Identification of the somata of common inhibitory motoneurons in the metathoracic ganglion of the cockroach

The somata of the three common inhibitory neurons known to innervate many muscles of the metathoracic legs of the cockroach have been identified by allowing cobalt chloride to diffuse up the cut axons of these cells and by precipitating the cobalt with ammonium sulfide. The black precipitate of cobalt sulfide allowed the somata and axonal pathways of these three cells to be clearly visualized. All three somata are located near the midline on the ventral surface of the ganglion. The most posterior of these somata is just contralateral and sends branches directly out lateral nerves 3, 4, and 6, and indirectly into nerve 5 via a small connective between nerves 4 and 5. The other two somata each send a branch out only nerve 5. The somata of the fast and slow excitatory motor axons to the coxal depressor muscles were also identified in this study.