Resonant properties in the paddlefish electrosensory system caused by delayed feedback

Introduction The paddlefish electrosensory system consists of receptor cells in the skin that sense minute electric fields from their prey, small water fleas. The receptors thereby measure the difference of the voltage at the skin surface against the voltage inside the animal. Due to a high skin impedance, this internal voltage is considered to be relatively fixed. Results We found, however, that this internal voltage can fluctuate. It shows damped oscillations to a single short electric field pulse and changes, with some time delay, according to the previous history of stimulation, and shows resonance at a certain frequency. Conclusions Computer simulations show that these phenomena can be explained by the presence of delayed feedback where the internal voltage is part of the feedback loop.     

Receptive field organization of electrosensory neurons in the paddlefish (Polyodon spathula)

Paddlefish use their electrosense to locate small water fleas (daphnia), their primary prey, in three-dimensional space. High sensitivity and a representation of object location are essential for this task. High sensitivity can be achieved by convergence of information from a large number of receptors and object location is usually represented in the nervous system by topographic maps. However the first electrosensory center in the brain, the dorsal octavolateral nucleus in the hindbrain, is neither topographically organized nor does it show a higher sensitivity than primary afferent fibers. Here, we investigated the response properties of electrosensory neurons in the dorsal octavolateral nucleus (DON), the lateral mesencephalic nucleus (LMN) and the tectum mesencephali (TM). LMN units are characterized by large receptive fields, which suggest a high degree of convergence. TM units have small receptive fields and are topographically arranged, at least in the rostro-caudal axis, the only dimension we could test. Well-defined receptive fields, however, could only be detected in the TM with a moving DC stimulus. The receptive fields of TM units, as determined by slowly scanning the rostrum and head with a 5 Hz stimulus, were very large and frequently two or more receptive fields were present. The receptive fields for LMN units were located in the anterior half of the rostrum whereas TM units had receptive fields predominantly on the head and at the base of the rostrum. A detailed analysis of the prey catching behavior revealed that it consists of two phases that coincide with the location of the receptive fields in LMN and TM, respectively. This suggests that LMN units are responsible for the initial orienting response that occurs when the prey is alongside the anterior first half of the rostrum. TM units, in contrast, had receptive fields at locations where the prey is located when the fish opens its mouth and attempts the final strike.     

Representation of lateral line and electrosensory systems in the midbrain of the axolotl,Ambystoma mexicanum

Summary The study focussed on the representation of the electrosensory and lateral line units in the midbrain of the axolotl Ambystoma mexicanum. In addition, the responses to photic and acoustic/vibrational stimuli were determined. Unit properties were characterized with respect to baseline activity, sensitivity, latency, directional specificity and number of input modalities. The anatomical arrangement of the units was determined using stereotactic and histological measurements of the electrode positions.Of 106 units recorded, 29 units were unimodal, 77 units responded to more than one modality. Most units discharged only in response to stimuli. Thresholds of electrosensory units were about 100 V/cm field strength; lateral line units had thresholds below 5 m pp amplitude. The shortest latencies (8–17 ms) were found for responses to visual stimuli. Lateral line and vestibular units responded after 35–58 ms, electroreceptive units after 79–150 ms. All electrosensory and about 50% of the lateral line units were sharply tuned to definite stimulus directions.Electrosensory and lateral line units formed topographical maps in the tectum. The map in each tectal hemisphere contained information about the contralateral surroundings. The electrosensory, lateral line and visual representations were only partly in register; especially in the caudal areas of the midbrain the alignment was poor.     

The morphology of somatostatin-immunoreactive neurons in the lateral nucleus of the rat amygdala

Three types of somatostatin-immunoreactive neurons are described in the lateral nucleus of the rat amygdala. These three types closely correspond to neurons previously reported in Golgi preparations of the lateral nucleus. Class I somatostatin neurons have triangular- or piriform-shaped somata with large primary dendrites and spiny secondary dendrites. Class II somatostatin neurons have small to medium-sized oval perikarya and are fusiform or multipolar in shape. Class III somatostatin neurons have small spheroid somata with small thinner relatively aspinous dendrites. Class I somatostatin neurons give rise to axons which project outside the lateral nucleus whereas class II and III neurons innervate other somatostatin-positive and non-somatostatin neurons within the lateral nucleus. Somatostatin neurons within the lateral nucleus are hypothesized to function as part of a network of somatostatin neurons extending from cortical regions through the amygdala to basal telencephalic and lower brain stem regions.     

