Sensory System Functions in Nurse Sharks (Ginglymostoma cirratum): Acquisition and Interpretation of Electrophysiology in Olfactory and Acoustic Nerve Pathways

Lindsay R. Rubin and Jennifer E. Smith, Albion College 2006

Introduction/Background
The study of the sensory systems in sharks in the marine environment is largely unexplored. The electrophysiology of olfactory and acoustical systems in nurse sharks (Ginglymostoma cirratum) can be studied by implanting electrodes to measure and record single nerve cell potentials (Kajiura, 2003 & Kajiura et. al., 2005). These two sensory systems are finely tuned and play a crucial role in shark survival. The present study involves investigating the relationship between sensory physiology of the olfactory and acoustical systems in nurse sharks and how sensory input translates to behavioral responses.

Methods
In order to study single nerve cell electrical activities, microscale silicon- and polymer-substrate neural probes were designed in collaboration with the University of Michigan’s Biomedical Engineering Department. These prototypical electrodes are implanted into the olfactory tract and acoustical system to measure neural signals in response to a variety of odorants or acoustical stimuli. The ultimate goal will be to characterize basic functions of the olfactory and acoustical systems and how they translate to behavioral responses.

Results
Preliminary reports show that single nerve cell recordings using silicon- and polymer-substrate electrodes are possible and can be quantitatively studied and distinct nerve cell potentials recorded from olfactory neurons located in the olfactory tract. Initial studies for acoustical system are set on locating auditory nerve pathways. Electrophysiological interpretation of the acoustical endorgan is pending.

Discussion
Interpretation of electrophysiological responses shows that different olfactory neurons respond to different odorants and that single nerve cells might respond to a variety of different odorants. This neural analysis is also applicable to the study of the acoustical system. Preliminary investigation suggests that auditory neurons exhibit unit activity in response to vibrational stimuli. Additional research took place during the summer of 2006 with support from FURSCA and will carry over into next year. Further study will provide a unique opportunity to relate sensory and motor responses to the animals’ behaviors in both the laboratory and ocean environments.

Literature Cited
Carlson, TJ. 1998. Application of sound and other stimuli to control fish behavior. American Fisheries Society 127: 673-707.

Kajiura, SM. 2003. Electroreception in neonatal bonnethead sharks, Sphyrna tiburo. Marine Biology143: 603-611.

Kajiura, SM, JB Forni & AP Summers. 2005. Olfactory morphology of carcharhinid and sphyrnid sharks – does the cephalofoil confer a sensory advantage? Journal of Morphology 264: 253-263.

Lu, A. AN Popper & RR Fay. 1996.Behavior detection of acoustic particle motion by a teleost fish Astronotus ocellatus): sensitivity and directionality. 179: 227-233.

Acknowledgments
We would like to acknowledge the University of Michigan Biomedical Engineering Department, the shark lab, Dave Carey and most importantly, Dr. Carrier for his guidance and instruction.

Presentations/Posters

Implantable neural interfaces for characterizing population responses to odorants and electrical stimuli in the nurse sharks Ginglymostoma cirratum. Lehmkuhle, M.J., R.J. Vetter, H. Parikh, J.C. Carrier, and D.R. Kipke. 2006. CHEMICAL SENSES 31(5): A14-A14 JUN 2006. Abstract (see page 14).