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Masashi Kawasaki - One of the best experts on this subject based on the ideXlab platform.

  • Behavioral/Systems/Cognitive Nonlinear Response Properties of Combination-Sensitive Electrosensory Neurons in the Midbrain of
    2016
    Co-Authors: Gymnarchus Niloticus, Bruce A. Carlson, Masashi Kawasaki
    Abstract:

    The jamming avoidance response of the weakly electric fish Gymnarchus niloticus relies on determining the sign of the frequency difference (Df) between the fish’s own electric organ discharge (EOD) and that of a neighbor, which is achieved by comparing modulations in amplitude (AM) and phase (PM) that result from the summation of their EODs. These two stimulus features are processed in separate pathways that converge in the torus semicircularis on combination-sensitive neurons, many of which are selective for the sign of Df. We recorded extracellular single-unit responses to independent stimulation with AM and PM and combined AM–PM stimulation to deter-mine how sign selectivity is established. Responses to AM and PM frequently summated nonlinearly, leading to sign-selective responses as a result of facilitation to the preferred sign of Df and/or suppression to the nonpreferred sign of Df. Facilitation typically occurred when responses to AM and PM were aligned, whereas suppression typically occurred when they were offset. By experimentally manipulating the degree of alignment between these two responses, we found that the summed response was dependent on their relative timing. In addition, we found a unique class of units that were sensitive to differences in amplitude between two body surfaces. This sensitivity rendered such units immune to the problem of orientation ambiguity, in which the sign selectivity of a single neuron reverses with changes in stimulus orientation. We discuss potential synaptic mechanisms for driving nonlinear responses in these and other combination-sensitive neurons. Key words: electric fish; mormyriform; facilitation; suppression; torus semicircularis; jamming avoidance respons

  • Interruption of pacemaker signals is mediated by GABAergic inhibition of the pacemaker nucleus in the African electric fish Gymnarchus niloticus.
    Journal of comparative physiology. A Neuroethology sensory neural and behavioral physiology, 2007
    Co-Authors: Ying Zhang, Masashi Kawasaki
    Abstract:

    The wave-type African weakly electric fish Gymnarchus niloticus produces electric organ discharges (EODs) from an electric organ in the tail that is driven by a pacemaker complex in the medulla, which consists of a pacemaker nucleus, two lateral relay nuclei and a medial relay nucleus. The prepacemaker nucleus (PPn) in the area of the dorsal posterior nucleus of the thalamus projects exclusively to the pacemaker nucleus and is responsible for EOD interruption behavior. The goal of the present study is to test the existence of inhibition of the pacemaker nucleus by the PPn. Immunohistochemical results showed clear anti-GABA immunoreactive labeling of fibers and terminals in the pacemaker nucleus, but no apparent anti-glycine immunoreactivity anywhere in the pacemaker complex. GABA injection into the pacemaker nucleus could induce EOD interruptions that are comparable to the interruptions induced by glutamate injection into the PPn. Application of the GABAA receptor blocker bicuculline methiodide reversibly eliminated the effects of stimulation of the PPn. Thus the EOD interruption behavior in Gymnarchus is mediated through GABAergic inhibition of the pacemaker nucleus by the PPn.

  • Interruption of pacemaker signals by a diencephalic nucleus in the African electric fish, Gymnarchus niloticus
    Journal of Comparative Physiology A, 2006
    Co-Authors: Ying Zhang, Masashi Kawasaki
    Abstract:

    The African electric fish Gymnarchus niloticus rhythmically emits electric organ discharges (EODs) for communication and navigation. The EODs are generated by the electric organ in the tail in response to the command signals from the medullary pacemaker complex, which consists of a pacemaker nucleus (PN), two lateral relay nuclei (LRN) and a medial relay nucleus (MRN). The premotor structure and its modulatory influences on the pacemaker complex have been investigated in this paper. A bilateral prepacemaker nucleus (PPn) was found in the area of the dorsal posterior nucleus (DP) of the thalamus by retrograde labeling from the PN. No retrogradely labeled neurons outside the pacemaker complex were found after tracer injection into the LRN or MRN. Accordingly, anterogradely labeled terminal fibers from PPn neurons were found only in the PN. Iontophoresis of l -glutamate into the region of the PPn induced EOD interruptions. Despite the exclusive projection of the PPn neurons to the PN, extracellular and intracellular recordings showed that PN neurons continue their firing while MRN neurons ceased their firing during EOD interruption. This mode of EOD interruption differs from those found in any other weakly electric fishes in which EOD cessation mechanisms have been known.

  • Interruption of pacemaker signals by a diencephalic nucleus in the African electric fish, Gymnarchus niloticus
    Journal of comparative physiology. A Neuroethology sensory neural and behavioral physiology, 2006
    Co-Authors: Ying Zhang, Masashi Kawasaki
    Abstract:

    The African electric fish Gymnarchus niloticus rhythmically emits electric organ discharges (EODs) for communication and navigation. The EODs are generated by the electric organ in the tail in response to the command signals from the medullary pacemaker complex, which consists of a pacemaker nucleus (PN), two lateral relay nuclei (LRN) and a medial relay nucleus (MRN). The premotor structure and its modulatory influences on the pacemaker complex have been investigated in this paper. A bilateral prepacemaker nucleus (PPn) was found in the area of the dorsal posterior nucleus (DP) of the thalamus by retrograde labeling from the PN. No retrogradely labeled neurons outside the pacemaker complex were found after tracer injection into the LRN or MRN. Accordingly, anterogradely labeled terminal fibers from PPn neurons were found only in the PN. Iontophoresis of l-glutamate into the region of the PPn induced EOD interruptions. Despite the exclusive projection of the PPn neurons to the PN, extracellular and intracellular recordings showed that PN neurons continue their firing while MRN neurons ceased their firing during EOD interruption. This mode of EOD interruption differs from those found in any other weakly electric fishes in which EOD cessation mechanisms have been known.

  • Neuronal sensitivity to microsecond time disparities in the electrosensory system of Gymnarchus niloticus.
    The Journal of neuroscience : the official journal of the Society for Neuroscience, 2005
    Co-Authors: Atsuko Matsushita, Masashi Kawasaki
    Abstract:

    To perform the jamming avoidance response (JAR), the weakly electric fish Gymnarchus detects time disparities on the order of microseconds between electrosensory signals received by electroreceptors in different parts of the body surface. This paper describes time-disparity thresholds of output neurons of the electrosensory lateral line lobe (ELL), where the representation of timing information is converted from a time code to a firing-rate code. We recorded extracellular single-unit responses from pyramidal cells in the ELL to sinusoidally modulated time disparity with various depths (0-200 micros). Threshold sensitivity to time disparities measured in 123 units ranged from 0.5 to 100 micros and was < or =5 micros in 60% of the units. The units from pyramidal cells in the inner and outer cell layers of the ELL responded equally well to small time disparities. The neuronal thresholds to time disparities found in the ELL are comparable with those demonstrated in behavioral performance of the JAR. The sensitivity of ELL units to small time disparities was unaffected when the center of the cyclic time-disparity modulation was shifted over a wide range (up to 250 micros), indicating an adaptation mechanism for steady-state time disparities that preserves the sensitivity to small dynamic changes in time disparities. Phase-locked input neurons, which provide time information to the ELL by phase-locked firing of action potentials, did not adapt to steady-state time shifts of sensory signals. This suggests that the adaptation emerges within the ELL.

Atsuko Matsushita - One of the best experts on this subject based on the ideXlab platform.

