Slowly adapting stretch-receptor organs: Periodic stimulation with and without perturbations

The length of isolated slowly adapting stretch-receptor organs (SAO) from crayfish was submitted to approximately sinusoidal modulations of 0.030–0.800 mm at frequencies of about 0.2, 1.0 or 3.0 cps. Sines were imposed either by themselves (clean) or mixed with (perturbed by) fast irregular length fluctuations or jitter. The amplitude of the latter remained within a specified fraction of the modulation, usually two-thirds (or x0.66), though from one twentieth to twice (or x0.05–2.00) were explored. The afferent impulse discharge was recorded: rate over bins of about 1/10 of the period was plotted as function of ongoing time. Within stationary epochs, average cycles were analyzed primarily in terms of lengths and discharge intensities. Each point in the displays corresponded to a particular bin along the average cycle, the abscissa and the ordinate being the length and the corresponding discharge rate, respectively; points were numbered in the order of their generation. Similar displays were constructed for rate vs velocity, rate vs acceleration, and rate-change vs velocity. Experiments without jitter. The non-perturbed state. With 0.2 and 1.0 cps, the rate vs length display had a clockwise loop with a flat extension to the left. The SAO at its shortest did not discharge and remained silent for some time. As length augmented, it eventually started firing, reaching maximum rate while being stretched (lead) or at maximum length. While length decayed, the organ fired less, slowing down, stopping at a length greater than where it had started, and then remaining silent until the end of the cycle. With 3.0 cps, the display had a counterclockwise loop with a flat extension on the left. The SAO did not discharge at its shortest, and fired more during relaxation than during stretching, peaking when relaxing (lag) and stopping at a length greater than where it had started. Artificial introduction of time separations between length and rate converted displays into acceptably straight lines only in a few, usually 0.2 cps, cases. The rate vs length relation exhibited consistent departures from monotonic increase and from linearity: departures were large fractions of the overall swings involving flat extensions, leads, lags, saturation effects, asymmetric rate sensitivities, and locking (which was frequent with 1.0 or 3.0 cps and could conceivably be more common with faster modulations). Other experimental paradigms have demonstrated multivaiued steady-state-rate-length relations. The variability from cycle to cycle of the rate in a particular bin was high or low for bins with low or high rates, respectively. Rate vs velocity plots were counter-clockwise loops with a base upon the abscissae, higher rates when velocity was decaying than when augmenting, and maxima at non-negative velocities. Rate-change vs velocity plots showed shortening associated with either discharge, decreases or small changes, and lengthenings associated with discharge increases, greater when augmenting if at 0.2 cps or when decaying if at 3.0 cps. Rate vs stimulus acceleration plots were, for the three tested frequencies, counterclockwise loops with a base upon the abscissae and higher rates when acceleration was decaying than when augmenting, suggesting a particular role in sensing accelerations. The sensitivity to length was evaluated by comparing the rate-swings at each frequency using identical bin-widths and depths. This procedure is considered to be most meaningful physiologically. Sensitivity was contingent upon the bin-width: with small bins (30 and 120 ms) it was highest for 3.0 cps, with intermediate bins (160 ms) it was highest for 1.0 cps, and with larger bins it was practically uniform. Differences involved factors of under x1.7. Experiments with jitter. The perturbed state. Jitter changed radically the rate vs length displays, converting all of them into clockwise folium-like loops, which implied a shift from lag to lead at 3.0 cps. Introduction of appropriate lags brought points acceptably close to straight, positively sloped segments: this occurred often at 0.2 cps, sometimes at 1.0 cps, and exceptionally at 3.0 cps. Jitter altered the variability profile along the cycle, decreasing peak variability and not affecting or increasing the minimum; variability along the cycle was thus reduced and uniformed and identification of stimuli on the basis of discharges was improved. Jitter amplitude was an important issue. The larger ones, about the modulation size, increased the lowest bin-rates, particularly at 0.2 and 1.0 cps, and increased the peaks at 0.2 cps, decreasing them at 1.0 and 3.0 cps. The smaller jitter, about 1/10 of the modulation, affected the lowest rates little, but increased the peak rate at 0.2 cps, decreasing it at 1.0 and 3.0 cps; display shapes changed little. A qualitative model of the SAO involves subsystems with linear features, as well as rectification, stiction-like and saturation-like properties. Depending upon back-ground length, modulation depth, jitter and several other issues, the organ can perform frankly nonlinearly, piece-wise linearly or linearly. Within each context, a particular stimulus is of interest and can be referred to as the signal; others are not, and can be referred to as noise, acting as perturbations. Small, erratic perturbations influence strongly transduction of large steps or sines, simplifying and making it more proportionate. Large regular perturbations act upon small signals too, but their influence has been explored less extensively.Supported by grants from NIH and NSF     

