Outline for today

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

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) 5- 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 • perforant path, mossy fibers, Schaffer collaterals, excitatory interneurons • NMDA and metabotropic R • GABA • 5HT