Epilepsia partialis continua as a manifestation of dengue encephalitis

Reflex epilepsy is characterized by seizures that are precipitated by a specific identifiable factor. We describe here the case of a 21-year-old man with notable absence epilepsy since the age of 11 who experienced generalized convulsions 2 years after onset (in the absence of antiepileptic therapy) and reflex absence seizures triggered by walking 7-10 steps. To our knowledge, this case report is the first describing reflex absence epilepsy seizures induced by gait.     

Buried bumper syndrome: cut and leave it alone!

Buried bumper syndrome (BBS) occurs due to the overgrowth of gastric mucosa over the inner bumper of a gastrostomy tube. Various therapeutic approaches have been described for the management of BBS. However, no standardized clinical protocol deals with this complication. The authors describe their experience of dealing with BBS. Case notes of the patients undergoing percutaneous endoscopic gastrostomy (PEG) between February 2002 and December 2007 at their institute were reviewed retrospectively, and cases of BBS were analyzed. During this 71-month period, 356 PEG procedures were preformed. Seven patients with BBS were identified from the case note review (incidence of 1.97%). Attempts at endoscopic removal of the buried bumper were made but unfortunately failed. In view of the patients' associated comorbidity, the buried bumpers in these patients were left in situ, and a new PEG was inserted adjacent to the first site in 6 individuals. In 1 patient, a jejunal extension tube was inserted through the original PEG tube for feeding. No complications from the buried bumper arose in these patients during a median follow-up of 18 months (range, 1-46 months). Some patients being fed by a PEG tube are in poor general health and have significant comorbidities. They are therefore poor candidates for surgical or endoscopic removal of a buried bumper. In such patients, leaving the internal bumper in situ should be considered as a relatively safe treatment option.     

Two size-selective mechanisms specifically trap bacteria-sized food particles in Caenorhabditis elegans

Caenorhabditis elegans is a filter feeder: it draws bacteria suspended in liquid into its pharynx, traps the bacteria, and ejects the liquid. How pharyngeal pumping simultaneously transports and filters food particles has been poorly understood. Here, we use high-speed video microscopy to define the detailed workings of pharyngeal mechanics. The buccal cavity and metastomal flaps regulate the flow of dense bacterial suspensions and exclude excessively large particles from entering the pharynx. A complex sequence of contractions and relaxations transports food particles in two successive trap stages before passage into the terminal bulb and intestine. Filtering occurs at each trap as bacteria are concentrated in the central lumen while fluids are expelled radially through three apical channels. Experiments with microspheres show that the C. elegans pharynx, in combination with the buccal cavity, is tuned to specifically catch and transport particles of a size range corresponding to most soil bacteria.     

An olfactory neuron responds stochastically to temperature and modulates Caenorhabditis elegans thermotactic behavior

Caenorhabditis elegans navigates thermal gradients by using a behavioral strategy that is regulated by a memory of its cultivation temperature (T_c). At temperatures above or around the T_c, animals respond to temperature changes by modulating the rate of stochastic reorientation events. The bilateral AFD neurons have been implicated as thermosensory neurons, but additional thermosensory neurons are also predicted to play a role in regulating thermotactic behaviors. Here, we show that the AWC olfactory neurons respond to temperature. Unlike AFD neurons, which respond to thermal stimuli with continuous, graded calcium signals, AWC neurons exhibit stochastic calcium events whose frequency is stimulus-correlated in a T_c-dependent manner. Animals lacking the AWC neurons or with hyperactive AWC neurons exhibit defects in the regulation of reorientation rate in thermotactic behavior. Our observations suggest that the AFD and AWC neurons encode thermal stimuli via distinct strategies to regulate C. elegans thermotactic behavior.     

From the Cover: PNAS Plus: Pan-neuronal imaging in roaming Caenorhabditis elegans