A role for GABAergic inhibition in electrosensory processing and common mode rejection in the dorsal nucleus of the little skate, Raja erinacea

The electrosensory primary afferents in elasmobranchs are responsive to electric potentials created by the animal's own ventilation, while the second-order neurons (AENs) which receive this afferent input in the medulla suppress responses to ventilatory potentials but retain their extreme sensitivity to electric signals in the environment. Ventilatory potentials are common mode signals in elasmobranchs and a common mode rejection mechanism is one way the AENs suppress ventilatory noise. By pressure injecting the GABA-A receptor antagonist SR95531 while extracellularly recording from AENs, we tested the hypothesis that the subtractive circuitry that selectively reduces common mode signals in AENs utilizes GABA, and that a GAB-Aergic component of the dorsal nucleus commissural pathway mediates crossed inhibition of AENs. Local application of SR95531 increased the spontaneous activity and the responsiveness of AENs to electrosensory stimuli. AEN responses to a common mode stimulus were selectively increased compared to responses to a localized stimulus due to SR95531 application. Contralateral inhibition of AENs was blocked by SR95531, indicating that GABAergic commissural cells may inhibit AENs when the contralateral side of the body is stimulated, as with common mode stimulation. We conclude that GABAergic inhibition contributes significantly to the shaping of AEN responses including common mode rejection.Abbreviations AENs ascending efferent neurons - GABA gamma-aminobutyric acid     

Commissural neurons of the electrosensory lateral line lobe of Apteronotus leptorhynchus: morphological and physiological characteristics

Extracellular injections of horseradish peroxidase were used to label commissural cells connecting the electrosensory lateral line lobes of the weakly electric fish Apteronotus leptorhynchus. Multiple commissural pathways exist; a caudal commissure is made up of ovoid cell axons, and polymorphic cells' axons project via a rostral commissure. Intracellular recording and labeling showed that ovoid cells discharge spontaneously at high rates, fire at preferred phases to the electric organ discharge, and respond to increased receptor afferent input with short latency partially adapting excitation. Ovoid cell axons ramify extensively in the rostro-caudal direction but are otherwise restricted to a single ELL subdivision. Polymorphic cells are also spontaneously active, but their firing is unrelated to the electric organ discharge waveform. They respond to increased receptor afferent activity with reduced firing frequency and response latency is long. Electrical stimulation of the commissural axons alters the behavior of pyramidal cells in the contralateral ELL. Basilar pyramidal cells are hyperpolarized and nonbasilar pyramidal cells are depolarized by this type of stimulation. The physiological results indicate that the ovoid cells participate in common mode rejection mechanisms and also suggest that the ELLs may function in a differential mode in which spatially restricted electrosensory stimuli can evoke heightened responses.Abbreviations ccELL caudal commissure of the ELL - CE contralaterally excited - DML dorsal molecular layer - ELL electrosensory lateral line lobe - EOD electric organ discharge - HRP horseradish peroxidase - IE ipsilaterally excited - MTI mouth-tail inverted - MTN mouth-tail normal - rcELL rostral commissure of the ELL - TRI transverse inverted - TRN transverse normal     

