Ralph A. DiCaprio, Ph.D.

     My laboratory is interested in the integrative properties of nonspiking neurons. Nonspiking neurons transmit information using graded (or analog) changes in their membrane potential in contrast with the discrete action potentials that encode information in a digital manner in spiking neurons. One system used in the lab is the ventilatory central pattern generator of the shore crab, Carcinus maenas, as it is almost exclusively composed of nonspiking neurons.  This is the case at all levels of the motor hierarchy, including frequency modulating interneurons, CPG interneurons, and sensory neurons.  Current projects include a determination of the circuitry of the nonspiking neurons in the CPG using dual intracellular recordings and a quantitative analysis of neuronal structure which will be correlated with a determination of the intrinsic membrane properties of single neurons using single electrode voltage clamp.

     We have recently initiated a study of the transfer functions of nonspiking and spiking proprioceptors in the first two joints of the crab leg.  The basal leg joint in the crab is monitored by a single proprioceptor, the TCMRO, that contains two nonspiking and one spiking neuron.  The position, velocity and acceleration of the next most distal joint is monitored by a single spiking receptor, the CB chordotonal organ, and two nonspiking elastic strand receptors.  One therefore can make a direct comparison of these two distinct modes of information transmission, although the physiological functions of the receptors are very similar as are the motor behaviors that they mediate.  The experimental approach uses linear and nonlinear (Wiener kernel) systems analysis methods.  This study will be extended to investigate the overall transfer properties of the synapses and motor reflex responses to sensory inputs.  ; In addition, we are determining the extent and fidelity of the information transmission characteristics of these nonspiking and spiking receptors using information theoretic methods.

     We are also conducting a collaborative study of the properties of a strain sensitive receptor, the campaniform sensilla, in the cockroach.  This information is being used in a larger effort aimed at determining various aspects of sensorimotor integration in the cockraoch leg in a  project utilizing biological principles in robot design.

Selected References:

• DiCaprio, R.A.(1999) Gating of primary afferent input by a central pattern generator. J. Neurophys 81: 950-953.

• Frazier,S.F., Larsen, G.S., Neff, D., Quimby, L., Carney, M., DiCaprio, R.A. and S.N. Zill. (1999). Joint elasticity and movements of the cockroach tarsus in walking. J. Comp. Physiol, In Press.

• Zill, S. N., Ridgel, A.L.,DiCaprio, R.A. and S. F. Frazier. (1999). Load signaling by cockroach trochanteral campaniform sensilla. Brain Res 822: 271-275.

• Ridgel, A.L., Frazier, S.F.,DiCaprio, R.A. and S.N. Zill. (1999) Active signaling of leg loading and unloading in the cockroach. J. Neurophys 81: 1432-1437.

• DiCaprio, R.A. (1997) Plateau potentials in motor neurons in the crab ventilatory system. J. Exp. Biol 200(12): 1725-1736.