Biomedical subjects

M A Bierlaagh

Publications and source records attributed to M A Bierlaagh.

3 recordsLinked to original sources

PubMed2001

Raloxifene affects brain activation patterns in postmenopausal women during visual encoding.

Recent brain imaging studies have shown that estrogens alter brain activation patterns upon working memory tasks in postmenopausal women. Estrogens, however, have many systemic side effects. We investigated the effect of the Selective estrogen receptor modulator (SERM) raloxifene on brain activation patterns during a memory task in postmenopausal women with functional magnetic resonance imaging (fMRI). Twenty postmenopausal and right handed women (mean age 65.7 years; SD 3.0) were included in this double blind, placebo controlled and randomized study. Whole brain fMRI was performed before and after three months of daily treatment with raloxifene 60 mg or placebo. Each scanning session consisted of a visual encoding task, a recognition test and a simple photic simulation test. Data analyses was performed with SPM99b software. Specific regions of interest for the tasks were defined based in previous experiments. Visual encoding activated the ventral route, posterior medial temporal lobe and frontal cortex in both groups. Treatment interactions for raloxifene compared to placebo were a decrease in activation in the left parahippocampal gyrus and left lingual gyrus, an increase in activation in the right superior frontal gyrus. The mean recognition test and the simple photic stimulation test showed no treatment interactions. Our results show that raloxifene affects brain activation patterns upon visual encoding in postmenopausal women.

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PubMed1997

Cellular mechanisms underlying spontaneous firing in rat suprachiasmatic nucleus: involvement of a slowly inactivating component of sodium current.

Neurons constituting the pacemaker of circadian rhythms, located in the suprachiasmatic nucleus, generate spontaneous firing patterns that change across the day-night cycle. Their average spontaneous firing rate is considered an important functional marker of clock activity because it is highest during daytime and low at night. In this study we investigate the ionic mechanisms underlying spontaneous firing in acutely prepared slices and dissociated neurons of the suprachiasmatic nucleus. In current-clamp mode, spontaneous action potentials were consistently preceded by depolarizing ramps. These ramps were Na+ dependent, were sensitive to tetrodotoxin (TTX), and disappeared on hyperpolarization. Ramps and associated spikes were not abolished by blockers of the H current (1 mM cesium) or calcium currents (50 microM nickel or 200 microM cadmium). In voltage-clamped neurons in slices or dissociated neurons, TTX-sensitive and Na+-dependent inward current was observed to activate well below firing threshold (-60 to -50 mV). The low-threshold component of Na+ current inactivated slowly as compared with the fast component that mediates action potentials. However, its inactivation proceeded more rapidly than has been reported for the persistent Na+ current in cortical structures. Persistent Na+ current was generally absent or small in amplitude. The voltage dependence and kinetics of the slowly inactivating component of Na+ current are consistent with the hypothesis that it is partially deinactivated during spike afterhyperpolarizations and contributes significantly to subsequent depolarizing ramps. These observations implicate the slowly inactivating component of Na+ current in ionic mechanisms governing spontaneous firing in suprachiasmatic nucleus neurons.

Action Potentials↗

PubMedDate not supplied

Functional MR imaging in Alzheimer's disease during memory encoding.

BACKGROUND AND PURPOSE: We applied functional MR imaging with a learning task in healthy elderly volunteers and in patients with Alzheimer's disease to study brain activation during memory performance. The purpose was to determine the feasibility of functional MR imaging during a learning task in healthy elderly volunteers and in patients with Alzheimer's disease and to test our hypothesis that brain activation is decreased in the medial temporal lobe (MTL) memory system in patients with Alzheimer's disease compared with control volunteers. METHODS: In 12 patients with mild to moderate forms of Alzheimer's disease and 10 elderly control volunteers, activation of the MTL memory system was studied. We used two learning tasks that required the encoding of new information into memory. After the functional MR imaging experiment, participants were tested for recognition of the encoded objects. RESULTS: In the elderly control volunteers, activation during memory encoding was observed in medial and lateral temporal lobe structures (fusiform, parietal and occipital parts, and hippocampal formation) and in the frontal cortex, as reported previously in studies of young control volunteers. Focusing on the MTL, we observed that activation was significantly decreased in patients with Alzheimer's disease compared with control volunteers in the left hippocampus and parahippocampal gyrus bilaterally during the first encoding task but not during the second (P < .05, uncorrected). CONCLUSION: Functional MR imaging with a learning task seems feasible in elderly volunteers and in patients with Alzheimer's disease. The measured functional signal decrease in MTL areas warrants further exploration of the (early) diagnostic usefulness of functional MR imaging in cases of Alzheimer's disease and other dementias.

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