Habituation of the auditory evoked potential in a short interstimulus interval paradigm.

The present experiment was carried out to investigate elicitation and habituation of the auditory event related potentials with stimulus trains utilizing a short interstimulus intervals (ISI) of 1500 ms. Scalp event related potentials elicited by auditory stimuli were recorded in 10 male subjects. Thirty auditory stimuli were presented binaurally over headphones to every subject with a duration of 1000 ms, each with a constant ISI of 1500 ms. No task relevance was given to the stimuli. Wave-forms were collected using a Pentium 100 computer. All analyses were carried out over the 30 trials. In each single trial event related potentials, latencies and amplitudes of N1-P2 components were analyzed separately for four frequency bands (0.3-70, 0.3-4, 4-7, 7-13 Hz). Trend effects were tested with linear-regression analyses (N1-P2 amplitude x stimuli number). We found that the amplitude from the first stimulus decreased reliably across trial blocks of the N1-P2 components and that it was directly affected by ISI. The relevance of these results for the habituation is discussed.

The effect of sex differences on event-related potentials in young adults.

Female/male cognitive differences have been studied for some time; however, such differences in Turkish population is unknown. Evoked potentials (EPs) of the brain have been applied as an index of information processing in a wide variety of normal and cognitive impaired subjects. Scalp event-related potentials (ERP) evoked by auditory stimuli were recorded in 20 male and 18 female neurologically and audiologically normal young Turkish subjects of 18-25 years (Av. 20.6) of age. Standard auditory "Oddball" paradigm involving simple discrimination task of concentrating on infrequent (target) stimulus and ignoring frequent (non-target) stimulus was employed. EEG activity was recorded at the Fz, Cz, Pz and Oz electrode sites of the 10-20 system using Ag/AgCl electrodes. Wave forms were collected and averaged off-line by a Pentium 100 computer, which also controlled the stimulus presentation. In general, significant main effects of gender and electrode site on evoked potential components were found. The interpeak amplitudes N1-P2 and N2-P3 were higher in the male subjects than in the female subjects at Cz. N2-P3 were higher in the male subjects than in the female subjects at Oz. The latencies of N1, P2, N2, P3 components were not different between both sex. For both sexes we found that N1-P2 amplitude was higher at Fz and Cz than Pz and Oz. N2-P3 amplitude was higher at Fz than Oz for only female subject. In male subjects, latency of N2 was longer at Fz than Oz. There were no significant differences in the latencies of N1, P2, and P3 components between electrode sites in both sexes. We suggest that ERP components could be affected by sex, electrode site, and cognitive performance.

Effect of grayanotoxin II on in vitro mitotic activity of human lymphocytes.

Extracts of Rhododendron species and honey obtained from such species, which are used in folk medicines in Japan and Turkey, contain grayanotoxins. The effects of one of these toxins, grayanotoxin II, on the mitotic activity of cultured human lymphocytes were investigated. The mitotic index of the lymphocytes was increased by concentrations of 10(-4) and 10(-3) M grayanotoxin II, significantly so in the case of the higher concentration; the increase appeared to be proportional to the concentration of the toxin.

In vitro antioxidant effect of Ginkgo biloba extract (EGb 761) on lipoperoxidation induced by hydrogen peroxide in erythrocytes of Behçet's patients.

Excessive superoxide radical production and an impaired antioxidant mechanism in both the neutrophils and plasma of patients with Behçet's disease (BD) have been reported. To provide clinical support for the earlier data, erythrocyte membrane integrity was investigated by measuring malondialdehyde (MDA, a marker of lipid peroxidation) levels in the erythrocytes of BD patients. In addition, the antioxidant effect of Ginkgo biloba extract (EGb 761) at 25 and 250 microg/ml concentrations on lipoperoxidation induced by hydrogen peroxide (H2O2) in erythrocyte obtained from BD patients was examined in in vitro conditions. When compared to healthy controls, basal erythrocyte MDA levels were found to be higher in BD patients. In the in vitro study, there was also a significant increase in H2O2-induced MDA production in the medium containing no EGb 761 in the patient group, whereas significant decreases in MDA levels were observed in the mediums containing EGb 761 both in the patient and control groups. The decrease in MDA production was found to be related to EGb 761 concentration. These data indicate that an oxidative damage is present in erythrocytes obtained from Behçet's patients, and EGb 761, which may strengthen the antioxidant defense system, may contribute to the treatment of BD.

Effects of grayanotoxin-I on threshold intensity and compound action potential of frog sciatic nerve.

Effects of (Grayanotoxin-I) GTX-I, one of the second group of sodium channel toxins, have been investigated on threshold stimulus voltage and upstroke velocity of isolated frog sciatic nerve. GTX-I was isolated from toxic honey obtained from the Black Sea Region of Turkey, and used in the experiments at the concentrations of 3.50(-5), 3.10(-4), 3.10(-3) M. The threshold stimulus voltage and upstroke velocity of CAP were decreased and conduction velocity of frog sciatic nerve preparations was increased by GTX-I. The effects were dose-dependent. As a results, it is suggested that the decrease of threshold stimulus voltage and upstroke velocity of CAP and the increase of conduction velocity of frog sciatic nerve is mainly due to an increase in resting membrane permeability to sodium ions.

Oxidative stress and antioxidant defenses in plasma of patients with Behçet's disease.

Plasma myeloperoxidase (MPO) and glutathione peroxidase (GSH-Px) activities, and malondialdehyde (MDA), ceruloplasmin (Cp), transferrin (TF), thiol (SH), selenium (Se) and copper (Cu) levels were determined in patients with Behçet's disease (BD), in order to investigate whether the plasma antioxidant defense system is impaired in BD. When compared to controls, plasma MDA, Cp, Cu levels and also plasma MPO activity were significantly higher in patients, whereas plasma TF, SH and Se levels, and also plasma GSH-Px activity were lower in BD patients than those in controls. In addition, there were significant and positive correlations between MDA-Cp, MDA-Cu, MDA-MPO, MPO-Cp, GSH-Px-Se, Cp-Cu, and TF-SH parameters, but negative correlations between MPO-TF and Cp-TF parameters in BD patients. Based on these findings, it is concluded that plasma antioxidant defense system is insufficient and impaired in BD.

Effects of honey containing grayanotoxin I on frog gastrocnemius muscle.

The presence of grayanotoxins (GTX-I, GTX-II and GTX-III) in honey samples from the Mediterranean Sea and Black Sea regions of Turkey and the effect of honey containing GTX-I on the threshold stimulus voltage of frog gastrocnemius muscle were studied. We used 2 groups of gastrocnemius muscles isolated from curarized or noncurarized frogs. The threshold voltage was measured by external perfusion with a polygraphic system. Isolated muscle preparations were perfused separately with Clark-frog-Ringer's solution containing honey solutions from the Mediterranean Sea region (normal) or with honey solutions from the Black Sea region (GTX-I-containing, poisonous). There was no significant difference between the normal and poisonous honey groups data with the curarized preparations. But in the noncurarized preparations, the honey containing GTX-I significantly decreased the threshold voltage in comparison with normal honey. These findings suggest the effect of GTX-I on frog neuromuscular junctions is due to an increase in membrane permeability to sodium ions.