Navigational choice between reversal and curve during acidic pH avoidance behavior in Caenorhabditis elegans

BACKGROUND

Under experimental conditions, virtually all behaviors of Caenorhabditis elegans are achieved by combinations of simple locomotion, including forward, reversal movement, turning by deep body bending, and gradual shallow turning. To study how worms regulate these locomotion in response to sensory information, acidic pH avoidance behavior was analyzed by using worm tracking system.

RESULTS

In the acidic pH avoidance, we characterized two types of behavioral maneuvers that have similar behavioral sequences in chemotaxis and thermotaxis. A stereotypic reversal-turn-forward sequence of reversal avoidance caused an abrupt random reorientation, and a shallow gradual turn in curve avoidance caused non-random reorientation in a less acidic direction to avoid the acidic pH. Our results suggest that these two maneuvers were each triggered by a distinct threshold pH. A simulation study using the two-distinct-threshold model reproduced the avoidance behavior of the real worm, supporting the presence of the threshold. Threshold pH for both reversal and curve avoidance was altered in mutants with reduced or enhanced glutamatergic signaling from acid-sensing neurons.

CONCLUSIONS

C. elegans employ two behavioral maneuvers, reversal (klinokinesis) and curve (klinotaxis) to avoid acidic pH. Unlike the chemotaxis in C. elegans, reversal and curve avoidances were triggered by absolute pH rather than temporal derivative of stimulus concentration in this behavior. The pH threshold is different between reversal and curve avoidance. Mutant studies suggested that the difference results from a differential amount of glutamate released from ASH and ASK chemosensory neurons.

Chemotaxis behavior toward an odor is regulated by constant sodium chloride stimulus in Caenorhabditis elegans

We studied the chemotaxis behavior of Caenorhabditis elegans toward a chemoattractant in the presence of background sensory stimulus. Chemotaxis toward an odor butanone was greater in the presence of sodium chloride (NaCl) than that without NaCl. By contrast, chemotaxis toward NaCl was not affected by a butanone background. The salt-sensing ASE neuron-deficient che-1(p674) mutants and worms with ASE genetically ablated showed high chemotaxis toward butanone, regardless of the presence of a NaCl background. Therefore, in wild-type worms, information from ASE in the absence of NaCl suppresses butanone chemotaxis, while the suppression is removed in the presence of NaCl.

Evaluation of Head Movement Periodicity and Irregularity during Locomotion of Caenorhabditis elegans

Caenorhabditis elegans is suitable for studying the nervous system, which controls behavior. C. elegans shows sinusoidal locomotion on an agar plate. The head moves not only sinusoidally but also more complexly, which reflects regulation of the head muscles by the nervous system. The head movement becomes more irregular with senescence. To date, the head movement complexity has not been quantitatively analyzed. We propose two simple methods for evaluation of the head movement regularity on an agar plate using image analysis. The methods calculate metrics that are a measure of how the head end movement is correlated with body movement. In the first method, the length along the trace of the head end on the agar plate between adjacent intersecting points of the head trace and the quasi-midline of the head trace, which was made by sliding an averaging window of 1/2 the body wavelength, was obtained. Histograms of the lengths showed periodic movement of the head and deviation from it. In the second method, the intersections between the trace of the head end and the trace of the 5 (near the pharynx) or 50% (the mid-body) point from the head end in the centerline length of the worm image were marked. The length of the head trace between adjacent intersections was measured, and a histogram of the lengths was produced. The histogram for the 5% point showed deviation of the head end movement from the movement near the pharynx. The histogram for the 50% point showed deviation of the head movement from the sinusoidal movement of the body center. Application of these methods to wild type and several mutant strains enabled evaluation of their head movement periodicity and irregularity, and revealed a difference in the age-dependence of head movement irregularity between the strains. A set of five parameters obtained from the histograms reliably identifies differences in head movement between strains.

Evolution of vertebrate transient receptor potential vanilloid 3 channels: opposite temperature sensitivity between mammals and western clawed frogs

Transient Receptor Potential (TRP) channels serve as temperature receptors in a wide variety of animals and must have played crucial roles in thermal adaptation. The TRP vanilloid (TRPV) subfamily contains several temperature receptors with different temperature sensitivities. The TRPV3 channel is known to be highly expressed in skin, where it is activated by warm temperatures and serves as a sensor to detect ambient temperatures near the body temperature of homeothermic animals such as mammals. Here we performed comprehensive comparative analyses of the TRPV subfamily in order to understand the evolutionary process; we identified novel TRPV genes and also characterized the evolutionary flexibility of TRPV3 during vertebrate evolution. We cloned the TRPV3 channel from the western clawed frog Xenopus tropicalis to understand the functional evolution of the TRPV3 channel. The amino acid sequences of the N- and C-terminal regions of the TRPV3 channel were highly diversified from those of other terrestrial vertebrate TRPV3 channels, although central portions were well conserved. In a heterologous expression system, several mammalian TRPV3 agonists did not activate the TRPV3 channel of the western clawed frog. Moreover, the frog TRPV3 channel did not respond to heat stimuli, instead it was activated by cold temperatures. Temperature thresholds for activation were about 16 °C, slightly below the lower temperature limit for the western clawed frog. Given that the TRPV3 channel is expressed in skin, its likely role is to detect noxious cold temperatures. Thus, the western clawed frog and mammals acquired opposite temperature sensitivity of the TRPV3 channel in order to detect environmental temperatures suitable for their respective species, indicating that temperature receptors can dynamically change properties to adapt to different thermal environments during evolution.

Evolution of temperature perception is crucial for adaptation to thermal environments; however, this process is poorly understood. Here we investigated the evolution of the vertebrate TRPV subfamily which contains several mammalian temperature receptors. We identified several novel TRPV genes that have not been found previously and discovered evolutionary flexibility of the TRPV3 gene during vertebrate evolution. TRPV3 channels perceive warm temperature and serve as sensors to detect ambient temperatures near the body temperature of homeothermic animals such as mammals. To examine the functional evolution of TRPV3 channels in vertebrate evolution, we cloned the gene from the western clawed frog and found that its N- and C-terminal regions were highly diversified from those of other terrestrial vertebrate TRPV3 channels. Characterization of the channel properties of western clawed frog TRPV3 revealed that it was not activated by heat stimuli, but instead was activated by cold stimuli. Temperature thresholds for activation were about 16 °C, slightly below the lower temperature limit for the western clawed frog. Thus, the western clawed frog and mammals acquired opposite temperature sensitivity of TRPV3 channels to detect environmental temperatures suitable for their respective species, indicating that temperature receptors can dynamically change properties to adapt to thermal environments during evolution.

