Ultrastructure of the blowfly chemoreceptor sensillum (Phormia regina)

The ultrastructure of a well studied insect chemosensory unit is presented in this report. Two separate lumina are present in this chemosensory unit, the trichogen and sensillar lumina. The fluid within the trichogen lumen exclusively bathes the dendritic terminals, and may be involved with the reception and/or modulation of environmental stimuli. Cytoplasmic extensions of the trichogen cell which line the trichogen lumen may be involved in the production of the cuticular sheath. The sensillar lumen is bordered by the tormogen and a sleeve cell, and is continuous with the unoccupied channel of the setal shaft. Functions for the various cellular components of the blowfly chemoreceptor sensillum are offered.     

Birth times of neurons in labellar taste sensilla of the blowfly Phormia regina

We studied the birth times of neurons of labellar taste sensilla in blowflies using incorporation of the thymidine analogue 5-bromodeoxyuridine (BrdU) as an indicator of birth time. We found that one of the two main sensillum types, the taste papillae, arise according to a clear spatial gradient of birth times, whereas the other sensillum type, taste hairs, arise without any apparent spatial ordering. Within each sensillum type, there was a strong tendency for either all or none of the neurons to have incorporated BrdU. Among those rare sensilla in which only some of the neurons incorporated BrdU, there were clear patterns of the distribution of labeled and unlabeled neurons per sensillum. These results suggest that subsets of the neurons of a sensillum are siblings, and thus argue against the possibility that the several neurons of a sensillum arise from a single stem cell precursor through repeated asymmetrical divisions. © 1995 John Wiley & Sons, Inc.     

Central projections of labellar taste hairs in the blowfly,Phormia regina Meigen

Summary We have traced the central projections of the receptor neurons associated with each of the eleven largest taste hairs on the labellum of the blowfly, Phormia regina (Meigen), by staining them with cobaltous lysine. The eleven hairs fall into three groups which reflect their peripheral locations and their branching patterns in the subesophageal ganglion. Group 1, consisting of the anterior hairs (numbers 1 and 2) and Group 3, consisting of the posterior hairs (numbers 9–11) project bilaterally, while Group 2, consisting of the middle hairs (numbers 3–8) projects primarily ipsilaterally. The central projections of the hairs within a single group are similar. Each hair houses four chemoreceptors, which have differing chemical sensitivities and behavioral roles, and one mechanoreceptor. In some cases, there were indications that the different cells within a single hair have different central branching patterns. For some hairs, however, it was clear that a single central branching region and pattern was shared by more than one receptor cell. We failed to find either a continuous somatotopic representation of a hair's position on the periphery, or an anatomical segregation of receptors coding for different modalities. Behavioral experiments indicate that the fly is informed both of the identity of the hair stimulated and of the chemical nature of the stimulus. Our results suggest that this information is not represented on a gross anatomical level.     

The distribution and neuroanatomy of the labellar sense organs of the blowfly Phormia regina Meigen

The labellar hairs of the blowfly Phormia regina Meigen are arranged in a definite pattern. Topographically they can be divided into the following groups: prickles, bristles, intermediate hairs, large hairs, largest hairs, marginal hairs. On the basis of dimensions they fall into four groups. The total number of hairs is somewhat variable. The mean for males is 122.65 hairs on one lobe; for females, 128.82 hairs. The interpseudotracheal papillae vary both in position and number. The mean for males is 65.9 papillae; for females, 67.65. The labial nerve divides, in the labellum, into four principal branches which consist of proximal processes of the sense cells of all hairs and interpseudotracheal papillae. Preparations stained by methylene blue revealed numerous multipolar cells. It was impossible to decide with certainty whether they are nerve cells, perilemma cells, or tracheal cells. They did not stain with silver. Numerous free endings revealed in preparations by use of Kenyon's method appeared to be the finest tracheoles seen on preparations stained by the method of Romanes.     

Mode of action of straight chain hydrocarbons on primary chemoreceptors of the blowfly, Phormia regina

The fundamental actions of straight-chain hydrocarbons on the three known primary chemoreceptor cell types of the blowfly, Phormia regina, were studied in quantitative terms. Lower alcohols and long-chain amines act in two stages: first a reversible inhibition, and then injury, of the salt, water, and sugar receptors in the labellar sensilla. The primary effects on salt and water receptors resemble hydrocarbon narcosis of nerve. Effects on sugar receptors, when analyzed kinetically, superficially resemble competitive inhibition. Other evidence, however, indicates that a non-specific effect on sugar receptor sites is more likely. The electrophysiological results from labellar chemoreceptors indicate that the previously reported hydrocarbon behavioral rejection thresholds are best explained by the inhibition of the sugar receptors. This conclusion is strengthened by further electrophysiological and behavioral tests on tarsal chemoreceptors.     

