Somatotopic localization of the eye muscle afferents in the semilunar ganglion.

In the medial dorsolateral portion of the semilunar ganglion of curarized and anaesthetized lambs a cellular pool has been identified which contains the perikarya of the first-order neurons of the eye muscle proprioception. Responses to moderate manual stretch of individual eye muscles were recorded by means of tungsten microelectrodes, from single units of the ganglion. They were of the type induced by muscle spindle excitation. Such responses showed a somatotopic localization. The superior rectus and the superior oblique muscles were represented in the most dorsal layers of the ganglion, while the inferior rectus and the inferior oblique muscles projected on the most ventral portion of the pool. The medial and the lateral recti were represented in the medial and lateral parts and occasionally wedged themselves between the cells innervating the superior and the inferior muscles. Thus a somatotopic arrangement of the eye muscle proprioception has been demonstrated for the first time in the semilunar ganglion.     

Somatotopic organization of the vestibulospinal tract in the toad

The origin of the vestibulospinal projection in the toad has been investigated by using the method of the retrograde axonal transport of HRP injected at various levels of the spinal cord. The vestibulospinal projection, in this species, was found to be somatotopically organized, since neurons projecting to the cervical segments of the spinal cord were located within the rostromedial part of the ventral vestibular nucleus and those neurons projecting to the lumbosacral segments of the spinal cord were located within the caudolateral part of that nucleus. This pattern of organization of the vestibulospinal projection in amphibia is similar to that described in mammals and birds.     

Somatotopic organization of autonomic reflexes by acupuncture

Acupuncture has been practiced for more than 2000 years in China and now all over the world. One core idea behind this medical practice is that stimulation at specific body regions (acupoints) can distantly modulate organ physiology, but the underlying scientific basis has been long debated. Here, I summarize evidence supporting that long-distant acupuncture effects operate partly through somato-autonomic reflexes, leading to activation of sympathetic and/or parasympathetic pathways. I then discuss how the patterning of the somatosensory system along the rostro–caudal axis and the cutaneous-deep tissue axis might explain acupoint specificity and selectivity in driving specific autonomic pathways, particularly those modulating gastrointestinal motility and systemic inflammation.     

Intracellular stainings of the large ocellar second order neurons in the cockroach

Summary The large ocellar second order neurons (L-neurons) in the cockroach,Periplaneta americana have been studied physiologically by intracellular recordings and morphologically by intracellular and whole nerve cobalt stainings. All the recorded L-neurons showed similar light responses, i.e., light on-hyperpolarization and a small number of off-spikes. All the stained L-neurons had an ocellar arborization covering the whole region of the ocellar neuropile and an central arborization in the region posterior to the protocerebral bridge.     

A second order mechanical model of muscle spindle primary endings

Summary With reference to experimental data and the failure of earlier proposed first order linear models of mammalian muscle spindles, a second order mechanical model of de-efferented primary endings is studied. The model takes into account the presence of two different types of intrafusal muscle fibres in a complete spindle organ. It further allows the incorporation of different gain of the mechano-electric conversion into a depolarization of the sensory terminals innervating the two types of fibres.It is shown that a closer approximation to the behaviour of the biological prototype is obtained if the transducer gain of the branch corresponding to the nuclear bag intrafusal fibres is chosen significantly higher than that corresponding to the nuclear chain branch.The marked nonlinear behaviour of muscle spindle primary endings as recently reported by Matthews and Stein (1968, 1969) is interpreted as a saturation effect of the high gain mechano-electric transducer of the nuclear bag branch. The saturation is considered to reflect a condition of complete depolarization of these sensory terminals. If a higher transducer gain actually is present, a complete depolarization of these terminals would occur at a lower degree of mechanical deformation than for the nuclear chain terminals. The mechano-electric transducer system of the nuclear chain fibres might thus behave approximately linearly within a larger range of input amplitudes. The greatly reduced gain of the primary endings at large emplitudes of imposed muscle vibrations as observed experimentally (Matthews and Stein, 1968, 1969) may thus be accounted for by the transducer gain of the nuclear chain fibres alone.List of Symbols Used C Viscous stiffness, or electrical capacitance - f Frequency of a signal - K Static gain of a system - k Elastic stiffness - R Electrical resistance - s The Laplace operator - H(s) General transfer function of a system - X (s) Laplace transform of the difference between instantanous and resting length of the complete intrafusal muscle fibre, according to the suggested model shown in Fig. 2 - (s) Laplace transform of the length of the elastic component of the proposed Maxwell branch of the sensory region of the model - (s) Laplace transform of the difference between instantanous and resting length of the lumped model of the polar (non-sensory) region of the intrafusal fibres - (s) Laplace transform of the length of the purely elastic branch of the model - The transducer gain of the output from the -branch relative to that of the -branch - v(s) Laplace transform of the total output signal (s) + (s) - Time constant defined by or =RC for the mechanical and the electrical system respectively - Angular frequency equal to 2f - Rate constant describing the relation between the lead and the lag time constant of a first order lead-lag filter network     

Electrophysiological organization of the eye of Aplysia

The eye of Aplysia californica was studied by electrophysiological and histological methods. It has a central spheroidal lens which is surrounded by a retina composed of several thousand receptor cells which are replete with clear vesicles, pigmented support cells, neurons which contain secretory granules, and glial cells. The thin optic nerve that connects the eye to the cerebral ganglion gives a simple "on" response of synchronized action potentials. Tonic activity occurs in the optic nerve in the dark and is dependent on previous dark adaptation. Micropipette recordings indicate that the ERG is positive (relative to a bathelectrode) on the outer surface of the eye and negative in the region of the distal segments of the receptors. Intracellular recordings show that receptor cells have resting potentials of 40–50 mv and respond to illumination with graded potentials of up to 55 mv. Dark-adapted receptors exhibit discrete bumps on the graded response to brief light flashes. Other elements in the retina that do not give large graded responses fall into two classes. One class responds to illumination with action potentials that are in synchrony with the extracellularly recorded compound optic nerve potentials. The other class is tonically active and is depolarized or hyperpolarized and inhibited upon illumination. It is apparent that complex excitatory and lateral inhibitory interactions occur among the elements of the retina.     

