INTERSEGMENTAL ASCENDING INTERNEURONS CONTROLLING UROPOD MOVEMENTS OFTHE CRAYFISH PROCAMBARUS-CLARKII

The premotor effects of intersegmental ascending interneurones upon ur opod motor neurones in the crayfish Procambarus clarkii (Girard) are e xamined with intracellular recording and staining techniques. We show that many ascending interneurones can affect the activity of the antag onistic opener and closer motor neurones in the terminal ganglion. Bas ed upon soma position, ascending interneurones are divided into three groups of rostral, medial, and caudal interneurones. Twenty-four ascen ding interneurones are characterized physiologically according to thei r inputs from the tailfan and their output effects on the uropod motor neurones of both sides. Each interneurone is identifiable as a unique individual by means of overall shape, soma position, number of main b ranches, the commissure in which primary neurites cross the midline, a xon position in the 5th-6th abdominal connective and physiological res ponses. They are classified into six classes; coactivating, coinhibiti ng, reciprocally closing, reciprocally opening, variably effective, an d not effective interneurones, according to their premotor effects on the uropod motor neurones. These ascending interneurones seem to act a s multifunctional units conveying sensory information from the tailfan to the anterior abdominal ganglia and, at the same time, influencing the uropod motor pattern in the terminal abdominal ganglion.