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.     

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.     

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,...     

Spatial organization of vestibulospinal neurons in the guinea pig

Quantitative characteristics of spatial organization of neuron populations of vestibular nuclei, forming projections into the spinal cord, were obtained in experiments on guinea pigs by the retrograde axonal transport of horseradish peroxidase, injected unilaterally into the upper cervical and lower thoracic segments of the spinal cord, method. Neurons accumulating the enzyme were found ipsilaterally in the lateral vestibular nucleus and bilaterally in the descending and medial vestibular nuclei. The distribution of vestibulospinal neurons along the length of the spinal cord was studied. Neuron populations of the medial and descending vestibular nuclei whose projection regions coincide with those of fibers of the corticospinal and rubrospinal systems were discovered. The role of vestibulospinal systems in the structure of supra-segmental control of the neuronal apparatus of the spinal cord is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 353–362, May–June, 1991.