Neuropeptide Y, enkephalin and noradrenaline coexist in sympathetic neurons innervating the bovine spleen. Biochemical and immunohistochemical evidence

Neural control of the spleen as an effector of immune responses to inflammation: mechanisms and treatments

Immune system responses are a vital defense mechanism against pathogens. Inflammatory mediators finely regulate complex inflammatory responses from initiation to resolution. However, in certain conditions, the inflammation is initiated and amplified, but not resolved. Understanding the biological mechanisms underlying the regulation of the immune response is critical for developing therapeutic alternatives, including pharmaceuticals and bioelectronic tools. The spleen is an important immune effector organ since it orchestrates innate and adaptive immune responses such as pathogen clearance, cytokine production, and differentiation of cells, therefore playing a modulatory role that balances pro- and anti-inflammatory responses. However, modulation of splenic immune activity is a largely unexplored potential therapeutic tool that could be used for the treatment of inflammatory and life-threatening conditions. This review discusses some of the mechanisms controlling neuroimmune communication and the brain-spleen axis.

Immunohistochemical analysis of the mouse celiac ganglion: An integrative relay station of the peripheral nervous system

Celiac ganglia are important sites of signal integration and transduction. Their complex neurochemical anatomy has been studied extensively in guinea pigs but not in mice. The goal of this study was to provide detailed neurochemical characterization of mouse celiac ganglia and noradrenergic nerves in two target tissues, spleen and stomach. A vast majority of mouse celiac neurons express a noradrenergic phenotype, which includes tyrosine hydroxylase (TH), vesicular monoamine transporter 2, and the norepinephrine transporter. Over 80% of these neuron also express neuropeptide Y (NPY), and this coexpression is maintained by dissociated neurons in culture. Likewise, TH and NPY were colocalized in noradrenergic nerves throughout the spleen and in stomach blood vessels. Somatostatin was not detected in principal neurons but did occur in small, TH-negative cells presumed to be interneurons and in a few varicose nerve fibers. Cholinergic nerves provided the most abundant input to the ganglia, and small percentages of these also contained nitric oxide synthase or vasoactive intestinal polypeptide. A low-to-moderate density of nerves also stained separately for the latter markers. Additionally, nerve bundles and varicose nerve fibers containing the sensory neuropeptides, calcitonin gene-related polypeptide, and substance P, occurred at variable density throughout the ganglia. Collectively, these findings demonstrate that principal neurons of mouse celiac ganglia have less neurochemical diversity than reported for guinea pig and other species but receive input from nerves expressing an array of neurochemical markers. This profile suggests celiac neurons integrate input from many sources to influence target tissues by releasing primarily norepinephrine and NPY.

Nerve growth factor facilitates perivascular innervation in neovasculatures of mice

It is well known that blood vessels including arterioles have a perivascular innervation. It is also widely accepted that perivascular nerves maintain vascular tone and regulate blood flow. Although there are currently prevailing opinions, unified views on the innervation of microcirculation in any organs have not been established. The present study was designed to investigate whether there are perivascular nerves innervated in microvessels and neovessels. Furthermore, we examined whether nerve growth factor (NGF) can exert a promotional effect on perivascular nerve innervation in neovessels of Matrigel plugs. A Matrigel was subcutaneously implanted in mouse. The presence of perivascular nerves in Matrigel on Day 7-21 after the implantation was immunohistochemically studied. NGF or saline was subcutaneously administered by an osmotic mini-pump for a period of 3-14 days. The immunostaining of neovasculatures in Matrigel showed the presence of perivascular nerves on Day 21 after Matrigel injection. Perivascular nerve innervation of neovessels within Matrigel implanted in NGF-treated mice was observed in Day 17 after Matrigel implantation. However, NGF treatment did not increase numbers of neovessels in Matrigel. These results suggest that perivascular nerves innervate neovessels as neovasculatures mature and that NGF accelerates the innervation of perivascular nerves in neovessels.

Neurotransmitter Switching? No Surprise

Among the many forms of brain plasticity, changes in synaptic strength and changes in synapse number are particularly prominent. However, evidence for neurotransmitter respecification or switching has been accumulating steadily, both in the developing nervous system and in the adult brain, with observations of transmitter addition, loss, or replacement of one transmitter with another. Natural stimuli can drive these changes in transmitter identity, with matching changes in postsynaptic transmitter receptors. Strikingly, they often convert the synapse from excitatory to inhibitory or vice versa, providing a basis for changes in behavior in those cases in which it has been examined. Progress has been made in identifying the factors that induce transmitter switching and in understanding the molecular mechanisms by which it is achieved. There are many intriguing questions to be addressed.

The B cell, arthritis, and the sympathetic nervous system

The pathogenesis of rheumatoid arthritis (RA) is still an unresolved puzzle. Many factors and inflammatory cells play together to initiate a chronic inflammatory process that, if untreated, leads to complete destruction of involved joints. Recent success in treating severe forms of RA with B cell-depleting or -modifying agents revived the concept that the B cell might play a pivotal role in the pathogenesis of some forms of arthritis. However, the rather unspecific treatment approach affecting all B cells, no matter if autoreactive or not, leads to potential harmful side-effects, e.g., severe infections. Therefore, finding regulatory systems that more specifically modulate B cell function is important to improve current treatment options. One such regulatory system is the sympathetic nervous system (SNS), which is known to modulate B cell function, but also profoundly influences arthritis development and severity. This review develops the hypothesis that the SNS via modulating B cell function influences arthritis development and progression. For this purpose data is presented that shows (1) how the SNS influences B cell function, (2) how the SNS influences arthritis development and severity, and (3) how B cells are involved in the disease process with an emphasis on possible contact points for SNS neuromodulation.

Sympathetic modulation of immunity: relevance to disease

Optimal host defense against pathogens requires cross-talk between the nervous and immune systems. This paper reviews sympathetic-immune interaction, one major communication pathway, and its importance for health and disease. Sympathetic innervation of primary and secondary immune organs is described, as well as evidence for neurotransmission with cells of the immune system as targets. Most research thus far has focused on neural-immune modulation in secondary lymphoid organs, has revealed complex sympathetic modulation resulting in both potentiation and inhibition of immune functions. SNS-immune interaction may enhance immune readiness during disease- or injury-induced 'fight' responses. Research also indicate that dysregulation of the SNS can significantly affect the progression of immune-mediated diseases. However, a better understanding of neural-immune interactions is needed to develop strategies for treatment of immune-mediated diseases that are designed to return homeostasis and restore normal functioning neural-immune networks.

Estrogen up-regulates neuropeptide Y Y1 receptor expression in a human breast cancer cell line

Normal breast tissue mainly expresses the neuropeptide Y (NPY) Y2 receptor whereas primary human breast carcinomas express the Y1 receptor (Y1R) subtype. We hypothesized that activation of estrogen signaling systems plays a role in the induction of Y1R. To investigate this possibility, we used estrogen receptor-positive (ER+) human breast carcinoma cell line, MCF-7, and examined the effect of estrogen on Y1R gene expression and its signaling pathways. Saturation binding studies revealed that MCF-7 cells express high-affinity NPY receptor. NPY inhibited forskolin-stimulated adenosine 3'5'-cyclic monophosphate (cAMP) accumulation and mobilized intracellular Ca(2+) in MCF-7 cells. Chronic estrogen treatment enhanced NPY-mediated inhibition of cAMP accumulation by 4-fold and caused a significant increase in Y1R mRNA expression through ERalpha. Similarly, estrogen increased Y1R mRNA expression in T-47D (ER+) but not in MDA-MB231 or MDA-MB468 (ER-) cell lines. Cycloheximide decreased basal Y1R mRNA expression; however, it did not affect its increase by estrogen. Moreover, estrogen treatment of MCF-7 cells did not increase Y1R mRNA stability. The up-regulation of Y1R expression by estrogen is prevented by hydroxyurea but not by nocodazole or IB-MECA (cell cycle inhibitors). Lastly, NPY inhibited estrogen-induced cell proliferation through Y1R. In conclusion, MCF-7 cells express a functional Y1R coupled to both Ca(2+) and cAMP pathways. Estrogen up-regulates Y1R expression through ERalpha. This effect is independent of increased Y1R mRNA stability or new protein synthesis, and likely occurs during S phase completion of the cell cycle. Estrogen plays an important role in the up-regulation of Y1R, which in turn regulates estrogen-induced cell proliferation in breast cancer cells.