  • Neuronal sensitivity to microsecond time disparities in the electrosensory system of Gymnarchus niloticus.
    The Journal of neuroscience : the official journal of the Society for Neuroscience, 2005
    Co-Authors: Atsuko Matsushita, Masashi Kawasaki
    Abstract:

    To perform the jamming avoidance response (JAR), the weakly electric fish Gymnarchus detects time disparities on the order of microseconds between electrosensory signals received by electroreceptors in different parts of the body surface. This paper describes time-disparity thresholds of output neurons of the electrosensory lateral line lobe (ELL), where the representation of timing information is converted from a time code to a firing-rate code. We recorded extracellular single-unit responses from pyramidal cells in the ELL to sinusoidally modulated time disparity with various depths (0-200 micros). Threshold sensitivity to time disparities measured in 123 units ranged from 0.5 to 100 micros and was < or =5 micros in 60% of the units. The units from pyramidal cells in the inner and outer cell layers of the ELL responded equally well to small time disparities. The neuronal thresholds to time disparities found in the ELL are comparable with those demonstrated in behavioral performance of the JAR. The sensitivity of ELL units to small time disparities was unaffected when the center of the cyclic time-disparity modulation was shifted over a wide range (up to 250 micros), indicating an adaptation mechanism for steady-state time disparities that preserves the sensitivity to small dynamic changes in time disparities. Phase-locked input neurons, which provide time information to the ELL by phase-locked firing of action potentials, did not adapt to steady-state time shifts of sensory signals. This suggests that the adaptation emerges within the ELL.

  • Unitary giant synapses embracing a single neuron at the convergent site of time‐coding pathways of an electric fish, Gymnarchus niloticus
    The Journal of comparative neurology, 2004
    Co-Authors: Atsuko Matsushita, Masashi Kawasaki
    Abstract:

    Phase-locking neurons in the electrosensory lateral line lobe (ELL) of a weakly electric fish, Gymnarchus niloticus, fire an action potential in response to each cycle of the sinusoidal electrosensory signal (350 –500 Hz) created by the fish’s own electric organ. The exact firing times of the phase-locking neurons are altered (time-shifted) by capacitance of electrolocation objects or by electric organ discharges of other individuals. The magnitude of the time shifts depends on the location of the neurons’ receptive field on the skin; thus, time disparities arise between the firing of phase-locking neurons. To compute these disparities, there should be a site where these phase-locking neurons converge. In this study we morphologically identified a novel cell type, which we named the “ovoidal cell”, that receives the convergent projections of phase-locking neurons in the inner cell layer (ICL) of the ELL. We labeled these neurons with biocytin and examined them by light and electron microscopy. The giant cells and the S-type primary afferents, two types of phase-locking neurons, respectively terminate on the soma via chemical synapses and on the dendrite of the ovoidal cells via mixed synapses. Each terminal of the giant cells embraces the soma of an ovoidal cell, covering as much as 84% of the somatic membrane. The giant cell terminals and ovoidal cell somata were immunoreactive to SV2, a synaptic vesicle protein, but the S-afferent terminals were not, even though they contain numerous synaptic vesicles. The dendrite of the ovoidal cells also contacts the pyramidal cells of the ICL, which are known to be sensitive to time disparities. The anatomical connections of the phase-locking neurons to the ovoidal cells strongly suggest that they are involved in computing time disparity. J. Comp. Neurol. 472:140 –155, 2004. © 2004 Wiley-Liss, Inc.

  • unitary giant synapses embracing a single neuron at the convergent site of time coding pathways of an electric fish Gymnarchus niloticus
    The Journal of Comparative Neurology, 2004
    Co-Authors: Atsuko Matsushita, Masashi Kawasaki
    Abstract:

    Phase-locking neurons in the electrosensory lateral line lobe (ELL) of a weakly electric fish, Gymnarchus niloticus, fire an action potential in response to each cycle of the sinusoidal electrosensory signal (350 –500 Hz) created by the fish’s own electric organ. The exact firing times of the phase-locking neurons are altered (time-shifted) by capacitance of electrolocation objects or by electric organ discharges of other individuals. The magnitude of the time shifts depends on the location of the neurons’ receptive field on the skin; thus, time disparities arise between the firing of phase-locking neurons. To compute these disparities, there should be a site where these phase-locking neurons converge. In this study we morphologically identified a novel cell type, which we named the “ovoidal cell”, that receives the convergent projections of phase-locking neurons in the inner cell layer (ICL) of the ELL. We labeled these neurons with biocytin and examined them by light and electron microscopy. The giant cells and the S-type primary afferents, two types of phase-locking neurons, respectively terminate on the soma via chemical synapses and on the dendrite of the ovoidal cells via mixed synapses. Each terminal of the giant cells embraces the soma of an ovoidal cell, covering as much as 84% of the somatic membrane. The giant cell terminals and ovoidal cell somata were immunoreactive to SV2, a synaptic vesicle protein, but the S-afferent terminals were not, even though they contain numerous synaptic vesicles. The dendrite of the ovoidal cells also contacts the pyramidal cells of the ICL, which are known to be sensitive to time disparities. The anatomical connections of the phase-locking neurons to the ovoidal cells strongly suggest that they are involved in computing time disparity. J. Comp. Neurol. 472:140 –155, 2004. © 2004 Wiley-Liss, Inc.

Lin-cheng Shen - One of the best experts on this subject based on the ideXlab platform.

  • Bionic asymmetry: from amiiform fish to undulating robotic fins
    Chinese Science Bulletin, 2009
    Co-Authors: Lin-cheng Shen, Kin Huat Low
    Abstract:

    Similar to bionic non-smooth which has been successfully applied in anti-resistance and anti-adhesion, bionic asymmetry is also an inherent property of biological systems and is worth exploring for conceivable pragmatic applications. Therefore, bionic asymmetry for undulations is of main interest in this paper. We initially investigate bionic asymmetry with a case study of the undulating robotic fin, RoboGnilos, which evolved from the long dorsal fin of Gymnarchus niloticus in the amiiform mode. Since the performance of the pre-existing undulating fins is hardly satisfactory, we obtain bionic inspirations of undulatory asymmetry through observations and measurements on the specimen of G. niloticus, to improve upon the performance. Consequently, the newly acquired innovation for bionic asymmetry is incorporated into the previously derived kinematics model, and also applied to the experimental prototype. Both computational and experimental results verify that bionic asymmetric undulation generates better propulsion performance (in terms of linear velocity and efficiency) than the traditional symmetric modes with the same undulatory parameters.

  • Biological inspirations, kinematics modeling, mechanism design and experiments on an undulating robotic fin inspired by Gymnarchus niloticus
    Mechanism and Machine Theory, 2009
    Co-Authors: Lin-cheng Shen, Longxin Lin
    Abstract:

    Abstract This paper suggests and then presents a whole procedure of biomimetics with a case study starting from amiiform fish ( Gymnarchus niloticus ) to an undulating robotic fin. The procedure includes biological observation, kinematics modeling, mechanism design, prototype implementation, and initial experiments. To investigate undulatory median fin propulsion and its potential for applications in man-made underwater vehicles, a motor-driven fin actuator, RoboGnilos , has been developed with inspirations from G. niloticus , which generally swims by undulations of a long flexible dorsal fin. In the kinematics modeling, the ruled surface based model is proposed to describe the undulation characteristics and used as a guide for the biomimetic mechanism design and implementation. Next, a modular independent motor-driven mechanism is adopted to implement the undulating prototype fin by virtue of reconfigurable features. Finally, initial experiments have been carried out to analyse how undulation dynamics is affected with the morphological parameters (i.e., the asymmetry of waveforms, the fin surface material, and the fin ray length) and the undulatory parameters (in terms of the wave length, the amplitude, and the undulation frequency). The kinematics simulation presented in this paper shows that the proposed ruled surface model can better describe and fit more undulation characteristics than other models. And the experiments verify that the design of the modular motor-driven mechanism is convenient and effective.