The lateral cervical nucleus in the cat

Summary Profiles of 14 neurons all sectioned through the nucleolar plane and 87 isolated dendritic profiles have been analyzed with respect to the surface area covered by boutons and astroglial processes. This analysis has revealed two different types of neurons within the lateral cervical nucleus (LCN) of the cat. The cell types also differ in other ultrastructural respects. One type, which probably consists of projection neurons, is characterized by a rather large size, a relatively small nucleus, numerous mitochondria, well developed granular and agranular endoplasmic reticulum. The cell membrane of these cells shows somatic spines and the perikaryon is covered with boutons to a mean extent of 42%. The other cell type, which probably is internuncial, is smaller, has a proportionally larger nucleus, few mitochondria and a poorly developed granular and agranular endoplasmic reticulum. These cells show no somatic spines and the perikaryal membrane is covered with boutons to an extent of about 10%. Also the bouton populations contacting the two cell types differ from one another. The proportion of internuncial neurons within the LCN has been estimated to about 8%. The internuncial neurons seem to have no preferential localization.The primary dendrites of the projection neurons have a bouton covering of about 48%. No proportional differences in covering could be revealed between different sizes of dendrites.The results are discussed in relation to what is known about the anatomical and physiological organization of the LCN, and also compared with the results obtained in other similar investigations on other parts of the central nervous system.The author is grateful to fil.kand. Göran Engholm for his help with the statistical considerations.This work was supported by grants from Anders Otto Swärds Stiftelse, Stiftelsen Lars Hiertas minne, Åhlén och Holms stiftelse, Åke Wibergs stiftelse and the Swedish Medical Research Council (Project No B70-12X-2710).     

On the neurons and synapses of the lateral geniculate nucleus of the monkey,and the effects of eye enucleation

Summary Two neuron types are distinguished by electron microscopy in the lateral geniculate nucleus (LGN) of the monkey-a large cell (P cell) interpreted as a geniculostriate relay cell, and a small cell (I cell) interpreted as an inhibitory interneuron. The I cell, distinguished by its small size, infolded nucleus, small mitochondria, cilium and small granular bodies, forms about 10% of the total neuron population. It could not be determined whether this cell has an axon, but its dendrites, which contain aggregates of flattened vesicles, are thought to form a proportion of the F processes, profiles which are post-synaptic to the retinal (RLP) axons and presynaptic to the dendrites of the P cells. The small dark (RSD) axon terminals of unknown origin contact the dendrites of both cell types.After eye enucleation the P cells of the affected laminae of the LGN shrink and partially withdraw their dendrites from the neuropil. By 29 months' survival, they have only a narrow cytoplasmic rim around the nucleus. A necrotic process also occurs, affecting fine dendrites by 22 days and large profiles by 45 days, but it is not clear whether whole cells are destroyed by this process. At 45 days the I cells are commonly seen to form somatodendritic synapses. The appearance of these synapses is interpreted as the result of a withdrawal to the soma of the presynaptic dendrites.It is concluded that the I cells are probably inhibitory interneurons subject to excitation and presynaptic inhibition by the RLP and RSD axons, and a diagram is presented to demonstrate the possible significance of these connections for the transmission of information through the LGN.The author wishes to thank Dr. J. Campos-Ortega for much practical advice.     

Transformation of peripheral inputs by the first-order lateral line brainstem nucleus

Extracellular recording techniques were used to record the responses of medial nucleus cells and posterior lateral line nerve fibers in mottled sculpin, Cottus bairdi, and goldfish, Carassius auratus, to a 50-Hz dipole source (vibrating sphere). Responses were characterized in terms of (1) receptive fields that relate responsiveness (spike rate and phase-locking) to the location of the source along the length of the fish, (2) input-output functions that relate responsiveness to vibration amplitude for a fixed source location, and (3) peri-stimulus time histograms that relate responsiveness to time during a sustained period of vibration. Relative to posterior lateral line nerve fibers, medial nucleus cells in both species were similar in showing (1) lower spontaneous and evoked rates of spike activity, (2) greater degrees of adaptation, (3) greater heterogeneity in all response characteristics, and (4) evidence for inhibitory/excitatory interactions. Whereas receptive fields of nerve fibers in both species faithfully reflect both pressure gradient amplitudes (with rate changes) and directions (with phase-angle changes) in the stimulus field, receptive fields of medial nucleus were more difficult to relate to the stimulus field. Some, but not all, receptive fields could be modeled with excitatory center/inhibitory surround and inhibitory center/excitatory surround organizations. Accepted: 26 November 1997     

Morphological and physiological evidence of a synaptic connection between the lateral parabrachial nucleus and neurons in the A7 catecholamine cell group in rats

Background

The descending noradrenergic (NAergic) system is one of the important endogenous analgesia systems. It has been suggested that noxious stimuli could activate descending NAergic system; nevertheless, the underlying neuronal circuit remains unclear. As NAergic neurons in the A7 catecholamine cell group (A7) are a part of the descending NAergic system and the lateral parabrachial nucleus (LPB) is an important brainstem structure that relays ascending nociceptive signal, we aimed to test whether LPB neurons have direct synaptic contact with NAergic A7 neurons.

