Subcellular storage and axonal transport of neuropeptide Y (NPY) in relation to catecholamines in the cat

PC12 cells that lack synaptotagmin I exhibit loss of a subpool of small dense core vesicles

Neurons communicate by releasing neurotransmitters that are stored in intracellular vesicular compartments. PC12 cells are frequently used as a model secretory cell line that is described to have two subpools of vesicles: small clear vesicles and dense core vesicles. We measured transmitter molecules released from vesicles in NGF-differentiated PC12 cells using carbon-fiber amperometry, and relative diameters of individual vesicles using electron microscopy. Both amperometry and electron micrograph data were analyzed by statistical and machine learning methods for Gaussian mixture models. An electron microscopy size correction algorithm was used to predict and correct for observation bias of vesicle size due to tangential slices through some vesicles. Expectation maximization algorithms were used to perform maximum likelihood estimation for the Gaussian parameters of different populations of vesicles, and were shown to be better than histogram and cumulative distribution function methods for analyzing mixed populations. The Bayesian information criterion was used to determine the most likely number of vesicle subpools observed in the amperometric and electron microscopy data. From this analysis, we show that there are three major subpools, not two, of vesicles stored and released from PC12 cells. The three subpools of vesicles include small clear vesicles and two subpools of dense core vesicles, a small and a large dense core vesicle subpool. Using PC12 cells stably transfected with short-hairpin RNA targeted to synaptotagmin I, an exocytotic Ca(2+) sensor, we show that the presence and release of the small dense core vesicle subpool is dependent on synaptotagmin I. Furthermore, synaptotagmin I also plays a role in the formation and/or maintenance of the small dense core vesicle subpool in PC12 cells.

Novel expression pattern of neuropeptide Y immunoreactivity in the peripheral nervous system in a rat model of neuropathic pain

Background

Neuropeptide Y (NPY) has been implicated in the modulation of pain. Under normal conditions, NPY is found in interneurons in the dorsal horn of the spinal cord and in sympathetic postganglionic neurons but is absent from the cell bodies of sensory neurons. Following peripheral nerve injury NPY is dramatically upregulated in the sensory ganglia. How NPY expression is altered in the peripheral nervous system, distal to a site of nerve lesion, remains unknown. To address this question, NPY expression was investigated using immunohistochemistry at the level of the trigeminal ganglion, the mental nerve and in the skin of the lower lip in relation to markers of sensory and sympathetic fibers in a rat model of trigeminal neuropathic pain.

Results

At 2 and 6 weeks after chronic constriction injury (CCI) of the mental nerve, de novo expression of NPY was seen in the trigeminal ganglia, in axons in the mental nerve, and in fibers in the upper dermis of the skin. In lesioned animals, NPY immunoreactivity was expressed primarily by large diameter mental nerve sensory neurons retrogradely labelled with Fluorogold. Many axons transported this de novo NPY to the periphery as NPY-immunoreactive (IR) fibers were seen in the mental nerve both proximal and distal to the CCI. Some of these NPY-IR axons co-expressed Neurofilament 200 (NF200), a marker for myelinated sensory fibers, and occasionally colocalization was seen in their terminals in the skin. Peptidergic and non-peptidergic C fibers expressing calcitonin gene-related peptide (CGRP) or binding isolectin B4 (IB4), respectively, never expressed NPY. CCI caused a significant de novo sprouting of sympathetic fibers into the upper dermis of the skin, and most, but not all of these fibers, expressed NPY.

Conclusions

This is the first study to provide a comprehensive description of changes in NPY expression in the periphery after nerve injury. Novel expression of NPY in the skin comes mostly from sprouted sympathetic fibers. This information is fundamental in order to understand where endogenous NPY is expressed, and how it might be acting to modulate pain in the periphery.

Perivascular innervation: a multiplicity of roles in vasomotor control and myoendothelial signaling

