Dynamics in cortical activity revealed by resting-state MEG rhythms

The brain is a biophysical system subject to information flows that may be thought of as a many-body architecture with a spatiotemporal dynamics described by its neuronal structures. The oscillatory nature of brain activity allows these structures (nodes) to be described as a set of coupled oscillators forming a network where the node dynamics and that of the network topology can be studied. Quantifying its dynamics at various scales is an issue that claims to be explored for several brain activities, e.g., activity at rest. The resting-state (RS) associates the underlying brain dynamics of healthy subjects that are not actively compromised with sensory or cognitive processes. Studying its dynamics is highly non-trivial but opens the door to understand the general principles of brain functioning, as well as to contrast a passive null condition vs the dynamics of pathologies or non-resting activities. Here, we hypothesize about how the spatiotemporal dynamics of cortical fluctuations could be for healthy subjects at RS. To do that, we retrieve the alphabet that reconstructs the dynamics (entropy-complexity) of magnetoencephalography (MEG) signals. We assemble the cortical connectivity to elicit the dynamics in the network topology. We depict an order relation between entropy and complexity for frequency bands that is ubiquitous for different temporal scales. We unveiled that the posterior cortex conglomerates nodes with both stronger dynamics and high clustering for α band. The existence of an order relation between dynamic properties suggests an emergent phenomenon characteristic of each band. Interestingly, we find the posterior cortex as a domain of dual character that plays a cardinal role in both the dynamics and structure regarding the activity at rest. To the best of our knowledge, this is the first study with MEG involving information theory and network science to better understand the dynamics and structure of brain activity at rest for different bands and scales.

A new paradigm in low-risk papillary microcarcinoma: active surveillance

Classical papillary thyroid microcarcinoma (PTMC) is a variant of papillary thyroid carcinoma (PTC) known to have excellent prognosis. It has a mortality of 0.3%, even in the presence of distance metastasis. The latest American Thyroid Association guidelines state that although lobectomy is acceptable, active surveillance can be considered in the appropriate setting. We present the case of a 37-year-old female with a history of PTMC who underwent surgical management consisting of a total thyroidectomy. Although she has remained disease-free, her quality of life has been greatly affected by the sequelae of this procedure. This case serves as an excellent example of how first-line surgical treatment may result more harmful than the disease itself.

Subacute thyroiditis and dyserythropoesis after influenza vaccination suggesting immune dysregulation

Subacute thyroiditis (SAT) is an extremely rare complication of influenza vaccination. Several infectious agents have been related with SAT. It is also well known the association between HLA-B35 and the development of SAT. We describe a case of subacute thyroiditis and dyserythropoesis occurring shortly after administration of an influenza vaccine in a 55-year-old man with history of diabetes and psoriasis, family history of autoimmunity without clinical evidence of acute viral infection prior to the onset of symptoms. We propose that, the events occurring in the patient may be explained as result of complex interactions between the individual genetic background and environmental exposure to infectious agents that generated a pro-inflammatory status, where the vaccine was the trigger for the subsequent alterations in thyroid and bone marrow. These findings highlight the importance of immunogenetic factors involved in response to vaccination that is the central theme in the growing field of 'vaccinomics'.

An evaluation of the antiinflammatory effects of intraarticular synthetic beta-endorphin in the canine model

We sought to evaluate the antiinflammatory effects of synthetic human beta-endorphin (SHB) when injected into the canine knee joint. Sixteen healthy dogs, aged 1-2 yr, were selected. SHB was injected pre- and postinjury into each knee. The sample size was n = 32 after a randomized factorial arrangement; 2 x 4 with four cases per treatment being performed. Factors considered were: Factor A with two levels: A1 = Preinjury and A2 = Postinjury; Factor B (SHB dose) with four levels: B1 = Control, B2 = 250 micrograms, B3 = 500 micrograms, B4 = 1000 micrograms. The control group received 0.9% NaCl solution. Anesthesia was induced with intravenous thiopental, 14 mg/kg, and acepromazine, 0.5 mg/kg. Injury was produced with an intraarticular injection of 4 mL HCl 0.5 M, which was left in situ for 20 min. Inflammation was measured using the 610 nm absorbency of Evans blue extravasate in biopsy specimens. Histopathologic studies were performed on each knee. We found that beta-endorphin has a clear, dose-related, antiinflammatory effect, reducing the tissue extravasation of Evans blue and its absorbency, especially with large doses. This finding was consistent with the histopathologic observations. We conclude that SHB has an antiinflammatory effect. It is still not clear which mechanisms inhibit polymorphonuclear cell adhesion to vascular endothelium or cell and plasmatic protein extravasation.

Action of endogenous proteases on the distribution of tyrosinase isozymes in Harding-Passey mouse melanoma

A high percentage of the total tyrosinase found in Harding-Passey mouse melanoma occurs as a soluble form. This paper shows that melanosomal tyrosinase can be solubilized by several endogenous proteases to yield active tyrosinase. This enzyme, once proteolytically solubilized, can be further degraded, leading to enzyme inactivation. The nature and specificity of the main proteases involved in the solubilization process change depending on the size and necrosis stage of the tumour. Cathepsin B could be the main protease responsible for the solubilization in small tumours (less than 0.5 g). Large tumours are rich in necrotic cells, and cathepsin D and serine-proteases are the main hydrolytic enzymes involved in the proteolytic action on melanosomes. These results support the view that the high activity of tyrosinase found in the soluble fraction of malignant melanoma is mainly an artefact resulting from degradation of melanosomes by a variety of endogenous proteases, rather than the result of the actual occurrence of high levels of an independent cytosolic isozyme.

