Cuneyt Goksoy

Differences between the N1 waves of the responses to interaural time and intensity disparities: scalp topography and dipole sources☆

OBJECTIVES Being the two complementary cues to directional hearing, interaural time and intensity disparities (ITD and IID, respectively), are known to be separately encoded in the brain stem. We address the question as to whether their codes are collapsed into a single lateralization code subcortically or they reach the cortex via separate channels and are processed there in different areas. METHODS Two continuous trains of 100/s clicks were dichotically presented. At 2 s intervals either an interaural time delay of 1ms or an interaural level difference of 20 dB (HL) was introduced for 50 ms, shifting the intracranial sound image laterally for this brief period of time. Long-latency responses to these directional stimuli, which had been tested to evoke no potentials under monotic or diotic conditions, as well as to sound pips of 50 ms duration were recorded from 124 scalp electrodes. Scalp potential and current density maps at N1 latency were obtained from thirteen normal subjects. A 4-sphere head model with bilaterally symmetrical dipoles was used for source analysis and a simplex algorithm preceded by a genetic algorithm was employed for solving the inverse problem. RESULTS Inter- and intra-subject comparisons showed that the N1 responses evoked by IID and ITD as well as by sound pip stimuli had significantly different scalp topographies and interhemispheric dominance patterns. Significant location and orientation differences between their estimated dipole sources were also noted. CONCLUSIONS We conclude that interaural time and intensity disparities (thus the lateral shifts of a sound image caused by these two cues) are processed in different ways and/or in different areas in auditory cortex.

Antiepileptic activity of melatonin in guinea pigs with pentylenetetrazol-induced seizures

Abstract Background: Antiepileptic and neuroprotective effects of melatonin (N-acetyl-5-methoxytryptamine) have been shown at higher doses (50–160 mg/kg). We aimed to investigate the antiepileptic effects of low-dose melatonin (10 mg/kg) on pentylenetetrazol (PTZ)-induced experimental epilepsy model. Materials and Methods: Twelve male albino guinea pigs weighing 500–800 g were used in our work. Initially, latent period, seizure intensity and mortality parameters were evaluated during the epileptic seizure induced by PTZ. After a recovery period of 7 days, effects of the neuroprotective agent, melatonin (which is dissolved in 2.5% ethanol–saline solution), on epileptic seizures induced by PTZ were evaluated. Effects of 2.5% ethanol, which is an anticonvulsant agent when administered acutely in high concentrations, on PTZ-induced seizures were also evaluated. Results: Data obtained from the study groups (PTZ, PTZ + melatonin and PTZ + ethanol) were evaluated by paired t-test, and p<0.005 was considered statistically significant. The differences of latent periods between the PTZ and PTZ + melatonin groups were found to be statistically significant (p<0.001). Conclusion: Although melatonin does not have a primary anticonvulsant effect at low doses (10 mg/kg), it lowers the mortality rates and attenuates seizure severity while increasing the latent period.

Interaural delay-dependent changes in the binaural interaction component of the guinea pig brainstem responses ☆

Auditory brainstem responses to monaural and binaural clicks with 23 different interaural time differences (ITDs) were recorded from ten guinea pigs without anesthesia. Binaural interaction component was obtained by subtracting the sum of the appropriately time-shifted left and right monaural responses from the binaural one. With increasing ITD, the most prominent peak of the binaural difference potential so obtained shifted to longer latencies and its amplitude gradually decreased. The way these changes depended on binaural delay was basically similar to that previously observed in a cat study [P. Ungan, S. Yagcioglu, B. Ozmen. Interaural delay-dependent changes in the binaural difference potential in cat auditory brainstem response: implications about the origin of the binaural interaction component. Hear. Res. 106 (1997) 66-82]. The data were successfully simulated by the model suggested in that report. We therefore concluded that the same model, which was based on the difference between the mean onset latencies of the ipsilateral excitation and contralateral inhibition in a typical neuron in the lateral superior olive, their standard deviations, and the duration of the contralateral inhibition, should also be valid for the binaural interaction in the guinea pig brainstem. The results, which were discussed in connection with sound lateralization models, supported a model based on population coding, where the lateral position of a sound source is coded by the ratio of the discharge intensity in the left and right lateral superior olives, rather than the models based on coincidence detection.

