Guest post by @DrAnaDaugherty on hippocampal (Hc) vascularization.

Brought to you by “anastomosis” (noun): a cross-connection between adjacent blood vessels; plural “anastomoses”.

As in, “Wow! 54 years of mapping anastomoses”

#SubfieldWednesday 🧵 1/ Figure 3 from Muller & Shaw...Figure 6 from Spallazzi et ...
The unique features of its arteries make Hc vulnerable to anoxia. Superficial arteries travel long tangential routes, and intrahippocampal arteries have few anastomoses and travel with the rolling CA and dentate gyrus tissue. 2/

#SubfieldWednesday
Posterior cerebral (PCA) & anterior choroidal (AChA) arteries supply Hc. Variations are noted: PCA supply is typical and dominant, AChA supply is not seen in 30-40% of hemispheres.

🚨Anastomosis Alert (arrows) 3/

tinyurl.com/2hjaw6vj

#SubfieldWednesday Figure 7 from Erdem et al.,...
PCA supplies middle (body) and posterior (tail) superficial Hc arteries; when present, AChA supplies anterior (head) superficial arteries, otherwise majority blood supply is from PCA branches. 4/
tinyurl.com/85tsx9fw

#SubfieldWednesday Figure 1 from Muller & Shaw...Figure 2 from Muller & Shaw...
Recent 7T in vivo study replicated past histological observations, and identified when AChA diameter is large, more PCA anastomoses are present (especially in uncus).

Check out the beautifully illustrated paper by Spallazzi et al. 5/
tinyurl.com/p3cd4tn4

#SubfieldWednesday Figure 7 from Spallazzi et ...
Ventral intrahippocampal arteries primarily supply CA1, cross DG & end in CA2. Dorsal arteries are short & curve to CA3-DG & sometimes CA2. Large arteries travel long, oblique routes even with right angles; small arteries are straight with small territories. 6/
#SubfieldWednesday
There is individual variability. Commonly CA1 is only supplied by large ventral arteries, all other Hc subfield regions have several supplies. This describes body and tail portions; but the arterial arcade in the head is arranged within each digitation. 7/

#SubfieldWednesday
Hc anastomoses do not efficiently correct for fluctuations in blood supply, causing vulnerability to ischemia; CA1 is least vascularized of all regions and so is most sensitive to this. 8/

tinyurl.com/3rprp6z3 Figure 1 from Bartsch et al...
Variation in blood supply by PCA and AChA correlate with cog performance; may contribute to risk for Hc sclerosis and the mixed evidence of aerobic exercise increasing Hc blood flow.

High-res MRI creates new study opportunities! 9/

tinyurl.com/tw6dpjej
#SubfieldWednesday Figure 2 from Perosa et al....
References

Bartsch et al. (2015) JCBFM
Duvernoy (2005), The Human Hippocampus, p. 73ff
Erdem et al. (1993), JNS
Muller & Shaw (1965), Arch Neurol
Perosa et al. (2020), Brain
Spallazzi et al. (2019), NeuroImage: Clinical

10/fin

#SubfieldWednesday

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More from @hipposubfields

12 May
Last week we talked about hippocampal variability in the hippocampal head.

The hippocampal tail is another area of the hippocampus that can vary anatomically across individuals

#SubfieldWednesday (1/n)
But first, what do we mean by the hippocampal tail? Definitions vary, but one way to define the tail is the part of the hippocampus located posterior to the corpora quadrigemina (i.e. superior and inferior colliculi).

#SubfieldWednesday (2/n) Hippocampal tail is outlined in purple on T1 and T2 weightedHand drawn depiction of the hippocampus with the head, body,
The hippocampal dentations that can be visualized in the hippocampal body on the sagittal plane (pointed out earlier by @thomcat992). But they can also often be seen in the coronal plane in the hippocampal tail (as shown by @lemwisse and colleagues).