Innervation and functional changes in mesenteric perivascular calcitonin gene-related peptide- and neuropeptide Y-containing nerves following topical phenol treatment

We have previously shown that age-related reduction of innervation and function in mesenteric perivascular calcitonin gene-related peptide-containing vasodilator nerves takes place in spontaneously hypertensive rats. The present study was performed to investigate innervation and functional changes in perivascular calcitonin gene-related peptide- and adrenergic neuropeptide Y-containing nerves after topical treatment with phenol, which damages nerve fibers, around the rat superior mesenteric artery. Under pentobarbital-Na anesthesia, 8-week-old Wistar rats underwent in vivo topical application of phenol (10% phenol in 90% ethanol) or saline (sham rats) to the superior mesenteric artery proximal to the bifurcation of the abdominal aorta. After the treatment, the animals were subjected to immunohistochemistry of the 3rd branch of small arteries proximal to the intestine and to vascular responsiveness testing on day 3 through day 14. The innervation levels of calcitonin gene-related peptide-like immunoreactivity containing fibers and neuropeptide Y-like immunoreactivity containing fibers were markedly reduced on day 3 to day 14 and on day 5 to day 14 after the treatment, compared with those in sham-operated rats, respectively. In perfused mesenteric vascular beds isolated from phenol-treated rats, adrenergic nerve-mediated vasoconstriction and calcitonin gene-related peptide nerve-mediated vasodilation in response to periarterial nerve stimulation (2-12 Hz) were significantly decreased on day 3 and day 7. Neurogenic release of norepinephrine in phenol-treated rats on day 7 was significantly smaller that that in sham-operated rats. Nerve growth factor content in the mesenteric arteries of phenol-treated rats was significantly lower than that in sham-operated rats. Administration of nerve growth factor using osmotic mini-pumps for 7 days after the phenol treatment resulted in greater density of calcitonin gene-related peptide- and neuropeptide Y-like immunoreactivity fibers than in phenol-treated rats and restored decreased vascular responses to periarterial nerve stimulation. These results suggest that topical phenol-treatment of the mesenteric artery effectively induces functional denervation of perivascular nerves, which can be prevented or reversed by nerve growth factor treatment.

Separate modulation of neuropeptide Y1 receptor on purinergic and on adrenergic neuroeffector transmission in canine splenic artery

Our previous study demonstrated that the vasoconstrictor responses to trains of up to 10 pulses at 1 Hz of stimulation appeared to be purinergic monophasic, whereas a longer train of 30 pulses induced a biphasic vasoconstriction consisting of an initial, transient purinergic constriction followed by a prolonged adrenergic response. Neuropeptide Y (NPY) at doses of 0.01 and 0.1 microM produced a dose-dependent inhibition on the monophasic and biphasic vasoconstrictor responses to nerve stimulation. The treatment with Leu31 Pro34 neuropeptide Y (LP-NPY) (0.03 microM) did not affect the monophasic responses to short pulse trains of stimulation. However, LP-NPY markedly potentiated the second phase response to 30 pulse trains of stimulation, although it did not modify the first one. The LP-NPY-induced potentiation was abolished by BIBP 3226 (1 microM), a selective NPY Y1 receptor antagonist. The results indicate that the activation of NPY Y1 receptors may enhance the prolonged adrenergic vasoconstriction but not the transient purinergic response in the canine splenic artery.

Postganglionic, direct axo-axonal contacts on the splenic nerve

The splenic nerve is made up almost exclusively of adrenergic fibers. Consequently it was used as a model system in the study of autonomic sympathetic neurotransmission. The splenic nerve regulates the vasoconstriction and volume reduction of the spleen. Brain-immune interactions via modulation of the splenic nerve activity may regulate peripheral cellular immunity. An inhibition of noradrenaline release by alpha(2)-adrenoceptor activation has been reported. As we were interested in a structurally detailed distribution of synaptophysin, immunocytochemical methods were applied to splenic nerve axons. In 1 microm plastic sections a network of synaptophysin-positive varicosities could be observed all along the splenic nerve. They were also positive for dopamine-beta-hydroxylase and cytochrome b561. At the ultrastructural level the varicosities were seen to establish direct contact with the splenic axons. In normal morphology the varicosities revealed small synaptic vesicles and several dense granules. It is demonstrated that a network of direct symmetric contacts of adrenergic nature is present all along the nerve. These terminals may have an inhibitory effect on the splenic nerve activity via axonal receptors. This finding opens new perspectives for the study of the splenic nerve in general and more particularly for its role in the regulation of peripheral cellular immunity.

Pathway specific expression of neuropeptides and autonomic control of the vasculature

In this article, we review the immunohistochemical evidence for the pathway-specific expression of co-existing neuropeptides in autonomic vasomotor neurons, and examine the functional significance of these expression patterns for the autonomic regulation of the vasculature. Most final motor neurons in autonomic vasomotor pathways contain neuropeptides in addition to non-peptide co-transmitters such as catecholamines, acetylcholine and nitric oxide. Neuropeptides also occur in preganglionic vasomotor neurons. The precise combinations of neuropeptides expressed by neurons in vasomotor pathways vary with species, vascular bed, and the level within the vascular bed. This applies to both vasoconstrictor and vasodilator pathways. There is a similar degree of variation in the expression of neuropeptide receptors in the vasculature. Consequently, the contributions of different peptides to autonomic vasomotor control are closely matched to the functional requirements of specific vascular beds. This arrangement allows for a high degree of precision in vascular control in normal conditions and has the potential for considerable plasticity under pathophysiological conditions.

Effects of a selective neuropeptide Y Y(1) receptor antagonist BIBP 3226 on double peaked vasoconstrictor responses to periarterial nerve stimulation in canine splenic arteries

The periarterial electrical nerve stimulation (30 s trains of pulses at a frequency of 1, 4 or 10 Hz) induced a double peaked vasoconstriction consisting of an initial transient constriction (first peak) followed by a prolonged response (second peak) in the isolated, perfused canine splenic artery. At low frequencies (1 and 4 Hz), a neuropeptide Y (NPY) Y(1) receptor antagonist BIBP 3226 (0.1-1 microM) produced a dose-dependent inhibitory effect on the second peak, but did not modify the first peak. At a high frequency (10 Hz), 1 microM BIBP 3226 induced a slight, but significant inhibition on both the first and second peaked responses. At a low frequency (1 Hz), the first peak was not influenced by blockade of alpha(1)-adrenoceptors or NPY Y(1) receptors with prazosin (0.1 microM) or BIBP 3226 (1 microM), respectively, but abolished by P2X receptor desensitization with alpha,beta-methylene ATP (alphabeta-m ATP, 1 microM). At a high frequency (10 Hz), the first peak was mostly inhibited by alphabeta-m ATP and partially by prazosin and BIBP 3226. On the other hand, the second peak at a low frequency was largely decreased by BIBP 3226 and partially by prazosin and alphabeta-m ATP, whereas at a high frequency, it was largely attenuated by prazosin and partially by alphabeta-m ATP and BIBP 3226. The results suggest that at a low frequency, the firstly transient constriction of double peaked responses is mainly induced via an activation of P2X-receptors, whereas at a high frequency, it is mostly mediated by the P2X-receptors, and partially by alpha(1)-receptors and NPY Y(1)-receptors. The secondary prolonged vasoconstriction at frequencies used is predominantly mediated via both alpha(1)-receptor and NPY Y(1) receptor activations, and in part by P2X-receptors. Furthermore, an activation of NPY Y(1) receptors may play an important role in evoking the prolonged vasoconstrictor response to longer pulse trains of stimulation at a low frequency, whereas an alpha(1)-adrenoceptor activation exerts a main vasomotor effect for the prolonged response at a high frequency.

