In the cricket auditory system, single nerve cells have been identified that are maximally sensitive to particular sound frequencies and to the direction of a sound source. These neurons are believed to play a key role in acoustic communication. Peripheral sensory cells send their information through functional contacts, called synapses, onto the fingerlike dendrites that extend from the central cells to receive them. The structure of each dendrite, including its diameter, length, and location of synapses, affects the way in which sensory input produces an output signal from the central neuron. This project analyzes how synaptic contacts that are excitatory can interact with contacts that are inhibitory on these central neurons. Excitation or inhibition is shown by physiologically recording the small voltage changes, called post-synaptic potentials, produced across the cell membrane of the identified neuron by inputs from known stimuli. One key cell is labeled Int-1, and its selectivity to sound frequency and direction appears to depend crucially on post-synaptic inhibitory processes. Synaptic inputs onto Int-1 dendrites will be characterized by physiological and anatomical localization of synapses, by determining how auditory peripheral neurons overlap with Int-1 dendrites, and by using dual intracellular recordings to identify neurons that make inhibitory synapses on Int-1. Functional and morphological correlations will establish whether such inhibitory neurons have activity that is necessary and sufficient to provide a mechanism for the specific acoustic responses of Int-1. Results will be extremely valuable for clarifying this excellent model system for analyzing hearing, and should have impact on studies of communication, signal processing, insect biology, and neural mechanisms of integration in general.
