Distribution of Ih Channels and their Function in the Stomatogastric Ganglion

Generation of rhythmic patterns in the absence of descending commands is an essential and powerful trait of many motor networks. Cyclic rhythmic discharges of motoneurons in repeated motor activities like locomotion, mastication and respiration require underlying circuits of neurons, which are called central pattern generators (CPG). This study examined the possible roles of Ih cation channels in the pyloric network of the stomatogastric nervous system, a rhythmically active network of motoneurons that controls movements of the lobster foregut. Of specific interest were the H-current�s involvement in maintaining firing properties, the distribution of Ih channels within the stomatogastric ganglion, and a potential role for Ih in regulation of synaptic strength. I was able to confirm a homeostatic interaction of Ih with A-type potassium channels, where the over-expression of the IA shal gene after RNA injection evoked a compensatory increase of Ih in different motoneuron types. I observed an additional, non-Ih component of the hyperpolarization activated current, which was more likely to occur in shal-RNA and gfp-RNA injected neurons, compared to untreated neurons. Further, I showed that the homeostatic response of Ih increase is unidirectional; overexpression of the Ih protein PIIH did not lead to an increase of IA. In an immunocytochemical study, I found high concentrations of Ih protein localized in the fine neuropil of the stomatogastric ganglion, an area which is rich in synaptic contacts. Finally, I demonstrate a potential role for Ih in regulating synaptic transmission, for which I found evidence in electrophysiological experiments, where the amplitude of inhibitory postsynaptic potentials decreased with increasing activation of Ih

Temperate fish detection and classification: a deep learning based approach

A wide range of applications in marine ecology extensively uses underwater cameras. Still, to efficiently process the vast amount of data generated, we need to develop tools that can automatically detect and recognize species captured on film. Classifying fish species from videos and images in natural environments can be challenging because of noise and variation in illumination and the surrounding habitat. In this paper, we propose a two-step deep learning approach for the detection and classification of temperate fishes without pre-filtering. The first step is to detect each single fish in an image, independent of species and sex. For this purpose, we employ the You Only Look Once (YOLO) object detection technique. In the second step, we adopt a Convolutional Neural Network (CNN) with the Squeeze-and-Excitation (SE) architecture for classifying each fish in the image without pre-filtering. We apply transfer learning to overcome the limited training samples of temperate fishes and to improve the accuracy of the classification. This is done by training the object detection model with ImageNet and the fish classifier via a public dataset (Fish4Knowledge), whereupon both the object detection and classifier are updated with temperate fishes of interest. The weights obtained from pre-training are applied to post-training as a priori. Our solution achieves the state-of-the-art accuracy of 99.27% using the pre-training model. The accuracies using the post-training model are also high; 83.68% and 87.74% with and without image augmentation, respectively. This strongly indicates that the solution is viable with a more extensive dataset.publishedVersio

Regulation of voltage-gated K+ currents in motor neurons: activity-dependence and neuromodulation

Neuronal output is shaped by extrinsic modulation as well as modulation of intrinsic properties of individual neurons, mediated by activity-dependent changes in the expression levels of voltage-gated ionic currents. Activity-dependent regulation of ionic currents is a mechanism by which electrical output of a neuron feeds back onto the expression of its own ion channels to alter cellular excitability in response to stimuli. Neurons alter their intrinsic properties to achieve long lasting changes involved in development, learning and memory formation and vital functions of organ systems such as locomotion and digestion. At the same time, plasticity of neuronal excitability driven by previous experience requires mechanisms to promote stability to maintain physiological function, and many examples of this type of homeostatic plasticity changes have been reported. At the same time, neuromodulation can alter electrical output indirectly via ligand-gated receptors and second messenger pathways and potentially affect activity-dependent effects. Activity-dependent regulation of ionic currents functions to allow neurons to track their own electrical activity and adjust their intrinsic properties in response to changing synaptic drive or other inputs to maintain their functional output. This phenomenon has been demonstrated to occur over the course of minutes and is a relatively fast process. Neuromodulators exert long-term effects on ionic currents via activation of cellular signaling pathways that do not directly affect ionic current levels. Neuromodulation and activity-dependent effects can alter neuronal networks on different time scales, e.g. over several hours to days to accommodate the needs of the behaving organism such as in transitions between sleep and waking states. However, this is not necessarily so, and the possibility of real-time interactions exist and needs to be examined. This dissertation demonstrates that activity-dependent regulation of K+ currents is gated by the neuromodulatory environment and can be altered depending on the activation of a ligand-gated peptide receptor. This study demonstrates novel findings of interactions between metabotropic receptor activation and modulation of highly K+ currents after acute changes to activity and neuromodulatory input

Temperature Effects On An Axon’s Ability To Maintain Phasing Of A Rhythmic Motor System

