Oscillatory potentials

Effects of a Long Range Oscillatory Potential on the Radial Distribution... 

In a randomized monotherapy trial in newly diagnosed epilepsy, seven of 32 patients who were stiU taking vigabatrin after 3-9 years had concentrically constricted visual fields, and the defect was rated as severe in two (35). Of the seven patients with field defects, five had reduced oscillatory potentials and two also had abnormal a and b waves in rod and cone electroretinography. In contrast, none of the 20 patients who were stiU taking carba-mazepine had abnormal visual fields. There is also preliminary evidence that a pre-existing visual field defect increases susceptibility to vigabatrin-induced visual field constriction. 

Fig. 3. Typical ERG waveforms obtained from the rat. These signals were collected for a range of light intensities (shown on the right-hand side). Note how at low light levels, a (positive) slow, rod driven b-wave is seen. This grows and speeds up as a result of cone contribution and develops oscillatory potentials (OPs). The negative trough is called the a-wave and rcllects photoreceptor activation see Fig. 2).

Stable Strontium. Cardiovascular effects of strontium have been investigated by intravenous infusion studies in dogs. Infusions of strontium (as chloride or gluconate) averaging 172 mg strontium/kg under conditions of lowered potassium induced accelerated ventricular escape beats, ventricular tachycardia, or atrial fibrillation (Foster et al. 1977). High levels of strontium also induced oscillatory potentials and... 

Gonzalez MD, Vassalle M. 1990. Strontium induces oscillatory potentials in sheep cardiac Purkinje fibers. Int J Cardiol 27 87-99. 

Of most note, spherules made from proteinoid and lecithin have been recently shown to possess electrical membrane phenomena. Membrane, action, and oscillatory potentials were next recorded in the microspheres made from proteinoid only. While many of the functions of the model protocells are much weaker than the corresponding functions in modern cells, e.g., the catalytic functions, the electrical behavior is quantitatively comparable. Consequently the units are models of modern excitable cells, as well as of excitable protocells, and are treated mainly as such in this chapter. 

The actuation study of IPMC under a constant current is shown in Fig. 3.19. The figure shows that the oscillatory potential results in oscillatory deformation of IPMC. During the oxidation of formaldehyde, the intermediate (CO) of the reaction strongly binds to the platinum surface of the IPMC and blocks active sites. In this process, the resistance of platinum is increased, which leads to weaker field strength between electrodes of IPMC. Platinum also adsorbs OH which then oxidizes the CO on adjacent platinum sites to CO2. Due to this reaction, conductivity of platinum improves and results in a stronger field strength between the electrodes. This is believed to be the cause for self-oscillatory actuation of IPMC. 

EADs interrupt either Phase 2 or 3 repolarisation of the AP. If these afterdepolarisations attain sufficient thresholds, they may produce triggered responses and induce single or multiple extrasystoles and even VT. The EAD is an oscillatory potential that is sensitive to frequency and often occurs at slow stimulation rates. EAD activity has been shown in vitro using many types of isolated cardiac muscle and various cell types including mid-myocardial cells (M-cell) (Antzelevitch 2004). Induction of EAD activity can be induced by a variety of drugs that block sodium and potassium channels as well as by catecholamines. 

Vertical line at 20 ms denotes time of flash. Arrows indicate peaks of a- and b-waves and oscillatory potentials (O.P.). A-wave amplitude is measured fix)m baseline to the a-wave peak. B-wave anq>litude is measured fix>m the a-wave peak to b-wave peak at intensities where the a-wave is present, from baseline otherwise. Implicit latency time is measured from stimulus onset to the peak of the ERG component of interest. The sampling duration was not long enough to record a c-wave in this example. 

B. Same as above, but filter bandwidth adjusted to 100 - 1000 Hz to isolate the oscillatory potentials. 

Nakatake, N., Hori, A., Yasuhara, A., Naito, H., and Yasuhara, M. 1993. Oscillatory potentials of visual evoked potentials using source derivation techniques in rabbits. J. Neurolog. Sci. 114 144-151. 

Peachey, N.S., Alexander, K.R., Derlacki, D.J., Bobak, P., and Fishman, G.A. 1991. Effects of light adaptation on the response characteristics of human oscillatory potentials. Electroenc. Clin. Neurophvs. 78 27-34. 

Figure 3. Effects of an intravitreal injection of 500 pig norfloxacin (NFLX) on the ERG of an albino rabbit. The oscillatory potentials were greatly suppressed in the NFLX-injectedq e. Stimulus intensity was 5 x 10 lux at the cornea. Amplifier time constant was 3 msec.

Fluoroquinolones are promising antimicrobials with a broad spectrum. An intravitreal injection of 500 ptg norfloxadn greatly suppressed the c-wave and the oscillatory potentials (Figure 3), leaving other ERG components virtually unchanged. 

Viral endophthalmitis has become a major concern in AIE management, and some of uveitis are shown to arise from viral origin (e.g. acute retinal necrosis). Intravitreal antiviral therapy is surely one of the crucial modalities. The b-wave, the c-wave, the oscillatory potentials and the VEP remained unchanged after 5 repetitive weekly (once a week) intravitreal injections of 200 pig ganciclovir. 

B V ara U is a newly-developed antiviral drug particularly effective to varicella zoster virus. No changes in the b-wave, the c-wave or the oscillatory potentials were induced by an intravitreal injection of 100 pig BV area U or by intravitreal irrigation with 20 pig/m BV ara U. The concentration of BV ara U after an oral administration was much lower in the vitreous than in the serum, which indicates that intraocular penetration of B V ara U is very poor. Furthermore, an enteral use of B V ara U in conjunction with some of antimetabolites reportedly causes serious systemic adverse effects. Therefore, a topical intraocular application of BV ara U is much preferable. 

The ERG from an excised eye-cup or an isolated retina is useful especially for studying the effects of chemicals at very predse concentrations by dissolving the chemicals in the perfusates. The a-wave, the b-wave and the oscillatory potentials are recordable from in-vitro preparations of even mammals for more than several hours (Figure 5),... 

C. Karwoski and K. Kawasaki. Oscillatory potentials. 125-128, in Principle and Practice of Clinical Hectrophysiology of Vision, J. R. Heckenlively and G. B. Arden, eds., Mosby Year Book, St. Louis (1991). 

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