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D G Moulton

Publications and source records attributed to D G Moulton.

15 recordsLinked to original sources
PubMed1987

Olfactory bulb responses telemetered during an odor discrimination task in rats.

Electrodes were chronically implanted in eight rats to record multiple-unit activity during the acquisition and performance of an isoamyl acetate (10(-3) concentration)/air discrimination task in order to obtain a water reward. Localized stimulus choice points permitted each rat to regulate its time of exposure to the two positive reinforcing stimuli. Each rat had stimulus sampling times of much less than 1 s while performing at an 80% or more correct choice level. Whereas four of the rats exhibited only occasional neural activity, probably due to electrode position, the other four developed individual neural burst patterns, after learning, which were different for the two stimuli. Changes in the neural patterns during testing, when they occurred in two of the four responsive animals, appeared to correlate with changes in stimulus sampling. These results confirm that much less than 1 s is needed for odor identification and demonstrate that multiunit activity can show differential response patterns. The results have possible implications for future studies.

Action Potentials↗
PubMed1982

Chemosensitivity of rat nasal trigeminal receptors.

Electrophysiological responses to odorants delivered via an air dilution olfactometer were recorded from the ethmoid branch of the trigeminal nerve innervating the nasal cavity. Thresholds were obtained for nine compounds with those for heptanol (21-137 ppm) and propionic acid (39-49) ppm consistently being the lowest. Not all odorants e.g., phenethyl alcohol, elicited responses in all rats even at vapor saturation. A striking degree of correlation was present between the rat whole-nerve electrophysiological response magnitudes of this study and the human anosmic intensity ratings established in the work of Doty et al. [9] to vapor saturated stimuli. These results suggest that the rat is an excellent model for assessing the stimulatory effectiveness of odorants on human trigeminal receptors. The possible role of the trigeminal system in the perception of odors as well as the physiologic effects of odorants due to trigeminal stimulation are discussed.

Animals↗
PubMed1982

Topographic coding of olfactory quality: odorant-specific patterns of epithelial responsivity in the salamander.

1. Electrophysiological recordings were made on the ventral olfactory epithelium of the salamander Ambystoma tigrinum in order to investigate whether individual odorants can elicit unique patterns of receptor neuron responses. 2. Slow transepithelial voltage transients, Veog(-), were recorded from 30 sites on each epithelium. For each odorant a topographic pattern was derived from the Veog(-) amplitudes across the 30 recording sites. 3. Nine odorants were tested, each in seven animals, and topographic patterns of Veog(-) amplitudes were drawn for each animal. Due to the morphological variability among animals, the electrode sites for each animal were assigned to six epithelial regions for which responses were then compared by analysis of variance. 4. Odorant-specific regional differences in responsivity were observed. The odorants can be grouped according to the similarity of the topographic distributions of responses elicited by them. We observed that no two odorants elicited exactly the same response patterns. This suggests that olfactory receptor neurons with similar responses are grouped together in the same region of the epithelium. 5. Dramatic differences in responsivity among the various epithelial regions, irrespective of the test odorant, were also noted. This observation may be due to regional differences in receptor neuron density or overall sensitivity. 6. It is concluded that differences between the topographic distributions of receptor cell responses, elicited by the nine test odorants, permits these responses to be discriminated as unique patterns of information at the olfactory bulb.

Ambystoma↗
PubMed1979

Adaptation and cross-adaptation to odor stimulation of olfactory receptors in the tiger salamander.

We have used the effects of self- and cross-adaptation on the unitary responses of olfactory receptors of the tiger salamander to odor stimulation to investigate the stimulus-specific components of these responses and to provide information about the cross-cell variations in the numbers and numbers of types of constitutent receptive sites. An olfactometer delivered sequential odorous pulses, either juxtaposed or separated by a variable time delay. We used four pairs of odorants judged to be similar within a given pair. The unitary response to the test stimulation relative to that of the conditioning stimulation varied from being unchanged to being completely eliminated. We sometimes observed substantial poststimulus increases in the firing rate following stimulation with juxtaposed odorous pulse. Except in the case of one odorant pair, cross-adaptation occurred both with juxtaposed pulses and with pulses separated in time. With the methyl butyrate/ethyl butyrate odorant pair, however, statistically significant cross-adaptation appeared only with juxtaposed pulses. We propose a simple model to aid in explaining these phenomena. The experimental observations in conjunction with this model are used to obtain estimates of the maximal and minimal number of receptive site types available for interaction with the chosen odorants.

