Chitin/Chitosan-Active Enzymes Involved in Plant-Microbe Interactions.

Plant chitinase hydrolyzing ß-1,4-glycosidic linkages of chitin are major enzymes acting in plant-microbe interactions and are involved in self-defense against fungal pathogens. Chitosanases from soil bacteria are also involved in plant defense by hydrolyzing chitosan components of the fungal cell wall. The crystal structures of these enzymes in complex with their substrates have been solved, and the mechanisms of substrate binding were elucidated at the atomic level. These findings enabled us to speculate on the enzyme targets under physiological conditions, leading us to define the physiological roles of the enzymes. The structures and functions of chitin/chitosan-binding modules appended to modular chitinases/chitosanases were analyzed by NMR and isothermal titration calorimetry (ITC), and the enzymes were found to form an appropriate modular organization to fulfill their roles in plant-microbe interactions.

Effects of forced movements on learning: Findings from a choice reaction time task in rats.

To investigate how motor sensation facilitates learning, we used a sensory-motor association task to determine whether the sensation induced by forced movements contributes to performance improvements in rats. The rats were trained to respond to a tactile stimulus (an air puff) by releasing a lever pressed by the stimulated (compatible condition) or nonstimulated (incompatible condition) forepaw. When error rates fell below 15%, the compatibility condition was changed (reversal learning). An error trial was followed by a lever activation trial in which a lever on the correct or the incorrect response side was automatically elevated at a preset time of 120, 220, 320, or 420 ms after tactile stimulation. This lever activation induced forepaw movement similar to that in a voluntary lever release response, and also induced body movement that occasionally caused elevation of the other forepaw. The effects of lever activation may have produced a sensation similar to that of voluntary lever release by the forepaw on the nonactivated lever. We found that the performance improvement rate was increased by the lever activation procedure on the incorrect response side (i.e., with the nonactivated lever on the correct response side). Furthermore, the performance improvement rate changed depending on the timing of lever activation: Facilitative effects were largest with lever activation on the incorrect response side at 320 ms after tactile stimulation, whereas hindering effects were largest for lever activation on the correct response side at 220 ms after tactile stimulation. These findings suggest that forced movements, which provide tactile and proprioceptive stimulation, affect sensory-motor associative learning in a time-dependent manner.

Tracking spike-amplitude changes to improve the quality of multineuronal data analysis.

During extracellular electrophysiological recording experiments, the waveform of neuronal spikes recorded from a single neuron often changes. These spike-waveform changes make single-neuron identification difficult, particularly when the activities of multiple neurons are simultaneously recorded with a multichannel microelectrode, such as a tetrode or a heptode. We have developed a tracking method of individual neurons despite their changing spike amplitudes. The method is based on a bottom-up hierarchical clustering algorithm that tracks each neuron's spike cluster during temporally overlapping clustering periods. We evaluated this method by comparing spike sorting with and without cluster tracking of an identical series of multineuronal spikes recorded from monkey area-TE neurons responding to a set of visual stimuli. According to Shannon's information theory, errors in spike-amplitude tracking reduce the expected value of the amount of information about a stimulus set that is transferred by the spike train of a cluster. In this study, cluster tracking significantly increased the expected value of the amount of information transferred by a spike train (p < 0.01). Additionally, the stability of the stimulus preference and that of the cross-correlation between clusters improved significantly (p < 0.000001). We conclude that cluster tracking improves the quality of multineuronal data analysis.

A choice reaction-time task in the rat: a new model using air-puff stimuli and lever-release responses.

We have developed a two-lever choice reaction-time (RT) task to investigate the behavioral and neural mechanisms of stimulus-response compatibility in rats. In the task, the rat pressed two levers with its forepaws during the preparation period of each trial, and then quickly responded to an air-puff stimulus on its left or right forepaw by releasing the lever on the same side (compatible condition) or the opposite side (incompatible condition) of the stimulus. Twenty rats successfully learned the task in both the compatible and incompatible conditions. Two stimulus-response compatibility effects were observed: the RT was shorter and the error rate was lower in the compatible condition than in the incompatible condition. The trial sequence also affected the results and a speed-accuracy tradeoff was observed. These results are consistent with those reported for human RT tasks. Furthermore, a lesion in the forepaw-sensorimotor cortex caused increases in the RTs for stimulus detection and/or response movement with the contralateral forepaw, suggesting that the task was mediated by this brain area. We conclude that this instrumental task for rats can be regarded as a model for human RT tasks and can be used to investigate the neural basis of the compatibility effects.

Hyperexcitability-associated rapid plasticity after a focal cerebral ischemia.