Modifications of dynamic and static behavior by small-length perturbations in crayfish stretch receptor organs

To investigate whether static and dynamic sensitivities of slowly and rapidly adapting stretch receptor organs (SAO and RAO, respectively) or crayfish are different when perturbed compared with those in conventional laboratory experiments, receptors were submitted to ramplike length changes of different velocities separated by long-duration, constant lengths of different values. They were perturbed at random by fast, small-amplitude length variations called "jitter." First-order afferent discharges were recorded extracellularly. Quantifications involved the separate estimation of static and dynamic response components. In the SAO, jitter (1) augmented the static sensitivity, (2) decreased the dynamic sensitivity, (3) simplified response profiles by decreasing nonlinearities and increasing transduction fidelity in terms of coding length. In the RAO, jitter (1) changed the behavior from phasic to tonic with length sensitivity, (2) decreased the dynamic sensitivity to values close to those of the unperturbed SAO, (3) increased transduction fidelity for stimulus length and decreased nonlinearities. Perturbation effects suggest that differences between SAO and RAO are more quantitative than qualitative. Moreover, they have general implications and are relevant to other mechanoreceptors at other levels in the CNS.     

Adaptive trunk sway velocities following repeated perturbations in subjects with and without low back pain

Faster trunk motions could be a strategy to prevent loss of balance and fall injuries due to unexpected perturbations. However, it is unclear how trunk sway velocities can be compensated during stepping in subjects with low back pain (LBP). The purpose of this study was to investigate lower limb reaction, swing, and step times, as well as trunk sway velocities at heel strike and toe-off, following repeated step perturbations between subjects with and without LBP. There were 30 subjects with LBP and 42 control subjects who were exposed to treadmill-induced perturbations at a velocity of 0.12 m/sec for 0.62 m. The treadmill-induced steps caused subjects to walk forward for 4.90 sec after the perturbation. The groups demonstrated significant interactions on the lower limb reaction times and on the number of repeated perturbations (F = 4.83, p = 0.03) due to a decreased step time at the first perturbation (t = 2.52, p = 0.01) in the LBP group. For the trunk sway velocities, the repeated perturbations demonstrated a significant interaction between groups (F = 4.65, p = 0.03). This adaptive trunk strategy for gait stability increased step times with repeated perturbations in the LBP group. The group interactions on the trunk sway velocities also indicated a possible somatosensory integration for step time adjustments to avoid potential fall hazards. This adaptive response with repeated step perturbations could result in compensatory trunk sway for gait stability.     

The Effects of Starvation on Crayfish Responses to Alarm Odor

The effect of starvation on responses to alarm odor was tested with individuals of an invasive and a native species of crayfish. I predicted that chemical predator cues would inhibit feeding less in starving than well-fed animals, and that this decrease would be stronger in a native compared with an invasive species. Individuals were exposed to food odor and then alarm odor after 3 and 10 d of starvation. The inhibition of food-related behavior patterns was similar on the 2 d of testing for individuals of the invasive species, Orconectes rusticus. Individuals of O. virilis showed a significant reduction in the effects of alarm odor detection on day 10 compared with day 3 of starvation. The lack of a change in responses to alarm odors between days of testing by individuals of O. rusticus may be because they are more responsive to alarm odors than individuals of O. virilis. This behavioral difference could contribute to the successful range extension of O. rusticus.     

Prevalence of the Crayfish Plague Pathogen Aphanomyces astaci in Populations of the Signal Crayfish Pacifastacus leniusculus in France: Evaluating the Threat to Native Crayfish

Aphanomyces astaci, the crayfish plague pathogen, first appeared in Europe in the mid-19^th century and is still responsible for mass mortalities of native European crayfish. The spread of this parasite across the continent is especially facilitated by invasive North American crayfish species that serve as its reservoir. In France, multiple cases of native crayfish mortalities have been suggested to be connected with the presence of the signal crayfish Pacifastacus leniusculus, which is highly abundant in the country. It shares similar habitats as the native white-clawed crayfish Austropotamobius pallipes and, when infected, the signal crayfish might therefore easily transmit the pathogen to the native species. We investigated the prevalence of A. astaci in French signal crayfish populations to evaluate the danger they represent to local populations of native crayfish. Over 500 individuals of Pacifastacus leniusculus from 45 French populations were analysed, plus several additional individuals of other non-indigenous crayfish species Orconectes limosus, O. immunis and Procambarus clarkii. Altogether, 20% of analysed signal crayfish tested positive for Aphanomyces astaci, and the pathogen was detected in more than half of the studied populations. Local prevalence varied significantly, ranging from 0% up to 80%, but wide confidence intervals suggest that the number of populations infected by A. astaci may be even higher than our results show. Analysis of several individuals of other introduced species revealed infections among two of these, O. immunis and P. clarkii. Our results confirm that the widespread signal crayfish serves as a key reservoir of Aphanomyces astaci in France and therefore represents a serious danger to native crayfish species, especially the white-clawed crayfish. The prevalence in other non-indigenous crayfish should also be investigated as they likely contribute to pathogen transmission in the country.     