A small nucleolar RNA functions in rRNA processing in Caenorhabditis elegans

CeR-2 RNA is one of the newly identified Caenorhabditis elegans noncoding RNAs (ncRNAs). The characterization of CeR-2 by RNomic studies has failed to classify it into any known ncRNA family. In this study, we examined the spatiotemporal expression patterns of CeR-2 to gain insight into its function. CeR-2 is expressed in most cells from the early embryo to adult stages. The subcellular localization of this RNA is analogous to that of fibrillarin, a major protein of the nucleolus. It was observed that knockdown of C/D small nucleolar ribonucleoproteins (snoRNPs), but not of H/ACA snoRNPs, resulted in the aberrant nucleolar localization of CeR-2 RNA. A mutant worm with a reduced amount of cellular CeR-2 RNA showed changes in its pre-rRNA processing pattern compared with that of the wild-type strain N2. These results suggest that CeR-2 RNA is a C/D snoRNA involved in the processing of rRNAs.

In vivo calcium imaging of OFF-responding ASK chemosensory neurons in C. elegans

BACKGROUND

How neurons and neuronal circuits transform sensory input into behavior is not well understood. Because of its well-described, simple nervous system, Caenorhabditis elegans is an ideal model organism to study this issue. Transformation of sensory signals into neural activity is a crucial first step in the sensory-motor transformation pathway in an animal's nervous system. We examined the properties of chemosensory ASK neurons of C. elegans during sensory stimulation.

METHOD

A genetically encoded calcium sensor protein, G-CaMP, was expressed in ASK neurons of C. elegans, and the intracellular calcium dynamics of the neurons were observed.

RESULTS

After application of the attractants l-lysine or food-related stimuli, the level of calcium in ASK neurons decreased. In contrast, responses increased upon stimulus removal. Opposite responses were observed after application and removal of a repellent.

CONCLUSION

The observed changes in response to external stimuli suggest that the activity of ASK neurons may impact stimulus-evoked worm behavior. The stimulus-ON/activity-OFF properties of ASK neurons are similar to those of vertebrate retinal photoreceptors.

GENERAL SIGNIFICANCE

Analysis of sensory-motor transformation pathways based on the activity and structure of neuronal circuits is an important goal in neurobiology and is practical in C. elegans. Our study provides insights into the mechanism of such transformation in the animal.

Phase-dependent preference of thermosensation and chemosensation during simultaneous presentation assay in Caenorhabditis elegans

Background

Multi-sensory integration is necessary for organisms to discriminate different environmental stimuli and thus determine behavior. Caenorhabditis elegans has 12 pairs of amphid sensory neurons, which are involved in generating behaviors such as thermotaxis toward cultivation temperature, and chemotaxis toward chemical stimuli. This arrangement of known sensory neurons and measurable behavioral output makes C. elegans suitable for addressing questions of multi-sensory integration in the nervous system. Previous studies have suggested that C. elegans can process different chemoattractants simultaneously. However, little is known about how these organisms can integrate information from stimuli of different modality, such as thermal and chemical stimuli.

Results

We studied the behavior of a population of C. elegans during simultaneous presentation of thermal and chemical stimuli. First, we examined thermotaxis within the radial temperature gradient produced by a feedback-controlled thermoregulator. Separately, we examined chemotaxis toward sodium chloride or isoamyl alcohol. Then, assays for simultaneous presentations of 15°C (colder temperature than 20°C room temperature) and chemoattractant were performed with 15°C-cultivated wild-type worms. Unlike the sum of behavioral indices for each separate behavior, simultaneous presentation resulted in a biased migration to cold regions in the first 10 min of the assay, and sodium chloride-regions in the last 40 min. However, when sodium chloride was replaced with isoamyl alcohol in the simultaneous presentation, the behavioral index was very similar to the sum of separate single presentation indices. We then recorded tracks of single worms and analyzed their behavior. For behavior toward sodium chloride, frequencies of forward and backward movements in simultaneous presentation were significantly different from those in single presentation. Also, migration toward 15°C in simultaneous presentation was faster than that in 15°C-single presentation.

Conclusion

We conclude that worms preferred temperature to chemoattractant at first, but preferred the chemoattractant sodium chloride thereafter. This preference was not seen for isoamyl alcohol presentation. We attribute this phase-dependent preference to the result of integration of thermosensory and chemosensory signals received by distinct sensory neurons.

Modulation of Caenorhabditis elegans chemotaxis by cultivation and assay temperatures

The chemotaxis behaviors of the nematode Caenorhabditis elegans cultivated at various temperatures (15 degrees C, 20 degrees C and 25 degrees C) were examined at various temperatures (10 degrees C, 15 degrees C, 20 degrees C and 25 degrees C) to determine the multi-sensory integration of physical (thermal) and chemical sensory information within its nervous system. Chemotaxis behavior toward sodium acetate and ammonium chloride were differently affected by both assay and cultivation temperatures, suggesting that the temperature effect on chemotaxis is not general, but rather distinctive for each chemosensory pathway. Since thermosensory cues are likely encountered constantly in C. elegans, we supposed that the chemotaxis behaviors of worms are achieved by the integration of chemo- and thermosensory information. To verify the possible contribution of thermosensory function in chemotaxis, we examined the chemotaxis behaviors of ttx-1(p767) mutant worms with defective AFD thermosensory neurons. The chemotaxis behaviors toward sodium acetate or ammonium chloride of mutant worms cultivated at 20 degrees C and 25 degrees C were reduced relative to those of wild-type worms. These results indicate the important role of multi-sensory integration of chemosensory and thermosensory information in chemotaxis behavior of the C. elegans.

