Bilateral local non-spiking interneurons in the terminal (sixth) abdominal ganglion of the crayfish,Procambarus clarkii

Abstract

The function of local bilateral non-spiking interneurons (BNSs) in the crayfish terminal (sixth) abdominal ganglion has been studied using intracellular recording and staining techniques. The results show that BNSs function not only in sensory processing but also in motor control. 1. One identified BNS, LDS (Reichert et al. 1983), is connected to the ascending interganglionic interneurons that carry sensory information from the tailfan to rostral ganglia, but not to the uropod motoneurons. Other BNSs have measurable postsynaptic effects upon the motoneurons. 2. Depolarizing current injected into BNSs affects the spike activity of uropod motoneurons in a graded manner. Hyperpolarization of BNSs, however, has no effect upon motoneurons. 3. BNSs have a small diameter (less than 5 μm) transverse process across the ganglionic midline and thin branches emerging from it. LDS has a large diameter (more than 15 μn) transverse process with thick branches. 4. The branches of BNSs have both input and output connections in each hemiganglion, though in LDS the input (soma side) and output (contralateral side) branches are separated. 5. The voltage change elicited on one side of LDS is conducted to the opposite side with a decrement in amplitude of only 10–20%. This indicates that LDS operates as a single functional unit. 6. Injection of a small amount of depolarizing current into BNSs can affect the motoneurons on the same side only. This suggests that the branches of BNSs on each side might function as local processing sites of neural information that operate independent of each other.