We have found that, relative to control rats, the streptozotocin-induced diabetic rat exhibits a higher amount of kiss-and-run exocytosis whilst releasing identical amounts of neurotransmitter and this can be partially be explained by the diabetic terminals exhibiting a larger increase in intracellular calcium upon the application of a stimulus. In control animals N- and P-type calcium channels can regulate glutamate release whilst L-type calcium channels appear to play a role in regulating the mode of exocytosis. Neither L or P-type channels appear to play a role in neuroexocytosis from diabetic terminals implicating a major role for N-type channels alone.
The use of sub- maximal doses of N-type Ca channel blockers has enabled the diabetic phenotype to be converted to the normal non-diabetic phenotype. Treatment inducing sub-maximal blockade of N-channels should help reveal if other Ca channels can play a role in exocytosis when there is not excess entry of Calcium through the N-channels. The reason for the excessive activity of the N-type channels will be investigated to determine whether there is over-expression of this type of channel , under expression of other Ca channel subtypes or whether N-type channels are less inactivated in the diabetic rats.
We have hypothesised that such distinct neuronal biochemical changes in these diabetic rats may also change the behaviour of these rats and this is being monitored using LABORAS animal behaviour equipment. Animals are monitored for 24 hours twice a week for 12 weeks following streptozotocin injections. This will reveal changes in behaviour between the control and diabetic animals. Attempts will be made to convert the behaviour of the diabetic animals to control animal behaviour by the use of various drugs known to regulate the mode of synaptic vesicle exocytosis including the use of N-type Ca channel blockers.
There is a need to ensure that changes observed in the streptozotocin-treated rats is truly due to a deficiency in insulin. Thus, rats will be injected with streptozotocin but then given daily injections of insulin to prevent the onset of diabetes. We can then check that the animals’ exhibit exocytosis similar to that of control rats and that their behaviours are identical. Furthermore, this will enable us to study the possible role of insulin signalling pathways in regulating the mode of synaptic vesicle exocytosis.
Project lead: Dr Anthony Christopher Ashton
Project staff: Dr Anthony Christopher Ashton
Work presented at the Annual Society of Neuroscience Conference, Neuroscience 2011 Washington USA 10th to 16th November 2011, Regulation of modes of synaptic vesicle release in control and diabetic nerve terminals.
One paper submitted 2013, and two others that require further work.
2007 - present