Simulation of C. elegans thermotactic behavior in a linear thermal gradient using a simple phenomenological motility model

The nematode Caenorhabditis elegans has been reported to exhibit thermotaxis, a sophisticated behavioral response to temperature. However, there appears to be some inconsistency among previous reports. The results of population-level thermotaxis investigations suggest that C. elegans can navigate to the region of its cultivation temperature from nearby regions of higher or lower temperature. However, individual C. elegans nematodes appear to show only cryophilic tendencies above their cultivation temperature. A Monte-Carlo style simulation using a simple individual model of C. elegans provides insight into clarifying apparent inconsistencies among previous findings. The simulation using the thermotaxis model that includes the cryophilic tendencies, isothermal tracking and thermal adaptation was conducted. As a result of the random walk property of locomotion of C. elegans, only cryophilic tendencies above the cultivation temperature result in population-level thermophilic tendencies. Isothermal tracking, a period of active pursuit of an isotherm around regions of temperature near prior cultivation temperature, can strengthen the tendencies of these worms to gather around near-cultivation-temperature regions. A statistical index, the thermotaxis (TTX) L-skewness, was introduced and was useful in analyzing the population-level thermotaxis of model worms.

Caenorhabditis elegans mutants having altered preference of chemotaxis behavior during simultaneous presentation of two chemoattractants

Upon presentation of two distinct chemoattractants such as sodium acetate and diacetyl simultaneously, the nematode Caenorhabditis elegans was preferentially attracted by one of these chemoattractants. We isolated two mutants having altered preference of chemotaxis behavior toward simultaneous presentation of sodium acetate and diacetyl. The chep-1(qr1) (CHEmosensory Preference) mutant preferred sodium acetate to diacetyl, while the chep-2(qr2) mutant preferred diacetyl to sodium acetate in simultaneous presentation of these chemoattractants. The chemotaxis behavior of chep-2(qr2) mutant in simultaneous presentation suggests a function of chep-2 gene products within the chemosensory informational integration pathway as well as in the chemosensory pathway.

Evolution of thermoTRP ion channel homologs in vertebrates

In mammalian thermosensation, nine temperature-sensitive ion channels that are activated by distinct temperature thresholds have been identified as thermosensors. These ion channels belong to the transient receptor potential (TRP) superfamily and are referred to as "thermoTRPs" (TRPV1, TRPV2, TRPV3, TRPV4, TRPM2, TRPM4, TRPM5, TRPM8, and TRPA1). To elucidate the evolutionary processes of thermoTRPs, we conducted comprehensive searches for mammalian thermoTRP gene homologs in the draft genome sequences of chicken (Gallus gallus), western clawed frog (Xenopus tropicalis), zebrafish (Danio rerio), and pufferfish (Fugu rubripes). Newly identified homologs were compared with known thermoTRPs, and phylogenetic analyses were conducted. Our comparative analyses revealed that most of the mammalian thermo-TRP members already existed in the common ancestor of fishes and tetrapods. Tetrapods shared almost the same repertoire, except that the western clawed frog expanded TRPV4s (six copies) and TRPM8s (two copies), which were diversified considerably. Comparisons of nonsynonymous and synonymous substitution rates among TRPV4s suggested that one copy of the TRPV4 channel in the western clawed frog retained its original function, while the other copies diversified and obtained slightly different properties. In fish lineages, several members of thermo-TRPs have duplicated in the whole genome duplication occurred in the ancestral ray-finned fish; however, some of the copies have subsequently been lost. Furthermore, fishes do not possess the three members of thermoTRPs existed in mammals, e.g., thermoTRPs activated by noxious heat, warm, and cool temperatures. Our results suggest that thermosensation mechanisms have changed through vertebrate evolution with respect to thermosensor repertoires.

Interactions between Caenorhabditis elegans individuals during chemotactic response

The chemotactic response of the nematode Caenorhabditis elegans is known to be affected by the population density on an assay plate, suggesting the existence of interactions between individual animals. To clarify the interactions between individuals during chemotaxis, we investigated the effect of population density at an attractant area on the chemotactic response to water-soluble sodium acetate and odorant diacetyl using wild-type N2 animals and daf-22 (m130) mutants, which have defective pheromone secretion but can sense pheromone. The chemotaxis index of N2 animals at 90 min of the assay negatively correlated with the number of animals on the assay plate regardless of the type of attractant used (p<0.01). On the other hand, there was no significant difference in the chemotaxis indices of daf-22 (m130) mutants for either of the attractants between the low-and high-population groups. When daf-22 (m130) mutants of a high population density were placed at the attractant location in advance, the chemotaxis index of N2 animals was almost the same as that in the control assay in which no animals were placed at the attractant location in advance. When N2 animals of a high population density were placed at the attractant location in advance, the chemotaxis indices of N2 animals and daf-22 (m130) mutants were significantly smaller than those obtained in the control assay (p<0.05). In the absence of an attractant, we observed a decline in the fraction of animals in the neighborhood of N2 animals of a high population density, although the nematodes were not influenced by daf-22 (m130) mutants of a high population density. These results suggest that the attraction of nematodes to chemicals is inhibited by an increase in the concentration of the pheromone generated by N2 animals at the attractant location.

Computer-driven automatic identification of locomotion states in Caenorhabditis elegans

We developed a computer-driven tracking system for the automated analysis of the locomotion of Caenorhabditis elegans. The algorithm for the identification of locomotion states on agar plates (forward movement, backward movement, rest, and curl) includes the identification of the worm's head and tail. The head and tail are first assigned, by using three criteria, based on time-sequential binary images of the worm, and the determination is made based on the majority of the three criteria. By using the majority of the criteria, the robustness was improved. The system allowed us to identify locomotion states and to reconstruct the path of a worm using more than 1h data. Based on 5-min image sequences from a total of 230 individual wild-type worms and 22 mutants, the average error of identification of the head/tail for all strains was 0.20%. The system was used to analyze 70 min of locomotion for wild-type and two mutant strains after a worm was transferred from a seeded plate to a bacteria-free assay plate. The error of identifying the state was less than 1%, which is sufficiently accurate for locomotion studies.

Serotonin deficiency shortens the duration of forward movement in Caenorhabditis elegans

Serotonin has been implicated in numerous behaviors in a wide variety of animals. We examined the effect of serotonin deficiency, induced by genetic perturbations and cell ablations, on the duration of Caenorhabditis elegans forward movement. Mutants with defective serotonin biosynthesis or worms with ablated serotonergic neurons showed a markedly decreased duration of forward movement, suggesting involvement of this neuromodulator in the regulation of the duration of worm locomotion.

