Jiro Okada

The role of antennal hair plates in object-guided tactile orientation of the cockroach (Periplaneta americana).

Abstract. The searching behavior of blinded cockroaches was examined under unrestrained conditions, in an arena, and on a treadmill. When cockroaches searching in a circular arena touched a stationary object (metal pole) with their antennae, they frequently approached the object more closely, and then climbed up it. Similar orientation behavior was observed in tethered animals in open loop conditions, walking on a Styrofoam ball. In these restrained cockroaches, a single antenna sufficed to distinguish the angular positions of an object, in the horizontal plane (0°, 45°, and 90°). A group of mechanosensitive hairs on the basal segment of the antenna (scapal hair plate) appears to play a major role in antennal object detection in the horizontal plane, as gauged by shaving off these scapal hair plates. In unrestrained cockroaches, shaving the scapal hair plate increased the time needed to approach an object. Under tethered conditions, the ability to turn towards and to establish antennal contact with a test object was significantly impaired.

Multineuronal spike classification based on multisite electrode recording, whole-waveform analysis, and hierarchical clustering

We proposed here a method of multineuronal spike classification based on multisite electrode recording, whole-waveform analysis, and hierarchical clustering for studying correlated activities of adjacent neurons in nervous systems. Multineuronal spikes were recorded with a multisite electrode placed in the hippocampal pyramidal cell layer of anesthetized rats. If the impedance of each electrode site is relatively low and the distance between electrode sites is sufficiently small, a spike generated by a neuron is simultaneously recorded at multielectrode sites with different amplitudes. The covariance between the spike waveform at each electrode site and a template was calculated as a damping factor due to the volume conduction of the spike from the neuron to the electrode site. Calculated damping factors were vectorized and analyzed by hierarchical clustering using a multidimensional statistical test. Since a cluster of damping vectors was shown to correspond to an antidromically identified neuron, spikes of different neurons are classified by referring to the distributions of damping vectors. Errors in damping vector calculation due to partially overlapping spikes were minimized by successively subtracting preceding spikes from raw data. Clustering errors due to complex spike bursts (i,e., spikes with variable amplitudes) were avoided by detecting such bursts and then using only the first spike of a burst for clustering. These special procedures produced better cluster separation than conventional methods, and enabled multiple neuronal spikes to be classified automatically. Waveforms of classified spikes were well superimposed. We concluded that this method is particularly useful for separating the activities of adjacent neurons that fire partially overlapping spikes and/or complex spike bursts.

Antennal and locomotor responses to attractive and aversive odors in the searching cockroach

The behavioral responses to attractive and aversive odors were examined in blinded adult male cockroaches under tethered-walking conditions. A sex pheromone-like stimulant derived from adult virgin females and artificially synthesized limonene were used as attractive and aversive odor sources, respectively. When a searching animal was stimulated with the attractive female-derived odor, the horizontal deflections of both the antennae were increased, and in most cases the vertical antennal positions were shifted downward. The stimulation also significantly decreased the walking speed of the animal. These behavioral changes imply a careful search in the immediate surroundings. The aftereffect of the sex pheromone was more pronounced on locomotion than on antennal movement. On the other hand, stimulation with the aversive odor (limonene) tended to suppress active antennal movement, and also increased the walking speed. Immediately after the withdrawal of the aversive odor, the active movement of the antennae was resumed, and the walking speed rapidly decreased to a level approximately the same as that of the control period. These results indicate that the responses to the qualitatively opposite types of odor are reciprocal to each other with regard to both antennal movement and locomotion.

Intracellular Responses of Antennal Chordotonal Sensilla of the American Cockroach

The responses of mechanoreceptor neurons in the antennal chordotonal organ have been examined in cockroaches by intracellular recording methods. The chordotonal organ was mechanically stimulated by sinusoidal movement of the flagellum. Stimulus frequencies were varied between 0.5 and 150 Hz. Receptor neurons responded with spike discharges to mechanical stimulation, and were classed into two groups from plots of their average spike frequencies against stimulus frequency. Neurons in one group responded to stimulation over a wide frequency range (from 0.5 to 150 Hz), whereas those in a second group were tuned to higher frequency stimuli. The peak stimulus frequency at which receptor neurons showed maximum responses differed from cell to cell. Some had a peak response at a stimulus frequency given in the present study (from 0.5 to 150 Hz), whereas others were assumed to have peak responses beyond the highest stimulus frequency examined. The timing for the initiation of spikes or of a burst of spikes plotted against each stimulus cycle revealed that spike generation was phase-locked in most cells. Some cells showed phase-independent discharges to stimulation at lower frequency, but increasing stimulus frequencies spike initiation began to assemble at a given phase of the stimulus cycle. The response patterns observed are discussed in relation to the primary process of mechanoreception of the chordotonal organ.