Action Potentials↗
PubMed1978

Patterned response to odor in single neurones of goldfish olfactory bulb: influence of odor quality and other stimulus parameters.

Responses of 75 single units in the goldfish olfactory bulb were analyzed in detail for their relationship to the time-course of the change in odor concentration during each odor stimulus. Odor stimuli were controlled for rise time, duration, and peak concentration by an apparatus developed for the purpose. This apparatus enabled aqueous odor stimuli to be interposed into a constant water stream without changes in flow rate. The time-course of the concentration change within the olfactory sac was inferred from conductivity measurements at the incurrent and excurrent nostrils. Temporal patterns of firing rate elicited by stimuli with relatively slow rising and falling phases could be quite complex combinations of excitation and suppression. Different temporal patterns were produced by different substances at a single concentration in most units. Statistical measures of the temporal pattern of response for a small number of cells at a given concentration were more characteristic of the stimulus substance than any of three measures of magnitude of response. The temporal patterns change when the peak concentration, duration, and rise time of the stimuli are varied. The nature of these changes suggests that the different patterns are due primarily to the combined influence of two factors: (a) a stimulus whose concentration varies over time and (b) a relationship between concentration and impulse frequency which varies from unit to unit. Some units produce patterns suggestive of influence by neural events of long time constant. The importance of temporal patterns in odor quality and odor intensity coding is discussed.

Amino Acids↗
PubMed1976

Spatial patterning of response to odors in the peripheral olfactory system.

The low odor specificities of the olfactory receptors suggest that odor recognition depends on the simultaneous activity in an ensemble of receptor neurons. This ensemble could conceivably code quality without reference to the point of origin of each input on the receptor sheet. However, the nose-to-bulb projection appears sufficiently precise to provide the bulb with a topographical map of the receptor sheet although it is poorly delineated in the anteroposterior plane. (It is also known that the morphological changes that follow prolonged exposure to odors are more differentiated in the coronal than in the anteroposterior plane.) Furthermore, it is clear from work at both epithelial and bulbar levels that a spatiotemporal pattern of excitation is generated by odor stimulation of the receptor sheet and that this pattern differs for different odors. This evidence, then, supports the view that there is a spatial component to odor quality coding. This spatial pattern has two elements. One is imposed and depends (at least in part) on differences in the retentivity of different odorants by the mucous sheet, which has powerful sorptive properties. It effectiveness seems particularly weak for odorants with relatively long retention times. The second component is inherent and depends on the tendency of receptors with similar peak odor specificities to aggregate in the same region (or regions) of the epithelium. Different odors or groups of odors maximally excite different regions, which may overlap. The imposed component could not, in itself, provide an adequate mechanism for odor recognition, partly because many compounds have comparable or even identical mean retention times (e.g., enantiomeric isomers). The inherent component, on the other hand, possesses this potential. However, either or both forms of patterning may cooperate with a third nonspatial mechanism (based on differential responsiveness of receptors to different odors) in coding odor quality.

Animals↗
PubMed1974

Responses of olfactory bulb neurones to odour stimulation of small nasal areas in the salamander.

1. Previous experiments have suggested that one way odours may be discriminated is by different spatial patterns of response at both the olfactory bulb and receptor level. The present experiments were designed to test to what extent the position of an odour on the receptor mucosa can influence the activity of olfactory bulb neurones.2. To deliver odours to small areas on the nasal receptor sheet a new method for local application of odour was developed. The flow rate, concentration, and time course of the odour were controlled using the olfactometer described in the preceding paper.3. In thirty olfactory bulb units in the salamander it was found that if the response of a unit to odour delivered to the entire exposed receptor epithelium were suppression (type S), then the unit tended to be suppressed when odour was delivered to a number of localized epithelial regions. If the response were excitation (type E) to stimulation of the entire epithelium, then stimulation to only one or two localized regions would elicit the maximum response.4. Different epithelial regions had the ability to cause excitation in the same bulbar unit depending on the odour being used. Two odours, camphor and amyl acetate, elicited maximum excitation when they were presented to different mucosal areas. The areas at which presentation of these odours gave excitation were surprisingly consistent from unit to unit and animal to animal.5. The data presented here suggest the presence of restricted excitatory receptive fields for some olfactory bulb neurones for a particular odour.6. The presence of spatial response patterns using odour delivery to small nasal receptor regions and thus the presence of receptive fields is discussed with reference to bulbar neuronal circuitry.

Action Potentials↗