Biomedical subjects

N J Vickers

Publications and source records attributed to N J Vickers.

6 recordsLinked to original sources

PubMed2002

Unusual pheromone receptor neuron responses in heliothine moth antennae derived from inter-species imaginal disc transplantation.

Single-cell electrophysiological recordings were obtained from olfactory receptor neurons housed in sensilla trichodea along the adult antennae arising from transplantation of the antennal imaginal discs between larval male Helicoverpa zea and Heliothis virescens. The olfactory receptor neurons from the majority of type C sensilla sampled on transplanted antennae displayed response characteristics consistent with those of the species that donated the antennae. However, some of the sensilla type C sampled in either transplant type contained olfactory receptor neurons that responded in a manner typical of the recipient species or other neurons that have not previously been found in the type C sensilla of either species. The single-cell data help to explain behavioral results showing that some transplant males do fly upwind to both species' pheromone blends, an outcome not expected based on known antennal sensory phenotypes. Our results suggest that host tissue can influence antennal olfactory receptor neuron development, and further that because of a common phylogenetic ancestry the donor tissue has the genetic capability to produce a variety of sensillar and receptor types.

Action Potentials↗

PubMed2001

Odour-plume dynamics influence the brain's olfactory code.

The neural computations used to represent olfactory information in the brain have long been investigated. Recent studies in the insect antennal lobe suggest that precise temporal and/or spatial patterns of activity underlie the recognition and discrimination of different odours, and that these patterns may be strengthened by associative learning. It remains unknown, however, whether these activity patterns persist when odour intensity varies rapidly and unpredictably, as often occurs in nature. Here we show that with naturally intermittent odour stimulation, spike patterns recorded from moth antennal-lobe output neurons varied predictably with the fine-scale temporal dynamics and intensity of the odour. These data support the hypothesis that olfactory circuits compensate for contextual variations in the stimulus pattern with high temporal precision. The timing of output neuron activity is constantly modulated to reflect ongoing changes in stimulus intensity and dynamics that occur on a millisecond timescale.

Action Potentials↗

PubMed2000

Mechanisms of animal navigation in odor plumes.

Chemical signals mediate many of life's processes. For organisms that use these signals to orient and navigate in their environment, where and when these cues are encountered is crucial in determining behavioral responses. In air and water, fluid mechanics impinge directly upon the distribution of odorous molecules in time and space. Animals frequently employ behavioral mechanisms that allow them to take advantage of both chemical and fluid dynamic information in order to move toward the source. In turbulent plumes, where odor is patchily distributed, animals are exposed to a highly intermittent signal. The most detailed studies that have attempted to measure fluid dynamic conditions, odor plume structure, and resultant orientation behavior have involved moths, crabs, and lobsters. The behavioral mechanisms employed by these organisms are different but generally integrate some form of chemically modulated orientation (chemotaxis) with a visual or mechanical assessment of flow conditions in order to steer up-current or upwind (rheo- or anemo-taxis, respectively). Across-stream turns are another conspicuous feature of odor-modulated tracks of a variety of organisms in different fluid conditions. In some cases, turning is initiated by detection of the lateral edges of a well-defined plume (crabs), whereas in other animals turning appears to be steered according to an internally generated program modulated by odor contacts (moth counterturning). Other organisms such as birds and fish may use similar mechanisms, but the experimental data for these organisms is not yet as convincing. The behavioral strategies employed by a variety of animals result in orientation responses that are appropriate for the dispersed, intermittent plumes dictated by the fluid-mechanical conditions in the environments that these different macroscopic organisms inhabit.

Animals↗

PubMed1998

A combinatorial model of odor discrimination using a small array of contiguous, chemically defined glomeruli.

The macroglomerular complex (MGC) is a sexually dimorphic array of contiguous glomeruli in male moths, located at the base of the antennal nerve where it enters the primary olfactory processing area of the brain, the antennal lobe. A new three-dimensional reconstruction method was used to map this glomerular array, and images obtained with the laser scanning confocal microscope revealed the precise location and spatial arrangement of the MGC glomeruli in two related species of Heliothine moth. Intracellular recording and staining of projection neurons (PNs) that arborize within the MGC has revealed that information about the two attractive components of the pheromone blend is segregated to different glomeruli in both species. In one species, Helicoverpa zea, a third glomerulus serves as the locus for the processing of odors that antagonize upwind flight. Thus, activation of different but overlapping sets of glomeruli within the MGC may provide a neural substrate for discriminating attractant vs antagonist chemical signals.

Animal Communication↗

PubMed1998

Combinatorial odor discrimination in the brain: attractive and antagonist odor blends are represented in distinct combinations of uniquely identifiable glomeruli.

The rules governing the central discrimination of odors are complex and poorly understood, but a growing body of evidence supports the hypothesis that olfactory glomeruli may represent functionally distinct coding modules in the brain. Testing this hypothesis requires that both the functional characteristics and the spatial position of the glomerulus under study be uniquely identifiable. To address these questions, we examined a specialized array of glomeruli (the macroglomerular complex; MGC) in the antennal lobe of male moths that receives input from olfactory receptor cells tuned specifically to female-released odorants that either promote upwind flight (conspecific sex pheromones) or inhibit it (interspecific antagonists). By using a three-dimensional reconstruction method based on high-resolution laser-scanning confocal microscopy, we generated precise spatial maps of the MGC glomeruli in two related noctuid species with similar pheromone chemistry, Heliothis virescens and Helicoverpa zea. To determine the breadth of tuning of individual MGC glomeruli in processing information about these social signals, we used intracellular recording and staining methods to examine the responses of projection (output) neurons that innervate MGC glomeruli and that each project an axon to higher integrative centers. In both species, a close correspondence was found between the odor specificity of the projection neurons and the glomerulus (or glomeruli) supplied by them. The binary blend of pheromone components for each species was represented by neural activity in only two distinct glomeruli in both H. virescens and H. zea. Odorants that antagonize upwind flight when they are added to the respective pheromonal blends evoked excitatory activity in output neurons restricted to a third glomerulus in the MGCs of both species. In summary, these results suggest that the selective activation of different combinations of functionally distinct MGC glomeruli is a general means for discriminating these specific attractant and antagonist chemical signals in the brain.

Animals↗

PubMed1994

Reiterative responses to single strands of odor promote sustained upwind flight and odor source location by moths.

We characterized single upwind surges of flying male Heliothis virescens moths in response to individual strands of pheromone generated experimentally in a wind tunnel. We then showed how this surge functions in this species as a basic 13.4-cm, 0.38-sec-long building block that is strung together repeatedly during typical male upwind flight in a normal pheromone plume. The template for a single iteration, complete with crosswind casting both before and after the straighter upwind surging portion, was exhibited by males flying upwind to pheromone and experiencing filament contacts just frequently enough to produce successful upwind flight to the source, as hypothesized by an earlier model. Also as predicted, with more frequent filament contact by males, only the straightest upwind portions of the surges were reiterated, producing direct upwind flight with little crosswind casting. Electroantennogram recordings made from males in free flight upwind in a normal point source pheromone plume further support the idea that a high frequency of filaments encountered under the usual pheromone plume conditions promotes only these repeated straight surges. In-flight electroantennogram recordings also showed that when filament contacts cease, the casting, counterturning program begins to be expressed after a latency period of 0.30 sec. Together these results provide a plausible explanation for how male and female moths, and maybe other insects, fly successfully upwind in an odor plume and locate the source of odor, using a surging-casting, phasic-tonic response to the onset and disappearance of each odor strand.

Journal Article↗