Vasopressin as neurotransmitter

A neurotransmitter is an endogenous chemical. It is also named as chemical messenger and is responsible for chemical transmission of nerve impulse by neurons. They cause the transmission across the synapse between the neuron and the target neuron that can be a muscle or gland cell. They are released from the synaptic vesicles at synaptic cleft and stimulate the receptor cells by transmitting nerve impulse. Neurotransmitter such as arginine vasopressin can be amino acids, mono amines and purines also.

Role as neurotransmitter

Vasopressin is one the representative hormone of the neuro-hypophysial family that are closely related to each other in structure and functions as well. The vasopressin molecule consists of nine polypeptide subunits. This is an antidiuretic hormone that is synthesized in hypothalamus and is stored in posterior pituitary lobe to be used when required. Also, some neurosecretory cells in peripheral nervous system and some neuron in central nervous system releases vasopressin.

A neurotransmitter molecule is that which produces response in some target cells. The same task is done by vasopressin in the form of vasoconstriction and vasodilation of blood vessels. The only exception in vasopressin activity is that its response is slow but long lasting as compared to some other neurotransmitters. Not only it can act as neurotransmitter but also stimulate the production of some other hormones as well acting as neuromodulator.

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In most of the mammalian species, vasopressin contains arginine so it may be termed as arginine vasopressin.

Functions in body

  • Acts as neurotransmitter in stressed condition
  • Acts as neuromodulator controlling some of other hormones and the release of some neurotransmitter
  • Mainly it maintains the homeostatic state of water and its dissolved nutrients in blood as hormone
  • Direct effect on the size of blood vessels by means of vasoconstriction and vasodilatation
  • Water retention
  • In stress condition, it acts as neurotransmitter chemical

How Neurotransmission occur?

Neurotransmission is the process of transmission of nerve impulse by means of the chemical messengers or the neurotransmitters. It is also termed as the synaptic transmission as it involves releases of neurotransmitter at the synapse point or junction.

Synaptic cleft is the junction point of axon of one neuron and the dendrites of second neuron. These neurons are pre-synaptic (before synapse) and the post-synaptic (after synapse) neurons. It depends upon the direction of flow of nerve impulse. Threshold stimulus or the action potential is that required to excite the neuron and then transmit the nerve impulse.  The arrival of threshold stimulus, release the neurotransmitter by phenomenon of exocytosis in synapse.

As neurotransmitter molecules are released in synapse, the receptors of post-synaptic neuron capture them. Binding of neurotransmitters can excite the post-synaptic neuron by creating a change in membrane potential of the neuron.

Changes in membrane potential

The change in membrane potential from the resting membrane potential (when no transmission of nerve impulse is done) to the action potential of membrane is done by change in voltage. At the arrival of nerve impulse, the voltage dependent Na+ gates open and the bulk of Na+ ions move inside the neuron body. This inward movement of Na+ ions excites the neuron and also generates the action potential in it. The action potential then passes to the next neuron.

The response of neurons to the nerve impulse is based on the “ALL OR NONE” principle that either all the neurons will participate in response otherwise not a single neuron.

Vasopressin when produced in the posterior pituitary lobe moves down the axon by means of the infundibulum. It remains stored at the axon terminal until its requirement in body.

Effects of vasopressin on body

Vasopressin basically acts for retention of water in body in the state of dehydration by increasing the rate of water reabsorption in collecting ducts of nephron. Vasoconstriction is the induced constriction of the blood vessels that result in increased blood pressure in stress states.

When released in brain, vasopressin causes:

  • The neuron of suprachiasmatic nucleus release vasopressin and it involves in circadian rhythms of body.
  • In association with the corticotrophin hormone, it controls the releases of corticoid from the adrenal glands. Thus, it acts as modulator.
  • Distribution of vasopressin and the vasopressin receptors V1 & V2 in brain in a precise manner suggests that the vasopressin is also associated with the behavioral patterns of organisms.

Regulation

The release of vasopressin depends on:

  • Increase in plasma osmotic pressure indicated by the hypothalamus
  • Decrease in blood plasma volume and receptors in blood vessels mediate it
  • Ethanol and angiotensin stimulate its release

Role of vasopressin in diseases

The equilibrium of vasopressin concentration in body is critical. Any problem with its normal production can cause health issues.

When released in low concentration

Low production of the vasopressin due to some drugs etc or the mutation in its receptors V1 & V2 (that belong to G-protein coupled receptors family) cause diabetes, polydepsia (thirst) and polyuria(increased urine production).

when released in excess

Hyponatremia refers to the low sodium supply in blood due to elevated levels of vasopressin. Similar condition of high vasopressin concentration in blood may cause cardiac problems and also the kidney failure.

Bottom line

The production and supply of neurotransmitter in body is of critical importance. Diseases and the mutation causes issue with the normal production of their production that can cause health issues like Alzheimer’s disease, Parkinson disease and dementia etc. Alcohol and drugs causes brain disease because they cause problems with the normal neurotransmitter production by brain cells.

 

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