Sadaharu Takagi

Dorsal light response and changes of its responses under varying acceleration conditions

In order to improve our understanding about functions of the gravity sensors, we have conducted four experiments in goldfish: 1) To define the effect of visual information influx on the static labyrinthine response, the dorsal light response (DLR) which had been proposed by von Holst as a model for postural adjustment in fish was reexamined with a newly designed, rotatory illumination device. The fish responded to illumination from the upper half of the visual field and a narrow range around 180 degrees of the lower half visual field. The maximal tilting angle of normal fish was about 40 degrees under horizontal illumination. 2) Under the changes of the gravito-inertial force level produced by a linear sled, the threshold of the gravity sensors was determined from postural adjustment responses. 3) Under hypogravic conditions during the parabolic flight of an airplane, the light-dependent behavior was investigated in intact and labyrinthectomized goldfish. 4) As one of the most likely candidates of the neural centers for the DLR, the valvula cerebelli, which receives its visual information not through the optic tectum but through the pretectal areas, is confirmed by the brain lesion experiments.

Neuroanatomical substrate for the dorsal light response. II: Effects of kainic acid-induced lesions of the valvula cerebelli on the goldfish dorsal light response

The dorsal light response (DLR) to the continuously rotating light source was investigated in goldfish that had lesioned the valvula cerebelli. The body inclination was observed and analyzed for every 10 degrees of light rotation. The effects of selective lesions of the medial and lateral valvula cerebelli on the DLR were compared. After the lesion of the medial valvula cerebelli, the fish responded to the rotating light in the similar pattern to that seen preoperatively. However, after the unilateral lesion of the lateral valvula cerebelli, the fish did not respond to light from the side contralateral to the lesion, as if the fish had been unilaterally blindfolded. The lesion induced by kainic acid of the rostral and caudal part of the lateral valvula cerebelli differently influenced on the DLR. The DLR was impaired only after the caudal part of the lateral valvula cerebelli was lesioned by kainic acid. These findings suggest that the lateral valvula cerebelli in goldfish mediate the induction of the visually guided aspects of the DLR.

Space experiment using large-sized fish: In case of carp in Spacelab-J mission

Two carp of 26 cm in size, intact and otolith-removed (LB), were flown on the Spacelab-J for 8 days in September 12-20, 1992. Light-dependent reaction to alternating direction of illumination was recorded for 10 min twice a day together with the cerebellar EEG activity, on 2 days before the launch, during the flight and for 4 days after the landing, in same fish chamber. Reproducing the video image, it was revealed that both carp were healthy during the mission, but the LB fish was almost immobilized from the 3rd test session (48 hours in flight) by tight twisting of the EEG cable. Both fish after landing tended to stay still on the bottom of the fish chamber. Findings that the body weight reduced remarkably in both fish and that nitrite and nitrate levels of the fish water were usually high, suggested that the fish metabolism might have been enhanced during the flight.

Electroencephalographic analysis of activities in the optic tectum of unrestrained carp

Electroencephalographic activity of the optic tectum in unrestrained resting carp was classified into three dominant frequency ranges of 4-7, 8-13 and 14-25 HZ, peaking at 6, 10, and 17 and 22 HZ, respectively, under power spectral analysis. All these activities were suppressed in the dark. The suppression was most prominent in the 8-13 HZ waves, but less so in the 4-7 HZ. However, while the fish was swimming actively, the 4-7 HZ spectrum increased in power and no actual increase could be observed for the higher frequency waves. Thus, it is probable that the 4-7 HZ waves involve rich motor activity, while the 8-13 HZ waves are mainly visual. The tectal activity was enhanced in the hypoxic state, with an increase in all frequency components, and enhanced further after loading, each of which corresponds to the hypoxic and post-hypoxic activations described for the mammalian cortex. A component analysis for the photically evoked response in restrained carp supported the four peaks of fundamental tectal rhythm being obtained as the spontaneous activity. In addition, each component belonging to the lower two peaks could be decomposed into the others, suggesting that the 17 and 22 HZ waves might be elementary for the tectal activity.

Telescience testbed experiments for biomedical studies: fertilization potential recording of amphibian eggs using tele-manipulation under stereoscopic vision.

The telescience testbed experiments were carried out to test and investigate the tele-manipulation techniques in the intracellular potential recording of amphibian eggs. Implementation of telescience testbed was set up in the two separated laboratories of the Tsukuba Space center of NASDA, which were connected by tele-communication links. Manipulators respective for a microelectrode and a sample stage of microscope were moved by computers, of which command signals were transmitted from a computer in a remote control room. The computer in the control room was operated by an investigator (PI) who controlled the movement of each manipulator remotely. A stereoscopic vision of the microscope image were prepared by using a head mounted display (HMD) and were indispensable to the intracellular single cell recording. The fertilization potential of amphibian eggs was successfully obtained through the remote operating system.

Intracellular recordings from Xenopus oocyte by using telescience technique

Abstract By using telescience techniques, we developed and tested a system for remotely conducting intracellular recordings, an indispensable method for biomedical studies. As a representative experiment we chose to study on the adenosine-induced responses of Xenopus oocyte. Experimental materials were placed in a room simulating an orbital laboratory. The experiment was controlled and monitored by a principal investigator (PI) from another room simulating a ground control room. The two rooms were connected by a telecommunication simulator that could impose the communication delay and limit the data transfer rate. The PI inserted one or two microelectrodes into an oocyte using remote control on the micro-manipulators and on the platform of microscope with stereoscopic pictures observed through a head mounted display. By inserting one electrode, we could successfully study the adenosine responses at various concentrations. Then, we tried to perform the “voltage clamp” recordings by inserting two electrodes into one oocyte. Though insertion of two electrodes was troublesome, we finally succeeded the voltage clamp recordings. Result indicate the usefulness of the telescience for conducting intracellular recordings in space.