Akifumi Iwama

Properties of Wave Propagation in the Oscillatory Neural Network in Limax marginatus

Abstract The olfactory center (procerebral lobe; PC lobe) of the terrestrial slug, Limax marginatus, shows oscillatory behavior with a frequency of about 1 Hz and an activity wave that propagates from the apical to distal regions of the PC surface. To study the dynamic properties of this oscillatory network, serotonin, glutamate and acetylcholine were applied to the PC lobe. Serotonin and acetylcholine increased the frequency of PC oscillation and decreased the velocity of wave propagation. The effect of serotonin on the frequency was long-lasting and there was a delay before it caused a decrease in the wave propagation velocity. In contrast, the effect of acetylcholine on the frequency was phasic, and no delay was observed. Glutamate first decreased, then increased, the frequency. However, specific changes in the wave propagation velocity were not observed. From these experimental results, it is suggested that the oscillatory neural network of PC lobe has a potential to represent odor information as a series of spatially and temporally distributed ensembles of coherent firing neurons.

Contributions of Superior and Inferior Tentacles to Learned Food-Avoidance Behavior in Limax marginatus

Abstract We investigated learned food-avoidance behavior of conditioned slugs in detail, and examined the effect of removing the inferior or superior tentacles (ITs and STs) on the avoidance behavior. The conditioning procedure significantly lowered the preference level of slugs to the conditioned odor, and the decrease of the preference was maintained for at least 48 hr. Video analysis experiments showed that change in the crawling direction during an aversion response occurred consistently accompanied by an average of 1.2 head swings. The first head swing was usually observed within 1 cm from the conditioned odor. Removal of the ITs after conditioning reversed the trend towards a lowered preference level. On the other hand, removal of the STs did not change the level. These results suggest that the IT inputs are needed to induce conditioned behavior. The contribution of STs to the conditioning behavior is indicated by the significant increase in the average number of head swings (3.6 swings) in a trial after their removal. In some trials, the slugs lacking STs avoided the odor source after crossing it. These observations indicate that removal of STs decreases the orientation ability of conditioned slugs.

Development of Measurement and Assessment Technology for Evaluation of Bone Regeneration

Since 2001, we have clinically utilized human bone marrow-derived mesenchymal stem cells (MSCs) for bone regeneration. The osteogenic ability of MSCs has been assessed by measurement of alkaline phosphatase activity and calcium deposition. As for the detection of in vitro calcium deposition, we have established the method using calcein, which is a calcium-binding fluorescence material. Using this fluorescence material, we could observe the calcium deposition and then estimate the value of calcium deposition. In this report, we cultured rat MSCs on culture plate as well as transparent β-TCP, and calcium deposition was visualized and quantitated using an image analyzer. After 2 weeks differentiation of rat MSCs to osteoblasts, calcium deposition on β-TCP was observed as a signal of calcium-binding fluorescence. This fluorescence signal was also quantitated with an image analyzer.

Rhythm, memory and coding in slug olfactory system.

Early phase of slugs olfactory information processing occurs on an oscillatory network showing rhythmic activities. We found that the network consists of three different oscillator systems; tentacle, terminal mass and cell layer oscillators. The tentacle oscillators changed the oscillation amplitude during odor presentation. The nerve cutting experiment revealed that the neural activity in the tentacle ganglion modulates the coherency between the terminal and cell mass oscillators. Furthermore, it was revealed that the change of coherency between the cell mass and the terminal mass oscillators also modulates the spatio-temporal oscillatory behavior of cell layer oscillator network. It was shown that aversively learned odors applied to the inferior tentacle changed the spatio-temporal oscillatory behavior of cell layer oscillator network. Based on these facts, we speculated that learned odors changed the coherency between the cell mass and the terminal mass oscillators and induced changes in spatiotemporal oscillatory behavior of the cell mass oscillator network.

1909 Models of slug's olfactory center with two-layered nonlinear oscillators

YOICHI OGAWA Single unit activities from the olfactory bulb were recorded during the period that the rat was sniffing. Spectral analysis by Walsh transform was applied to the spike train of unit. In addition, the inter spike intervals were measured to estimate post-spike excitability and serial correlations. The modulation of firing due to respiration cycles was observed in only 4 units (10%). Thirty-three units (82.5%) displayed low-frequency fluctuation in the spectrum of spike train. These units also showed recurrent facilitation in post spike excitability. Furthermore, the serial correlation of the first order was significantly positive in 36 units (90%). The degree of fluctuation was significantly correlated with the amplitude of recurrent facilitation and with the serial correlation. These results suggest that recurrent facilitation cause fluctuation in firing.

1910 A dual oscillator system in the procerebral lobe of Limax brain

A. Iwama, A. Yamada, T. Kimura, E. Kono, T. Sekiguchi Oscillatory activities were studied by recordings of field potential at multiple sites in an olfactory center, the procerebral lobe, of the terrestrial slug Limaz marginatus brain. The cell mass of the procerebral lobe shows an about 1 Hz oscillation in its local fieldpotential. Multiple site-recordings showed that the terminal mass of the lobe also exhibited an oscillation synchronized with the cell mass oscillation, and that the terminal mass oscillation was decoupled from the cell mass oscillation by an application of serotonin or by a taste stimulation with quinidine sulfate to the lip. These results suggest that the terminal mass oscillators differ from the cell mass oscillators and such a novel oscillator system is localized in the terminal mass. Both types of oscillations were also modulated by an odor stimulation to the olfactory epithelium. Therefore, it is likely that a dual oscillator system in the procerebral lobe is involved in processing of olfactory information in slugs.