Periodic firing pattern in afferent discharges from electroreceptor organs of catfish

Spontaneous afferent activity was recorded from 26 single ampullary electroreceptive organs of freshwater catfish (Ictalurus nebulosus LeS) at various temperatures. Regular grouping of action potentials was apparent in this secondary sensory system at 35°C and occasionally at 30°C. Impulse groups consisted of up to seven impulses. The precise timing of impulse generation and the temporal sequence of impulses indicated that oscillating processes are involved. Expectation density functions were calculated for records of afferent activity obtained at various temperatures below 35°C. In the majority of records the function was periodic. Impulse grouping and expectation density functions became more distinct in units exhibiting extremely high thresholds (i.e. being insensitive) to electrical stimuli. The results suggest that the oscillations originate from the postsynaptic membrane. The temporal pattern of impulse generation within impulse groups of ampullary electroreceptor organs and of specific warm and cold receptors was compared and found to be similar. Application of cadmium and menthol, which both reduce calcium entry, suppressed spontaneous activity in normal and insensitive electroreceptor systems, attenuated the sensitivity of normal receptors and modified the periodic pattern. This indicates that calcium is implicated in sensory transduction and in postsynaptic mechanisms. The data suggest that an oscillating process is one component of signal transmission in ampullary electroreceptor organs of teleost fish.     

Hypoxia increases the cutaneous threshold for the sensation of cold

Cutaneous temperature sensitivity was tested in 13 male subjects prior to, during and after they breathed either a hypocapnic hypoxic (HH), or a normocapnic hypoxic (NH) breathing mixture containing 10% oxygen in nitrogen. Normocapnia was maintained by adding carbon dioxide to the inspired gas mixture. Cutaneous thresholds for thermal sensation were determined by a thermosensitivity testing device positioned on the plantar side of the first two toes on one leg. Heart rate, haemoglobin saturation, skin temperature at four sites (arm, chest, thigh, calf) and adapting temperature of the skin (T_ad; degrees centigrade), i.e. the temperature of the toe skin preceding a thermosensitivity test, were measured at minute intervals. Tympanic temperature (T_ty; degrees centigrade) was measured prior to the initial normoxic thermosensitivity test, during the hypoxic exposure and after the completion of the final normoxic thermosensitivity test. End-tidal carbon dioxide fraction and minute inspiratory volume were measured continuously during the hypoxic exposure. Ambient temperature, T_ty, T_ad and mean skin temperature remained similar in both experimental conditions. Cutaneous sensitivity to cold decreased during both HH (P<0.001) and NH conditions (P<0.001) as compared with the tests undertaken pre- and post-hypoxia. No similar effect was observed for cutaneous sensitivity to warmth. The results of the present study suggest that sensitivity to cold decreases during the hypoxic exposure due to the effects associated with hypoxia rather than hypocapnia. Such alteration in thermal perception may affect the individuals perception of thermal comfort and consequently attenuate thermoregulatory behaviour during cold exposure at altitude.     

Intra-abdominal thermosensitivity in the rabbit as compared with spinal thermosensitivity

Summary In rabbits, intra-abdominal temperature sensors of the dorsal wall of the abdominal cavity were selectively stimulated by means of thermodes perfused with water of temperatures ranging from 12–50°C. Respiratory acceleration and vasodilatation of the skin could be elicited as thermoregulatory responses by intraabdominal warming. By intra-abdominal cooling a depression of an elevated respiratory frequency could be induced. This depressing effect was already fully developed at a perfusion temperature of 36°C and could not be further augmented by stronger cooling.Neural afferent activity recorded from filaments of the N. splanchnicus was found to increase with rising perfusion temperatures beginning with 36–37°C. It is concluded from these results that abdominal thermosensitivity is predominantly a warmth-sensitivity in contrast to spinal cord thermosensitivity which comprises both cold and warmth sensitivity.Heating intensities and heat inputs, respectively, of equally effective periods of spinal cord and intra-abdominal warming were compared with each other. It was found that heat input into the abdominal thermode had to be four times greater than that supplied to the vertebral canal thermode in order to evoke identical responses. Simultaneous application of equally effective thermal stimuli to the abdomen and the spinal cord reinforced the thermoregulatory responses.     