The control of vascular resistance and tissue perfusion reflect coordinated changes in the diameter of feed arteries and the arteriolar networks they supply. Against a background of myogenic tone and metabolic demand, vasoactive signals originating from perivascular sympathetic and sensory nerves are integrated with endothelium-derived signals to produce vasodilation or vasoconstriction. PVNs release adrenergic, cholinergic, peptidergic, purinergic, and nitrergic neurotransmitters that lead to SMC contraction or relaxation via their actions on SMCs, ECs, or other PVNs. ECs release autacoids that can have opposing actions on SMCs. Respective cell layers are connected directly to each other through GJs at discrete sites via MEJs projecting through holes in the IEL. Whereas studies of intercellular communication in the vascular wall have centered on endothelium-derived signals that govern SMC relaxation, attention has increasingly focused on signaling from SMCs to ECs. Thus, via MEJs, neurotransmission from PVNs can evoke distinct responses from ECs subsequent to acting on SMCs. To integrate this emerging area of investigation in light of vasomotor control, the present review synthesizes current understanding of signaling events that originate within SMCs in response to perivascular neurotransmission in light of EC feedback. Although often ignored in studies of the resistance vasculature, PVNs are integral to blood flow control and can provide a physiological stimulus for myoendothelial communication. Greater understanding of these underlying signaling events and how they may be affected by aging and disease will provide new approaches for selective therapeutic interventions.

Titration of synaptotagmin I expression differentially regulates release of norepinephrine and neuropeptide Y

Synaptotagmin (syt) I is a Ca(2+) sensor that has been thought to trigger all vesicle secretion with similar mechanisms. However, given the calcium and stimulation requirements of small clear, and large dense core vesicles, we hypothesized that syt I expression differentially regulates vesicle release. Therefore, in this study, we generated multiple stable cell lines of PC12 cells that each had a different and stable level of syt I expression. We determined the functional effects of titrated syt I expression on transmitter release from the two vesicle types, and showed that the transmitters, norepinephrine (NE) and neuropeptide Y (NPY), each have a threshold level of syt I expression required for their release that is different for the two transmitter types. We used carbon fiber amperometry to measure release of NE from single vesicles, and found that release ranged from 50% to 100% in the syt I-targeted cells compared to release from control cells. We used an immunoassay to measure NPY release and found that NPY release was abolished in cells that had abolished syt I expression, but cell lines that expressed 50-60% of control levels of syt I exhibited NPY release levels comparable to release of NPY from control cells. Furthermore, the vesicle fusion pore exhibited a reduced open duration when syt I was abolished, but a longer open duration time for 50% syt I expression than control cells. Therefore, vesicles have a threshold for syt I that is required to control opening of the fusion pore, expansion, and full fusion to release large dense core proteins, but not for full fusion of the small molecules like NE.

Sympathetic co-transmission: the coordinated action of ATP and noradrenaline and their modulation by neuropeptide Y in human vascular neuroeffector junctions

The historical role of noradrenaline as the predominant sympathetic neurotransmitter in vascular neuroeffector junctions has matured to include ATP and the modulator action of neuropeptide Y (NPY). Numerous studies with isolated blood vessels rings demonstrate the presence of key enzymes responsible for the synthesis of ATP, noradrenaline and NPY, their co-storage, and their electrically evoked release from sympathetic perivascular nerve terminals. Functional assays coincide to demonstrate the integral role of these neurochemicals in sympathetic reflexes. In addition, the detection of the diverse receptor populations for ATP, noradrenaline and NPY in blood vessels, either in the smooth muscle, endothelial cells or nerve endings, further contribute to the notion that sympathetic vascular reflexes encompass the orchestrated action of the noradrenaline and ATP, and their modulation by NPY. The future clinical opportunities of sympathetic co-transmission in the control of human cardiovascular diseases will be highlighted.

Increase of sympathetic outflow measured by neuropeptide Y and decrease of the hypothalamic-pituitary-adrenal axis tone in patients with systemic lupus erythematosus and rheumatoid arthritis: another example of uncoupling of response systems

OBJECTIVE

To study in parallel the outflow of the sympathetic nervous system (SNS) and the hypothalamic-pituitary adrenal (HPA) axis tone in systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA).

METHODS

32 patients with SLE, 62 with RA, and 65 healthy subjects (HS) were included. To measure the tone of the HPA axis, plasma ACTH and serum cortisol were determined. Serum neuropeptide Y (NPY) was used to evaluate the sympathetic outflow.

RESULTS

Patients with SLE had increased NPY levels in comparison with HS, irrespective of prior prednisolone treatment (p<0.001). For patients with RA, only those with prednisolone treatment had increased NPY levels in comparison with HS (p = 0.016). Daily prednisolone dose correlated positively with serum NPY in RA (R(Rank) = 0.356, p = 0.039). In contrast, plasma ACTH levels were generally decreased significantly in comparison with HS in SLE with prednisolone, and in RA with/without prednisolone. Similarly, serum cortisol levels were also decreased in SLE with/without prednisolone, and in RA with prednisolone. The NPY/ACTH ratio was increased in SLE and RA, irrespective of prior prednisolone treatment. The NPY/cortisol ratio was increased in SLE with/without prednisolone, and in RA with prednisolone. Twelve weeks' anti-TNF antibody treatment with adalimumab did not decrease NPY levels in RA, irrespective of prednisolone treatment.

