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Biomedical subjects

V J Wilson

Publications and source records attributed to V J Wilson.

At least 91 records · Page 5Linked to original sources
PubMed1977

Saccular and utricular input to cat neck motoneurons.

1. In two series of cats all vestibular afferents except those innervating the saccular or utricular macula were transected and allowed to degenerate. Subsequent anatomical and physiological verification showed that the saccular nerve had been selectively spared in six cats. The utricular nerve was wholly or partly spared in five cats, but there was some possibility of contamination from other vestibular afferents. 2. The connections of the remaining nerve with dorsal neck motoneurons were studied 27-179 days after the initial surgery in preparations anesthetized with chloralose. 3. Stimulation of the saccular nerve usually evoked IPSPs in contralateral, EPSPs in ipsilateral neck motoneurons. Some of the potentials were disynaptic, many were later and probably trisynaptic. 4. The effects of utricular nerve stimulation were more complex, perhaps because of contamination by other vestibular, particularly canal, afferents. The predominant pattern consisted of ipsilateral inhibition and contralateral excitation, opposite to the effects of saccular nerve stimulation. Many potentials were disynaptic. 5. Various factors that may complicate interpretation of the results, including plastic changes following denervation, are considered. It is concluded that they are not a significant factor. 6. Our main result is a demonstration that the sacculus can contribute to vestibulospinal reflexes acting on the head.

Animals↗
PubMed1976

Mossy fiber neck and second-order labyrinthine projections to cat flocculus.

In five decerebrate cats and in two under N2O-O2 anesthesia, a bipolar electrode array was inserted into a granular layer in the rostral flocculus. At this location MF field potentials were evoked by stimulation of the ipsilateral vestibular nerve and of the C2 dorsal root ganglion. Stimulation through the array was used to fire brain stem neurons antidromically. The activity of these neurons was recorded extracellularly with glass microelectrodes. Stimulation of the C2 dorsal root ganglion evoked in the caudal lateral brain stem a field potential caused by the arrival of impulses in primary afferent fibers. Cells projecting to the flocculus also responded to the stimulus, usually monosynaptically. These neurons were fired by stimulation of the area of the atlantoaxial joint. They did not respond to stimulation of the contralateral C2 dorsal root ganglion, and responded only rarely to stimulation of the dorsal rami of the C2 and C3 spinal nerves. Stimulation of the vestibular nerve was ineffective. Another group of cells projecting to the flocculus was fired at short latency by stimulation of the ipsilateral vestibular nerve. These neurons were usually inhibited by stimulation of the contralateral vestibular nerve. They were not affected by stimulation of any neck afferents. The location of many recording locations was identified by means of fast green dye marks. Most neurons relaying neck activity were in group x of Brodal and Pompeiano (4), a few were in the external cuneate nucleus, and one was in the descending vestibular nucleus. Neurons relaying labyrinthine activity were in the descending vestibular nucleus; one was found in the medial nucleus, in which tracks were made only rarely. There are two parallel pathways relaying neck and labyrinthine activity to the flocculus. While they are separate at the level of the brain stem, they converge in the same rostral areas of the flocculus. The neck afferent information may be required for proper performance of the flocculus in eye-movement control.

Animals↗
PubMed1975

Labyrinthine influence on cat forelimb motoneurons.

1. Intracellular responses in forelimb motoneurons to electrical stimulation of the whole labyrinth and of individual semicircular canal nerves were studied in decerebrated, unanesthetized cats. 2. Stimulation of the whole labyrinth typically produced EPSPs, usually bilaterally, in forelimb extensor (LON, LAT, MED) and shoulder (SI) motoneurons and bilateral IPSPs in forelimb flexor (BIC) motoneurons. 3. Latencies of PSPs indicated that most of those in extensor motoneurons were trisynaptic and many seen in flexor motoneurons may involve four synapses. 4. In the cells sampled, stimulation of the anterior, horizontal or posterior canal nerves often evoked EPSPs in extensor and IPSPs in flexor motoneurons, both ipsi- and contralaterally. Responses to canal stimulation were weaker and more variable than those to stimulation of the whole nerve. 5. Transection of the MLF in the lower medulla had no effect on PSPs evoked in forelimb motoneurons. Lesions in the medulla in the area of the LVST greatly reduced the occurrence of contralateral EPSPs in extensor and IPSPs in flexor motoneurons. The pathway linking labyrinths to forelimb motoneurons therefore appears to include the LVST. Hemisection shows that the pathway to contralateral motoneurons descends in the cord on the side of the stimulated labyrinth before crossing to influence these cells. 6. Labyrinthine control of forelimb motoneurons is less direct than control of neck and back motoneurons. It is suggested that the interneuron in the pathway to forelimb motoneurons is the site of integration of labyrinthine with other reflexes.

Animals↗
PubMed1974

Cervical branching of lumbar vestibulospinal axons.

1. We have investigated the possibility that individual lateral vestibulospinal tract (LVST) axons branch so as to innervate more than one spinal cord level.2. LVST cells in Deiters' nucleus were activated antidromically by means of electrical stimulation applied through fine metal electrodes inserted into the spinal cord. Both by directly measuring the spread of effect of stimulus current, and from theoretical considerations (Appendix), we determined that in most cases an estimate of spread of effect of stimulus current was 10 mum/muA. From the magnitude of the threshold stimulus and from the location of the stimulus point we could often exclude the possibility that the stimulus was spreading to the LVST instead of activating local branches.3. Movable stimulating electrodes, or multi-electrode arrays placed in fixed position, were used to activate 115 LVST neurones antidromically by stimulation of local branches in the lower cervical or upper thoracic cord. Of these cells, 50% were also fired antidromically by stimulation of the LVST at levels ranging from L1 to L4 (L(c) cells). The remaining cells were not activated by the lumbar stimulus (C cells). An additional group of cells was only fired by the lumbar tract stimulus (L cells).4. The distribution of locations of L(c) cells within Deiters' nucleus more closely resembles that of L cells than that of C cells. In addition the median conduction velocity of L(c) cells is similar to that of L cells, but higher than that of C cells.5. Much of the information reaching the lower cervical level from neurones of the LVST is information that is also simultaneously being passed downward to the lumbar region. Such integration makes it possible for a single neurone to be used to co-ordinate widespread motor activity.6. A theory is presented in a separate section (Appendix) to account for the spread of effect of stimulus current upon a myelinated axon submerged in an isotropic medium. The threshold for stimulation of a node by a nearby monopolar electrode is predicted to be proportional to the electrode-node spacing. The constant of proportionality is given in a closed form that depends on the electrical properties of both the neurone and the surrounding medium. The predictions of the theory are shown to be in good accord with the experimental results.

Action Potentials↗