#SubfieldWednesday (3/n) coronal slice of hippocampal tail on ex vivo MRI. from FigurSagittal slice of hippocampus (T2 MRI) submitted by Thomas SCoronal slice of hippocampal tail (taken from ex vivo MRI) s
Read 9 tweets
5 May
Today we continue our thread series discussing anatomical variability in the medial temporal lobe (MTL). Today’s topic is anatomical variability in the hippocampal head with a focus on the hippocampal digitations. 🍤🤓📢

#SubfieldWednesday (1/n)
But first, what do we mean by the hippocampal head? We are talking about the anterior part of the hippocampus that contains or is adjacent to the uncus.

#SubfieldWednesday (2/n) Figure 1 from https://doi.org/10.1038/nrn.2015.24 a| A schem
Now what about those “hippocampal digitations” ?

Ding & Van Hoesen (2015) describe external and internal digitations. The external digitations are the “bumps” that extend dorsally and the interior digitations are the “bumps” that extend ventrally.

#SubfieldWednesday (3/n) Figure 2A from https://doi.org/10.1002/cne.23786  HippocampaFigure 1B from https://doi.org/10.1016/j.neuroimage.2017.11.
Read 7 tweets
14 Apr
Happy #SubfieldWednesday! Today we will be sharing a 🧵 on anatomical variability in the medial temporal lobe (MTL). MTL subregions vary in size and shape across individuals & these variations can make landmark identification and segmentation difficult

#SubfieldWednesday (1/n)
Today we will focus on the *most* consistent structure in the MTL: the hippocampal body. Most of our followers will be familiar with this canonical hippocampal body shape shown below in the coronal plane.

#SubfieldWednesday (2/n) Coronal plane from a T2 MRI depicting the canonical C shape
The shape is characterized by a consistent “C-shape” when viewed in the coronal plane. The C is formed by the cornu ammonus (CA) subfield on the lateral part of the hippocampal body.

#SubfieldWednesday (3/n)
Read 10 tweets
10 Feb
We are pleased to announce that today we have a guest #SubfieldWednesdsay 🧵 from @MarkCembrowski !

Check it out below!

(1/n)
When you look at a textbook diagram hippocampus, one sees a series of subfields - DG, CA3, and CA1. All of these regions have specialized properties relative to one another. But it raises the question: within each region, are the cell types uniform?

#SubfieldWednesdsay (2/n) Image courtesy of the Cembrowski lab: https://www.cembrowski
CA1 pyramidal cells of the rodent brain, one of the most studied neuron types in the brain, provide a good starting point to answer this question from both structural and functional perspectives.

#SubfieldWednesdsay (3/n) Image courtesy of Erik Bloss
Read 10 tweets
17 Dec 20
Is anyone planning to do some reading about hippocampal neuroanatomy over the holidays?

If you answered, "yes", this week's #SubfieldWednesday is for you! We will give you a list of "must read" atlas references about our favorite brain structure. 🍤❣️

#SubfieldWednesday (1/n)
In our 2015 paper (Yushkevich et al., NeuroImage, 2015), we provided a list of common atlases used for hippocampal subfield definition across labs.

#SubfieldWednesday (2/n) Table 2 from http://dx.doi.org/10.1016/j.neuroimage.2015.01.
One of the most commonly used atlases cited was:

Duvernoy, H. M. (2005). The human hippocampus: functional anatomy, vascularization and serial sections with MRI. Springer Science & Business Media.

#SubfieldWednesday (3/n)
Read 10 tweets
9 Dec 20
This week I thought I would share some terminology that you may or may not know!

#SubfieldWednesday (1/n)
Most of our followers probably already know how that the name "hippocampus" means "seahorse" in Greek.

#SubfieldWednesday (2/n) https://www.wbur.org/npr/505754756/the-seahorse-in-your-brai
What do you think? When it's dissected like this, I can definitely see the similarity!

#SubfieldWednesday (3/n) Hippocampus removed from the brain (left), in comparison to
Read 8 tweets

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