Pergamon 0022-1910(95)00001-1 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFED J. Insect Physiol. Vol. 41, No. 7, 597-602, 1995 pp. Copyright 0 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0022-1910/95 $9.50 + 0.00 Sensitivity to Albumin and its Terminal Amino Acids of Labellar Taste Chemoreceptors in Protophormia terraenovae (Diptera: Calliphoridae) A. LISCIA,* J. G. STOFFOLANO JR,? I. TOMASSINI BARBAROSSA,* P. MURONI,* R. CRNJAR* zyxwvutsrqpo Received 3 May IYY4; revised 28 November IYY4 Stimulation with bovine serum albumin (BSA) evokes spikes discharges from three receptor cells of the labellar chemosensilla in Protophormiu, the “sugar” cell being the most sensitive. Confrontation of the spike frequency profiles across all three chemoreceptor cells by the vector space analysis suggests that L-alanine (the C-terminal amino acid of the BSA molecule), but not L-aspartic acid (N-terminal amino acid), may account for the stimulator effectiveness of BSA. Chemoreceptors Albumin Amino acids Blowflies INTRODUCTION Ingestion of protein in blowflies is affected by sex and reproductive condition (Dethier, 1976; Yin and Stoffolano, 1995). Dethier (1976) argued that flies must be able to discriminate between proteinaceous and non- proteinaceous food, and that the fly is quite able to make choices on the basis of gustatory information alone. The labellar sensilla provide the primary source of taste input. Each labellar chemosensillum in blowflies con- tains four receptor cells that are named according to the best stimulus as water, salt, sugar and fifth (anion) cells (Dethier, 1976; Schnuch and Hansen, 1990, 1992). In- deed, a rigid specificity in the response does not exist and each cell can also respond to other chemicals, such as amino acids (Dethier, 1976; Schnuch and Hansen, 1990, 1992). The action potentials generated by each of the four cells in a chemosensillum are consistently different in size and shape and can be differentiated from one another (Dethier, 1976; Schnuch and Hansen, 1990, 1992). Investigations on the effects of proteins and amino acids on taste chemosensilla in flies have been conducted by Wolbarsht and Hanson (1967) Shiraishi and Kuwabara (1970), Goldrich (1973) Dethier (1961, 1976) Gritsai (1978), Shimada and Tanimura (1981) Barton Browne and Kerr (1985). Albumin is one of the most used molecules for the study of protein effects on *Dipartimento di Biologia Sperimentale, Sezione di Fisiologia Gen- erale, Universita di Cagliari, Viale Poetto 1, I-09126 Cagliari, Italy. TDepartment of Entomology, University of Massachusetts, Amherst, MA 01003, U.S.A. chemosensilla, but results are not consistent: Wolbarsht and Hanson (1967) found that albumin is not stimu- latory for insects; Gritsay (1978) reported instead that a solution of albumin is stimulatory for the labellar chemosensilla of Musca domestica, but failed to indicate what kind of albumin was tested. On the basis of these considerations, we decided to test whether the stimulatory effectiveness of bovine serum albumin (BSA) on the largest labellar chemosensilla of the blowfly Protophormia terraenovae, is attributable to the protein molecule itself or to its terminal amino acids, L-aspartic acid (N-terminal) and L-alanine (C-terminal), as suggested by Shimada and Tanimura ( 1981). MATERIALS AND METHODS Adult female blowflies, P. terraenovae, (3- 5 days old) used in the experiments were taken from our laboratory colony reared under standard conditions. Tests were performed on the “largest” labellar chemosensilla (Wilczek, 1967). The tip-recording method described by Hodgson et al. (1955) was adopted: the indifferent electrode (an Ag/AgCl wire) was inserted in the foramen magnum of an isolated head; the recording electrode was a glass micropipette filled with the test solution, which made contact with an Ag/AgCl wire connected to the input of the preamplifier (WPI 707). Spike discharges were displayed on a CR0 oscillo- scope (Taktronix 5100), recorded on magnetic tape, digitized with a Metrabyte DAS-16 A/D converter (10,000 points/s) and stored on disk for later analysis. 597