Biology:Dentate gyrus

From HandWiki
Short description: Region of the hippocampus in the brain
Dentate gyrus
HippocampalRegions.jpg
Diagram of hippocampal regions. DG: Dentate gyrus.
Gray717.png
Coronal section of brain immediately in front of pons. (Label for "Gyrus dentatus" is at bottom center.)
Details
Part ofTemporal lobe
ArteryPosterior cerebral
Anterior choroidal
Identifiers
Latingyrus dentatus
Anatomical terms of neuroanatomy

The dentate gyrus (DG) is part of the hippocampal formation in the temporal lobe of the brain, which also includes the hippocampus and the subiculum. The dentate gyrus is part of the hippocampal trisynaptic circuit and is thought to contribute to the formation of new episodic memories,[1][2] the spontaneous exploration of novel environments[2] and other functions.[3]

It is notable as being one of a select few brain structures which may have significant rates of adult neurogenesis in many species of mammals, from rodents to primates.[4] Other sites of adult neurogenesis may include the subventricular zone, the striatum[5] and the cerebellum.[6] However, whether significant neurogenesis exists in the adult human dentate gyrus has been a matter of debate.[7][8][9][10][11]

Structure

Location of the dentate gyrus and relations to other structures.

The dentate gyrus, like the hippocampus, consists of three distinct layers: an outer molecular layer, a middle granule cell layer, and an inner polymorphic layer.[12] (In the hippocampus the outer layer is the molecular layer, the middle layer is the pyramidal layer, and the inner layer the stratum oriens). The polymorphic layer is also the hilus of the dentate gyrus (CA4, the junction of the hippocampus and dentate gyrus).[13][14]

The granule layer is between the overlying molecular layer and the underlying hilus (polymorphic layer).[10] The granule cells of the granule layer project their axons known as mossy fibers to make excitatory synapses on the dendrites of CA3 pyramidal neurons. The granule cells are tightly packed together in a laminated manner that dampens the excitability of neurons.[15]

Some of the basal dendrites of the granule cells curve up into the molecular layer. Most basal dendrites enter the hilus. These hilar dendrites are shorter and thinner, and have fewer side branches.[16]

A second excitatory cell type in the hilus is the mossy cell,[13] which projects its axons widely along the septotemporal axis (running from the septal area to the temporal lobe) with the ipsilateral projection skipping the first 1–2 mm near the cell bodies,[17] an unusual configuration, hypothesized to prepare a set of cell assemblies in CA3 for a data retrieval role, by randomizing their cell distribution.[18]

Between the hilus and the granule cell layer is a region called the subgranular zone which is a site of adult neurogenesis.[10]

The anteromedial continuation of the dentate gyrus is called the tail of the dentate gyrus, or the band of Giacomini. Most of the dentate gyrus is not exposed on the surface of the brain but the band of Giacomini is visible, and makes an important landmark of the inferior surface of the uncus.[19]

Trisynaptic circuit

The trisynaptic circuit consists of excitatory cells (mostly stellate cells) in layer II of the entorhinal cortex, projecting to the granule cell layer of the dentate gyrus via the perforant path.[20][21] The dentate gyrus receives no direct inputs from other cortical structures.[22] The perforant path is divided into the medial and lateral perforant paths, generated, respectively, at the medial and lateral portions of the entorhinal cortex. The medial perforant path synapses onto the proximal dendritic area of the granule cells, whereas the lateral perforant path does so onto their distal dendrites. Most lateral views of the dentate gyrus may appear to suggest a structure consisting of just one entity, but medial movement may provide evidence of the ventral and dorsal parts of the dentate gyrus.[23] The axons of the granule cells called mossy fibres, make excitatory synaptic connections with the pyramidal cells of CA3 and CA1.[21]

