Distribution of secretoneurin-like immunoreactivity in comparison with that of substance P in the human brain stem

Granin-derived peptides

The granin family comprises altogether 7 different proteins originating from the diffuse neuroendocrine system and elements of the central and peripheral nervous systems. The family is dominated by three uniquely acidic members, namely chromogranin A (CgA), chromogranin B (CgB) and secretogranin II (SgII). Since the late 1980s it has become evident that these proteins are proteolytically processed, intragranularly and/or extracellularly into a range of biologically active peptides; a number of them with regulatory properties of physiological and/or pathophysiological significance. The aim of this comprehensive overview is to provide an up-to-date insight into the distribution and properties of the well established granin-derived peptides and their putative roles in homeostatic regulations. Hence, focus is directed to peptides derived from the three main granins, e.g. to the chromogranin A derived vasostatins, betagranins, pancreastatin and catestatins, the chromogranin B-derived secretolytin and the secretogranin II-derived secretoneurin (SN). In addition, the distribution and properties of the chromogranin A-derived peptides prochromacin, chromofungin, WE14, parastatin, GE-25 and serpinins, the CgB-peptide PE-11 and the SgII-peptides EM66 and manserin will also be commented on. Finally, the opposing effects of the CgA-derived vasostatin-I and catestatin and the SgII-derived peptide SN on the integrity of the vasculature, myocardial contractility, angiogenesis in wound healing, inflammatory conditions and tumors will be discussed.

New insights into granin-derived peptides: evolution and endocrine roles

The granin protein family is composed of two chromogranin and five secretogranin members that are acidic, heat-stable proteins in secretory granules in cells of the nervous and endocrine systems. We report that there is little evidence for evolutionary relationships among the granins except for the chromogranin group. The main granin members, including chromogranin A and B, and secretogranin II are moderately conserved in the vertebrates. Several small bioactive peptides can be generated by proteolysis from those homologous domains existing within the granin precursors, reflecting the conservation of biological activities in different vertebrates. In this context, we focus on reviewing the distribution and function of the major granin-derived peptides, including vasostatin, bovine CgB(1-41) and secretoneurin in vertebrate endocrine systems, especially those associated with growth, glucose metabolism and reproduction.

First localization and biochemical identification of chromogranin B- and secretoneurin-like immunoreactivity in the fetal human vagal/nucleus solitary complex

The human vagal/nucleus solitary complex is a primary visceral relay station and an integrative brain stem area which displays a high density of chromogranin B- and secretoneurin-like immunoreactivity. In this study, we localized and biochemically identified these proteins during prenatal development. At prenatal week 11, 15, 20 and 37, we performed a chromatographic analysis to identify the molecular forms of PE-11, a peptide within the chromogranin B sequence, and secretoneurin, a peptide within secretogranin II. Their localization was studied with immunocytochemistry, and was compared to that of substance P which is well established as a functional neuropeptide in the vagal/nucleus solitary complex. At prenatal week 11, chromogranin B-, secretoneurin- and substance P-like immunoreactivities were detected consisting of varicosities, varicose fibers and single cells. At the same time, PE-11 and secretoneurin appeared as a single peak in chromatographic analysis. Prohormone convertases PC1- and PC2-like immunoreactivities were also present at week 11. In general, the density for each peptide increased during later fetal stages with the highest density at week 37. These results demonstrate that each chromogranin peptide is expressed during human fetal life in neurons of the vagal/nucleus solitary complex indicating that these peptides could be important during prenatal development.

Lack of a distinctive behavioural effect of chromogranin-derived peptides in rodents

Chromogranins are neuropeptide precursors stored in large dense core vesicles in which they are processed to smaller peptides. Although these peptides are widespread in the CNS, it is still unknown if they are behaviourally active. For example, even though secretoneurin, a 33-amino acid peptide derived from secretogranin II, was shown to induce release of dopamine from rat striatal neurons, work on the functional significance of this result is still missing. In order to investigate the behavioural effects of chromogranin-derived peptides, we studied the total locomotor activity and rearing behaviour of male albino Sprague-Dawley rats in the open field experimental paradigm. Measurements were performed every 5 min during half an hour before and 2 h after an intracerebroventricular injection of GE-19, GAIPIRRH, secretoneurin or vehicle. None of the tested chromogranin-derived peptides (at a concentration of 20 microM) affected locomotion and rearing behaviour. However, the administration of secretoneurin and GAIPIRRH increased the thigmotaxis, suggesting a possible anxiolytic action. In male Swiss albino mice, which were tested in the black-and-white box paradigm, only GE-19 produced sedation at a dose of 0.72 nmol in 41% of the mice. Overall, there is only little evidence that any of the examined chromogranin-derived peptides produces a behaviourally significant effect, even when given intracerebroventricularly.

Chromogranins in temporal lobe epilepsy

PURPOSE

Chromogranins are neuropeptide precursors stored in large dense core vesicles. Because physiological functions have been postulated for peptides originating from chromogranins, we investigated the distribution of chromogranins A and B and secretoneurin (a peptide derived from secretogranin II) in the control and epileptic hippocampus of humans and rats.

