contradictory data - interpretation

[Jiajun Zhang]

Dear all,

I am looking on the number of synapses of one neuron in a certain neuropil. I used the following methods in natverse.

method 1:

syn_1005611449 = neuprint_get_synapses(1005611449,roi = "ATL(R)")

nrow(filter(syn_1005611449,prepost == 1))
[1] 196

nrow(filter(syn_1005611449,prepost == 0))

[1] 1245

as it mentioned in the document, 

"prepost=0 a downstream or output partner, postsynaptic to the query neuron; 

prepost=1 an upstream or input partner, presynaptic to the query neuron",

I would interprete that the neuron has 1245 output synaspes in ATL(R).

method 2:

ids_ATL = neuprint_bodies_in_ROI("ATL(R)")

in the return the matrix, there is one row:

    
bodyid, voxels, pre, post, roipre, roipost
1005611449, 1034935340, 615, 1308, 130, 195

I would then interprete the neuron has 195 output synapses in ATL(R).

The data from above two methods are quite different. The roipost number 195 is close to the prepost=1 number 196 from method 1, but the roipre number 130 is far different from the prepost=0 number 1245.

Which number should I take? Thank you in advance!

Cheers,

Jiajun Zhang

[Greg Jefferis]

This discrepancy results ultimately from the fact that fly synapses are polyadic. The data model for synapses in neuprint defines each pre-synapse by a T bar. There may be multiple synaptic links to different postsynapses associated with that pre-synapse. If you do:

> neuprintr::neuprint_get_meta(1005611449)
      bodyid pre post upstream downstream status    statusLabel     voxels cropped            name
1 1005611449 615 1308     1308       5410 Traced Roughly traced 1034935340   FALSE ATL028(PDM13)_L
    type cellBodyFiber        notes soma
1 ATL028          <NA> CL-IbAtl(b)1 TRUE

There are 4 numbers related to synapse counts for that neuron. pre contains the number of presynaptic sites and downstream contains the number of outgoing synaptic links made by those presynaptic sites. So you can see that there are 5410/615=8.8 synaptic links per presynaptic site on average for this neuron. In contrast post==downstream since there are normally not multiple presynapses upstream of a single downstream postsynapstic site.

Best wishes,

Greg.

[Jiajun Zhang]

Hi Greg,

Thank you very much for your quick reply and patient explanation!

Cheers,

Jiajun