Number Of Active Zones Research Articles

Two structural adaptations for regulating transmitter release at lobster neuromuscular synapses

The distal accessory flexor muscle (DAFM) in the lobster (Homarus americanus) walking leg consists of 5 muscle fiber bundles. All five bundles, one proximal, one distal, and 3 medial, are innervated by one excitatory and one inhibitory motor neuron. Both neurons release more transmitter on the distal bundle than on the proximal bundle. The aim of our studies was to investigate the structural basis of this differentiation. Thin sections cut at 50 microns intervals showed a similar number of excitatory synapses on the two bundles. Freeze-fracture views of excitatory synapses showed that synapse size, active zone number per synapse, and intramembrane particle density in the postsynaptic membrane are similar proximally and distally. Active zones at synapses on the distal bundle are larger and contain about 50% more large intramembrane particles, which are thought to include the voltage-gated Ca2+ channels that couple the action potential to transmitter release, than their counterparts on the most proximal bundle. This difference in channel number appears to produce a disproportionate increase in the probability of transmitter release sufficient to account for most of the proximal-distal disparity in the amplitude of the excitatory postsynaptic potential. In contrast, staining the inhibitor for antibodies to the inhibitory neurotransmitter, GABA, showed that it forms more varicosities on the distal bundle than on the proximal bundle. Because most of the synapses are located in the varicosities, differences in synapse number likely regulate the proximal-distal disparity in the amount of inhibitory transmitter released. Therefore, the regional differentiation in the amount of transmitter released in the DAFM appears to be based on two distinct mechanisms. In the inhibitor, transmitter release appears to be regulated differentially by differences in synapse number. In the excitor, transmitter release appears to be regulated differentially from a similar number of synapses by differences in active zone structure.

Presynaptic calcium concentration microdomains and transmitter release

n-Aequorin J, a luminescent protein which responds to calcium concentration changes in the order of several hundred micromoles, was injected into the preterminal fiber in the squid giant synapse. The activation of the presynaptic terminal leading to release of transmitter was accompanied by light emission at well-defined sites at the active zone in the presynaptic terminal. Location of these light emission sites was very much the same from one stimulus to the next, indicating that light emission was triggered by the inward calcium current occurring at specific and invariant locations. The distribution, size and number of these QEDs (quantum emission domains) coincides well with the location and number of active zones in the presynaptic terminal. The results imply that transmitter release is triggered by very well-localized calcium concentration changes that may be as high as several hundred micromoles.

Active zone organization and vesicle content scale with bouton size at a vertebrate central synapse

A common observation in studies of neuronal structure is that axons differ in the size of their synaptic boutons. The significance of this size variation is unclear, in part because we do not know how the size of synaptic boutons is related to their internal organization. The present study has addressed this issue by using three-dimensional reconstruction of serial thin sections to examine the ultrastructure of synaptic boutons that vary in size. Our observations are based on complete or near-complete reconstructions of 53 synaptic boutons contacting large neurons in the ventromedial gray matter of the upper cervical spinal cord (probable neck motor neurons). We characterized bouton size in terms of volume and total area of membrane apposed to the motor neuron surface (apposition area). Boutons vary in apposition area by a factor of 40, and there is a significant positive correlation between our two measures of bouton size. In addition, bouton size is systematically related to four ultrastructural variables: 1) total active zone area, 2) number of active zones, 3) individual active zone area, and 4) number of synaptic vesicles. The correlations between these variables and both of our measures of bouton size are positive and significant. These data suggest that bouton size may be an index of ultrastructural features that are thought to influence transmitter storage and release.

Structural plasticity at identified synapses during long-term memory in Aplysia.

