Neurohormones,Neurotransmitters, Neuromodulators & Neuroregulators

The terms are commonly confused. I am trying to clarify using reference books that I have and material available on internet.
Neurohormones are hormones secreted into the peripheral circulation from nerve terminals in the posterior pituitary gland. e.g., Vasopressin, oxytocin and hypothalamic releasing factors (GnRH, CRH,GHRH) or inhibiting factors (e.g., SST) are released into a specialized pituitary portal vasculature as neurohormones that direct secretion of anterior pituitary hormones.

Neurotransmitters
They conduct information synaptically between neurons. A peptide released from the fiber terminal of one neuron into the synaptic cleft to act on the membrane of another neuron is a neurotransmitter. This action is relatively fast and short lasting.
Excercise on Neurotransmitters

Neuromodulators

They affect the response of a neuron to other neurotransmitters released from some or other neurons.

In neuroscience, neuromodulation is the process in which several classes of neurotransmitters in the nervous system regulate diverse populations of neurons (one neuron uses different neurotransmitters to connect to several neurons). As opposed to direct synaptic transmission, in which one presynaptic neuron directly influences a postsynaptic partner (one neuron reaching one other neuron), neuromodulatory transmitters secreted by a small group of neurons diffuse through large areas of the nervous system, having an effect on multiple neurons. Examples of neuromodulators include dopamine, serotonin, acetylcholine, histamine and others.(paragraph courtesy )

Neurotransmitters vrs Neuromodulators

Neurotransmitters:  -  elicit the changes in membrane potential 

-  can be small MW classic neurotransmitters or neuropeptides or gaseous nt.

-  rapid, brief action

Neuromodulators:    -  typically, they do not affect membrane potential themselves, but modulate (enhance or     suppress) the effects of neurotransmitters at the synapse

-  typically neuropeptides; one particular peptide may serve a neurotransmitter role at one synapse and a neuromodulator role at another synapse

-  slow, prolonged action

-  small MW neurotransmitters and peptide neuromodulators often coexist and corelease

Neuroregulators

Neuropeptides such as endorphins distributed throughout the CNS are expressed at many levels of the neuroaxis and act as neuroregulators via opiate receptors and function as analgesics.Opioid peptides e.g., Methionine enkaphaline, leucine enkephalin and  β-endorphins.

 

Q: How can one single peptide (neurotransmitter) affect the function of a complex network (i.e., modulate a complex neural function)?

 Ans:

1.  As a neurotransmitter at a strategic point in a neural network.

Inhibition of the peptide action suppresses the activity of the network.

Stimulation of the peptide action increases the activity of the network.

2.  As an endocrine agent present in the blood.

The peptide triggers the action of the neuronal network  ® ® complex response

3.  As both an endocrine agent triggering and a neurotransmitter sustaining the function of a network.

-  opioid peptides in pain suppression

-  cholecystokinin in the regulation of feeding

  

Synthesis and Storage of Neurotransmitters

Neurological Control