Hans-Georg Heinzel

Modulation of Oscillator Interactions in the Crab Stomatogastric Ganglion by Crustacean Cardioactive Peptide

The modulation of the pyloric rhythm of the stomatogastric ganglion of the crab, Cancer borealis, by crustacean cardioactive peptide (CCAP) is described. CCAP activated pyloric rhythms in most silent preparations, and altered the phase relationships of pyloric motor neuron firing in all preparations. In CCAP, the pyloric rhythms were characterized by long lateral pyloric (LP) neuron bursts of action potentials. The threshold for CCAP action was ∼10−10 M, with increasing effects at higher CCAP concentrations. The changes in motor pattern evoked by CCAP produced significant changes in LP-innervated muscle movement. These movements were additionally potentiated by CCAP applications to isolated nerve–muscle preparations. Thus, enhanced motor neuron firing and increase of the gain of the neuromuscular junctions are likely to operate coordinately in response to hormonally released CCAP. High CCAP concentrations sometimes resulted in modification of the normal 1:1 alternation between the pyloric dilator (PD) and LP neurons to patterns of 2:1, 3:1, or 4:1 alternation. CCAP seems to activate slow intrinsic oscillations in the LP neuron, as well as enhance faster oscillations in the pacemaker group of PD/anterior burster (AB) neurons. Simulations of fast and slow oscillators with reciprocal inhibitory coupling suggest mechanisms that could account for the mode switch from 1:1 alternation to multiple PD bursts alternating with one LP neuron burst.

The brain can eat: establishing the existence of a central pattern generator for feeding in third instar larvae of Drosophila virilis and Drosophila melanogaster.

To establish the existence of a central pattern generator for feeding in the larval central nervous system of two Drosophila species, the gross anatomy of feeding related muscles and their innervation is described, the motor units of the muscles identified and rhythmic motor output recorded from the isolated CNS. The cibarial dilator muscles that mediate food ingestion are innervated by the frontal nerve. Their motor pathway projects from the brain through the antennal nerves, the frontal connectives and the frontal nerve junction. The mouth hook elevator and depressor system is innervated by side branches of the maxillary nerve. The motor units of the two muscle groups differ in amplitude: the elevator is always activated by a small unit, the depressor by a large one. The dorsal protractors span the cephalopharyngeal skeleton and the body wall hence mediating an extension of the CPS. These muscles are innervated by the prothoracic accessory nerve. Rhythmic motor output produced by the isolated central nervous system can simultaneously be recorded from all three nerves. The temporal pattern of the identified motor units resembles the sequence of muscle contractions deduced from natural feeding behavior and is therefore considered as fictive feeding. Phase diagrams show an almost identical fictive feeding pattern is in both species.

Feel the heat: The effect of temperature on development, behavior and central pattern generation in 3rd instar Calliphora vicina larvae

Like in all poikilothermic animals, higher temperatures increase developmental rate and activity in Calliphora vicina larvae. We therefore could expect temperature to have a persistent effect on the output of the feeding and crawling central pattern generators (CPGs). When confronted with a steep temperature gradient, larvae show evasive behavior after touching the substrate with the cephalic sense organs. Beside this reflex behavior the terminal- and dorsal organ might also mediate long term CPG modulation. Both organs were thermally stimulated while their response was recorded from the maxillary- or antennal nerve. The terminal organ showed a tonic response characteristic while the dorsal organ was not sensitive to temperature. Thermal stimulation of the terminal organ did not affect the ongoing patterns of fictive feeding or crawling, recorded from the antennal- or abdominal nerve respectively. A selective increase of the central nervous system (CNS) temperature accelerated the motor patterns of both feeding and crawling. We propose that temperature affects centrally generated behavior via two pathways: short term changes like thermotaxis are mediated by the terminal organ, while long term adaptations like increased feeding rate are caused by temperature sensitive neurons in the CNS which were recently shown to exist in Drosophila larvae.

See the light: electrophysiological characterization of the Bolwig organ's light response of Calliphora vicina 3rd instar larvae.