Development

The granule cells in the dentate gyrus are distinguished by their late time of formation during brain development. In rats, approximately 85% of the granule cells are generated after birth.[24] In humans, it is estimated that granule cells begin to be generated during gestation weeks 10.5 to 11, and continue being generated during the second and third trimesters, after birth and all the way into adulthood.[25][26] The germinal sources of granule cells and their migration pathways[27] have been studied during rat brain development. The oldest granule cells are generated in a specific region of the hippocampal neuroepithelium and migrate into the primordial dentate gyrus around embryonic days (E) 17/18, and then settle as the outermost cells in the forming granular layer. Next, dentate precursor cells move out of this same area of the hippocampal neuroepithelium and, retaining their mitotic capacity, invade the hilus (core) of the forming dentate gyrus. This dispersed germinal matrix is the source of granule cells from that point on. The newly generated granule cells accumulate under the older cells that began to settle in the granular layer. As more granule cells are produced, the layer thickens and the cells are stacked up according to age—the oldest being the most superficial and the youngest being deeper.[28] The granule cell precursors remain in a subgranular zone that becomes progressively thinner as the dentate gyrus grows, but these precursor cells are retained in adult rats. These sparsely scattered cells constantly generate granule cell neurons,[29][30] which add to the total population. There are a variety of other differences in the rat, monkey and human dentate gyrus. The granule cells only have apical dendrites in the rat. But in the monkey and human, many granule cells also have basal dendrites.[1]

Function

The subgranular zone (in rat brain). (A) Regions of the dentate gyrus: the hilus, subgranular zone (sgz), granule cell layer (GCL), and molecular layer (ML). Cells were stained for doublecortin (DCX). (B) Closeup of subgranular zone, located between the hilus and GCL,[31] a site of adult neurogenesis.
Phenotypes of proliferating cells in the dentate gyrus. A fragment of an illustration from Faiz et al., 2005.[32]

The dentate gyrus is thought to contribute to the formation of memories, and to play a role in depression.

The role of the hippocampus in learning and memory has been studied for many decades particularly since the late 1950s, following the results of surgery, in an American male, to remove most of the hippocampus.[33] It remains unclear how the hippocampus enables new memory formation, but one process, called long term potentiation (LTP), occurs in this brain region.[34] LTP involves long-lasting strengthening of synaptic connections after repeated stimulation.[20] While the dentate gyrus shows LTP, it is also one of the few regions of the mammalian brain where adult neurogenesis (the formation of new neurons) takes place. Some studies hypothesize that new memories could preferentially use newly formed granule cells of the dentate gyrus, providing a potential mechanism for distinguishing multiple instances of similar events or multiple visits to the same location.[35] Correspondingly, it has been proposed that the immature, newborn granule cells are receptive to form new synaptic connections with the axons arriving from the layer II of the entorhinal cortex, this way a particular new constellation of events is remembered as an episodic memory by first associating the events in the young granule cells that have the appropriate, permissive age.[36] This concept is reinforced by the fact that increased neurogenesis is associated with improved spatial memory in rodents, as seen through performance in a maze.[37]

The dentate gyrus is known to serve as a pre-processing unit. While the CA3 subfield is involved in encoding, storage, and retrieval of memory, the dentate gyrus is important in pattern separation.[21] When information enters via the perforant path, the dentate gyrus separates very similar information into distinct and unique details.[38][39] This ensures that new memories are encoded separately without input from previously stored memories of similar feature,[10] and prepares the relevant data for storage in the CA3 region.[38] Pattern separation gives the ability to differentiate one memory from other stored memories.[40] Pattern separation begins in the dentate gyrus. Granule cells in the dentate gyrus process sensory information using competitive learning, and relay a preliminary representation to form place fields.[41] Place fields are extremely specific, as they are capable of remapping and adjusting firing rates in response to subtle sensory signal changes. This specificity is critical for pattern separation, as it distinguishes memories from one another.[40]

The dentate gyrus shows a specific form of neural plasticity resulting from the ongoing integration of newly formed excitatory granule cells.[10]

