Chemical Senses - current issue

Nearest Neural Neighbors: Moth Sex Pheromone Receptors HR11 and HR13

Baker, T. C. — 2009-06-12

In moth sex pheromone olfaction systems, there is a stereotypical cocompartmentalization of two or sometimes three olfactory receptor neurons (ORNs) within single trichoid sensilla on which pheromone-sensitive odorant receptors (ORs) are differentially expressed. In this issue of Chemical Senses, Krieger et al. show through elegant double and triple in situ hybridization studies that in the moth, Heliothis virescens, a pheromone component–related OR (HR11) is expressed on an ORN that is reliably cocompartmentalized in the same sensillum as another OR (HR13) whose ligand is known to be (Z)-11-hexadecenal, the H. virescens major pheromone component. Although the ligand for HR11 is not yet known, mapping this OR to this particular ORN represents a key advance in piecing together the puzzle of H. virescens sex pheromone olfaction.

HR11 and HR13 Receptor-Expressing Neurons Are Housed Together in Pheromone-Responsive Sensilla Trichodea of Male Heliothis virescens

Krieger, J., Gondesen, I., Forstner, M., Gohl, T., Dewer, Y., Breer, H. — 2009-06-12

The highly specific recognition of female-released sex pheromones in insects by sensory neurons of the male antenna requires specific receptors. Recently, a small family of related candidate pheromone receptors has been identified for a few moth species. In this study, the candidate pheromone receptor HR11 from Heliothis virescens has been characterized. HR11 was found to be expressed in numerous cells located in short and long sensilla trichodea on the male antenna. The HR11 cells are stereotypically arranged in a paired pattern together with HR13 cells, which respond to the major component of the sex pheromone blend. Triple in situ hybridization approaches revealed that each pair of an HR11 cell and an HR13 cell was ensheathed by supporting cells, which express pheromone-binding proteins, thus constituting a structural unit. The paired pattern of HR11/HR13 cells is reminiscent of the pattern described for BmOR-1- and BmOR-3-expressing cells in the antenna of Bombyx mori, which respond to bombykol and bombykal, respectively. These results suggest that the ligand for HR11 may be related to the HR13 ligand and furthermore imply that an arrangement of cells expressing related receptor types in the same sensillum may be a general principle in moth pheromone detection systems.

Potential Chemosignals Associated with Male Identity in the Amphisbaenian Blanus cinereus

Lopez, P., Martin, J. — 2009-06-12

Pheromone-based chemosensory sex discrimination occurs in many reptiles, but the specific chemosignals responsible for this discrimination have been rarely identified. Chemoreception is especially important for amphisbaenians, a group of fossorial, almost blind, reptiles. We analyzed the role of semiochemicals produced by precloacal glands in intraspecific communication and chemosensory sex recognition of the amphisbaenian Blanus cinereus. We expected that sexual discrimination in amphisbaenians would be based on those chemicals that show intersexual differences in precloacal secretions, with squalene being the chemical that shows the greatest difference in relative abundance between sexes. Tongue-flick assays and behavioral responses to the scent of conspecifics confirmed that amphisbaenians are capable of detecting and discriminating between scent of conspecific males and females by using chemosensory cues alone. Differential responses of amphisbaenians to chemical compounds that are naturally found in precloacal secretions indicated that males can readily discriminate between different chemicals. Squalene, in particular, elicited in male amphisbaenians’ chemosensory and aggressive responses that were similar to those elicited by precloacal secretions. This result suggests that squalene alone allows male discrimination by male amphisbaenians. Furthermore, squalene might also signal dominance status or aggressiveness of a male amphisbaenian because higher concentrations of squalene elicited higher levels of aggression by males.

Orosensory Responsiveness to and Preference for Hydroxide-Containing Salts in Mice

St. John, S. J., Boughter, J. D. — 2009-06-12

Historically, taste researchers have considered the possibility that the gustatory system detects basic compounds, such as those containing the hydroxide ion, but evidence for an "alkaline taste" has not been strong. We found that, in 48 h, 2-bottle preference tests, C3HeB/FeJ (C3) mice showed a preference for Ca(OH)₂, whereas SWR/J (SW) mice showed avoidance. Strain differences were also apparent to NaOH but not CaCl₂. Follow-up studies showed that the strain difference for Ca(OH)₂ was stable over time (Experiment 2) but that C3 and SW mice did not differ in their responses to Ca(OH)₂ or NaOH in brief-access tests, where both mice avoided high concentrations of these compounds (Experiment 3). In order to assess the perceived quality of Ca(OH)₂, mice were tested in 2 taste aversion generalization experiments (Experiments 4 and 5). Aversions to Ca(OH)₂ generalized to NaOH but not CaCl₂ in both strains, suggesting that the generalization was based on the hydroxide ion. Both strains also generalized aversions to quinine, suggesting the possibility that the hydroxide ion has a bitter taste quality to these mice, despite the preference shown by C3 mice to middle concentrations in long-term tests.