CONCLUSIONS

An increased outflow of the SNS was shown and a decreased tone of the HPA axis in patients with SLE and RA. Low levels of cortisol in relation to SNS neurotransmitters may be proinflammatory because cooperative anti-inflammatory coupling of the two endogenous response axes is missing.

Combinatorial code of growth factors and neuropeptides define neuroendocrine differentiation in PC12 cells

Adrenal chromaffin cells constitute one of the first cell types to have been defined as a neuroendocrine cell type. Since they produce dopamine, these cells have been proposed for the treatment of neuronal deficits in human Parkinson's disease. However, the factors involved in the development of chromaffin cells are still poorly understood. Based on recent insights from stem cell research, we decided to study the role of extracellular matrices, growth factors and neuropeptides on the neuroendocrine differentiation in a serum-free medium of PC12 cells. Employing immunohistochemistry, quantitative PCR and HPLC analysis, neuroendocrine differentiation was determined by evaluating neurite outgrowth, catecholamine biosynthesis and release as well as neuropeptide and vesicular protein mRNA expression. The combination of bFGF, NGF and PACAP could prevent the inhibition of neurite process development induced by dexamethasone in PC12 cells cultured on ECM. Whereas glucocorticoids were essential in the regulation of enzymes of catecholamine biosynthesis and metabolism, growth factors and PACAP were more efficient in inducing neuropeptide and chromogranin B expression as well as release of dopamine and 3-methoxytyramine. Therefore, in addition to glucocorticoids, chromaffin cells need a gradient of matrix, growth factors, and neuropeptides to develop the full functional phenotype of a neuroendocrine cell.

alpha2-Adrenoceptors control the release of noradrenaline but not neuropeptide Y from perivascular nerve terminals

Neuropeptide Y (NPY) and noradrenaline (NA) are co-transmitters at many sympathetic synapses, but it is not yet clear if their release is independently regulated. To address this question, we quantified the electrically evoked release of these co-transmitters from perivascular nerve terminals to the mesenteric circulation in control and drug-treated rats. 6-Hydroxydopamine reduced the tissue content and the electrically evoked release of ir-NPY and NA as well as the rise in perfusion pressure. A 0.001 mg/kg reserpine reduced the content of ir-NPY and NA, but did not modify their release nor altered the rise in perfusion pressure elicited by the electrical stimuli. However, 0.1mg/kg reserpine reduced both the content and release of NA but decreased only the content but not the release of ir-NPY; the rise in perfusion pressure was halved. Clonidine did not affect the release of ir-NPY while it lowered the outflow of NA, not altering the rise in perfusion pressure elicited by the electrical stimuli. Yohimbine, did not modify the release of ir-NPY but increased the NA outflow, it antagonized the clonidine effect. Therefore, presynaptic alpha2-adrenoceptors modulate the release of NA but not NPY, implying separate regulatory mechanisms.

Pharmacological analysis of functional neurovascular transmission in canine splenic arteries: role of neuropeptide Y

1 The effects of neuropeptide Y (NPY) upon the isolated vasculature are reviewed. 2 The vasconstrictor responses to periarterial nerve stimulation (PNS) and neurotransmission by noradrenaline (NA) and ATP are discussed and illustrated using canine isolated perfused splenic artery. 3 Modulation of the vascular responses to PNS by NPY via pre- and post-junctional NPY Y2 and Y1 receptors is discussed. 4 Evidence is presented for different alpha1-adrenoceptor subtypes mediating vasoconstriction to exogenous and endogenously released NA and their different locations in the neurovascular junction and extrajunctional regions. 5 Activation of NPY Y1-receptors potentiates sympathetic nerve activated alpha1-adrenoceptor vasoconstriction. The proposal that the postjunctional alpha1B adrenoceptor may be linked to the NPY Y1-receptor and is responsible for co-operation between sympathetic and NPYergic interactions in the vasculature is discussed.