PREVENTION OF FURTHER CYCLOPHOSPHAMIDE INDUCED HEMORRHAGIC CYSTITIS BY HYPERBARIC OXYGEN AND MESNA IN GUINEA PIGS

PURPOSE Hyperbaric oxygen therapy and mesna have been successfully used for hemorrhagic cystitis. We defined the protective effects of hyperbaric oxygen and mesna in further cyclophosphamide induced hemorrhagic cystitis in guinea pigs. MATERIALS AND METHODS A total of 48 male guinea pigs were divided into 6 groups. All groups received 2 doses of 68.1 mg./kg. cyclophosphamide intraperitoneally at the same time intervals but group 1 served as controls. Group 2 received cyclophosphamide only, group 3 received hyperbaric oxygen treatment (2.8 ATA for 90 minutes twice daily) before and the day after further cyclophosphamide, group 4 received 21.5 mg./kg. mesna intraperitoneally only with further cyclophosphamide, group 5 received hyperbaric oxygen and mesna with further cyclophosphamide, and group 6 received hyperbaric oxygen before initial cyclophosphamide, between the 2 doses and after the further dose of cyclophosphamide, and mesna on the days of cyclophosphamide. RESULTS Although mesna alone provided protection against cyclophosphamide induced cystitis in animal bladders, there was also significant damage compared with controls. When the uroprotective efficacy of mesna was supported with hyperbaric oxygen, bladder protection was promoted since mean histological scores and hematuria levels in this group did not differ from those in controls. CONCLUSIONS According to this animal study using hyperbaric oxygen as adjuvant therapy in humans may be a better tool than mesna alone for the prophylaxis and treatment of cyclophosphamide induced hemorrhagic cystitis.

Binaural interaction component and white-noise enhancement in middle latency responses: differential effects of anaesthesia in guinea pigs.

Abstract. It is known that the response to binaural clicks is smaller in amplitude than the sum of two monaural responses. The difference is called the binaural interaction component (BIC). Also, an amplitude enlargement occurs in guinea pig middle latency responses (MLRs) to monaural clicks when white noise is applied to the other ear. This study was conducted to find out whether these two signs of binaural interaction result from the same mechanism. White noise enhancement (WNE) and BIC were computed from the evoked potential data simultaneously recorded in different phases of anaesthesia. WNE gradually decreased and disappeared with anaesthesia, but the relative amplitude of the BIC remained unchanged. This differential effect showed that different neural mechanisms must be responsible for BIC and WNE in guinea pig MLR.

Dynamics of the contralateral white noise-induced enhancement in the guinea pig's middle latency response.

The peak-to-peak amplitude of temporal middle latency response (MLR) of the guinea pig, evoked by a click in the contralateral ear, according to the recording side, is increased with the presence of continuous white noise (CWN) in the ipsilateral ear and this specialty is defined as the white noise enhancement (WNE). This phenomenon is evaluated as an interesting electrophysiological finding from the viewpoint of binaural interaction and in this study, its dynamic specifications were investigated. After the beginning of ipsilateral CWN, significant WNE was observed at 275th ms and it reached to a maximum, with an increase more than 40%, at 350th ms. After a habituation occurred, WNE reached to 20% on the 4th second by gradually decreasing and came to a steady state. In the time window between 2 and 5 ms after CWN started, a surprising amplitude decrease is observed. Therefore, CWN causes an effect, like a click, in the short-term and this on-response type effect originates from low level binaural centers, which decreases the MLR amplitude. However, the same CWN increases the MLR amplitude (WNE) by the effects over the high level binaural centers in the succeeding period, by its continuous characteristic.

Binocular interactions in the guinea pig's visual-evoked potentials

In this study, binocular interaction in guinea pigs is evaluated using bioelectrical activities. A difference potential, as evidence of an interaction, is calculated by subtracting the sum of visual-evoked potentials recorded by left and right monocular visual stimulations from the potential recorded by binocular stimulation. A negative monophasic wave with an average amplitude of 15.1 microV and an average latency of 106 ms is observed in the difference potential. This finding implies that the P100 is the main guinea pig visual-evoked potential wave that is affected by binocular interaction. Binocular interaction is also observed in the waves N75 and N140, although with a smaller amplitude. No interaction is observed in the segments of P55 and P200 waves.