Chemotaxis of Caenorhabditis elegans during simultaneous presentation of two water-soluble attractants, l-lysine and chloride ions

Lysine and chloride ions are water-soluble attractants for Caenorhabditis elegans. When chemotaxis behavior to either of these attractants was assayed separately, the radial concentration gradients of 3 M lysine and 0.1 M ammonium chloride had similar potencies for attracting worms. However, when the concentration gradients of lysine and ammonium chloride at these concentrations were presented simultaneously, worms preferred lysine to ammonium chloride more than expected from the results obtained in separate experiments, suggesting the presence of an interaction between these two sensory information pathways within the nervous system. Chemotaxis behavior toward the radial concentration gradient of one of these attractants superimposed on a uniform concentration of the other attractant showed that the chemotaxis was augmented or attenuated by the ammonium chloride background depending on the background concentration, and attenuated by the lysine background, further supporting the interaction between the two sensory information pathways.

Neurons regulating the duration of forward locomotion in Caenorhabditis elegans

The locomotory behavior of Caenorhabditis elegans consists of four simple events, forward and backward movements, omega-shaped turns and rests. The wide variety of behaviors of this worm is achieved through a combination of these simple locomotions. To gain insight into the neuronal mechanisms regulating this locomotion, we analyzed the locomotory behavior of C. elegans over a long time period. By using an automatic worm tracking system, we revealed the existence of at least two distinct behavioral states -- pivoting and traveling -- in the forward locomotion of C. elegans in the absence of food. Pivoting is characterized by pronounced directional switching and resulting in short-duration forward movement, whereas in the traveling state forward movement is of longer duration. Pivoting occurred when we transferred a well-fed worm to an unseeded plate, and then the transition to traveling occurred, successively. We showed that, by laser ablation, antagonistic neuronal pathways consisting of nine classes of sensory neurons and four classes of interneurons were involved in this regulation. Loss of any one of these neurons altered the locomotory behavior.

Neural network model to generate head swing in locomotion of Caenorhabditis elegans

Computer simulation of the neural network composed of the head neurons of Caenorhabditis elegans was performed to reconstruct the realistic changes in the membrane potential of motoneurons in swinging the head for coordinated forward locomotion. The model neuron had ion channels for calcium and potassium, whose parameters were obtained by fitting the experimental data. Transmission properties of the chemical synapses were set as graded. The neural network involved in forward movement was extracted by tracing the neuronal activity flow upstream from the motoneurons connected to the head muscles. Simulations were performed with datasets, which included all combinations of the excitatory and inhibitory properties of the neurons. In this model, a pulse input entered only from motoneuron VB1, and activation of the stretch receptors on SAA neurons was necessary for the periodic bending. The synaptic output property of each neuron was estimated for the alternate contraction of the dorsal and ventral muscles. The AIB neuron was excitatory, RIV and SMD neurons seemed to be excitatory and RMD and SAA neurons seemed to be inhibitory. With datasets violating Dale's principle for the SMB neuron, AIB neuron was excitatory and RMD neuron was inhibitory. RIA, RIV and SMD neurons seemed to be excitatory.

Effect of simultaneous presentation of multiple attractants on chemotactic response of the nematode Caenorhabditis elegans

Chemotactic behaviors of the nematode, Caenorhabditis elegans in response to chemical attractants, such as water-soluble sodium acetate and an odorant diacetyl, which were sensed by different sensory neurons, were investigated using various concentrations of these chemical attractants. In the presence of only sodium acetate attractant, the fraction of animals that were roaming around the outside of the attractant and original locations correlated negatively with the chemotaxis index for sodium acetate (P < 0.01). In contrast, the fraction of animals that remained in the original location correlated negatively with the chemotaxis index in the presence of only diacetyl attractant (P < 0.05). These results indicate that the manner of chemotaxis responses differs between sodium acetate and diacetyl. In order to investigate the effect of multiple attractants on chemotactic behaviors, the chemotactic responses to simultaneous presentation of sodium acetate and diacetyl were examined. The fraction of animals that gathered at the 0.7 M sodium acetate location was greater than that at the 0.1% diacetyl location in the presence of both attractants (P < 0.05), although the chemotaxis indexes for 0.7 M sodium acetate and 0.1% diacetyl were similar in the presence of a single attractant. On the other hand, the fraction of animals that gathered at the 0.02% diacetyl location was greater than that at the 0.1M sodium acetate location in the presence of both attractants (P < 0.05), although the chemotaxis indexes for 0.02% diacetyl and 0.1M sodium acetate were similar in the presence of a single attractant. These results suggest the existence of excitatory and/or inhibitory connections in the neuronal circuit for attractant selection, and that the efficacy of these connections may change according to the concentrations of both attractants.

Inhibition of willardiine-induced currents through rat GluR6/KA-2 kainate receptor channels by Zinc and other divalent cations

Heteromeric GluR6/KA-2 kainate receptor were expressed in HEK293 cells and an inhibition of willardiine-induced currents by cations was studied. Zinc was much more effective than Ca(2+), Ba(2+) and Mg(2+) at 235, 265 and 1382 fold increase in IC(50), respectively. The inhibition was not voltage-dependent. The present data showed that the binding site for the cations are different from that for willardiine and that the currents are inhibited by the cations via at least two distinct binding sites to Zn(2+) and Ca(2+). These data suggest that Zn(2+) play an important role in modulating glutamate receptors at the nervous system because of a presence of Zn(2+) and various effects of Zn(2+) on the receptors.

trans-4-Amino-2-methylbut-2-enoic acid (2-MeTACA) and (+/-)-trans-2-aminomethylcyclopropanecarboxylic acid ((+/-)-TAMP) can differentiate rat rho3 from human rho1 and rho2 recombinant GABA(C) receptors

