Joseph C. Holt, PhD
Assistant Professor

Affiliations: Neuroscience Graduate Program; Cell Biology Graduate Program

Email: jcholt@utmb.edu
Office:  (409) 772-2784
Fax:  (409) 772-2694

(Click photo to enlarge)

BIOGRAPHICAL INFORMATION:

Dr. Holt received his undergraduate degree in Biology and Chemistry from the University of North Carolina at Pembroke.  He attended graduate school at Tulane University School of Medicine in New Orleans, Louisiana where he received his Ph.D. in Pharmacology and Toxicology in 2000.  Dr. Holt continued his professional training as both a postdoctoral fellow and research associate at the University of Chicago. He joined the Department of Otolaryngology at UTMB in the summer of 2005 as an Assistant Professor.

RESEARCH INTERESTS:

Neuropharmacological Basis of Synaptic Transmission in the Vestibular Periphery

In the inner ear of most animals, there is a collection of tubular and sac-like organs that monitor both balance and motion of the head and body.  The ability of these organs to detect head movements resides in a specialized, neuroepithelial cell called the hair cell.   The direction, speed, magnitude, and frequency of head and body movements are relayed from these hair cells to the brain via afferent neurons traveling in cranial nerve VIII.  The brain, as it turns out, also communicates with these same hair cells and their afferent fibers through an efferent innervation, thus providing the means to modulate incoming sensory information at a very early stage. As one moves up the vertebrate scale from fish and amphibians to reptiles, birds, and mammals, the physiology and microanatomy of these organs, and organization of their neural pathways to and from the brain, become more complex. The increase in complexity parallels, and is most likely necessitated by, the increasing repertoire of head and body movements experienced by the animal.  Hair cells are predominantly glutamatergic while efferents are mainly cholinergic but other neurotransmitters have been implicated including GABA, ATP, CGRP, and the opioid peptides.  At its simplest level, many neurotransmitter receptors and effector ion channels are intimately involved in the exchange of information in the vestibular periphery among efferent neurons, hair cells, and afferent nerve fibers.    In Dr. Holt’s lab, the use of electrophysiological, pharmacological, molecular biological, and immunocytochemical techniques will be applied in three model organisms to answer two fundamental questions: (1) What are the synaptic mechanisms by which these hair cells encode and impart such a wealth of information about head movements to afferents?; and, (2) What are the synaptic mechanisms and functional significance of efferent pathways? 

RECENT PUBLICATIONS

Holt J.C., Xue J-T, Goldberg J.M. (2006) Transmission between type II hair cells and bouton afferents in the turtle posterior crista. J Neurophysiol 95: 428-452.

Holt J.C., Lioudyno M., Guth P.S. (2003) A pharmacologically distinct nicotinic ACh receptor is found in a subset of frog semicircular canal hair cells. J Neurophysiol. 90: 1526-36.

Lioudyno M.I., Verbitsky M., Glowatzki E., Holt J.C., Boulter J., Zadina J.E., Elgoyhen A.B., Guth P.S.  (2002) The alpha9/alpha10-containing nicotinic ACh receptor is directly modulated by opioid peptides, endomorphin-1, and dynorphin B, proposed efferent cotransmitters in the inner ear. Mol Cell Neurosci. 20: 695-711.

Holt, J.C., Lioudyno M., Athas, G.B., Garcia, M.M., Perin, P., Guth, P.S. (2001) The effects of proteolytic enzymes on the alpha9-nicotinic receptor-mediated response in isolated frog vestibular hair cells.  Hear Res. 152: 25-42.

Lioudyno M.I., Verbitsky M., Holt J.C., Elgoyhen A.B., Guth P.S. (2000) Morphine inhibits an alpha9-acetylcholine nicotinic receptor-mediated response by a mechanism which does not involve opioid receptors. Hear Res. 149:167-77.

Holt, J.C., Pantoja, A.M., Athas, G.B., Guth, P.S. (2000) A role for chloride in the hyperpolarizing effect of acetylcholine in isolated frog vestibular hair cells. Hear Res 146:17-27.

Guth, P.S., Holt, J.C., Perin, P., Athas, G., Garcia, M., Puri, A., Zucca, G., Botta, L., Valli, P. (1998) The metabotropic glutamate receptors of the vestibular organs. Hear Res. 125:154-62.

Norris, C.H., Miller, A.J., Perin, P., Holt, J.C., Guth, P.S. (1998) Mechanisms and effects of transepithelial polarization in the isolated semicircular canal.  Hear Res. 123:31-40.

Perin, P., Holt, J.C., Guth, P.S., Norris, C.H. (1998) A comparison of the cholinergic properties of the leopard frog vestibular organs. Primary Sensory Neuron 2(4):282-275.

Pantoja AM, Holt JC, Guth PS. (1997) A role for chloride in the suppressive effect of acetylcholine on afferent vestibular activity. Hear Res. 112:21-32.