Synaptic connections between sensory afferents and the common inhibitory motoneuron in crayfish

The sensory inputs to the common inhibitory motoneuron that innervates every leg muscle of the crayfish Procambarus clarkii (Girard) were analyzed by performing intracellular recordings from its neurite within the neuropil of the 5th thoracic ganglion. Two types of sensory inputs involved in locomotion were studied, those from a movement coding proprioceptor (the coxobasal chordotonal organ) and those from sensory neu rons coding contact forces exerted at the tip of the leg on the substrate (the dactyl sensory afferents). Sinusoidal movements applied to the chordotonal organ strand induced a stable biphasic response in the common inhibitory motoneuron that consisted of bursts of spikes during release and stretch of the strand, corresponding to raising and lowering of the leg, respectively. Using ramp movements imposed on the chordotonal strand, we demonstrated that only movement-coding chordotonal afferents produce excitatory post-synaptic potentials in the common inhibitory motoneuron; these connections are monosynaptic. Mechanical or electrical stimulation of the dactyl sensory afferents resulted in an increase in the tonic discharge of the common inhibitory motoneuron through polysynaptic excitatory pathways. These two types of sensory cues reinforce the central command of the common inhibitory motoneuron and contribute to enhancing its activity during leg movements, and thus facilitate the relaxation of tonic muscle fibres during locomotion.Abbreviations ADR anterior distal root - A Lev anterior levator nerve - CB coxo-basipodite joint - CBCO coxo-basal chordotonal organ - CI common inhibitory motoneuron - Dep depressor nerve - DSA dactyl sensory afferents - EPSP excitatory post-synaptic potential - IN interneuron - MN motoneuron - PDR posterior distal root - P Lev posterior levator nerve - Pro promotor nerve - Rem remotor nerve     

The antennal motor system of the stick insect Carausius morosus: anatomy and antennal movement pattern during walking

The stick insect Carausius morosus continuously moves its antennae during locomotion. Active antennal movements may reflect employment of antennae as tactile probes. Therefore, this study treats two basic aspects of the antennal motor system: First, the anatomy of antennal joints, muscles, nerves and motoneurons is described and discussed in comparison with other species. Second, the typical movement pattern of the antennae is analysed, and its spatio-temporal coordination with leg movements described. Each antenna is moved by two single-axis hinge joints. The proximal head-scape joint is controlled by two levator muscles and a three-partite depressor muscle. The distal scape-pedicel joint is controlled by an antagonistic abductor/ adductor pair. Three nerves innervate the antennal musculature, containing axons of 14-17 motoneurons, including one common inhibitor. During walking, the pattern of antennal movement is rhythmic and spatiotemporally coupled with leg movements. The antennal abduction/adduction cycle leads the protraction/retraction cycle of the ipsilateral front leg with a stable phase shift. During one abduction/adduction cycle there are typically two levation/depression cycles, however, with less strict temporal coupling than the horizontal component. Predictions of antennal contacts with square obstacles to occur before leg contacts match behavioural performance, indicating a potential role of active antennal movements in obstacle detection.     

Projection of sensory neurons from a homeotic mutant appendage,Antennapedia, in Drosophila melanogaster

Central projections of sensory neurons from homeotic mutant appendages (Antennapedia) of Drosophila melanogaster were compared with those of wild-type antennae and wild-type legs by means of degeneration and cobalt backfilling methods. Sensory axons originating from wild-type thoracic legs terminate within the ventral ipsilateral half of the corresponding neuropile segment and do not project to the brain. Sensory fibers from the third antennal segment (AIII) of wild-type animals project into the ipsilateral antennal glomerulus (AG) and to a lesser extent into the contralateral AG, whereas those from the second antennal segment terminate principally within the ipsilateral posterior antennal center. The sensory terminals of femur, tibia, and tarsi of the homeotic leg show a distribution very similar to that of the homologous wild-type antennal segment AIII, differing to a minor degree only in the size and precise localization of terminals within the antennal glomeruli. No degenerating axons were evident in ultrastructural examination of neck connectives after removal of homeotic legs. It is thus very improbable that any sensory fibers of the homeotic leg project to normal leg projection areas in the thoracico-abdominal ganglion. Several alternative explanations are offered for the apparent retention of antennal specificity by axons from the transformed appendage.     