Role of neuropeptide Y in renal sympathetic vasoconstriction: studies in normal and congestive heart failure rats

Sympathetic nerve activity, including that in the kidney, is increased in heart failure with increased plasma concentrations of norepinephrine and the vasoconstrictor cotransmitter neuropeptide Y (NPY). We examined the contribution of NPY to sympathetically mediated alterations in kidney function in normal and heart failure rats. Heart failure rats were created by left coronary ligation and myocardial infarction. In anesthetized normal rats, the NPY Y(1) receptor antagonist, H 409/22, at two doses, had no effect on heart rate, arterial pressure, or renal hemodynamic and excretory function. In conscious severe heart failure rats, high-dose H 409/22 decreased mean arterial pressure by 8 +/- 2 mm Hg but had no effect in normal and mild heart failure rats. During graded frequency renal sympathetic nerve stimulation (0 to 10 Hz), high-dose H 409/22 attenuated the decreases in renal blood flow only at 10 Hz (-36% +/- 5%, P <.05) in normal rats but did so at both 4 (-29% +/- 4%, P <.05) and 10 Hz (-33% +/- 5%, P <.05) in heart failure rats. The glomerular filtration rate, urinary flow rate, and sodium excretion responses to renal sympathetic nerve stimulation were not affected by high-dose H 409/22 in either normal or heart failure rats. NPY does not participate in the regulation of kidney function and arterial pressure in normal conscious or anesthetized rats. When sympathetic nervous system activity is increased, as in heart failure and intense renal sympathetic nerve stimulation, respectively, a small contribution of NPY to maintenance of arterial pressure and to sympathetic renal vasoconstrictor responses may be identified.

Neuropeptide Y Y1 receptors in vascular pharmacology

The existence of neurogenic mediator candidates apart from noradrenaline and acetylcholine involved in the control of vascular tone has attracted enormous attention during the past few decades. One such mediator is neuropeptide Y (NPY), which is co-localized with noradrenaline in sympathetic perivascular nerves. Stimulation of sympathetic nerves in vitro and in vivo causes non-adrenergic vasoconstriction which can be blocked by experimental manipulations that inhibit NPY mechanisms. Thus, the vasopressor response to stimulation of sympathetic nerves can be attenuated by chemical or surgical sympathectomy, treatment with reserpine or other pharmacological agents, and tachyphylaxis to NPY or by NPY antagonists. The NPY field was long plagued by a lack of specific antagonists, but with the recently developed, selective, non-peptide and stable NPY antagonists it has now become possible to study subtypes of this receptor family. For instance, it has become clear that the NPY Y1 receptor mediates most of the direct peripheral effects of NPY on vascular tone. These antagonists promise to stimulate NPY research and will likely unravel the true significance of NPY in cardiovascular control under physiological conditions as well as in pathophysiological states.

Dental innervation: functions and plasticity after peripheral injury

Oral tissues including the periodontal ligament, gingiva, and tooth pulp have a relatively dense sensory innervation and a rich vascular supply. Teeth and supporting tissues are susceptible to tissue injury and inflammation, partly due to lack of collateral blood and nerve supply and to their low compliance. This review focuses on dental nerve functions and adaptive changes in the trigeminal ganglion and tooth pulp after peripheral injuries. An overview of the peptidergic innervation of oral tissues is presented, followed by a discussion of plasticity in neuropeptide expression in trigeminal peripheral neurons after local insults to teeth and peripheral nerve injuries. The functional implications of these adaptive changes are considered, with special reference to nerve regeneration, inflammation, and hemodynamic regulation.

Evidence of systemic neuropeptide Y release after carbachol administration into the posterior hypothalamic nucleus

The unilateral microinjection of the cholinergic agonist carbachol (CCh) directly into the posterior hypothalamic nucleus (PHN) of conscious rats evokes a dose-dependent increase in mean arterial pressure (MAP). Blockade of peripheral alpha-adrenoceptors and V1-vasopressin receptors completely inhibits this response, suggesting that the increase in MAP is mediated by increases in sympathoadrenal excitation and circulating vasopressin. Combining beta-adrenoceptor blockade with alpha-adrenoceptor and V1-vasopressin receptor blockade results in the return of a pressor response. To determine if neuropeptide Y (NPY) might be responsible for this increase, the putative NPY and irreversible alpha 1-adrenoceptor antagonist benextramine was added to alpha 2- and beta-adrenoceptor and V1-vasopressin receptor blockade provided by yohimbine, propranolol, and [D(CH2)5-Tyr(Me)]AVP (AVPX), respectively. Benextramine noncompetitively inhibited the pressor response to intravenous injection of NPY and the increase in MAP evoked by CCh microinjection into adrenergic and V1-vasopressin receptor-blocked rats, whereas benextramine competitively inhibited the pressor response to angiotensin II (AII). Furthermore, the combination of losartan, the selective AT1-AII receptor antagonist that completely blocked the increase in MAP evoked by intravenous AII, and adrenergic and V1-vasopressin receptor antagonists did not attenuate the pressor response evoked by CCh microinjection into the PHN or the increase in MAP evoked by intravenous injection of NPY. These results indicate that AII was not responsible for the CCh-evoked increase in MAP in the presence of adrenergic and V1-vasopressin receptor blockade. The similarity in the antagonism of the increase in MAP evoked by intravenous NPY injection and by CCh microinjection into the PHN of adrenergic- and V1-vasopressin receptor-blocked rats suggests that NPY might be released from sympathetic neurons after activation of the sympathetic nervous system by central administration of CCh into the PHN.

