The cercus-to-giant interneuron system of crickets

Summary

• 1. The pattern of connections between cereal sensory neurons and a single sensory interneuron, the medial giant interneuron (MGI), was examined using intracellular methods.

• 2. Two types of sound sensitive hairs are located on each cercus. Each type was examined for its ability to excite, or inhibit the MGI.

• 3. The effect of stimulating a large population of one hair type was examined by blocking movement of all other types, recording intracellularly from MGI, and stimulating the preparation with tones.

• 4. T-hairs on the ipsilateral cercus powerfully excited MGI initiating a train of action potentials. L-hairs on either cercus weakly excited MGI. T-hairs on the contralateral cercus inhibited MGI.

• 5. The effect of stimulating individual receptor hairs was examined by blocking the movement of all but a single hair. Intracellular recordings from MGI exhibit subthreshold synaptic potentials when L-or ipsi-T hairs are stimulated. When the hair was removed the potentials disappeared. Ipsilateral T-hairs excite MIG with a high probability (approximately 75%) while ipsilateral L-hairs excite MGI with a lower probability (approximately 50%).

• 6. Thus the strengths of connection between hair type and MGI can be ranked as follows: Ipsilateral T-hairs provide the strongest excitatory input and therefore determine the overall directional characteristics of MGI. Ipsilateral L-hairs provide weaker, often subthreshold excitatory inputs and contralateral L-hairs provide the weakest excitatory input to MGI. Finally the contralateral T-hairs inhibit MGI.