Effect of ouabain and potassium-free solution on mammalian thermosensitive afferents in vitro

Summary Studies have been performed on the afferent fibers innervating the scrotal skin of the rat to test the hypothesis that the generator potential mechanism underlying cold thermosensitivity of these afferent fibers is an electrogenic sodium pump. In these experiments a pudendal nerve-scrotal skin preparation was isolated from the animal and, maintained in oxygenated mammalian Ringer's where composition could be varied and drugs added. Application of ouabain resulted in an increase in the discharge of cold sensitive afferent fibers which was more pronounced at 38–41° C than at temperatures below 30° C. In most of the cases transient accelerations on cooling were reduced, but often a transient response to warming appeared. The effects of ouabain administration were reversible. Removal of extracellular K at 35° C resulted in an increased discharge of cold sensitive afferents. This observation is consistent with the effects of ouabain, since removal of extracellular K also blocks Na transport. The generator potential mechanism underlying cold sensitivity of these afferent fibers appears to be an electrogenic Na pump.     

Tonic influence of the efferent vestibular system on the spontaneous afferent activity from semicircular canals in the frog (Rana esculenta L.)

Summary In the frog we have recorded the spontaneous activity of single afferent fibres of the ampullary nerves of the left horizontal semicircular canal (HC) and vertical anterior canal (VAC) in isolated head preparations. The recordings have been made in 4 experimental situations: intact preparations; preparations whose brain was destroyed; preparations whose contralateral vestibular nerve had been cut between Scarpa's ganglion and the brain; preparations where either an ampullary nerve (that of the HC or of the VAC) or the utricular nerve had been cut contralaterally. From our results, it appears that the efferent vestibular system has a tonic influence on the afferent activity from HC and VAC; the influence of the part of the efferent vestibular system (EVS) activity depending on contralateral vestibular inputs is inhibitory, while the influence of the part of the EVS activity depending on ipsilateral vestibular inputs might be facilitatory.     

The effect of spinal and skin temperatures on the firing rate and thermosensitivity of preoptic neurones

1. In anaesthetized rabbits, preoptic single unit activity was recorded while preoptic, spinal cord and skin temperatures were independently manipulated.2. The units that were insensitive to preoptic temperature were characterized by low firing rates and also by a very low incidence of extrahypothalamic thermosensitivity.3. Thirty-seven units having positive coefficients to preoptic temperature were tested for their response to spinal or skin temperature. Of these, twenty-two units responded to extrahypothalamic temperature, seventeen with positive thermal coefficients. In addition, the incidence of extrahypothalamic thermosensitivity generally increased among the higher firing units.4. Twenty-two units had negative coefficients for preoptic temperature and were tested for their extrahypothalamic thermosensitivities. Of these, sixteen units had dual thermosensitivities, ten with negative coefficients for the extrahypothalamic temperatures. In addition, there was no correlation between the incidence of extrahypothalamic thermosensitivity and the level of firing rate.5. In the units having positive coefficients for preoptic temperature, an increased firing rate, due to extrahypothalamic temperature, generally resulted in a decreased preoptic thermosensitivity. Conversely, a decreased firing rate usually resulted in an increased preoptic thermosensitivity.6. In the units having negative coefficients for preoptic temperature, an increased firing rate, due to extrahypothalamic temperature, usually increased the preoptic thermosensitivity; while a decreased firing rate tended to decrease the sensitivity to preoptic temperature.     

Noise-induced transition to bursting in responses of paddlefish electroreceptor afferents

The response properties of ampullary electroreceptors of paddlefish, Polyodon spathula, were studied in vivo, as single-unit afferent responses to external electrical stimulation with varied intensities of several types of noise waveforms, all Gaussian and zero-mean. They included broadband white noise, Ornstein-Uhlenbeck noise, low- or high-frequency band-limited noise, or natural noise recorded from swarms of Daphnia zooplankton prey, or from individual prey. Normally the afferents fire spontaneously in a tonic manner, which is actually quasiperiodic due to embedded oscillators. 1) Weak noise stimuli increased the variability of afferent firing, but it remained tonic. 2) In contrast, stimulation with less-weak broadband noise led to a qualitative change of the firing patterns, to parabolic bursting, even though the mean firing rate was scarcely affected. 3) The transition to afferent bursting was marked by the development of two well-separated timescales: the fast frequency of spiking inside bursts at 相似文献   

