Interneuron: characteristics of this type of nerve cell

Internal neurons are a type of nerve cell that connects motor neurons with sensory neurons. Their axons and dendrites project into a single region of the brain, unlike most cells in the nervous system, which typically have axonal projections in more distant regions. As we will see throughout the article, interneurons act as inhibitory neurons via the neurotransmitter GABA

Next, we will explain in more detail what these nerve cells are, what are their main characteristics and what functions they perform.

    Interneuron: definition and characteristics

    An interneuron is a type of nerve cell that is usually located in the integration areas of the central nervous system, Axons (and dendrites) are limited to a single area of ​​the brain. This characteristic distinguishes them from main cells, which often have axonal projections outside the area of ​​the brain where their cell bodies and dendrites are located.

    Major neurons and their networks underlying the processing and storage of local information and represent the major sources of output information from any region of the brain, while interneurons, by definition, have local axons that manage l neuronal activity as a whole.

    While stem cells are primarily excitatory, when using glutamate as a neurotransmitter, interneurons they usually use gamma-aminobutyric acid (GABA) to inhibit their targets. Because GABA works primarily by opening ion channels in the postsynaptic neuron, interneurons achieve their functional effects by hyperpolarizing large groups of major cells (although in some circumstances depolarizing).

    Interneurons in the spinal cord can use glycine, along with GABA, to inhibit stem cells, while interneurons in the cortical area or basal ganglia can release various neuropeptides (cholecystokinin, somatostatin, encephalins, etc.) in addition of GABA. In some regions, such as the basal ganglia and the cerebellum, the major neurons are also gabaergic.

    type

    Most interneurons innervate different types of target cells (both main cells and interneurons) approximately in proportion to their appearance in the neuropil (the region between several cell bodies or sums of neurons in the gray matter of the brain and spinal cord. spinal cord), and therefore they synapse mainly into the most abundant cell type, which are the local main cells.

    The two main types of cortical interneurons are: perisomatic and dendritic inhibitor cells.

    1. Perisomatic inhibitor cells

    The precise location of the termination as well as the specific entry characteristics allow this group of cells to be dissected into two main types of interneurons: Axoaxon or spider cells, which exclusively innervate the initial segments of the axon of the main cells and occur in both the hippocampus and neoscort; and basket cells, which form multiple synaptic contacts in the proximal somes and dendrites of major cells.

    Due to the strategic location of their axonal terminations, it has been suggested that axoaxon cells simultaneously inhibit the production of large populations of major cells. However, recent evidence suggests that its postsynaptic GABA receptor-mediated effect may be depolarizing and, therefore, may offload the entire population of innervating pyramidal cells, with the aim of synchronizing their production or restoring conductances in their dendritic trees.

    Basket cells are found in many different areas of the brain, including the cerebral and cerebellar cortices.a (in the cerebellum, they inhibit Purkinje cells). In the neoscort and the hippocampus, several basket cell subtypes have been distinguished. The two main subtypes of hippocampal basket cells can be more easily distinguished based on their content of neuropeptides and calcium-binding proteins.

    2. Dendritic inhibitor cells

    This group of interneurons it is the most diverse, both morphologically and functionally. Dendritic inhibitor cells are found in many different parts of the nervous system, including the cerebellum, olfactory bulb, and all areas of the cerebral cortex. In fact, a wide variety of dendritic inhibitory interneurons have been described in the neocortex.

    These types of interneurons include Martinotti cells, which primarily target the apical region of pyramidal cell feathers and contain the neuropeptide somatostatin; dual regime cells; and bipolar cells, which primarily target basal dendrites. However, the precise functions of these types of neocortical cells have been difficult to identify.

    Different types of dendritic interneurons have evolved to control glutamatergic inputs to main cells from different sources. It should be noted that individual dendritic inhibitor cells of any type provide 2 to 20 synapses in a single target pyramidal cell, which are scattered throughout the dendritic tree.

      Functions of cortical interneurons

      What has been discovered so far is that interneurons they regulate the levels of physiological activity in the brain, Avoid creeping excitement in recurrent cortical networks. A similar role in stabilizing cortical network dynamics has also been attributed to inhibition of Renshaw cell-mediated feedback in motor regions of the spinal cord.

      There is evidence that lasting changes in the level of arousal are accompanied by a corresponding change in the general level of inhibition; however, transient imbalances between excitation and inhibition can also be induced. In the hippocampus and neocortex, changes in the level of interneuronal firing have been observed to accompany innovative experiments relevant to behavior, and probably help to enable the plastic changes induced by these learning events.

      interneurons they make an essential contribution to the generation of network oscillations and synchronize the activity of the main cells during oscillatory and transient brain states. Perisomatic interneurons in particular are considered indispensable for the generation of gamma rhythms (involved in conscious perception), although the exact nature of their contribution may vary between different regions.

      In addition to maintaining homeostasis and providing a time frame for major cellular activity, interneurons are likely to play a more direct role in cortical neuronal activity. Interneurons that target specific dendritic regions can selectively block excitatory input from different sources, thereby altering their contributions relative to cell output. Dendritic inhibition can also control various forms of synaptic and cellular plasticity through its interaction with active dendritic processes.

      Inhibiting feedback also introduces direct competition among members of a local stem cell population, so that an increase in the activity of one cell tends to decrease the activity of other cells. This competition can be a simple but effective means of noise suppression and, especially if complemented by recurrent local excitation, can arbitrate the selection between competing inputs, and can even involve complex activities such as working memory. and decision making in the neoscort.

      Bibliographical references:

      • DeFelipe, J. (2002). Cortical interneurons: from Cajal to 2001. Ongoing in brain research (Vol. 136, pp. 215-238). Elsevier.
      • Pi, HJ, Hangya, B., Kvitsiani, D., Sanders, JI, Huang, ZJ and Kepecs, A. (2013). Cortical interneurons specialized in disinhibitory control. Nature, 503 (7477), 521.
      • Wonders, CP and Anderson, SA (2006). The origin and specification of cortical interneurons. Nature Reviews Neuroscience, 7 (9), 687.

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