1. This study investigated the effects of a number of GABA analogues on rat rho3 GABA(C) receptors expressed in Xenopus oocytes using 2-electrode voltage clamp methods. 2. The potency order of agonists was muscimol (EC(50)=1.9 +/- 0.1 microM) (+)-trans-3-aminocyclopentanecarboxylic acids ((+)-TACP; EC(50)=2.7 +/- 0.9 microM) trans-4-aminocrotonic acid (TACA; EC(50)=3.8 +/-0.3 microM) GABA (EC(50)=4.0 +/- 0.3 microM) > thiomuscimol (EC(50)=24.8 +/- 2.6 microM) > (+/-)-cis-2-aminomethylcyclopropane-carboxylic acid ((+/-)-CAMP; EC(50)=52.6 +/-8.7 microM) > cis-4-aminocrotonic acid (CACA; EC(50)=139.4 +/- 5.2 microM). 3. The potency order of antagonists was (+/-)-trans-2-aminomethylcyclopropanecarboxylic acid ((+/-)-TAMP; K(B)=4.8+/-1.8 microM) (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA; K(B)=4.8 +/-0.8 microM) > (piperidin-4-yl)methylphosphinic acid (P4MPA; K(B)=10.2+/-2.3 microM) 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP; K(B)=10.2+/-0.3 microM) imidazole-4-acetic acid (I4AA; K(B)=12.6+/-2.7 microM) > 3-aminopropylphosphonic acid (3-APA; K(B)=35.8+/-13.5 microM). 4. trans-4-Amino-2-methylbut-2-enoic acid (2-MeTACA; 300 microM) had no effect as an agonist or an antagonist indicating that the C2 methyl substituent is sterically interacting with the ligand-binding site of rat rho3 GABA(C) receptors. 5. 2-MeTACA affects rho1 and rho2 but not rho3 GABA(C) receptors. In contrast, (plus minus)-TAMP is a partial agonist at rho1 and rho2 GABA(C) receptors, while at rat rho3 GABA(C) receptors it is an antagonist. Thus, 2-MeTACA and (+/-)-TAMP could be important pharmacological tools because they may functionally differentiate between rho1, rho2 and rho3 GABA(C) receptors in vitro.

Kinetic analyses of alcohol-induced potentiation of the response of GABA(A) receptors composed of alpha(1) and beta(1) subunits

To investigate the kinetics of both the potentiation and desensitization of the response of ionotropic GABA receptors (GABA(A) receptors) in the presence of various compounds, we expressed receptors composed of alpha(1) and beta(1) subunits by injecting cells with the cRNAs synthesized from cloned bovine GABA(A) receptor cDNAs and measured the electrical responses of the cells electrophysiologically with or without the compounds. The potentiation of the GABA(A) receptor-mediated response was quantitatively analyzed using a simple model with the assumption that the receptors have two identical binding sites for GABA molecules with a dissociation constant of K(1), and one potentiation site for the compound with a dissociation constant of K(p), and that the binding of the compound to the potentiation site only increases the affinity of the GABA binding sites, changing K(1) to K(1p). The estimated K(p) and K(1p) were dependent on the functional groups and the chain length of the compounds. These results could be satisfactorily analyzed using this simple model. The potentiation of the GABA(A) receptor-mediated response by the components of essential oils used for aromatherapy was also examined. These compounds accelerated the decay of the response, possibly due to desensitization of the receptors, which was also analyzed on the basis of the model.

Effects of bisphenol A and its derivatives on the response of GABA(A) receptors expressed in Xenopus oocytes

To study the effects of bisphenol-A (BPA) known to have estrogenic actions, and its derivatives, 3,5-dimethylphenol (DMP) and p-t-butylphenol (TBP), on ionotropic gamma-aminobutyric acid (GABA) receptors, GABA(A) receptors were expressed in Xenopus oocytes by injecting both poly(A)+ RNA prepared from rat whole brain and cRNAs synthesized from cloned cDNAs of alpha1 and beta1 subunit of the bovine receptors, and their electrical responses were measured by the voltage clamping method. BPA caused the potentiation and inhibition of the former receptor-responses, while it caused only inhibition of the latter ones. In the presence of low concentrations of GABA, DMP and TBP potentiated the responses of both receptors. DMP and TBP also increased the rate of decay of the response, possibly by desensitization of the receptors when GABA solution was continuously bath-applied. Diethyl terephthalate (DTP), which is also known to have estrogenic actions, had little effect on both the responses and the decay of both receptors.

Adrenocorticotropic hormone activates an outward current in cultured mouse peritoneal macrophages

To define the effects of adrenocorticotropic hormone (ACTH) in immunocompetent cells, ion channel activities in cultured mouse peritoneal macrophages were analyzed by the perforated patch-clamp method. ACTH induced outward currents at smaller holding potentials than K+ equilibrium potentials. Reversal potentials of ACTH-induced currents were dependent on external K+ concentrations, but not on external Cl- concentration. Quinine potently blocked the outward current and tetraethylammonium (TEA) partially suppressed that current. ACTH did not induce the response in Ca2+ free solution containing EGTA. These results suggest that ACTH can modulate macrophage functions through the activation of Ca2+ dependent K+ channels.

Calcium inhibits willardiine-induced responses in kainate receptor GluR6(Q)/KA-2

A number of studies have demonstrated that willardiine [(S)-1-(2-amino-2-carboxyethyl) pyrimidine-2,4-dione] is a useful agonist for the activation of AMPA/kainate receptors. Here we examine the effect of extracellular calcium on currents evoked by willardiine in HEK 293 cells expressing the GluR6(Q)/KA-2 kainate receptor subunits. At a concentration of 1.8 mM, Ca2+ inhibited the currents induced by 100 microM willardiine by approximately 50%. When extracellular Na+ ions were replaced with Ca2+ ions there were no measurable inward currents. We conclude that Ca2+ inhibition of the willardiine-induced response is concentration dependent.

Durations and frequencies of free locomotion in wild type and GABAergic mutants of Caenorhabditis elegans

We investigated how much time wild-type Caenorhabditis elegans (Bristol N2) nematodes and the GABA-deficient unc25 mutant and the vesicular GABA transporter-deficient unc47 mutant spent moving. The worms were allowed to move freely on the surface of agarose plates either with or without the food bacterium OP50. We identified forward movement, backward movement, resting and turns by watching images on video and computer displays. Forward movement lasted longer and rests were briefer without, than with, bacteria. Frequency distributions except for backward movement fitted a sum of two exponential functions. The duration of backward movement was not strongly influenced by exposure to bacteria, whereas the frequency of backward movements increased in their presence. The duration of forward movement of unc25 nematodes had no long component, thus differing from that of N2 and unc47 strain nematodes in treatments with and without bacteria. The durations of resting in these mutants were much longer than in the N2 strain, especially in the absence of bacteria. The turn frequency of unc47 nematodes had a higher short component than that of the wild type N2 and unc25 nematodes, in the absence of bacteria. A neural network model is discussed in conjunction with the features of mutants and current knowledge of GABAergic neural transmission.