The anatomy and development of the larval cyclorraphous Diptera visual system is well established. It consists of the internal Bolwig organ (BO), and the associated nerve connecting it to the brain. The BO contributes to various larval behaviors but was never electrophysiologically characterized. We recorded extracellulary from the Bolwig nerve of 3rd instar Calliphora vicina larvae to quantify the sensory response caused by BO stimulation with light stimuli of different wavelengths, intensities and directions. Consistent with previous behavioral experiments we found the BO most sensitive to white and green, followed by blue, yellow, violet and red light. The BO showed a phasic-tonic response curve. Increasing light intensity produced a sigmoid response curve with an approximate threshold of 0.0105 nW/cm(2) and a dynamic range from 0.105 nW/cm(2) to 52.5 nW/cm(2). No differences exist between feeding and wandering larvae which display opposed phototaxis. This excludes reduced BO sensitivity from causing the switch in behavior. Correlating to the morphology of the BO frontal light evoked the maximal reaction, while lateral light reduced the neural response asymmetrically: Light applied ipsilaterally to the recorded BO always produced a stronger response than when applied from the contralateral side. This implies that phototacic behavior is based on a tropotactic mechanism.

Activity of Command Fibres in Free-Ranging Crayfish, Orconectes limosus Raf.

of maternal sex steroid hormones to the offspring. Thus the brain-pituitaryovary axis and possibly other neuroendocrine systems may function to modify offspring development in response to conditions in the maternal environment. The numerous transgenerational effects on behavior that have been demonstrated in laboratory mammals in association with maternal social stress [19–22] seem less puzzling from such a point of view. Instead of representing maladaptive consequences of stress they may indicate that maternal neuroendocrine responses function to modify offspring development [23]. Such maternal hormonal effects may enhance fitness by producing phenotypes in the next generation that are prepared for the prevailing social conditions in the maternal generation.

The course control system of beetles walking in an air-current field

SummaryThe wind-orientated walk of carrion beetles Necrophorus humator F. was analysed under closed-loop conditions with a walking compensator and under openloop conditions with a paired tread wheel (Fig. 1).1.On the walking compensator an animal runs stable courses with a preferred direction relative to an air current (velocity =; 100 cm/s, Fig. 2B-D). A change in the air-current direction causes a corresponding adjustment of the mean walking direction (Fig. 3). Such course adjustment works best for changes in the air-current direction by an absolute value of 90° (Table 2).2.Under closed-loop conditions the animal shows deviations of less than ± 45° around its preferred direction relative to the wind (Fig. 2B-D). The characteristic curve which describes the animals angular velocity as a function of the animals walking direction relative to the air-current stimulus is therefore revealed only in this angular range (Fig. 3, top).3.Under open-loop conditions, however, complete characteristic curves can be obtained because the animals walking reaction in response to any given angle of air-current stimulus is measurable on the paired tread wheel (Fig. 4). The characteristic curves are approximately sinusoidal functions. They can either show a shift parallel to the ordinale by a superimposed direction-independent constant angular velocity alone or, at the same time, they can independently exhibit an angular shift along the abscissa (Fig. 5).4.The walking tracks straighten with increasing air-current velocity (Fig. 6A, insets), i.e. the animal more rapidly compensates deviations from a preferred course. This corresponds to higher amplitudes of the characterisic curve and steeper slopes at the negative zero-crossing point under open- as well as under closed-loop conditions (Fig. 6).5.Walking in an air-current field can be explained by a model of the course control system using a feedback loop (Fig. 7). This model operates according to a sinusoidal characteristic function on which is superimposed a Gaussian white noise process of angular velocity which is independent of walking direction. The model produces realistic walking tracks in an air-current field (Fig. 8).

The thoracic muscular system and its innervation in third instar Calliphora vicina Larvae. I. Muscles of the pro- and mesothorax and the pharyngeal complex

