Tarsal receptors

The axons of the sensory receptor cells conduct the nerve impulses to the central nervous system. In the thoracic ganglion some second-order neurons connecting via synapses with the axons of tarsal receptor cells have been identified (Dethier, 1976 Rook et al., 1980). The corresponding second-order neurons for the labellar sensory neurons are located in the suboesophagal ganglion (Dethier, 1976 van Mier et al., 1980 Stocker and Schorderet, 1981). 

When the natural product source contains racemic mixtures (of isomeric forms), then clearly the assignment of signal value to either or both variants of a compound needs to be determined. Alterations in receptor detection of chirality can change sensitivity to the geometrically alternate compound over the range 101 to 106. Of the lactones passed into urine and deposited on tarsal hairs of Black-tailed deer (Odocoileus... 

Duncan, D.M., E.A. Burgess and I. Duncan. Control of distal antennal identity and tarsal development in Drosophila by spineless-aristapedia, a homolog of the mammalian dioxin receptor. Genes Dev. 12 1290-1303, 1998. 

Non-volatile pheromones exist, but their chemical isolation and identification has largely just begun. Consequently, few specific receptor cells have been characterized. Using behaviorally active extracts, contact chemoreceptive sensilla with sensitive cells have been identified (Table 1.1). In Fig. 1.5, representative recordings from a tarsal D-hair of Rhagoletis cerasi are presented. Only artificial fruits which were contacted by females can stimulate a receptor cells, and thus activity due to food residues can be excluded. Similar recordings were ailso obtained from D-hairs of Ceratitis capitata (Stadler and Boiler, unpublished). 

The generated spike activity of the-different sensory cells in response to stimuli is decoded by the central nervous system (CNS). To investigate the sensory code of the receptor cells of a sensillum or several sensilla, different approaches can be used. The most direct method is to record from central neurons. In contrast to the investigation of central neurons responding to olfactory stimulations (Chapter 2), such recordings have been performed only recently from interneurons of the thoracic ganglion of the blowfly in response to the stimulation of tarsal contact chemoreceptive sensilla (Rook et al., 1980). 

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