Mossy fiber (hippocampus)

For the major input axonal pathway bundle to the cerebellum, see mossy fiber (cerebellum).
Diagram of a Timm-stained cross-section of the mouse hippocampus. The hippocampal subregion CA3–CA4 is indicated in black, stippled, and hatched areas. Black areas: suprapyramidal (SP), intra- and infrapyramidal (IIP) and hilar (CA4) mossy fiber terminal fields originating from the dentate gyrus. Stippled area: strata oriens (OR) and radiatum (RD). Hatched area: stratum lacunosum-moleculare (LM). CA1, subregion of the hippocampus without mossy fibers; FI, fimbria hippocampi; FD, fascia dentata; OL and ML, outer and middle molecular layers of the fascia dentata; SG, supragranular layer; GC, granular cells.[1]

In the hippocampus, the mossy fiber pathway consists of unmyelinated axons projecting from granule cells in the dentate gyrus that terminate on modulatory hilar mossy cells[2][3] and in Cornu Ammonis area 3 (CA3),[4] a region involved in encoding short-term memory.[5][6] These axons were first described as mossy fibers by Santiago Ramón y Cajal as they displayed varicosities along their lengths that gave them a mossy appearance.[7]

The axons that make up the pathway emerge from the basal portions of the granule cells and pass through the hilus (or polymorphic cell layer) of the dentate gyrus before entering the stratum lucidum of CA3. Granule cell synapses tend to be glutamatergic (i.e. excitatory), though immunohistological data has indicated that some synapses contain neuropeptidergic elements including opiate peptides such as dynorphin and enkephalin. There is also evidence for co-localization of both GABAergic (i.e. inhibitory) and glutamatergic neurotransmitters within mossy fiber terminals.[8][9] GABAergic and glutamatergic co-localization in mossy fiber boutons has been observed primarily in the developing hippocampus,[10] but in adulthood, evidence suggests that mossy fiber synapses may alternate which neurotransmitter is released through activity-dependent regulation.[11]

  1. ^ Sluyter F, Jamot L, Bertholet JY, Crusio WE (April 2005). "Prenatal exposure to alcohol does not affect radial maze learning and hippocampal mossy fiber sizes in three inbred strains of mouse". Behavioral and Brain Functions. 1 (1): 5. doi:10.1186/1744-9081-1-5. PMC 1143778. PMID 15916699.
  2. ^ Sun Y, Grieco SF, Holmes TC, Xu X (2017-03-01). "Local and Long-Range Circuit Connections to Hilar Mossy Cells in the Dentate Gyrus". eNeuro. 4 (2): ENEURO.0097–17.2017. doi:10.1523/ENEURO.0097-17.2017. PMC 5396130. PMID 28451637.
  3. ^ Henze DA, Buzsáki G (2007). "Hilar mossy cells: functional identification and activity in vivo". The Dentate Gyrus: A Comprehensive Guide to Structure, Function, and Clinical Implications. Progress in Brain Research. Vol. 163. pp. 199–216. doi:10.1016/s0079-6123(07)63012-x. ISBN 9780444530158. PMID 17765720.
  4. ^ Amaral DG, Scharfman HE, Lavenex P (2007). "The dentate gyrus: fundamental neuroanatomical organization (dentate gyrus for dummies)". The Dentate Gyrus: A Comprehensive Guide to Structure, Function, and Clinical Implications. Progress in Brain Research. Vol. 163. pp. 3–22. doi:10.1016/S0079-6123(07)63001-5. ISBN 9780444530158. PMC 2492885. PMID 17765709.
  5. ^ Kesner RP (November 2007). "Behavioral functions of the CA3 subregion of the hippocampus" (PDF). Learning & Memory. 14 (11): 771–81. doi:10.1101/lm.688207. PMID 18007020.
  6. ^ Farovik A, Dupont LM, Eichenbaum H (January 2010). "Distinct roles for dorsal CA3 and CA1 in memory for sequential nonspatial events". Learning & Memory. 17 (1): 12–17. doi:10.1101/lm.1616209. PMC 2807176. PMID 20028733.
  7. ^ Scharfman HE, Myers CE (2012). "Hilar mossy cells of the dentate gyrus: a historical perspective". Frontiers in Neural Circuits. 6: 106. doi:10.3389/fncir.2012.00106. PMC 3572871. PMID 23420672.
  8. ^ Sandler R, Smith AD (January 1991). "Coexistence of GABA and glutamate in mossy fiber terminals of the primate hippocampus: an ultrastructural study". The Journal of Comparative Neurology. 303 (2): 177–92. doi:10.1002/cne.903030202. PMID 1672874. S2CID 42502573.
  9. ^ Gutiérrez R, Romo-Parra H, Maqueda J, Vivar C, Ramìrez M, Morales MA, Lamas M (July 2003). "Plasticity of the GABAergic phenotype of the "glutamatergic" granule cells of the rat dentate gyrus". The Journal of Neuroscience. 23 (13): 5594–8. doi:10.1523/jneurosci.23-13-05594.2003. PMC 6741238. PMID 12843261.
  10. ^ Safiulina VF, Fattorini G, Conti F, Cherubini E (January 2006). "GABAergic signaling at mossy fiber synapses in neonatal rat hippocampus". The Journal of Neuroscience. 26 (2): 597–608. doi:10.1523/JNEUROSCI.4493-05.2006. PMC 6674413. PMID 16407558.
  11. ^ Caiati MD (January 2013). "Is GABA co-released with glutamate from hippocampal mossy fiber terminals?". The Journal of Neuroscience. 33 (5): 1755–6. doi:10.1523/JNEUROSCI.5019-12.2013. PMC 6619118. PMID 23365214.