A qualitative and quantitative study on the enkephalinergic innervation of the pig gastrointestinal tract

Enkephalins are involved in neural control of digestive functions such as motility, secretion, and absorption. To better understand their role in pigs, we analyzed the qualitative and quantitative distribution of enkephalin immunoreactivity (ENK-IR) in components of the intestinal wall from the esophagus to the anal sphincter. Immunohistochemical labelings were analyzed using conventional fluorescence and confocal microscopy. ENK-IR was compared with the synaptophysin immunoreactivity (SYN-IR). The results show that maximal ENK-IR levels in the entire digestive tract are reached in the myenteric plexuses and, to a lesser extent, in the external submucous plexus and the circular muscle layer. In the longitudinal muscle layer, ENK-IR was present in the esophagus, stomach, rectum, and anal sphincter, whereas it was absent from the duodenum to the distal colon. In the ENK-IR plexuses and muscle layers, more than 60% of the nerve fibers identified by SYN-IR expressed ENK-IR. No ENK-IR was observed in the internal submucous plexus and the mucosa; the latter was found to contain ENK-IR endocrine cells. These results strongly suggest that, in pigs, enkephalins play a major role in the regulatory mechanisms that underlie the neural control of digestive motility.

Adenosine 5'-triphosphate and neuropeptide Y are co-transmitters in conjunction with noradrenaline in the human saphenous vein

1. Human saphenous veins were used to assess the cooperative participation of adenosine 5-triphosphate (ATP), neuropeptide Y (NPY), and noradrenaline (NA) in the vasomotor responses elicited following electrical depolarization of the perivascular nerve terminals. Rings from recently dissected human biopsies were mounted to record isometric muscular contractions; the motor activity elicited in the circular muscle layer following electrical depolarization (2.5-20 Hz, 50 V, 0.5 msec) were recorded. 2. Incubation of the biopsies with either 100 nM tetrodotoxin (TTX) or 1 microM guanethidine abolished the vasomotor response elicited by electrical nerve depolarization. The independent application of either ATP or NA to vein rings induced concentration-dependent contractions. 3. Tissue incubation with 30 microM suramin or 10 nM prazosin produced 10 fold rightward displacements of the alpha,beta-methylene ATP and NA concentration-response curves respectively. NPY contracted a limited number of biopsies, the vasoconstriction elicited was completely blocked by 1 microM BIBP 3226. A 5 min incubation of the biopsies with 10-100 nM NPY synergized, in a concentration-dependent fashion, both the ATP and the ATP analogue-induced contractions. Likewise, tissue preincubation with 10 nM NPY potentiated the vasomotor responses evoked with 20-60 nM NA. 4. Neither suramin, BIBP 3226, nor prazosin was individually able to significantly modify the derived frequency-tension curves. In contrast, the co-application of 30 microM suramin and 10 nM prazosin or 30 microM suramin and 1 microM BIBP 3226, elicited a significant (P<0.01) downward displacement of the respective frequency-tension curves. 5. The simultaneous application of the three antagonists-30 microM suramin, 1 microM BIBP 3226 and 10 nM prazosin-caused a significantly greater displacement of the frequency-tension curve than that achieved in experiments using two of these antagonists. 6. Electrically-evoked vasomotor activity is blocked to a larger extent by tissue incubation with 2.5 microM chloroethylclonidine and 30 microM suramin rather than with 10 nM 5 methyl urapidil and 30 microM suramin. As a result, the alpha1-adrenoceptor involved in the vasomotor activity has tentatively been associated with the alpha1B adrenoceptor family subtype. 7. Results support the physiological role of ATP in sympathetic neurotransmission. The present results are consistent with the working hypothesis that human sympathetic vasomotor reflexes involve the coordinated motor action of ATP, NPY, and NA acting on vascular smooth muscle cells. The present results support the concept of sympathetic co-transmission in the human saphenous vein.

Differential ultrastructural distribution of synapsin and synaptophysin proximal to a ligation in bovine splenic nerve

Synaptophysin and synapsin, closely correlated on synaptic vesicles in terminals, may show a differential distribution at synapse formation and maturation. In order to disclose the fine structural details of these differences, synapsin and synaptophysin distribution was studied by immunocytochemistry on ligated bovine splenic axons in vitro and compared with terminals in the vas deferens. In the synaptic differentiations taking place proximally synapsin could only be detected on the accumulating elements of the axonal reticulum. Large dense granules and clusters of small synaptic vesicles were negative. Synaptophysin was restricted to these clusters. In the vas deferens, co-localization of synapsin and synaptophysin could be seen on small vesicles. From their formation small synaptic vesicles carry synaptophysin. Synapsin may be involved in the dynamic membrane changes taking place at the ligation. At a functional terminal, synapsin shifts to small synaptic vesicles.

Distribution of enkephalin-like immunoreactivity in the cat digestive tract

Immunohistochemical investigations were carried out to determine the pattern of distribution of methionine- and leucine-enkephalin-like materials in the cat pylorus, duodenum, ileum and proximal and distal colon. The present results indicate that leucine-enkephalin-like materials are less densely distributed than methionine-enkephalin-like materials, but that the two patterns of distribution show some similarities. Considerable regional differences exist however in the distribution of these enkephalin-like materials in the muscular layers. In the duodenum, ileum and proximal colon, the immunoreactivity was mainly confined to the myenteric plexus and the circular muscle layer, where it was present in nerve cell bodies and in numerous fibres. In the longitudinal muscle and submucous layers, a few immunoreactive fibres were observed which sometimes surrounded blood vessels. In the pylorus and the distal colon, however, numerous immunoreactive fibres were observed in the longitudinal and circular muscle layers; the immunoreactivity was detected in the cell bodies of numerous myenteric plexus neurons but those of only a few submucous plexus neurons. In addition, the pylorus tissues contained immunoreactive plexi which were localized either within the longitudinal muscle or between the serosa and the longitudinal muscle layer. These plexi were connected to the myenteric plexus by immunoreactive nerve strands. In all the small intestinal segments studied, numerous immunoreactive varicosities were present in the deep muscular plexus, in the inner part of the circular muscle layer. Our results suggest that in cats, the nervous control of external muscular layers mediated by enkephalins shows regional differences. In the pylorus and the distal colon, it involves both the longitudinal and circular muscle layers, whereas in other intestinal segments, only the circular muscle layer is involved.

Coronary vasoconstrictive effects of neuropeptide Y and their modulation by the ATP-sensitive potassium channel in anesthetized dogs

OBJECTIVES

This study examined the coronary vasoconstrictive action of endogenous neuropeptide Y (NPY) during sympathetic nerve stimulation and its modulation by the adenosine triphosphate (ATP)-sensitive potassium (KATP) channel in vivo.

BACKGROUND

Exogenous NPY was characterized by its potent vasoconstrictive effect. However, endogenous NPY has failed to show any vasoconstrictive activity in vivo.

METHODS

We studied 70 anesthetized dogs with vagotomy under beta-adrenergic blockade. Ansae subclaviae stimulation and intracoronary administration of the neurotransmitters (NPY and norepinephrine) were done with or without alpha-adrenergic blockade, NPY antagonist BIBP3226 or KATP channel acting agents. We measured coronary vascular resistance (CVR) and the neurotransmitter levels in systemic arteries and the great cardiac vein, and the amount of overflow (venoarterial difference times myocardial blood flow).

RESULTS

During nerve stimulation, NPY levels correlated significantly with CVR at the highest r value (r = 0.850, p < 0.0001) obtained for the venous level under alpha-blockade, but norepinephrine showed no correlation. Treatment with BIBP3226 abolished the correlation between NPY level and CVR under alpha-blockade. Without alpha-blockade, norepinephrine levels correlated significantly with CVR; however, NPY showed no correlation. The amount of NPY overflow during the stimulation was nearly 1,000-fold lower than norepinephrine overflow. Exogenous NPY had a 100-fold more potent coronary vasoconstrictive action than that of norepinephrine. The KATP channel antagonist glibenclamide enhanced vasoconstriction of NPY, and the agonist pinacidil suppressed it with a predominant effect in the subepicardial region.