Proprioceptive reflex interactions with central motor rhythms in the isolated thoracic ganglion of the shore crab

Summary Experiments were carried out on an isolated central nervous system preparation of the shore crab,Carcinus maenas, comprising the fused thoracic ganglion complex with two proprioceptors of one back leg still attached. These, the thoracic-coxal muscle receptor organ and the coxo-basal chordotonal organ, monitor movement and position of the first and second joints, respectively. Motor activity was recorded extracellularly from the central cut ends of the nerves innervating the promotor and remotor muscles of the thoracic-coxal joint, and the levator and depressor muscles of the coxal-basal joint of the same leg. Simultaneous intracellular recordings were made from central processes of individual motoneurones of each muscle.In the absence of any sensory input, the isolated ganglion exhibited rhythmic bursting in the motor nerve roots, with a slow, usually irregular cycle period of 5–50 s.Both receptor organs had both intra-joint and inter-joint effects on the rhythmically active preparation. In most cases the coxo-basal receptor organ had the greater effect.Resistance reflexes initiated by each of the joint proprioceptors were modulated by the rhythmic activity.It may be concluded that, while the isolated thoracic ganglion of the crab is capable of generating rhythmic motor output, proprioceptive feedback from the two basal joints is important in shaping the motor patterns underlying locomotion. Inappropriate reflexes which would impede active movements about these joints are modulated or reversed so as to permit and even reinforce intended locomotory movements.     

Reactions of the spiny lobster,Palinunis vulgaris,to substrate tilt (I.)

Summary Movements of legs on a tilting footboard during fore-aft and side-side tilts elicit a number of different reactions in the spiny lobster,Palinurus vulgaris. Most prominent among these are the predominantly phasic equilibrium reactions of the antennae in the direction opposite to footboard tilt, and the compensatory phasic and tonic deviations of the eyestalks in the direction of footboard movement. Systematic movements of the abdomen and uropods also take place, and the legs display resistance reactions which oppose board movement. Stimulation of a single leg is sufficient to produce the major components of these responses. After stiffening of the C-B joints reactions fail to appear. Mechanism and functional significance of these reactions are discussed in the context of the relevant biological stimuli.The support of D.M. Neil by the British Council Younger Research Workers Interchange Scheme is gratefully acknowledged. We would also like to express our thanks to Peter Heinecke for the expert work of developing and factoring the electronic control devices, Eberhard Göldner and Jörg Stadier for the skilful construction of the setup. We are furthermore indebted to Russ Fernald for his help with the computer work.     

Tonic and modulatory subsystems of the complex gravity receptor system in crickets, Gryllus bimaculatus

The gravity receptor system of crickets Gryllus bimaculatus is composed of antennal, cercal and leg subsystems. The cercal gravity receptors are the club-shaped sensilla. Each of these subsystems elicits compensatory head movements during passive roll.The extent of compensatory head movements depends on the strength of the gravitational stimulus applied to the leg subsystem. Amputation of 2 legs never causes a decrease in reflex amplitude. Unilateral amputation of 1 to 3 legs always induces a roll movement of the head to the intact body side. Therefore, the leg gravity receptor system exerts a modulatory and tonic effect on the neck muscles.The gravity receptors of 1 cercus or 1 antenna only elicit compensatory head movements. They exert no tonic effect on the neck muscles.The results are discussed with respect to (i) the proposed connectivity of the cercus-neck muscle pathway, (ii) mutual inhibitory interactions between the sensory pathways originating in the leg gravity receptors, and (iii) the influence of non-gravitationally induced excitation on the occurrence of compensatory head movements during passive roll of the crickets.     

