Abnormal cortical responses to somatosensory stimulation in medication-overuse headache

BACKGROUND: Medication-overuse headache (MOH) is a frequent, disabling disorder. Despite a controversial pathophysiology convincing evidence attributes a pivotal role to central sensitization. Most patients with MOH initially have episodic migraine without aura (MOA) characterized interictally by an absent amplitude decrease in cortical evoked potentials to repetitive stimuli (habituation deficit), despite a normal initial amplitude (lack of sensitization). Whether central sensitization alters this electrophysiological profile is unknown. We therefore sought differences in somatosensory evoked potential (SEP) sensitization and habituation in patients with MOH and episodic MOA. METHODS: We recorded median-nerve SEPs (3 blocks of 100 sweeps) in 29 patients with MOH, 64 with MOA and 42 controls. Episodic migraineurs were studied during and between attacks. We measured N20-P25 amplitudes from 3 blocks of 100 sweeps, and assessed sensitization from block 1 amplitude, and habituation from amplitude changes between the 3 sequential blocks. RESULTS: In episodic migraineurs, interictal SEP amplitudes were normal in block 1, but thereafter failed to habituate. Ictal SEP amplitudes increased in block 1, then habituated normally. Patients with MOH had larger-amplitude block 1 SEPs than controls, and also lacked SEP habituation. SEP amplitudes were smaller in triptan overusers than in patients overusing nonsteroidal anti-inflammatory drugs (NSAIDs) or both medications combined, lowest in patients with the longest migraine history, and highest in those with the longest-lasting headache chronification. CONCLUSIONS: In patients with MOH, especially those overusing NSAIDs, the somatosensory cortex becomes increasingly sensitized. Sensory sensitization might add to the behavioral sensitization that favors compulsive drug intake, and may reflect drug-induced changes in central serotoninergic transmission

Entropy-based design considerations for water quality monitoring networks

Assessment of water quality monitoring networks requires potential methods to delineate the efficiency and cost-effectiveness of current monitoring programs. To this end, the concept of entropy has been considered as a promising method in previous studies as it quantitatively measures the information produced by a network. The paper presented discusses an entropy-based approach for the assessment of combined spatial/temporal frequencies of monitoring networks. The results are demonstrated in the case of water quality data observed along the Mississippi River in Louisiana

Comparison of optimization and entropy methods in assessment of water quality sampling sites

This paper examines the application of two different methods that can be used to assess an existing water quality monitoring network with respect to its sampling sites. The first method uses an optimization procedure, i.e., dynamic programming, to evaluate the reduction of the number of sampling sites in a basin with respect to different monitoring objectives. The second methodology is biased on the entropy concept of Information Theory, which serves to assess sampling sites on the basis of their informativeness. Both methodologies are demonstrated in the case of the Gediz River basin in western Turkey

Buccal micronucleus cytome assay

The Buccal Micronucleus Cytome (BMCyt) assay is a minimally invasive method for studying DNA damage, chromosomal instability, cell death and the regenerative potential of human buccal mucosal tissue. This method is increasingly used in molecular epidemiological studies for investigating the impact of nutrition, lifestyle factors, genotoxin exposure and genotype on DNA damage, chromosome malsegregation and cell death. The biomarkers measured in this assay have been associated with increased risk of accelerated ageing, cancer and neurodegenerative diseases. This protocol describes one of the current established methods for buccal cell collection using a small-headed toothbrush, the generation of a single-cell suspension, slide preparation using cytocentrifugation, fixation and staining using Feulgen and Light Green for both bright field and fluorescence microscopic analysis. The scoring criteria for micronuclei and other nuclear anomalies are also described in detail. The protocol in its current form takes approximately 4 h to complete from the time of buccal cell collection to the generation of stained slides for microscopic analysis.Philip Thomas, Nina Holland, Claudia Bolognesi, Micheline Kirsch-Volders, Stefano Bonassi, Errol Zeiger, Siegfried Knasmueller & Michael Fenec

Neurophysiology of migraine with aura

In this chapter, we review the findings obtained by neurophysiological studies in migraine with aura (MA). Spontaneous electroencephalography activity in MA is characterized by abnormalities in alpha rhythm power and symmetry, and the presence of slowing, and increased, information flow in a wide range of frequency bands. Evoked potential (EP) studies indicate the occurrence of increased grand-average cortical response amplitudes, interhemispheric response asymmetry, as well as deficient habituation to any kind of repetitive sensory stimulation, in MA patients. Transcranial magnetic stimulation (TMS) methods applied in MA confirm abnormalities in cortical responsivity, such as greater motor evoked potential (MEP) amplitude, lower threshold for phosphene production, and paradoxical effects induced by depressing or enhancing repetitive TMS. Brainstem reflex studies indicate a deficit of blink reflex habituation in MA. Mild abnormalities of neuromuscular transmission shown by single-fibre electromyography were more pronounced in migraineurs with aura, and positively correlated to the complexity of their aura. The few studies performed in patients during the aura described suppression of evoked potentials, desynchronization in extrastriate areas and the temporal lobe, and large variations in direct current potentials using magnetoelectroencephalography. In contrast, patients affected by familial hemiplegic migraine had opposite neurophysiological patterns in comparison with patients suffering from the common forms of migraine