Effects of adjuvant on neuropeptide-like immunoreactivity in experimentally induced temporomandibular arthritis in rats

Substance P (SP)-, neurokinin A (NKA)-, calcitonin gene-related peptide (CGRP)- and neuropeptide Y (NPY)-like immunoreactivities (-LI) were examined in cerebrospinal fluid (CSF), plasma and temporomandibular joint (TMJ) perfusates in rats 1 and 12 h after inoculation at the base of the tail (0.05 ml) or injection into the right TMJ (0.01 ml) of heat-killed Mycobacterium butyricum in paraffin oil. In the rats inoculated at the base of the tail (polyarthritic rats), there was a significant increase of CGRP-LI and NKA-LI. The changes in neuropeptide-LI were not as marked in the CSF of rats injected with adjuvant in one TMJ (monoarthritic rats) as in the polyarthritic group. Instead, the most significant changes in the monoarthritic rats were seen in the perfusates of both TMJs. The increases in SP-, NKA-, CGRP- and NPY-LI were significant for both TMJs and more pronounced than in the polyarthritic rats. The results show that inoculation of adjuvant at the base of the tail induces significant changes of neuropeptide-LI predominantly in CSF, whilst an intra-articular injection induces bilateral changes in neuropeptide-LI in joint perfusate. Therefore, two different neural mechanisms may be involved early in adjuvant-induced poly- and monoarthritis.

Ultrastructure of sympathetic axons and their structural relationship with vascular smooth muscle

This review focuses on the more recent findings of the structure of sympathetic postganglionic axons and the association of their varicose terminals with vascular smooth muscle. These studies have investigated the innervation of a wide range of vessels from different regions of the vasculature in the rat, guinea pig and rabbit and have predominantly used serial sections and computerised three-dimensional reconstructions of entire varicosities. They have shown, contrary to previous studies conducted in the 1960s and 1970s, that sympathetic axon varicosities commonly form structurally specialised neuromuscular junctions with vascular smooth muscle cells of most resistance arteries and some small veins. In addition, they have shown that most axon varicosities innervating small arterioles and small mesenteric veins form neuromuscular junctions, indicating that neurotransmitter is primarily released at such neuromuscular junctions. This review discusses the structure of sympathetic neuromuscular junctions, their development, structural diversity and distribution on vessels from different regions of the vasculature. These more recent structural findings and their possible significance for our understanding of mechanisms involved in neural transmission in blood vessels is discussed.

Prejunctional regulation of reserpine-resistant sympathetic vasoconstriction and release of neuropeptide Y in the pig

The prejunctional regulation of non-adrenergic sympathetic vasoconstriction and release of neuropeptide Y (NPY) was investigated in vivo. In reserpinized pigs (with depleted noradrenaline (NA)), it was demonstrated that brief sympathetic nerve stimulation (2 pulses of 20 Hz) of the spleen, kidney and hind limb in the presence of the alpha 2-adrenoceptor agonist UK 14,304 (1 micrograms/kg per min i.v.) evoked reproducible vasoconstrictor responses which were reduced by 40-80% in comparison to that in the absence of UK 14,304. In addition, the splenic overflow of NPY-like immunoreactivity (-LI) was reduced. After cessation of the UK 14,304 infusion all these effects were reversed by addition of the alpha 2-adrenoceptor antagonist yohimbine (0.2 mg/kg i.v.). Also the Y2 receptor agonist NPY(13-36) reduced the splenic overflow of NPY-LI. Splenic vasoconstriction per se was evoked by another Y2 receptor agonist N-acetyl[Leu28Leu31]NPY(24-36), while no vascular effects in the kidney or hind limb were observed. Both Y2 agonists displaced [125I]NPY binding to splenic membranes with higher potency than the Y1-receptor agonist [Leu31Pro34]NPY(1-36). No evidence was obtained for angiotensin II mechanisms being important for the enhanced NPY release after reserpine in spite of elevated renin release. The present results show that in the absence of NA, repetition of brief sympathetic nerve stimulation evokes vascular effects and NPY-LI release which are repeatable and these effects are efficiently modulated via alpha 2-adrenoceptors. Furthermore, the Y2 receptors may mediate both prejunctional inhibition of NPY release, as well as postjunctional vasoconstrictor effects in the pig spleen.

