Vertebrate neuropeptides

Among vertebrate species, the neuro-endocrine-immime system is responsible for many complex, inter-related physiological processes including neuronal, homeostatic, reproductive and immune functions. There are four main types of hormone polypeptides, eicosanoids, steroids and thyroid hormones. Reflecting the inter-dependency of the neiiro-endocrine and immune systems, hormones, neuropeptides and other neiirotransmitters are known to be produced by some immune cells and play a role in the regulation of the immune system, while endocrine and nervous tissues express receptors for many substances produced by the immune system. The major focus of interest in endocrine disruption has... 

The literature contains numerous references to the use of MS/MS in the determination of new neuropeptides in identified cells of invertebrates (Bulau et al., 2004, for a recent example) and this technique is now being applied to in situ analysis of vertebrate tissues (Fournier et al., 2003). MS/MS is also used for studies of neuropeptide processing (Nilsson et al., 2001), pharmacokinetics of synthetic peptides (Mock et al., 2002), nonpeptide drug metabolism (Kamel et al., 2003), identification of peptides purified by immunoaffinity (Suresh Babu et al., 2004), and MALDI/MS/MS techniques adaptable to brain dialysis (Bogan and Agnes, 2004). 

Neuropeptides Y (NFY) and YY are 36-residue amidated peptides that are members of the pancreatic polypeptide (PP) family (Fig. 30-5). NPY is produced both in the peripheral nervous system and in the brain,110 134 where it is one of the most abundant neuropeptides. Another member of the PP family is semi-nalplasmin, a regulator of calcium ion transport in bovine sperm.135 NPY is best known for its stimulation of appetite. It also inhibits anxiety and increases memory retention. It has a vasoconstrictive effect on blood vessels, participating in cardiovascular regulation.136 137 Peptide YY is formed in endocrine cells of the intestine, while NPY is formed in neurons of the parasympathetic system.138 Both participate in regulation of fluid and electrolyte secretion. Both are found in other vertebrate species.139... 

Fig. 2.12. Scolex of Diphyllobothrium dendriticum plerocercoid. The neural elements have been labelled with growth hormone releasing factor (GRF), a vertebrate neuropeptide. In the main nerve cord (n) one GRF-immunoreactive cell body can be seen (large arrow) in the peripheral nervous system (P) several GRF-immunoreactive cells bodies occur (large arrows). The small arrows point to nerve terminals beneath the basal lamina of the tegument along the inner border of the bothridia. Sections stained with Stemberger s immunoperoxidase-antiperoxidase (PAP) technique. (Courtesy Dr Margaretha K. S. GustafFson.)...

The impressive advances made over the years in the identification and functional interpretation of bioactive neuropeptides are the result of a broadly based comparative and multidisciplinary approach. The insights gained from studies in insects and vertebrates show remarkable parallelisms between the two groups. What we have learned is that neuropeptides are engaged in multiple forms of intercellular communication in the control of a variety of biologically important integrative functions. 

Numerous tests carried out in insects with antibodies raised against mammalian neuropeptides revealed reaction products within and outside of the nervous system. Conversely, certain neuropeptides first identified in invertebrates were shown to occur also in mammals and other vertebrates. These commonalities are indicative of a long evolutionary history, as well as a wide distribution of active neuropeptides in neural and non-neural tissues. One of the new insights gained from the use of multiple antisera and carefully conducted specificity tests was the immunocytochemical detection in the insect brain of molecules closely resembling mammalian ACTH, prolactin, and insulin,. The localization of these substances suggests a neurotransmitterlike or neuromodulatory rather than a hormonal role. 

In recent years, the improvement of appropriate techniques has facilitated the chemical identification of a number of insect neuropeptides as well as comparison with their respective counterparts in vertebrates. Among these are metabolic, myotropic, allatotropic, and allatostatic factors. 

Neuropeptide degradation in vertebrates involves both soluble and membrane associated enzymes (1121 Similar mechanisms probably exist in insects. In fact, both soluble and membrane-bound proteolytic activities directed at bioactive peptides have been demonstrated in insect systems (107-1101 A vertebrate-like endopeptidase activity, the Zn-metalloendoprotease (endopeptidase-24 l 1), is present in the locust and is sensitive to the specific inhibitor, phosphoramidon (107-108.1111... 

Additional myotropic/inhibitory neuropeptide structures will be characterized on the basis of immunological similarity to vertebrate and invertebrate peptide structures, and also with the techniques of molecular biology. Two initial successes with those methods are discussed in this report (17,25). In addition, antibodies raised against FMRFamide were used to isolate and structurally characterize a nonapeptide containing C-terminal FMRFamide from head extracts of Drosophila (26). Subsequently, the gene that codes for this nonapeptide and eight other FMRFamide-related structures was isolated and sequenced (27,28). 

Figure 3. Schematic diagram of structural relationships between vertebrate and invertebrate neuropeptides discussed in the text. The similarity in sequences suggests that they may have been derived from a common ancestral source.

Antibodies can also be used as probes to screen expression libraries, and this strategy has been used successfully in the cloning of vertebrate neuropeptides (17). It is likely that this technique will be helpful in cases in which structural data is particularly difficult to obtain and a variety of highly specific antibodies is available. While these and other techniques will prove valuable in special circumstances, screening with synthetic oligonucleotide probes based on protein data is likely to be the principal method of identifying other peptide precursors in the near future. 

A striking feature of neurotransmitter ch istry is the precise regulation of synthesis, that, for example, results in a few neurons synthesizing a particular neuropeptide while all the rest do not. It appears from the vertebrate literature that mature neurons also precisely regulate the rate of neuropeptide synthesis... 

RfteeN years have elapsed since Alvin N. Starratt and Brian E. Brown released their pioneering publication announcing the initial determination of a primary structure for an insect neuropeptide—the penta-peptide proctolin. In the early 1980s, only a few American, Japanese, and European universities, as well as the Zoecon Corporation in the United States, were engaged in insect neuropeptide research. Neuropeptide discoveries in vertebrates and molluscs—and the advent of exquisitely sensitive techniques for isolation, sequence determination, and synthesis of neuropeptides—rapidly accelerated discoveries in both the mammalian and insect arenas. More than SO insect neuropeptides have been sequenced and reported in the literature, and that number is increasing rapidly. Concomitant with these developments have been several symposia, conferences, and workshops that address various aspects of insect neuroscience. 

Sublimaze fentanyl. substance K neurokinin A neuropeptide K. substance P (SP) is a naturally occurring 11 amino acid residue C-terminally amidated peptide, and is a tachykinin present in the brain of vertebrate species, in spinal ganglia and in the intestines. It is formed from the precursor preprotachykinin A (PPT-A). It acts as a tachykinin RECEPTOR AGONIST and Stimulates extravascular smooth muscle, is a powerful VASODILATOR and transient HYPOTENSIVE, and causes salivation and increased capillary permeability. Notably, Af-terminally deleted fragments (e.g. SP(4-11)) are as active as substance P itself on many systems. It is used as a pharmacological tool. 

CCK, endolhelin, tachykinin, neuropeptide Y, TRH, neurotensin, bombesin, and growth hormone secnitagogues receptors plus vertebrate opsins... 

Vertebrate-like neuropeptides are present in insects as demonstrated immunologically, and probably vice versa, but it is unclear what the function is for these peptides in their heterologous animal system. The structural similarities between these molecules suggest that common, biologically-active ancestral molecules may have existed and evolved to perform different functions depending on the physiological diversity and needs of the animals involved. 

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