CONCLUSIONS

During sympathetic nerve stimulation, the vasoconstrictive actions of NPY are masked by norepinephrine under intact alpha-adrenoceptor conditions, manifest during alpha-blockade and modulated by KATP channel activity.

Ultralow concentrations of proenkephalin and [met5]-enkephalin differentially affect IgM and IgG production by B cells

Resting mouse splenic B cells were activated with lipopolysaccharide/dextran sulfate (LPS/DxS) to measure both B cell proliferation and IgM/IgG isotype production when increasing concentrations of [Met5]-enkephalin (MENK) and proenkephalin (PENK) (10-16 to 10(-8) M) were added at increasing times after B cell activation (0, 3, 6, or 24 h). Results show that proliferation was not affected by either peptide, but that IgM, IgG3 and IgG2a production were inhibited in a concentration- and time-dependent manner by MENK. IgG1 production was unaffected by MENK. In contrast, PENK induced no change in the production of Ig isotypes at any time point of addition, with the exception of IgG1 and IgG2a that were enhanced when PENK was added 6 h after cell activation. In the absence of LPS/DxS activation, no change in the level of any Ig isotype was induced by either peptide.

Ultrastructural evidence for a separate, small synaptic vesicle (SSV) pathway in ligated bovine splenic nerves, incubated in vitro

In sympathetic nerves the tubules of the axonal reticulum make up the immature elements of the neurosecretory apparatus. The formation of the mature large dense granules occurs via a less dense tubular intermediate, representing the maturing part. At a terminal small synaptophysin-positive vesicles are found intermingled with the dense granules. The biogenesis of these clear, small synaptic vesicles and their relationship with dense granules remains to be determined. In search for the small synaptic vesicles we undertook a careful ultrastructural examination of the axons proximal to a ligation in bovine splenic nerve incubated in vitro for 3 h. The distended axons were crowded with tubules, granulo-tubular elements and dense granules. Occasionally homogeneous clusters of small, uniform vesicles were detected. They were shown to be positive for synaptophysin and were negative for dopamine-beta-hydroxylase, a marker for the granular pathway. The clusters of small vesicles could be found in close spatial relationship with the maturing and mature elements of granular secretion. Our findings argue for the presence of two separate neurosecretory pathways in sympathetic nerves and favour the idea that both small synaptic vesicles and dense granules are a differentiation product of the axonal reticulum. This configuration can explain the biogenesis of small synaptic vesicles and dense granules both in the cell body and at the nerve terminal.

Peptidergic transmission: from morphological correlates to functional implications

Like non-peptidergic transmitters, neuropeptides and their receptors display a wide distribution in specific cell types of the nervous system. The peptides are synthesized, typically as part of a larger precursor molecule, on the rough endoplasmic reticulum in the cell body. In the trans-Golgi network, they are sorted to the regulated secretory pathway, packaged into so-called large dense-core vesicles, and concentrated. Large dense-core vesicles are preferentially located at sites distant from active zones of synapses. Exocytosis may occur not only at synaptic specializations in axonal terminals but frequently also at nonsynaptic release sites throughout the neuron. Large dense-core vesicles are distinguished from small, clear synaptic vesicles, which contain "classical' transmitters, by their morphological appearance and, partially, their biochemical composition, the mode of stimulation required for release, the type of calcium channels involved in the exocytotic process, and the time course of recovery after stimulation. The frequently observed "diffuse' release of neuropeptides and their occurrence also in areas distant to release sites is paralleled by the existence of pronounced peptide-peptide receptor mismatches found at the light microscopic and ultrastructural level. Coexistence of neuropeptides with other peptidergic and non-peptidergic substances within the same neuron or even within the same vesicle has been established for numerous neuronal systems. In addition to exerting excitatory and inhibitory transmitter-like effects and modulating the release of other neuroactive substances in the nervous system, several neuropeptides are involved in the regulation of neuronal development.

Peptides as neurotransmitters in vascular autonomic neurons

1. Neuropeptides are present in the majority of autonomic neurons projecting to blood vessels, where they are co-localized with non-peptide transmitters and sometimes with other peptides. 2. Neuropeptides are released from vasoconstrictor and vasodilator nerve terminals after high frequency stimulation ( > 2-5Hz) with trains of impulses. 3. Neuropeptides can have potent post-synaptic effects on vascular tone, but often these effects are restricted to selected regions of the vasculature. 4. Post-synaptic effects of neuropeptides tend to be more slowly-developing and more long-lasting than those of non-peptide transmitters. 5. Autonomic vasoconstrictor and vasodilator responses often have multiple phases, with the faster phases being mediated by non-peptide transmitters and the slower phases medicated predominantly by one or more neuropeptides. 6. Some neuropeptides do not seem to have post-synaptic effects in a particular vascular bed, but can have presynaptic actions on neurotransmitter release. 7. Neuropeptides form an important component of the repertoire of neurotransmitters used by vascular autonomic neurons to regulate regional blood flow in response to a range of physiological stimuli.

Existence and co-existence of vasoactive substances in nerve fibres supplying the abdomino-pelvic arterial tree of the female pig and cow

The occurrence and co-localization of several presumed vasoactive neuropeptides, serotonin, and catecholamine-synthesising enzymes--tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (D beta H) and phenylethanolamine-N-methyltransferase (PNMT)--were investigated in perivascular nerves supplying the systemic and distributing arteries of the abdomino-pelvic arterial tree of the female pig and certain arteries supplying female reproductive organs in the cow. As revealed by single immunofluorescence, perivascular axons immunoreactive for TH, D beta H, neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP) and Leu-enkephalin (LENK) occurred in both species examined, whereas galanin-immunoreactive (GAL-IR) nerve fibres were found exclusively in the pig. PNMT-, serotonin-, dynorphin A-, alpha-neoendorphin-, bombesin- or cholecystokinin-IR nerve terminals were not observed. The following classes of perivascular nerve fibres might be distinguished in the present study: 1) noradrenergic (i.e. TH/D beta H-IR), 2) NPY-, 3) GAL- (pig only), 4) LENK-, 5) VIP-, 6) SP-, 7) VIP/NPY-, 8) SP/CGRP-, 9) SP/GAL- (pig only), 10) SP/VIP- (cow only), 11) TH/D beta H/NPY- and 12) TH/D beta H/NPY/LENK-IR. Distinct differences in the distribution of LENK- and SP-IR axons around particular parts of the studied arterial tree in individual species were also observed. The present data indicate that the abdomino-pelvic arterial tree of the pig and cow receive perivascular nerve fibres that exhibit diverse chemical codes, and that different chemical coding of perivascular nerve fibres in individual species may depend on the target organ of the particular artery.

Pro-enkephalin opioid peptides are abundant in porcine and bovine splenic nerves, but absent from nerves of rat, mouse, hamster, and guinea-pig spleen

The opioidergic innervation of the mammalian spleen and possible species differences were investigated. Light-microscopic immunohistochemistry revealed that splenic nerves of bovine and porcine spleen, but not of rat, mouse, hamster and guinea-pig spleen contained proenkephalin-derived opioidergic innervation. Immunoreactivity to both prodynorphin and pro-opiomelanocortin was absent from splenic nerves. In bovine and porcine spleen, fibers immunoreactive for met-enkephalin, met-enkephalin-Arg-Phe, met-enkephalin-Arg-Gly-Leu, leu-enkephalin and peptide F formed perivascular plexus, traveled in trabecular connective tissue, and extended into the capsule. Spatial relationships with immune cells were apparent in the white and red pulp, excluding lymphoid follicles. Colocalization of enkephalin immunoreactivity with immunoreactivities for tyrosin hydroxylase, dopamin-beta-hydroxylase, and neuropeptide Y, but not for substance P or calcitonin gene-related peptide were found. Our results provide evidence that opioid expression in splenic innervation is strongly species-dependent and exclusively proenkephalin-derived. Colocalization with marker enzymes of noradrenergic neurons indicates a mainly postganglionic sympathetic origin of proenkephalinergic splenic innervation. Opioidergic perivascular nerves probably control the splenic blood flow. A close interrelationship of opioidergic fibers with immune cells provides the anatomical basis for direct effects of neurally released opioids on splenic immune functions.