  • Design of an artificial bionic neural network to control fish-robot's locomotion
    Neurocomputing, 2007
    Co-Authors: Daibing Zhang, Lin-cheng Shen, Haibin Xie
    Abstract:

    An artificial bionic neural network to control fish-robot locomotion is presented. The fish-robot, which is inspired from ''Gymnarchus niloticus'', is modeled as a multi-joint dynamic system with parallel connections and composed of several motors. The principle of the central pattern generators (CPGs) governing the locomotion of fish is analyzed. An artificial neural network which has many comparability with the biological CPGs is designed to control the fish-robot. Experimental results of startup, stop, forward swimming and backward swimming show its validity and efficiency.

  • kinematic modeling and dynamic analysis of the long based undulation fin of Gymnarchus niloticus
    Simulation of Adaptive Behavior, 2006
    Co-Authors: Guangming Wang, Lin-cheng Shen
    Abstract:

    Within median and/or paired fin (MPF) propulsion, many fish routinely use the long-based undulatory fins as the sole means of locomotion In this paper, the long-based undulatory fin of an Amiiform fish“G niloticus”was investigated We brought forward a simplified physical model and a kinematic model to simulate the undulations of the long-based dorsal fin Further, the equilibrium equations of the undulatory fin were obtained by applying the membrane theory of thin shells in which the geometrical non-linearity of the structure is taken into account Last, we apply the derived kinematic model and equilibrium equations of the undulatory fin to analyze the thrust and propulsive efficiency varying with the aspect ratio of the fin and the maximum swing amplitude.

  • CFD validation of the optimal arrangement of the propulsive dorsal fin of Gymnarchus niloticus
    Journal of Bionic Engineering, 2006
    Co-Authors: Lin-cheng Shen, Pei-ling Gong
    Abstract:

    Abstract Gymnarchus niloticus , a typical freshwater fish, swims by undulations of a long-based dorsal fin aided by the two pectoral fins, while commonly it holds its body rigid and straight. The long flexible dorsal fin is the main propulsor of G niloticus ; it has also considerable influence on the streamline profile. This paper proposes a CFD approach to validate that the natural arrangement of the propulsive dorsal fin is optimal. Using morphological data and a smoothness-keeping algorithm, the dorsal fin is ‘virtually’ moved forward and backward with several displacements from the natural location. For each case, we reconstruct geometry, generate CFD grids, and calculate the pressure, viscous and total drag coefficients respectively. The results show that the pressure and total drag coefficients increase whether the dorsal fin is displaced forward or backward, and that greater displacement from its original position leads to greater pressure and total drag coefficients. This suggests that the natural position of the dorsal fin is significant for maintaining the fish's streamline profile and reducing drag.

Yuan-xing Guo - One of the best experts on this subject based on the ideXlab platform.

  • Emergence of temporal-pattern sensitive neurons in the midbrain of weakly electric fish Gymnarchus niloticus.
    Journal of Physiology-paris, 2002
    Co-Authors: Masashi Kawasaki, Yuan-xing Guo
    Abstract:

    Sensitivity of neurons in the torus semicircularis of a weakly electric fish, Gymnarchus niloticus, to two stimulus parameters that are critical for its behavior the jamming avoidance response was examined. The first parameter is the sign of frequency difference between discharge frequencies of fish's own electric organ and that of a neighbor's. The second parameter is the spatial orientation of neighbor's electric field. Whereas neuronal ambiguity of frequency coding for different orientations of neighbor's electric field is predicted, unambiguous JAR occurs at the behavioral level. Most neurons in the torus semicircularis showed sensitivity to the sign of frequency difference. Although a small number of neurons showed preference to a consistent sign of the frequency difference, the coding of the sign of frequency differences was found to be ambiguous with a highly variable pattern of responses for different orientations in most of neurons.

