GABerge cellen in het dorsaal lateraal geniculatum en de visuele cortex van de kat (Felis catus)

KULeuven Campusbibliotheek Exacte Wetenschappen / UCL - Université Catholique de LouvainSIGLEBEBelgiu

Identification of the target neuronal elements in electrical deep brain stimulation

The aim of this study is to identify the primary neuronal target elements in electrical deep-brain stimulation, taking advantage of the difference in strength–duration time constant (τsd) of large myelinated axons (≈ 30–200 µs), small axons (≈ 200–700 µs) and cell bodies and dendrites (≈ 1–10 ms). Strength–duration data were measured in patients suffering from Parkinson's disease or essential tremor and treated by high-frequency stimulation in the ventral intermediate thalamic nucleus or the internal pallidum. Threshold voltages for the elimination of tremor were determined at various pulsewidths and a pulse rate of 130 pulses per second. The τsd was calculated using Weiss's linear approximation. Its mean value was 64.6 ± 25.4 µs (SD) for the thalamic nucleus and 75.3 ± 25.5 µs for the internal pallidum. Corrections to the mean values were made because the τsd values were based on voltage–duration measurements using polarizable electrodes. Apart from this systematic error, a resolution error, due to the relatively large increment steps of the pulse amplitude, was taken into account, resulting in mean τsd estimates of 129 and 151 µs for the thalamic nucleus and the internal pallidum, respectively. It is concluded that the primary targets of stimulation in both nuclei are most probably large myelinated axons

Chronaxie calculated from current–duration and voltage–duration data

To determine the rheobase and the chronaxie of excitable cells from strength–duration curves both constant-current pulses and constant-voltage pulses are applied. Since the complex impedance of the electrode-tissue interface varies with both the pulsewidth and the stimulation voltage, chronaxie values estimated from voltage–duration measurements will differ from the proper values as determined from current–duration measurements. To allow a comparison of chronaxie values obtained by the two stimulation methods, voltage–duration curves were measured in human subjects with a deep brain stimulation electrode implanted, while the current and the load impedance of the stimulation circuit were determined in vitro as a function of both stimulation voltage and pulsewidth. Chronaxie values calculated from voltage–duration data were shown to be 30–40% below those estimated from current–duration data. It was also shown that in the normal range of stimulation amplitudes (up to 7 V) the load impedance increases almost linearly with the pulsewidth. This result led us to present a simple method to convert voltage–duration data into current–duration data, thereby reducing the error in the calculated chronaxie values to ≈6%. For this purpose voltage–duration data have to be measured for pulses up to 10–20 times the expected chronaxie

Calcium binding proteins and neuropeptides as molecular markers of GABAergic interneurons in the cat visual cortex.

In the cat visual cortex, almost all parvalbumin-positive cells are GABAergic, and about 80% of the calbindin D-28K-positive neurons are also GABA-immunoreactive. About 37% of the GABAergic neurons contain parvalbumin and a smaller fraction (about 18%) contains calbindin. Furthermore, parvalbumin and calbindin are localized in two separate neuronal populations in the cat visual cortex, suggesting that two GABAergic populations can be distinguished, one containing parvalbumin and one containing calbindin. Double staining for parvalbumin and neuropeptides (CCK, SRIF and NPY), revealed no double-labeled cells, with the exception of a few SRIF- and parvalbumin-positive neurons. These results show that cortical GABAergic cells can be differentiated on basis of their calcium binding protein and neuropeptide immunoreactivity.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Calcium binding proteins as molecular markers for cat geniculate neurons.

Immunocytochemistry revealed that in the cat dorsal lateral geniculate nucleus (dLGN) almost all parvalbumin-positive cells are GABAergic and about 56% of the calbindin D-28K (calbindin-immunoreactive neurons are also GABA-positive. On the other hand, in the same nucleus, almost all GABAergic neurons contain parvalbumin, and about 89% of the GABA-immunoreactive neurons contain calbindin. Double-labeling with calbindin and parvalbumin revealed that approximately 50% of the immunoreactive neurons are double-stained. In the PGN, virtually all neurons are GABA and parvalbumin-positive. Only a few scattered cells were also calbindin-immunoreactive. These results show that GABAergic geniculate cells can be differentiated on the basis of their calcium-binding protein immunoreactivity. Four types of immunoreactive cells are described here: (1) cells positive for GABA, parvalbumin and calbindin, (2) cells positive for GABA and parvalbumin, but negative for calbindin, (3) cells negative for GABA and parvalbumin, but positive for calbindin, (4) cells negative for GABA, parvalbumin and calbindin.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Effect of sensory deafferentation on immunoreactivity of GABAergic cells and on GABA receptors in the adult cat visual cortex

To investigate the effects of sensory deafferentation on the cortical GABAergic circuitry in adult cats, glutamic acid decarboxylase (GAD) and gamma-aminobutyric acid (GABA) immunoreactivity and GABA receptor binding were studied in the visual cortex of normal cats and compared with cats that had received restricted binocular central lesions of the retina and had survived for 2 weeks postlesion in a normal visual environment. In the visual cortex of lesioned cats, two changes were observed in the number of GAD-immunoreactive elements in the regions affected by the retinal lesions: the number of GAD-positive puncta decreased, whereas that of GAD-immunoreactive somata increased. In contrast, no detectable changes were measured in the number of GABA-immunopositive somata or puncta. At the receptor level, we observed no differences in either the laminar distribution or the affinity of cortical GABAA and GABAB receptors labeled with [3H]-muscimol and [3H]-baclofen, respectively, in the lesioned versus normal cats. We present the hypothesis that sensory deafferentation in these adult cats (1) leads to a reduction of cortical GABAergic inhibition in the deafferented region, and (2) that this decreased inhibition may permit changes in efficiency of synapses and (3) that these changes may represent a first stage of events underlying the retinotopic reorganization preceeding the structural changes.status: publishe

Risk of misinterpretation of ebola virus PCR results after rVSV ZEBOV-GP vaccination

SCOPUS: le.jinfo:eu-repo/semantics/publishe

Risk of misinterpretation of Ebola virus PCR results after rVSV ZEBOV-GP vaccination

status: publishe