We have used the gill- and siphon-withdrawal reflex of Aplysia californica to determine the morphological basis of the prolonged changes in synaptic effectiveness that underlie long-term habituation and sensitization. We have found that clear structural changes accompany behavioral modification and have demonstrated that these can be detected at the level of identified sensory neuron synapses, a critical site of plasticity for the short-term forms of both types of learning. These alterations occur at two different levels of synaptic organization and include (1) changes in focal regions of synaptic membrane specialization--the number, size and vesicle complement of sensory neuron active zones are larger in sensitized animals and smaller in habituated animals compared with controls--and (2) a parallel but more dramatic and global trend involving modulation of the total number of presynaptic varicosities per sensory neuron. Quantitative analysis of the time course over which these structural alterations occur during sensitization has further demonstrated that changes in the number of varicosities and active zones persist in parallel with the behavioral retention of the memory. This increase in the number of sensory neuron synapses during long-term sensitization in Aplysia is similar to changes in the number of synapses in the mammalian brain following various forms of environmental manipulations and learning (Greenough, 1984). Therefore learning may involve a form of neuronal growth across a broad segment of the animal kingdom, thereby suggesting a role for structural synaptic plasticity during long-term behavioral modifications.

Structural plasticity at crustacean neuromuscular synapses.

Crustacean motor axons innervate muscle fibers via a multiplicity of synaptic terminals which release small but variable amounts of transmitter. Differences in release performance appear to be correlated with the size of synaptic contacts and presynaptic dense bars (active zones). These structural parameters proliferate via sprouting from existing synaptic terminals and relocate to ever more distal sites during development and growth of an identified axon. Moreover, alterations in number of synaptic contacts and active zones occur in adults following stimulation or decentralization, demonstrating structural plasticity of crustacean neuromuscular synapses.

Time course of structural changes at identified sensory neuron synapses during long-term sensitization in Aplysia

We have used the gill- and siphon-withdrawal reflex of Aplysia californica to explore the morphological basis of the synaptic plasticity that underlies long-term sensitization. In earlier studies (Bailey and Chen, 1983, 1988a), we described 2 classes of structural changes at identified sensory neuron synapses that occur following long-term sensitization: (1) increases in the number, size, and vesicle complement of active zones and (2) an overall increase in the total number of synaptic varicosities per sensory neuron. In the present study, we have begun to examine which of these anatomical changes might be necessary for the maintenance of long-term sensitization by exploring the time course over which they occur and, in particular, their duration relative to the persistence of the memory assessed behaviorally. Toward this end we have quantitated changes in both the total number of varicosities and their active zone morphology in single HRP-labeled sensory neurons taken from long-term sensitized and control animals at different intervals (1-2 d, 1 week, and 3 weeks) following training. We have found that long-term sensitized animals examined within 48 hr after the completion of training demonstrate an increase in the total number of varicosities per sensory neuron as well as an increase in the incidence, size, and vesicle complement of their synaptic active zones compared with control animals. The increase in the number of varicosities and active zones persists unchanged for at least 1 week, and the increase in active zone number is only partially reversed at the end of 3 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Bouton ultrastructure and synaptic growth in a frog autonomic ganglion.

Postmetamorphic growth in the frog, Xenopus laevis, is accompanied by an increase both in the size of autonomic neurons in the heart and in the number of synaptic boutons that contact their surface. To determine whether the properties of individual boutons change as their number increases, serial-section electron microscopy was used to examine bouton ultrastructure at the end of metamorphosis and in the adult. The area of bouton contact, number of active zones per bouton, active zone size, percent of bouton area occupied by active zone, and vesicle density were examined. No differences were found between the two bouton populations for any of the parameters examined. These results support the hypothesis that boutons are structural units of synaptic growth, whereby the total area of synaptic contact increases through the addition of boutons without a change in their morphological properties.

