Deforest Mellon, Jr.

Professor of Biology
255B Gilmer Hall
(434) 982-5766

Education

  • B.S., Yale University, 1957
  • Ph.D., The Johns Hopkins University, 1961
  • Postdoctoral, Stanford University, 1961-1963

Research Interests

To be optimally effective, escape behaviors depend upon the synchronized action of dedicated sensory systems that excite central nervous targets and motor systems with minimal time delays. Among the neurophysiological adaptations that accomplish this in the central nervous system of shrimps are electrical synaptic connections between myelinated giant interneurons and myelinated giant motor neurons that galvanize contractions in the abdominal flexor muscles. Axonal conduction velocities of the myelinated medial giant interneurons (MdG) are the highest recorded in any animal (220 m/sec @ 18o C); voltage-gated sodium ion channels in MdG nodal membrane in the vicinity of the synaptic membrane in turn have extremely fast activation and inactivation kinetics, e.g., onset to peak conductance in 100 µsec, nearly twice as steep the voltage/current transition found in mammalian axonal membrane.  and with a maximum inward sodium current density estimated at 500 mAmp/cm2. I have been interested in characterizing the electrical and time-dependent properties of the electrical synaptic connection between MdG and MoG. My experimental results lead to the conclusion that this very fast synaptic transfer is based upon a novel bioelectrical mechanism, possibly involving in-series capacitative discharge currents. This hypothesis is currently being tested using theoretical and experimental electrophysiological models.

Proposed electrical analogue of the medial giant-to-motor giant synaptic circuitry;   myelin and  non-synaptic axonal membrane capacitances omitted for clarity.

 

Representative Publications