Calcium and sodium currents evoked by action potential waveforms in rat sympathetic neurones

1. Calcium channel currents evoked by action potential waveforms were recorded from rat sympathetic neurones using the whole-cell variant of the patch-clamp technique. A voltage template was created in which the unmodified action potential (AP) was played back followed by a rectangular pulse. 2. The inhibitory effects of noradrenaline (NA) and neuropeptide Y (NPY) on the AP and rectangular pulse-evoked currents, were compared. The percentage inhibition of the Ca2+ current produced by NA and NPY was significantly greater in the case of currents evoked using AP waveforms. 3. A train of APs was applied in the voltage command (40 or 75 Hz) and the inhibition produced by NPY on the AP-evoked Ca2+ currents was examined. The inhibitory effect of NPY on the Ca2+ currents evoked by the high frequency APs did not change significantly during the train. 4. The AP falling phase was artificially prolonged and the resulting Ca2+ currents were compared. AP prolongation increased the amount of Ca2+ entering into the cell. However, the peak value of the Ca2+ current was primarily determined by the AP height. The AP plateau phase was also prolonged in defined voltage ranges. Prolongation in the positive voltage region was most effective in increasing the Ca2+ current. 5. Ion substitution studies were used to isolate Na+ and Ca2+ currents evoked by AP waveforms. The inhibitory effects of NA and oxotremorine (OXO-M) on Ca2+ currents evoked by AP waveforms were examined in the presence and absence of the Na+ current.(ABSTRACT TRUNCATED AT 250 WORDS)

An immunoelectron microscopic study of methionine-enkephalin structures in cat prevertebral ganglia

Methionine-enkephalin-like immunoreactivity was detected in presynaptic nerve fibers and SIF cells in cat prevertebral ganglia. The immunoreactive nerve fibers contained a mixture of numerous small clear vesicles and a few large vesicles; the immunoreactivity was only confined to the large vesicles. Most of the immunoreactive fibers were in apposition with non-immunoreactive neuronal profiles, without any detectable synaptic membrane specializations. The other immunoreactive fibers formed synaptic contacts mainly with non-immunostained dendrites and to a lesser extent with axons and neuronal soma. The characterization at the ultrastructural level of the enkephalin-like immunoreactive structures is discussed as regards the modalities whereby opiates may be involved in sympathetic ganglionic transmission.

Evidence against differential release of noradrenaline, neuropeptide Y, and dopamine-beta-hydroxylase from adrenergic nerves in the isolated perfused sheep spleen

The subcellular storage and release of noradrenaline (NA), dopamine-beta-hydroxylase (D beta H), and neuropeptide Y (NPY) was studied in the isolated perfused sheep spleen. Subcellular distribution studies showed a bimodal distribution for NA which was well reflected by D beta H and indicated the occurrence of two types of NA storage vesicles. The most dense, presumably large dense-cored vesicles (LDV), contain both membrane-bound and soluble D beta H; the less dense presumably corresponds to small dense-cored vesicles (SDV) and at least does not contain soluble D beta H. The distribution of NPY is extended but shows a peak only at the position of LDV, indicating that LDV contain NPY. Continuous electrical stimulation of the splenic nerve at 2 Hz, 5 Hz, 10 Hz, and 20 Hz or at 20 hz with bursts induced the release of NA, NPY, and D beta H. The ratio among these components was constant. The fractional release of D beta H and NA was comparable at all frequencies used; that of NPY was 10-20 times lower, suggesting the occurrence of a large nonreleasable NPY pool. The present data argue against a high frequency stimulation or intermittent stimulation-induced preferential release of NPY from adrenergic neurons and question the concept of frequency-dependent chemical coding of sympathetic transmission in general. The simplest interpretation of our data is that NA and NPY are released at all frequencies from a single pool. The present finding might signify that only large dense-cored vesicles are involved in the sympathetic stimulation-evoked secretion of catecholamines from adrenergic nerve terminals of the isolated sheep spleen.

Noradrenergic and peptidergic innervation of lymphoid organs in the beluga, Delphinapterus leucas: an anatomical link between the nervous and immune systems

The presence of peptidergic and noradrenergic sympathetic nerve fibers in specific compartments of both primary and secondary lymphoid organs of the rodent is well established. These nerve fibers directly contact lymphocytes and macrophages, as well as vascular and trabecular smooth muscle. We investigated the noradrenergic and neuropeptide-Y innervation of lymphoid organs in the cetacean, Delphinapterus leucas (beluga whale). The spleen, thymus, tonsil, gut-associated lymphoid tissue, and assorted lymph nodes were collected from five belugas, obtained during sanctioned hunts, and processed for catecholamine fluorescence histochemistry and for tyrosine hydroxylase and neuropeptide-Y immunocytochemistry. Innervation studies revealed fluorescent nerve fibers, tyrosine hydroxylase, and neuropeptide-Y positive nerve fibers in parenchymal lymphoid compartments, where they were closely associated with cells of the immune system, and in vascular and trabecular compartments. In lymphoid zones, tyrosine hydroxylase and neuropeptide-Y positive nerve fibers were observed in the periarteriolar lymphatic sheath and marginal zone of the spleen; in the outermost portion of the cortex, the corticomedullary zone, and medulla of the lymph nodes; in the parafollicular zones, and diffuse lymphocyte layer below the epithelium of the tonsil; in the outermost portion of some thymic lobules; and in the lamina propria of the gut. These findings are similar to those described for other mammals and substantiate an anatomical link between the nervous and immune systems in the beluga, whereby central nervous system activity may influence autonomic outflow to lymphoid organs and effect immunologic reactivity.

Ultrastructural localization of neuropeptide Y-immunoreactivity in the axonal reticulum elements, accumulating anterogradely in transected rat sciatic nerve

The detection of dopamine-beta-hydroxylase and cytochrome B561 on the membranes of the axonal reticulum demonstrated that in sympathetic neurons the different compartments of the axonal reticulum participate in the formation of neurosecretory vesicles. In the present study we tried to reveal that the components of the vesicular content are also channeled along the axonal reticulum, by examining whether neuropeptide Y could be localized in elements of the axonal reticulum. Therefore 6 h transected rat sciatic nerve was embedded in glycolmethacrylate and an immunogold labeling was performed. Counterstaining with phosphotungstic acid at low pH selectively contrasted the accumulated axonal reticulum elements and associated granules. In the non-myelinated axons gold labeling was localized on granules and on tubular and granular profiles, demonstrating the presence of neuropeptide Y in the accumulated axonal reticulum elements. This indicates that neuropeptides are indeed transported via the axonal reticulum to the nerve ending and suggests that the accumulation of large dense-cored vesicles at a block is mainly due to local new formation rather than down transport.

Changes in enkephalin immunoreactivity of sympathetic ganglia and digestive tract of the cat after splanchnic nerve ligation

The aim of the present study was to analyze changes in the enkephalin immunoreactivity of sympathetic prevertebral ganglia coeliac plexus and inferior mesenteric ganglion) and intestinal tract (myenteric plexus and external muscle layers) in cats 2 days after left thoracic splanchnic nerve ligation, using radioimmunoassay and immunohistochemical techniques. Specific polyclonal antibodies directed against methionine- and leucine-enkephalin were used. The nerve ligation led to a considerable increase in the enkephalin immunoreactivity in the cranial part of the ligated nerves. This finding confirms the presence, in the cat, of an enkephalin output originating from thoracic spinal structures which are probably enkephalin-containing preganglionic neurons. In prevertebral ganglia the nerve ligation induced a marked decrease in the enkephalin immunoreactivity, which was probably due to the interruption of thoracic enkephalin efferents projecting towards both the coeliac plexus and the inferior mesenteric ganglion. In the digestive tract, the nerve ligation depressed the methionine-enkephalin immunoreactivity only in the gastro-duodenal region, and had no effect on the ileo-colonic region. The results of the present study add to the growing evidence that the sympathetic nervous system is involved in regulating the enteric enkephalinergic innervation, which is probably involved in controlling the intestinal motility.