Quantal transmission at Mauthner axon target synapses in the goldfish brainstem

The Mauthner axon contacts two principal neurons within the brainstem: the cranial relay neuron and the follower neuron. The cranial relay neuron is excited through axoaxonic contacts by both Mauthner axons, while the follower neuron is excited by the Mauthner axon ipsilateral to its soma and inhibited (through an interposed neuron) by the contralateral Mauthner axon. We have investigated the properties of these two Mauthner axon target synapses with simultaneous pre and postsynaptic recordings in order to determine if transmission can be described in terms of the quantal hypothesis and to determine what quantal parameters change with alterations in the frequency of Mauthner cell activation. Small depolarizing postsynaptic potentials, recorded in the cranial relay neurons, increase their frequency of occurrence when depolarizing currents are applied to the Mauthner axon, without changing their mean amplitude, indicating that they arise from the Mauthner axon terminal and represent quantal units of the evoked cranial relay neuron excitatory postsynaptic potentials. Similar small, spontaneous potentials can also be recorded from the follower neurons. Amplitude histograms of evoked postsynaptic potentials (in both cranial relay neurons and follower neurons) can be fit by binomial models based on the amplitude and variance of the spontaneous potentials, suggesting that the quantal hypothesis is a valid descriptor of synaptic transmission at these contacts. Quantal content (“ m”), the number of releasable quanta (“ n”), and the probability of release (“ p”) are relatively high for both the cranial relay neurons and follower neurons. Increasing the frequency of Mauthner axon stimulation results in a decrement in the postsynaptic potential amplitude in both target cells. There is no change in the amplitude of the small, spontaneous potentials (measured during the stimulation period) with stimulus frequency, indicating a decrease in quantal content, but not quantal size. The change in quantal content is explained in binomial terms by a decrease in the number of releasable quanta, but not the probability of release in both the cranial relay neurons and the follower neurons. These findings suggest that the supply of transmitter available to be released decreases with increasing stimulus frequency without affecting the nerve terminal's ability to release transmitter (at these stimulus frequencies). Synaptic vesicles, observed in clusters in the terminals at the ultrastructural level, may be a physical correlate of the binomial parameter (“ n”). It is predicted that the decrease in the binomial parameter (“ n”) with increasing frequency of stimulation is accompanied by a decrease in the number of active zones occupied by vesicles. The Mauthner axon-cranial relay neuron synapse shows a greater decrement in postsynaptic potential amplitude with increasing stimulus frequency than does the follower neuron postsynaptic potential. That the Mauthner cell-mediated startle reflex is activated infrequently, while the neuron interposed between the follower neuron and the Mauthner axon may be activated by other cells at a higher frequency, implies that these synapses are each adapted to the uses to which the organism employs them.

Morphological basis of short-term habituation in Aplysia

We have explored the morphological basis of the synaptic depression that underlies short-term habituation of the gill-withdrawal reflex in Aplysia by examining the fine structure of the presynaptic terminals of identified sensory neurons--a critical site of plasticity for the biochemical and biophysical changes that underlie this elementary form of learning. The structure of sensory neuron synapses from control (unstimulated) cells was compared with that of sensory neuron synapses from cells in which synaptic transmission had been depressed by repeated activation. We focused our analysis, as we had in an earlier study of long-term memory (Bailey and Chen, 1983), on the morphology of active zones at sensory neuron synapses. We found that both the incidence and size of serially reconstructed active zones were not changed in cells exposed to short-term habituation. This contrasts sharply with the reduction in both the frequency and surface area of sensory neuron active zones that accompanies long-term habituation, and suggests that modulation of active zone number and size may be an anatomical correlate that lies in the long-term domain. A quantitative analysis of the relationship between the active zone and nearby vesicle populations revealed a possible morphological substrate for the homosynaptic depression that underlies short-term habituation. Habituation leads to a depletion of synaptic vesicles immediately adjacent to the active zone. The ratio of this readily releasable pool of vesicles to the total population of vesicles associated with the active zone is 28% for control terminals, but only 11.5% for habituated terminals.(ABSTRACT TRUNCATED AT 250 WORDS)

A quantitative analysis of 2-D gels identifies proteins in which labeling is increased following long-term sensitization in Aplysia

Long-term memory for sensitization of the gill- and siphon-withdrawal reflex in Aplysia, produced by 4 days of training, is associated with increased synaptic efficacy of the connection between the sensory and motor neurons. This training is also accompanied by neuronal growth; there is an increase in the number of synaptic varicosities per sensory neuron and in the number of active zones. Such structural changes may be due to changes in the rates of synthesis of certain proteins. We have searched for proteins in which the rates of [ 35S]methionine labeling are altered during the maintenance phase of long-term memory for sensitization by using computer-assisted quantitative 2-D gel analysis. This method has allowed us to detect 4 proteins in which labeling is altered after 4 days of sensitization training.

