Heribert Gras

Prothoracic DUM neurons of the cricket Gryllus bimaculatus - responses to natural stimuli and activity in walking behavior

SummaryResponses to sensory stimuli and spike activity uring walking were investigated in bilaterally symmetrical dorsal unpaired median (DUM) neurons of the cricket. Intracellular recordings within the prothoracic ganglion were made either in restrained animals or in stationary walking specimens whilst parameters of their intended locomotion were measured. Three types of DUM cells were distinguished morphologically and physiologically. DUMa neurons send axons through segmental nerves. They often generated spontaneously large action potentials with low frequencies. Most DUMa neurons showed multimodal sensitivity, preferentially to cereal wind puffs and 15 kHz sound. Mean latencies ranged from 25 to 349 ms. Their large intraindividual variability could be correlated with behavioral modes during walking. Generally, the spike frequency increased with increased forward speed, while it was not related to turning. DUMb neurons projected either through the anterior or posterior connectives, but seemed physiologically similar to DUMa neurons. DUMc neurons were H-shaped with axons in both pairs of connectives. No external stimulus led to discrete spikes, but the regular spontaneous activity was modulated following cereal wind puffs to a restrained animal. During wind evoked escape the spike activity of another DUMc cell was modulated in phase with the rhythmic running behavior. The possibly different functions of DUMa and DUMc neurons during walking are discussed.

Types, numbers and distribution of synapses on the dendritic tree of an identified visual interneuron in the brain of the locust.

Abstract The descending contralateral movement detector (DCMD), an identified descending interneuron in the brain of the locust Schistocerca gregaria has been investigated by using light and electron microscopy. We describe the fine structure, distribution and numbers of synapes that it receives from another identified brain neuron, the lobular giant movement detector (LGMD), and from unidentified neurons. The DCMD dendrites emerging from the integrative segment vary in form and number between individuals and sexes but always form a flattened dendritic domain. The arborizations and the integrative segment appear to be exclusively postsynaptic. Two types of synaptic contacts (Type 1 and 2) onto the DCMD can be discerned as having either round (Type 1) or pleiomorphic synaptic vesicles (Type 2) and by large (Type 1) or small (Type 2) subsynaptic appositions. Contact zones of Type 1 synapses are smaller than those of Type 2. LGMD-synapses are of Type 1 and occur intermingled with presynaptic sites of unidentified units. Some branches of the DCMD receiving input from unidentified units are devoid of contacting LGMD processes. Synapses of both types are randomly distributed over the DCMD integrative segment and at fibres with similar sizes.Type 1 synapses are much more frequent than Type 2 synapses and their number is negatively correlated with fibre diameter. For a whole DCMD dendritic arborization, a total of 8500 active zones of chemical synapses has been calculated, including a mininum of 2250 LGMD-synapses and about 1000 Type 2 synapses. The DCMD may thus receive a considerable amount of input from as yet unidentified neurons.

Patterns of serotonin-immunoreactive neurons in the central nervous system of the earthworm Lumbricus terrestris L.

SummaryThe distribution of serotonin-immunoreactive cell bodies and fibers in the ventral nerve cord of the earthworm has been investigated from whole-mount preparations and serial sections. Serotonin-immunoreactive neurons are organized in seven soma groups per ganglion; these are defined by cell number, soma shape, diameter and fiber projections. Positional variations of this pattern have been studied quantitatively. The number of labeled perikarya is constant in midbody ganglia, but increases markedly rostral to the posterior margin of the clitellum. Variability of position and cell number differs between the cell groups. Stained nerve fibers could only be partially traced; their distribution is described in relation to defined neuronal fiber bundles and segmental nerves. The distribution and morphology of serotonin-immunoreactive cells are compared with previous observations, based on pattern analysis of primary catecholamines and indolamines with the use of a formaldehyde-induced fluorescence technique. The possible role of serotonin-immunoreactive nervous elements in different nerve cord compartments is discussed with respect to physiological effects of serotonin in earthworms and other invertebrates.

A ‘hidden line’ algorithm for 3D-reconstruction from serial sections — An extension of the NEUREC program package for a microcomputer

An algorithm is described to generate pictures in arbitrary perspective from serially sectioned biological material. Only those parts of the object which lie on a direct line of sight to the observer are included into the computed paper-plot, while hidden lines are omitted. The program was written for an inexpensive Apple II+ microcomputer as an extension of an earlier program library (NEUREC) for three-dimensional reconstruction. Application examples of neuronal and cardiac tissues are presented.

NEUREC — a program package for 3D-reconstruction from serial sections using a microcomputer

A software package is described to reconstruct three-dimensional pictures in true perspective from a series of parallel sections using a low-cost computer system (Apple II plus). Data sampling via a graphic tablet and graphical output on the monitor screen or a digital plotter are assigned to different programs under control of a menu program. The number of data representing the object under study is unlimited. Originally written in BASIC, the programs were translated to machine language. As an application of the package, reconstructions of an identified large interneuron of the locust brain are presented.