Results

Stereotaxic injections of an anterograde tracer, biotinylated dextran-amine (BDA), were administered to LPB in rats. The BDA-labeled axonal terminals that have physical contacts with tyrosine hydroxylase-positive (presumed noadrenergic) neurons were identified in A7. Consistent with these morphological observations, the excitatory synaptic currents (EPSCs) were readily evoked in NAergic A7 neurons by extracellular stimulation of LPB. The EPSCs evoked by LPB stimulation were blocked by CNQX, a non-NMDA receptor blocker, and AP5, a selective NMDA receptor blocker, showing that LPB-A7 synaptic transmission is glutamatergic. Moreover, the amplitude of LPB-A7 EPSCs was significantly attenuated by DAMGO, a selective μ-opioid receptor agonist, which was associated with an increase in paired-pulse ratio.

Conclusions

Taken together, the above results showed direct synaptic connections between LPB and A7 catecholamine cell group, the function of which is subject to presynaptic modulation by μ-opioid receptors.     

Neuronal types in the lateral geniculate nucleus of man

Summary Nerve cell types of the lateral geniculate body of man were investigated with the use of a transparent Golgi technique that allows study of not only the cell processes but also the pigment deposits. Three types of neurons have been distinguished:Type-I neurons are medium-to large-sized multipolar nerve cells with radiating dendrites. Dendritic excrescences can often be encountered close to the main branching points. Type-I neurons comprise a variety of forms and have a wide range of dendritic features. Since all intermediate forms can be encountered as well, it appears inadequate to subdivide this neuronal type. One pole of the cell body contains numerous large vacuolated lipofuscin granules, which stain weakly with aldehyde fuchsin.Type-II and type-III neurons are small cells with few, sparsely branching and extended dendrites devoid of spines. In Golgi preparations they cannot be distinguished from each other. Pigment preparations reveal that the majority of these cells contains small and intensely stained lipofuscin granules within their cell bodies (type II), whereas a small number of them remains devoid of any pigment (type III). Intermediate forms do not occur.     

Free postsynaptic sites in the lateral geniculate nucleus of adult cats following chronic decortication

Summary Following chronic decortication, free postsynaptic sites were found in the lateral geniculate nucleus of adult cat. Quantitative electron-microscopic analysis of the free postsynaptic sites revealed that they were not identical with the original, vacant postsynaptic sites, but were newly assembled formations. The ability of both relay cells and local interneurons of the adult lateral geniculate nucleus to assemble and/or maintain postsynaptic sites indicates that these nerve cells may be involved in the formation of new synapses.     

Sensitivity and response dynamics of elasmobranch electrosensory primary afferent neurons to near threshold fields

Elasmobranch fishes localize weak electric sources at field intensities of <5 ηV cm⁻¹, but the response dynamics of electrosensory primary afferent neurons to near threshold stimuli in situ are not well characterized. Electrosensory primary afferents in the round stingray, Urolophus halleri, have a relatively high discharge rate, a regular discharge pattern and entrain to 1-Hz sinusoidal peak electric field gradients of ≤20 ηV cm⁻¹. Peak neural discharge for units increases as a non-linear function of stimulus intensity, and unit sensitivity (gain) decreases as stimulus intensity increases. Average peak rate-intensity encoding is commonly lost when peak spike rate approximately doubles that of resting, and for many units occurs at intensities <1 μV cm⁻¹. Best neural sensitivity for nearly all units is at 1–2 Hz with a low-frequency slope of 8 dB/decade and a high-frequency slope of −23 dB/decade. The response characteristics of stingray electrosensory primary afferents indicate sensory adaptations for detection of extremely weak phasic fields near 1–2 Hz. We argue that these properties reflect evolutionary adaptations in elasmobranch fishes to enhance detection of prey, communication and social interactions, and possibly electric-mediated geomagnetic orientation. Accepted: 20 June 1997     