Behavioral responses of Phormia regina (Meigen) to labellar stimulation with amino acids

Behavioral responses to labellar stimulation with 19 L-amino acids were predicted on the basis of electrophysiological responses of largest labellar hairs. With the exceptions alanine, aspartic and glutamic acids, and valine tests of these predictions confirmed that Phormia can discriminate amino acids, and that these acids may be grouped according to their effects. Electrophysiological investigation of the four exceptions was repeated and results were consistent with the behavioral data. In particular, these acids elicited previously unreported responses from the salt receptor. The discrepancies between this and earlier studies may be explainable, in part, on methodological grounds. There was evidence for response differences among hairs of different sizes and among the largest labellar hairs themselves. The significance of amino acid discrimination for the problem of protein recognition can only be speculated upon until more complete electrophysiological and nutritional information is available.     

Insoluble alpha-glucosidase: possible pyranose site of the sugar receptor of the labellar of the blowfly, Phormia regina.

The insoluble α-glucosidase activity was examined in three kinds of preparations of the fly labella: labellar integuments with intact chemosensilla, fragments of nerve bundles, and sensilla cut off from the labella.α-Glucosidases having a similar affinity for substrates to isozyme P-II were found in each preparation.Kinetics, inhibition by tris(hydroxymethyl)amino methane (Tris), and pH dependence were examined on the activity of both the membrane-fixed and solublized glucosidase isozymes.Most of the insoluble activity was observed in the nerve bundle fractions, which showed the same properties as P-II in the soluble fraction but were not solubilized by chaotropic anion or by addition of EDTA (insoluble P-II). A different type of insoluble α-glucosidase has been suggested to exist in the labellar chemosensilla in addition to insoluble P-II. It showed a very broad pH dependence and had a larger inhibition constant for Tris. It was inferred to be identical with the enzyme found at the tip of the intact chemosensilla. The hypothesis that the above isozyme might be the pyranose site of the sugar receptor was supported.     

Localization of adenylate cyclase in the blowfly labellar chemoreceptors

Adenylate cyclase activity has been demonstrated in tissue of the blowfly, Phormia regina, chemoreceptor sensillium and in labellar epidermal cells. Sensillar tissue included sensory neurons innervating the sensillum and associated supportive cells. Epidermal cells which surround the internal labellar apophysis and those below the external cuticles both displayed enzyme activity. Possible explanations for these data are discussed.     

Central control of feeding in the diapausing adult blowfly Phormia regina.

1. The tarsal acceptance threshold of non-diapausing adult blowflies rises with age. 2. Diapausing flies have a non-significantly elevated tarsal acceptance threshold, but drink significantly less sucrose solution than their non-diapausing counterparts. 3. Removal of diapausing flies to non-diapause inducing conditions resulted in a lowering of the threshold. 4. Failure to demonstrate a significant difference between the input signal from the peripheral receptors of non-diapausing and diapausing flies showed that the inhibition of feeding in diapausing flies was not due to peripheral inhibition but was controlled centrally.     

Patterns of selective protein ingestion by the blowfly Phormia regina

ABSTRACT. The patterns of protein ingestion by Phormia regina were reexamined with an apparatus more sensitive than that used in Dethier's (1961) original study. During the first vitellogenic cycle, females exhibited two peaks of protein consumption if given access to protein from the time of emergence. The first occurred during days 1–2 post-eclosion; the second during days 3–5, when oocytes were developing. Once the eggs were mature, protein ingestion remained depressed until oviposition; it peaked again for 1–2 days following each oviposition. In the male fly only the first peak of elevated protein ingestion occurred; thereafter, protein ingestion remained low. For both sexes, protein-deprivation, enforced since eclosion, intensified initial protein meals, which thereafter tailed off rapidly.     

Conditioning odor-shock associations in the black blowfly,Phormia regina

Discriminative classical conditioning of an olfactory avoidance response was demonstrated in the blowfly, Phormia regina.Learning indices were calculated as the fraction of flies avoiding the CS+ (conditioned stimulus paired with electric shock reinforcement) minus the fraction of flies avoiding the CS-(conditioned stimulus not paired with electric shock), averaged over two different groups of flies, in which reciprocal odors were used as the CS+. Avoidance responses to both odors presented simultaneously at a T-maze choice point yielded mean learning indices of zero for naive flies or pseudoconditioned (shock alone) or sensitized (odors alone) controls. In contrast, pairing an odor with electric shock produced a mean learning index significantly greater than zero. These results are similar to those reported for Drosophila melanogaster.Blow flies, however, showed much lower levels of associative learning than fruit flies.     