Physiological Experimentation with the Crayfish Hindgut: A Student Laboratory Exercise

The purpose of the report is to describe dissection techniques for preparing the crayfish hindgut and to demonstrate how to make physiological recordings with a force transducer to monitor the strength of contraction. In addition, we demonstrate how to visually monitor peristaltic activity, which can be used as a bioassay for various peptides, biogenic amines and neurotransmitters. This preparation is amenable to student laboratories in physiology and for demonstrating pharmacological concepts to students. This preparation has been in use for over 100 years, and it still offers much as a model for investigating the generation and regulation of peristaltic rhythms and for describing the mechanisms underlying their modulation. The pharmacological assays and receptor sub-typing that were started over 50 years ago on the hindgut still contribute to research today. This robust preparation is well suited to training students in physiology and pharmacology.     

Effects of Some Organic Cations on Generator Potential of Crayfish Stretch Receptor

The generator potential of both slowly and rapidly adapting crayfish stretch receptor cells can still be elicited by mechanical stimuli when all the Na of the bathing medium is replaced by various organic cations. In the presence of tris(hydroxymethyl)aminomethane (Tris), the generator potential is particularly large, about 30–50 % of that in the control saline, while spike electrogenesis of the cell is abolished. Persistence of the generator response is not due to retention of Na by a diffusion barrier, and ionic contributions to the electrogenesis by Ca and Cl can also be excluded. Thus, whereas the electrogenesis of the generator membrane must be due to an increased permeability to monovalent cations, the active receptor membrane appears to be less selective for different monovalent cations than is the receptor component of some other cells, or the conductile component of the stretch receptor neuron.     

Fused organs in the adherent1 mutation in maize show altered epidermal walls with no perturbations in tissue identities

In the absence of wounding, the epidermis is only rarely involved in cell or organ fusion events; in fact, intact epidermal layers prevent graft unions. In Zea mays L. the mutation adherent1 (ad1) shows abnormal fusions between cells and organs. Fusions involve epidermal cells of vegetative and floral organs and occur early in the ontogeny of organs. Even so, epidermal cell types differentiate normally in the fused regions and internal tissue identities are maintained. In contrast, the extracellular matrix (cell wall and cuticle) of the epidermal cells is perturbed. Epidermal cell walls in adherent leaves are thicker than normal. Epicuticular wax particles appear reduced in size and number and altered in shape in mutant leaves. In addition, the outer epidermal cell walls of adherent leaves fluoresce when stained with aniline blue, a reagent that binds to callose. Immunolocalizations to specific cell wall epitopes suggest that pectins but not arabinogalactans may have a role in the fusion events. Taken together, these results suggest that the ad1 mutation results in cell-wall and epicuticular-wax defects similar to responses seen in wounding, pollination by incompatible pollen, or pathogen attack. Since cell wall components and epicuticular waxes are extracellular secreted products, the ad1 mutation may disrupt normal functioning and/or composition of the secretory pathway and its cargo. Received: 30 January 1998 / Accepted: 5 March 1998     

Effects of Lithium on Different Membrane Components of Crayfish Stretch Receptor Neurons

Unlike several other varieties of input membrane, that of the crayfish stretch receptor develops a generator potential in response to stretch when all the Na of the medium is replaced with Li. However, Li depolarizes the receptor neuron, the soma membrane becoming more depolarized than that of the axon. During exposure to Li the cell usually fires spontaneously for a period, and when it becomes quiescent spike electrogenesis fails in the soma but persists in the axon. These effects are seen in the rapidly adapting as well as the slowly adapting cells. The block of spike electrogenesis of the soma membrane is only partly due to the Li-induced depolarization and a significant role must be ascribed to a specific effect of Li.     

Effects of Illumination on the Circadian Motor Rhythm of the Chelipeds of Crayfish

The effects of different illumination conditions on the main parameters of the circadian motor rhythms of the two chelipeds of the crayfish, Procambarus digueti , were compared. Under either constant darkness (DD) or constant light (LL) the phase relationship between the two circadian rhythms was more stable than under entrained conditions (LD cycles). These results suggest that the oscillators responsible for these rhythms differ in their sensitivity to light. The role of paired organs in the internal temporal order of the crayfish is discussed.     

