The large fourth abdominal intersegmental interneuron: a new type of wind-sensitive ventral cord interneuron in locusts.

A large interneuron in Locusta migratoria is described that extends from the fourth abdominal ganglion to the brain. The morphology was revealed by injection of cobaltous ions or Lucifer yellow into the cell. As its cell body lies within the fourth abdominal ganglion it is named A4I1, the first-identified intersegmental interneuron of the fourth abdominal ganglion. This neuron receives input from highly flexible, wind-sensitive hairs on the prosternum, the pronotum, and the head (field 1). Sensory connections with A4I1 are made within the prothoracic ganglion. Stimulation of the receptive field initiates spikes in A4I1 which travel anteriorly and posteriorly from the prothoracic ganglion. Intracellular recording from the axon and the soma shows that the cell membrane becomes inactive within the fourth abdominal ganglion. Spikes could be generated within the fourth abdominal ganglion by current injection into the soma. Occasionally excitatory postsynaptic potentials were observed in a soma recording, but up to now there is no evidence for a second spike initiation site. By intracellular current injection into the soma of the left and right A4I1 cell it is shown that the two cells are not electrically coupled.