A Global In Vivo Drosophila RNAi Screen Identifies a Key Role of Ceramide Phosphoethanolamine for Glial Ensheathment of Axons

Glia are of vital importance for all complex nervous system. One of the many functions of glia is to insulate and provide trophic and metabolic support to axons. Here, using glial-specific RNAi knockdown in Drosophila, we silenced 6930 conserved genes in adult flies to identify essential genes and pathways. Among our screening hits, metabolic processes were highly represented, and genes involved in carbohydrate and lipid metabolic pathways appeared to be essential in glia. One critical pathway identified was de novo ceramide synthesis. Glial knockdown of lace, a subunit of the serine palmitoyltransferase associated with hereditary sensory and autonomic neuropathies in humans, resulted in ensheathment defects of peripheral nerves in Drosophila. A genetic dissection study combined with shotgun high-resolution mass spectrometry of lipids showed that levels of ceramide phosphoethanolamine are crucial for axonal ensheathment by glia. A detailed morphological and functional analysis demonstrated that the depletion of ceramide phosphoethanolamine resulted in axonal defasciculation, slowed spike propagation, and failure of wrapping glia to enwrap peripheral axons. Supplementing sphingosine into the diet rescued the neuropathy in flies. Thus, our RNAi study in Drosophila identifies a key role of ceramide phosphoethanolamine in wrapping of axons by glia.

A comparison of spontaneous and wind-evoked running modes in crickets and cockroaches

Abstract We studied the effects of repetitive wind pulses on the escape behaviour of tethered male cockroaches and crickets walking on a styrofoam ball (open-loop stimulation). The movements of this sphere were recorded to measure duration, forward and turning speed of walking and standing phases during the insects intended locomotion. All tested parameters were quantitatively similar for spontaneous walking in both species. During stimulation crickets generated a sequence of running bouts very regular both in duration and forward speed. Interposed were standing phases the mean duration of which was inversely correlated with the wind puff frequency. The mean distance run per period varied only between 100 and 150 mm for the tested frequencies. Cockroaches often showed continuous high speed running for seconds, variable in duration and followed by variable standing phases. Both parameters together with the mean forward speed of walking phases depended on the stimulus frequency in a non-linear manner. Therefore, the longest distance per period was run during stimulation with medium frequencies. Crickets were much better than cockroaches in turning away from the wind source in the range of 5–10 Hz stimulation. In cockroaches, the escape reaction was partly retained after cercus ablation, but ceased completely when the styli were also removed.

Sprouting interneurons in mushroom bodies of adult cricket brains

In crickets, neurogenesis persists throughout adulthood for certain local brain interneurons, the Kenyon cells in the mushroom bodies, which represent a prominent compartment for sensory integration, learning, and memory. Several classes of these neurons originate from a perikaryal layer, which includes a cluster of neuroblasts, surrounded by somata that provide the mushroom bodys columnar neuropil. We describe the form, distribution, and cytology of Kenyon cell groups in the process of generation and growth in comparison to developed parts of the mushroom bodies in adult crickets of the species Gryllus bimaculatus. A subset of growing Kenyon cells with sprouting processes has been distinguished from adjacent Kenyon cells by its prominent f‐actin labelling. Growth cone‐like elements are detected in the perikaryal layer and in their associated sprouting fiber bundles. Sprouting fibers distant from the perikarya contain ribosomes and rough endoplasmic reticulum not found in the dendritic processes of the calyx. A core of sprouting Kenyon cell processes is devoid of synapses and is not invaded by extrinsic neuronal elements. Measurements of fiber cross‐sections and counts of synapses and organelles suggest a continuous gradient of growth and maturation leading from the core of added new processes out to the periphery of mature Kenyon cell fiber groups. Our results are discussed in the context of Kenyon cell classification, growth dynamics, axonal fiber maturation, and function. J. Comp. Neurol. 508:153–174, 2008.

Physiological properties of some descending neurons in the cricket brain

cursors. Activity and/or amount of the TG synthetase per oocyte increases during oocyte development and reaches a maximum in the largest oocytes. The 1,2-DG needed for TG synthesis is possibly derived from two sources: the hemolymph contains a DG-carrying lipoprotein which can transport large amounts of D G (for review see [4]); in addition, hemolymph of egg-maturing female locusts contains the yolk protein vitellogenin, which is selectively sequestered by oocytes [5, 6]. Twenty three percent of the lipids bound to vitellogenin are 1,2-DG; after incorporation the D G content decreases to 9% [7]. The results presented provide direct evidence for an autosynthesis of TG stored in locust eggs from incorporated D G by a TG synthetase present and active in oocytes during oogenesis.

rtime: a program for time-series measurements and evaluation in electrophysiology with the AT-PC

This work describes a program which uses a standard RS232-serial interface of an IBM-AT-compatible microcomputer to receive via four data lines input from any laboratory equipment (spike discriminators, stimulus equipment, etc.) generating pulses between 0 to -15 V (low) and +5 to +15 V (high). Therefore, program operation is independent from any hardware extensions of the computer. The time of occurrence of input pulses is recorded with a resolution of 10 microseconds. Depending on processor speed and optional on-line display of interval histograms, a maximum sampling rate of 1.3-6 kHz is attained. Designed primarily for electrophysiological applications, the program comprises an extensive set of functions for off-line analysis of data either in the time- or in the phase-domain. The program is controlled by menu-selectable commands with detailed on-line explanation and is therefore suited for use even by operators without computer experience, e.g., students on courses in experimental physiology. Elaborate schemes of evaluation can be defined as macro commands to speed up and simplify complex data analysis in actual research.