Neuropeptides

Neuropeptides are small protein-like molecules used by neurons to communicate with each other. They are neuronal signaling molecules. The brain largely functions by virtue of neuropeptides.A neuropeptide is any of the variety of peptides found in neural tissue; e.g. endorphins, enkephalins. There are cells in the brain that produce various neuropeptides, and these neuropeptides are involved in almost all the body functions. More than 100 different peptides are known to be released by different populations of neurons in the mammalian brain.

The word neuropeptide, coined by Candace Pert, a neuroscientist and psychopharmacologist In the early 1970s, in her research on brain function, refers to the “chemical messengers” that travel throughout the body whenever we think a thought or speak a word. ( Donald J Glassey )

 Neuropeptides are peptides released by neurons (brain cells) as intercellular messengers. Some neuropeptides function as neurotransmitters, and others function as hormones.
 
They can be either pro-inflammatory or anti-inflammatory, with anti-inflammatory being preferred. They are responsible for many functions:
 
They control our mood, energy levels, pain and pleasure reception, body weight, and ability to solve problems; they also form memories and regulate our immune system.
 
 Their major role seems to be the modulation of amine and amino acid neurotransmission. This appears to be achieved at many sites by the co-release of peptide with the primary transmitter. The presynaptic biochemistry and physiology of neuropeptides ensure that neuromodulation is highly plastic with almost infinite adaptive potential. The recent development of novel drugs (termed peptoids) that mimic or block neuropeptide function have opened up new clinical approaches to a number of conditions (Hughes J, Woodruff GN).

Neuropeptide Y (NPY) has been implicated in the hypothalamic regulation of reproduction and energy homeostasis. The perikarya located primarily in the arcuate nucleus (ARC) of the hypothalamus constitute a common source of NPY. Projections from these neurons along two distinct pathways, namely, the reproductive axis of the ARC–median eminence–medial preoptic area and the orexigenic axis of the ARC–paraventricular nucleus and neighboring regions, participate in regulation of these two neuroendocrine functions. Additionally, the NPY neuronal system within the basal hypothalamus is morphologically and functionally linked with galanin(Galanin is a 30 amino acid neuropeptide which is cleaved from preprogalanin. It is involved in a number of physiological processes such as regulation of food intake, metabolism and reproduction, regulation of neurotransmitter and hormone release, nociception, intestinal contraction and secretion, and more recently in nervous system development and response to injury.)and the opioid networks which also play roles in the control of reproduction and ingestive behavior. Recent experimental evidence indicates that genetic, hormonal, and environmental factors that cause nutritional imbalance and metabolic disturbances, along with depressed pituitary gonadal function, produce alterations in the synthesis, storage, and release of NPY and in other connected peptidergic systems in the hypothalamus (Satya P. Kalra and Pushpa S. Kalra )

The functional significance of neuropeptides and neurohormones throughout the neuroaxis has been the focus of considerable research over the past 25 years. They have been localized within nuclei responsible for the relay of visceral afferent information to the forebrain.. Numerous studies have shown that the exogenous administration of these neurochemicals directly into visceral afferent nuclei significantly alters blood pressure, heart rate, autonomic tone and the sensitivity of the baroreceptor reflex (an index of sympatho-vagal balance). A strong inverse correlation has been demonstrated between the sensitivity of the baroreceptor reflex and susceptibility to lethal cardiac arrhythmias which lead ultimately to sudden cardiac death. The differential effects of various neurochemicals on the sensitivity of the baroreceptor reflex suggests that some neurochemicals may act as preventatives while others may actually contribute to the pathogenesis of neurogenic cardiac arrhythmias. Hormones such as estrogen, in addition to their neuroprotective properties, may also play a role in modulating the cardiovascular consequences to neurogenic pathologies including stroke and epilepsy Saleh T.M 

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