Olfactory responses of Drosophila larvae.

We studied complete dose-response curves for 53 odorants in the third instar larvae of Drosophila melanogaster. All odorants, except one, elicited an attraction response. Some odorants also elicited a decrease from their peak response at higher concentrations. This concentration-dependent decrease in olfactory response could be due to either desensitization or repulsion, 2 possibilities that we cannot distinguish in our current assay. We observed high variations in factors like slopes, thresholds, and peaks of responses that, in agreement with previous studies, suggest that the responses of different receptors are quite different for the similar change in concentration of various ligands. We also observed that lower attraction thresholds predicted higher peak amplitude. This suggests that if odor responses encompassed wider concentration range than can be covered by the dynamic range of a single receptor, then responses tend to be high in magnitude.

Post-eclosion odor experience modifies olfactory receptor neuron coding in Drosophila.

Olfactory responses of Drosophila undergo pronounced changes after eclosion. The flies develop attraction to odors to which they are exposed and aversion to other odors. Behavioral adaptation is correlated with changes in the firing pattern of olfactory receptor neurons (ORNs). In this article, we present an information-theoretic analysis of the firing pattern of ORNs. Flies reared in a synthetic odorless medium were transferred after eclosion to three different media: (i) a synthetic medium relatively devoid of odor cues, (ii) synthetic medium infused with a single odorant, and (iii) complex cornmeal medium rich in odors. Recordings were made from an identified sensillum (type II), and the Jensen-Shannon divergence (D(JS)) was used to assess quantitatively the differences between ensemble spike responses to different odors. Analysis shows that prolonged exposure to ethyl acetate and several related esters increases sensitivity to these esters but does not improve the ability of the fly to distinguish between them. Flies exposed to cornmeal display varied sensitivity to these odorants and at the same time develop greater capacity to distinguish between odors. Deprivation of odor experience on an odorless synthetic medium leads to a loss of both sensitivity and acuity. Rich olfactory experience thus helps to shape the ORNs response and enhances its discriminative power. The experiments presented here demonstrate an experience-dependent adaptation at the level of the receptor neuron.

Reduced odor responses from antennal neurons of G(q)alpha, phospholipase Cbeta, and rdgA mutants in Drosophila support a role for a phospholipid intermediate in insect olfactory transduction.

Mechanisms by which G-protein-coupled odorant receptors transduce information in insects still need elucidation. We show that mutations in the Drosophila gene for G(q)alpha (dgq) significantly reduce both the amplitude of the field potentials recorded from the whole antenna in responses to odorants as well as the frequency of evoked responses of individual sensory neurons. This requirement for G(q)alpha is for adult function and not during antennal development. Conversely, brief expression of a dominant-active form of G(q)alpha in adults leads to enhanced odor responses. To understand signaling downstream of G(q)alpha in olfactory sensory neurons, genetic interactions of dgq were tested with mutants in genes known to affect phospholipid signaling. dgq mutant phenotypes were further enhanced by mutants in a PLCbeta (phospholipase Cbeta) gene, plc21C. Interestingly although, the olfactory phenotype of mutant alleles of diacylglycerol kinase (rdgA) was rescued by dgq mutant alleles. Our results suggest that G(q)alpha-mediated olfactory transduction in Drosophila requires a phospholipid second messenger the levels of which are regulated by a cycle of phosphatidylinositol 1,4-bisphosphate breakdown and regeneration.

Sensory correlates of imaginal conditioning in Drosophila melanogaster.

Chemotactic responses of Drosophila to certain esters and alcohols are experience dependent. When the flies are exposed after eclosion to these chemicals, the odorants become strongly attractive. We show that behavioral conditioning is accompanied by an increase in the electrophysiological responses of single neurons in sensilla basiconica. Sensitization involves odorants that act on a common olfactory receptor. The possible mechanism of imaginal conditioning and its ecological and evolutionary significance are discussed.

A Randomized Control Trial of Awake Oral to Submental Conversion versus Asleep Technique in Maxillofacial Trauma.