Projection pattern of sensory neurons in the central nervous system of a homeotic mutation of the moth Manduca sexta

Octopod (Octo) is a mutation of the moth Manduca sexta, which transforms the first abdominal segment (A1) in the anterior direction. Mutant animals are characterized by the appearance of homeotic thoracic-like legs on A1. We exploited this mutation to determine what rules might be used in specifying the fates of sensory neurons located on the body surface of larval Manduca. Mechanical stimulation of homeotic leg sensilla did not cause reflexive movements of the homeotic legs, but elicited responses similar to those observed following stimulation of ventral A1 body wall hairs. Intracellular recordings demonstrated that several of the motoneurons in the A1 ganglion received inputs from the homeotic sensory hairs. The responses of these motoneurons to stimulation of homeotic sensilla resembled their responses to stimulation of ventral body wall sensilla. Cobalt fills revealed that the mutation transformed the segmental projection pattern of only the sensory neurons located on the ventral surface of A1, resulting in a greater number with intersegmental projection patterns typical of sensory neurons found on the thoracic body wall. Many of the sensory neurons on the homeotic legs had intersegmental projection patterns typical of abdominal sensory neurons: an anteriorly directed projection terminating in the third thoracic ganglion (T3). Once this projection reached T3, however, it mimicked the projections of the thoracic leg sensory neurons. These results demonstrate that the same rules are not used in the establishment of the intersegmental and leg-specific projection patterns. Segmental identity influences the intersegmental projection pattern of the sensory neurons of Manduca, whereas the leg-specific projections are consistent with a role for positional information in determining their pattern. © 1995 John Wiley & Sons, Inc.     

An antennal-specific role for bowl in repressing supernumerary appendage development in Drosophila

In Drosophila, antennae and legs are serially homologous appendages, and yet they develop into organs of very different structure and function. This implies that different genetic mechanisms operate onto a common developmental ground state to produce antennae and legs. Still few such mechanisms have been uncovered. During leg development, bowl, a member of the odd-skipped gene family, has been shown to participate in the formation of the leg segmental joints. Here we report that, in the antennal disc, bowl has a dramatically different role: bowl is expressed in the ventral antennal disc to prevent inappropriate expression of wg early during development. The removal of bowl function leads to the activation of wg in the dpp-expressing domain. This ectopic expression of wg, together with dpp, results in a new proximo-distal axis that promotes non-autonomous antennal duplications. The role of bowl in suppressing a supernumerary PD axis is maintained even when the antennal disc is homeotically transformed into a leg-like appendage. Therefore, bowl is part of a genetic program that suppresses the formation of supernumerary appendages specifically in the fly's head.     

Intersegmental transfer of sensory signals in the stick insect leg muscle control system

Intersegmental coordination during locomotion in legged animals arises from mechanical couplings and the exchange of neuronal information between legs. Here, the information flow from a single leg sense organ of the stick insect Cuniculina impigra onto motoneurons and interneurons of other legs was investigated. The femoral chordotonal organ (fCO) of the right middle leg, which measures posture and movement of the femur-tibia joint, was stimulated, and the responses of the tibial motoneuron pools of the other legs were recorded. In resting animals, fCO signals did not affect motoneuronal activity in neighboring legs. When the locomotor system was activated and antagonistic motoneurons were bursting in alternation, fCO stimuli facilitated transitions from flexor to extensor activity and vice versa in the contralateral leg. Following pharmacological treatment with picrotoxin, a blocker of GABA-ergic inhibition, the tibial motoneurons of all legs showed specific responses to signals from the middle leg fCO. For the contralateral middle leg we show that fCO signals encoding velocity and position of the tibia were processed by those identified local premotor nonspiking interneurons known to contribute to posture and movement control during standing and voluntary leg movements. Interneurons received both excitatory and inhibitory inputs, so that the response of some interneurons supported the motoneuronal output, while others opposed it. Our results demonstrate that sensory information from the fCO specifically affects the motoneuronal activity of other legs and that the layer of premotor nonspiking interneurons is a site of interaction between local proprioceptive sensory signals and proprioceptive signals from other legs.     

