Anatomy and in vivo activity of neurons connecting the crustacean stomatogastric nervous system to the brain

In decapod crustaceans., the inferior ventricular nerve connects the cerebr al ganglia (brain) with the stomatogastric nervous system (STNS). In the iv n of the crayfish, eight axons with diameters between 3.5 mum and 10 mum we re found in close proximity to the oesophageal ganglion. Two of these axons terminate with their cell body within the ivn. The projections of the othe r six axons spread inside many neuropiles of the brain, mainly within the p rotocerebrum and the neuropils of the first and second antennae. Several fi bers also send neurites via the circumoesophageal connectives toward the pa ired commissural ganglia and further down to the ventral nerve cord. The ac tivity of motoneurons within the STNS and of axons in the ivn was recorded with implanted electrodes before, during and after times of feeding. At the beginning of feeding all tonically active ivn neurons accelerated their di scharge rate and initially silent neurons also started to fire. Spike frequ ency was correlated with the quantity of food consumed. The ivn response wa s accompanied by a corresponding increase in pyloric frequency and an initi ation of a gastric rhythm. The two motor rhythms showed a strong phasic int eraction, but there was no phase coupling to the ivn activity.