The role of sulfhydryl compounds in mammalian melanogenesis: the effect of cysteine and glutathione upon tyrosinase and the intermediates of the pathway

The effect of cysteine and glutathione on mammalian melanogenesis has been studied. It has been shown that their action is mediated by two different mechanisms. (a) The reaction of the thiol groups with dopaquinone after the tyrosinase-catalyzed oxidation of tyrosine and dopa. This mechanism leads to the formation of sulfhydryl-dopa conjugates and finally sulfur-containing pigments, phaeomelanins instead of eumelanins. This fact might produce an inhibition of melanogenesis due to the slower rate of chemical reactions involved in the polymerization of such thiol-conjugates when compared to that of indoles. (b) The direct interaction between the sulfhydryl compounds and the tyrosinase active site. This interaction may regulate the activity of the enzyme. It is shown that Harding-Passey mouse melanoma tyrosinase is more sensitive to sulfhydryl compounds than mushroom tyrosinase. Cysteine always produces an inhibition of the tyrosinase hydroxylase and dopa oxidase activities of melanoma tyrosinase, this inhibition becoming greater as the cysteine concentration increases. On the other hand, glutathione produces an activation of the tyrosine hydroxylase activity below 3 mM and an inhibition at higher concentrations. The limit between the enzymatic activation and inhibition appears at glutathione concentrations similar to the physiological levels of this compound found in melanocytes. Although the switch from eumelanogenesis to phaeomelanogenesis occurs at much lower concentrations of glutathione, taking into account these data it is discussed that this sulfhydryl compound may regulate not only the type but also the amount of melanin formed inside melanocytes.

Half-lives of tyrosinase isozymes from Harding-Passey mouse melanoma

The half-lives of tyrosinase isozymes, a key enzyme in melanogenesis, have been determined using two different approaches: (a) cycloheximide treatment of mice bearing growing tumors and measurement of the residual enzymatic activity. This approach detected two soluble forms of cytosolic tyrosinase with half-lives of 1/2 and 8 h, respectively. The melanosomal isozyme showed a t1/2 of 3 1/2 h. (b) Metabolic labelling of tyrosinase with [35S]Met and immunoprecipitation analysis using a monoclonal antityrosinase. This method gave values slightly longer, 5 h and 9 1/2 h for the melanosomal and cytosolic tyrosinase, respectively. The origin of soluble tyrosinase and its utility to employ that enzymatic activity in melanoma chemotherapy using catechols as tyrosinase-dependent precursors of cytotoxic quinones is discussed.

The effect of polyamines on tyrosinase activity

The effect of several polyamines on the activity of tyrosinase from different sources has been studied. Diaminoethane, 1,3-diaminopropane and putrescine activated tyrosinase from Harding-Passey mouse melanoma but did not activate frog epidermis or mushroom tyrosinases. 1,3-diaminopropane was the strongest activator (Ka = 0.23 mM). The activation was saturable and dependent on the ionic strength. Cadaverine, 1,6-diaminohexane and spermidine had no effect on any tyrosinase. However, spermine inhibited melanoma tyrosinase more than the mushroom and frog epidermis enzymes. These results show that the effect of polyamines on mammalian tyrosinase is due to direct enzyme-oligoamine interactions rather than to a nonspecific action on L-dopa oxidation products, and suggest that physiological polyamines might play a modulatory role on mammalian melanogenesis.

Comparative study of tyrosinases from different sources: relationship between halide inhibition and the enzyme active site

The inhibition of tyrosinases from frog epidermis (Rana esculenta ridibunda), mushroom (Agaricus bisporus) and Harding-Passey mouse melanoma by halides is compared. In all cases, the inhibition is pH dependent, increasing when the pH decreases. The order of inhibition is I- greater than Br- greater than Cl- much greater than F- for frog epidermis tyrosinase, F- greater than I- greater than Cl- greater than Br- for mushroom tyrosinase and F- greater than Cl- much greater than Br- greater than I- for the mouse melanoma enzyme. These results are discussed in terms of the active site accessibility to exogenous ligands. The activation energies of the enzyme-catalysed L-dopa oxidation were also calculated, being the values 6.86, 17.01 and 20.25 kcal/mol for frog epidermis, mushroom and Harding-Passey mouse melanoma, respectively. A relationship between these values and the evolutionary adaptation of these enzymes is proposed.

Regulation of the cytosolic and melanosome-bound tyrosinase activities in Harding-Passey mouse melanoma

Mouse melanoma tyrosinases exist in the cytoplasm of melanocytes and also in a particulate form, bound to melanosomes. The cytosolic isoenzyme activity is not expressed in the melanocytes in vivo. One of the mechanisms for the activity regulation is the existence of a soluble inhibitor. This inhibition is non-competitive with regard to L-dopa. Particulate tyrosinase can be solubilized from the melanosome by several agents, Brij 35 and Triton X-100 being the most effective ones. Melanin accumulation in the organelle produces a competitive inhibition of the activity.