Modulation of the enkephalinergic phenotype of rat sympathetic neurons by hormonal and transsynaptic mechanisms

Most sympathetic neurons contain one or more neuropeptides in addition to catecholamines. Although the regulation of catecholamines has been studied extensively, comparatively little is known about the regulation of neuropeptides. Since glucocorticoids and preganglionic innervation regulate catecholaminergic properties in chromaffin cells, we examined the effects of these factors on a co-localized neuropeptide, leucine enkephalin (L-Enk), in adult rat sympathetic neurons in vivo. Lowered serum glucocorticoid levels as a consequence of bilateral adrenalectomy resulted in a reduction of ganglionic L-Enk content that was reversed by exposure of adrenalectomized animals to the synthetic glucocorticoid, dexamethasone. Surgical denervation of the SCG eliminated L-Enk-IR preganglionic fibers and caused a dramatic increase in the number of L-Enk-IR neurons. Inhibition of the enkephalinergic component of the preganglionic innervation by chronic exposure to the opiate receptor antagonist naloxone increases the number of L-Enk-IR cell bodies and total ganglionic L-Enk content. None of the experimental manipulations noticeably altered the number or distribution of NPY-IR neurons, suggesting that the effects of glucocorticoids and the innervation on ganglionic L-Enk levels were specific and not simply an alteration of the biosynthetic state of the cells. These results demonstrate that circulating glucocorticoids and the preganglionic innervation regulate L-Enk levels in sympathetic neurons. Since both glucocorticoid levels and preganglionic activity are known to be altered by stressful stimuli, acute regulation of sympathetic L-Enk levels may constitute an important component of the autonomic response to stress.

Enkephalin-containing neurons in the inferior mesenteric ganglion projecting to the distal colon of cat: evidence from combined retrograde tracing by fluorescent microspheres and immunohistochemistry

Retrograde tracing with rhodamine fluorescent microspheres combined with fluorescein immunolabelling of methionine-enkephalin showed the presence of enkephalin-like material in neurons of the inferior mesenteric ganglion (sympathetic prevertebral ganglion) projecting to the distal colon in cat. Two weeks after injecting the microspheres into the wall of the distal colon, the inferior mesenteric ganglion was dissected out and incubated for 24 hours in a colchicine-containing culture medium in order to facilitate the detection of enkephalins in the soma of ganglion neurons. It was observed that retrogradely labelled ganglion cells contained enkephalin-like immunoreactive material. These ganglion cells corresponded to enkephalin-like postganglionic neurons, the terminals of which were located inside the wall of the distal colon. These enkephalin-like neurons were numerous and scattered throughout the ganglion. Sometimes enkephalin-like immunoreactive fibers, probably originating from spinal preganglionic neurons, ran close to immunoreactive and non-immunoreactive retrogradely labelled ganglion cells. This suggests that enkephalin-like immunoreactive fibers may make synaptic connections with enkephalin-like and non-enkephalin-like postganglionic neurons projecting to the distal colon. The present study establishes for the first time the existence of an enkephalin-like postganglionic pathway to the digestive tract originating from a sympathetic prevertebral ganglion. This finding indicates that the enkephalinergic innervation of the cat digestive tract may have at least two possible sources: (i) the sympathetic prevertebral ganglia; and (ii) the enteric nervous ganglia.

Presence of a dynorphin-like peptide in a restricted subpopulation of catecholaminergic neurons in rat nucleus tractus solitarii

Immunofluorescence colocalization techniques were used to examine the extent of coexistence of the endogenous opioid peptide dynorphin with catecholamines and the related opioid peptide enkephalin within neurons of the rat medulla oblongata. Immunoreactivities for dynorphin and the catecholamine-synthesizing enzyme tyrosine hydroxylase were found to coexist within a limited subpopulation of A2 catecholamine cells, localized to the medial nucleus of the nucleus tractus solitarii. Colocalization of the two opioid peptides was found mainly within perikarya situated in the medial and ventrolateral nuclei of the nucleus tractus solitarii. Triple-labeling studies revealed only rare cases of catecholamine/dynorphin/enkephalin coexistence. These data demonstrate that dynorphin is present within a restricted subpopulation of catecholamine neurons in the dorsal medulla oblongata. In addition, the content of either of the opioids enkephalin or dynorphin appears to distinguish subsets of medullary catecholamine neurons.

Neuropeptide Y in the primate model of subarachnoid hemorrhage

The cause of cerebral vasospasm after subarachnoid hemorrhage (SAH) remains unknown. Recently, an association between the potent vasoconstricting peptide, neuropeptide Y, and delayed cerebral vasospasm after SAH has been postulated. This was based on the findings of increased neuropeptide Y levels in the cerebrospinal fluid (CSF) and plasma after SAH in animals and humans. For this study, the primate model of SAH was used to assess the possible role of neuropeptide Y in delayed vasospasm after SAH. Fifteen cynomolgus monkeys underwent placement of a clot of either whole blood or red blood cells in the subarachnoid space around the middle cerebral artery (MCA). Sequential arteriography for assessment of MCA diameter and sampling of blood and CSF for neuropeptide Y were performed: before SAH (Day 0); 7 days after SAH, when signs of delayed cerebral vasospasm peak in this model and in humans; 12 days after SAH; and 28 days after SAH. Subarachnoid hemorrhage did not evoke changes in CSF or plasma levels of neuropeptide Y. Nine monkeys had arteriographic evidence of vasospasm on Day 7, but no change in neuropeptide Y levels occurred in plasma or CSF. In addition, neuropeptide Y levels did not change, even after resolution of vasospasm on Day 12 or Day 28. Neuropeptide Y levels were substantially higher in CSF than in arterial plasma (p less than 0.003 at each interval). No correlation was found between neuropeptide Y levels in CSF and in plasma. These results do not confirm a relationship between neuropeptide Y levels in the CSF or peripheral plasma and delayed cerebral vasospasm in SAH.

Innervation of lymphoid organs and implications in development, aging, and autoimmunity

We now have substantial evidence demonstrating noradrenergic sympathetic and peptidergic innervation of both primary and secondary lymphoid organs. We have established criteria for norepinephrine, and some of the neuropeptides, as neurotransmitters, and have found changes in immune responsiveness following pharmacological manipulation of noradrenergic sympathetic or peptidergic nerves. Classic receptor binding studies have demonstrated a wide variety of target cells that possess beta-adrenoceptors and receptors for neuropeptides on cells of the immune system, including lymphocyte subsets, macrophages, accessory cells, or stromal elements. In this chapter we describe noradrenergic and peptidergic innervation of primary and secondary lymphoid organs in development, at maturation and during the normal aging process, and discuss possible functional implications of direct neural signals onto cells of the immune system at critical time points in the lifespan of an animal. Further, we examine for involvement of noradrenergic sympathetic and peptidergic innervation in the development and progression of several autoimmune disorders, including adjuvant-induced arthritis, New Zealand mice strains as a model for hemolytic anemia and lupus-like syndrome, and the experimental allergic encephalomyelitis model for multiple sclerosis.