METHODS

Chromogranin immunoreactivity (IR) was investigated in paraformaldehyde-fixed hippocampal specimens from 24 temporal lobe epilepsy patients with intractable seizures, postmortem from 15 patients deceased from nonneurological disorders, in rats 30 days after kainate-induced limbic seizures, and in control rats.

RESULTS

In control rats and in humans, chromogranin A and B IR and secretoneurin IR were present in mossy fibers. In addition, chromogranin B IR was found in granule cells, and chromogranin A IR was found in granule and CA2 pyramidal cells in the human hippocampus. In both species, chromogranin B and secretoneurin were unevenly distributed in the molecular layer of the dentate gyrus. The most intriguing change seen in human temporal lobe epilepsy specimens and in the kainic acid model of the rat was the prominent staining of the inner molecular layer, indicating storage of chromogranins A and B and secretoneurin in terminals of reorganized mossy fibers, from which they may be released upon nerve stimulation.

CONCLUSION

Chromogranins A and B and secretoneurin are valid markers for hippocampal neurons and delineate epilepsy-induced reorganization of mossy fibers.

Co-distribution patterns of chromogranin B-like immunoreactivity with chromogranin A and secretoneurin within the human brainstem

As members of the chromogranin family, chromogranin A, chromogranin B, and secretogranin II are acidic proteins found in large, dense core vesicles. They are endoproteolytically processed to smaller peptides and released after neuronal stimulation. Using immunocytochemistry, this study closely examines chromogranin B-like immunoreactivity within the human brainstem and then takes a comparative view of co-distribution patterns by chromogranin B, chromogranin A, and secretogranin II. We used an antiserum raised against a synthetic peptide (PE-11) present in the chromogranin B molecule. Secretogranin II was localized with an antiserum against secretoneurin, a 33 amino acid peptide, found within the secretogranin II precursor. Like chromogranin A and secretoneurin, chromogranin B is expressed through all levels of the human brainstem. Chromogranin B was exclusively detected in neuronal structures. The medial part of the substantia nigra pars reticulata, the nucleus interpeduncularis, the area of the central gray, and the raphe complex displayed a high density of PE-11-like immunoreactivity. Furthermore, a prominent staining was found in the medial, dorsal and gelatinous subnuclei of the solitary tract and the dorsal motor nucleus of vagus. The substantia gelatinosa of the caudal trigeminal nucleus and spinal cord were also very strongly PE-11-immunopositive. In conclusion, chromogranin B and secretogranin II showed similar distributions while neuronal localization typically differed from chromogranin A aside from a few exceptions. These findings may provide a framework for future research in revealing a functional role of chromogranin peptides in the human brainstem.

PE-11, a peptide derived from chromogranin B, in the human brain

This study was performed to investigate the distribution of chromogranin B in the human central nervous system. We used an antiserum raised against a synthetic peptide (PE-11) present in the chromogranin B molecule. PE-11-like immunoreactivity was characterized by molecular size exclusion and reversed-phase high-performance liquid chromatography. Its localization was studied using immunocytochemistry. Only the free peptide and an N-terminally elongated peptide were detected by molecular size exclusion high-performance liquid chromatography, indicating that proteolytic processing of chromogranin B is quite extensive. PE-11-like immunoreactivity was present in differently shaped fibers, varicosities and neurons, but not in glial cells. Its density varied throughout the brain. An especially high density was observed in the bed nucleus of the stria terminalis, the central and cortical nuclei of the amygdala, the hypothalamus, the hippocampus, the raphe complex, the nucleus interpeduncularis, the nucleus of the solitary tract, and laminae I and II of the spinal cord. This study demonstrates a significant processing of chromogranin B and indicates that chromogranin B constitutes a precursor for smaller peptides which are derived by endoproteolytic processing. It provides the neuroanatomical basis to investigate the chromogranin B molecule as a widespread component of large dense-core vesicles in the human central nervous system.

Secretoneurin, a novel neuropeptide, in the human dental pulp

Secretoneurin is a neuropeptide that is stored in and released from primary afferent neurones. By radioimmunoassay and immunohistochemistry, secretoneurin was here demonstrated in the human dental pulp and localized in varicose nerve fibres that were frequently associated with blood vessels. No significant correlation was found between the levels of immunoreactive secretoneurin and immunoreactive calcitonin-gene related peptide. The results suggest that primary afferent neurones of the human dental pulp contain secretoneurin, which may influence local inflammatory responses if it is released together with other neuropeptides.

