Methanogenic Activity in Human Periodontal Pocket

Samples of subgingival dental tissues were examined for the presence of methanogenic activities. Using enrichment cultures, methanogenic activities were detected in 9 of 17 individuals. A mesophilic, Gram-positive, irregular coccoid methanogen, which showed close resemblance to a Methanosarcina sp., was isolated from one sample collected from a patient with type IV periodontal pocket (the periodontal pocket is a space bounded by the tooth on one side and by ulcerated epithelium lining the soft tissue wall on the other). The isolate used methanol, methylamine, acetate, and H₂-CO₂ as the sole source of carbon. However, the isolate was unable to use formate and trimethylamine as growth substrates. The organism had an optimum pH of 6.5 and an optimum temperature of 37°C. The isolate not only used ammonia, but also used nitrate as a nitrogen source. The niche of this methanogen in periodontal pockets may be to carry out terminal oxidation of simple organic compounds such as methanol and acetate produced by other obligate anaerobes present in periodontal pockets. This methanogen may also play a vital role in interspecies hydrogen transfer, as demonstrated by its use of H₂-CO₂ as a substrate. The isolate produced significant amount of methane in vitro. Received: 27 February 2002 / Accepted: 29 March 2002     

Your Resting Brain CAREs about Your Risky Behavior

Background

Research on the neural correlates of risk-related behaviors and personality traits has provided insight into mechanisms underlying both normal and pathological decision-making. Task-based neuroimaging studies implicate a distributed network of brain regions in risky decision-making. What remains to be understood are the interactions between these regions and their relation to individual differences in personality variables associated with real-world risk-taking.

Methodology/Principal Findings

We employed resting state functional magnetic resonance imaging (R-fMRI) and resting state functional connectivity (RSFC) methods to investigate differences in the brain''s intrinsic functional architecture associated with beliefs about the consequences of risky behavior. We obtained an individual measure of expected benefit from engaging in risky behavior, indicating a risk seeking or risk-averse personality, for each of 21 participants from whom we also collected a series of R-fMRI scans. The expected benefit scores were entered in statistical models assessing the RSFC of brain regions consistently implicated in both the evaluation of risk and reward, and cognitive control (i.e., orbitofrontal cortex, nucleus accumbens, lateral prefrontal cortex, dorsal anterior cingulate). We specifically focused on significant brain-behavior relationships that were stable across R-fMRI scans collected one year apart. Two stable expected benefit-RSFC relationships were observed: decreased expected benefit (increased risk-aversion) was associated with 1) stronger positive functional connectivity between right inferior frontal gyrus (IFG) and right insula, and 2) weaker negative functional connectivity between left nucleus accumbens and right parieto-occipital cortex.

Conclusions/Significance

Task-based activation in the IFG and insula has been associated with risk-aversion, while activation in the nucleus accumbens and parietal cortex has been associated with both risk seeking and risk-averse tendencies. Our results suggest that individual differences in attitudes toward risk-taking are reflected in the brain''s functional architecture and may have implications for engaging in real-world risky behaviors.     

Pocket protein function in melanocyte homeostasis and neoplasia

Melanoma is the most lethal of human skin cancers and its incidence is increasing worldwide [L.K. Dennis (1999). Arch. Dermatol. 135, 275; C. Garbe et al. (2000). Cancer 89, 1269]. Melanomas often metastasize early during the course of the disease and are then highly intractable to current therapeutic regimens [M.F. Demierre and G. Merlino (2004). Curr. Oncol. Rep. 6, 406]. Consequently, understanding the factors that maintain melanocyte homeostasis and prevent their neoplastic transformation into melanoma is of utmost interest from the perspective of therapeutic interdiction. This review will focus on the role of the pocket proteins (PPs), Rb1 (retinoblastoma protein), retinoblastoma-like 1 (Rbl1 also known as p107) and retinoblastoma-like 2 (Rbl2 also known as p130), in melanocyte homeostasis, with particular emphasis on their functions in the cell cycle and the DNA damage repair response. The potential mechanisms of PP deregulation in melanoma and the possibility of PP-independent pathways to melanoma development will also be considered. Finally, the role of the PP family in ultraviolet radiation (UVR)-induced melanoma and the precise contribution that each PP family member makes to melanocyte homeostasis will be discussed in the context of a number of genetically engineered mouse models.