Modulation of the immune response by tachykinins

Neuro-immunology is becoming an increasingly important discipline of immunology. This review has examined the immunomodulatory function of one group of neuropeptides, the TK, particularly SP and NKA. These peptides are localized in primary afferent nerves which have been shown to innervate several immune organs. In addition, binding sites for the TK have been demonstrated in thymus, spleen and lymph node. Several immune cell types also express neurokinin receptors including human circulating lymphocytes with binding to the Th/i class predominating, murine T and B cells, a human T lymphoblastoid cell line, human monocytes, rabbit polymorphonuclear leucocytes and guinea-pig macrophages. The apposition of nerves with immune cells and receptors for neuropeptides thus produces an environment for interaction between the nervous and immune systems. Studies in vitro and, more recently, in vivo have examined how the TK regulate immune cell responses. The TK stimulate proliferation of T cells, enhance mitogen-induced release of cytokines including IFN-gamma, TNF-alpha, IL-1 and IL-6 from mononuclear cells and macrophages, enhance immunoglobulin secretion and affect cellular chemotaxis and phagocytosis. Studies in vivo have shown a role for TK in lymphocyte recirculation of sheep lymph nodes, reversal of stress-induced thymic involution and Ig production in both rat and mouse. Many of these effects appear to be mediated via NK-2 type receptors. To date, most of the work has involved studies in vitro, but the results from these are now being validated by studies in vivo where both the immune system and neuropeptides are able to interact at many anatomical sites. The complexities of the immune and the nervous systems mean that only a small number of potential interactions has been examined. Future studies can be expected to amplify these observations, especially with respect to the understanding of inflammatory and immune diseases in humans.

Galanin and neuropeptide Y in chromaffin granules from the guinea-pig

We have examined the subcellular distribution of galanin-like immunoreactivity, neuropeptide Y-like immunoreactivity and the catecholamines noradrenaline and adrenaline in the adrenal medulla from guinea-pigs. By differential centrifugation of the adrenal medulla homogenate the neuropeptides as well as the catecholamines sedimented in a 10,000 g pellet. This pellet was resuspended and further examined in discontinuous and continuous density gradients. In the discontinuous gradient the catecholamines peaked in the heavy bottom fraction, assumed to contain chromaffin granules. Galanin-like immunoreactivity and neuropeptide Y-like immunoreactivity were also enriched in this fraction. However, both neuropeptides showed high levels of sedimentable material also in a fraction of intermediate density. In the continuous density gradient, the sum of sedimentable and soluble catecholamines showed peak values in two fractions corresponding to 1.07 and 1.47 M sucrose, respectively. The NA peak in the denser fraction was more pronounced than the corresponding A peak. Galanin-like immunoreactivity showed only one peak, in the fraction corresponding to 1.07 M sucrose. The data suggest that galanin-like immunoreactivity and neuropeptide Y-like immunoreactivity are partly stored with catecholamines in chromaffin granules. However, galanin-like immunoreactivity and neuropeptide Y-like immunoreactivity was also found in fractions lighter than those containing the bulk of the catecholamines.

Molecular anatomy of the neuro-immune connection

Light microscopic immunohistochemistry was employed to elucidate and compare the presence, distribution, and coexistence of various peptides, neuroendocrine markers and enzymes of the catecholamine pathway in nerves supplying lymphoid tissues in a variety of mammalian species. All lymphoid organs and tissues receive innervation by fibers containing dopamine-beta-hydroxylase and/or tyrosine hydroxylase, neural markers like protein gene product 9.5, synaptophysin and neurofilament and a varied spectrum of peptides. The prominent peptides were tachykinins (substance P, neurokinin A), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), and vasoactive intestinal polypeptide/peptide histidine isoleucine (VIP/PHI). Opioid innervation was variable. Double immunofluorescence revealed coexistence of tachykinins and CGRP and of tyrosine hydroxylase and NPY. A minor proportion of fibers showed coexistence of NPY and tachykinins and of VIP/PHI and tachykinins. The possible importance of the complex peptidergic innervation of lymphoid tissues in inflammation, allergy, inflammatory pain and psycho-neuro-immuno-endocrine network function is discussed. A special immunomodulatory role of the sensory neurons is suggested.

Neuropeptide-Y innervation of the rat spleen: another potential immunomodulatory neuropeptide

Neuropeptide-Y (NPY) is a 36 amino acid peptide that acts as a chemical messenger in the central and peripheral nervous systems. NPY often is found colocalized with the classical neurotransmitter norepinephrine (NE) and can potentiate the effects of this neurotransmitter postsynaptically in many systems. Using immunocytochemistry for NPY and specific lymphoid cell markers, we mapped the distribution of NPY-positive nerve fibers in the rat spleen. NPY-positive nerve fibers were present along the vasculature, trabeculae, and capsule, and also were found associated with specific lymphoid parenchymal compartments of the spleen, in close contact with lymphocytes and macrophages. These contacts were investigated further at the electron microscopic level. NPY-positive nerve terminals were found in close apposition with lymphocytes in the periarteriolar lymphatic sheath, and with lymphocytes and macrophages in the marginal zone. Previous studies have reported that postganglionic noradrenergic nerve fibers innervate specific lymphoid compartments of the rat spleen, with nerve terminals forming direct appositions with cells of the immune system. The possible colocalization of NPY and NE in these nerve fibers was investigated by chemical sympathectomy with 6-hydroxydopamine, followed by immunocytochemical labeling of NPY and tyrosine hydroxylase (TH), the rate-limiting enzyme in norepinephrine synthesis. Colocalization also was investigated by labeling for NPY with a fluorescent label, eluting the NPY, and staining for TH with diaminobenzidine as the label. These studies demonstrate that norepinephrine and NPY are colocalized in the postganglionic sympathetic nerve fibers of the rat spleen.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical localization and development of multiple kinds of neuropeptides and neuroendocrine proteins in the chick ultimobranchial gland

The ultimobranchial gland is an endocrine organ consisting of C cell groups. In chickens, the glands are richly supplied by nerve fibers immunoreactive for neurofilaments. It was found by immunocytochemical staining that C cells of chick ultimobranchial glands showed immunoreactivities for multiple kinds of neuropeptides and neuroendocrine proteins in addition to calcitonin, i.e., calcitonin gene-related peptide (CGRP), somatostatin, neurotensin, chromogranin A, and tyrosine hydroxylase. Furthermore, enkephalin-immunoreactive cells that showed long cytoplasmic processes and large cell bodies, being distinct from the C cell feature, were detected. The densities of these cells per unit area of ultimobranchial gland were assessed using computer-assisted image analysis system; calcitonin cells were 42.9 +/- 10.0%; CGRP cells 26.9 +/- 5.6%; neurotensin cells 8.6 +/- 6.9%; somatostatin cells 3.1 +/- 1.4%; chromogranin A cells 11.8 +/- 1.8%; tyrosine hydroxylase cells 10.0 +/- 5.2%; enkephalin cells 2.9 +/- 1.3%. Dense distributions of peptidergic nerve fibers were also detected in chick ultimobranchial glands. Numerous varicose fibers immunoreactive for substance P were distributed in the close vicinity to C cell clusters and blood vessels. Enkephalin-immunoreactive fibers were also prominent around C cell clusters. Galanin-, vasoactive intestinal peptide (VIP)-, and tyrosine hydroxylase-immunoreactive fibers were distributed around blood vessels only. Subsequently, the ontogeny of these neuropeptides, neuroendocrine proteins, and peptidergic innervations was examined in chickens at various developmental stages. In 10-day-old embryos, weak to moderately intense immunoreactivity for calcitonin was already present in almost all C cells. Immunoreactivities for somatostatin, CGRP, and tyrosine hydroxylase began to appear at this age. At 12 days of incubation, substance P-immunoreactive fibers were first detected in the parenchyma of ultimobranchial glands. Considerable numbers of enkephalin-immunoreactive fibers and cells were also observed. At 14 days of incubation, the largest populations of somatostatin- and enkephalin-immunoreactive cells were attained; the densities of somatostatin- and enkephalin-immunoreactive cells per unit area were 21.2 +/- 3.2% and 12.9 +/- 3.1%, respectively. Substance P-immunoreactive fibers became numerous throughout the gland at this age. Thereafter, calcitonin-, CGRP-, tyrosine hydroxylase-immunoreactive cells progressively increased in number with embryonic age, whereas somatostatin- and enkephalin-immunoreactive cells started to decrease. Chromogranin A- and neurotensin-immunoreactive cells began to appear at 16 days and 18 days of incubation, respectively. Galanin-, VIP-, and tyrosine hydroxylase-immunoreactive fibers were inconspicuous during embryonic life.