Synaptic transmission mediated by single club endings on the goldfish Mauthner cell. II. Plasticity of excitatory postsynaptic potentials

Simultaneous pre- and postsynaptic intracellular recordings were used to analyze the properties of chemically mediated synaptic transmission between single club endings of eighth nerve afferents and the goldfish Mauthner (M-) cell lateral dendrite. The EPSPs exhibited pronounced facilitation when the presynaptic fiber fired high-frequency bursts of 2 or 3 impulses at intervals of 2-4 msec. The amplitudes of the EPSPs evoked by the second and third presynaptic impulses of a burst were, on average, 99 and 108% larger than that evoked by the first impulse. A cross-correlation analysis showed that the amplitudes of the control and facilitated EPSPs fluctuated independently, indicating that the facilitation was mediated by a presynaptic mechanism. This conclusion was supported by a comparison of the coefficient of variation for the control and facilitated EPSPs, on the basis of a binomial release model. In addition, the value of binomial n, the number of presynaptic release units, was not changed during facilitation. The origin of EPSP fluctuations was analyzed by examining the correlation between the amplitudes of EPSPs and those of the electrotonic coupling potentials associated with them. The absence of correlation between the 2 variables suggested that the fluctuations of EPSPs were not due to a variable presynaptic impulse invasion. The EPSP fluctuations were further analyzed by assuming that the facilitation was associated with an increase in the probability (p) of transmitter release and that the release process followed simple binomial statistics. The binomial variables thus calculated were n = 6-11, p = 0.29-0.44, and q = 31-61 microV, values comparable to the estimates for other CNS synapses. More importantly, these parameters provided satisfactory fits to the amplitude histograms of the control and facilitated EPSPs. The number of release units, n, was smaller than, but in a range similar to, the number of active zones identified in the freeze-fracture study of the club endings (Kohno and Noguchi, 1986). This correlation is consistent with the notion that active zones are the structural correlates of quantal release units. In the preceding paper, it was shown that impulses in a majority of club endings electrotonically coupled to the M-cell do not produce a detectable chemically mediated EPSP, although the contacts have the morphological correlates of chemical synapses. In an attempt to activate these "silent" connections, 2 approaches were used. First, the burst-firing paradigm, which could effectively facilitate EPSPs already present, failed to reveal any EPSPs at the silent junctions.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphological basis of long-term habituation and sensitization in Aplysia.

The morphological basis of the persistent synaptic plasticity that underlies long-term habituation and sensitization of the gill withdrawal reflex in Aplysia californica was explored by examining the fine structure of sensory neuron presynaptic terminals (the critical site of plasticity for the short-term forms of both types of learning) in control animals and in animals whose behavior had been modified by training. The number, size, and vesicle complement of sensory neuron active zones were larger in animals showing long-term sensitization than in control animals and smaller in animals showing long-term habituation. These changes are likely to represent an anatomical substrate for the memory consolidation of these tasks.

Normal variations in presynaptic active zones of frog neuromuscular junctions

Neuromuscular junctions of frog cutaneous pectoris muscles were examined by the complementary-replica freeze-fracture technique. The large number of active zones revealed in this way permitted quantitation of normal and disrupted zones in control muscles and in muscles deprived of external calcium for periods of up to eight hours. Although some 87% of the active zones examined had the usual appearance of two double rows of intramembrane particles flanking a low ridge, several varieties of disrupted active zones appeared in which the rows were interrupted, dispersed, rotated, or reduced to single rows. The frequency of disruptions was not increased by calcium deprivation. Disorganized active zones at tips of neuromuscular junctions may represent normal remodelling of the junctions.