Effects of global electrosensory signals on motion processing in the midbrain of <Emphasis Type="Italic">Eigenmannia</Emphasis>

Wave-type weakly electric fish such as Eigenmannia produce continuous sinusoidal electric fields. When conspecifics are in close proximity, interaction of these electric fields can produce deficits in electrosensory function. We examined a neural correlate of such jamming at the level of the midbrain. Previous results indicate that neurons in the dorsal layers of the torus semicircularis can (1) respond to jamming signals, (2) respond to moving electrosensory stimuli, and (3) receive convergent information from the four sensory maps of the electrosensory lateral line lobe (ELL). In this study we recorded the intracellular responses of both tuberous and ampullary neurons to moving objects. Robust Gaussian-shaped or sinusoidal responses with half-height durations between 55 ms and 581 ms were seen in both modalities. The addition of ongoing global signals with temporal-frequencies of 5 Hz attenuated the responses to the moving object by 5 dB or more. In contrast, the responses to the moving object were not attenuated by the addition of signals with temporal frequencies of 20 Hz or greater. This occurred in both the ampullary and tuberous systems, despite the fact that the ampullary afferents to the torus originate in a single ELL map whereas the tuberous afferents emerge from three maps.     

Detection of multiple stimulus features forces a trade-off in the pyramidal cell network of a gymnotiform electric fish's electrosensory lateral line lobe

Modification of an existing neural structure to support a second function will produce a trade-off between the two functions if they are in some way incompatible. The trade-off between two such sensory functions is modeled here in pyramidal neurons of the gymnotiform electric fish's medullar electrosensory lateral line lobe (ELL). These neurons detect two electric stimulus features produced when a nearby object interferes with the fish's autogenous electric field: (1) amplitude modulation across a cell's entire receptive field and (2) amplitude variation within a cell's receptive field produced by an object's edge. A model of sensory integration shows that detection of amplitude modulation and enhancement of spatial contrast involve an inherent mechanistic trade-off and that the severity of the trade-off depends on the particular algorithm of sensory integration. Electrophysiology data indicate that of the two algorithms for sensory integration modeled here for the gymnotiform fish Brachyhypopomus pinnicaudatus, the algorithm with the better trade-off function is used. Further, the intrinsic trade-off within single cells has been surmounted by the replication of ELL into multiple electrosensory map segments, each specialized to emphasize different sensory features. Accepted: 14 June 1997     

Neuronal and synaptic organization of the lateral geniculate nucleus of the tree shrew,Tupaia glis

Summary The ultrastructural study of the lateral geniculate nucleus (LGN) of the tree shrew (Tupaia glis) revealed two types of neurons: (1) a large thalamocortical relay cell (TCR), which may bear cilia, and (2) a small Golgi type-II interneuron (IN) with an invaginated nucleus. The narrow rim of pale cytoplasm of the IN contains fewer lysosomes and fewer Nissl bodies than the cytoplasm of the TCR. The IN perikarya, which in some cases establish somatosomatic contacts, frequently contain flattened or pleomorphic synaptic vesicles. The ratio of TCR to IN is 31.Three types of axon terminals were observed in the LGN. Two of them contain round synaptic vesicles but differ in size. The large RL boutons undergo dark degeneration after enucleation; they are the terminals of retino-geniculate fibers. The smaller RS boutons show dark degeneration after ablation of the visual cortex; they are the terminals of the cortico-geniculate fibers. The third type of bouton (F₁ does not degenerate after either intervention. The boutons of this type are filled with flattened vesicles and are believed to be intrageniculate terminals. F₂-profiles were interpreted as presynaptic dendrites of the IN. The characteristic synaptic glomeruli found in the LGN contain in their center an optic terminal. These optic terminals establish synaptic contacts with dendrites or spine-like dendritic protrusions of TCRs as well as with presynaptic dendrites. Synaptic triads were also seen. The distribution of the individual types of synaptic contacts in layers 3 and 4 was determined. Layer 4 contains only one third of the retino-geniculate synapses and of the synaptic contacts of F₁-terminals.     