Catecholamine-synthesizing enzymes and neuropeptides in rat heart epicardial ganglia; an immunohistochemical study

The subepicardial atrial ganglia of rat hearts were examined using immunohistochemical techniques and antibodies against the catecholamine-synthetic enzymes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH), and the neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP) and met-5-enkephalin (ENK). Some of the ganglion cells present in the ganglia exhibited DBH-like immunoreactivity (LI) and NPY-LI, whilst these cells never exhibited TH-, VIP-, CGRP-, SP- or ENK-LI. Groups of small cells exhibiting an intense TH-LI, corresponding to cells referred to as catecholamine-containing cells and sometimes small intensely fluorescent cells in the literature, were observed in the ganglia. A subpopulation of these cells exhibited immunoreactivity to one of the neuropeptides tested, namelyu SP. Only a few of the cells showing TH-LI displayed DBH-LI. Nerve fibres showing SP-, CGRP-, DBH- and TH-LI were present in the ganglia; some of these fibres being closely associated with the ganglion cells or with the cells showing TH-LI. The observation provide new information on the catecholamine-synthetic enzyme/neuropeptide expression of the ganglion and catecholamine-containing cells and of the associated nerve fibres of rat heart subepicardial ganglia.

Neuropeptides, mast cells and allergy: novel mechanisms and therapeutic possibilities

Diverse neuropeptides are released by neuroendocrine and immune cells at the sites of allergic and inflammatory reactions. The neuropeptides and other neuromediators affect functions of smooth muscle, microvasculature and secretory cells, and are potent stimuli of mast cell, lymphocyte and other leucocyte contributions to such reactions. The distinctive immune sources, structures and cellular receptors for neuromediators suggest the possibility of novel pathogenetic mechanisms and levels of pharmacological intervention specific for neuroregulation of immunity and hypersensitivity.

Peptide-containing nerve fibres in guinea-pig coronary arteries: immunohistochemistry, ultrastructure and vasomotility

The peptidergic innervation of guinea-pig coronary arteries was investigated by means of immunohistochemical, ultrastructural and in vitro pharmacological techniques. A network of nerves was demonstrated in all major epicardial arteries by means of an antiserum to the neuronal marker protein gene product 9.5. The majority of nerve fibres possessed neuropeptide Y (NPY) and tyrosine hydroxylase (TH) immunoreactivity, the number and distribution of nerves immunoreactive for NPY being similar to that of nerves containing TH immunoreactivity. Numerous nerve fibres displaying immunoreactivity for substance P, neuropeptide K and calcitonin gene-related peptide (CGRP) were also found. In double-stained preparations substance P immunoreactivity was co-localized with CGRP and with neuropeptide K immunoreactivities in the same varicose nerve fibres. Ultrastructural studies revealed the presence of numerous axon varicosities at the adventitial-medial border. NPY immunoreactivity was localized in large granular vesicles in nerve varicosities which also contained numerous small granular vesicles. Large granular vesicle-containing nerves also displayed immunoreactivity for dopamine-beta-hydroxylase. With an in vitro method, the vasomotor responses to perivascular peptides were characterized in epicardial and intramyocardial arteries. In epicardial arteries neither noradrenaline nor NPY elicited a contractile response. Only in some intramyocardial arteries was an NPY-mediated contraction demonstrated. No potentiating effect of noradrenaline and NPY was observed in either epicardial or intramyocardial arterial segments. In contrast, CGRP, substance P and vasoactive intestinal peptide (VIP) all produced a concentration-dependent relaxation of both epicardial and intramyocardial arteries. These results suggest that peptide-containing nerves associated with guinea-pig coronary arteries may predominantly be involved in mediating vasodilation.

Substance P innervation of the rat thymus

Immunohistochemistry for substance P (SP) in the rat thymus revealed fine varicose neural profiles in specific regions of the thymus. Thymic SP innervation was abundant within the capsule and interlobular septa. The majority of SP+ nerve fibers within the septa were free of vascular association, although some fibers were associated with the vasculature deep within the septa. SP+ nerve fibers entered the thymic cortex from the septa and distributed among cortical thymocytes and mast cells. Along the corticomedullary junction, SP+ nerve fibers were found in association with the vasculature. The medullary region of the thymus received only a sparse innervation of SP+ fibers. In addition, SP+ nerve fibers coursed adjacent to OX-8+ cells and mast cells in the extrathymic connective tissue surrounding the thymus. The present study provides evidence that SP is present in nerve fibers in the thymus, and may be available to interact with thymocytes, mast cells, and other cells in the thymus, and affect their development and function.

Neuropeptide Y neuromodulation of sympathetic co-transmission in the guinea-pig vas deferens

1. We examined the neuromodulatory effects of neuropeptide Y (NPY) on purinergic and adrenergic co-transmission in the guinea-pig vas deferens. 2. In superfused vas deferens preparations, NPY (0.3 microM) inhibited the stimulus-evoked overflow of both ATP and [3H]-noradrenaline ([3H]-NA) at 2 Hz, but only the stimulus-evoked release of [3H]-NA at 20 Hz. 3. Postjunctionally, NPY greatly enhanced responses to alpha,beta-methylene ATP and to a lesser extent to exogenous NA. 4. Preparations stimulated in organ baths showed frequency-dependent contractions to field stimulation. NPY abolished responses to field stimulation at low frequency and a small number of pulses. At high frequency (20 Hz), NPY abolished responses elicited by 10 pulses, inhibited responses by 50% at 20 pulses and had little effect on preparations stimulated for 240 pulses. 5. Our study suggests that NPY neuromodulates co-transmission in the vas deferens by inhibiting the release of ATP and NA and that these effects predominate over the postjunctional enhancement by NPY. These results also show that the physiological effect of NPY will be determined both by the frequency at which the nerves are discharging and the duration of their firing.

Are NPY and enkephalins costored in the same noradrenergic neurons and vesicles?

Separate studies show that NPY and enkephalins are widely distributed in peripheral noradrenergic neurons. In the present study, the subcellular costorage and release in response to intense sympathetic stimulation and reserpine at near therapeutic doses (0.05 mg/kg every other day) were examined. In young pig arteries and vas deferens, enkephalin and D beta H immunofluorescence show consistent but not total overlap. Also NPY is colocalized with D beta H in many fibers but with VIP (nonnoradrenergic) in others. Ultrastructural immunogold labeling indicates that individual terminals contain large dense cored vesicles (LDVs) which store either NPY or enkephalins, even though costorage of both peptides occurs. Some LDVs costore NPY and VIP, especially in the middle cerebral artery and in the lamina propria of vas deferens. Acute CNS ischemia depletes enkephalins and norepinephrine in all tissues analyzed without parallel loss of NPY. Reserpine depletes norepinephrine 70-85% but does not deplete NPY or enkephalins. The latter is in contrast to commonly used high doses known to produce nonspecific, detergent-like effects. In fact, low doses of reserpine induce a time-dependent new synthesis and processing of NPY precursor peptides in vas deferns. Contrasting effects of reserpine on NPY and enkephalin contents, new synthesis and apparent processing, and a differential response to acute CNS ischemia were found in every tissue studied. Activation of precursor neuropeptide processing occurred immediately upon intense sympathetic stimulation in most tissues. Dual localization of NPY in noradrenergic and nonnoradrenergic fibers and differences in subcellular LDV storage help explain why enkephalin correlates better than NPY with norepinephrine loss in response to acute CNS ischemia. Furthermore, the costorage of NPY and enkephalins in distinct subpopulations of noradrenergic fibers, which varies according to tissue, is likely to be under separate CNS control.