Electrophysiological analysis of synaptic interactions within peg sensilla of scorpion pectines.

Pectines are unique, midventral sensory appendages that help direct mating and food-finding behaviors in scorpions. Dense two-dimensional arrays of bimodally sensitive (chemical and mechanical) peg sensilla form the primary sensory structures on pectines. Several qualities of peg sensilla make them well suited to electrophysiological investigation, including accessibility, stability of extracellular recordings, and the ease with which spiking cells can be identified and categorized. Cross-correlations of spontaneous neural activity show signs of synaptic interactions between sensillar neurons in all species examined to date (Paruroctonus mesaensis, Hadrurus arizonensis, Centruroides vittatus) representing three families and two superfamilies. Both excitatory and inhibitory interactions have been observed, as well as possible dyadic synaptic arrangement. Computer simulations of cross-correlograms are consistent with experimental data and may help provide additional insight into functionality of synaptic connections. Intra-sensillar interactions, coupled with the topographic order of peg sensilla and their central nervous system projections, may allow scorpions to precisely resolve microfeatures of chemical stimuli. Future research directions include inter-sensillar recordings to determine whether synaptic interactions extend between adjacent sensilla. Other unresolved questions that can be approached electrophysiologically are whether mechanosensory cells interact with chemosensitive cells and how the synaptic circuits function under specific chemical and mechanical stimulation.