  • Parallel projection of amplitude and phase information from the hindbrain to the midbrain of the African electric fish Gymnarchus niloticus.
    The Journal of neuroscience : the official journal of the Society for Neuroscience, 1998
    Co-Authors: Masashi Kawasaki, Yuan-xing Guo
    Abstract:

    Two distinct sensory cues in electrosensory signals, amplitude modulation and differential phase modulation, are essential for an African wave-type electric fish, Gymnarchus, to perform the jamming avoidance responses. Individual neurons in the first brain station for central processing, the electrosensory lateral line lobe (ELL), were investigated by the in vivo whole-cell recording and labeling technique for their physiological responses, location, morphology, and projection areas. Neurons in the dorsal zone of the ELL responded selectively to amplitude modulation. Neurons in the outer cell layer of the medial zone were categorized physiologically into two groups: amplitude-sensitive and differential phase-sensitive. All but one neuron in the inner cell layer of the medial zone responded exclusively to differential phase modulation. All neurons recorded and labeled in the ELL had pyramidal morphology with large and extensive apical dendrites and less extensive basal dendrites. They were found to project to two midbrain nuclei: the nucleus praeeminentialis and the torus semicircularis. Amplitude-sensitive neurons in the dorsal zone projected exclusively to the lateral posterior subdivision, the torus semicircularis. Neurons in the medial zone projected to the medial dorsal and lateral anterior subdivisions of the torus semicircularis. Although some neurons in the ELL responded to both amplitude and differential phase modulation, they did not differentiate between temporal patterns of the two cues that encode necessary information for the jamming avoidance response. Overlapping projection of amplitude and differential phase-sensitive neurons to the torus semicircularis suggests integration of the two sensory cues in this nucleus.

  • Representation of Accurate Temporal Information in the Electrosensory System of the African Electric Fish,Gymnarchus niloticus
    The Journal of neuroscience : the official journal of the Society for Neuroscience, 1997
    Co-Authors: Yuan-xing Guo, Masashi Kawasaki
    Abstract:

    Differential-phase-sensitive neurons in the electrosensory lateral line lobe (ELL) of the African electric fish, Gymnarchus niloticus, are sensitive to time disparities on the order of microseconds between afferent action potentials. These action potentials fire in a phase-locked manner in response to the animal’s own wave-type electric organ discharges (EODs) ([Kawasaki and Guo, 1996][1]). The time disparity is one of the essential cues for an electrical behavior, the jamming avoidance response (JAR). To gain an insight into the accurate temporal processing in the ELL, firing time accuracy and dynamic response properties of action potentials of the phase-locked neurons (PLNs) in the ELL were examined. The temporal accuracy of the entire neuronal circuit for the JAR was also measured using behavioral responses. Standard deviation of firing times of PLNs’ action potentials was ∼6 μsec. The PLNs represent zerocrossing times of each stimulus cycle with this accuracy even when stimulus phase was modulated at high frequencies (∼50 Hz). Distinct JAR occurred when time disparity was diminished below 1 μsec, and a marginal JAR could still be detected with a time disparity of 100 nsec. Standard deviation of the firing times of EODs was approximately several hundred nanoseconds. This stability of the EOD, however, was demonstrated to be unnecessary for the JAR. JARs occurred even when a large artificial jitter (∼60 μsec) was introduced to a stimulus that mimicked fish’s own EOD and the time disparity for JAR was diminished to 1 μsec. This immunity of JAR to the EOD jitter is explained by the insensitivity of the differential-phase-sensitive neurons in the ELL to a common phase modulation. The JAR of the South American electric fish, Eigenmannia , also occurs in response to stimuli that generate comparably small phase differences ([Rose and Heiligenberg, 1985b][2]; [Carr et al., 1986a][3]). The present study revealed that the independently evolved Eigenmannia and Gymnarchus exhibit a comparative level of remarkable temporal accuracy. [1]: #ref-25 [2]: #ref-36 [3]: #ref-8

