Quantitative analysis of the mitochondrial and plastid proteomes of the moss Physcomitrella patens reveals protein macrocompartmentation and microcompartmentation.

Extant eukaryotes are highly compartmentalized and have integrated endosymbionts as organelles, namely mitochondria and plastids in plants. During evolution, organellar proteomes are modified by gene gain and loss, by gene subfunctionalization and neofunctionalization, and by changes in protein targeting. To date, proteomics data for plastids and mitochondria are available for only a few plant model species, and evolutionary analyses of high-throughput data are scarce. We combined quantitative proteomics, cross-species comparative analysis of metabolic pathways, and localizations by fluorescent proteins in the model plant Physcomitrella patens in order to assess evolutionary changes in mitochondrial and plastid proteomes. This study implements data-mining methodology to classify and reliably reconstruct subcellular proteomes, to map metabolic pathways, and to study the effects of postendosymbiotic evolution on organellar pathway partitioning. Our results indicate that, although plant morphologies changed substantially during plant evolution, metabolic integration of organelles is largely conserved, with exceptions in amino acid and carbon metabolism. Retargeting or regulatory subfunctionalization are common in the studied nucleus-encoded gene families of organelle-targeted proteins. Moreover, complementing the proteomic analysis, fluorescent protein fusions revealed novel proteins at organelle interfaces such as plastid stromules (stroma-filled tubules) and highlight microcompartments as well as intercellular and intracellular heterogeneity of mitochondria and plastids. Thus, we establish a comprehensive data set for mitochondrial and plastid proteomes in moss, present a novel multilevel approach to organelle biology in plants, and place our findings into an evolutionary context.

Does 'mental kinesiophobia' exist?

In this study the relevance of the concept of mental kinesiophobia (respectively cogniphobia or fear of mental exertion) for clients with chronic stress problems was explored. It was hypothesized that cognitive, chronic stress complaints, such as concentration problems or decreased problem solving abilities, could be catastrophized as signs of heightened personal vulnerability, with a chance of becoming permanent. As a consequence, mental exertion is avoided. This line of reasoning comes from the existing concept of kinesiophobia. This concept describes the avoidance behavior in chronic benign pain patients and refers to their fear of inflicting irreversible bodily damage due to physical exertion.An illustrative case of cogniphobia is presented. In an explorative pilot-study it was demonstrated that chronically stressed clients scored significantly higher on an experimental questionnaire measuring avoidance tendencies for mental exertion, compared with actively working employees. Consequences for treatment and suggestions for further study are discussed.

The relationship between spouse solicitousness and pain behavior: searching for more experimental evidence.

In this study 42 chronic back pain patients participated twice in a treadmill test. During 1 of these 2 sessions, the partner was present. Walking time, pain intensity ratings, and heart rate were measured before and after the tests. From the results of previous studies it was expected that, in the presence of a relatively solicitous spouse, patients would report more pain, would have a shorter walking time, and would exert themselves less physically. Spouse solicitousness was measured in 2 ways: from the patient's perspective as well as from that of the spouse. Results based on the patient's interpretation of his/her partner's responses are not in accordance with previous findings. Results based on the spouse's view demonstrate, however, that patients with solicitous spouses do, in fact, report more pain and walk for a shorter duration in the presence of the spouse than patients with relatively non-solicitous spouses. Theoretical and practical implications are discussed.

Chronic back pain, acute postoperative pain and the activation of diffuse noxious inhibitory controls (DNIC).

The effect of the presence of either chronic or acute clinical pain on pain threshold and on the nociceptive flexion reflex (RIII) threshold was studied. The experimental pain sensation and the flexion reflex were evoked by trains of short electrical pulses. It was hypothesized that both kinds of clinical pain would be able to induce 'diffuse noxious inhibitory controls' (DNIC) and thereby raise the 2 experimental thresholds. Patients with chronic low back pain, patients with postoperative pain from oral surgery, and pain-free subjects were tested in 3 conditions: during baseline, after i.v. administration of a placebo, and after i.v. administration of naloxone. In comparison with 2 pain-free control groups, the 2 pain groups had a significantly higher pain threshold in all conditions. However, the RIII threshold was not significantly elevated in chronic or acute pain patients compared to controls. Naloxone had no effect on the RIII or pain threshold in any of the groups. It is concluded that the increased pain threshold which is frequently found in chronic pain patients, and which could be confirmed in the present study, does not result from a DNIC effect. The adaptation level theory offers an alternative explanation. Also, the acute postoperative pain in this study did not seem to induce DNIC. Because other forms of acute pain have been found to be effective in activating DNIC, future research should establish which pains are and which pains are not effective.

A comparison of two-point discrimination threshold of tactual, non-painful stimuli between chronic low back pain patients and controls.

Differences in pain sensitivity between chronic pain patients and healthy controls have been reported. Seltzer and Seltzer extended this line of research in studying the sensitivity to non-painful stimuli. They reported that the 2-point discrimination threshold of chronic pain patients was higher than that of control subjects. However, the study of Seltzer and Seltzer suffered from several methodological shortcomings. Therefore, in the present study we tried to replicate the findings in a group of chronic low back pain patients using a design that was believed to be methodologically stronger. Replication failed: no evidence was found for the hypothesis that chronic pain patients are less sensitive to non-painful stimuli. Further studies on various defined types of acute and chronic pain patients are required.

Chronic low back pain and the reaction to repeated acute pain stimulation.

Previous research has shown an interaction between chronic and acute pain behavior. Chronic low back pain (CLBP) patients seem to have a higher pain perception threshold and a lower pain tolerance than pain-free controls. The major focus is, however, on another aspect of pain behavior: habituation of the pain response after repeated stimulation. Habituation of the pain perception threshold was found for control subjects but not for CLBP patients. Inability to habituate to pain may be regarded as a risk factor in the development of CLBP.

Learning processes in the persistence behavior of chronic low back pain patients with repeated acute pain stimulation.

Twenty-one chronic low back pain (CLBP) patients and 20 control subjects participated in 8 successive cold pressor tests (CPT). The hypotheses were that: (1) CLBP patients would demonstrate poorer acute pain tolerance and report higher acute pain, and (2) CLBP patients would become sensitized during 8 successive CPT trials, while control subjects would habituate, resulting in increasing differences in test behavior between both groups. The results show that the first hypothesis was confirmed. The second hypothesis requires modification, as the control group both habituated and became sensitized, while within the CLBP group no learning or training effect was found. These findings lead one to conclude that the deviant acute pain behavior of CLBP patient may be regarded either as a consequence of CLBP or as an important risk factor in the development of CLBP. Patients with relatively high CLBP levels performed poorly on the CPT as compared with patients with relatively low CLBP levels.

The behavioral management of pain: a criticism of a response.

In response to an earlier published paper by Fordyce, some assumptions underlying the behavior management paradigm of chronic pain are critically discussed. While operant treatment has proved successful, the conclusion that operant factors play an important role in the development and maintenance of chronic benign pain is debated. Some empirical studies, regularly used to demonstrate this role, are re-evaluated. An alternative theory is proposed for chronic pain behavior, in which the role of a lower tolerance to proprioceptive stimuli, which may include more than just pain stimuli, is emphasized.