An anatomical description is given by the muscles in the pro‐ and mesothorax, and those associated with the feeding apparatus (cephalopharyngeal skeleton, CPS) that participate in feeding behavior in third instar Calliphora larvae. The body wall muscles in the pro‐ and mesothoracic segments are organized in three layers: internal, intermedial, and external. The muscles were labeled with roman numerals according to the nomenclature in use for the abdominal segments. Muscles associated with the CPS are labeled according to their function. The prothorax bears five pairs of lateral symmetrically longitudinal segmental body wall muscles and lacks the transversal muscle group present in the mesothorax and abdominal segments. Additionally, four pairs of intersegmental muscles project from the prothorax to the second, fourth, and fifth segment. The mesothorax bears 15 pairs of segmental longitudinal and 18 pairs of transversal muscles. The accessory pharyngeal muscles span the CPS and the cuticle. Three pairs of protractors and retractors and two pairs of mouth hook accessors (MHAC) exist, which move the CPS relative to the body. The pharyngeal muscles are exclusively attached to the structures of the CPS. The mouth hook elevators and depressors, which mediate the hooks rotation are attached to the ventral arm of the CPS and project to a dorsal (elevators) or ventral (depressors) protuberance of the mouth hooks. The cibarial dilator muscles (CDM) span the dorsal arms of the CPS and the dorsal surface of the esophagus and mediate food ingestion. The labial retractors (LRs) lack antagonists and project from the ventral surface of the CPS to the unpaired labium. Contractions of these muscles open the mouth cavity. J. Morphol. 271:960–968, 2010.

The cephalic and pharyngeal sense organs of Calliphora vicina 3rd instar larvae are mechanosensitive but have no profound effect on ongoing feeding related motor patterns.

The anterior segments of cyclorraphous Diptera larvae bear various sense organs: the dorsal- and terminal organ located on the cephalic lobes, the ventral- and labial organs associated with the mouthplate and the internal labral organ which lies on the dorsal surface of the esophagus. The sense organs are connected to the brain via the antennal nerve (dorsal- and labral organ) or the maxillary nerve (terminal-, ventral-, labial organ). Although their ultrastructure suggests also a mechanosensory function only their response to olfactory and gustatory stimuli has been investigated electrophysiologically. Here we stimulated the individual organs with step-, ramp-, and sinusoidal stimuli of different amplitude while extracellulary recording their afferents from the respective nerves. The external organs show a threshold of approximately 2 microm. All organs responded phasically and did not habituate to repetitive stimuli. The low threshold of the external organs combined with their rhythmically exposure to the substrate suggested a putative role in the temporal coordination of feeding. We therefore repetitively stimulated individual organs while simultaneously monitoring the centrally generated motor pattern for food ingestion. Neither the dorsal-, terminal- or ventral organ afferents had an obvious effect on the ongoing motor rhythm. Various reasons explaining these results are discussed.

Mechanoreception by cuticular sensilla on the pectines of the scorpion Pandinus cavimanus

On the pectines of scorpions, several types of cuticular receptors are located. Of these receptors, only the chemo- and mechanosensory peg sensilla have been studied so far while the response characteristics of the long, straight hair sensilla are unknown. As these sensilla protrude in the walking direction and to the ground, we assume that these receptors are most likely involved in observed reflex behaviours. The sensilla constitute rather robust shafts, comparable to other touch-receptors. Their innervation pattern reveals that 5–6 sensory cells are associated with one sensillum. It was possible to record up to three different spike classes (units) which could be distinguished by size, response characteristics and conduction velocity. Two units were analysed in more detail. The response characteristics showed two phasic units, one large and one small, coding the velocity of a stimulus. One medium-sized unit showed phasic-tonic characteristics, coding also the duration of a stimulus. Taking together the morphological and electrophysiological results, we suggest that these sensilla belong to the group of long hair sensilla distributed all over the scorpion body. Furthermore, their response characteristics and the timing between sensory and motor activity within the pectine nerve enable them to be involved in reflex behaviours.

Connections of the Head to Networks of the Stomatogastric System in Crayfish

A tiny brain nerve, the inferior ventricular nerve (ivn), connecting the brain to the stomatogastric nervous system contains eight axons with two of them terminating in cell bodies within the nerve. The other six axons have widespread dendritic arborizations throughout the protocerebrum and the antenna I and II neuropils. Several fibres branch in the brain, but also send neurites via the connectives towards the paired commissural ganglia and from there towards the stomatogastric ganglion or further down the ventral nerve cord. During feeding there is always a strong increase of firing in the ivn before increased pyloric activity and initiation of rhythmic activity in the gastric network. In vivo and in vitro recordings from the ivn in a newly developed head-stomatogastric preparation show six ascending and just two descending units which respond to mechanical stimulation of the antenna. The preparation reacts to illumination of the eyes with a state-dependent light response of the pyloric rhythm, which is not conveyed via the ivn but via the connectives.