Morphology,physiology and in vivo activity of cuticular stress detector afferents in crayfish

Cuticular Stress Detector afferents (CSD1 and CSD2) in the 5th walking legs of crayfish (Pacifastacus leniusculus, Procambarus clarkii) have been studied in an in vitro preparation allowing intracellular recordings to be made from the central terminals of primary afferent fibres during mechanical stimulation of the sense organs. Biocytin anterograde fills and transverse sections of the sensory nerves showed CSD1 to comprise fewer and more heterogeneous fibres than CSD2. Lucifer yellow filling of single fibres showed branching patterns compatible with monosynaptic projections to some motorneuronal groups. Whole nerve recordings during sinusoidal or ramp stimuli showed an important contribution from units with phasic properties. The intracellular recordings identified three features unique to CSD1: 1. Many on-off units have a phasic response to both increases and decreases of force. 2. Many high threshold units respond only to high amplitude vibratory stimuli. 3. A few sensory fibres have a main branch projecting rostrally within the interganglionic connectives, possibly as far as the brain. In vivo recordings of CSD1 activity during forward locomotion on a treadmill showed a discharge occurring in advance of, as well as during, the power stroke. It is therefore suggested that at least some CSD1 fibres encode active as well as passive force during locomotion.Abbreviations AEP Anterior extreme position of a leg during walking - CSDs (CSD1 and CSD2) Cuticular stress detector organs - PEP Posterior extreme position of a leg during walking - VNC Ventral nerve cord     

Visualization of proprioceptors in Drosophila larvae and pupae

Proprioception is the ability to sense the motion, or position, of body parts by responding to stimuli arising within the body. In fruitflies and other insects proprioception is provided by specialized sensory organs termed chordotonal organs (ChOs). Like many other organs in Drosophila, ChOs develop twice during the life cycle of the fly. First, the larval ChOs develop during embryogenesis. Then, the adult ChOs start to develop in the larval imaginal discs and continue to differentiate during metamorphosis. The development of larval ChOs during embryogenesis has been studied extensively. The centerpiece of each ChO is a sensory unit composed of a neuron and a scolopale cell. The sensory unit is stretched between two types of accessory cells that attach to the cuticle via specialized epidermal attachment cells. When a fly larva moves, the relative displacement of the epidermal attachment cells leads to stretching of the sensory unit and consequent opening of specific transient receptor potential vanilloid (TRPV) channels at the outer segment of the dendrite. The elicited signal is then transferred to the locomotor central pattern generator circuit in the central nervous system. Multiple ChOs have been described in the adult fly. These are located near the joints of the adult fly appendages (legs, wings and halters) and in the thorax and abdomen. In addition, several hundreds of ChOs collectively form the Johnston's organ in the adult antenna that transduce acoustic to mechanical energy. In contrast to the extensive knowledge about the development of ChOs in embryonic stages, very little is known about the morphology of these organs during larval stages. Moreover, with the exception of femoral ChOs and Johnston's organ, our knowledge about the development and structure of ChOs in the adult fly is very fragmentary. Here we describe a method for staining and visualizing ChOs in third instar larvae and pupae. This method can be applied together with genetic tools to better characterize the morphology and understand the development of the various ChOs in the fly.     

Muscular forearm activation in hand-grip tasks with superimposition of mechanical vibrations

The purpose of this paper is to evaluate the muscular activation of the forearm, with or without vibration stimuli at different frequencies while performing a grip tasks of 45 s at various level of exerted force. In 16 individuals, 9 females and 7 males, the surface electromyogram (EMG) of extensor carpi radialis longus and the flexor carpi ulnari muscles were assessed. At a short latency from onset EMG, RMS and the level of MU synchronization were assessed to evaluate the muscular adaptations. Whilst a trend of decay of EMG Median frequency (MDF_d) was employed as an index of muscular fatigue. Muscular tasks consists of the grip of an instrumented handle at a force level of 20%, 30%, 40%, 60% of the maximum voluntary force. Vibration was supplied by a shaker to the hand in mono-frequential waves at 20, 30, 33 and 40 Hz. In relation to EMG, RMS and MU synchronization, the muscular activation does not seem to change with the superimposition of the mechanical vibrations, on the contrary a lower MDF_d was observed at 33 Hz than in absence of vibration. This suggests an early muscular fatigue induced by vibration due to the fact that 33 Hz is a resonance frequency for the hand-arm system.     

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.