Temperature effects on neuronal membrane potentials and inward currents in rat hypothalamic tissue slices

Preoptic–anterior hypothalamic (PO/AH) neurones sense and regulate body temperature. Although controversial, it has been postulated that warm-induced depolarization determines neuronal thermosensitivity. Supporting this hypothesis, recent studies suggest that temperature-sensitive cationic channels (e.g. vanilloid receptor TRP channels) constitute the underlying mechanism of neuronal thermosensitivity. Moreover, earlier studies indicated that PO/AH neuronal warm sensitivity is due to depolarizing sodium currents that are sensitive to tetrodotoxin (TTX). To test these possibilities, intracellular recordings were made in rat hypothalamic tissue slices. Thermal effects on membrane potentials and currents were compared in PO/AH warm-sensitive, temperature-insensitive and silent neurones. All three types of neurones displayed slight depolarization during warming and hyperpolarization during cooling. There were no significant differences in membrane potential thermosensitivity for the different neuronal types. Voltage clamp recordings (at −92 mV) measured the thermal effects on persistent inward cationic currents. In all neurones, resting holding currents decreased during cooling and increased during warming, and there was no correlation between firing rate thermosensitivity and current thermosensitivity. To determine the thermosensitive contribution of persistent, TTX-sensitive currents, voltage clamp recordings were conducted in the presence of 0.5 μ m TTX. TTX decreased the current thermosensitivity in most neurones, but there were no resulting differences between the different neuronal types. The present study found no evidence of a resting ionic current that is unique to warm-sensitive neurones. This supports studies suggesting that neuronal thermosensitivity is controlled, not by resting currents, but rather by currents that determine rapid changes in membrane potential between successive action potentials.     

Determinants of spatial and temporal coding by semicircular canal afferents

The vestibular semicircular canals are internal sensors that signal the magnitude, direction, and temporal properties of angular head motion. Fluid mechanics within the 3-canal labyrinth code the direction of movement and integrate angular acceleration stimuli over time. Directional coding is accomplished by decomposition of complex angular accelerations into 3 biomechanical components-one component exciting each of the 3 ampullary organs and associated afferent nerve bundles separately. For low-frequency angular motion stimuli, fluid displacement within each canal is proportional to angular acceleration. At higher frequencies, above the lower corner frequency, real-time integration is accomplished by viscous forces arising from the movement of fluid within the slender lumen of each canal. This results in angular velocity sensitive fluid displacements. Reflecting this, a subset of afferent fibers indeed report angular acceleration to the brain for low frequencies of head movement and report angular velocity for higher frequencies. However, a substantial number of afferent fibers also report angular acceleration, or a signal between acceleration and velocity, even at frequencies where the endolymph displacement is known to follow angular head velocity. These non-velocity-sensitive afferent signals cannot be attributed to canal biomechanics alone. The responses of non-velocity-sensitive cells include a mathematical differentiation (first-order or fractional) imparted by hair-cell and/or afferent complexes. This mathematical differentiation from velocity to acceleration cannot be attributed to hair cell ionic currents, but occurs as a result of the dynamics of synaptic transmission between hair cells and their primary afferent fibers. The evidence for this conclusion is reviewed below.     

Spatial tuning and dynamics of vestibular semicircular canal afferents in rhesus monkeys

Rotational head motion in vertebrates is detected by the three semicircular canals of the vestibular system whose innervating primary afferent fibers encode movement information in specific head planes. In order to further investigate the nature of vestibular central processing of rotational motion in rhesus monkeys, it was first necessary to quantify afferent information coding in this species. Extracellular recordings were performed to determine the spatial and dynamic properties of semicircular canal afferents to rotational motion in awake rhesus monkeys. We found that the afferents innervating specific semicircular canals had maximum sensitivity vectors that were mutually orthogonal. Similar to other species, afferent response dynamics varied, with regular firing afferents having increased long time constants (t ₁), decreased cupula velocity time constants (t _v), and decreased fractional order dynamic operator values (s ^k) as compared to irregular firing afferents.     