BACKGROUND AND PURPOSE: This article addresses how neuroplastic changes are initiated after an ischemic stroke. METHODS: A focal cerebral ischemia was photochemically induced on the primary somatosensory cortex of rats, and in vivo electrophysiological recordings were performed on the peri-infarct cortex before and from 1 to 6 hours after the infarction. RESULTS: Paired-pulse analysis of evoked field potentials to peripheral electrical stimuli showed statistically significant neuronal hyperexcitability that was associated with rapid expansion of receptive fields (146.1% at 1 hour and 553.6% at 6 hours) as early as 1 hour after the infarction (P<0.05). Current source density analysis revealed increased current sinks in cortical layer II/III. CONCLUSIONS: Our electrophysiological results showed, for the first time to our knowledge, rapid plastic changes in the peri-infarct cortex during the hyperacute stage of an ischemic stroke. Manipulation of this rapid plasticity may affect subsequent plastic changes.

Sensitization of glutamate release and N-methyl-D-aspartate receptor response by transient dopamine pretreatment in prefrontal cortex of rats.

We studied biochemically the effect of transient dopamine pretreatment on the regulation of glutamate transmission in medial prefrontal cortex of rats in vivo and in vitro. Aversive stimuli transiently increased the glutamate concentration and its repetition reduced the response in the medial prefrontal microdialysate of freely moving rats. The rate of habituation obeyed linear regression. The medial prefrontal intracellular calcium response to repetitive N-methyl-D-aspartate perfusion showed linearly regressive desensitization in fluorescence videomicroscopy of the fura-2 stained slice in vitro. Transient dopamine treatment 10-20 min prior to repetition restored both decreased responses in a linearly regressive manner, also indicating that their decrease was not due to fatigue. These findings suggest that the effect of transient dopamine pretreatment continues redundantly to sensitize/resensitize subsequent pre- and postsynaptic prefrontal glutamate transmission in an orderly manner.

Multineuronal vectorization is more efficient than time-segmental vectorization for information extraction from neuronal activities in the inferior temporal cortex.

In order for patients with disabilities to control assistive devices with their own neural activity, multineuronal spike trains must be efficiently decoded because only limited computational resources can be used to generate prosthetic control signals in portable real-time applications. In this study, we compare the abilities of two vectorizing procedures (multineuronal and time-segmental) to extract information from spike trains during the same total neuron-seconds. In the multineuronal vectorizing procedure, we defined a response vector whose components represented the spike counts of one to five neurons. In the time-segmental vectorizing procedure, a response vector consisted of components representing a neuron's spike counts for one to five time-segment(s) of a response period of 1 s. Spike trains were recorded from neurons in the inferior temporal cortex of monkeys presented with visual stimuli. We examined whether the amount of information of the visual stimuli carried by these neurons differed between the two vectorizing procedures. The amount of information calculated with the multineuronal vectorizing procedure, but not the time-segmental vectorizing procedure, significantly increased with the dimensions of the response vector. We conclude that the multineuronal vectorizing procedure is superior to the time-segmental vectorizing procedure in efficiently extracting information from neuronal signals.

Epileptiform discharges and neuronal plasticity in the acute peri-infarct cortex of rats.

While the peri-infarct cortex is thought to be responsible for functional recovery, the site is also a strong candidate for post-stroke seizures. Since it is crucial to identify the conditions when the site is changed with such beneficial or detrimental results, the peri-infarct changes were investigated before and just after inducing a focal infarct on rat cortex. The receptive fields in the peri-infarct cortex began to increase a few hours after the infarct, and reached a statistical significance at 6 hours (Dunnett post hoc tests; p<0.05). In temporal association with these changes, EEG in the peri-infarct cortex showed epileptiform activities containing large-amplitude spike-and-wave discharges. The gross amplitude, peak-to-peak amplitude and burst frequency showed statistically significant increases within 4 hours, in comparison to those of the controls (Dunnett post hoc tests; p<0.05). FFT power spectrum analyses showed a distinct increase in approximately 25 Hz frequency bands in the post-stroke groups. The homogeneous area of the contralateral hemisphere in the infarct group, in contrast, did not show such plastic or excitability changes. This study demonstrated, for the first time, that the peri-infarct cortex acquires the characteristics of potential epileptogenesis and functional recovery within hours of a stroke.

Color Doppler sonographic findings in splenic hamartoma.

We present the gray-scale and color Doppler sonographic findings in a case of a splenic hamartoma in a 40-year-old man. Gray-scale sonograms showed a 2 x 2 cm, hypoechoic splenic mass that was homogeneous without evidence of cystic change or calcification. Color Doppler sonograms showed multiple radial blood-flow signals inside the mass, and spectral analysis confirmed arterial and venous flow. Arteriograms showed multiple small, hypervascular masses with fine tumor vessels and tumor stains within the spleen. Histologic analysis following a splenectomy showed dilated vessels and congestion consistent with the color Doppler sonographic findings.