Clinical significance

Memory

One of the most prominent early cases of anterograde amnesia (inability to form new memories) linking the hippocampus to memory formation was the case of Henry Molaison (anonymously known as Patient H.M. until his death in 2008).[34] His epilepsy was treated with surgical removal of his hippocampi (left and right hemispheres each have their own hippocampus) as well as some surrounding tissue. This targeted brain tissue removal left Mr. Molaison with an inability to form new memories, and the hippocampus has been thought critical to memory formation since that time, though the processes involved are unclear.[34]

Stress and depression

The dentate gyrus may also have a functional role in stress and depression. For instance, in the rat, neurogenesis has been found to increase in response to chronic treatment with antidepressants.[42] The physiological effects of stress, often characterized by release of glucocorticoids such as cortisol, as well as activation of the sympathetic nervous system (a division of the autonomic nervous system), have been shown to inhibit the process of neurogenesis in primates.[43] Both endogenous and exogenous glucocorticoids are known to cause psychosis and depression,[44] implying that neurogenesis in the dentate gyrus may play an important role in modulating symptoms of stress and depression.[45]

Blood sugar

Studies by researchers at Columbia University Medical Center indicate that poor glucose control can lead to deleterious effects on the dentate gyrus, resulting in memory decline.[46]

Other

Some evidence seen in the mouse suggests that neurogenesis in the dentate gyrus increases in response to aerobic exercise.[47] Several experiments have shown neurogenesis (the development of nerve tissues) often increases in the dentate gyrus of adult rodents when they are exposed to an enriched environment.[48][49]

Spatial behavior

Studies have shown that after having about 90% of their dentate gyrus cells destroyed, rats had extreme difficulty in maneuvering through a maze they had previously navigated. When being tested a number of times to see whether they could learn a maze, the results showed that the rats did not improve at all, indicating that their working memories were severely impaired. Rats had trouble with place strategies because they could not consolidate learned information about a maze into their working memory, and, thus, could not remember it when maneuvering through the same maze in a later trial. Every time a rat entered the maze, the rat behaved as if it was seeing the maze for the first time.[50]