We present an imaging system for pan-neuronal recording in crawling Caenorhabditis elegans. A spinning disk confocal microscope, modified for automated tracking of the C. elegans head ganglia, simultaneously records the activity and position of ∼80 neurons that coexpress cytoplasmic calcium indicator GCaMP6s and nuclear localized red fluorescent protein at 10 volumes per second. We developed a behavioral analysis algorithm that maps the movements of the head ganglia to the animal’s posture and locomotion. Image registration and analysis software automatically assigns an index to each nucleus and calculates the corresponding calcium signal. Neurons with highly stereotyped positions can be associated with unique indexes and subsequently identified using an atlas of the worm nervous system. To test our system, we analyzed the brainwide activity patterns of moving worms subjected to thermosensory inputs. We demonstrate that our setup is able to uncover representations of sensory input and motor output of individual neurons from brainwide dynamics. Our imaging setup and analysis pipeline should facilitate mapping circuits for sensory to motor transformation in transparent behaving animals such as C. elegans and Drosophila larva.Understanding how brain dynamics creates behaviors requires quantifying the flow and transformation of sensory information to motor output in behaving animals. Optical imaging using genetically encoded calcium or voltage fluorescent probes offers a minimally invasive method to record neural activity in intact animals. The nematode Caenorhabditis elegans is particularly ideal for optical neurophysiology owing to its small size, optical transparency, compact nervous system, and ease of genetic manipulation. Imaging systems for tracking the activity of small numbers of neurons have been effective in determining their role during nematode locomotion and navigational behaviors like chemotaxis, thermotaxis, and the escape response (1–6). Recordings from large numbers of interconnected neurons are required to understand how neuronal ensembles carry out the systematic transformations of sensory input into motor patterns that build behavioral decisions.Several methods for fast 3D imaging of neural activity in a fixed imaging volume have been developed for different model organisms (7–14). High-speed light sheet microscopy, light field microscopy, multifocus microscopy, and two-photon structured illumination microscopy have proved effective for rapidly recording large numbers of neurons in immobilized, intact, transparent animals like larval zebrafish and nematodes (15–19). However, these methods are problematic when attempting to track many neurons within the bending and moving body of a behaving animal. Panneuronal recording in moving animals poses higher demands on spatial and temporal resolution. Furthermore, extracting neuronal signals from recordings in a behaving animal requires an effective analysis pipeline to segment image volumes into the activity patterns of discrete and identifiable neurons.Here, we use high-speed spinning disk confocal microscopy—modified for automated tracking using real-time image analysis and motion control software—to volumetrically image the head ganglia of behaving C. elegans adults at single-cell resolution. Our setup can simultaneously track ∼80 neurons with 0.45 × 0.45 × 2-μm resolution at 10 Hz. Activity was reported by the ultrasensitive calcium indicator GCaMP6s expressed throughout the cytosol under the control of the pan-neuronal rgef-1 promoter (a gift from D. Pilgrim, University of Alberta, Edmonton, Alberta, Canada) (20). To facilitate segmentation into individual identifiable neurons, nuclei were tracked using calcium-insensitive, nuclear-bound red fluorescent protein (RFP), TagRFP, under the control of another pan-neuronal rab-3 promoter (a gift from O. Hobert, Columbia University, New York) (21). We developed an image analysis pipeline that converts the gross movements of the head into the time-varying position and posture of the crawling worm, and converts fluorescence measurements into near simultaneous activity patterns of all imaged neurons.A similar approach to brainwide imaging in moving C. elegans using the same transgenic strain has recently been reported (22). Although both setups use customized spinning disk confocal microscopes, the strategies for tracking the moving neurons and analyzing behavioral and neural activity patterns are different. Nguyen et al. (22) use a low power objective to track the posture of the animal and a high power objective to locate and image the nerve ring. The advantage of our single objective setup is that it affords the flexibility, for example, to deliver thermosensory inputs using an opaque temperature controlled stage below the animal. The advantage of low-magnification imaging is that it provides a direct measurement of animal posture, which we must infer. These new technologies for pan-neuronal imaging in roaming animals now enables correlating brainwide dynamics to sensory inputs and motor outputs in transparent behaving animals like C. elegans and Drosophila larvae.     

Sensorimotor structure of Drosophila larva phototaxis

The avoidance of light by fly larvae is a classic paradigm for sensorimotor behavior. Here, we use behavioral assays and video microscopy to quantify the sensorimotor structure of phototaxis using the Drosophila larva. Larval locomotion is composed of sequences of runs (periods of forward movement) that are interrupted by abrupt turns, during which the larva pauses and sweeps its head back and forth, probing local light information to determine the direction of the successive run. All phototactic responses are mediated by the same set of sensorimotor transformations that require temporal processing of sensory inputs. Through functional imaging and genetic inactivation of specific neurons downstream of the sensory periphery, we have begun to map these sensorimotor circuits into the larval central brain. We find that specific sensorimotor pathways that govern distinct light-evoked responses begin to segregate at the first relay after the photosensory neurons.Navigating organisms must extract spatial information about their surroundings to orient and move toward preferred environments. Phototaxis of fly larvae has long been a paradigm for understanding the mechanisms of animal orientation behavior (1). The study of phototaxis in the Drosophila larva provides an opportunity to investigate the circuits for orientation behavior from sensory input to motor output in a small nervous system. First, however, the sensorimotor structure of responses to illumination must be defined by studying larval behavior in controlled environments.The tropism theory of Jacques Loeb states that bilateral body plans allow animals to extract spatial information through the sensation of external forces acting asymmetrically on symmetric body halves. The navigation of fly larvae away from incident light rays was interpreted as a direct demonstration of tropism. However, temporal comparisons performed by moving animals, also known as klinotaxis, also can encode spatial information (2). Like most fly larvae, Drosophila larvae are negatively phototactic during most of their development (3–9). To navigate away from light, the Drosophila larva uses two sets of photosensors, the Rhodopsin-expressing Bolwig''s organs (BO) that mediate phototaxis at low light levels and the non–Rhodopsin-expressing class IV multidendritic (md) neurons that respond to intense light levels comparable to direct sunlight (10). Here, we sought to resolve the sensorimotor structure of larval phototaxis to understand how these photosensitive structures extract and use information about ambient light conditions to control motor behavior.We developed a tracking assay and illumination system that allowed us to quantify the movements of individual animals in defined spatiotemporal illumination patterns at both low and high light intensities. We uncovered a set of sensorimotor relationships that allow the larva to navigate away from light based on temporal processing of sensory inputs. Even the capacity to navigate away from directed illumination is mediated by temporal processing of sensory input resulting from structural specializations of the BO. The BO is directionally sensitive because it sits in an eye cup formed by the pharyngeal sclerites, and temporal processing of input coupled to head movements allow the larva to discern the actual direction of incoming light. Furthermore, we found that the fifth lateral neuron (LN) encodes several components of the photosensory response and is essential for one particular photosensory response, dark-induced pausing, that was observed in our analysis. Calcium imaging reveals the sensitivity of the fifth LN to temporal changes in photosensory input. In the visual system of the Drosophila larva, sensorimotor pathways that are required for specific components of the overall phototactic response begin to segregate at the first relay after photosensory input.