Modulation by L- and D-isoforms of amino acids of the L-glutamate response of N-methyl-D-aspartate receptors

N-Methyl-D-aspartate (NMDA) receptor subtypes epsilon 1 and zeta 1 were coexpressed in Xenopus oocytes for the investigation of the magnitude of augmentation of the L-glutamate response by 20 common L-amino acids and their 19 D-isoforms. Simultaneous application of L- and D-alanine, -cysteine, and -serine, or glycine and L-glutamate potentiated the glutamate-induced current. Other amino acids produced only marginal effects. Analysis of the relationship between the response and amino acid size revealed that the critical threshold size is between those of cysteine and aspartate. No amino acid alone induced a current. The effects of L- and D-alanine, -cysteine, and -serine applied with L-glutamate were concentration-dependent. Molecular modeling of these three amino acids revealed a positive relationship between the charge at an atom of the side chain and the receptor sensitivity, which may explain the efficacies of these amino acids.

Localization of GABA receptor rho 2 and rho 3 subunits in rat brain and functional expression of homooligomeric rho 3 receptors and heterooligomeric rho 2 rho 3 receptors

Ionotropic GABA receptors that are composed of rho subunits act to gate bicuculline-insensitive Cl- currents. Reverse transcription-polymerase chain reaction analysis revealed that the expression of rho 2 mRNA in adult rat brain was approximately eight times higher than mRNA in the rat brain at embryonic day 16, while that of rho 3 in the embryonic brain was approximately six times higher than in the adult brain. In the adult rat brain the rho 3 mRNA was present in the mesencephalon, hippocampus, cerebellum, thalamus and basal ganglia. In situ hybridization has been used to demonstrate the presence of rho 2 mRNA in the hippocampal CA1 region of the 8-day-old rat, and in the CAl region of the hippocampus, lateral geniculate nucleus, superficial gray layer of the superior colliculus and the pars compacta of the substantia nigra of the adult rat. When the homooligomeric rho 3 receptors were expressed in Xenopus oocytes, applications of agonists induced ionic currents. The order of potency of the agonists was muscimol > GABA = trans-4-amino-crotonic acid > cis-4-aminocrotonic acid. The ionic currents induced by GABA were blocked by picrotoxinin and Zn2+ in dose-dependent manner. In heterooligomeric rho 2 rho 3 receptors, picrotoxinin sensitivity was significantly reduced.

Localization of gamma-aminobutyric acid (GABA) receptor rho 3 subunit in rat retina

We used digoxigenin-labelled single strand DNA probes to examine the expression of the mRNA encoding gamma-aminobutyric acid receptor rho 3 subunit in sections of the adult rat retina. Transcript for the rho 3 subunit was found in cell somata of a portion of cells lying in the ganglion cell layer.

Functional expression of GABA rho 3 receptors in Xenopus oocytes

Homomeric rat GABA rho 3 receptors were expressed in Xenopus oocytes, and their pharmacological profile was investigated electrophysiologically. GABA activated the rho 3 receptors with an EC50 value of 7.5 microM and a Hill coefficient of 1.6. The GABA-induced current was not antagonized by bicuculline (100 microM), but was blocked by picrotoxin (IC50: 0.68 microM for 100 microM GABA). The current was almost insensitive to pentobarbital, diazepam and a neurosteroid, 3 alpha-OH-DHP. Many of the pharmacological properties of the rho 3 subunit were similar to those of the previously reported rat rho 1 and rho 2 subunits and GABAC receptors.

Expression of taste reception response of fleshfly in Xenopus oocytes

Functional expression of the gustatory sensitivity to amino acids and sugars was investigated in Xenopus oocytes injected with poly(A+) RNA extracted from fleshfly labellar taste organs. The current induced by the application of amino acids and sugars that stimulate fleshfly sugar receptor cells was recorded under voltage clamp conditions. L-Phenylalanine and L-valine induced a large transient inward current in poly(A+) RNA-injected oocytes but only small responses in uninjected control oocytes. Glucose and fructose also produced inward currents in the RNA-injected oocytes. N-methylated compounds or D-isomers of these amino acids induced either no response or a much smaller response than L-amino acids as they did in the fleshfly sugar receptor cells. The oocyte expression system is a useful tool for characterizing the taste transduction mechanism.

A phenomenological model describing pharyngeal pulsing in the nematode Caenorhabditis elegans anesthetized by alcohol

The recovery process of the suppressed pharyngeal pulsation in the nematode has been investigated for several concentrations of a homologous primary alcohol series (CnH2n-1OH, n = 1,2,3). A mathematical model describing the time course of the recovery process is phenomenologically constructed by using two time constants of delay time tD and recovery time tau. The values of tD and tau are obtained by fitting the equation to experimental data. The obtained values increase with increasing alcohol concentration. To observe the characteristics of tD and tau against the alcohol of order n, the inverse of these time constants are computed at 25 v/v% concentration and plotted on a semi-logarithmic scale. The plot curves decrease non-linearly and are dissimilar to the well-known curves illustrating the importance of lipid solubility in the cell membrane in anesthetic phenomena.

Cloning of a putative gamma-aminobutyric acid (GABA) receptor subunit rho 3 cDNA

Cloned cDNA encoding a putative member of GABA receptor rho-subunit class was isolated from rat-retina-mRNA-derived libraries. The cDNA encodes a signal peptide of 21 amino acids followed by the mature rho 3 subunit sequence of 443 amino acids. The proposed amino acid sequence exhibits 63 and 61% homology to the previously-reported human rho 1 and rat rho 2 sequences, respectively. Northern blot analysis demonstrated the expression of mRNA for rho 3 subunit in retina.

