Thyroid Hormone Economy in the Perinatal Mouse Brain: Implications for Cerebral Cortex Development.

Thyroid hormones (THs, T4 and the transcriptionally active hormone T3) play an essential role in neurodevelopment; however, the mechanisms underlying T3 brain delivery during mice fetal development are not well known. This work has explored the sources of brain T3 during mice fetal development using biochemical, anatomical, and molecular approaches. The findings revealed that during late gestation, a large amount of fetal brain T4 is of maternal origin. Also, in the developing mouse brain, fetal T3 content is regulated through the conversion of T4 into T3 by type-2 deiodinase (D2) activity, which is present from earlier prenatal stages. Additionally, D2 activity was found to be essential to mediate expression of T3-dependent genes in the cerebral cortex, and also necessary to generate the transient cerebral cortex hyperthyroidism present in mice lacking the TH transporter Monocarboxylate transporter 8. Notably, the gene encoding for D2 (Dio2) was mainly expressed at the blood-cerebrospinal fluid barrier (BCSFB). Overall, these data signify that T4 deiodinated by D2 may be the only source of T3 during neocortical development. We therefore propose that D2 activity at the BCSFB converts the T4 transported across the choroid plexus into T3, thus supplying the brain with active hormone to maintain TH homeostasis.

Combined in vitro and in silico approaches to the assessment of stimulant properties of novel psychoactive substances - The case of the benzofuran 5-MAPB.

Novel psychoactive substances (NPS) are increasingly prevalent world-wide although their pharmacological characteristics are largely unknown; those with stimulant properties, due to interactions with the dopamine transporter (DAT), have addictive potential which their users may not realise. We evaluated the binding of 1-(1-benzofuran-5-yl)-N-methylpropan-2-amine (5-MAPB) to rat striatal DAT by means of quantitative autoradiography with [125I]RTI-121, and the effects of 5-MAPB on electrically-evoked dopamine efflux by fast-cyclic voltammetry in rat brain slices. 5-MAPB displaced [125I]RTI-121 in a concentration-dependent manner, with significant effects at 10 and 30µM. The voltammetry data suggest that 5-MAPB reduces the rate of dopamine reuptake; while the peak dopamine efflux was not increased, the area under the curve was augmented. 5-MAPB can also cause reverse dopamine transport consistent with stimulant properties, more similar to amphetamine than cocaine. Molecular modelling and docking studies compared the binding site of DAT in complex with 5-MAPB to dopamine, amphetamine, 5-APB, MDMA, cocaine and RTI-121. This structural comparison reveals a binding mode for 5-MAPB found in the primary binding (S1) site, central to transmembrane domains 1, 3, 6 and 8, which overlaps with the binding modes of dopamine, cocaine and its analogues. Atomistic molecular dynamics simulations further show that, when in complex with 5-MAPB, DAT can exhibit conformational transitions that spontaneously isomerize the transporter into inward-facing state, similarly to that observed in dopamine-bound DAT. These novel insights, offered by the combination of computational methods of biophysics with neurobiological procedures, provide structural context for NPS at DAT and relate them with their functional properties at DAT as the molecular target of stimulants.

Α4ß2 and α7 nicotinic acetylcholine receptor binding predicts choice preference in two cost benefit decision-making tasks.

Nicotinic receptors have been linked to a wide range of cognitive and behavioral functions, but surprisingly little is known about their involvement in cost benefit decision making. The goal of these experiments was to determine how nicotinic acetylcholine receptor (nAChR) expression is related to two forms of cost benefit decision making. Male Long Evans rats were tested in probability- and delay-discounting tasks, which required discrete trial choices between a small reward and a large reward associated with varying probabilities of omission and varying delays to reward delivery, respectively. Following testing, radioligand binding to α4ß2 and α7 nAChR subtypes in brain regions implicated in cost benefit decision making was examined. Significant linear relationships were observed between choice of the large delayed reward in the delay discounting task and α4ß2 receptor binding in both the dorsal and ventral hippocampus. Additionally, trends were found suggesting that choice of the large costly reward in both discounting tasks was inversely related to α4ß2 receptor binding in the medial prefrontal cortex and nucleus accumbens shell. Similar trends suggested that choice of the large delayed reward in the delay discounting task was inversely related to α4ß2 receptor binding in the orbitofrontal cortex, nucleus accumbens core, and basolateral amygdala, as well as to α7 receptor binding in the basolateral amygdala. These data suggest that nAChRs (particularly α4ß2) play both unique and common roles in decisions that require consideration of different types of reward costs.

Monte Carlo simulation of electron dose from (131)I-targeted tumor cells within a heterogeneous tumor.

