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Bone remodeling requires bone resorption by osteoclasts, bone formation by osteoblasts, and a poorly investigated reversal phase coupling resorption to formation. Likely players of the reversal phase are the cells recruited into the lacunae vacated by the osteoclasts and presumably preparing these lacunae for bone formation. These cells, called herein reversal cells, cover80% of the eroded surfaces, but their nature is not identified, and it is not known whether malfunction of these cells may contribute to bone loss in diseases such as postmenopausal osteoporosis. Herein, we combined histomorphometry and IHC on human iliac biopsy specimens, and showed that reversal cells are immunoreactive for factors typically expressed by osteoblasts, but not for monocytic markers. Furthermore, a subpopulation of reversal cells showed several distinctive characteristics suggestive of an arrested physiological status. Their prevalence correlated with decreased trabecular bone volume and osteoid and osteoblast surfaces in postmenopausal osteoporosis. They were, however, virtually absent in primary hyperparathyroidism, in which the transition between bone resorption and formation occurs optimally. Collectively, our observations suggest that arrested reversal cells reflect aborted remodeling cycles that did not progress to the bone formation step. We, therefore, propose that bone loss in postmenopausal osteoporosis does not only result from a failure of the bone formation step, as commonly believed, but also from a failure at the reversal step.

According to international standards, Denmark's production of scientific papers is high, but is slowly losing ground. The reformed research education was intended to strengthen Denmark's position, but some fear that it will have the opposite effect.Based on the Registry of Ph.D. students and data from the Central Office of Civil Registration, we conducted a survey among 1170 persons previously enrolled in a Ph.D. program. Data on published papers were stratified according to gender, age, master degree, institution, year and length of enrolment. The response rate was 46%.A total of 6-7 papers, including 3 first authorships, were published during the Ph.D. study and the first three years thereafter. Only about 10% did not publish in these periods. Over a 10-year time span, the number of publications before, during and three years after the Ph.D. degree was stable. Women and men published the same number of papers based on the Ph.D. project; however the total number of research publications was higher for men.As measured by the number of publications, the Danish Ph.D. education is solid and independent of gender, age, and time. However, in order to strengthen the overall Danish biomedical research production additional public funding and time allocated to clinical research is necessary.

Scientific production by Ph.D. students is a matter of ongoing debate. The key issues for the number of publications during and after the Ph.D. study are not sufficiently described.Based on the Registry of Ph.D. students and data from the Central Office of Civil Registration, we conducted a survey among 1170 persons previously enrolled in a Ph.D. programme in medicine or pharmaceutical sciences. Data on activities such as supervision and teaching, social issues and economy in the research team were stratified according to sex, age, master degree, institution, year and length of enrolment. The data were modelled in multiple linear regression using the number of peer-reviewed publications as the outcome. The response rate was 60%.The number of publications based on the Ph.D. project was only marginally influenced by the investigated variables. A high total number of publications was associated with men, with having been a Ph.D. supervisor, with research groups described as having a good atmosphere and sufficient financial funding.The medical and pharmaceutical Ph.D. programmes display an inherent strength concerning the process. Although our study supplies confirmatory data, it also shows that the team spirit is important to scientific productivity.