Realistic Neuronal Models

William Calvin wcalvin at u.washington.edu
Fri Jul 29 11:49:30 EST 1994

herwin at mason1.gmu.edu (HARRY R. ERWIN) writes:

>I just finished Bartlett Mel (1993) "Synaptic Integration in an Excitable 
>Dendritic Tree" (J. Neurophys., Vol 70, Nr. 3, September 1993, 
>1086-1101). It's on modelling pyramidal neurons in detail. (He used Hines 
>and Moore's NEURON model.)

>1. Mel indicates that triggering the active zone around at the axonal 
>hillock results in an antidromic signal that apparently wipes clean the 
>accumulating signal in the basal dendrites. Is this the case? He doesn't 
>discuss the apical dendrites.

	Haaven't read this particular paper yet, but most analyses show 
that it merely discharges the capacitance.  Probably in dendrites as 
well, since retrograde AP spread is pretty good (unlike orthograde spread).

>2. I'm trying to understand the interaction between Golgi Type I and Type 
>II neurons at reciprocal synapses. Do these fire in the absence of firing 
>at the axonal hillock? I assume they do when hit by the antidromic 
>signal in any case. 

	Reciprocal synapses (where pre- and postsynaptic profiles are 
seen on the same side of a cell membrane in an EM) are common in thalamus 
but not in cortex.  They can release transmitter continuously, in most 
places they've been studied.  Our 1979 paper has the principles laid 
out:  Graubard and Calvin, "Presynaptic Dendrites..." THE NEUROSCIENCES 
FOURTH STUDY PROGRAM (MIT Press), ed Schmitt & Worden.

>3. The soma serves for the most part as a sink for the signals from the 
>basal dendrites, isolating them from each other. On the other hand, the 
>apical system operates similarly in some ways to Freemans NCA (my 
>"activation network"). It tends to kindle and then fire massively. Golgi 
>Type II neurons are built like pyramidal cells without the axon and 
>apical system. Does this mean the soma is also an isolating mechanism in 
>Type II neurons?

	Unlikely.  In cortex, BTW, Golgi IIs are all thought to be 
inhibitory outputs except for the spiny stellate neuron which is excitatory.

>4. Is there evidence that the amplitude signal in pyramidal neurons is 
>contributed by the apical dendrites, while the carrier wave is contributed 
>by the basal dendrites?

	Haven't heard it mentioned.

>5. Based on anatomy, I would expect the inhibitory cells of the cortex to 
>synapse on the basal dendrites and soma. Do the cortico-corticals attach 
>there as well?

	Yes, there are more inhibitory synapses on the soma than 
dendrites.  Corticocorticals >0.5mm are usually excitatory, usually end 
in layers 2/3 though some on the soma.

		William H. Calvin  WCalvin at U.Washington.edu

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