Responses of thoracic spinal interneurons to vestibular stimulation

• Published in: Experimental brain research 2009-05, Vol.195 (1), p.89-100
• Main Authors: Miller, D. M, Reighard, D. A, Mehta, Amar S, Mehta, Ajeet S, Kalash, R, Yates, B. J
• Format: Article
• Language: English
• Subjects: Action Potentials - physiology; Afferent Pathways - physiology; Animals; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; Biophysics; Cats; Decerebrate State - physiopathology; Electric Stimulation - methods; Fundamental and applied biological sciences. Psychology; Interneurons - physiology; Laboratory animals; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Nervous system; Neurology; Neurons; Neurosciences; Peripheral nervous system. Autonomic nervous system. Neuromuscular transmission. Ganglionic transmission. Electric organ; Reaction Time - physiology; Reflex, Vestibulo-Ocular - physiology; Research Article; Spinal cord; Spinal Cord - cytology; Vertebrates: nervous system and sense organs; Vestibular Nerve - physiology
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s00221-009-1754-0

Vestibular influences on outflow from the spinal cord are largely mediated via spinal interneurons, although few studies have recorded interneuronal activity during labyrinthine stimulation. The present study determined the responses of upper thoracic interneurons of decerebrate cats to electrical stimulation of the vestibular nerve or natural stimulation of otolith organs and the anterior and posterior semicircular canals using rotations in vertical planes. A majority of thoracic interneurons (74/102) responded to vestibular nerve stimulation at median latencies of 6.5 ms (minimum of ~3 ms), suggesting that labyrinthine inputs were relayed to these neurons through trisynaptic and longer pathways. Thoracic interneuronal responses to vertical rotations were similar to those of graviceptors such as otolith organs, and a wide array of tilt directions preferentially activated different cells. Such responses were distinct from those of cells in the cervical and lumbar enlargements, which are mainly elicited by ear-down tilts and are synchronous with stimulus position when low rotational frequencies are delivered, but tend to be in phase with stimulus velocity when high frequencies are employed. The dynamic properties of thoracic interneuronal responses to tilts were instead similar to those of thoracic motoneurons and sympathetic preganglionic neurons. However, the preferred tilt directions of the interneurons were more heterogeneous than thoracic spinal outputs, showing that the outputs do not simply reflect an addition of local interneuronal activity.