LOCAL INTERNEURONS DEFINE FUNCTIONALLY DISTINCT REGIONS WITHIN LOBSTER OLFACTORY GLOMERULI

Whole-cell recording coupled with biocytin injection revealed four typ es of interneurons intrinsic to the olfactory lobe (OL) of the spiny l obster Panulirus argus. Each type of neuron had a distinct pattern of arborization within the three anatomically defined regions of OL glome ruli (cap, subcap and base). Type I interneurons innervated all three regions, while types II, III and IV branched only in the cap, subcap a nd base, respectively. Type I interneurons responded to electrical sti mulation of the antennular (olfactory) nerve with a burst of 1-20 acti on potentials and a 1-10s depolarization. Type II (cap) interneurons r esponded to the same input with a burst of 1-3 action potentials follo wed by a shorter hyperpolarization. Type III (subcap) interneurons res ponded with a burst of 1-6 action potentials followed by a delayed, 0. 5-4s depolarization. Type IV (base) interneurons responded with a brie f depolarization or a burst of 1-3 action potentials followed by a 1 s hyperpolarization. The regionalized arborization and the different re sponse properties of the type II, III and IV interneurons strongly imp ly that lobster olfactory glomeruli contain functionally distinct regi ons, a feature that should be useful in understanding the multiple syn aptic pathways involved in processing olfactory input.