Ultrastructure of the synapses of sensory neurons that mediate the gill-withdrawal reflex in Aplysia.

We have identified the processes of mechanoreceptor sensory neurons by intracellular injection of horseradish peroxidase in order to study the structure of synapses which exhibit profound, behaviourally-relevant plasticity. These synapses are located at small, varicose expansions along or at the end of the fine, microtubule-containing neurites, and they are crowded with vesicles some of which are associated with the varicosity membrane at regions of membrane specialization morphologically equivalent to active zones described in other species. These active zones occur between pre- and postsynaptic processes at two varieties of apposition: a conventional flat one, and a more elaborate indented one. At indented appositions, the presynaptic varicosity is invaginated by a thin (less than 0.25 micrometer diameter) spine of variable length. The active zones of indented synapses have approximately twice the vesicle frequency of flat synapses, suggesting that indented synapses are more effective. Sensory neuron terminals are relatively uniform in their structure, having similar concentrations of vesicles and numbers of active zones, and the majority of the processes postsynaptic to them are less than 0.5 micrometer in diameter. These regularities, and the presence of two strikingly-different types of synaptic apposition, flat and indented, should facilitate structural comparisons of neurons from naive and behaviourally-modified animals. The possible dynamic interconversion of indented and flat appositions at the synaptic terminals of sensory neurons and its behavioural relevance are discussed.

Formation, storage, and release of neurosecretory material studied by quantitative electron microscopy in the fresh water snail Lymnaea stagnalis (L.).

The process of neurosecretion in the fresh water snail Lymnaea stagnalis was analysed quantitatively at the ultrastructural level. Special attention was paid to the phloxinophilic neurones in the cerebral ganglia, the Caudo-Dorsal Cells (CDC). The rates of synthesis, storage and release of neurosecretory elementary granules were studied in the CDC of animals fixed at time intervals of 4 hours, during a 24 hour period. The processes concerned show a diurnal rhythmicity. In the cell bodies synthetic activity, as determined by counting the number of active golgi zones per surface unit, is high during the night and low during the day. The reverse was found for the amount of secretory material (number of elementary granules per surface unit) stored in the cytoplasm. From these results it is concluded that also the rate of transport of the elementary granules through the axons fluctuates rhythmically. It has its maximum during the night and its minimum during the day. This conclusion was substantiated by the observation that the highest number of granules in the axons is found during the night. The axon terminals of the CDC pass through four different stages during the 24 hour period. In axons being in the accumulation stage, which are found from the morning until the evening, the number of elementary granules increases rapidly. The neurohaemal zone increases in thickness during this process. In axons in the release stage, which predominate during the evening and the night, the contents of the elementary granules are extruded from the axon terminals, apparently by exocytosis. The rate of release of the secretory material into the body fluid, which is very low during the day, shows a rapid increase a few hours before sunset, and is probably correlated with the light intensity. A marked decrease of the amount of secretory material is noted in the neurohaemal area during the release stage. A daily turnover of nearly all secretory material accumulated in the axon terminals is suggested by the observations. Axons being in the reconstruction stage are mainly found during the night. They are distinguished by the presence of vesicular and tubular structures. These probably originate by fusion of microvesicles, which are considered to arise from the membranes of the elementary granules after exocytosis. After disappearance of the vesicles and tubules the axons enter the empty stage. This is frequently found in the night and in the early morning hours. In the morning the axon terminals enter the accumulation stage again. Furthermore, accumulation and release phenomena were quantified in the axon terminals of 5 other neurosecretory cell types present in the ganglia. A diurnal pattern rather similar to that of the CDC was found in the Light Green Cells (the Medio- and Latero-Dorsal Cells in the cerebral ganglia). No rhythmicity was found in the neurohaemal areas of the four types of secretory neurones located in the ganglia of the visceral ring. A constant level of storage and release was established during the 24 hour period. The relationship between synthesis, storage and release of the secretory material of the CDC is discussed.

