Trapezoidal mechanical movement of whiskers was used to study the responses of 44 single thalamic ventral posteromedial (VPM) neurons to dynamic and static stimulus components in ...urethane-anesthetized rats. The effects of local administration of the GABAA receptor antagonist, bicuculline, and the GABAB receptor antagonist, 2-hydroxysaclofen, were tested to determine whether and to what extent the responses altered when GABA-mediated inhibitory synaptic transmission was blocked. Two classes of phasically responding neurons were identified, ON/OFF and movement-sensitive types. Bicuculline enhanced the magnitudes of the responses from both types by 2.5-fold and ON/OFF responses were converted to movement-sensitive ones in 17 (43%) of the 40 ON/OFF neurons. 2-hydroxysaclofen either had no effect or appeared to act like a GABA agonist. In 21 (48%) neurons, a significantly reduced responsiveness was observed during a 100-ms period following the ON and OFF responses. This discharge suppression was especially prominent during the plateau phase of the stimulus, and in some cases extended for several 100 ms following its onset. This suppression was overcome neither by the GABA receptor antagonists, nor by ejection of AMPA or glutamate at currents that otherwise produced vigorous excitation. These results suggest that one functional role for GABAA-receptor-mediated synaptic inhibition in the somatosensory thalamus is the intramodal regulation of the form of expression of phasically responding neurons. Other thalamic inhibitory processes not mediated by GABAA or GABAB receptors that help to shape the expression of the responses of certain phasic neurons to maintained stimulation may exist. Overall, these mechanisms appear to mediate the precision of timing of thalamic neuronal firing in response to the rat's tactile environment.
Fluorodeoxyglucose (FDG) positron emission tomography-magnetic resonance (PET/MR) is useful for the evaluation of cognitively-impaired patients. This study aims to assess two different attenuation ...correction (AC) methods (Dixon-MR and atlas-based) versus index-standard computed tomography (CT) AC for the visual interpretation of regional hypometabolism in patients with cognitive impairment. Two board-certified nuclear medicine physicians blindly scored brain region FDG hypometabolism as normal versus hypometabolic using two-dimensional (2D) and 3D FDG PET/MR images generated by MIM software. Regions were quantitatively assessed as normal versus mildly, moderately, or severely hypometabolic. Hypometabolism scores obtained using the different methods of AC were compared, and interreader, as well as intra-reader agreement, was assessed. Regional hypometabolism versus normal metabolism was correctly classified in 16 patients on atlas-based and Dixon-based AC map PET reconstructions (vs. CT reference AC) for 94% (90%–96% confidence interval CI) and 93% (89%–96% CI) of scored regions, respectively. The averaged sensitivity/specificity for detection of any regional hypometabolism was 95%/94% (P = 0.669) and 90%/91% (P = 0.937) for atlas-based and Dixon-based AC maps. Interreader agreement for detection of regional hypometabolism was high, with similar outcome assessments when using atlas- and Dixon-corrected PET data in 93% (Κ =0.82) and 93% (Κ =0.84) of regions, respectively. Intrareader agreement for detection of regional hypometabolism was high, with concordant outcome assessments when using atlas- and Dixon-corrected data in 93%/92% (Κ =0.79) and 92/93% (Κ =0.78). Despite the quantitative advantages of atlas-based AC in brain PET/MR, routine clinical Dixon AC yields comparable visual ratings of regional hypometabolism in the evaluation of cognitively impaired patients undergoing brain PET/MR and is similar in performance to CT-based AC. Therefore, Dixon AC is acceptable for the routine clinical evaluation of dementia syndromes.
With only a few atoms of seaborgium (Sg, element 106), in the form of volatile SgO2Cl2, it was possible to determine the sublimation enthalpy of this compound using gas chromatography. Furthermore, ...it was demonstrated that in Group 6 Sg is chemically more similar to W than to Mo.
The MINOS scintillator calorimeter system Adamson, P.; Alexandrov, K.; Anderson, B. ...
IEEE transactions on nuclear science,
2002-June, 2002-6-00, 20020601, Letnik:
49, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The MINOS (Main Injector Neutrino Oscillation Search) detectors will use extruded plastic scintillator strips, which are read out by wavelength-shifting fibers coupled to multipixel photodetectors. ...This technique provides excellent energy and spatial resolution. The MINOS detectors are described in detail along with results from light output tests. (Author)
The hypothesis has been tested that inhibitory mechanisms, active spatially and temporally between the input and the output of thalamic neurons, determine the nature of the information transmitted to ...the cerebral cortex. To enable this assessment, in barbiturate-anesthetized cats and urethane-anesthetized rats juxtacellular recordings were performed together with microiontophoretic ejection of transmitter agonists and antagonists. The effects of these drugs were studied on responses evoked by mechanical stimulation of cutaneous receptive fields (RFs) of neurons in the thalamic ventrobasal complex (VB). Neurons from different parts of the VB were investigated: 29 units were located medially, in the ventral posteromedial nucleus (VPM; facial RFs), and 11 units were located laterally, in the ventral posterolateral nucleus (VPL; forepaw and body RFs). A further eleven VB units had no detectable RF. Twenty-six neurons were tested with electrical stimulation of the somatosensory cortex (SI), 17 of these being identified as thalamo-cortical relay neurons and 5 being classified as presumed interneurons; the remaining 4 could not be activated. Four additional recordings were from trigemino-thalamic or thalamo-cortical fibers. For the quantitative assessment of the neurons' input and output, neuronal activity was induced by feedback-controlled, mechanical trapezoidal and/or sinusoidal stimuli applied to sinus hairs, fur or skin and the numbers of prepotentials and soma spikes were compared in peristimulus time histograms (PSTHs) generated simultaneously for both types of signal from 'DC' recordings. Iontophoretic administration of excitatory amino acids (EAAs) or bicuculline methiodide (BMI) increased output-input ratios in 87% of the cases tested, due to a higher rate of conversion of prepotentials into soma spikes taking place. In cases of neurons exhibiting a sustained-to-transient response pattern, changes to sustained-to-sustained patterns were demonstrated. Tests with gamma-aminobutyric acid (GABA) produced decreased output-input ratios in 90% of the neurons, due to a lower conversion rate of prepotentials into soma spikes taking place. In cases of neurons exhibiting high output-input ratios (sustained-to-sustained type), the responses changed to the sustained-to-transient pattern. For cortically evoked antidromic spikes of VB neurons, GABA produced a failure of the initial segment (IS-) spike to invade the soma, whereas BMI and glutamate (Glu) facilitated soma depolarization. When ejected with relatively higher currents than those needed to alter output-input ratios, EAAs decreased prepotential amplitudes while GABA produced increases in 16 of 18 neurons.
PDF
