Hirotaka Satake

Mode of [14C] 2-deoxy-D-glucose uptake into retrosplenial cortex and other memory-related structures of the monkey during a delayed response

Physiological studies on the monkey retrosplenial (RS) cortex have been few, and its functional role remains to be investigated. In the present study, activity of the RS cortex was investigated using radioactive 2-DG while the monkey was performing a visual tracking task with a delay (a delayed-response task) for 45 minutes. A remarkable increase in 2-DG uptake was observed equally in the left as well as in the right RS cortex. The anterior nucleus of the thalamus also showed increased 2-DG uptake. In addition, other memory-related structures (prefrontal cortex, dorsomedial nucleus of the thalamus, amygdala and hippocampus) showed a similar increase in 2-DG uptake compared to control monkeys, though their respective absolute values were different from one another. Since the RS cortex receives afferents from the anterior nucleus of the thalamus, which is one of the main nuclei of the Papez circuit, it is assumed that the RS cortex is important in memory function. Therefore, the remarkable increase in 2-DG uptake in the present study could reflect some aspects of memory or learning processes required to perform the delayed response.

A strong constant magnetic field affects muscle tension development in bullfrog neuromuscular preparations.

Effects of a constant magnetic field (CMF) of 0.65 T on muscle tension over 9 h were studied in the neuromuscular preparation of the bullfrog sartorius muscle. Tension was developed every 30 min by stimulation of the sciatic nerve (nerve stimulation) or of the sartorius muscle itself (muscle stimulation). In sciatic nerve stimulation, tension decreased rapidly for the first 3-4 h at a similar rate in both test (exposed to CMF) and control muscles. However, the rate of decrease became smaller and almost leveled off after 3-4 h in the test muscles, whereas tension continued to decrease monotonically in control muscles. The slope of the decrease for these later periods was significantly different between the test and the control conditions. Accordingly, tension was larger in test than in control muscles. In muscle stimulation, tension decreased monotonically from the start of experiments in control muscles, while tension in test muscles maintained their initial values for almost 3 h. Thereafter they started to decrease with a similar rate to the control. Hence, tension was always larger in test than in control muscles. A similar pattern of temporal change was observed for the rate of rise of the maximum tension for nerve or muscle stimulation. However, a significant difference was detected only in the case of muscle stimulation. The present results showed that a strong CMF of 0.65 T had biological effects on tension development of the bullfrog sartorius muscle by stimulation of the sciatic nerve as well as by stimulation of muscle itself. The presence of a small AC magnetic field component leaves open the possibility of an AC, rather than a CMF effect.

The vestibulo-autonomic function viewed from cardiac responses in centrifuged monkeys.

Vestibulo-autonomic function was examined as the change of cardiac parameters (HR and SV) to +Gz and -Gx accelerations for 1,000 s in intact and bilaterally labyrinthectomized monkeys. Under anesthetized conditions, HR and SV slightly changed to +2Gz acceleration in both monkeys. In +3Gz acceleration, changes were remarkable and significant. HR increased in intact monkeys by as much as 30% while it decreased in labyrinthectomized monkeys, although a moderate initial increase was observed. SV decreased in intact as well as labyrinthectomized monkeys, but the reduction was significant and larger for the latter. This implies that vestibular input could modulate autonomic function. For larger +Gz, both intact and labyrinthectomized monkeys could tolerate no more due to severe cardiac dysfunction (rapid HR and SV decrease) which appeared soon after +4Gz application. In case of -Gx application, HR increased, although slightly, in proportion to the amplitude of applied -Gx in both monkeys, with less changes in labyrinthectomized ones. SV hardly changed in smaller -Gx, while it increased in larger -Gx. Difference between intact and labyrinthectomized monkeys was observed in -6Gx and -8Gx conditions.

Neuronal responses to vestibular and callosal stimulation in the anterior suprasylvian gyrus of the cat

Neuronal responses to electrical stimulation at the horizontal ampulla (HA), vestibular nerve (at the windows) and corpus callosum (CC) were investigated in neurons in the anterior suprasylvian gyrus of the cat. The field potentials to HA stimulation had short latency: 2.9 +/- 0.3 (mean +/- SD) ms from the stimulus to the onset and 5.6 +/- 1.9 ms to the peak. The focus of the evoked potentials was located in the anterior suprasylvian (ASS) gyrus or near the ASS sulcus. HA stimulation activated 6 neurons out of 674 examined, with the mean latency of 4.3 +/- 1.1 ms. Of these 6, four neurons also responded to window stimulation. Fifty-six neurons responded to window stimulation with the mean latency of 6.1 +/- 2.4 ms. The mean latency for CC stimulation was 1.9 +/- 0.9 ms (n = 76). Four neurons responded to CC stimulation antidromically (mean = 0.9 +/- 0.3 ms) and one of them also responded orthodromically. The convergence of CC inputs in relation to HA or window stimulation was examined. One (17%) of the 6 HA-activated cells responded to CC stimulation, compared with 8 (14%) of the 56 neurons activated by window stimulation. The other 612 neurons did not respond to either HA or window stimulation, and 80 (13%) of the 612 responded to CC stimulation. Therefore, it is concluded that neurons in the ASS gyrus received callosal input equally irrespective of the presence or absence of responses to ampulla or window stimulation. WGA-HRP was injected in the ASS gyrus to identify the passing callosal fibers in the CC. Fibers from the ASS area passed at the rostral third of the CC. The present results indicate that the ASS area received vestibular projection with short latency, but responses of this projection did not seem to be very strong, at least from the present unit study, to HA stimulation. Discussion was made on the poor neuronal responses to electrical HA stimulation in comparison with previous studies. Also consideration was made on neuronal activity to CC stimulation.

Cardiovascular responses to KC-135 hyper-gravity.

The present study was designed with two intentions; Are the effects of angular velocity detectable in the cardiovascular responses during the hyper-G? Another is object to examine how the otolith signal could modify the cardiovascular responses provoked by the exposure to the hyper-G. NASA/KC-135 hyper-gravity flight was used to generate high gravito-inertial forces to exclude a possible effect of angular velocity. Six healthy subjects was indicated to make dorsal flexion of the neck to reduce the otolith input. An exposure to +l.8Gz stress resulted in a remarkable increase of systolic and diastolic blood pressure, thereby pulse pressure became a little bit narrower. R-R interval revealed a tachycardia during the hyper-G except one subject. The present experiment bore the similar cardiovascular responses as those observed in the previous studies with a short rotating radius, suggesting that almost no effect of angular velocity acts on their responses. A weaker otolith input could possibly work on them. However a systematical observation can not recognize among the subjects for the vestibular effect on the cardiovascular responses. This fact of vestibular qualification leads us to speculate that it would depend on the subjects or other factors.

Role of the Medial Limbic System in the Memory Process: A Hypothesis Based on a Radioactive 2-Deoxyglucose Study

Alzheimer or Parkinson patients suffer from some memory deficits in the later course of their illness. It is also reported that MPTP-treated monkeys showed cognitive disturbances without Parkinsonian motor deficits.1 Therefore, it would be very helpful to determine the activity of memory-related structures in the normal brain for the development of more appropriate therapeutic or clinical treatments. In the present study, the 2-deoxy-d-glucose (2-DG) method2 was employed to reveal active sites in the brain while the monkey was performing a delayed response. This paradigm is known to test for short-term memory. The results have been already published in final form.3,4