References

  1. ↑ 1.0 1.1 Amaral, David G.; Scharfman, Helen E.; Lavenex, Pierre (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. 163. pp. 3–790. doi:10.1016/S0079-6123(07)63001-5. ISBN 9780444530158. 
  2. ↑ 2.0 2.1 "NCS-1 in the dentate gyrus promotes exploration, synaptic plasticity, and rapid acquisition of spatial memory.". Neuron 63 (5): 643–56. 2009. doi:10.1016/j.neuron.2009.08.014. PMID 19755107. 
  3. ↑ Scharfman, Helen E., ed (2011). The Dentate Gyrus: A Comprehensive Guide to Structure, Function, and Clinical Implications. Elsevier. ISBN 978-0-08-055175-3. https://www.sciencedirect.com/bookseries/progress-in-brain-research/vol/163/suppl/C. [page needed]
  4. ↑ "Adult neurogenesis produces a large pool of new granule cells in the dentate gyrus". J. Comp. Neurol. 435 (4): 406–17. July 2001. doi:10.1002/cne.1040. PMID 11406822. https://zenodo.org/record/1229141. 
  5. ↑ Ernst, A; Alkass, K; Bernard, S; Salehpour, M; Perl, S; Tisdale, J; Possnert, G; Druid, H et al. (27 February 2014). "Neurogenesis in the striatum of the adult human brain.". Cell 156 (5): 1072–83. doi:10.1016/j.cell.2014.01.044. PMID 24561062. 
  6. ↑ "Genesis of neuronal and glial progenitors in the cerebellar cortex of peripuberal and adult rabbits". PLOS ONE 3 (6): e2366. 2008. doi:10.1371/journal.pone.0002366. PMID 18523645. Bibcode: 2008PLoSO...3.2366P. 
  7. ↑ "Human hippocampal neurogenesis drops sharply in children to undetectable levels in adults". Nature 555 (7696): 377–381. March 2018. doi:10.1038/nature25975. PMID 29513649. Bibcode: 2018Natur.555..377S. 
  8. ↑ "Human Hippocampal Neurogenesis Persists throughout Aging". Cell Stem Cell 22 (4): 589–599.e5. April 2018. doi:10.1016/j.stem.2018.03.015. PMID 29625071. 
  9. ↑ Abbott, Louise C.; Nigussie, Fikru (January 2020). "Adult neurogenesis in the mammalian dentate gyrus". Anatomia, Histologia, Embryologia 49 (1): 3–16. doi:10.1111/ahe.12496. PMID 31568602. 
  10. ↑ 10.0 10.1 10.2 10.3 10.4 Tuncdemir, Sebnem Nur; Lacefield, Clay Orion; Hen, Rene (November 2019). "Contributions of adult neurogenesis to dentate gyrus network activity and computations". Behavioural Brain Research 374: 112112. doi:10.1016/j.bbr.2019.112112. PMID 31377252. 
  11. ↑ Zhou, Yi; Su, Yijing; Li, Shiying; Kennedy, Benjamin C.; Zhang, Daniel Y.; Bond, Allison M.; Sun, Yusha; Jacob, Fadi et al. (July 2022). "Molecular landscapes of human hippocampal immature neurons across lifespan". Nature 607 (7919): 527–533. doi:10.1038/s41586-022-04912-w. ISSN 1476-4687. PMID 35794479. 
  12. ↑ Treves, A.; Tashiro, A.; Witter, M.P.; Moser, E.I. (July 2008). "What is the mammalian dentate gyrus good for?". Neuroscience 154 (4): 1155–1172. doi:10.1016/j.neuroscience.2008.04.073. PMID 18554812. 
  13. ↑ 13.0 13.1 Scharfman, Helen E. (September 2016). "The enigmatic mossy cell of the dentate gyrus". Nature Reviews Neuroscience 17 (9): 562–575. doi:10.1038/nrn.2016.87. PMID 27466143. 
  14. ↑ Haines, D; Mihailoff, G (2018). Fundamental neuroscience for basic and clinical applications (Fifth ed.). Elsevier. p. 461. ISBN 9780323396325. 
  15. ↑ Nadler, J. Victor (2003). "The recurrent mossy fiber pathway of the epileptic brain". Neurochemical Research 28 (11): 1649–1658. doi:10.1023/a:1026004904199. PMID 14584819. 
  16. ↑ Seress, László; Mrzljak, Ladislav (March 1987). "Basal dendrites of granule cells are normal features of the fetal and adult dentate gyrus of both monkey and human hippocampal formations". Brain Research 405 (1): 169–174. doi:10.1016/0006-8993(87)91003-1. PMID 3567591. 