A proprioception based regulation model to estimate the trunk muscle forces

Evaluation of loads acting on the spine requires the knowledge of the muscular forces acting on it, but muscles redundancy necessitates developing a muscle forces attribution strategy. Optimisation, EMG, or hybrid models allow evaluating muscle force patterns, yielding a unique muscular arrangement or/and requiring EMG data collection. This paper presents a regulation model of the trunk muscles based on a proprioception hypothesis, which searches to avoid the spinal joint overloading. The model is also compared to other existing models for evaluation. Compared to an optimisation model, the proposed alternative muscle pattern yielded a significant spine postero-anterior shear decrease. Compared to a model based on combination of optimisation criteria, present model better fits muscle activation observed using EMG (38% improvement). Such results suggest that the proposed model, based on regulation of all spinal components, may be more relevant from a physiologic point of view.     

A biophysical approach to the Spatial Function of eye movements extraocular proprioception and the vestibulo-ocular reflex

The eyeball and the extraocular muscles are used as a paradigm to design a linear spatial model of a single joint with a redundant set of muscles. On the basis of this model relations are derived between orientation, torque, motor commands, and proprioceptive signals. These relations show that the tenet underlying the tensorial interpretation of neural signals in sensorimotor systems does not have general validity. A mechanism is proposed to show how proprioception may play a role in optimizing the coordination of muscles during spatial tasks. Further, a new concept is suggested that allows one to predict the neural connectivities mediating the redundant spatial vestibulo-ocular reflex. This concept has the advantage of minimizing both sensorial error and motor effort.     

Role of knee ligaments in proprioception and regulation of muscle stiffness

Physiologic evidence for the sensory role of the knee joint ligaments are reviewed. The cruciate and collateral ligaments accomodate morphologically different sensory nerve endings with different capabilities of providing the central nervous system (CNS) with information not only about noxious and chemical stimuli but also about mechanical events, e.g., movement- and position-related stretches of the ligaments. Available data show that low-threshold joint/ligament receptor (i.e., mechanoreceptor) afferents evoke only weak and rare effects in skeletomotor neurons (α-motoneurons), whereas they frequently and powerfully influence fusimotor neurons (γ-motoneurons). The effects on the γ-muscle-spindle system in the muscles around the knee are so potent that even stretches of the cruciate ligaments at relatively moderate loads (not noxious) may induce major changes in responses of the muscle spindle afferents. As the activity in the primary muscle spindle afferents modifies stiffness in the muscles, the cruciate ligament receptors may, through the γ-muscle-spindle system, participate in regulation and preparatory adjustment of the stiffness of the muscles around the knee joint and thereby of knee joint stiffness. Thus, the sensory system of the cruciate ligaments is able to contribute significantly to the functional stability of the knee joint. The possible role of (ligamentous) joint receptors in genesis and spread of muscular tension in occupational muscle pain and in chronic musculoskeletal pain syndromes is also discussed.     

Time constants of vestibular nuclei neurons in the goldfish: A model with ocular proprioception

A simple model of the vestibular-ocular reflex with a proprioceptive eye velocity feedback loop is used to simulate recent data on the vestibular responses of neurons in the vestibular nuclei of spinal goldfish. The data support the hypothesis that a proprioceptive feedback loop elongates the vestibular nucleus time constant to equal that of the slow phase eye movements of vestibular nystagmus.     

Higher order organization of human placental aromatase

Aromatase (CYP19A1) is an integral membrane enzyme that catalyzes the removal of the 19-methyl group and aromatization of the A-ring of androgens. All human estrogens are synthesized from their androgenic precursors by this unique cytochrome P450. The crystal structure of active aromatase purified from human placenta has recently been determined in complex with its natural substrate androstenedione in the high-spin ferric state of heme. Hydrogen bond forming interactions and tight packing hydrophobic side chains closely complement puckering of the steroid backbone, thereby providing the molecular basis for the androgenic specificity of aromatase. In the crystal, aromatase molecules are linked by a head-to-tail intermolecular interaction via a surface loop between helix D and helix E of one aromatase molecule that penetrates the heme-proximal cavity of the neighboring, crystallographically related molecule, thus forming in tandem a polymeric aromatase chain. This intermolecular interaction is similar to the aromatase-cytochrome P450 reductase coupling and is driven by electrostatics between the negative potential surface of the D-E loop region and the positively charged heme-proximal cavity. This loop-to-proximal site link in aromatase is rather unique—there are only a few of examples of somewhat similar intermolecular interactions in the entire P450 structure database. Furthermore, the amino acids involved in the intermolecular contact appear to be specific for aromatase. Higher order organization of aromatase monomers may have implications in lipid integration and catalysis.     

Spectral organization of the eye of a butterfly,Papilio

Journal of Comparative Physiology A - This review outlines our recent studies on the spectral organization of butterfly compound eyes, with emphasis on the Japanese yellow swallowtail butterfly,...