Motohiro Yasuhara

Blink reflex elicited by auditory stimulation in the rabbit

The pathway of the blink reflex, elicited by auditory stimulation, was investigated electrophysiologically. The reflex was recorded as microvibrations of the eyelid and was named the auditory-evoked eyelid microvibration (AMV). Pharmacophysiological studies suggest that AMV is closely related to the midbrain reticular formation and studies of electrical lesions in the midbrain reticular formation support this. Lesions in several parts of the central nervous system provide evidence that the inferior colliculus has an important role in AMV, and the cerebral cortex may have an inhibitory influence. Studies of brainstem transections indicate that the reflex pathway of AMV exists between the lower midbrain and the upper medulla. Because of its ease and simplicity, AMV is believed to be a useful test for evaluation of the function of the brainstem.

Effects of TRH-T and DN-1417 on the Central Nervous System: An Electrophysiological Study of Arousal Reaction and Evoked Muscular Discharges

For the purpose of elucidating the effects of TRH and DN-1417 on the CNS, electrophysiological experiments were performed and the following observed. 1. TRH and DN-1417 exerted threshold-decreasing action not only on the threshold for arousal reaction but also on the threshold for evoked muscular discharges, which occur on stimulation of the brainstem reticular formation. 2. The threshold decreasing effect of DN-1417 was stronger than that of TRH, not only for the arousal reaction but also for the evoked muscular discharges. 3. Both TRH and DN-1417, with facilitating effects on the brainstem reticular formation, increased the number of spontaneous unit discharges. DN-1417 increased the number of reticular units, to the same degree as TRH with a smaller dose. These results indicate that both TRH and DN-1417 act on the nerve cells in the brainstem reticular formation, awaken consciousness and facilitate the function of the motor system.

Potential changes and eyelid microvibration elicited by flash stimulation

The photopalpebral reflex evoked in the upper eyelid of the rabbit by flash stimulation was studied in terms of potential change (PPR) and microvibration (MV) and the following conclusions drawn. (1) Of the PPR components, the early components from PPR1 to PPR4 are mainly ERG components, while PPR5 to PPR9 and MV are components appearing via the central nervous system. (2) Excitation of the brainstem reticular formation is involved in the appearance of the central PPR components and MV. Components PPR6 to PPR8 and MV originate in excitation of the same nervous tissue, but PPR9 occurs by excitation of different nervous tissue. (3) Contraction of the extraocular muscles, as well as the orbicularis oculi muscles, is involved in the appearance of MV. (4) Unit discharge takes place in the brainstem reticular formation coinciding with the occurrence of MV and an increase in discharge takes place later. The relation of the increase in this late discharge to PPR9 must be further investigated.

Steady-state auditory evoked potentials (SSAEPs) in the rabbit. Contribution of the inferior colliculus

Steady-state auditory evoked potentials (SSAEPs) were recorded in rabbits with both surface and depth electrodes. Surface recording from the bregma provided the largest and most typical SSAEPs as compared to other surface locations when a stimulus rate of 50 Hz was used. The medial geniculate body (MGB) showed no potential corresponding to the surface SSAEP. On the other hand, the latency of SSAEP in the inferior colliculus (IC) corresponded closely to that of the surface potential. Furthermore, the amplitude of the IC potential tended to become large with the stimulus rate of 50 Hz as compared with transient stimuli. Although other auditory nuclei in the brain-stem, the ventral nucleus of the lateral lemniscus, the trapezoid body and the auditory nerve responded to transient stimuli with an amplitude larger than that of the IC, no amplification occurred with 50 Hz stimuli in these nuclei. These findings suggest that the IC contributes to the generation of SSAEP to a great extent.

Effects of hyperosmolality on the central nervous system and intracranial hemorrhage.

The relationship between hyperosmolality and intracranial hemorrhage as well as brain dysfunction was studied. Hyperosmolality was induced by continuous infusion of hyperosmotic solutions, such as 7% sodium bicarbonate (1,666 mOsm/1), 4.64% sodium chloride (1,666 mOsm/1), 20% glucose (about 1,200 mOsm/1), 20% mannitol (about 1,200 mOsm/1), and 10% glycerol with 0.9% sodium chloride and 5% fructose (about 2,000 mOsm/1). 1) Intracranial hemorrhage was observed without exception after the rabbits had died of hyperosmolality due to the infusion of these agents. The intracranial hemorrhage was mostly subdural hemorrhage in the subtentorial region. 2) The plasma osmolality just before death varied according to the agents administered and was lowest in the case of 7% sodium bicarbonate with a level of 441 mOsm/1. 3) The plasma osmolality in the case of 10% glycerol was higher than the case of 20% mannitol at the death. 4) The arousal reaction was suppressed by hyperosmotic solutions which contain sodium ions, and when the plasma osmolality surpassed 320 mOsm/1, dysfunction of the CNS began to appear. 5) The evoked muscular discharges caused by stimulation of the midbrain reticular formation were suppressed only by the administration of 7% sodium bicarbonate, so this result is related to alkalosis.

Oscillatory potentials of visual evoked potentials using source derivation technique in rabbits

The topographic distribution of epidurally recorded flashed visual evoked potentials (VEPs) in unanesthetized rabbits was studied using 2 montages. VEPs with linked ears reference and source derivation were compared. With the linked-ears reference, N34 of VEPs which consisted of slow potentials and superimposed oscillations were recorded diffusely over the head. When source derivation was used, the slow negative potentials of N34 present on the recordings in P3 and P4 were not obtained in F3, Fz and F4. In a digital filtering study of the oscillatory potentials, N34 in oscillatory potentials which were recorded diffusely over the head were localized to the visual cortex by source derivation. It was concluded that N34 in the oscillatory potentials generated from the visual cortex are enhanced and localized with source derivation.