Autoantibody against 70 kD heat shock protein in patients with autoimmune liver diseases

BACKGROUND/AIMS

It has recently been suggested that heat shock proteins are implicated in the pathogenesis and teh pathophysiology of various immunological disorders, and the presence of antibodies against heat shock proteins has been reported in several autoimmune diseases.

METHODS

We investigated autoantibodies against the two major human heat shock proteins (hsp70 and hsp90) in sera from patients with primary biliary cirrhosis and autoimmune hepatitis, the two major autoimmune liver disease. Reactivity with human heat shock proteins obtained from phytohemagglutinin stimulated cells was investigated by immunoblots with sera at 1:20 dilution.

RESULTS

Reactivity with human hsp90 was not found in any sera from patients or normal controls. In contrast, reactivity with human hsp70 was found in 16 of 35 (45.7%) primary biliary cirrhosis patients and in 9 of 17 (52.9%) autoimmune hepatitis patients, but similar reactivity was found in only 2 of 15 patients with chronic hepatitis B and 1 of 13 patients with chronic hepatitis C. All the normal controls showed a negative reaction. Two-dimensional immunoblots and immunoabsorption experiments established that the autoantibody recognized only human hsc70 (73 kD/pI 5.5), a constitutive form of the hsp70 family.

CONCLUSIONS

Although the pathological significance of the autoantibody against hsc70 in these autoimmune liver diseases remains unknown, the serum autoantibody detected in primary biliary cirrhosis patients is closely related to clinical variables including serum total bilirubin, alanine aminotransferase, IgG, IgM, titers of antimitochondrial antibodies, and major symptoms (pruritus and/or icterus). These observations may suggest that the anti-hsc70 antibody is an indicator for the disease activity of primary biliary cirrhosis.

Identification of GABAA receptor subunits in rat retina: cloning of the rat GABAA receptor rho 2-subunit cDNA

We identified GABAA receptor subunits in rat retina using PCR. The high degree of conservation among previously described members of ligand-gated anion channels in transmembrane domains was used to design degenerate sense and antisense oligonucleotides. These oligonucleotides were used as primers for PCR, which was applied to the rat retina cDNA. Analysis of clones derived from the PCR amplification identified the GABAA alpha 1, beta 1, beta 3, and gamma 2 subunits and the glycine alpha 1 subunit. In addition, two clones closely related to the human GABAA rho-subunit class were obtained. Molecular cloning revealed one of them as the rat counterpart of the human rho 2 subunit. Northern blot analysis demonstrated the expression of mRNAs for rho subunits in retina. These results further support the hypothesis that bicuculline-insensitive GABA channels in rat retina are comprised of rho subunits.

Relationship between resting cytosolic Ca2+ and responses induced by N-methyl-D-aspartate in hippocampal neurons

Cytosolic calcium concentrations ([Ca2+]i) in cultured hippocampal neurons from rat embryos were measured using fura-2. Neurons with higher resting [Ca2+]i showed greater [Ca2+]i responses to N-methyl-D-aspartate (NMDA) and K+ depolarization. There was a strong relationship between resting [Ca2+]i and the maximal changes in [Ca2+]i (delta[Ca2+]i), which fit the our proposed equation to describe this relationship.

Effect of nebracetam on nicotinic and muscarinic acetylcholine receptors expressed in Xenopus oocyte by injecting exogenous mRNA

Using voltage- and current-clamp methods the effects of nebracetam 4-aminomethyl-1-benzylpyrrolidine-2-one hemifumarate, WEB 1881 FU, CAS 118607-07-1), a new agent with nootropic property, on the nicotinic (nAChRs) and muscarinic acetylcholine receptors (mAChRs) were studied, which were expressed in Xenopus oocytes by injecting E. electricus mRNA and rat brain mRNA, respectively. Simultaneous application of nebracetam (0.03-2 mmol/l) with acetylcholine (ACh) (0.01-1 mmol/l) inhibited the ACh-responses of both nAChRs and mAChRs, whereas preapplication of these concentrations of nebracetam for 30 s to 1 min potentiated such inhibition. A simple competitive inhibition model for the effects of both drugs simultaneously applied yielded the inhibition constant, K1 of 0.419 and 0.212 mmol/l for nAChRs and mAChRs, respectively, indicating that the action on mAChRs is a little more potent than on nAChRs. Nebracetam induced a concentration-dependent slight increase in inward currents on mAChRs but not on nAChRs. It is suggested that the direct effects of nebracetam on nAChRs and mAChRS, which were induced only by a rather high concentration, as compared with the clinically expected plasma level, may be a contributing factor to the clinical effectiveness of the drug only if there is some critical change in the sensitivity to the drug.

Effects of subunit types of the recombinant GABAA receptor on the response to a neurosteroid

When vertebrate brain poly(A)+ RNA is expressed in Xenopus oocytes the response of the GABA receptors formed is found to be inhibited allosterically by a neurosteroid, pregnenolone sulphate (PS). This negative modulation was reproduced after expressing RNAs encoding bovine GABAA receptor subunits in the combinations alpha i + beta 1, or alpha i + beta 1 + gamma 2 (where i = 1, 2 or 3). The characteristics of this inhibition vary significantly with the type of the alpha subunit (alpha 1, alpha 2, or alpha 3) used. When the bovine gamma 2L alternate form of the gamma 2 subunit was replaced by the human gamma 2S subunit, the behaviour was unchanged: the human gamma 2S subunit used is a newly-cloned form, which encodes a polypeptide with two amino acid differences from the human gamma 2 subunit previously described. The results of co-application of PS and 3 alpha-hydroxy-5 alpha-pregnan-ol-20-one, a neurosteroid which is a positive modulator of the GABAA receptor, indicate that these act at different sites on the receptor. PS also increases the desensitisation of the receptor by GABA. This effect, also, is alpha-subunit-type dependent and occurs by an acceleration of the fast phase of desensitisation.

