|Dr W. (Liam) Burke||Emeritus Professor (Professor from 1967)||1956-|
Research in this Laboratory in 1994 was in two separate areas: (i) central visual pathways, research carried out in association with Chun Wang and Bogdan Dreher in the Department of Anatomy & Histology, and (ii) the myoclonic effects of gallamine and curare.
Monocular inhibitory interactions between the X and Y channels in the dorsal lateral geniculate nucleus (LGNd) of the cat
The selective pressure-blocking technique was used to eliminate conduction in the Y optic nerve fibres and the centre-surround antagonism in the receptive fields of LGNd cells was used to show that Y fibres contribute to this antagonism in X LGNd cells. Recent papers have suggested that there is no interaction between the X and Y systems at the LGNd level. In contrast results from the above research showed a considerable cross-talk.
Sensitivity of neurones in area 21a and posteromedial lateral suprasylvian (PMLS) area in the visual cortex of the cat to the motion of two-dimensional textured background ('visual noise')
Only a small proportion (25%) of neurones in area 21a can be excited (and then only weakly) by the movement of visual noise per se. By contrast, it was found that nearly half of the neurones in the PMLS area can be excited by this stimulus and this excitation is strong. These results were consistent with the notion that area 21a is mainly involved in visual pattern analysis while the PMLS area is mainly concerned with visual motion analysis, including that of self-induced motion. There is, however, some interaction between the 'form' and 'motion' channels in area 21a. In particular, the magnitude of responses of area 21a neurones to elongated contours was significantly reduced during the simultaneous movement of the textured visual background. Furthermore, relative motion between the noise background and the contour stimuli had a modulatory effect on the direction selectivity of area 21a neurones.
Myoclonus due to gallamine and curare
These neuromuscular blocking agents do not normally cross the blood-brain barrier to any significant degree, however, in a decerebrate cat they gradually pass into the brain. If a neuromuscular blocking concentration of gallamine is maintained in the cardiovascular system, after about 3 days the concentration in the cerebro-spinal fluid (CSF) becomes equal to that in the plasma. In the brain these substances were found to induce widespread synchronized contractions of all muscles which became very rhythmical at about 8-10 Hz. The substances were equally effective if injected into the CSF of a normal (i.e., not decerebrated) cat. The contractions of the muscles were found to be synchronized with slow waves in the inferior olive, but it remained to be demonstrated that the contractions were initiated in the inferior olive. The myoclonic effects of gallamine persisted for a day or more after the concentration in the CSF had dropped to a very low level. At the same time an unidentified substance appeared in the CSF.
The following will be investigated: myoclonic effects of gallamine and curare; elucidation of the nature of the unidentified substance referred to above; demyelination and remyelination in pressure-blocked optic nerves; properties of axonal conduction in demyelinated optic nerve fibres; role of Y input to area PMLS; role of Y system in the plasticity of visual cortical neurones.
The Laboratory occupies room 241 of the Anderson Stuart building. Electrophysiological equipment comprises probes, amplifiers, oscilloscopes, stimulators, tape recorders, pen recorder, MacLab and facility for recording in the conscious animal. Stereotaxic equipment comprises headholders, coarse- and fine-manipulators and a lesion maker. For visual stimulation there is a photo-stimulator, tangent screen, projectors, and wands. There are surgical instruments, an autoclave and oven for surgery and sterilization; and facility for making electrodes: stainless steel, enamelled and platinum/iridium-in-glass. Prof. Burke's office is in room 365.
|NHMRC||The Y system and the visual
cortex of the cat
(Lab share = 50%)
|NHMRC|| Autoradiography of high affinity
uptake of L-glutamate in the CNS
(Lab share = 50%)
|NHMRC||The role of intrinsic and feedback
connections in cat visual cortex
(Lab share = 50%)
|ARC|| Interactions between the
information channels in the
visual forebrain of the cat
(Lab share = 0%)
Total for 1994: $20,657
Total for 1995: $39,280