AIM: This study was designed to evaluate the efficacy of awake oral to submental conversion over asleep technique. MATERIALS AND METHODS: This randomized clinical study was conducted in maxillofacial department of a tertiary care hospital in patients who had panfacial or mandibular fractures requiring elective surgical correction. The patients were randomly divided into two groups of 12 patients each, asleep fiberoptic-assisted submental intubation (SMI) (Group G; n = 12) and awake fiberoptic-assisted SMI (Group A; n = 12). The primary predictor was mean conversion time of oral to SMI while other predictors were overall success rate, ease of conversion, and complications. Data are presented as mean (±standard deviation) and frequencies (%) as appropriate. Statistical analysis done using unpaired t-test or Chi-square test was performed and P < 0.05 was considered statistically significant. RESULTS: Twenty-four patients (19:5;Male:Female) aged 18-55 years (Group G = 35.96; Group A = 32.43 years) were included in the study. SMI was successful in all except two patients in group G. Overall success rate was similar in both groups. Time to convert orotracheal intubation to SMI was significantly less in group A (Group G = 9.55 ± 1.42, Group A = 5.67 ± 1.73; P < 0.001). Ease of SMI was found Grade I in 30% and 83% of the patients of group G and A, respectively. No serious complications were observed except 2 cases of bleeding, and 1 case of tube damage. CONCLUSION: Awake oral to submental conversion requires lesser time in comparison to asleep technique besides improving the ease (Δ = 53%) of the procedure.

Comparison of endotracheal intubation time in neutral position between C-Mac® and Airtraq® laryngoscopes: A prospective randomised study.

BACKGROUND AND AIMS: In the recent past, many novel devices such as AirTraq® and C-MAC® video laryngoscope (VL) have been introduced in an attempt to reduce anaesthetic morbidity and mortality associated with difficult intubation. In this study, we aimed to evaluate and compare C-MAC® VL with a standard Macintosh blade and the AirTraq® optical laryngoscope as a intubating devices with the patient's head in neutral position. METHODS: Sixty American Society of Anesthesiologist Physical Status I-II patients were randomly assigned to be intubated with C-MAC® VL (Group CM; n = 30) or AirTraq® (Group AT; n = 30) in the neutral position, with or without the application of optimization manoeuvres. The primary outcomes of this study were the success rate and the time taken to intubate. Glottic view, ease of tracheal intubation and haemodynamic responses were considered as secondary end points. RESULTS: The incidence of successful intubation was similar in both the groups (P = 1.00). However, the time for intubation was significantly less with C-MAC® VL (Group CM = 14.9 ± 12.89 s, Group AT = 26.3 ± 13.34 s; P = 0.0014). There was no significant difference between the two groups in terms of ease of intubation and glottic view. However, the haemodynamic perturbations were much less with C-MAC® VL. CONCLUSION: We conclude that both the devices were similar in visualising larynx in the neutral position with similar success rates of intubation. However, the C-MAC® VL was better with respect to intubation time and haemodynamic stability.

Synergism and Combinatorial Coding for Binary Odor Mixture Perception in Drosophila.

Most odors in the natural environment are mixtures of several compounds. Olfactory receptors housed in the olfactory sensory neurons detect these odors and transmit the information to the brain, leading to decision-making. But whether the olfactory system detects the ingredients of a mixture separately or treats mixtures as different entities is not well understood. Using Drosophila melanogaster as a model system, we have demonstrated that fruit flies perceive binary odor mixtures in a manner that is heavily dependent on both the proportion and the degree of dilution of the components, suggesting a combinatorial coding at the peripheral level. This coding strategy appears to be receptor specific and is independent of interneuronal interactions.

Odor reception in antenna and antennal lobe of Drosophila.

In early years of neurogenetics of Drosophila, most of us were inclined to believe that behavior of the fruit fly is largely stereotyped and hard-wired. This, at least, was a common prejudice when genetic analysis of olfaction began. We now know that Drosophila like other insects is capable of several types of learning or experience-dependent modification of behavior.

Odour avoidance learning in the larva of Drosophila melanogaster.

Drosophila larvae can be trained to avoid odours associated with electric shock. We describe here, an improved method of aversive conditioning and a procedure for decomposing learning retention curve that enables us to do a quantitative analysis of memory phases, short term (STM), middle term (MTM) and long term (LTM) as a function of training cycles. The same method of analysis when applied to learning mutants dunce, amnesiac, rutabaga and radish reveals memory deficits characteristic of the mutant strains.