Differences in the neuropeptide Y-like immunoreactivity of the plasma and platelets of human volunteers and depressed patients

In this study, patients with recurrent major depression were found to have significantly lower neuropeptide Y-like immunoreactivity (NPY-LI) in platelet-poor plasma (p < 0.01) and significantly higher NPY-LI in platelets (p < 0.001) compared to controls. Also, qualitative differences in the NPY-LI in platelet-poor plasma (PPP) and platelets were detected when the samples were analyzed by HPLC followed by RIA of the collected fractions.

Plasma neuropeptide Y and catecholamines in women and men with essential hypertension

Neuropeptide-Y (NPY) is a peptide proposed to modulate the effect of the sympathetic nervous system on blood pressure control and contribute to the development of essential hypertension. To assess the possible influence of gender on its role, we evaluated plasma NPY, noradrenaline (NA) and adrenaline (A) concentrations in men and women with essential hypertension. No difference in NPY concentration was found between genders, but NPY concentration was elevated in both hypertensive men and women. NA levels were similar in all investigated hyper- and normotensives, while A was increased only in hypertensive men. These results suggest various patterns of sympatho-adrenal activity in gender subgroups of patients with essential hypertension.

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.

Repeated renal and splenic sympathetic nerve stimulation in anaesthetized pigs: maintained overflow of neuropeptide Y in controls but not after reserpine

The overflow and the arterial vascular effects of neuropeptide Y (NPY) in response to repeated sympathetic nerve stimulation of kidney and spleen were investigated in anaesthetized pigs. The responses under control conditions were compared to those evoked in pigs with tissue stores of noradrenaline (NA) selectively depleted by reserpine pretreatment combined with sympathetic nerve transection. The renal and splenic sympathetic nerves were repeatedly stimulated at 1 h intervals with one 5 Hz stimulation for 48 s and transmitter overflow determined. Between these stimulations, 5 min stimulations with bursts of 20 Hz (for 1 s every 10 s) were given in order to induce a depletion of nerve transmitter. In the control group, overflow of NPY and NA and vasoconstrictor responses were almost identical for the 5 consecutive stimulations in the kidney, whereas in the spleen the parameters showed a slight tendency to be reduced. In the reserpine-treated group, the initial evoked overflow of NPY was increased 8-fold and 3-fold in the kidney and spleen, respectively, compared to the control group. Upon each subsequent stimulation the overflow decreased gradually, in parallel with the evoked vasoconstrictor response. After a 2 h recovery period no change in evoked overflow of NPY compared to the amount released by the previous stimulation was observed. The present study illustrates, the high capacity of maintenance of not only NA but also NPY overflow and vascular responses in control conditions, whereas the enhanced release of NPY in the absence of NA cannot be maintained. It is therefore possible that the NA-mediated prejunctional feedback mechanism is important for the maintenance of a constant NPY release in situations of high sympathetic activation.

Axonal transport and MR imaging: prospects for contrast agent development

Axonal transport plays a critical role in the physiology and pathology of neurons, yet there have been virtually no clinical tools for its evaluation in human subjects. A wide variety of molecules that can act as axonal transport facilitators have been discovered and, in many cases, used to deliver labels detectable with histologic methods. Recently a number of investigators have reported preliminary success in developing intraneural contrast agents based on various versions of dextran-coated magnetite that may render magnetic resonance imaging capable of depicting axonal transport. It is not yet clear whether any clinically useful agents will eventually be developed, but there has been considerable progress in identifying design factors for such a pharmaceutical agent.

