1. Outline for today
Structures
Cell types
Circuitry
Function

2. structure c-shaped in coronal or transverse sections
outline resembles rams horn (Ammons horn)
dorsal and ventral commissures

4. major components of the hippocampal formation
hippocampal proper (CA1,CA2,CA3)
dentate gyrus
entorhinal cortex
Subiculum
Presubiculum
parasubiculum

10. How many cell layers are in…
Dentate gyrus
Hippocampal proper
Entorhinal cortex

11. 3 main Layers of DG molecular layer
granule cell layer (striatum granulosum)
polymorphic (or hilus)

12. 3 main layers of hippocampus
molecular layer (stratum radiatum. stratum lacunosum, moleculare)
pyramidal layer – stratum pyramidale
polymorphic (stratum oriens)

14. DG cell types diverse variety of interneurons
mossy fibers – axons from DG granule cells – unmyelinated axons – synapse on CA3
only excitatory output from DG
but not as simple as reduced interneurons - tissue from patients or models of temporal lobe epilepsy
found evidence of normal or enhanced granule cell inhibition. GABAA receptor density is greater in acutely isolated granule cells from epileptic rats compared with controls. In epileptic rats, granule cells had prolonged EPSPs, and they discharged more action potentials than controls.

15. basket cells
axons form plexuses surrounding cell body of granule cells
GABA

16. cells and layers of the dentate gyrus
1- granule cell; axons (mossy fiber) – collateralize in PL and then to CA3
2- dentate pyramidal basket cell 3 – stellate cells (give rise to basket plexus)
4- mossy cell (GLU) inhibitory cells

17. DG studied in relation to kindling, LTP
DG has the most consistent cell loss in temporal lobe epilepsy – (in part interneurons in the hilus of DG)

18. typical CA1 pyramidal cell

20. some of the connections
mossy fibers – axons from DG granule cells – unmyelinated axons – synapse on CA3
sole excitatory output from DG
multiple granule cells can synapse on a single pyramidal cell
Schaffer collaterals- projections from CA3 to CA1 (ipsilateral and contralateral)

21. some of the connections
perforant pathway – major input to hippocampus
axons arise primariy from layers II and III of EC

22. Entorhinal cortex (perforant path)
Recurrent (Schaffer) collaterals
of hippocampal pyramidal cells inCA3
Raphe, septal region
Commissural axons; intrinsic short axon
cells
Basket cells
Short axon cells; commissural axons
Alveus

23. some more connections
alveus - thin layer of fibers originating from pyramidal cells and subiculum; on route to subcortical termination or contralateral hipp
covers the ventricular surface of the hippocampus
bundle thickens – lateral extreme end of hipp – fimbria; descending into forebrain - fornix.

24. What are the main afferents to hippocampus and DG?
entorhinal cortex***
septum, contralateral hippocampus

25. Cortical inputs to the hippocampal formation

26. What are the afferents to the entorhinal cortex?
projections from brainstem, raphe, LC, VTA,
hypothalamic afferents
thalamic nuclei
telencephalic cortical areas
other hippocampal regions

27. Hippocampal Efferents
Many fibers sent directly back to the entorhinal cortex.
Most anatomically prominent output pathway is the fornix

28. efferents of EC perforant pathway
amygdala, cortical nuclei, central nucleus,

29. Subcortical outputs via the fornix

30. Cortical projections from hippocampus via entorhinal cortex

33. subiculum
one of most important efferents of hippocampal formation – only its axons leave the telencephalon to terminate in the diencephalon

34. fimbria/fornix
carry efferent from hippocampal formation and subcortical afferent fibers to hippocampus

35. trisynaptic circuit perforant pathway synapse on granule cells
granule cells send their mossy fiber axons to CA3
CA3 pyramidal cells send their shaffer collateral axons to CA1

38. neurotransmitters? GLU GABA 5HT
perforant path, mossy fibers, Schaffer collaterals, excitatory interneurons
NMDA and metabotropic R
GABA
5HT