Hippocampal granule cells

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Hippocampal granule cells are neurons that compose the middle or granular layer of the dentate gyrus of the mammalian hippocampus.


Basic Information

Hippocampal granule cells are one of the few types of neurons that are capable of neurogenesis throughout the adult life of an organism (Gómez-Lira, 2005). Granule neuron progenitor cells are generated in the subgranular zone of the dentate gyrus. These progenitor cells migrate into the granule layer, differentiate, and extend axons. Newborn hippocampal granular neurons in adult organisms are functionally integrated into existing neural circuitry (Jiang 2005).

Neuronal Type: projection neuron.

Anatomy

hippocampal regions; image taken from http://en.wikipedia.org/wiki/Dentate_gyrus

The hippocampus has a very simple structure and organization, making it a useful model brain structure for studying synaptic transmission. It is composed of two thin layers of neurons, called the dentate gyrus and Ammon's horn, folded onto each other. It is located in the medial temporal lobe of the brain and its structure is very similar in all mammals. Hippocampal granule cells are approximately 10 micrometers in diameter. They give rise to mossy fibers which synapse on CA3 neurons.

Molecular profile

  • Fully differentiated hippocampal granule neurons use the neurotransmitter glutamate. Developing hippocampal granule neurons express both glutamatergic and GABAergic phenotypes, but fully developed hippocampal granule neurons almost exclusively express a glutamatergic phenotype. It has been shown that neurotransmitter choice of hippocampal granule cells is dependent on both programmed and environmental factors (Gómez-Lira, 2005).

Physiology

Synaptic Inputs

Hippocampal granule neurons receive inputs from the entorhinal cortex via the perforant path. This axis has been indicated to be involved in spatial memory (Hafting 2005).

Synaptic Outputs

Hippocampal granule neurons emit mossy fibers that synapse on pyramidal neurons of area CA3 of Ammon's horn, which synapse on pyramidal neurons of area CA1 of Ammon's horn. These connections are involved in long-term potentiation and long-term depression (Bear, 2007).

Additional information

It has been suggested that the cannabinoid receptor system and its ligands may play a role in hippocampal granule cell neurogenesis (Jiang 2005). A 2002 study showed that the anandamide analogue methanandamide decreased neurogenesis in the adult dentate gyrus, both in culture and in vivo, and the CB1 antagonist SR141716 increased neurogenesis (Rueda 2002).

References

Bear Mark F., Connors Barry W., Paradiso Michael A (2007). Neuroscience: Exploring the Brain -3rd ed. Lippincott Williams and Wilkins. pp. 777-782.

Cameron HA, McKay RD (2001). "Adult neurogenesis produces a large pool of new granule cells in the dentate gyrus". J Comp Neurol 435 (4): 406–17. doi:10.1002/cne.1040. PMID 11406822.

Gisela Gómez-Lira, Mónica Lamas, Héctor Romo-Parra, and Rafael Gutiérrez (2005). "Programmed and Induced Phenotype of the Hippocampal Granule Cells." The Journal of Neuroscience, July 27, 2005, 25(30):6939-6946; doi:10.1523/JNEUROSCI.1674-05.2005

Hafting T, Fyhn M, Molden S, Moser M, Moser E (2005). "Microstructure of a spatial map in the entorhinal cortex." Nature 436 (7052): 801–6. doi:10.1038/nature03721. PMID 15965463.

Jiang Wen, Yun Zhang, Lan Xiao, Jamie Van Cleemput, Shao-Ping Ji, Guang Bai, Xia Zhang (2005). "Cannabinoids promote embryonic and adult hippocampus neurogenesis and produce anxiolytic- and antidepressant-like effects." J. Clin. Invest. 115(11): 3104-3116 (2005). doi:10.1172/JCI25509.

Rueda D, Navarro B, Martinez-Serrano A, Guzman M, Galve-Roperh I (2002). "The endocannabinoid anandamide inhibits neuronal progenitor cell differentiation through attenuation of the Rap1/B-Raf/ERK pathway." J Biol Chem. 2002 Nov 29;277(48):46645-50. Epub 2002 Sep 16.