Degradation Behavior and Biocompatibility of PEG/PANI-Derived Polyurethane Co-polymers

A series of polyurethane (PU) co-polymers with designable molecular weight between cross-linking dots was synthesized by a hydrogen transfer polymerization route from polyaniline (PANI), poly(ethylene glycol) (PEG), various curing agents and chain extenders using dibutyltin dilaurate as a catalyst. Their swelling, hydrophilicity, degradation and biocompatibility were inspected and assessed based on different degrees of polymerization of PANI and PEG, and their component proportion. Fourier transformation infrared spectrometry (FT-IR), ¹H-NMR spectroscopy, scanning electron microscopy (SEM), gel-permeation chromatography (GPC) and goniometry were used to characterize the structure and surface morphology of the synthesized PEG/PANI-based PU co-polymers, PU residues after degradation and degraded polymers at different time periods of hydrolysis. The thermal properties, aggregate structure and surface microstructure were examined by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and atomic force microscopy (AFM). Hemolysis, static platelet adhesion, dynamic clotting measurements and MTT assays were adopted to evaluate the hemo- or cytocompatibility. The experimental results indicated that these polymers exhibit various degrees of micro-phase separation, depending on the concentration and degree of polymerization of PANI, molecular weight of PEG, type of curing agent and chain extender, which further influence their swelling, hydrophilicity, degradable properties and biological performances in vitro. The incorporation of PANI and PANI* in co-polymers led to decreased thermal stability but slower decomposition rates than typical PEG-based PUs. The stress–strain tests showed that the as-prepared PU co-polymers possessed increased tensile strength and modulus, and decreased toughness in comparison with the blank PEG-based PU. These co-polymers are expected to find specific applications in tissue engineering or controlled drug release.     

The fine structure of ampullary and tuberous electroreceptors in the South American blind catfish Pseudocetopsis spec

Summary Two types of electroreceptors, the ampullary and the tuberous electroreceptor (silurid knollenorgan) in the epidermis of the catfish, Pseudocetopsis spec., were investigated with semithin and ultrathin serial sections. The ampullary organ contains one or two sensory cells which are embedded in supporting cells at the base of open epithelial canals. They bear some slender microvilli on their apical surface and form several synaptic bars. The afferent myelinated nerve fiber arborizes in the connective tissue papilla and looses its myelin sheath about 30 m below the supporting cell layer. A second thin myelinated axon occur up to the supporting cell layer. The tuberous electroreceptor organ contains one large receptor cell. Most of the cell body is exposed to the lumen of a specialized proximal canal segment and is closely covered with microvilli. A single myelinated axon looses its myelin sheath within the supporting cell layer about 1 m before terminating as a flat calyx at the base of the sensory cell. A functional significance of the two types of receptors will be discussed.     

Static and dynamic response characteristics, receptive fields, and interaction with noxious input of midline medullary thermoresponsive neurons in the rat

Thermal clamping of deep-body temperature and 16 fields covering the total truncal skin surface enabled characterization of thermal transmission neurons distributed in a midline medullary location. The total data set comprised 136 neurons from 54 female rats. Relative abundance of neuronal types was 27 to 34 to 75 for cold-responsive, warm-responsive, and thermally unresponsive neurons. Response maxima of thermoresponsive neurons to static thermal stimulation of the total truncal surface were 55 +/- 4 ips (mean +/- SE) at 5 degrees C for cold-responsive neurons and 6.0 +/- 1.6 ips at 35 degrees C for warm-responsive neurons. Dynamic thermal stimulation of the total truncal surface at rates up to +/- 1.6 degrees C/s failed to reveal a clear dynamic thermosensitivity in either cold- or warm-responsive neuronal pools. Instead, the data suggest a preferential passing of the static response relative to the dynamic response. Cutaneous thermal receptive fields were diffuse, occupying most of the truncal surface. Subparts of these fields drove thermoresponsive neurons to variable extents, suggesting convergence from unequally represented multiple cutaneous sources. Noxious stimulation at widely distributed body sites consistently augmented activity in cold-responsive neurons. A thermoregulatory rather than somatesthetic role is proposed for the midline medullary neurons studied here.     

