Biomedical Engineering Reference
In-Depth Information
well as MEA, recordings of epileptiform activity in slices. Felbamate and
phenobarbital effects upon the overall power of the recorded signal were
assessed using power spectral density (PSD) measures. The speed and paths of
propagation were also assessed and compared in the absence and presence of
phenobarbital and felbamate. Hill et al. have demonstrated validation of
MEAs method in comparison with previous extracellular recording data from
the same models, and also described previously unreported background
changes in burst characteristics important to the use of these models. MEA
recording of epileptiform slice activity increases the depth and quality of data
gathered, and represents an important method for the early in vitro screening of
novel antiepileptic drugs.
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3.10.5.3 Microelectrode Arrays for Retinal Studies
One interesting application is related to the exploration of explanted retina
tissue using MEAs.
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The retina is a peripheral, easily accessible part of the
central nervous system. Stimulation by light results in a complex signaling by
neurons within the layers of the retina. The retinal ganglion cells transmit
retinal information to higher visual centers in the brain via their axons that
form the optic nerve. Retinal function can be affected by acute injuries,
intoxications or retinal diseases, either inherited or acquired, resulting in visual
impairment or even blindness.
In clinical practice the so-called electroretinogram (ERG) is a widely used
ocular electrophysiological test to diagnose impaired vision. Light impulses falling
on the retina synchronously activate a large number of neurons and Muller glia
cells, which regulate the extracellular potassium concentration. The resulting
change in trans-retinal voltage is measured as the ERG. The ERG has a multi-
phasic waveform. Its shape depends mainly on the stimulus conditions, the state
of the retina's adaptation and the species. The full-field ERG of a dark adapted
retina in response to a bright flash of white light consists of four major compo-
nents—the fundamental a-, b- and c-wave at light onset and the d-wave at light
offset. Each of the components can be attributed to the activity of certain retinal
cells. Under pathophysiological conditions the shape and amplitude of these
components is altered and can be influenced by pharmacological compounds.
A retina sensor, based on multisite recording of local ERGs in vitro, has been
developed to easily and effectively assess effects of pharmacological compounds
and putative therapeutic, drug side effects, and the consequences of
degeneration-related processes on retinal signaling (Figure 3.20).
For the recording of light-evoked activity, a retinal segment with the pigment
epithelium, dissected from an explanted chicken retina, is placed ganglion cell
site down on a MEA. Local ERGs (microERGs) with the typical components
and ganglion cell spikes can be recorded with the appropriate filter settings. The
prominent components of the microERG can be pharmacologicaly identified
for the b-wave, which is smaller in recordings from isolated retinas than
in recordings from intact eyes. During superfusion with drugs in defined
concentrations, specific alteration of the ERGs can be monitored. In its present
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