The document summarizes key aspects of the hippocampus. It describes the hippocampus as a curved structure in the medial temporal lobe that plays important roles in memory consolidation and spatial navigation. It notes that humans and other mammals have two hippocampi, one in each side of the brain. It then details the various subregions of the hippocampus, including the Cornu Ammonis regions CA1-CA4 and the dentate gyrus. It provides information on the characteristic cell layers and connections within and between these subregions.

1. Kursk State Medical University
Department of Histology, Embryology, Cytology
HIPPOCAMPUS
Student: A.H. Borzacchini
Supervisor: T.A. Ishunina
Kursk-2012

2. Hippocampus
• Is a neural structure in the
medial temporal lobe of the
brain that has a distinctive,
curved shape which
resembles a shape of a
seahorse.
• It belongs to the limbic
system and plays important
roles in the consolidation of
information from short-
therm memory to long-
therm memory and spatial
navigation.
• Humans and other
mammals have two
hippocampi, one in each
side of the brain.

4. Hippocampal Cells and Layers
• The hippocampus is composed of multiple subfields:
• Cornu Ammonis (CA)
• CA1
• CA2
• CA3
• CA4
• Dentate Gyrus
• Fascia Dentata
• Hilus (region CA4)

5. Nissl-stained coronal section of the brain of a monkey, showing hippocampus (circled).

6. Hippocampus Regions

7. Drawing of Hippocampus by Camilo Golgi
Subregions of the hippocampus exhibit histologial differences.

8. CA regions and their layers
• 1) Alveus
• Deepest layer
• Contains axons from pyramidal layer, passing toward to the fornix
(fimbria)
• One of the major outputs of the hippocampus
• 2) Stratum Oriens
• Next superficial layer
• Contains cell bodies of inhibitory basket cells and horizontal
trilaminar cells (their axons innervate 3 layers: oriens, pyramidal
and radiatum)
• Also contains basal dendrites of pyramidal neurons, where they
receive input from others pyramidal cells, septal fibers and
commissural fibers from the colateral hippocampus (especially in
CA3 and CA2)

9. • 3) Stratum Pyramidale
• One of the more visible strata to the naked eye
• Contains the cell bodies of the pyramidal neurons, which are the
principal excitatory neurons of the hippocampus
• In CA3 region, this stratum contains synapses from the mossy fibers,
cell bodies of many interneurons, including axo-axonic cells,
bistratified cells, and radial trilaminar cells
• 4) Stratum Lucidum
• Only found in CA3 region
• One of the thinnest strata of hippocampus
• Contains the mossy fibers from the dentate gyrus and granule cells
• 5) Stratum Radiatum
• Contains septal and commissural fibers, Schaffer collateral fibers (are
an integral part of memory formation and the emotional network
and they have the projection forward from CA3 to CA1)
• Some interneurons can be found here, basket cells, bistratified cells,
and radial trilaminar cells

10. • 6) Stratum Lacunosum
• Thin stratum that is often grouped togehter wiht stratum
moleculare (stratum lacunosum-moleculare)
• Contains Schaffer colateral fibers and perforant path fibers from
the superficial layers of the entorhinal cortex
• 7) Stratum Moleculare
• Most superficial layer
• Perforant path fibers form synapses onto the distal, apical
dendrites of pyramidal cells
• Hippocampal sulcus
• Cell-free region that separates the CA1 region from the dentate
gyrus
• The sulcus is often used as a fixed reference point for recording
electroencephalography (EEG), bacause the phase of recorded
theta rhythm varies systematically through the strata.

13. CA Regions
• Region CA4
• Also called Hilus (when considered part of the dentate
gyrus)
• Contains mossy cells – receive inputs from granule cells
located nearby in the dentate gyrus in the form of mossy
fibers
• Receive a small number of connections from pyramidal cells
located in CA3, and in turn, project back into the dentate
gyrus at distant septotemporal levels.