Effects of Illumination on the Circadian Motor Rhythm of the Chelipeds of Crayfish

The effects of different illumination conditions on the main parameters of the circadian motor rhythms of the two chelipeds of the crayfish, Procambarus digueti, were compared. Under either constant darkness (DD) or constant light (LL) the phase relationship between the two circadian rhythms was more stable than under entrained conditions (LD cycles). These results suggest that the oscillators responsible for these rhythms differ in their sensitivity to light. The role of paired organs in the internal temporal order of the crayfish is discussed.     

Effects of temperature perturbations on circadian conidiation in neurospora

Studies on the circadian rhythm of conidiation in the bd strain of Neurospora crassa Shear and Dodge have shown that temperature step-up and step-down perturbations produce phase advances and delays, respectively. Pulse-up and pulse-down treatments lead to both phase advances and delays. The resulting phase shifts can be very large, and few to no transients are observed.     

Effects of alcohols on lipid bilayers with and without cholesterol: the dipalmitoylphosphatidylcholine system

Differential scanning calorimetry is a useful method to study the thermotropic phase transitions of a phospholipid bilayer. In the present study DSC is used to determine the effects of methanol and ethanol on DPPC and DPPC/2 mol% cholesterol bilayers. The biphasic effect of the main transition and the presence of an extra peak on the DSC cooling scans were observed above certain alcohol concentrations. In the presence of 2% cholesterol, the concentration at which the biphasic effect occurs is increased by both short-chain alcohols. 1,6-Diphenyl-1,3,5-hexatriene (DPH) is used as a fluorescent probe to directly determine the onset of interdigitation in these systems as reflected by a drop in the DPH fluorescence intensity.     

Effects of ethanol on lipid bilayers with and without cholesterol: the distearoylphosphatidylcholine system

Differential scanning calorimetry (DSC) and fluorescence spectroscopy are useful techniques for investigating the phase transitions of phospholipid bilayers. In this study, these methods have been extended to determine the effects of ethanol on DSPC and DSPC/2 mol.% cholesterol bilayers. The biphasic effect of the main transition was observed on the DSC heating scans above 0.60 M ethanol. In addition, the concentration at which the biphasic effect occurs is not significantly changed in the presence of 2 mol.% cholesterol. For the fluorescence studies, 1,6-diphenyl-1,3,5-hexatriene (DPH) has been incorporated into the bilayer to monitor the phase transitions through the displacement of DPH. This fluorescent probe is used to directly determine the onset of interdigitation in the bilayer systems as indicated by a large decrease in the DPH fluorescence intensity. The addition of cholesterol lowered and broadened the transition temperatures of the phosphatidylcholine (PC) system. However, 2 mol.% cholesterol did not have a significant effect on the induction of the interdigitated phase in DSPC as observed from the small difference in ethanol threshold concentration for the two systems. This suggests that DSPC forms a more stable interdigitated gel phase than other PCs with shorter acyl chains.     

Measurement of O2 consumption in isolated organs without venous cannulation

A new two-sensor technique for measurement of O2 consumption in isolated organs without venous cannulation was successfully applied to the isolated rat heart. Because this technique eliminates the net exchange of O2 between venous effluent and the environment, measurement of the O2 concentration is conveniently made by use of a polarographic sensor in a collected pool of effluent at the bottom of a closed organ chamber. The method was validated against conventional techniques using cannulation of the pulmonary artery. The two-sensor technique allows O2 consumption measurements to be made in isolated organ preparations in which representative venous cannulation is prohibitively difficult, for example in organs with multiple venous drains, or those in which cannulation would be expected to cause excessive perturbation of physiological status.     

Predatory Efficiency of Crayfish: Comparison Between Indigenous and Non-Indigenous Species

The invasive crayfish Procambarus clarkii is highly dispersed within lentic waters in northern and central Italy. It is a polytrophic predator, exerting a strong influence on animal communities, including amphibians, fish, gastropods, and insect larvae. The indigenous species Austropotamobius italicus, inhabiting lotic waters, behaves as a generalist – but not opportunistic – species. The object of this study was to compare the predatory pressure exercised by the two species on potential prey, i.e., anuran tadpoles, urodelan larvae, fish fry, larvae of insects, and gastropods. Three main conclusions were drawn: (1) both species are skilled predators, adopting a sit-and-wait strategy, (2) the two crayfish seemed to form a `search image' of familiar prey, as the result of either visual or chemical perceptual changes, and (3) at least in the laboratory, P. clarkii readily switched to naive prey for it (tadpoles of Rana italica and larvae of Limnephilidae), unlike the less opportunistic A. italicus. These results furnish suggestions on the trophic preferences of the two crayfish species and provide a partial understanding of the effects that the invasive species have on the community dynamics. This revised version was published online in July 2006 with corrections to the Cover Date.