ABSTRACT
The electrophysiological response of labellar and tarsal chemosensilla in the blowfly Phormia regina was studied in response to a complex stimulus naturally encountered by flies such as sheep faeces, and to beef liver, a proteinaceous feeding source. Responses were investigated both before or after injection of clonidine, an octopamine agonist previously shown to enhance sucrose ingestion, while decreasing that of proteins. As assessed by single sensillum recordings, the four different chemosensory - "salt", "sugar", "deterrent" and "water" - cells were all activated by both stimuli, regardless of sex and sensillum type, the "sugar" one being in all cases the most sensitive to beef liver before clonidine injection. Clonidine treatment affected neither labellar nor tarsal sensitivity to sucrose. Conversely, clonidine-injected flies showed a significant increase in the activity of the "deterrent" cell to beef liver, thus accounting for a decrease in protein ingestion. This study for the first time provides evidence of a key role of a clonidine-sensitive peripheral taste sensitivity in down-regulation of protein ingestion in blowflies. Correlation between peripheral sensitivity and behavioural output is discussed.
Subject(s)
Carbohydrate Metabolism , Clonidine/pharmacology , Diptera/drug effects , Diptera/physiology , Proteins/metabolism , Animals , Electrophysiology , Female , Male , Sense Organs/drug effects , Sense Organs/physiologyABSTRACT
The aim of this study was to examine the role of the olfactory system of the midge Culicoides imicola Kieffer as the major system mediating repellency to antihelminthic avermectins. Incidental observations indicate that treatment with Dectomax or Ivomec (commercial formula of the avermectins doramectin and ivermectin, respectively) protects sheep from infection by bluetongue (BT) viruses. Our electrophysiological data from midge antennae showed that the stimulating effectiveness of L- (+)-lactic acid, butanone, and sheep fleece odor decreased after addition of avermectins. The results show that these antihelminthics affect the olfactory sensitivity of the insect toward the animal host by reducing the response to those compounds that attract the insect, consequently reducing the possibility of biting the sheep and thereby transferring the BT virus.
Subject(s)
Ceratopogonidae/physiology , Insecticides/pharmacology , Ivermectin/analogs & derivatives , Smell/physiology , Animals , Bluetongue virus/drug effects , Butanones/pharmacology , Ceratopogonidae/drug effects , Ceratopogonidae/virology , Insect Vectors , Ivermectin/pharmacology , Lactic Acid/pharmacology , Smell/drug effectsABSTRACT
In the attempt to gain more information on the mechanisms underlying bitter and/or sweet taste reception, we have investigated the responses of labellar chemosensilla in the blowfly Protophormia terraenovae to Na-saccharin, as compared to sweet stimuli (sucrose or fructose) and bitter stimuli (denatonium benzoate or amiloride). Electrophysiological and behavioral results indicate that the sweetener Na-saccharin inhibits the "sugar" cell in the labellar taste sensilla of the blowfly P. terraenovae. In multichoice preference tests, flies ingested more of the solutions containing sugar to those with sugar+Na-saccharin. This finding is in good agreement with the spike frequency reduction observed for the "sugar" cell activity. Analysis of the spike discharges also shows a positive dose-response for the "deterrent" cell following stimulation with Na-saccharin and denatonium benzoate. Flies drank any of the Na-saccharin solutions, regardless of their concentration, less than water, thus indicating a weak deterring effect on water drinking. The prevailing activation of the "deterrent" cell by stimulation with Na-saccharin is not directly coupled with a coherent behavioral output. Cross adaptation was found to occur between responses to Na-saccharin and denatonium benzoate or amiloride regardless of the order of adapting stimuli. In the case of sweet stimuli, cross adaptation occurred when the adapting stimulus was Na-saccharin, but it did not when the adapting stimuli were sucrose or fructose. Addition of Na-saccharin to both sugars significantly depressed the spike firing frequency, while an increase was observed with denatonium benzoate or amiloride.
Subject(s)
Chemoreceptor Cells/physiology , Diptera/physiology , Evoked Potentials/physiology , Feeding Behavior/physiology , Neurons, Afferent/physiology , Sense Organs/physiology , Taste/physiology , Animals , Chemoreceptor Cells/drug effects , Drug Interactions , Electrophysiology , Evoked Potentials/drug effects , Feeding Behavior/drug effects , Fructose/pharmacology , Neurons, Afferent/classification , Neurons, Afferent/drug effects , Saccharin/pharmacology , Sense Organs/cytology , Sense Organs/drug effects , Sucrose/pharmacology , Sweetening Agents/pharmacologyABSTRACT
The present study investigates the effects of W-7 (a calmodulin antagonist involved in the Ca(++) cascade) on the response of the 'sugar' and 'water' cells of labellar chemosensilla in the blowfly Protophormia terraenovae to stimulation with sucrose or fructose. In order to ascertain whether Ca(++) conductance is involved, the effects of EGTA, one of the most used Ca(++) chelating agent, and of SK&F-96365, an inhibitor of receptor mediated calcium influx, were also studied. Our electrophysiological data indicate that W-7 addition strongly depresses the 'sugar' chemoreceptor response to both sugars and in the case of sucrose stimulation also influences adaptation rate. The Ca(++) chelator has no significant effects on the response of the 'sugar' cell following stimulation with sucrose, but lowers fructose stimulating effectiveness. In the presence of SK&F-96365 both sucrose and fructose responses are inhibited. A possible transduction mechanism for sugar reception is discussed.