  • Neuronal circuitry for comparison of timing in the electrosensory lateral line lobe of the African wave-type electric fish Gymnarchus niloticus
    The Journal of neuroscience : the official journal of the Society for Neuroscience, 1996
    Co-Authors: Masashi Kawasaki, Yuan-xing Guo
    Abstract:

    An African wave-type electric fish, Gymnarchus, compares timing on the order of microseconds of sensory feedback from from its high-frequency (approximately 400 Hz) electric organ discharges (EODs) received at different parts of its body surfaces. This capability is essential for and demonstrated by the jamming avoidance response (JAR). The organization of the timing comparison mechanisms was identified in the electrosensory lateral line lobe (ELL) in the hindbrain by field potential, extra- and intracellular recordings, and intracellular labeling with biotinylated agents. Timing of phase of the EOD feedback is carried by action potentials of S-type primary afferent fibers that project to the inner cellular layer (ICL) of the medial zone of the ELL and to the giant neurons in the ELL. The giant neurons bilaterally project to the ICL, where neurons sensitive to phase differences between different parts of the body occur. Although sensitive to dynamic phase changes of several microseconds, these differential-phase-sensitive neurons showed adaptation to steady-state changes of phase difference over a wide range (greater than +/- 100 microseconds) and continued to respond to small modulations after the mean difference was shifted. Gymnarchus and an independently evolved South American electric fish, Eigenmannia, exhibit nearly identical JARs and share a rather complex but identical set of computational algorithms for JAR. This study showed that one of the computational steps, the timing comparison between body surfaces, occurs in the hindbrain in Gymnarchus, in contrast to the midbrain in Eigenmannia. Thus, similar systems with a similar overall function may have evolved differently in different genera by assigning a subfunction to different substructures within the brain.

Matthew A Friedman - One of the best experts on this subject based on the ideXlab platform.

  • calretinin like immunoreactivity in mormyrid and gymnarchid electrosensory and electromotor systems
    The Journal of Comparative Neurology, 1997
    Co-Authors: Matthew A Friedman, Masashi Kawasaki
    Abstract:

    Calretinin-like immunoreactivity was examined in the electrosensory and electromotor systems of the two families of mormyriform electric fish. Mormyrid fish showed the strongest immunoreactivity in the knollenorgan electroreceptor pathway; in the nucleus of the electrosensory lateral line lobe (ELL) and the big cells of the nucleus exterolateralis pars anterior. Mormyromast and ampullary zones of the ELL showed calretinin-like immunoreactivity in the ganglion, granule, and intermediate cell and fiber layers. Mormyromast zones additionally showed labeling of apical dendrites and commissural cells, but the ampullary zone did not. In the electromotor system, two nuclei in the corollary discharge pathway showed labeling: in the paratrigeminal command-associated nucleus and the juxtalobar nucleus. Gymnarchus niloticus (Gymnarchidae) showed strongest calretinin-like immunoreactivity in part of the phase-coding pathway; in S-type electroreceptor afferents. Zones of the ELL not receiving phase-coder input had weak labeling. The electromotor system showed labeling in the lateral relay nucleus and less strongly in the medullary relay nucleus, but none in the pacemaker. The concentration of calcium-binding proteins in mormyrid and gymnarchid time-coding electrosensory pathways is consistent with the hypothesis that they play a role in preserving temporal information across synapses. Cell types that encode temporal characteristics of stimuli in precise spike times have high levels of calcium-binding proteins, but cells that re-code temporal information into presence or magnitude of activity have low levels. Some cell types in the electromotor pathways and early in the time-coding electrosensory pathways do not follow this hypothesis, and therefore preserve temporal information using a mechanism independent of calcium-binding proteins. In particular, electromotor systems may use extensive electrotonic coupling within nuclei to ensure precise timing.