Swallowing Is Differentially Influenced by Retronasal Compared with Orthonasal Stimulation in Combination with Gustatory Stimuli

Welge-Lussen, A., Ebnother, M., Wolfensberger, M., Hummel, T. — 2009-06-12

Identical stimuli are processed differently when presented ortho- or retronasally. In contrast to orthonasal olfaction, retronasal odorant perception is strongly associated with flavor and food intake, which is usually followed by swallowing. Along with other stimuli, gustatory stimuli are known to influence the swallowing reflex. It was therefore the aim of present study to examine whether retronasal olfaction, in combination with simultaneous gustatory stimuli, influences swallowing in a manner different from that of orthonasal olfaction. Fifty normosmic and normogeusic subjects took part in the study. A sweet taste (glucose, delivered via an intraoral taste dispenser) was presented simultaneously with vanillin, a food-like odor, either ortho- or retronasally at random using a computer-controlled olfactometer. Ultrasound imaging of the mouth floor was recorded on videotape to continuously monitor swallowing activity. After retronasal stimulation, swallowing occurred significantly faster (7.49 vs. 9.42 s; P < 0.001) and also took place more frequently compared with swallowing after orthonasal stimulation (1.38 times vs. 1.14 times; P < 0.001). These results show that a food-like odorant presented retronasally in combination with a congruent taste stimulus can influence swallowing. Whether these results can be assigned to other, unfamiliar, unpleasant nonfood-like odors has yet to be determined.

Identification and Expression Pattern of Putative Odorant-Binding Proteins and Chemosensory Proteins in Antennae of the Microplitis mediator (Hymenoptera: Braconidae)

Zhang, S., Zhang, Y.-J., Su, H.-H., Gao, X.-W., Guo, Y.-Y. — 2009-06-12

The parasitoids of Cotton Bollworm Microplitis mediator (Hymenoptera: Braconidae) find their hosts through the odor released by stressed plants. In this study, preliminary characterization and isolation of cDNAs from male M. mediator antennal libraries identified 8 putative odorant-binding proteins (OBPs). Real-time polymerase chain reaction method was used to study the expression pattern of these isolated genes. Their gene expression profiles under a wide range of conditions indicated that only 4 OBP genes in M. mediator were antenna specific. The remaining 4 genes are either expressed ubiquitously or strictly regulated in specialized tissues or during different developmental stages. Some OBP genes were gender specific. These findings support that OBPs play dynamic roles during development of M. mediator and are likely to be involved in broader physiological functions.

The Role of the Human Hippocampus in Odor-Place Associative Memory

Goodrich-Hunsaker, N. J., Gilbert, P. E., Hopkins, R. O. — 2009-06-12

Hippocampal lesions in rodents impair both object–place and odor–place associative memory. Subjects with hippocampal damage have impaired associative memory such as object–place memory. Whereas studies have investigated some types of associative memory, no investigation has specifically examined odor–place associative memory in subjects with well-defined amnesia. It is unknown whether amnesic subjects with hippocampal damage would be impaired on an odor–place associative task. We investigated the effect of hippocampal damage in amnesic subjects with hippocampal atrophy on odor–place associative memory and recognition memory tasks. Amnesic and healthy comparison subjects matched for age and education were tested on an odor–place associative task, an odor recognition task, and a place recognition task. The odor–place associative task required subjects to associate 6 odors with 6 spatial locations on a board. The recognition tasks required subjects to identify the 6 odors and the 6 locations that were presented during the associative task. Amnesic subjects were impaired for odor–place memory and place recognition, but not odor recognition compared with comparison subjects. These results suggest that the human hippocampus is necessary for odor–place associative memory and spatial recognition memory. These data provide support for the idea that odor–place associative memory is mediated by the hippocampus in both humans and rodents, suggesting an evolutionary continuity in cognitive function assigned to the hippocampus.

Comparison between Odor Thresholds for Phenyl Ethyl Alcohol and Butanol

Croy, I., Lange, K., Krone, F., Negoias, S., Seo, H.-S., Hummel, T. — 2009-06-12

Aim of the study was to compare results of odor threshold test using different numbers of dilution steps, separately for butanol and phenyl ethyl alcohol (PEA). Methods: A total of 116 subjects participated (29 patients with olfactory dysfunction and 87 normosmic subjects). The olfactory threshold for butanol and PEA was examined with 8 (wide step method) and 16 (narrow step method) dilutions. With a delay of about 1 week, all 4 tests were repeated. Results: Test time was shortened by approximately 2 min (25%) for patients when using the wide step method. Butanol and PEA thresholds were not significantly different; in addition, a significant correlation was found between thresholds for the 2 odors (r = 0.60, P < 0.001). Threshold test with both odorants as well as with wide or narrow step method provided satisfying reproducibility (test–retest reliability: r = 0.80–0.84, P < 0.001). Patients with olfactory dysfunction could be clearly separated from normosmic subjects using all 4 different tests. Discussion: The results indicate that threshold testing with PEA is an alternative to butanol. The wide step method provided similar results as the narrow step method but required less time.

Human Pheromone Detection by the Vomeronasal Organ: Unnecessary for Mate Selection?

Mast, T. G., Samuelsen, C. L. — 2009-06-12

Recently, Foltan and Sedy proposed a hypothesis stating that the adult human VNO is integral to the prevention of inappropriate mate selection. In this commentary, we address the authors’ assumption that humans have a functional VNO, that pheromones are detected exclusively by the VNO, and that human pheromones are responsible for negative stimuli during mate selection. After examining the published literature on human vomeronasal function, we argue that their hypothesis is critically flawed. We offer a brief review of the adult human VNO in support of our argument.