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Autoreceptor

Type of receptor located in the membranes of nerve cells

An autoreceptor is a type of receptor located in the membranes of nerve cells. It serves as part of a negative feedback loop in signal transduction. It is only sensitive to the neurotransmitters or hormones released by the neuron on which the autoreceptor sits. Similarly, a heteroreceptor is sensitive to neurotransmitters and hormones that are not released by the cell on which it sits. A given receptor can act as either an autoreceptor or a heteroreceptor, depending upon the type of transmitter released by the cell on which it is embedded.

Autoreceptors may be located in any part of the cell membrane: in the dendrites, the cell body, the axon, or the axon terminals.

Canonically, a presynaptic neuron releases a neurotransmitter across a synaptic cleft to be detected by the receptors on a postsynaptic neuron. Autoreceptors on the presynaptic neuron will also detect this neurotransmitter and often function to control internal cell processes, typically inhibiting further release or synthesis of the neurotransmitter. Thus, release of neurotransmitter is regulated by negative feedback. Autoreceptors are usually G protein-coupled receptors (rather than transmitter-gated ion channels) and act via a second messenger.

Examples

Autoreceptor inhibition increases respective neurotransmitter release. Clinically important autoreceptors include alpha 2(adrenergic receptor subtype 2), H 3(histamine receptor subtype 3), and 5 HT 1(serotonin receptor subtype 1). Clonidine, used in treatment of hypertension, acts as an agonist on alpha 2, which reduces release of norepinephrine and epinephrine from presynaptic neurons. Tizanidine, used as a centrally-acting skeletal muscle relaxant, also acts on alpha 2. 5 HT 1A is a target of Buspirone, which acts as a partial Agonist and is used as Atypical non-sedative anxiolytic. 5HT 1B/1D receptor Agonist are Triptans and Ergot alkaloids which are used in treatment of migraines. 5 HT 1F receptor subtype Agonist drug lesmiditan is also used in treatment of migraine. The H 3 receptor antagonist Pitolisant is used in narcolepsy. As an example, norepinephrine released from sympathetic neurons may interact with the alpha-2A and alpha-2C adrenoreceptors to inhibit further release of norepinephrine. Similarly, acetylcholine released from parasympathetic neurons may interact with M2 and M4 receptors to inhibit further release of acetylcholine. An atypical example is given by the β-adrenergic autoreceptor in the sympathetic peripheral nervous system, which acts to increase transmitter release.

The D2 autoreceptor has been shown recently to interact with the trace amine-associated receptor 1 (TAAR1), a G-Coupled Protein Receptor GPCR, to regulate monoaminergic systems in the brain.{{Cite journal Active TAAR1 opposes the autoreceptor's activity by inactivating the dopamine transporter (DAT).{{Cite journal

Autoreceptor activity may also decrease paired-pulse facilitation (PPF). A feedback cell is activated by the (partially) depolarized post-synaptic neuron. The feedback cell releases a neurotransmitter to which the autoreceptor of the presynaptic neuron is receptive. The autoreceptor causes the inhibition of calcium channels (slowing calcium ion influx) and the opening of potassium channels (increasing potassium ion efflux) in the presynaptic membrane. These changes in ion concentration effectively diminish the amount of the original neurotransmitter released by the presynaptic terminal into the synaptic cleft. This causes a final depression on the activity of the postsynaptic neuron. Thus the feedback cycle is complete.

References

he:קולטן#קולטנים עצמיים

References

(1999). "Basic Neurochemistry: Molecular, Cellular and Medical Aspects". Lippincott-Raven.
Bear. (2006). "Neuroscience: Exploring the Brain".

Info: Wikipedia Source

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cell-signaling signal-transduction receptors

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