Active tactile exploration for adaptive locomotion in the stick insect

Insects carry a pair of actively movable feelers that supply the animal with a range of multimodal information. The antennae of the stick insect Carausius morosus are straight and of nearly the same length as the legs, making them ideal probes for near-range exploration. Indeed, stick insects, like many other insects, use antennal contact information for the adaptive control of locomotion, for example, in climbing. Moreover, the active exploratory movement pattern of the antennae is context-dependent. The first objective of the present study is to reveal the significance of antennal contact information for the efficient initiation of climbing. This is done by means of kinematic analysis of freely walking animals as they undergo a tactually elicited transition from walking to climbing. The main findings are that fast, tactually elicited re-targeting movements may occur during an ongoing swing movement, and that the height of the last antennal contact prior to leg contact largely predicts the height of the first leg contact. The second objective is to understand the context-dependent adaptation of the antennal movement pattern in response to tactile contact. We show that the cycle frequency of both antennal joints increases after obstacle contact. Furthermore, inter-joint coupling switches distinctly upon tactile contact, revealing a simple mechanism for context-dependent adaptation.     

The functions of antennal mechanoreceptors and antennal joints in tactile discrimination of the honeybee (<Emphasis Type="Italic">Apis mellifera</Emphasis> L.)

Honeybees learn and discriminate excellently between different surface structures and different forms of objects, which they scan with their antennae. The sensory plate on the antennal tip plays a key role in the perception of mechanosensory and gustatory information. It is densely covered with small tactile hairs and carries a few large taste hairs. Both types of sensilla contain a mechanoreceptor, which is involved in the antennal scanning of an object. Our experiments test the roles of the mechanoreceptors on the antennal tip in tactile antennal learning and discrimination. Joints between head capsule and scapus and between scapus and pedicellus enable the bee to perform three-dimensional movements when they scan an object. The role of these joints in tactile antennal learning and discrimination is studied in separate experiments. The mechanoreceptors on the antennal tip were decisive for surface discrimination, but not for tactile acquisition or discrimination of shapes. When the scapus–pedicellus joint or the headcapsule–scapus joint was fixed on both antennae, tactile learning was still apparent but surface discrimination was abolished. Fixing both scapi to the head capsule reduced tactile acquisition.     

Central gustatory projections and side-specificity of operant antennal muscle conditioning in the honeybee

Gustatory stimuli to the antennae, especially sucrose, are important for bees and are employed in learning paradigms as unconditioned stimulus. The present study identified primary antennal gustatory projections in the bee brain and determined the impact of stimulation of the antennal tip on antennal muscle activity and its plasticity. Central projections of antennal taste hairs contained axons of two morphologies projecting into the dorsal lobe, which is also the antennal motor centre. Putative mechanosensory axons arborised in a dorso-lateral area. Putative gustatory axons projected to a ventro-medial area. Bees scan gustatory and mechanical stimuli with their antennae using variable strategies but sensory input to the motor system has not been investigated in detail. Mechanical, gustatory, and electrical stimulation of the ipsilateral antennal tip were found to evoke short-latency responses in an antennal muscle, the fast flagellum flexor. Contralateral gustatory stimulation induced smaller responses with longer latency. The activity of the fast flagellum flexor was conditioned operantly by pairing high muscle activity with ipsilateral antennal sucrose stimulation. A proboscis reward was unnecessary for learning. With contralateral antennal sucrose stimulation, conditioning was unsuccessful. Thus, muscle activity induced by gustatory stimulation was important for learning success and conditioning was side-specific.     

Social facilitation of insect reproduction with motor-driven tactile stimuli

Tactile stimuli provide animals with important information about the environment, including physical features such as obstacles, and biologically relevant cues related to food, mates, hosts and predators. The antennae, the principal sensory organs of insects, house an array of sensory receptors for olfaction, gustation, audition, nociception, balance, stability, graviception, static electric fields, and thermo-, hygro- and mechanoreception. The antennae, being the anteriormost sensory appendages, play a prominent role in social interactions with conspecifics that involve primarily chemosensory and tactile stimuli. In the German cockroach (Blattella germanica) antennal contact during social interactions modulates brain-regulated juvenile hormone production, ultimately accelerating the reproductive rate in females. The primary sensory modality mediating this social facilitation of reproduction is antennal mechanoreception. We investigated the key elements, or stimulus features, of antennal contact that socially facilitate reproduction in B. germanica females. Using motor-driven antenna mimics, we assessed the physiological responses of females to artificial tactile stimulation. Our results indicate that tactile stimulation with artificial materials, some deviating significantly from the native antennal morphology, can facilitate female reproduction. However, none of the artificial stimuli matched the effects of social interactions with a conspecific female.     