Ganglion cells immunoreactive for catecholamine-synthesizing enzymes, neuropeptide Y and vasoactive intestinal polypeptide in the rat adrenal gland

Immunohistochemistry has been used to demonstrate tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT), neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) immunoreactivities, and acetylcholinesterase (AChE) activity was demonstrated in rat adrenal glands. The TH, DBH, NPY and VIP immunoreactivities and AChE activity were observed in both the large ganglion cells and the small chromaffin cells whereas PNMT immunoreactivity was found only in chromaffin cells, and not in ganglion cells. Most intra-adrenal ganglion cells showed NPY immunoreactivity and a few were VIP immunoreactive. Numerous NPY-immunoreactive ganglion cells were also immunoreactive for TH and DBH; these cells were localized as single cells or groups of several cells in the adrenal cortex and medulla. Use of serial sections, or double and triple staining techniques, showed that all TH- and DBH-immunoreactive ganglion cells also showed NPY immunoreactivity, whereas some NPY-immunoreactive ganglion cells were TH and DBH immunonegative. NPY-immunoreactive ganglion cells showed no VIP immunoreactivity. AChE activity was seen in VIP-immunopositive and VIP-immunonegative ganglion cells. These results suggest that ganglion cells containing noradrenaline and NPY, or NPY only, or VIP and acetylcholine occur in the rat adrenal gland; they may project within the adrenal gland or to other target organs. TH, DBH, NPY, and VIP were colocalized in numerous immunoreactive nerve fibres, which were distributed in the superficial adrenal cortex, while TH-, DBH- and NPY-immunoreactive ganglion cells and nerve fibres were different from VIP-immunoreactive ganglion cells and nerve fibres in the medulla. This suggests that the immunoreactive nerve fibres in the superficial cortex may be mainly extrinsic in origin and may be different from those in the medulla.

Some noradrenergic neurons of locus ceruleus-olfactory pathways contain neuropeptide-Y

We report a specific tracing technique for studying projections of noradrenergic neurons that contain other transmitters. Autoradiography after retrograde axonal transport of tritiated-noradrenaline ([3H]NA) was combined with immunocytochemical detection of endogenous NA or neuropeptide Y (NPY). The specificity of [3H]NA retrograde labeling was dependent on the concentration of [3H]NA injected at the terminal region. At 2 x 10(-3) M, the specificity of [3H]NA retrograde labeling was confirmed by immunodetection of endogenous NA in radiolabeled cell bodies of the locus ceruleus. Combination of autoradiography of [3H]NA retrograde labeling with immunodetection of NPY demonstrated that a some scattered locus ceruleus noradrenergic neurons (about 26%) projecting to the olfactory bulb do contain NPY.

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.

Immunoreactive neuropeptide Y (NPY) in plasma and platelets of rat and mouse strains and human volunteers

Immunoreactive-neuropeptide Y (i-NPY) is present in platelets of rats, and has recently been demonstrated to be authentic rat NPY based on its amino acid sequence. This potent vasoconstrictor and putative smooth muscle mitogen is released during platelet activation, suggesting a role in platelet-vascular interactions. We have now extended this work to several strains of rats and mice, and humans of both sexes. Among mice, strains in which NPY mRNA has been demonstrated in megakaryocytes have markedly higher levels of i-NPY (0.63-1.11 pmol/ml in NZB/B1NJ, NZBWF1/J, BXSB/MpJYaa, BALB/cJ) in platelet rich plasma (PRP) than other strains (DBA/2J, CBA/J, C3H/HeJ, MRL/MpJ-lpr, C57BL/6J; each < 0.02 pmol/ml). In rats, high content of i-NPY was observed in PRP and platelets of all strains examined (Sprague-Dawley, Wistar, Wistar Kyoto). i-NPY level was 30.6, 3.7 and 10.1 pmol/ml in PRP of the three strains, respectively. In humans, low levels of i-NPY occur in plasma and platelet fractions compared to rodents (0.069 and 0.048 pmol/ml in male and female PRP, respectively), but they, too, have greater i-NPY in platelet rich plasma and platelets than in platelet poor plasma. Assuming this is authentic NPY, platelet-derived NPY might have a role in pathophysiological states involving activation of platelets in humans.

Dynamics of large dense-cored vesicles in synaptic boutons of the cat superior cervical ganglion

