Morphology of antennal motoneurons in the brains of two crickets, gryllus bimaculatus and gryllus campestris

The morphology of the antennal muscles of two cricket species, Gryllus campestris and G. bimaculatus, and their innervation are described. The motoneurons innervating the five tentorio-scapal muscles M4 and M5 and the two scapo-pedicellar muscles M6 and M7 were stained with cobalt chloride introduced via the cut axonal endings in the muscle. The seven antennal muscles are innervated by a total of 17 excitatory motoneurons and one common inhibitory neuron. These neurons branch in the dorsal neuropil of the deuto- and tritocerebrum. No difference in the morphology of the motoneurons between the two species was evident. Two dorsal-unpaired-medial (DUM) neurons located in the suboesophageal ganglion also innervate the antennal muscles. Intracellular recordings of some motoneurons combined with Lucifer Yellow injections corroborated the motoneuron morphology obtained by cobalt backfilling from the muscles. The recordings showed that the motoneurons are either of the fast or the slow type.