Brian D. Clark, Ph.D.
Research Assistant Professor, Dept. Neurobiology and Anatomy, Drexel University College of Medicine
Email: brian.clark@drexelmed.edu

Modulation of neural systems by monoamines

Pathophysiology of peripheral nerve in work-related musculoskeletal disorders

Research and Interests

Dr. Clark has recently joined the laboratory of Dr. Barry Waterhouse, where he is investigating the effects of monoamines on synaptic transmission in microcircuits in the brain. He is also engaged in a research collaboration with neuroscientists at Temple University, studying the mechanisms of work-related musculoskeletal disorder (WMSD) in an animal model.

Research tools include the graphical and statistical analysis of spike trains from interconnected neurons. One recent example, "snowflake plots" are shown to the right. These scatterplots demonstrate shifting relationships among three firing neurons in the prefrontal cortex of a rat before and after administration of the drug methylphenidate (Ritalin). The co-activity of all three cells is shown by the tight cluster of red points about 1/3 of the way out from the center, heading towards two o'clock.

Dr. Clark is also involved in the analysis of nerve compression in the carpal tunnel. The bottom figure on the right shows the withdrawal threshold (a measure of cutaneous sensitivity) in the fore- and hind limbs of rats over several weeks of performing a high force, repetitive reaching and grasping task. The observation that a decrease in sensitivity is seen in all four limbs, not just the forelimb used to perform the task, supports our recent contention of a systemic, in addition to the local inflammatory effect in this animal model or work-related musculoskeletal disorder. Dr. Clark is currently involved in measurements of the decrements in conduction velocity of the median nerve in the region of the carpal tunnel in rats that have been given ibuprofen or been allowed to take rest breaks during performance of the task.

Biography

Brian Clark did his Ph.D. at The University of Chicago, and his postdoctoral fellowship at Hahnemann University. He later served on the faculty of the Pennsylvania College of Podiatric Medicine and Temple University. He is now a research assistant professor in the Department of Neurobiology and Anatomy at Drexel University College of Medicine.

Active Funding

R01 AR0512121 Secondary Prevention of WMSD in a Rat Model. Ann E. Barr, P.I. 2004-2009. NIAMS
U01 OH008599 Effect of repetition in aged rats with WMSD. Mary F. Barbe, P.I. 2005-2008. NIOSH

These two studies extend an ongoing collaboration (see "Selected References") on the lesions developed in the neural, muscular and skeletal tissues of the forelimbs of rats that have performed a voluntary reaching and grasping task for several weeks. We have previously observed several signs of inflammation and fibrosis, especially in the region of the carpal tunnel, along with changes in behavior, grip strength, somatic sensation and conduction velocity of the median nerve - in short, the signs of human carpal tunnel syndrome. The current work extends our studies in two ways: First, we are beginning to evaluate possible interventions (oral ibuprofen, rest breaks) in preventing the onset of the lesions. Second, we are trying to determine whether aging is an additional risk factor in the development of the various changes and deficits we have observed in young animals.

Collaborators & Colleagues

Mary F. Barbe, Temple University
Ann E. Barr, Temple University

Selected Publications

1. Barr, A.E., Barbe, M.F., and Clark, B.D. (2004) Work-related musculoskeletal disorders of the hand and wrist: epidemiology, pathophysiology, and sensorimotor changes. J Orthop Sports Phys Ther., Special Issues of the hand: Repetitive Stress Injuries: the Pathophysiology; 34:610-627

2. Barr, A.E., Barbe, M.F. and Clark, B.D. (2004) Systemic inflammatory mediators contribute to widespread effects in work-related musculoskeletal disorders. Exerc Sport Sci Rev 32(4):135-142.

3. Clark, B.D., Al-Shatti, T.A., Barr, A.E., Amin, M. and Barbe, M.F. (2004) Performance of a high-repetition, high-force task induces carpal tunnel syndrome in rats. J Orthop Sports Phys Ther 34:244-253.

4. Clark, B.D., Barr, A.E., Safadi, F.F., Beitman, L., Al-Shatti, T., Amin, M., Gaughan, J.P., and Barbe, M.F. (2003) Median nerve trauma in a rat model of work-related musculoskeletal disorder. J. Neurotrauma 20: 681-695.

5. Prather, J. F., Clark, B.D., and Cope, T.C. (2002) Firing rate modulation of motoneurons activated by cutaneous and muscle receptor afferents in the decerebrate cat. J. Neurophysiol. 88: 1867-1879.

6. Clark, B.D. and Cope, T.C. (1998) Frequency-dependent synaptic depression modifies postsynaptic firing probability in cats. J. Physiol. 512: 189-196.