19 April, 2010

Sensory processing in scorpion peg sensilla

Douglas Gaffin is the leading man in scorpion sensory physiology and he has now published an analysis of sensory processing in scorpion peg sensilla.

Primary chemosensory afferents within each peg sensillum on scorpion pectines contain a dense plexus of synaptic contacts of unknown importance to informational processing within this simple sensory structure. These connections probably contribute to the processing of chemical signals from the substrate to the encoded pattern of spike activity ascending the pectinal nerves to the CNS. A key finding of earlier studies of this system was the apparent existence of strong and longlasting inhibitory interactions between one identifiable unit – type ‘‘B’’ cells – and at least two other sensory neurons – identified as ‘‘A1’’ and ‘‘A2’’ – cells within the same sensillum. Because peripheral synaptic interactions are rarely observed between primary sensory neurons, it is important to reject the alternative non-synaptic mechanism to account for the unusual spike waveform of inhibitory B units, namely, that it is derived from coincident discharge of the A1 and A2 units it is presumed to inhibit. High resolution waveform analysis of two or more units firing in close temporal proximity (within about 5 ms) showed unequivocally that type B units occur within the post excitatory period when the A units would be refractory to re-excitation. Furthermore, the number of these B/A1 or B/A2 doublets was in line with the number predicted for the observed spontaneous firing frequency of the B, A1, and A2 units in the peg. This analysis corroborates the original conclusion that B unit activity is the electrophysiological signature of an inhibitory processing event, one that strikingly transforms the information encoded and passed from each peg sensillum to the central nervous system.

Gaffin DD. Analysis of sensory processing in scorpion peg sensilla. Journal of Arachnology. 2010;38(1):1-8. [Subscription required for fulltext, but free fulltext after 12 months].

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