Osmotically Induced Changes in the Activity of Neurosecretory Cells Located in the Pleural Ganglia of the Fresh Water Snail Lymnaea Stagnalis (L.), Studied By Quantitative Electron Microscopy

The neurosecretory cells present in the pleural ganglia of the fresh water snail Lymnaea stagnalis, the Dark Green Cells, were studied to establish whether these neurones are engaged in osmoregulation. Groups of 5 snails were exposed to conditions which induce changes in the diuretic activity (de-ionized water or a 0.1 M sodium chloride solution) for 1, 8, and 15 days, respectively. Animals kept in tap water were used as controls. The cell bodies as well as the axon terminals of the Dark Green Cells were studied quantitatively at the ultrastructural level. To estimate the rate of secretory activity of the neurones changes in the relative extent of the granular endoplasmic reticulum (determined by lineal analysis) and in the number of active Golgi zones were used as parameters. Lineal analysis was also used to determine the fractional volume of the mitochondria and of the cytosomes. Variations in the amount of secretory material in the cell bodies were determined by counting the number of elementary granules per surface unit. Accumulation and release of the secretory material in cross sections of the main neurohaemal area (the right pleuro-parietal connective) were determined by counting the total number of granule-containing axon profiles, and the number of these axons showing release phenomena, respectively. Exposure to de-ionized water, presumably leading to enhanced diuresis, showed a statistically significant increase (a duplication in 15 days) of the extent of the granular endoplasmic reticulum and of the number of active Golgi zones per surface unit (2000 μ 2 ). Moreover, a twofold increase of the volume of the cytoplasm per cell body was noted. In the axon terminals located in the right parieto-pleural connective an enhanced release of secretory material was observed. These trends, which were statistically significant, point to an activation of the Dark Green Cells when the animals are exposed to de-ionized water. During exposure of the snails to 0.1 M sodium chloride, a solution, which is hypertonic to the blood and known to reduce the rate of urine formation, the secretory activity of the DGC was markedly reduced. The observed decrease of the extent of the granular endoplasmic reticulum and of the number of active Golgi zones per surface area was statistically significant. At day 8 the occurrence of cellular atrophy was indicated by the presence of large numbers of newly formed lysosomes of autophagous nature. After two weeks the cytoplasmic volume per cell body was reduced to at least half the control value. In the axon terminals release of secretory material was hardly observed. The secretory material in the axon terminals, rapidly accumulated during the first hours of exposure, gradually diminished during the experiment which was partly due to release, and partly to lysosomal breakdown. The changes observed in both experiments were reversible: the quantitative data obtained from snails kept in tap water for one week after a stay of 15 days in the experimental solutions was within the control range. The results are in line with the hypothesis that the Dark Green Cells synthesize a substance which acts in diuresis. Additional physiological evidence is, however, needed to define more accurately the function of these neurones in the maintenance of the water balance.

The enzymic deacylation of esterified mono- and di-saccharides. I. The isolation and purification of an esterase from wheat germ lipase.