Maintenance of Human Vertical Posture upon Asymmetric Leg Loading and Fixation of the Knee Joint of One Leg

Maintenance of a vertical posture was studied in standing subjects with a fixed knee joint of one leg and a different weight distribution between the legs. Knee fixation on one leg did not affect the speed of movements of the common center of pressure (CP) at any weight distribution between the legs, and the stability of vertical posture was therefore unchanged. However, the relative contributions of the legs to the posture control changed when knee movements of one leg were restricted. The speed of CP movements of the free leg was independent of the weight loading on the leg. The speed of CP movements of the leg with the knee fixed depended on the weight distribution and was higher when the leg was loaded. Thus, the leg with the fixed knee joint made a greater contribution to maintaining vertical posture when the leg was loaded. Yet its contribution was comparable with that of the unloaded free contralateral leg even in this case, as was evident from lack of differences in CP movements between the two legs. It was assumed that the leg with the free knee joint played a major role in maintaining equilibrium of vertical posture, while the leg with the fixed knee joint mostly acted to more finely adjust the body position.     

Unusual pheromone receptor neuron responses in heliothine moth antennae derived from inter-species imaginal disc transplantation

Single-cell electrophysiological recordings were obtained from olfactory receptor neurons housed in sensilla trichodea along the adult antennae arising from transplantation of the antennal imaginal discs between larval male Helicoverpa zea and Heliothis virescens. The olfactory receptor neurons from the majority of type C sensilla sampled on transplanted antennae displayed response characteristics consistent with those of the species that donated the antennae. However, some of the sensilla type C sampled in either transplant type contained olfactory receptor neurons that responded in a manner typical of the recipient species or other neurons that have not previously been found in the type C sensilla of either species. The single-cell data help to explain behavioral results showing that some transplant males do fly upwind to both species' pheromone blends, an outcome not expected based on known antennal sensory phenotypes. Our results suggest that host tissue can influence antennal olfactory receptor neuron development, and further that because of a common phylogenetic ancestry the donor tissue has the genetic capability to produce a variety of sensillar and receptor types.     

Antennal movements induced by odour and central projection of the antennal neurones in the honey-bee

Movements of the antennae induced by odour were investigated. Odour presented to the antenna of one side induced both antennae to move to that side. The EMGs recorded from the flexor muscles of both scapes showed that the latency of the movement of the ipsilateral flagellum when induced by odour was about 71 msec shorter than that of the contralateral flagellum. Recording electrical activities from the antennal nerve showed that there are more than 14 neurones in the antenno-motor externus.The distribution of the antennal nerve in the brain was investigated histologically by the injection of fluorescent dye. Antennal sensory neurones terminated at the glomeruli in the antennal lobe, in the dorsal lobe, in the protocerebrum, and in the commissural part of the suboesophageal ganglion. Injection of the fluorescent dye into the antennal nerve after degeneration of the antennal sensory neurones showed that the antennal motoneurones run in the ventral side of the antennal and dorsal lobes, and terminate in the marginal region of the ipsilateral oesophageal connective.The difference in latency of odour-induced flagellar movements is discussed in relation to the histological results and the unitary responses in the brain reported previously.     

Behavioural phase change in the Australian plague locust, Chortoicetes terminifera, is triggered by tactile stimulation of the antennae

Density-dependent phase polyphenism is a defining characteristic of the paraphyletic group of acridid grasshoppers known as locusts. The cues and mechanisms associated with crowding that induce behavioural gregarization are best understood in the desert locust, Schistocerca gregaria, and involve a combination of sensory inputs from the head (visual and olfactory) and mechanostimulation of the hind legs, acting via a transient increase in serotonin in the thoracic ganglia. Since behavioural gregarization has apparently arisen independently multiple times within the Acrididae, the important question arises as to whether the same mechanisms have been recruited each time. Here we explored the roles of visual, olfactory and tactile stimulation in the induction of behavioural gregarization in the Australian plague locust, Chortoicetes terminifera. We show that the primary gregarizing input is tactile stimulation of the antennae, with no evidence for an effect of visual and olfactory stimulation or tactile stimulation of the hind legs. Our results show that convergent behavioural responses to crowding have evolved employing different sites of sensory input in the Australian plague locust and the desert locust.     