Perception of noxious compounds by contact chemoreceptors of the blowfly,Phormia regina: putative role of an odorant-bindingpProtein

The blowfly, Phormia regina, has sensilla with four contact-chemoreceptor cells and one mechanoreceptor cell on its labellum. Three of the four chemoreceptor cells are called the sugar, the salt and the water receptor cells, respectively. However, the specificity of the remaining chemoreceptor cell, traditionally called the "fifth cell", has not yet been clarified. Referring to behavioral evaluation of the oral toxicity of monoterpenes, we measured the electrophysiological response of the "fifth cell" to these compounds. Of all the monoterpenes examined, D-limonene exhibited the strongest oral toxicity and induced the severest aversive behavior with vomiting and/or excretion in the fly. D-Limonene, when dispersed in an aqueous stimulus solution including dimethyl sulfoxide or an odorant-binding protein (OBP) found in the contact-chemoreceptor sensillum, the chemical sense-related lipophilic ligand-binding protein (CRLBP), evoked impulses from the "fifth cell". Considering the relationship between the aversive effects of monoterpenes and the response of the "fifth cell" to these effects, we propose that the "fifth cell" is a warning cell that has been differentiated as a taste system for detecting and avoiding dangerous foods. Here we suggest that in the insect contact-chemoreceptor sensillum, CRLBP carries lipophilic members of the noxious taste substances to the "fifth cell" through the aqueous sensillum lymph. This insect OBP may functionally be analogous to the von Ebner's grand protein in taste organs of mammals.     

Waning of repetitive hopping in the blowfly Phormia regina Meigen (Diptera: Calliphoridae)

Wingless blowflies (Phormia reginaMeigen)released on a flat uniform substrate hop repeatedly. The rate of hopping decreases with time. Decremental responsiveness resembles behavioral habituation. It can be reestablished by tactile stimulation and is due neither to muscle fatigue nor to sensory receptor adaptation. No effects of age or circadian rhythms were observed. The initial rate of hopping increases with increasing food deprivation, as does the time for waning to be completed. Decapitated flies and isolated wingless thoraxes hop almost as well as control flies and wane at the same rates.     

Electrical resistance of labellar taste hairs in the blowfly, Phormia regina M., as a function of age and sex

The electrical resistance of the labellar taste hairs of Phormia regina M. is enhanced by aging in both males and females; this increase is greater in males. Resistance variations, related to changes in response of stimulated chemoreceptors, may explain, at least in part, the reduction in reflex food intake, O2 consumption, weight increase and, on the whole, survival capabilities of males vis-à-vis female insects.     

Recurrent nerve inhibition of protein feeding in the blowfly Phormia regina

ABSTRACT. Stretch receptors located in the foregut appear to contribute negative feedback to the ingestion of protein by Phormia ; as fluid is consumed, the concomitant stretch impedes further drinking. This inhibitory feedback, transmitted to the frontal ganglion via the recurrent nerve, seems to depress protein ingestion less than carbohydrate ingestion. Such a disparity may help to ensure that the female fly acquires enough protein for egg development through the retention of her ability to consume available protein even after carbohydrate consumption has been terminated.     

Mechanism of beat reversal in semi-intact heart preparations of the blowfly Phormia regina (Meigen)

The blowfly pulsatile organ is a tubular vessel consisting of an abdominal heart and a thoracocephalic aorta. Its activity consists of the regular alternance of a fast phase with a slow phase at higher and lower beating frequencies, respectively. In adult Phormia blowflies the fast and slow phases are triggered by separate pacemakers at the abdominal and cephalic vessel endings, respectively. Owing to the position of the pacemakers, impulses propagate forwards along the vessel during the fast phase and backward during the slow phase. Accordingly, haemolymph flows to the head during the fast phase and to the abdomen during the slow phase. Interspike interval and conduction velocity decrease, while spike duration and risetime increase, from the beginning to the end of the fast phase, together with the emptying of the vessel compartment where it is generated. Prevention of systolic emptying of abdominal heart compartments at the beginning of the fast phase abolishes phase alternance. Possible stretch sensitivity of the Phormia myocardium accounts for this result.Abbreviations CRO cathode-ray oscilloscope - ECG electrocardiogram - UV ultraviolet     

Ion dependence of the tarsal sugar receptor of the blowfly Phormia regina.

The activity of the tarsal sugar receptor is greatly reduced following prolonged water exposure. The animal's behavior, which characteristícally reflects receptor input, also shows decreased acceptance of sucrose solutions following prolonged tarsal immersion in deionized water. Long exposure of the tarsi to Bodenstein's saline instead of water does not produce as large a decrement in the acceptance response as does water exposure.Recovery of the behavioral response occurs spontaneously after a few hours. The original response level can also be restored immediately if a moderate concentration (0.05 to 0.2 M) of KCl or NaCl is added to the sucrose stimulus. The effect of LiCl is ambiguous: it inhibits the normal sucrose response, thereby tending to mask any restorative effects. The electrophysiological data show that the cellular response level is also restored when Na⁺ or K⁺ ions are present in the stimulus.The above data are interpreted to mean that the effect of tarsal water exposure is to slowly leach out ions in the effective extracellular fluid surrounding the receptor membrane, thus lowering the membrane potential and deceasing the receptor potential upon stimulation. The fact that Na⁺ and K⁺ when supplied in the stimulating solution temporarily restore the original response level suggests that these extrinsically added ions can be used as current carrying ions to depolarize the cell. The data suggest that the sensillum contains three functional compartments interconnected by partial diffusion barriers: (1) a ‘receptor compartment’ (2) an axial cylinder which contains the dendrites and functions as the immediate extracellular ion source, and (3) a larger axial cylinder which serves as an ion reservoir.A method for statistically analyzing behavioral acceptance data is presented.