Autoreceptor

Autoreceptors or Autozeptoren are receptors of a nerve cell for their own neurotransmitters. They come in both the perikaryon, so the cell body ( soma), and at the dendrites and to the presynaptic terminals, ie the terminal axon before. The autoreceptors in the perikaryon and dendrites are called soma - dendritic autoreceptors, which are called the axon terminals presynaptic autoreceptors.

Discovery history

The first indications were pharmacological nature. It was observed that antagonists of neurotransmitter receptors not only the post-synaptic nerve effects weakened to the innervated cell, but also increased the release of neurotransmitters from presynaptic the axon terminals. An important example is the sympathetic neurotransmitter norepinephrine with his. Norepinephrine brings the smooth muscles of blood vessels to contract. It acts on α -adrenoceptors. Now It was observed that α -adrenoceptor antagonists such as phenoxybenzamine not only the blood vessel contraction in sympathetic activity weakened, but also increased the release of noradrenaline. Thank misinterpretations followed in 1971 by the now certain knowledge that this increase is due to the blockade of presynaptic α - Autozeptoren, through the normally noradrenaline inhibits its own release. They were the prototypes of the α2 -adrenoceptors. 1975 Arvid Carlsson coined the term " autoreceptor ".

It appears that most, if not all neurons have autoreceptors. There are mainly G- protein -coupled receptors. In general, they mediate inhibition of nerve cell.

Soma - dendritic autoreceptors

Soma - dendritic autoreceptors contribute to the regulation of the formation of action potentials in the perikaryon. An example are again neurons to the neurotransmitter norepinephrine. You have soma - dendritic α2 - autoreceptors. About it hyperpolarized the cell membrane norepinephrine, inhibiting the formation of action potentials. Another example are neurons to the neurotransmitter serotonin, which occur mainly in the brain. They have somatic dendritic 5-HT1A autoreceptors, on serotonin inhibits the formation of action potentials.

Presynaptic autoreceptors

They are among the numerous presynaptic receptors. The picture shows the presynaptic α2 - autoreceptors. We know today in humans three α2 - adrenoceptors? 2A, alpha 2b and α2C. All three can be installed as autoreceptors in the cell membrane of axon terminals to the transmitter norepinephrine, where? 2A and α2C are more important. All three couple to heterotrimeric G proteins of the Gi / o family. Their βγ subunit inhibits presynaptic calcium channels. Then, when an action potential arrives flows less calcium in the axon terminal, and decreases the release of noradrenaline. This results in a negative feedback.

Analog own nerve cells with the transmitter serotonin presynaptic autoreceptors of the 5 - HT1B receptors, neurons with the transmitter dopamine presynaptic autoreceptors on the type of dopamine D2 receptors and nerve cells with acetylcholine presynaptic autoreceptors on type of M2 and M4 muscarinic receptors. All of these receptors inhibit transmitter release. Neurons with the transmitter glutamic acid on the other hand have both inhibitory and release release -enhancing presynaptic autoreceptors.

Medical importance

The modulation of the activity of nerve cells by autoreceptors is part of their normal physiology. That may malfunction auto receptors lead to disease, is best documented for the α2 - autoreceptors. Experimental animals, which lack autoreceptors, put too much norepinephrine and prone to high blood pressure and heart disease. A reduction in the release of noradrenaline from the sympathetic nervous system contributes to the antihypertensive effect of clonidine and related substances. Changes in autoreceptors belong to the mechanism of action of psychotropic drugs.