Oriens Alveus Interneurons
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Contents |
Introduction
The oriens alveus cells are multipolar hippocampal interneurons. Interneurons, as the name implies, connect afferent and efferent neurons in neural pathways. The somata of interneurons, by definition, are located in the central nervous system (2,3).
Oriens alveus control many of the cognitive functions of the hippocampus. The hippocampus is a part of the brain that is critical for memory and learning. The cognitive functions of the hippocampus depend in part on the Ach and 5-HT receptors (see extrinsic afferens section). Improper functioning of these receptors is involved in certain neurological disorders and mental conditions, such as epilepsy, neurodegeneration, depression and schizophrenia (2,3,5).
Neuronal Type: Oriens alveus are present in mammals. They are interneurons located in the hippocampus (2,3).
Anatomy
They are multipolar cells with their somata located within the hippocampus (3).
The hippocampus is a paired structure, part of the limbic system of mammals that is closely associated with the cerebral cortex. It has a curved shape that resembles the shape of a sea horse, hence its name (5).
Molecular profile
- Neurotransmitter: Gamma-aminobutyric acid (GABA) -an inhibitory neurotransmitter in the central nervous system that regulates neuronal excitability (3).
Synaptic Connections
Oriens alveus interneurons connect intrinsic hyppocampal afferent cells with extrinsic afferens from the basal forebrain and the brainstem (2,4).
Intrinsic Afferens
The oriens alveus inhibitory interneurons are regulated by glutamate and Gamma-aminobutyric acid (GABA) from intrinsic hippocampus afferens (2,4).
Extrinsic Afferens
Oriens alveus are also regulated by Acetylcholine (ACh) from extrinsic afferens from the basal forebrain and serotonin (5-HT) from extrinsic afferens from the brainstem (2,3,4).
Ach and 5-HT have the expected slow modulatory effects but have also rapid modulatory effects. The rapid modulatory effects are mediated by the ligand-gated ion channels. The neurotransmitters ACh and 5-HT have a rapid excitatory action on hippocampal interneurons which is what allows these neurotransmitters to bring about their effects on the hippocampus circuit. Having both serotonergic and cholinergic innervation in the hippocampus results in fast synaptic transmission between the interneurons and the several types of neurons they synapse with (2,3,4).
Just like under classic conditions, the action potential (AP) initiation occurs preferentially in the axon with long threshold stimuli. However the AP initiation can be shifted to the soma and dendrite if a brief stimulus is applied. After initiation occurs, action potentials propagate maintaining a constant amplitude and a high velocity (1).
References
1. Gee, Christine E., Woodhall Gabin and Lacaille Jean-Claude (2001), "Synaptically Activated Calcium Responses in Dendrites in Hippocampal Oriens-Alveus Interneurons", The Journal of Neurophysiology, Vol. 85 No. 4 April 2001, pp. 1603-1613. Published by the American Physiological Society.
2. McBain, Chris J. (2001), "“Multiple forms of Feedback Inhibition by Stratum oriens inhibitory interneurons?", The Journal of Physiology, "Reviews and Perspectives in Physiology", Published by the American Physiological Society.
3. Jones, Susan and Yakel, Jerrel L. (1999), "Inhibitory Interneurons in Hippocampus", Journal of Cell Biochemistry and Biophysics, Vol. 31/2 June 1999, pp. 207-218. Published by Humana Press Incorporated.
4. Topolnik, Lisa, "Cellular Basis of Synaptic Communication between Inhibitory Interneurons in the Hippocampus", Universite Laval, Canada. http://www.neuronimaging.ca/current-projects.html