COX-2 expression of ampullary carcinoma: correlation with different histotypes and clinicopathological parameters

Epidemiological studies suggest that regular intake of nonsteroidal anti-inflammatory drugs (NSAIDs) are associated with reduced incidence of gastrointestinal cancer. Several lines of evidence indicate that the antineoplastic effect of NSAIDs is attributable to COX-2 inhibition. The aim of our study was to assess COX-2 expression in a series of primary untreated ampullary carcinomas and its possible correlation with clinicopathological parameters. In the present study, 45 surgical specimens of invasive ampullary carcinomas were histologically classified into pancreaticobiliary, intestinal, and unusual types. COX-2 expression by immunohistochemical method was analyzed. High COX-2 expression was detected in 35 (77.8%) ampullary carcinomas. Among these, 20/21 (95.2%) were classified as intestinal, 9/18 (50%) pancreaticobiliary, and 6/6 (100%) unusual type. A significant statistical difference in terms of COX-2 expression was found between pancreaticobiliary vs intestinal type (P=0.002). Furthermore, a negative significant statistical correlation was found between T factor and COX-2 expression (P=0.047). The different COX-2 expression among histopathological types supports the concept of histogenetical difference of ampullary carcinomas. Furthermore, the high rate of COX-2 expression in the intestinal subtype of ampullary carcinoma may represent the rational for a histotype-tailored therapy targeting COX-2.     

Influence of the saccule,lagena and vertical posterior canal on the ipsilateral horizontal and vertical anterior semicircular canals inRana esculenta: Role of receptor-receptor fibres

Summary The influence of the efferent vestibular system being eliminated, the spontaneous activity of single afferent fibres of the ampullary nerves of the horizontal and vertical anterior semicircular canals was recorded in the frog. By stimulating electrically the nerves of the vertical posterior canal, lagena or saccule as well as by sectioning these nerves and then using statistical methods, it is shown that the receptor-receptor fibres arising from the above mentioned receptors have generally an inhibitory influence on the afferent activity from the horizontal and vertical anterior canals.     

Phase transformation in poly(1-butene) blended with hydrogenated oligo(cyclopentadiene)

Isothermally crystallized blends of isotactic poly(1-butene) (PB-1) with hydrogenated oligo-(cyclopentadiene) (HOCP) were annealed for different periods of time and at different temperatures and then analyzed by differential scanning calorimetry. The HOCP, a glassy oligomer with a relatively high T_g value, results with PB-1 in a one-phase system in the melt. The kinetics of crystal transformation of poly(1-butene) from form II to form I are subject to the influence of the non-crystallizable component on the amorphous phase of PB-1. The phase transformation process was also analyzed by means of the Avrami equation. During the conversion process secondary crystallization of PB-1 was observed.     

Slowly adapting type I mechanoreceptor discharge as a function of dynamic force versus dynamic displacement of glabrous skin of raccoon and squirrel monkey hand

The effects of dynamic force and dynamic displacement on single unit discharge rate during ramp stimulation were examined in 10 raccoon and 8 squirrel monkey slowly adapting Type I (SAI) mechanoreceptive afferent fibers, all having receptive fields on glabrous skin of the hand. In all 18 cases, power function exponents were higher for effects of dynamic displacement than for effects of dynamic force on discharge frequency. Thus, these SAI mechanoreceptors are more sensitive to variations in dynamic displacement than to variations in dynamic force. This differential sensitivity may be explained by the fact that the relationship between dynamic force and dynamic displacement is, itself, nonlinear, dynamic displacement being a power function of dynamic force, with exponents less than 1.0.     

