Connections of the Head to Networks of the Stomatogastric System in Crayfish

A tiny brain nerve, the inferior ventricular nerve (ivn), connecting the brain to the stomatogastric nervous system contains eight axons with two of them terminating in cell bodies within the nerve. The other six axons have widespread dendritic arborizations throughout the protocerebrum and the antenna I and II neuropils. Several fibres branch in the brain, but also send neurites via the connectives towards the paired commissural ganglia and from there towards the stomatogastric ganglion or further down the ventral nerve cord. During feeding there is always a strong increase of firing in the ivn before increased pyloric activity and initiation of rhythmic activity in the gastric network. In vivo and in vitro recordings from the ivn in a newly developed head-stomatogastric preparation show six ascending and just two descending units which respond to mechanical stimulation of the antenna. The preparation reacts to illumination of the eyes with a state-dependent light response of the pyloric rhythm, which is not conveyed via the ivn but via the connectives.