BACKGROUND AND AIM: In internal radiotherapy, the variable distribution of target receptors within the tumoral tissue, and the variable ranges of electrons may be responsible for a heterogeneous dose distribution at the cellular level. The aim of the present study was to use Monte Carlo simulations to assess (131)I electron dose in a model of heterogeneous tumor containing multiple clusters of cancer cells, targeted by (131)I-labeled molecules. METHODS: The model consisted of 150-µm-diameter spherical tumor cell clusters, in which (131)I was homogeneously distributed. Clusters were placed 24 µm apart, separated by septa of nonradioactive connective tissue. The electron dose distribution to tumor cells in a single cluster was first assessed. Then was assessed the dose increase to these targets after adding multiple layers of neighboring clusters (total number of clusters = 15,624). RESULTS: Dose distribution within a single isolated cluster follows a decreasing gradient, the dose for the outermost cell layer being about half that at the center. When radioactive neighbors were added, the dose to the central cluster increased. The most important contribution was given by the nearest neighbors, whereas the contribution from neighbors beyond a distance of 1 mm was only for 5% of the final dose. If the central cluster was unlabeled, the absorbed dose to the outermost cell layer of this cluster was reduced by 27%, and that at the center by 45%. CONCLUSIONS: The electron cross-dose of (131)I falls rapidly as a function of distance and becomes negligible after just 1 mm. Small clusters of tumor cells that are not radiolabeled may receive a very small dose. Therefore, in internal radiotherapy it is important to aim at targeting tumor cells as homogeneously as possible, rather than relying on the cross-dose to achieve a therapeutic effect.

Nicotinic cholinergic receptors in the rat cerebellum: multiple heteromeric subtypes.

Nicotinic receptors (nAChRs) in the cerebellum have been implicated in the pathology of autism spectrum disorders (Lee et al., 2002; Martin-Ruiz et al., 2004). The subtypes of nAChRs in the cerebellum are not known in any detail, except that, in addition to the homomeric alpha7 subtype, there appears to be one or more heteromeric subtypes consisting of combinations of alpha and beta subunits. To begin to better understand the potential roles of these heteromeric nAChRs in cerebellar circuitry and their potential as targets for nicotinic drugs, we investigated their subunit composition. Using subunit-selective antibodies in sequential immunoprecipitation assays, we detected six structurally distinct heteromeric nAChR populations in the rat cerebellum. Among these were several subtypes that have not been encountered previously, including alpha3alpha4beta2 and alpha3alpha4beta4 nAChRs. This diversity suggests that nAChRs play multiple roles in cerebellar physiology.

Experimental and theoretical determination of dosimetric characteristics of IsoAid ADVANTAGE 125I brachytherapy source.

125I brachytherapy sources are being used for interstitial implants in tumor sites such as the prostate. Recently, the ADVANTAGE 125I, Model IAI-125, source became commercially available for interstitial brachytherapy treatment. Dosimetric characteristics (dose rate constant, radial dose function, and anisotropy function) of this source were experimentally and theoretically determined, following the AAPM Task Group 43 recommendations. Derivation of the dose rate constant was based on recent NIST WAFAC calibration performed in accordance with their 1999 standard. Measurements were performed in Solid Water phantom using LiF thermoluminescent dosimeters. The theoretical calculations were performed in both Solid Water and water using the PTRAN Monte Carlo code. The results indicated that a dose rate constant of the new source in water was 0.98 +/- 0.03 cGy h(-1) U(-1). The radial dose function of the new source was measured in Solid Water and calculated both in water and Solid Water at distances up to 10.0 cm. The anisotropy function, F(r, theta), of the new source was measured and calculated in Solid Water at distances of 2 cm, 3 cm, 5 cm, and 7 cm and also was calculated in water at distances ranging from 1 cm to 7 cm from the source. From the anisotropy function, the anisotropy factors and anisotropy constant were derived. The anisotropy constant of the ADVANTAGE 125I source in water was found to be 0.97 +/- 0.03. The dosimetric characteristics of this new source compared favorably with those from the Amersham Health Model 6711 source. Complete dosimetric parameters of the new source are presented in this paper.

Alterations in thyroid hormone economy during acute infection with Diplococcus pneumoniae in the rhesus monkey.

In order to study the alterations in thyroid hormone economy that accompany an acute bacterial infection, rhesus monkeys were inoculated i.v. with a virulent Diplococcus pneumoniae culture containing approximately 10(8) organisms per dose. This was found to produce a well-defined febrile illness followed in most instances by spontaneous recovery, thereby permitting sequential observations to be made during progression from the healthy state through acute infection into convalescence. During the acute febrile period of the infection, the clearance of both exogenously labeled L-thyroxine (T(4)) and 3,3',5-triiodo-L-thyronine (T(3)) from their peripheral pools was accelerated. This alteration was often evident by 8 hr after inoculation with the virulent culture and could not be ascribed to a decrease in extracellular binding. Despite the accelerated hormonal clearance, the concentrations of both endogenously labeled thyroid hormone and stable T(4) in the sera of the surviving monkeys remained essentially unchanged or increased, indicating that hormonal secretion must have increased during this period. During the convalescent period, hormonal clearance was similar to preinfection control values. Leukocytes isolated from blood obtained 6 hr after inoculation with the virulent culture displayed enhanced T(4)-deiodinative activity.