|Dr Paul R. Martin||Lecturer (in-charge)||University||1991-|
|Dr Ann Goodchild||Research Officer||NHMRC||1993-|
|Dr Ulrike Grünert||Feodor Lynen Fellow/
Senior Research Associate
|Krishna Ghosh||PhD student||ARC Scholarship||1994-|
|Heath Wilder||MSc student||1994-|
|Tricia Chan||BSc(Hons) student (MSc from '95)||1994-|
Current effective full-time personnel = 6.0
The work of this Laboratory concerns the substrates of visual perception. The anatomical properties of cells in the retina are studied using immunocytochemical and other neuroanatomical methods. Extracellular recording and linear systems analysis of single cell activity are used to study the responses of cells in the subcortical visual pathways. The Laboratory maintains active international research collaborations in Germany and the United States.
Analysis of small field and diffuse ganglion cells in the primate retina
The ganglion cells which project to the parvocellular layers of the lateral geniculate nucleus carry chromatic opponent signals from the different cone types in the retina, and thus are essential for colour vision. In 1994 Ann Goodchild and Krishna Ghosh found that a New World primate, the marmoset Callithrix jacchus contains cells which have practically identical morphology and dendritic field size as the small field bistratified cell described in the retina of macaque monkeys and humans (see figure). In these Old World primates, the small bistratified cell carries signals from short wavelength sensitive ('blue') cones. These results suggest that this pathway is a conserved feature of primate vision. These experiments were carried out in collaboration with Ann Sefton.
Retinal ganglion cell density in dichromatic and trichromatic marmosets
In collaboration with Barry Lee from the Max Planck Institute for Biophysical Chemistry in Göttingen, Germany and Ulrike Grünert from the Max Planck Institute for Brain Research in Frankfurt, Germany (now a Von Humboldt foundation/ARC Senior Research Associate in the Laboratory), Heath Wilder measured the sampling density of ganglion cells in dichromatic (colour blind) and trichromatic marmosets. They showed that all marmosets have a very high effective sampling density of ganglion cell in the fovea (see figure), thus supporting the Lab's hypothesis that trichromacy is not accompanied by overt changes in retinal cell populations. The central to peripheral ganglion cell density gradient is close to 900:1. This is close to recent estimates for Old World primates and is further evidence that this species can serve as a good model for human vision.
The left panel shows the spatial density of ganglion cells, cone pedicles and cone photoreceptors in the retina of a dichromatic marmoset. The sampling density of ganglion cells is over twice that of cone receptors within the first millimeter of the fovea. The right panel shows the dendritic field diameter of ganglion cells in the marmoset retina. The wide-field group C includes the small field bistratified cells. These cells have the same relative size as their counterparts in Old World monkey retina.
Responses of cells in the lateral geniculate nucleus of dichromatic and trichromatic marmosets
In collaboration with Barry Lee in Germany, and Iris Yeh from Northeastern University in the United States, the responses of cells in the lateral geniculate nucleus of dichromatic and trichromatic marmosets were recorded. Parvocellular cells in trichromatic females showed similar properties to those in Old World primates. The responses of cells in both di- and trichromatic animals could be accounted for using a linear phase summation model developed for macaque monkey. Cells in dichromat animals had quite different properties to cells in other dichromat species studied such as cat, suggesting that the parvocellular system may be unique to the primates.
Horizontal cells in the marmoset retina
Horizontal cells mediate spatial interactions between cones and bipolar cells in the outer retina. In 1994 Tricia Chan and Annie Goodchild showed that the same two types of horizontal cells found in Old World primate retina are present in dichromatic marmosets, suggesting that the bipartite division is not associated with the acquisition of trichromacy. Experiments are now underway to establish the cone connectivity of these cells.
Heath Wilder and Andrew White have developed a stimulating and recording system which allows simultaneous recording of action potentials from up to four cells. The Lab will make high density recordings in the lateral geniculate of marmosets to determine whether different functional cell groups are located in different subdivisions of the geniculate. The retinas from these animals will be processed to examine the morphology of horizontal, bipolar and ganglion cells in relation to blue and red-green cone pathways within the retina.
The Laboratory is located in room 419 of the Anderson Stuart Building. It has all of the electrophysiological equipment required for recording and analyzing single cell activity in the visual system: life support apparatus, stereotaxic headholder, micro-drives, fundus camera, projector- and video-based visual stimulators, two-channel recording system for action potentials, Macintosh computers for data acquisition and analysis, micro-electrode-making equipment and Zeiss FSM fixed stage microscope for injecting single cells in fixed or living tissue.
(Appointed in 1991; publications prior to 1991 arose from work at the Max Planck Institute, Germany)
MOST RECENT TOTAL ANNUAL CITATIONS (for 1993): 74
|NHMRC||The visual system in dichromatic
and trichromatic marmoset monkeys
(*Lab share (70%) = $42,944)
|ARC||Colour information processing in
the primate retina
Total for 1994: $42,944
Total for 1995: $92,944
|Sc 3||AdvN||Med 3||Dent2/
|Tutorials/discussion groups (no.)||6||36||(12)||-||9||||51|
|* 4 practicals to Dent2 & Sc2 only|
| 9 tutorials to Sc2 and ScAux only|
Total formal contact teaching time = 155 h
Time was also spent on lecture preparation, setting and marking exams and essays and answering student queries.