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A Mackay-Sim

Publications and source records attributed to A Mackay-Sim.

44 records · Page 3Linked to original sources
PubMed1984

Regional differences in cell density and cell genesis in the olfactory epithelium of the salamander, Ambystoma tigrinum.

The olfactory epithelium undergoes continuous regeneration. The present quantitative study uses tritiated thymidine autoradiography to investigate regional differences in the rate of olfactory epithelial cell genesis in the tiger salamander. There was a significant gradient in the incorporation of thymidine from the posterior to the anterior in the nasal cavity: the posterior epithelium underwent cell genesis much faster than the anterior. Additionally, the posterior epithelium was thinner and contained fewer cells than the anterior, although the proportions of receptor, supporting and basal cells remained about the same throughout the epithelium. After 5 or 20 days most of the labelled cells were found in the basal cell layer, although there were a few labelled supporting cells. This confirms observations in other species that there are two populations of dividing cells in the olfactory epithelium: the basal cells which give rise to receptor cells, and the supporting cells. The gradients in epithelial thickness, receptor cells, and the rate of cell genesis parallel a gradient in responsiveness to odorants observed in electrophysiological studies (Mackay-Sim et al. 1982; Mackay-Sim and Shaman 1984). The significance of these anatomical and physiological gradients is presently unclear.

Ambystoma↗
PubMed1984

The projection from the olfactory epithelium to the olfactory bulb in the salamander, Ambystoma tigrinum.

Odor quality may be represented as a "topographic" code of responses of receptor cells throughout the olfactory epithelium, with this code conveyed to the central nervous system by a topographic projection from the olfactory epithelium to the olfactory bulb. There is good evidence for topographic differences in odor-induced receptor cell activity in the tiger salamander but there is no evidence for a topographic epithelium-to-bulb projection in this species. In the present study 3H-leucine autoradiography was used to trace the projections of olfactory receptor neurons in the tiger salamander. Thirteen animals received small injections of tritiated leucine into different regions of the dorsal or the ventral olfactory epithelium, or into the ventrolateral, "vomeronasal organ". The results show that the anterior-to-posterior axes in the dorsal and ventral epithelia are represented along the ventral-to-dorsal axis in the rostral end of the olfactory bulb. The "vomeronasal organ" projects to the caudal end of the bulb. We conclude that the central projection of the olfactory epithelium in the tiger salamander is topographically organised only along the antero-posterior axis and not the medio-lateral axis. Thus epithelial receptor cell activity along the anteroposterior axis would be represented in the glomerular layer of the bulb by activity along its ventro-dorsal axis.

Ambystoma↗
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↗
PubMed1981

Cortical projections to visual centres in the rat: an HRP study.

We have investigated the relationships of the visual cortex to other visual centres in the rat: namely the lateral geniculate nucleus, the visually responsive part of the thalamic reticular nucleus and the superior colliculus. We injected horseradish peroxidase iontophoretically so as to restrict the injectate to each of the regions, and reacted sections using 3 different procedures. Areas 17, 18 and 18a project to both dorsal and ventral lateral geniculate nucleus as well as to the visually responsive part of the thalamic reticular nucleus and superior colliculus. Pyramidal cells in lamina VI project to the dorsal lateral geniculate nucleus and to the thalamic reticular nucleus, whereas cells of origin of the projection to the superior colliculus lie in lamina V; cells in lamina V also project to ventral lateral geniculate nucleus. The implications of these findings are discussed, particularly in terms of the functional relationships between the visual cortex, lateral geniculate nucleus and visual thalamic reticular nucleus.

Animals↗