The precise timing of action potentials generated in the nervous system is crucial for generating adequate behavior. Once generated, action potentials travel along axons towards the neurons or muscles they innervate. Axons are also responsible for preserving the temporal fidelity of the generated action potentials. One challenge axons face is that they can be of considerable length, and exposed to changes in internal and external conditions. Temperature fluctuations, for example, affect the ion channels that generate and propagate action potentials causing changes in action potential speed. It is unclear if, and how, the timing of action potentials can be preserved when action potential velocity changes. I used axons in the pyloric central pattern generator (CPG) of the crustacean stomatogastric nervous system to evaluate spike time arrival at different temperatures. CPGs are neural circuits that generate vital rhythmic behaviors including breathing and walking that must be robust to environmental challenges such as temperature fluctuations. To maintain functional behavior, the axons of CPG neurons must thus possess mechanisms to counterbalance detrimental temperature influences. The pyloric CPG in the crustacean stomatogastric nervous system creates a well-defined triphasic rhythm generated by the lateral pyloric (LP), pyloric dilator (PD), and pyloric constrictor (PY) neurons. The pyloric CPG is robust to temperature fluctuations and produces a triphasic motor pattern that - similar to other rhythmic behaviors - requires a particular sequence of neuronal activities (’phasing’) for adequate functioning. While the CPG itself is temperature compensated, it is unknown how temperature affects the pyloric axons’ ability to maintain adequate timing of action potentials. Pyloric axons possess different neuronal identities, indicating that their response to temperature may be heterogenous. I hypothesize that changes in conduction velocities during temperature changes are coordinated such that the functionally adequate phasic activity of the pyloric neurons is preserved in the periphery. To test this, I first measured the axonal diameters of LP, PD and PY using a voltage-sensitive dye technique. I found that LP’s axon is the largest and PY’s axon is the smallest (N=6 for all axons, One-Way-ANOVA). I then determined how temperature affects conduction velocity in the different sized axons. Across temperatures, the pyloric axons had different conduction velocities (LP \u3e PD \u3e PY), and conduction velocities increased equally (N=8, One-Way-ANOVA). Consequently, the effects of temperature on action potential travel times differed: at high temperatures, LP’s (largest axon) action potentials arrived much earlier than those of PY (smallest axon), disrupting functional behavior in the periphery. However, at lower temperatures the arrival times of LP\u27s and PY’s action potentials did not disrupt their phase relationships. In conclusion, phase relationships are maintained at lower temperatures at the muscles; however, at higher temperatures phase relationships were lost

Effect of Social Status on the Behavior and Neurophysiology of Crayfish

Adaptation to changing social conditions is important for many social animals. Here, the effects of social experience on the behavior and neurophysiology of the red swamp crayfish, Procambarus clarkii, were studied. Evidence is presented that shows juvenile crayfish interact and form social order, and their behavior patterns shift in accordance to social status. Dominant animals maintain a high level of aggressive behavior, while subordinates shift their behavior pattern from aggressive to submissive behavior. Adult male crayfish show similar behavior pattern during dominance formation. However, this work demonstrates that male crayfish adopt a unique strategy to signify the formation of a social order expressed in the form of pseudocopulation. Pseudocopulation between male crayfish signifies the acceptance of the social status and leads to the reduction of aggression of dominants and enhances the survival of subordinate animals. I investigated the long-term effects of social status on the behavioral and physiological responses of crayfish to unexpected sensory touch. I discovered that animals of different social experience display different orienting responses that correlate with in vivo electromyographic recordings from the legs’ depressor muscle. The status-dependent response patterns observed in vivo are retained in a reduced, in vitro, preparation that lacks descending input from the brain. The role of serotonin (5-HT) was investigated in mediating the motor output patterns of the depressor nerve. Putative serotonergic innervations of the depressor nerve were identified that originate from serotonergic neurons located in the first abdominal ganglion. Selective stimulation of the ipsilateral 5-HT neuron enhances the response of the depressor nerve to sensory stimulation. Application of 5-HT modestly increased the tonic firing activity of the depressor nerve in social isolates and subordinates but significantly decreased the activity in dominants. This work illustrates that the formation of a dominance relationship significantly and immediately alters the behavior of the participants. As the social relationship matures, the social experience that develops affects the underlying neurophysiology that mediates the behavior. It will be of great interest in future studies to identify not only the effects rather the mechanisms of how social experience induces physiological changes

Calcium phosphate mineralization is widely applied in crustacean mandibles

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 6 (2016): 22118, doi:10.1038/srep22118.Crustaceans, like most mineralized invertebrates, adopted calcium carbonate mineralization for bulk skeleton reinforcement. Here, we show that a major part of the crustacean class Malacostraca (which includes lobsters, crayfishes, prawns and shrimps) shifted toward the formation of calcium phosphate as the main mineral at specified locations of the mandibular teeth. In these structures, calcium phosphate is not merely co-precipitated with the bulk calcium carbonate but rather creates specialized structures in which a layer of calcium phosphate, frequently in the form of crystalline fluorapatite, is mounted over a calcareous “jaw”. From a functional perspective, the co-existence of carbonate and phosphate mineralization demonstrates a biomineralization system that provides a versatile route to control the physico-chemical properties of skeletal elements. This system enables the deposition of amorphous calcium carbonate, amorphous calcium phosphate, calcite and apatite at various skeletal locations, as well as combinations of these minerals, to form graded composites materials. This study demonstrates the widespread occurrence of the dual mineralization strategy in the Malacostraca, suggesting that in terms of evolution, this feature of phosphatic teeth did not evolve independently in the different groups but rather represents an early common trait.This study was supported in part by grants from the Israel Science Foundation (ISF, Grant 613/13) and the National Institute for Biotechnology in the Negev (NIBN)