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Professor Max Bennett was interviewed in 1996 for the Interviews with Australian scientists series. By viewing the interviews in this series, or reading the transcripts and extracts, your students can begin to appreciate Australia's contribution to the growth of scientific knowledge.
The following summary of Bennett's career sets the context for the extract chosen for these teachers notes. In the extract he discusses aspects of his work into how transmitter substances are released from nerve terminals to muscle cells. Use the focus questions that accompany the extract to promote discussion among your students.
Max Bennett was born in Melbourne in 1939. He earned a Bachelor of Engineering (Electrical) from the University of Melbourne in 1963. This background, combined with a philosophical interest in how the human mind works, led him to the study of neurophysiology. Continuing at the University of Melbourne, he investigated the transmission of impulses from autonomic nerves (the part of the nervous system that regulates individual organ function and homeostasis) to smooth muscle, receiving an MSc in 1965 and a PhD in 1967.
In 1969 Bennett joined the Department of Physiology at the University of Sydney and has remained there ever since. Initially appointed as a lecturer, he became a reader in 1974 and then served as Professor of Physiology (Personal Chair) from 1983 to 2000. Since 2001 Bennett has been Professor of Physiology (University Chair). He was Director of the Special Research Centre of Excellence in Neurobiology from 1982 to 1990.
His work has greatly improved our understanding of the function and formation of nerve synapses. He discovered that nerve terminals on muscles release transmitter molecules other than noradrenaline and acetylcholine, going against the prevailing scientific paradigm. He also found that nerve cells in the developing brain depend on growth factor molecules from other nerve cells and that molecular mechanisms determine the different transmission capacities of the individual synapses formed by a single nerve terminal.
Bennett has received numerous awards and honours for his work. In 1977 he was awarded a DSc from the University of Sydney for his studies on synaptic transmission. He received the Ramaciotti Medal for excellence in biomedical research in 1995 and in 1999 was awarded the Burnet Medal by the Australian Academy of Science. He was made an Officer of the Order of Australia (AO) in 2001 for service to the biological sciences in the field of neuroscience.
Bennett was elected to the Fellowship of the Australian Academy of Science in 1981.
A cocktail of transmitters
Are you continuing to work on growth factors?
No, in the last eight or nine years I've gone back to looking at the mechanism by which transmitter substances are released from nerve terminals onto muscle cells. That became possible because we were able to develop special imaging techniques to apply to a cell while it was normally functioning, and so to bring recording electrodes down to specific parts of the nerve terminal at our will.
Consider a nerve terminal abutting on a muscle cell. Each nerve terminal has little bulbous regions in it, and any of these little bulbs can release a packet of transmitter. Because we can now visualise these individual little bulbs – these boutons or varicosities, as they are called – we were able to bring electrodes up and record the release of transmitter from an individual element of the nerve terminal. And what we discovered was that, within a single synaptic arrangement on one nerve terminal, each of the boutons or varicosities has its own individuality. You can't treat a nerve terminal as if it is a homogeneous structure. Each one has quite a distinct capacity to release transmitter on the arrival of a nerve impulse down the axon.
Is it one transmitter or more?
It's more than one transmitter; it's mixtures. And that concept was due to my mentor Geoff Burnstock, who argued – against the establishment – that the packets of transmitter coming out don't just contain the classical transmitters but also lots of other things, such as neuropeptides. It's now known that all release of transmitter involves co-transmitters. For example, at nerve terminals on muscles that you use voluntarily, not only the classical transmitter acetylcholine is released but also substance P and calcitonin gene-related peptide, and adenosine triphosphate.
Our early work with Burnstock and Campbell, back in the 1960s, has led us to become interested in the release of different transmitters at different nerve terminals, and then also in the elaboration of Burnstock's concept that from within a single terminal a whole cocktail of transmitters is coming out, not just one or two transmitters. What is more, our work recently has shown that there is considerable heterogeneity within a single nerve terminal as to its capacity to release transmitter.
Are there many boutons on a nerve terminal?
Yes, there are massive clusters of hundreds of thousands of boutons on a single nerve terminal. And they all behave in ways which are not homogeneous – independently in the sense that they have different properties to release transmitter, but with an ability to interact with each other in complex ways.
The concept that the nerve terminal is inhomogeneous leads on to the fact that mostly it isn't doing anything until you actually bring it into action as a consequence of needing it, such as in the laying down of a memory. If you looked in the brain of a mature human being you would find that most of the nerve terminals there are not doing anything. If you're going to incorporate new information into, for example, the hippocampus (the part of the brain concerned with memory) you have to up-regulate some of these terminals so they become effective, but you can't do that if they're effective already. So there are great reserves.
An edited transcript of the full interview can be found at http://www.science.org.au/scientists/interviews/b/bennett.htm.
Focus questions
Select activities that are most appropriate for your lesson plan or add your own. You can also encourage students to identify key issues in the preceding extract and devise their own questions or topics for discussion.
axon
co-transmitter
nerve terminal
neuron
neurotransmitter
synapse
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