Response properties of visual neurons in the turtle nucleus isthmi

The optic tectum holds a central position in the tectofugal pathway of non-mammalian species and is reciprocally connected with the nucleus isthmi. Here, we recorded from individual nucleus isthmi pars parvocellularis (Ipc) neurons in the turtle eye-attached whole-brain preparation in response to a range of computer-generated visual stimuli. Ipc neurons responded to a variety of moving or flashing stimuli as long as those stimuli were small. When mapped with a moving spot, the excitatory receptive field was of circular Gaussian shape with an average half-width of less than 3°. We found no evidence for directional sensitivity. For moving spots of varying sizes, the measured Ipc response-size profile was reproduced by the linear Difference-of-Gaussian model, which is consistent with the superposition of a narrow excitatory center and an inhibitory surround. Intracellular Ipc recordings revealed a strong inhibitory connection from the nucleus isthmi pars magnocellularis (Imc), which has the anatomical feature to provide a broad inhibitory projection. The recorded Ipc response properties, together with the modulatory role of the Ipc in tectal visual processing, suggest that the columns of Ipc axon terminals in turtle optic tectum bias tectal visual responses to small dark changing features in visual scenes.     

The responses of peripheral and central mechanosensory lateral line units of weakly electric fish to moving objects

Mechanosensory lateral line afferents of weakly electric fish (Eigenmannia) responded to an object which moved parallel to the long axis of the fish with phases of increased spike activity separated by phases of below spontaneous activity. Responses increased with object speed but finally may show saturation. At increasingly greater distances the responses decayed as a power function of distance. For different object velocities the exponents (mean±SD) describing this response falloff were -0.71±0.4 (20 cm/s object velocity) and-1.9±1.25 (10 cm/s). Opposite directions of object movement may cause an inversion of the main features of the response histograms. In terms of peak spike rate or total number of spikes elicited, however, primary lateral line afferents were not directionally sensitive.Central (midbrain) lateral line units of weakly electric fish (Apteronotus) showed a jittery response if an object moved by. In midbrain mechanosensory lateral line, ampullary, and tuberous units the response to a rostral-tocaudal object movement may be different from that elicited by a caudal-to-rostral object motion. Central units of Apteronotus may receive input from two or more sensory modalities. Units may be lateral line-tuberous or lateral line-ampullary. Multimodal lateral line units were OR units, i.e., the units were reliably driven by a unimodal stimulus of either modality. The receptive fields of central units demonstrate a weak somatotopic organization of lateral line input: anterior body areas project to rostral midbrain, posterior body areas project to caudal midbrain.Abbreviation EOD electric organ discharge     

可卡因对外侧缰核神经元的作用及机制初探

目的：探讨可卡因对外侧缰核神经元的作用及可能机制。方法：腹腔注射可卡因,观察内、外侧缰核神经元c—Fos蛋白的表达;在外侧缰核微电泳可卡因,观察其痛相关神经元自发及痛诱发放电的改变：应用全细胞膜片钳技术观察可卡因对外侧缰核神经元延迟整流K^＋电流的影响：结果：①可卡因明显增加外侧缰核c—Fos蛋白表达,但不明显增加内侧缰核c—Fos蛋白表达。②微电泳可卡因至外侧缰核,引起外侧缰核痛兴奋神经元放电增加和痛诱发反应增强,痛抑制神经元放电减少和痛诱发反应减弱.③膜片钳研究显示,可卡因抑制外侧缰核延迟整流K^＋通道,导致K^＋电流减少。结论：外侧缰核神经元对可卡因有较高的敏感性,可卡因能兴奋多数外侧缰核神经元,可能是由于其抑制神经元延迟整流K^＋通道开放产生的.