Pulsation waves along the Ciona heart tube reverse by bimodal rhythms expressed by a remote pair of pacemakers.

The heart of ascidians (marine invertebrate chordates) has a tubular structure, and heartbeats propagate from one end to the other. The direction of pulsation waves intermittently reverses in the heart of ascidians and their relatives; however, the underlying mechanisms remain unclear. We herein performed a series of experiments to characterize the pacemaker systems in isolated hearts and their fragments, and applied a mathematical model to examine the conditions leading to heart reversals. The isolated heart of Ciona robusta autonomously generated pulsation waves at ∼20 to 25 beats min-1 with reversals at ∼1 to 10 min intervals. Experimental bisections of isolated hearts revealed that independent pacemakers resided on each side and also that their beating frequencies periodically changed as they expressed bimodal rhythms, which comprised an ∼1.25 to 5.5 min acceleration/deceleration cycle of a beating rate of between 0 and 25 beats min-1. Only fragments including 5% or shorter terminal regions of the heart tube maintained autonomous pulsation rhythms, whereas other regions did not. Our mathematical model, based on FitzHugh-Nagumo equations applied to a one-dimensional alignment of cells, demonstrated that the difference between frequencies expressed by the two independent terminal pacemakers determined the direction of propagated waves. Changes in the statuses of terminal pacemakers between the excitatory and oscillatory modes as well as in their endogenous oscillation frequencies were sufficient to lead to heart reversals. These results suggest that the directions of pulsation waves in the Ciona heart reverse according to the changing rhythms independently expressed by remotely coupled terminal pacemakers.

Motor state changes escape behavior of crickets.

Animals change their behavior depending on external circumstances, internal factors, and their interactions. Locomotion state is a crucial internal factor that profoundly affects sensory perception and behavior. However, studying the behavioral impacts of locomotion state in free-moving animals has been challenging due to difficulty in reproducing quantitatively identical stimuli in freely moving animals. We utilized a closed-loop controlled servosphere treadmill system, enabling unrestricted confinement and orientation of small animals, and investigated wind-induced escape behavior in freely moving crickets. When stimulated during locomotion, the crickets quickly stopped before initiating escape behavior. Moving crickets exhibited a higher probability of escape response compared to stationary crickets. The threshold for pausing response in moving crickets was also much lower than the escape response threshold. Moving crickets had delayed reaction times for escape and greater variance in movement direction compared to stationary crickets. The locomotion-related response delay may be compensated by an elevated sensitivity to airflow.

Neural mechanism of experience-dependent sensory gain control in C. elegans.

Animals' sensory systems adjust their responsiveness to environmental stimuli that vary greatly in their intensity. Here we report the neural mechanism of experience-dependent sensory adjustment, especially gain control, in the ASH nociceptive neurons in Caenorhabditis elegans. Using calcium imaging under gradual changes in stimulus intensity, we find that the ASH neurons of naive animals respond to concentration increases in a repulsive odor 2-nonanone regardless of the magnitude of the concentration increase. However, after preexposure to the odor, the ASH neurons exhibit significantly weak responses to a small gradual increase in odor concentration while their responses to a large gradual increase remain strong. Thus, preexposure changes the slope of stimulus-response relationships (i.e., gain control). Behavioral analysis suggests that this gain control contributes to the preexposure-dependent enhancement of odor avoidance behavior. Mathematical analysis reveals that the ASH response consists of fast and slow components, and that the fast component is specifically suppressed by preexposure for the gain control. In addition, genetic analysis suggests that G protein signaling may be required for the regulation of fast component. We propose how prior experience dynamically and specifically modulates stimulus-response relationships in sensory neurons, eventually leading to adaptive modulation of behavior.

The trunk-tail junctional region in Ciona larvae autonomously expresses tail-beating bursts at ∼20 second intervals.

Swimming locomotion in aquatic vertebrates, such as fish and tadpoles, is expressed through neuron networks in the spinal cord. These networks are arranged in parallel, ubiquitously distributed and mutually coupled along the spinal cord to express undulation patterns accommodated to various inputs into the networks. While these systems have been widely studied in vertebrate swimmers, their evolutionary origin along the chordate phylogeny remains unclear. Ascidians, representing a sister group of vertebrates, give rise to tadpole larvae that swim freely in seawater. In the present study, we examined the locomotor ability of the anterior and posterior body fragments of larvae of the ascidian Ciona that had been cut at an arbitrary position. Examination of more than 200 fragments revealed a necessary and sufficient body region that spanned only ∼10% of the body length and included the trunk-tail junction. 'Mid-piece' body fragments, which included the trunk-tail junctional region, but excluded most of the anterior trunk and posterior tail, autonomously expressed periodic tail-beating bursts at ∼20 s intervals. We compared the durations and intervals of tail-beating bursts expressed by mid-piece fragments, and also by whole larvae under different sensory conditions. The results suggest that body parts outside the mid-piece effect shortening of swimming intervals, particularly in the dark, and vary the burst duration. We propose that Ciona larvae express swimming behaviors by modifying autonomous and periodic locomotor drives that operate locally in the trunk-tail junctional region.

Enhanced polarotaxis can explain water-entry behaviour of mantids infected with nematomorph parasites.

A wide range of parasites manipulate the behaviours of their hosts in order to complete their life cycle1. Alteration of phototaxis is thought to be involved in host manipulation in many cases2,3. However, very little is known about what features of the light (intensity, spectrum, polarization) alter behaviour. Here we report that arboreal mantids (Hierodula patellifera) infected by nematomorph parasites (Chordodes sp.) are attracted to horizontally polarized light, which could induce the mantids to enter water, where the parasites can then emerge and reproduce. In a two-choice test, infected mantids were attracted to horizontally but not vertically polarized light. Uninfected mantids were not attracted to either. In a field experiment, 14 infected mantids entered a deep pool, where the water surface strongly reflected horizontally polarized light. By contrast, only two mantids entered a shallow pool, where the surface reflection had higher light intensity but weaker polarization. To our knowledge, this is the first study demonstrating that a manipulative parasite can take advantage of its hosts' ability to perceive polarized light stimuli to alter host behaviour. VIDEO ABSTRACT.

Clonidine premedication for sevoflurane anesthesia in upper abdominal surgery.

The effects of clonidine as a preanesthetic medication were compared with diazepam on clinical courses of sevoflurane anesthesia in 22 patients undergoing upper abdominal surgery. The patients were divided into two groups of 11 patients each according to preanesthetic medication: atropine 0.5 mg i.m. plus clonidine 0.3 mg p.o., or atropine 0.5 mg i.m. plus diazepam 10 mg p.o. 60-90 min prior to induction of anesthesia. Anesthesia was induced with fentanyl and thiopental, and was maintained with sevoflurane, 0.5%-1.5%, nitrous oxide and oxygen, supplemented with fentanyl, 0.5 µg·kg-1·hr-1. While only one patient needed a vasodilator in the clonidine group for treatment of hypertension, seven patients needed it in the diazepam group. Pain score after extubation was higher in the diazepam group than in the clonidine group. The time when patients responded to verbal command after discontinuation of anesthetics was similar in both groups. Therefore, clonidine pretreatment was useful for sevoflurane anesthesia in upper abdominal surgery.