N-methyl-D-aspartate increases cytosolic Ca2+ via G proteins in cultured hippocampal neurons

The changes of the cytosolic Ca2+ concentrations ([Ca2+]i) induced by N-methyl-D-aspartate (NMDA) in fura-2-loaded cultured hippocampal neurons from rat embryos were investigated by the fast application method, using a fine pipe under extracellular Mg(2+)-free conditions. In the presence of Ca2+, NMDA, at concentrations in excess of 3 microM, induced a biphasic increase of [Ca2+]i, which consisted of an initial increase with a second rise that occurred after cessation of drug application. Under Ca(2+)-free conditions, NMDA (greater than 100 microM) in the absence of glycine or NMDA (greater than 50 microM) in the presence of glycine (greater than 10 microM) induced intracellular Ca2+ mobilization, which was blocked by 30 microM 2-amino-5-phosphonovaleric acid (APV) and reduced by islet-activating protein. When the neurons were superfused with Ca(2+)-free solution, the application of 3-10 microM NMDA, which had been dissolved in Ca(2+)-containing solution, induced the second phase [Ca2+]i increase, whereas application of kainate, quisqualate, or stimulation by 50 mM K+ did not. Islet-activating protein, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), and D-sphingosine reduced the second phase [Ca2+]i increase. These results suggest that NMDA-induced intracellular Ca2+ mobilization is potentiated by the initial entry of Ca2+ into the cells and is regulated in an islet-activating protein-sensitive manner.

Intracellular cAMP regulates the response to NMDA in hippocampal neurons

We have studied the effects of intracellular cyclic AMP (cAMP) on the response to N-methyl-D-aspartate (NMDA) in hippocampal cultured neurons by loading them with 2'-o-dibutyryladenosine 3', 5'-cyclic monophosphate (dcAMP) and have obtained evidence for regulation of Ca2+ release from intracellular stores by cAMP. Extracellular Ringer's solution was either Ca(2+)-containing or Ca(2+)-free. A brief initial stimulation with NMDA (10-100 microM, 12 s) was required before the neurons were loaded with dcAMP to potentiate the changes in intracellular Ca2+ concentration induced by the second stimulus of NMDA. Forskolin (10 microM) mimicked dcAMP, but to a lesser extent. A phorbol ester 12-o-tetradecanoylphorbol-13-acetate (100 nM) inhibited the effect of dcAMP.

Effects of subunit types of the cloned GABAA receptor on the response to a neurosteroid

Combinations of cloned GABAA receptor subtypes, having the subunit combinations alpha i + beta 1 or alpha i + beta 1 + gamma 2 (i = 1, 2, 3), were expressed in Xenopus oocytes. The endogenous steroid 3 alpha-hydroxy-5 alpha-pregnan-20-one potentiates GABA currents induced therein by GABA. This potentiation was greater in the alpha 1 + beta and alpha 3 + beta 1 than in the alpha 2 + beta 1 combinations. The presence of the gamma 2-subunit increased the steroid potency in alpha 1 + beta 1 and alpha 2 + beta 1, but the combination alpha 3 + beta 1 + gamma 2 became much less steroid-sensitive. It is concluded that the steroid modification of the GABAA receptor is strongly influenced by the alpha- and the gamma 2-subunit types.

Sequence and functional expression of a single alpha subunit of an insect nicotinic acetylcholine receptor

We report the isolation and sequence of a cDNA clone that encodes a locust (Schistocerca gregaria) nervous system nicotinic acetylcholine receptor (AChR) subunit (alpha L1). The calculated molecular weight of the unglycosylated polypeptide, which contains in the proposed extracellular domain two adjacent cysteine residues which are characteristic of alpha (ligand binding) subunits, is 60,641 daltons. Injection into Xenopus oocytes, of RNA synthesized from this clone in vitro, results in expression of functional nicotinic receptors in the oocyte membrane. In these, nicotine opens a cation channel; the receptors are blocked by both alpha-bungarotoxin (alpha-Bgt) and kappa-bungarotoxin (kappa-Bgt). Reversible block of the expressed insect AChR by mecamylamine, d-tubocurarine, tetraethylammonium, bicuculline and strychnine has also been observed. These data are entirely consistent with previously reported electrophysiological studies on in vivo insect nicotinic receptors and also with biochemical studies on an alpha-Bgt affinity purified locust AChR. Thus, a functional receptor exhibiting the characteristic pharmacology of an in vivo insect nicotinic AChR can be expressed in Xenopus oocytes by injection with a single subunit RNA.

Hippocampal neurotrophic factors influence the perikaryal size of septal acetylcholinesterase-containing neurons in culture

The septal neurons were cultured under the following conditions: (1) treated with 7S nerve growth factor (NGF) (50 ng/ml); (2) grown with hippocampal cell-conditioned medium supernatant; (3) cocultivated with hippocampal cells; (4) cocultivated with cerebellar cells; (5) no treatment. Acetylcholinesterase histochemistry was used to identify cholinergic cells after pretreatment with diisopropylfluorophosphate. The mean values of the perikaryal major axis and minor axis at day 14 of culture were significantly larger in septal cells cocultivated with hippocampal cells than in septal cells grown under other conditions. NGF-treated septal cells showed a smaller, but significant, increase in the mean value of the major axis of these neurons.

Acetylcholinesterase-containing neurons in the striatum, septum and hippocampus of the rat in embryonic culture and adult in situ

Neurons of the rat brain, of either adult in situ or embryonic culture, have been studied by using a sensitive method for acetylcholinesterase (AChE) histochemistry. In the culture system, incubated for 6-18 days, AChE-positive neurons were found in tissues originating from the striatum and septum, but not in those from the hippocampus. These positive somata were morphometrically analyzed in terms of the cell size, i.e. the lengths of the major axis (Lmax) and the minor axis (Lmin) in cultured dishes of the striatum and septum; the mean Lmax was 20 and 22 microns, respectively. In in situ adult brain sections, a similar morphometric examination of AChE-positive neurons gave comparable results to those obtained in the culture system. An evaluation of both in vitro and in vivo through the histogramatical analysis revealed that the striatum contained more than two populations of AChE-positive cells differing in cell size. In contrast, a major single peak of Lmax was detected in the histogram of the septum. In both cases of striatum and septum in in situ adult brain, sagittal sections show larger size of Lmax, indicating that AChE-positive neurons are arranged in the sagittal direction. In studies on electrophysiological properties of large striatal cells in culture, both acetylcholine and glutamate induced changes in the membrane potential and/or the frequency of excitatory postsynaptic potential, while dopamine induced much smaller responses.