Neurogenic pacemakers in the legs of Opiliones

ABSTRACT. After autotomy, the legs of all the species of Opiliones examined, and of a Kenyan Pholcid spider, twitched spontaneously at the femoro-patellar and tibio-basitarsal joints, for periods of up to an hour. These joints lack extensor muscles, extension being achieved at the femoro-patellar joint probably by haemolymph pressure, but at the tibio-basitarsal joint of Opiliones by a cuticular spring which can extend the joint fully. Comparable twitching activity could be evoked without autotomy if the central nervous system was burnt, or by asphyxiation. Electromyograms from the femur or tibia of an isolated twitching leg showed regular motor bursts which accompanied flexions, and sensory activity during extension. Forced movements of the joints did not perturb the rhythm of the motor bursts. An isolated proximal half of a femur could still generate the same bursting pattern whereas no other region showed this activity after its isolation. Bursts recorded in the tibia were shown to be dependent on the integrity of the femur. By stimulation of the femur with 1 -ms current pulses it was possible to reset the rhythm. Stimulation with 1-s pulses caused an acceleration or inhibition of the rhythm according to the direction of the current. Spontaneous bursts could be evoked in silent isolated legs, or in intact quiescent legs, by similar 1-s current pulses. It is postulated that the femur contains independent neurogenic pacemakers which are activated by injury current from the damaged leg nerve; they produce regular bursts of motor impulses without the interplay of proprioceptive loops, and are responsible for the movements observed.     

Responses of non-spiking giant interneurons to substrate tilt in the crayfish, with special reference to multisensory control in the compensatory eyestalk movement system

In the brain of the intact crayfish, three pairs of non-spiking giant interneurons (G1, G2, G3; NGIs) scarcely responded to substrate tilt about the longitudinal axis of the body either in the dark or in the presence of an overhead light. However, when the statolith was removed, these NGIs responded with depolarizing and hyperpolarizing potentials respectively to upward movements of the ipsilateral legs (2nd–5th pereiopods) and upward movements of the contralateral legs produced by substrate tilt. The relationships between the polarity of the potential and the direction of movement in the contralateral legs were opposite to those in the ipsilateral legs. The amplitude of the responses was proportional to the frequency (0.5-0.05 Hz) and amplitude of tilting. When the legs were moved unilaterally, the NGIs responded with depolarizing and hyperpolarizing potentials to upward movements of the ipsilateral legs and to upward movements of the contralateral legs, respectively. When the legs were moved bilaterally in the same direction by upward or downward movement of the substrate, the NGIs scarcely responded to the leg movements. A hypothetical model is presented to account for the pathways of sensory inputs to the NGIs and the role of NGIs in compensatory oculomotor system.     

TRANSMITTER METABOLIZING ENZYMES AND FREE AMINO ACID LEVELS IN SENSORY AND MOTOR NERVES AND GANGLIA OF THE SHORE CRAB (CARCINUS MAENAS)

—The distribution of ChAT (choline acetyltransferase), GAD (glutamate decarboxylase) and acetylcholinesterase in some sensory and motor nerves of the shore crab, Carcinus maenas, has been investigated using micro-assay techniques. ChAT was concentrated in the afferent nerve fibres of the thoracic-coxal muscle receptor as well as in the coxo-basal chordotonal receptor nerve and other leg sensory fibres. GAD was found in leg motor nerves including the promotor and remotor muscle nerves, being undetectable in the sensory nerves. Acetylcholinesterase was found in similar levels in both sensory and motor nerves assayed. Amino acid analysis using a micro-dansylation technique showed that sensory nerves had low GABA levels, whereas the leg nerve including motor fibres had substantially higher GABA concentrations. GAD and GABA were also found in low amounts in the leg promoter mucle, which is consistent with GABA being a neuromuscular transmitter.