  17. ↑ "The three-dimensional organization of the hippocampal formation: a review of anatomical data". Neuroscience 31 (3): 571–591. 1989. doi:10.1016/0306-4522(89)90424-7. PMID 2687721. 
  18. ↑ "On the 'data stirring' role of the dentate gyrus of the hippocampus". Reviews in the Neurosciences 28 (6): 599–615. 2017. doi:10.1515/revneuro-2016-0080. PMID 28593904. 
  19. ↑ Elgendy, Azza. "Band of Giacomini | Radiology Reference Article | Radiopaedia.org". https://radiopaedia.org/articles/band-of-giacomini?lang=gb. 
  20. ↑ 20.0 20.1 Blumenfeld, Hal (2010). Neuroanatomy through clinical cases (2nd ed.). Sunderland, Mass.: Sinauer Associates. ISBN 978-0878936137. 
  21. ↑ 21.0 21.1 21.2 Senzai, Yuta (March 2019). "Function of local circuits in the hippocampal dentate gyrus-CA3 system". Neuroscience Research 140: 43–52. doi:10.1016/j.neures.2018.11.003. PMID 30408501. 
  22. ↑ Nolte, John (2002). The Human Brain: An Introduction to Its Functional Neuroanatomy (fifth ed.). pp. 570–573. 
  23. ↑ Rachel A. Dalley; Lydia L. Ng; Angela L. Guillozet-Bongaarts (2008). "Dentate Gyrus". Nature Precedings. doi:10.1038/npre.2008.2095.1. 
  24. ↑ "Hippocampal development in the rat: cytogenesis and morphogenesis examined with autoradiography and low-level X-irradiation". J. Comp. Neurol. 158 (1): 55–79. November 1974. doi:10.1002/cne.901580105. PMID 4430737. 
  25. ↑ The Human Brain During The Early First Trimester. 5 Atlas of Human Central Nervous System Development. 2008. Appendix, p. 497. 
  26. ↑ "Neurogenesis in the adult human hippocampus". Nat. Med. 4 (11): 1313–7. November 1998. doi:10.1038/3305. PMID 9809557. 
  27. ↑ "Migration and distribution of two populations of hippocampal granule cell precursors during the perinatal and postnatal periods". J. Comp. Neurol. 301 (3): 365–81. November 1990. doi:10.1002/cne.903010304. PMID 2262596. 
  28. ↑ "Time of neuron origin in the hippocampal region. An autoradiographic study in the mouse". Exp Neurol Suppl (Suppl 2): Suppl 2:1–70. October 1965. PMID 5838955. 
  29. ↑ "Neurons in the rat dentate gyrus granular layer substantially increase during juvenile and adult life". Science 216 (4548): 890–2. May 1982. doi:10.1126/science.7079742. PMID 7079742. Bibcode: 1982Sci...216..890B. 
  30. ↑ "Changes in the total number of dentate granule cells in juvenile and adult rats: a correlated volumetric and 3H-thymidine autoradiographic study". Exp Brain Res 46 (3): 315–23. 1982. doi:10.1007/bf00238626. PMID 7095040. 
  31. ↑ Oomen, Charlotte A.; Girardi, Carlos E. N.; Cahyadi, Rudy; Verbeek, Eva C.; Krugers, Harm; Joëls, Marian; Lucassen, Paul J. (29 January 2009). "Opposite Effects of Early Maternal Deprivation on Neurogenesis in Male versus Female Rats". PLOS ONE 4 (1): e3675. doi:10.1371/journal.pone.0003675. PMID 19180242. Bibcode: 2009PLoSO...4.3675O. 
  32. ↑ "Proliferation dynamics of germinative zone cells in the intact and excitotoxically lesioned postnatal rat brain". BMC Neurosci 6 (1): 26. 2005. doi:10.1186/1471-2202-6-26. PMID 15826306. 
  33. ↑ Benedict Carey (4 December 2008). "H. M., an Unforgettable Amnesiac, Dies at 82". The New York Times. https://www.nytimes.com/2008/12/05/us/05hm.html. "In 1953, he underwent an experimental brain operation in Hartford to correct a seizure disorder, only to emerge from it fundamentally and irreparably changed. He developed a syndrome neurologists call profound amnesia. He had lost the ability to form new declarative memories." 
  34. ↑ 34.0 34.1 34.2 Principles of neural science (5th ed.). McGraw Hill Professional. 2013. ISBN 978-0-07-139011-8. 