Secretoneurin-like immunoreactivity in rat sympathetic, enteric and sensory ganglia

Distribution of secretoneurin-like immunoreactivity (SN-LI) was studied in the rat sympathetic ganglia/adrenal gland, enteric and sensory ganglia by immunohistochemical methods. SN-LI nerve fibers formed basket-like terminals surrounding many of the postganglionic neurons of the superior cervical, stellate, paravertebral chain ganglia, coeliac/superior mesenteric and inferior mesenteric ganglia. Postganglionic neurons of the superior cervical and other sympathetic ganglia exhibited low-to-moderate levels of SN-LI. In all these sympathetic ganglia, clusters of small diameter (< 10 microm) cells, which may correspond to the small intensely fluorescent (SIF) cells, were found to be intensely labeled. Surgical sectioning or ligation of the cervical sympathetic trunk for 7-10 days resulted in a nearly total loss of SN-LI fibers in the superior cervical ganglia, whereas immunoreactivity in the postganglionic neurons and small diameter cells remained essentially unchanged. In the thoracolumbar and sacral segments of the spinal cord, SN-LI nerve fibers were detected in the superficial layers of the dorsal horn as well as in the intermediolateral cell column (ILp). Occasionally, SN-LI somata were noted in the ILp. SN-LI nerve fibers formed a delicate plexus underneath the capsule of the adrenal gland, some of which traversed the adrenal cortex and reached the adrenal medulla. While heavily invested with SN-LI nerve terminals, chromaffin cells seemed to express a low level of SN-LI. In the enteric plexus, varicose SN-LI nerve fibers and terminals formed a pericellular network around many myenteric and submucous ganglion cells; the ganglionic neurons were lightly to moderately labeled. A population of ganglion cells in the dorsal root, nodose and trigeminal ganglia exhibited moderate-to-strong SN-LI. The detection of SN-LI in nerve fibers and somata of various sympathetic ganglia, enteric plexus and adrenal medulla and in somata of the sensory ganglia implies an extensive involvement of this peptide in sympathetic, enteric and sensory signal processing.

Neurochemical compartments in the human forebrain: evidence for a high density of secretoneurin-like immunoreactivity in the extended amygdala

Secretoneurin is a 33-amino acid neuropeptide produced by endoproteolytic processing from secretogranin II, which is a member of the chromogranin/ secretogranin family. In this immunocytochemical study we investigated the localization of secretoneurin-like immunoreactivity in the human substantia innominata in relation to the ventral striatopallidal system, the bed nucleus-amygdala complex and the basal nucleus of Meynert. A high density of secretoneurin immunostaining was found in the medial part of the nucleus accumbens. All subdivisions of the bed nucleus of the stria terminalis displayed a very prominent immunostaining for secretoneurin, whereas substance P and enkephalin showed a more restricted distribution. A high concentration of secretoneurin immunoreactivity was also observed in the central and medial amygdaloid nuclei. In the lateral bed nucleus of the stria terminalis and the sublenticular substantia innominata, the appearance of secretoneurin immunoreactivity was very similar to that of enkephalin-like immunoreactivity, exhibiting mostly peridendritic and perisomatic staining. The ventral pallidum and the inner pallidal segment displayed strong secretoneurin immunostaining. Secretoneurin did not label cholinergic neurons in the basal forebrain. This study demonstrates that secretoneurin-like immunoreactivity is prominent in the bed nucleus-amygdala complex, referred to as extended amygdala. The distribution of secretoneurin-like immunoreactivity in comparison with that of other neuroanatomical markers suggests that this forebrain system is a discret compartment in the human forebrain.

Neurochemical modulation of cardiovascular control in the nucleus tractus solitarius

The central control of cardiovascular function has been keenly studied for a number of decades. Of particular interest are the homeostatic control mechanisms, such as the baroreceptor heart-rate reflex, the chemoreceptor reflex, the Bezold-Jarisch reflex and the Breuer-Hering reflex. These neurally-mediated reflexes share a common termination point for their respective centrally-projecting sensory afferents, namely the nucleus tractus solitarius (NTS). Thus, the NTS clearly plays a critical role in the integration of peripherally initiated sensory information regarding the status of blood pressure, heart rate and respiratory function. Many endogenous neurochemicals, from simple amino acids through biogenic amines to complex peptides have the ability to modulate blood pressure and heart rate at the level of the NTS. This review will attempt to collate the current knowledge regarding the roles of neuromodulators in the NTS, the receptor types involved in mediating observed responses and the degree of importance of such neurochemicals in the tonic regulation of the cardiovascular system. The neural pathway that controls the baroreceptor heart-rate reflex will be the main focus of attention, including discussion of the identity of the neurotransmitter(s) thought to act at baroafferent terminals within the NTS. In addition, this review will provide a timely update on the use of recently developed molecular biological techniques that have been employed in the study of the NTS, complementing more classical research.

Distribution of secretoneurin-like immunoreactivity in comparison with that of substance P in the human spinal cord

Secretoneurin (SN), a neuropeptide of 33 amino acids, was determined in comparison with substance P (SP) by immunocytochemistry in normal human spinal cord. The density of secretoneurin-like immunoreactivity (SN-IR) was high in the superficial dorsal horn and in the lateral column of autonomic arcs. The ventral horn displayed low to moderate density of SN-IR and prominently outlined motoneurons. The congruent distribution of SN and SP to the termination of primary afferents may indicate that SN is involved in modulation of pain.