The distribution of cutaneous sudomotor and alliesthesial thermosensitivity in mildly heat-stressed humans: an open-loop approach

The distribution of cutaneous thermosensitivity has not been determined in humans for the control of autonomic or behavioural thermoregulation under open-loop conditions. We therefore examined local cutaneous warm and cool sensitivities for sweating and whole-body thermal discomfort (as a measure of alliesthesia). Thirteen males rested supine during warming (+4°C), and mild (−4°C) and moderate (−11°C) cooling of ten skin sites (274 cm²), whilst the core and remaining skin temperatures were clamped above the sweat threshold using a water-perfusion suit and climate chamber. Local thermosensitivities were calculated from changes in sweat rates (pooled from sweat capsules on all limbs) and thermal discomfort, relative to the changes in local skin temperature. Thermosensitivities were examined across local sites and body segments (e.g. torso, limbs). The face displayed stronger cold (−11°C) sensitivity than the forearm, thigh, leg and foot ( P = 0.01), and was 2–5 times more thermosensitive than any other segment for both sudomotor and discomfort responses ( P = 0.01). The face also showed greater warmth sensitivity than the limbs for sudomotor control and discomfort ( P = 0.01). The limb extremities ranked as the least thermosensitive segment for both responses during warming, and for discomfort responses during moderate cooling (−11°C). Approximately 70% of the local variance in sudomotor sensitivity was common to the alliesthesial sensitivity. We believe these open-loop methods have provided the first clear evidence for a greater facial thermosensitivity for sweating and whole-body thermal discomfort.     

Effects of temperature on the discharges of muscle spindles and tendon organs

1. In anaesthetized cats the effects of temperature on the nervous outflow from skeletal muscle via thick myelinated afferent fibres were studied. Single unit recordings were made from afferents of muscle spindles and tendon organs during slow and fast temperature changes of the medial gastrocnemius muscle which was deefferented by ventral root section and prestretched to a tension of 100 p.
2. Group I afferent units from muscle spindles were activated by warming and depressed by cooling, the effect of warming being much more pronounced than that of cooling. Afferents from secondary spindle endings with a high background discharge behaved similar to Ia fibres, whereas those with a low initial discharge rate showed an activation by cooling and a depression (mostly to cessation of firing) by warming. The discharges of group I afferents from tendon organs varied; an activation by warming was the most frequently observed reaction.
3. Some of the afferents from muscle spindles and tendon organs showed signs of a dynamic sensitivity to thermal stimulation, but in general the dynamic component in the responses to temperature changes was only small.
4. The results suggest that the afferent outflow via thick myelinated fibres from a resting, moderately prestretched muscle strongly depends on temperature. At raised intramuscular temperatures (about 42°C) the nervous outflow is characterized by an increased activity in all of the I a and many of the I b afferents, while the majority of group II spindle afferents will be depressed. In contrast, in a cold muscle (about 29°C) the nervous outflow via afferents from primary spindle endings will be reduced, while the net activity from secondary spindle endings will be increased and no marked changes are expected to occur in the discharges of I b fibres.

     

Three-dimensional interactions of mean body and local skin temperatures in the control of hand and foot blood flows

Purpose

Much is known about the control of blood flow, yet gaps remain concerning the interactions of deep-body and peripheral thermal feedback. In this experiment, changes in the vascular tone of the hands and feet were mapped to demonstrate the separate and combined influences of mean body and local skin temperature changes.

Methods

Eight males participated in three trials. Three pre-experimental conditions were established via water immersion (oesophageal temperatures: 36.1, 37.0, 38.5 °C), with core and mean skin temperatures then clamped (water-perfusion garment) whilst five thermal treatments were applied to the right hand and left foot (5, 15, 25, 33, 40 °C). This yielded 15 thermal combinations under which hand and foot blood flows were measured (displacement plethysmography).

Results

Lower volume-specific blood flows were observed at the foot for almost all temperature combinations. When thermoneutral and moderately hyperthermic, the cutaneous thermosensitivity of the hand was significantly greater: thermoneutral: 0.2 vs. 0.1 (foot) mL 100 mL^?1 min^?1 °C^?1 (P < 0.05); moderate hyperthermia: 0.4 vs. 0.2 (foot) mL 100 mL^?1 min^?1 °C^?1 (P < 0.05). The hand was 13 times more responsive to core temperature elevations than an equivalent local skin temperature change. For the foot, this thermosensitivity differed by a factor of 26.

Conclusion

These observations identified the hands as heat radiators, with the feet resisting heat loss, and reinforce the dominance of central thermal feedback, particularly in controlling foot blood flow. However, thermosensitivity to local skin temperature changes was highly plastic, site-specific and dictated by thermal and regional variations in vaso- and venoconstrictor tone.