[Comp-neuro] Query: Calcium Spike

[Harry Erwin]

Just a query. I'm currently working on a model of an inferior  
colliculus rebound regular cell. These neurones contain calcium T  
(Cav3) channels and respond to the end of a period of  
hyperpolarisation with a 'hump' (a broad multi-msec calcium spike). In  
bats, sodium spikes can ride on this hump and are believed to indicate  
that the system has detected an echo after the end of an interval of  
GABAergic input. Thalamocortical relay and thalamic nucleus  
reticularis neurones seem to operate in very much the same fashion.  
Now for the $64,000 question--has anyone managed to model this calcium  
hump? I'm using the time constants from Huguenard and Prince (1992)  
and the small calcium spike I'm getting is much too short in duration  
and in magnitude. The somatic conductances I'm using (in nS/(sq  
micron)) are Nav1.2, 300; Kv1.4, (4AP-sensitive) 300; Kv1.4, (4AP- 
resistant) 100; and Cav3, 300. I'm aware that these conductance  
densities are probably too low, but I would expect the ratios to be  
more important than the absolute numbers.

--
Harry Erwin, PhD, Senior Lecturer of Computing, University of  
Sunderland. Computational neuroethologist:
http://scat-he-g4.sunderland.ac.uk/~harryerw/phpwiki/index.php/AuditoryResearch