Pain in Parkinson’s disease (PD)

Continuous infusion of substance P into rat striatum alleviates nociceptive behavior via phosphorylation of extracellular signal-regulated kinase 1/2

Intraplantar injection of 0.4% formalin into the rat hind paw leads to a biphasic nociceptive response; an 'acute' phase (0-15 min) and 'tonic' phase (16-120 min), which is accompanied by significant phosphorylation of extracellular signal-regulated kinase (ERK)1/2 in the contralateral striatum at 120 min post-formalin injection. To uncover a possible relationship between the slow-onset substance P (SP) release and increased ERK1/2 phosphorylation in the striatum, continuous infusion of SP into the striatum by reverse microdialysis (0.4 μg/mL in microdialysis fiber, 1 μL/min) was performed to mimic volume neurotransmission of SP. Continuous infusion for 3 h of SP reduced the duration of 'tonic' phase nociception, and this SP effect was mediated by neurokinin 1 (NK1) receptors since pre-treatment with NK1 receptor antagonist CP96345 (10 μM) blocked the effect of SP infusion. However, formalin-induced 'tonic' phase nociception was significantly prolonged following acute injection of the MAP/ERK kinase 1/2 inhibitor PD0325901 (100 pmol) by microinjection. The coinfusion of SP and PD0325901 significantly increased the 'tonic' phase of nociception. These data demonstrate that volume transmission of striatal SP triggered by peripheral nociceptive stimulation does not lead to pain facilitation but a significant decrease of tonic nociception by the activation of the SP-NK1 receptor-ERK1/2 system. Noxious stimulation induces a slow-onset substance P (SP) release as a volume transmitter, activating extra-synaptic NK1 receptors, and evokes phosphorylation of extracellular signal-regulated kinase (ERK) 1/2. The SP-NK1-ERK1/2 system in the striatum decreases tonic nociception.

Parkinson's disease patients' subjective descriptions of characteristics of chronic pain, sleeping patterns and health-related quality of life

OBJECTIVE

Nonmotor symptoms are common in Parkinson's disease (PD). Health-related quality of life (HRQoL) is negatively affected by different factors, of which pain and sleep disturbances are important contributors. This study was performed to evaluate and describe subjective experiences of pain, sleeping patterns, and HRQoL in a cohort of PD patients with chronic pain.

METHODS

A total of 45 participants with established PD for more than 2 years, and PD-related pain for the preceding three months, were recruited from three sites in Sweden. Data regarding time point for onset, duration and degree of pain parameters, body localization of pain, external influences, and treatments were obtained. HRQoL was evaluated with the Short Form-36(®) Health Survey, and sleeping patterns were registered with the Parkinson's disease Sleep Scale, both completed along with a questionnaire.

RESULTS

In one-third of participants, pain preceded the PD diagnosis. Median pain score measured with a visual analog scale was 6.6 and 5.9 (for females and males, respectively) the week before the study. In almost half of the participants, pain was present during all their waking hours. Significantly more females described their pain as troublesome, while more males described their pain as irritating. Feelings of numbness and creeping sensations at night were strongly associated with the maximal visual analog scale scores. Polypharmacy was common; 89% used medication for anxiety/insomnia, and 18% used antidepressants. Only one-third of patients who reported pain relief with analgesics had these prescribed on their drug lists. Sleep was characterized by frequent awakenings. Urinary urgency and restless legs were frequently reported as troublesome. Patients rated HRQoL as significantly worse in all items compared with a healthy reference population matched for age and sex.

CONCLUSIONS

Experiences of chronic PD-related pain are complex; there is substantial sleep fragmentation and negative impact on HRQoL.