Abstract
A key player in olfactory processing is the olfactory bulb (OB) mitral cell (MC). We have used dual whole-cell patch-clamp recordings from the apical dendrite and cell soma of MCs to develop a passive compartmental model based on detailed morphological reconstructions of the same cells. Matching the model to traces recorded in experiments we find: Cm = 1.91 ± 0.20 μF cm−2, Rm = 3547 ± 1934 Ω cm2 and Ri = 173 ± 99 Ω cm. We have constructed a six MC gap-junction (GJ) network model of morphologically accurate MCs. These passive parameters (PPs) were then incorporated into the model with Na+, Kdr, and KA conductances and GJs from Migliore et al. (2005). The GJs were placed in the apical dendrite tuft (ADT) and their conductance adjusted to give a coupling ratio between MCs consistent with experimental findings (~0.04). Firing at ~50 Hz was induced in all six MCs with continuous current injections (0.05–0.07 nA) at 20 locations to the ADT of two of the MCs. It was found that MCs in the network synchronized better when they shared identical PPs rather than using their own PPs for the fit suggesting that the OB may have populations of MCs tuned for synchrony. The addition of calcium-activated potassium channels (iKCa) and L-type calcium channels (iCa(L)) (Bhalla and Bower, 1993) to the model enabled MCs to generate burst firing. However, the GJ coupling was no longer sufficient to synchronize firing. When cells were stimulated by a continuous current injection there was an initial period of asynchronous burst firing followed after ~120 ms by synchronous repetitive firing. This occurred as intracellular calcium fell due to reduced iCa(L) activity. The kinetics of one of the iCa(L) gate variables, which had a long activation time constant (τ ~ range 18–150 ms), was responsible for this fall in iCa(L). The model makes predictions about the nature of the kinetics of the calcium current that will need experimental verification.
Highlights
The olfactory bulb (OB) represents an opportunity to access, in isolation, the first level of processing of sensory input (Shepherd and Greer, 1998)
Computational modeling has been used to understand these interactions at a macro level (e.g., Linster and Cleland, 2009, 2010; Marella and Ermentrout, 2010), there is a need to understand the biophysics of these interactions at a more detailed scale and to consider how the mitral cell (MC) integrate input and interact in local microcircuits
The correlation in electrical activity between pairs of MCs in these intra-glomerular populations has been studied in experimental recordings (Schoppa and Westbrook, 2001, 2002; Margrie and Schaefer, 2003) and modeling (Migliore et al, 2005). To incorporate these population properties of the MC, we extended our modeling to a small network of MCs coupled at the apical dendrite tuft (ADT) by gapjunctions (GJs)
Summary
The olfactory bulb (OB) represents an opportunity to access, in isolation, the first level of processing of sensory input (Shepherd and Greer, 1998). Computational modeling has been used to understand these interactions at a macro level (e.g., Linster and Cleland, 2009, 2010; Marella and Ermentrout, 2010), there is a need to understand the biophysics of these interactions at a more detailed scale and to consider how the MCs integrate input and interact in local microcircuits. To do this strategies have to be developed to constrain the variables. This was followed by adapting the model to look at intercellular synchronization via gap junctions, for which the morphology was Frontiers in Computational Neuroscience www.frontiersin.org
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
