A basic property of sensory systems is the opponent, center-surround organization of individual receptive fields of neurons. This organization results from the convergence of inputs from separate sensory cells, some of which contribute excitation, and others contribute inhibition. A single sensory cell in the leech synapses with a motoneuron involved in a simple reflex. This sensory cell generates an opponent receptive field in the motor neuron by means of conduction block and an inhibitory interneuron. Experiments being conducted under this award use electrophysiological recording and stimulation, marking of cells with intracellular tracers, laser microsurgery and electron microscopy to characterize the distribution and nature of synaptic contacts involved in the reflex connection and to analyze integration of those inputs by postsynaptic neurons. These experiments should reveal activity-dependent mechanisms that influence qualitative properties of the mechanosensory receptive field and the reflex connections of which it is a part. They will also help understand how postsynaptic cells such as motor neurons integrate sensory signals to reach threshold for firing action potentials and provide insight into the mechanisms by which cell geometry, particularly axonal and dendritic branching, influence neural signalling.
