group sizes reported in the literature. Reference intervals must take into account the purpose of cerebrospinal fluid examinations, whether they be prospective studies to explore physio-pathologic relationships or for diagnostic purposes. In the latter case, certain neurological disorders cannot be excluded if a single measured value is within the reference interval.

Postoperative pain treated by intravenous L-tryptophan: a double-blind study versus placebo in cholecystectomized patients

The effectiveness of intravenous administration (i.v.) of L-tryptophan, which is the precursor of cerebral serotonin, was verified in the treatment of postoperative pain. The study was carried out on 45 female patients, aged between 34 and 61 years, undergoing cholecystectomy who were randomly divided into three groups. Group 1 (age: 50.33 +/- 8.64 years) received 100 ml of 5% mannitol solution i.v.; group 2 (age: 49.80 +/- 11.11 years) 100 ml of a mannitol solution containing 7.5 mg/kg L-tryptophan; and group 3 (age: 53.46 +/- 9.60 years) 100 ml of a mannitol solution containing 15 mg/kg L-tryptophan. Vital capacity (preoperative VC) was measured before surgery. Anesthesia used was isoflurane. Narcotics or neuroleptics were not used. Pain was assessed before treatment (T-0 min), at the end of administration (T-30) and at T-60, 120, 180, 240, 300 and 360 min by the following variables: respiratory rate (RR), heart rate (HR), mean arterial pressure (MAP), Scott-Huskisson test (VAS), pain vital capacity (PVC), analgesic vital capacity (AVC), and respiratory restoration factor (RRF) calculated from Bromage's formula (RRF = (AVC - PVC/preoperative VC - PVC) X 100). As regards variables RR, HR, MAP and VAS, differences between the values from T-30 to T-360 and the value at T-0 were calculated. Means and S.E.M. were calculated on the obtained values and on RRF values for each group. The significance of the differences between groups was calculated using Student's t test and Bonferroni's test. Results show a significant decrease of pain in groups 2 and 3 treated with L-tryptophan, in comparison with group 1 (controls). No significant difference was observed between the treated groups, although more lasting pain relief was observed in group 3 in comparison with group 2. Intravenous L-tryptophan showed its effectiveness in the treatment of postoperative pain even when used alone. Its use may be considered for patients with renal failure, in order to strengthen pharmacological analgesia or to prevent postoperative pain by its intraoperative administration.

Neuropeptide converting enzyme activities in CSF of low back pain patients

The activity levels of a dynorphin converting enzyme (DCE), a substance P endopeptidase (SPE) and a substance P alpha-amidating enzyme (SP-GLYE) were measured in the cerebrospinal fluid (CSF) of 90 patients with chronic low back pain, sciatica and neurological signs of rhizopathy. The DCE activity was significantly higher in men than in women. Age was related to the DCE activity independent of sex, i.e., older patients had higher enzyme activity. The activities of two substance P converting enzymes were not related to sex or age. Self-reported pain experience and affective covariates (anxiety, depression, hostility, somatization) of pain, and myelography data were not found to be related to the enzyme activity levels once adjustment had been made for sex and age. The activity levels of the enzymes measured here had no predictive value for the long-term outcome of rehabilitation and therapy at the 5-year follow-up of the patients. The sex difference in DCE activity provides further evidence in favor of the role of gender in the psychoendocrine coping with pain distress.

Biological correlates of mental stress related to anticipated caesarean section

The relationships between self-reported assessments of acute anxiety and several biochemical and physiological indicators of stress reaction were investigated in pregnant women at term in connection with spinal analgesia for caesarean section. Fear and apprehension were statistically significantly associated only with blood pressure and with an increase in heart rate from the previous day. The subjective estimate of the quality of the preoperative night's sleep was negatively associated with biochemical plasma and cerebrospinal fluid (CSF) measures of sympatho-adrenal activity. The previously reported negative correlation between body height and 5-hydroxyindoleacetic acid (5-HIAA, an indicator of serotonin metabolism) in lumbar CSF was confirmed. The concentration of 5-HIAA in CSF was positively correlated with the levels of other acidic monoamine metabolites and cortisol in CSF. It is concluded that hormone and monoamine metabolite measurements in CSF and plasma have only limited usefulness as quantitative indicators of the intensity of preoperative fear and anxiety.

Complex temporal changes in 5-hydroxytryptamine synthesis in the central nervous system induced by experimental polyarthritis in the rat

The purpose of this study was to investigate modifications of 5-HT synthesis in a chronic pain model, the arthritic rat, at different times after the inoculation with Freund's adjuvant. This study confirms our previous findings that experimental induced polyarthritis is associated with a marked increase in free tryptophan levels in serum. During the acute phase of the disease (15-21 days after the adjuvant), the general increase in 5-HT synthesis observed in the CNS appeared to be related to an increase in tryptophan availability due to the elevation of free tryptophan in serum. During the post-acute phase of the disease (28-42 days after the adjuvant), the level of free tryptophan in the serum remained markedly increased but the levels in the CNS tended to return to normal values in all areas examined. At 42 days, 5-HT synthesis in the brain had also returned to normal values but was further increased at the spinal level. In addition, although 5-HT levels and 5-HT synthesis were increased in the dorsal as well as in the ventral part of the cord, an increase in the rate of disappearance of the amine after blockade of the decarboxylase (benserazide) was only observed in the dorsal part. This result tends to suggest that the descending serotonergic system projecting to the dorsal horn is preferentially activated during chronic pain.