  35. ↑ "Young dentate granule cells mediate pattern separation, whereas old granule cells facilitate pattern completion". Cell 149 (1): 188–201. March 2012. doi:10.1016/j.cell.2012.01.046. PMID 22365813. 
  36. ↑ "Episodic Memories: How do the Hippocampus and the Entorhinal Ring Attractors Cooperate to Create Them?". Frontiers in Systems Neuroscience 14: 68. September 2020. doi:10.3389/fnsys.2020.559186. PMID 33013334. 
  37. ↑ ""Food and the Aging Mind". First in a Series: Nutrition and Brain Function". USDA.gov. August 2007. http://www.ars.usda.gov/is/ar/archive/aug07/aging0807.htm.. 
  38. ↑ 38.0 38.1 Jonas, Peter; Lisman, John (10 September 2014). "Structure, function, and plasticity of hippocampal dentate gyrus microcircuits". Frontiers in Neural Circuits 8: 107. doi:10.3389/fncir.2014.00107. PMID 25309334. 
  39. ↑ Lamothe-Molina, Paul J.; Franzelin, Andreas; Auksutat, Lea; Laprell, Laura; Alhbeck, Joachim; Kneussel, Matthias; Engel, Andreas K.; Morellini, Fabio et al. (31 August 2020). cFos ensembles in the dentate gyrus rapidly segregate over time and do not form a stable map of space. doi:10.1101/2020.08.29.273391. https://www.biorxiv.org/content/biorxiv/early/2020/08/31/2020.08.29.273391.full.pdf. 
  40. ↑ 40.0 40.1 Moser, Edvard I.; Kropff, Emilio; Moser, May-Britt (1 July 2008). "Place Cells, Grid Cells, and the Brain's Spatial Representation System". Annual Review of Neuroscience 31 (1): 69–89. doi:10.1146/annurev.neuro.31.061307.090723. PMID 18284371. 
  41. ↑ Rolls, Edmund T. (2013). "The mechanisms for pattern completion and pattern separation in the hippocampus". Frontiers in Systems Neuroscience 7: 74. doi:10.3389/fnsys.2013.00074. PMID 24198767. 
  42. ↑ "Chronic antidepressant treatment increases neurogenesis in adult rat hippocampus". J. Neurosci. 20 (24): 9104–10. December 2000. doi:10.1523/JNEUROSCI.20-24-09104.2000. PMID 11124987. 
  43. ↑ "Proliferation of granule cell precursors in the dentate gyrus of adult monkeys is diminished by stress". Proc. Natl. Acad. Sci. U.S.A. 95 (6): 3168–71. March 1998. doi:10.1073/pnas.95.6.3168. PMID 9501234. Bibcode: 1998PNAS...95.3168G. 
  44. ↑ "Adult brain neurogenesis and psychiatry: a novel theory of depression". Mol. Psychiatry 5 (3): 262–9. May 2000. doi:10.1038/sj.mp.4000712. PMID 10889528. 
  45. ↑ "Antidepressants recruit new neurons to improve stress response regulation". Mol. Psychiatry 16 (12): 1177–88. December 2011. doi:10.1038/mp.2011.48. PMID 21537331. 
  46. ↑ "Blood Sugar Control Linked to Memory Decline, Study Says". The New York Times. 1 January 2009. https://www.nytimes.com/2009/01/01/health/31memory.html?_r=1&em=&pagewanted=print. 
  47. ↑ Praag, H (1999). "Running increases cell proliferation and neurogenesis in the adult mouse dentate gyrus". Nature Neuroscience 2 (3): 266–270. doi:10.1038/6368. PMID 10195220. 
  48. ↑ "More hippocampal neurons in adult mice living in an enriched environment". Nature 386 (6624): 493–5. April 1997. doi:10.1038/386493a0. PMID 9087407. Bibcode: 1997Natur.386..493K. 
  49. ↑ "Voluntary exercise alters the cytoarchitecture of the adult dentate gyrus by increasing cellular proliferation, dendritic complexity, and spine density". J. Comp. Neurol. 486 (1): 39–47. May 2005. doi:10.1002/cne.20493. PMID 15834963. 
  50. ↑ "Dentate gyrus and spatial behaviour". Prog. Neuropsychopharmacol. Biol. Psychiatry 33 (5): 762–73. August 2009. doi:10.1016/j.pnpbp.2009.03.036. PMID 19375476. 

External links



Retrieved from "https://handwiki.org/wiki/index.php?title=Biology:Dentate_gyrus&oldid=3714092"