Optical mapping of brainstem neuronal activity evoked by auditory electro-stimulation in rats

Shuping CAI; Jing SHEN; Tadashi DOI

ABSTRACT

BACKGROUND:

Optical mapping technique is a novel electrophysiological detection method in which voltage-sensitivity dye is medium and silicon photoelectrical diode transforming technology is characteristic, used for analyzing the spatial-temporal distribution of membrane potential in complex neural system.

OBJECTIVE:

To observe the spatial-temporal changes of brainstem auditory electro-stimulation evoked potential by using optical mapping technology, so as to probe into the influence of γ-Aminobutyric acid (GABA) and γ-GABA receptor antagonist-bicuculline (BMI) on auditory evoked potential.

DESIGN:

Randomized controlled study.

SETTING:

Aging Medicine Research Institute of Military General Hospital and E.T.N Department of Japanese Kansai Medical University.MATERIALSThis study was conducted at E.T.N Department of Japanese Kansai Medical University from May to November 2002. Totally 100 ddy/ddy rats, with age of 0-5 days, clear grade, either gender were selected.

METHODS:

All rats were put to death after cryo-anaesthetized, and brainstem was cut into slices under frozen state so as to remain activity.One side of brainstem slice was connected with the residual end of untraumatic auditory nerve, and slices were put on organic glass plate with the bottom covered with siliac gel and fixed by tungsten filament of 30 μm wide. The residual end of untraumatic auditory nerve was stimulated by tungsten electrode, meanwhile the evoke potentials were recorded at cochlea nuclei and vestibule nuclei. In control group slices were incubated in artificial CSF for 20 minutes, which added with 50 μmol/L γ-GABA in experimental group for observing the influence of γ-GABA on brainstem auditory evoked signals; or alternatively incubated with 50 μmol/L g-GABA and 200 μmol/L for 20 minutes for observing the influence of BMI on brainstem auditory evoked signals. Stimulation was positive rectangle-shape impulse with electric current of 5 mA and frequency of 0.1 Hz, lasting period of 5 ms, the onset time of electric stimulation was set at 89.9 ms.Brain stem slices were stained with electric-sensitivity dye of NK3041 and 16×16 pixel silicon photoelectrical diode device was used to record the auditory nerve stimulation evoked optical signals.fluence of γ-GABA and BMI on optical signals.

RESULTS:

Totally 100 ddy/ddy rats enrolled in this study and 56 died Character of brainstem auditory electrical-stimulation evoked optical signals Spatial-temporal changes of auditory evoked optical signals were recorded. The latency of optical signals was (4.63±1.01) ms cochlea nuclei and (6.00±0.89) ms at vestibule nuclei of the same side. Each optical sigual can be divided into two parts Quick peak-potential and slow long-term potential. The onset phage of quick potential displayed pre-synaptic property, while later phage displayed post-synaptic property; the slow long-term reaction due to γ-GABA and BMI administration 50 μmol/L γ-GABA was added into the perfusion fluid so as to reduce the amplitude of auditory evoked brainstem neuronal signals in maximum degree, the onset latency of quick potential did not prolonged, but amplitude slightly descended; while the latency and amplitude of later phage were obviously reduced. But such changes could be partly resumed due to the 200 μmol/L dicentrine administration.

CONCLUSION:

Auditory electro-stimulation evoked potentials can be detected by using multiple-site optical mapping system, which displaying spatial-temporal property. γ-GABA can obviously attenuate the amplitude of auditory electro-stimulation evoked brainstem signals, but such effect can be partly but not completely attenuated by γ-GABA A receptor antagonist-BMI, which implying that besides γ-GABA A receptor, such inhibition of γ-GABA energetic neurons on auditory electro-stimulation evoked potentials can be achieved by other γ-GABA subtype receptors.