Whereas wheat germ lipase was known to contain acid phosphatase (EC 3.1.3.2), esterase (EC 3.1.1.1), and lipase (EC 3.1.1.3) activity, a cursory examination of some commercial enzymes has demonstrated also the presence of phosphodiesterase (EC 3.1.4.1), α- and β-glucosidase (EC 3.2.1.20 and EC 3.2.1.21), α- and β-galactosidase (EC 3.2.1.22 and EC 3.2.1.23), α-mannosidase (EC 3.2.1.24), and β-xylosidase (EC 3.2.1.37) activities. Disc electrophoresis revealed a minimum of 12 electrophoretically distinct protein fractions. Different sources and different batches of enzyme had similar disc electrophoretic behavior and activities. Fractionation of the crude preparation on carboxymethylcellulose or Sephadex, and electrophoresis on Sephadex, failed to separate α-glucosidase and esterase activities. The inhibition of α- and β-glucosidase could be effected by D-glucono-1,5-lactone, but not by metal salts or Tris.Preparative polyacrylamide-gel electrophoresis of wheat germ lipase gave a large number of active zones including several esterases, acid phosphatase, and α- and β-glucosidase fractions. Evidence was established for the nonidentity of two neighboring esterase zones. One was found to be free of α- and β-glucosidase activity. Sulfhydryl reagents inhibited the esterases, whereas acetone activated some and inactivated others. The esterases were most stable at neutral pH and were extensively inactivated on lyophilization, dialysis, and desalting with molecular-sieving reagents. Some properties of the purified esterase were examined.

Studies of Active Faults in Japan

The term “active fault (Katsu-danso)” appeared in the 1920's in papers of some geomorphologists in Japan. It has been used for faults active in Quaternary or late Quaternary, although the usage of the word “active” and its age-limit are different by authors. At any rate, the active fault is significant in geology in that the evidence of fault movements is recorded in the topography on the fault trace which enables detail analysis of the faulting, and in that the faulting might be detectable by means of geophysical methods, and it might be closely related to the occurrence of an earthquake. Recent studies in Japan showed that an active fault moves under a regionally-stressed condition of the crust, which has persisted during recent geologic time. If so, an “active fault” could be defined as a fault which is active under the present-day stress system. Then, the origin, orientation, and variation in time and space, of the “present” stress system are to be an important and fruitful research subject on the Tertiary to Quaternary tectonic history of the Japanese Islands. Some of the recent investigation on the active fault began to focus on this line.Studies of active faults in Japan have started from two points: the geological studies of the earthquake faults by geologists and the studies of the fault topography by geomorphologists.The geological studies of the earthquake fault was commenced by Koto, B. (1894) who had observed the surface break of the Mino-Owari earthquake of 1891 along the Neo Valley fault. Since then, geologists have investigated and described more than ten earthquake faults from Japan and Formosa. Particularly through the experiences of 1927- and 1930-earthquakes, it became clear that the mode of displacement along the earthquake fault during the earthquake is the same in the sense of displacement as the mode of the long-term displacement through the geologic periods. For example, Kuno, H. (1936) found that the Tanna fault which moved a few meters left-laterally during 1930 earthquake, has accumulated left-lateral displacement ca. 1000m since the middle Pleistocene.Almost independently of the geologists'works, geomorphologists had investigated the fault topography of Japan. By these studies, it had become clear before the War II that there are many fault scarps and fault valleys in this country, which have been produced probably by Quaternary faulting. Tsujimura, T. (1932) published a distribution map of topographically-recognized faults, in which 413 fault systems were registered.Recently, the geological and geomorphological studies have been jointly performed and the movement-history of some active faults in Quaternary time are clarified quantitatively (Table 1). It is also shown that many active faults hitherto considered to have only vertical displacement are strike-slip faults accompanied by lesser dip-slip components. The Atera fault (Sugimura & Matsuda, 1965), the Atotsugawa fault (Matsuda, 1966), and the Median Tectonic line (Kaneko, S., 1966; Okada, A., 1968), which was described recently, are examples.Some features of the active strike-slip faults described from Japan may be summerized as follows:A number of active faults or fault zones are present particularly in central Japan (the Chubu, Kinki, and Shikoku districts). They are, however, less than one hundred kilometers in length and a few kilometers in total displacement of the basement rocks, except for the Median Tectonic line (and probably the Itoigawa-Shizuoka Tectonic line).There is a marked regularity in the fault systems of the central Japan between the trend of faults and the sense of the displacement: the NW-trending faults are left-lateral, whereas the NE-trending faults are right-lateral. This implies that the earth's crust of the region is under the same stress system having the maximum (compressional) principal axis of approximate east-west.