Antennal motor activity induced by pilocarpine in the American cockroach.

The antennal motor system is activated by the muscarinic agonist pilocarpine in the American cockroach Periplaneta americana, and its output patterns were examined both in restrained intact animals and in isolated CNS preparations. The three-dimensional antennal movements induced by the hemocoelic drug injection were analyzed in in vivo preparations. Pilocarpine effectively induced prolonged rhythmic movements of both antennae. The antennae tended to describe a spatially patterned trajectory, forming loops or the symbol of infinity (∞). Such spatial regularity is comparable to that during spontaneous tethered-walking. Rhythmic bursting activities of the antennal motor nerves in in vitro preparations were also elicited by bath application of pilocarpine. Cross-correlation analyses of the bursting spike activities revealed significant couplings among certain motor units, implying the spatial regularity of the antennal trajectory. The pilocarpine-induced rhythmic activity of antennal motor nerves was effectively suppressed by the muscarinic antagonist atropine. These results indicate that the activation of the antennal motor system is mediated by muscarinic receptors.

Classifying neuronal spikes from multiunit recording by using a multisite electrode

A method of classifying neuronal spikes was proposed and achieved by multiunit recording using a multisite electrode and by considering spatial damping vectors. The method consists of three procedures, i.e., separation of overlapping spikes, treatment of burst spikes, and clustering by a multi-dimensional statistical test. The first and second procedures clarify the border between clusters and the last procedure validates the classification statistically. By using this method, multiple neuronal spikes were automatically classified and the waveforms of the spikes in each class were well superimposed. The authors concluded that this method is superior to other methods of classifying neuronal spikes.

Directional cross-correlation analysis of neuronal burst firing

Elucidates the characteristics of the directional cross-correlation method for analyzing point process data, and applies it to the analysis of synchronous neuronal spike trains. As a result of analyzing some example data, we discovered that a spike of one neuron was remarkably synchronized with the last spike of a burst generated by another neuron. Since a directional cross-correlation coefficient indicates the probability of encountering any spike of a neuron as a function of time before or after a spike of another neuron, it is not affected by the firing rate difference between these neurons. We conclude that this method is efficient for detecting synchronous firing between neurons having different firing rates.

1920 A multielectrode analysis of barrel cortex neuronal responses to vibrissal stimulation

The purpose of this study is to evaluate analgetic effects of OCBZ, a keto derivative of Carbamazepine. To evoke nociceptive sensation we gave electrical stimulation (0.2-0.7 mA) to maxillary canine tooth pulp (CTP) in anesthetized (dialurethane), spontaneously breathing cats. The CTP-evoked compound potentials, recorded from caudal part of trigeminal spinal tract nucleus were composed of two main components, namely a negative component (N2, conduction velocity; -6rn/s) and a positive component (P3, c.v.; -2rn/s). Since OCBZ is not water soluble, it was dissolved in polyethylene glycol #/400 (PEG400). Three graded doses (1-3-lOmg/kg) were given intravenously in different animals, and statistical comparisons were made with the control obtained after injection of PEG400. The P3 component showed a dose-depeqdent inhibition, and was significantly (~0.05) suppressed by lOmg/kg of OCBZ; the maximum analgetic effect occurred rapidly within 10 minutes after the treatment, and the significant suppression lasted for more than two hours.

2804 A multielectrode analysis of hippocampal multineuronal actvities

Long-term slice culture of adult neocortex is difficult in general. However, we have shown that if the slice is made thin enough, then part of neurons can survive over one week. On the other hand, Frey et. al. have reported that hippocampal slice can be maintained if frequent medium exchange is made under 90% 02 atmosphere. Thus we have checked the effect of partial oxygen pressure on neuronal survival using 02 incubator. Adult rats (4-6week old)were perfused aseptically through the heart with saccharose Ringer solution. 150 microns-thick slice was then made by a slicer, incubated in an interface type reservoir for an hour to show normal electrical activities. Then, slices were transferred to standard culture medium in 02 incubator. Extracellular responses from slices incubated in culture medium was disappeared within 4 hours even in 90%02, while those obtained from slices in Ringer solution continued to be narmal. Thus we further investigated effect of continuous perfusion of culture medium on neuronal survival.

Classifying neuronal spikes from multiunit recording by using a triode

A method of classifying neuronal spikes was proposed and realized by multichannel multiunit recording with a triode and considering spatial damping vectors. Each element of a damping vector is the covariance between a template and a spike waveform observed by each channel. In the plot of damping vectors in 3-D space, the distribution showed some clusters. Assuming that a cluster corresponds to a neuron, the spikes were classified by referring to the 3-D distribution and the waveforms of the spikes in each class were well superimposed. The authors discussed the stability of the damping vectors and concluded that this method is promising for precise classification of neuronal spikes.