An implantable electrode design for both chronic in vivo nerve recording and axon stimulation in freely behaving crayfish

Abstract

A chronically implantable electrode design permitting alternate extracellular nerve recording and axon stimulation in freely behaving crayfish was developed. The electrode consists of a double hook made from 20 μm thin platinum wire that can be fitted to various nerve diameters, and is easily implantable. A fast curing, flexible two-component silicone was used for insulation. The double hook was connected to plugs and fixed on the carapace of a crayfish allowing the animals to roam freely. The setup also allows for repeated dis- and re-connection of the crayfish for alternating recording and stimulation. Two channel recordings were used to determine directionality and to discriminate between afferent activity of the two stretch receptor neurons and efferent activity of several motor neurons. In addition, they were also used to determine the conduction velocity of the recorded efferent activity. Stable two-channel recordings could be obtained for up to 5 months and 15 days without apparent effects on the animal. In vivo stimulation could be performed for at least 3 1 2 weeks. The implantable double hook is suitable for widespread use in invertebrate neurobiology.