14. Region CA4
Human hippocampus shows: - granular neuron (blue, diamond)
- protoplasmic astrocyte (brown, asteristic)
SG= stratum granulosum
Scale E= 20µm

15. Region CA4
SP= stratum pyramidale
SM= stratum moleculare
SG=stratum granulosum
Scale A= 500µm

16. • Region CA3
• Receives input along the mossy fibers from granule cells in the DG
and from projections cells in entorhinal cortex along the perforant
path
• Pyramidal cells (approximately 200,000 in each hemisphere in rats)
send some axons back to the hilus, but the majority project to
regions CA2 and CA1 (a pathway called the Schaffer collaterals)
• Divided into 3 divisions:
• CA3a – part of the cell band which is most distal from the DG and closest
to CA1
• CA3b – middle part of the band nearest to the fornix connection
• CA3c- most proximal to the DG, inserting into hilus
• Is considered to be the “pacemaker” of the hippocampus, much of
the synchronous bursing activity associated with interictaleptiform
activity apperars to be generated, the excitatory collateral
interconnectivity is responsible for this
• Has pyramidal axon collateralsramifying extensively with local region
and making excitatory contacts with neighbors
• CA3 has been implicated in a number of working theories on
memory and learning hippocampal processes; sharp EEG waves also
implicated in memory consolidation.

17. • Region CA2
• Small region located between CA1 and CA3
• Receive perforant path input entorhinal cortex, but do not
receive mossy fiber connections from DG
• Pyramidal cells are more similar to those of CA3 than those of
CA1, so it is grouped as a separate region
• Has a high resistance to epileptic damage
• Region CA1
• First region that yields a significant output pathway
• Sends significant output foward to the subiculum
• Like CA3, receives input from superficial entorhinal cortex along
perforant pathway, but unlike CA3, contains vey few recurrent
connections (in rats, CA1 contains approximately 250,000
pyramidal cells)
• Subiculum (“support”): most inferior component of the hippocampal
fomation, lies between the entorhinal cortex and the CA1 region.

18. Basic Circuit of Hippocampus

19. Dentate Gyrus
• Is composed of a similar series of strata:
• Polymorphic layer: -most superficial
-contains many interneurons, and the axons of
the dentate granules cells pass through this stratum on the way to
CA3.
• Stratum Granulosum: -contains the cell bodies of the dentate
granule cells
• Stratum Moleculare, inner 1/3: -is where both commissural
fibers from the contralateral DG run and form synapses as well as
where the inputs from the medial septum terminate, both on the
proximal dendrites of the granule cells.
• Stratum Moleculare, external 2/3: -deepest strata
-perforant path fibers run
through, making excitatory synapses onto the distal apical
dendrites of the granile cells.

21. • Fascia Dentata:
• Is the earliest stage of the hippocampal circuit
• Its primary input is the perforant path from the superficial layers
of the entorhinal cortex
• Its principal neurons are tiny granule cells which give rise to
unmyelinated axons called mossy fibers which project to the hilus
and CA3.
• Receives feedback connections from mossy cells in the hilus at
distant levels in the septal and temporal directions
• The Fascia Denata and the Hilus together make up the Dentate
Gyrus, as with all regions of the hippocampus, the DG also receive
GABAergic and cholinergic input from the medial septum and the
diagonal band of Broca.

22. Schematic showing regions of the hippocampus proper in relation to other structures.

23. Ultramicroscopy: 3-D visualization of neuronal networks in the
mouse brain
Pyramidal cell dendritic trees of population of CA1 neurons in isolated
hippocampi

24. “Brainbow” transgenic mouse hippocampus (40x)
2008 Small World Competition – 18th place
Photographer Dr. Tamily Weissman, Department of molecular and cellular Biology, Harvard University
Technique: confocal

25. References
• “Opera Omnia”, volume II – Camillo Golgi
• Histology of the Central Nervous System – Michael Hortsch,
Ph.D (University of Michigan)
• Functional Histology 2e – Prof. Jeffrey Kerr
• Histology-World – Floris G. Wouterlood, Ph.D
• Department of Bioelectronics, Institute of Solid State
Electronics, TU Vienna, Austria - H.U. Dodt , N. J ährling, S.
Saghafi, K. Becker
• "Ch 3. Hippocampal Neuroanatomy“ in The Hippocampus
Book - Andersen P, Morris R, Amaral D, Bliss T, O'Keefe J.
(Oxford University)

26. •Thank you for your
Attention!!!