Neuropeptides
Neuropeptides typically affect the neurons they targeted at lower concentrations than the usual neurotransmitters. Neuropeptides are short strings of amino acids having a great variety of effects. They can act as hormones, neurotransmitters, and neuromodulators. Some of the neuropeptides take action as neurotransmitters at some synapses and as neuromodulators at other synapses.
A neurotransmitter changes the degree to which the target cell conducts electricity, hence changing the membrane potential, a neuromodulator varies the strength of the synaptic transmission. A neuromodulator may spring into action pre-synaptically or it may act on a post-synaptic cell to modify its response to the neurotransmitter. Here is a list of some neuroactive peptides.(1)
Gut Brain Peptides
vasoactive intestinal polypeptide (VIP)
cholecystokinin octapeptide (CCK-8)
neurotensin
methionine enkephalin
leucine enkephalin
motilin
insulin
glucagon
Hypothalamic releasing hormones
thyrotropin releasing hormone (TRH)
luteinizing hormone releasing hormone (LHRH)
somatostatin (growth hormone releasing inhibiting factor {SRIF})
Pituitary peptides
Adrenocorticotropin (ACTH)
β-Endorphin
α-Melanocyte stimulating hormone (a-MSH)
Others
dynorphin
angiotensin II
bradykinin
oxytocin
carnosine
bombesin
The SP neuropeptide is a mediator of pain signals. The endorphin and enkephalin neuropeptides are our natural opiates, with the ability to increase our mood and reduce our interpretation of pain in stressful situations. Enkephalins do increase dramatically during child birth. Endorphins, on the other hand, produce what we all know as "runner's high." I.e. they increase dramatically during exercise. There are some theories playing with the idea, that neuropeptides might be responsible for the placebo effect because of their morphine or opiate effects in the body. Then there are neuropeptides which are generated by body tissues and are very common in the gastrointestinal tract. Such neuropeptides are somatostatin, VIP, and cholecystokinin, the gut-brain peptides. "I can feel it in my stomach…" could be a more accurate statement then we think of.
Neuropeptides are released by the brain, immune system, and nerve cells in other organs. To single out the limbic system, which regulates our emotional states, it is laced with a great population of receptor sites for neuropeptides. In concert with all of that, the brain contains receptor sites for protein molecules, manufactured by immune cells such as lymphokines and interleukins. Hence providing for a two-way communication stream between the brain and the immune system.(2)
Our exciting journey through the workings of the mind and the body will continue with the Immune Modulators and a summary of the Chemical Messengers. Then I will present some studies clearly showing that there is indeed a link between the CNS and the immune system. Just in case you still have doubts about the mind-body connection. I strongly encourage any questions, opinions, remarks on this exciting subject. Until then:
Beste Gesundheit,
Werner
1. Freeman L. Complementary and Alternative Medicine: A Research based Approach. St. Louis, Missouri. (2004)p:16
2. Carr D., Blalock J. Neuropeptide Hormones and Receptors Common to the Immune and Neuroendocrine Systems: Bidirectional Pathway of Intersystem Communication. In Ader R., Felton D., Cohen N. Editors: Psychoneuroimmunology. New York. (1991) Academic Press.
2. Goetzl E., Turck C., Sreedharan S. Production and Recognition of Neuropeptides by Cells of the Immune System. In Ader R., Felton D., Cohen N. Editors: Psychoneuroimmunology. New York. (1991) Academic Press.