We have shown previously that stimulation of the cat cervical sympathetic trunk for 2 h at 40 Hz depletes the large dense-cored vesicle store in synaptic boutons of the superior cervical ganglion and that post-depletion recovery of the store takes several days. In the present study, we examine the properties of the depletion and recovery mechanisms. Invaginations of the plasmalemma suggestive of the exocytosis of dense cores were seen frequently in boutons from stimulated ganglia. The depletion process is calcium dependent: in ganglia perfused with calcium-free Krebs solution no depletion was produced by 40 Hz preganglionic stimulation. The depletion process is rapid: during continuous stimulation of the cervical sympathetic trunk with 40 Hz, depletion observed by the end of 2 h was similar to depletion by the end of the initial 5 min of stimulation. The depletion process is frequently dependent: when the cervical sympathetic trunk was stimulated with a constant number of stimuli, no depletion occurred at the frequency of 2 or 10 Hz, while the frequencies of 20 and 40 Hz produced depletion, which was greater at 40 Hz. Recovery of the large dense-cored vesicle store during the initial 24 h after 10 min of 40 Hz stimulation was faster, and of approximately the same magnitude, than during the succeeding five days. Recovery of the store after stimulus-evoked depletion was prevented by application of colchicine to the cervical sympathetic trunk, which suggests dependence of recovery on fast axonal transport. Large dense-cored vesicles accumulated in the colchicine-treated segment of cervical sympathetic trunk axons. In conclusion, these observations suggest that the stimulus-evoked depletion of large dense-cored vesicle stores in synaptic boutons of the cat superior cervical ganglion is the result of calcium-dependent exocytosis of the large dense-cored vesicle core and that the post-stimulus recovery is critically dependent on microtubule-mediated axonal transport.

Multiple neuropeptide Y receptors are involved in cardiovascular regulation. Peripheral and central mechanisms

1. Neuropeptide Y (NPY) occurs in both the central and peripheral nervous system. In the periphery, NPY coexists with noradrenaline (NA) in perivascular sympathetic fibers. 2. NPY has a vasopressor effect, reflecting direct vasoconstriction of blood vessels and potentiation of the NA-evoked response. NPY also suppresses the release of NA from sympathetic fibers. 3. The post- and pre-junctional NPY receptors are referred to as Y1 and Y2, respectively. They recognize not only NPY but also the homologous gut hormone peptide YY (PYY). 4. The Y1 and Y2 receptors have been characterized in numerous test systems using analogs of NPY/PYY. Already the deletion of the first N-terminal amino acid (NPY 2-36) results in a marked loss of potency at the Y1 receptor. The Y2 receptor is much less dependent upon an intact N-terminus, and a wide range of C-terminal NPY fragments retain quite high potency. 5. Recently, yet another NPY receptor, Y3, that is distinct from Y1 and Y2 in that it recognizes PYY poorly, has been demonstrated in the brainstem and in the periphery. 6. Further attempts to characterize the various receptor types have relied on truncated and substituted analogs of NPY/PYY. Although such studies suggest the existence of at least three types of NPY receptors, the lack of antagonists has represented a problem. 7. Since NPY may regulate cardiovascular functions via peripheral and central receptors its physiological and possibly pathophysiological significance has attracted much attention. 8. The responsiveness to NPY seems to be altered in animal models of hypertension and elevated plasma levels of NPY have been found in patients under various conditions of stress and in primary hypertension. A number of studies have suggested that NPY may be a pathogenetic factor behind primary hypertension. 9. Antagonists for the various NPY receptors would be useful for an analysis of which effects of these peptides are physiologically relevant. It is tempting to predict that both agonists and antagonists of the NPY receptors could be useful as drugs, for instance, in the treatment of primary hypertension.

Development of cerebral arterial innervation: synchronous development of neuropeptide Y (NPY)- and vasoactive intestinal polypeptide (VIP)-containing fibers and some observations on growth cones

The pre- and postnatal development of sympathetic fibers containing neuropeptide Y (NPY) and parasympathetic fibers containing vasoactive intestinal polypeptide (VIP) supplying the cerebral arteries were studied with immunohistochemistry in rats. The innervation patterns and densities of NPY and VIP fibers were similar at all stages of development and similar to that previously reported for norepinephrine (NE). There was a striking reorganization of the innervation pattern of all three fiber systems between the first and second postnatal weeks. At all stages of development prior to the first postnatal week, growth cones were present on individual fibers at the distal part of major cerebral arteries and the middle segment of the basilar artery. The growth cones had a range of shapes from blunt to stellate, lanceolate or filiform. NPY and VIP immunoreactive granules were commonly present. The present results taken with our earlier developmental study of NE fibers (J. Comp. Neurol., 271 (1988) 435-444), demonstrate that: (1) both sympathetic and parasympathetic perivascular nerves on immature cerebral vessels develop with similar sequences: first longitudinal fibers and fiber bundles are present; these transform to a meshwork pattern and finally transform again into the mature, predominantly circumferential pattern; (2) both the classical (NE) and peptidergic transmitters (NPY) within the sympathetic system appear to develop identically in terms of time of appearance, innervation patterns, densities and reorganization.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y interaction with the adrenergic transmission line: a study of its effect on alpha-2 adrenergic receptors

Neuropeptide Y (NPY), first isolated in 1982, is widely distributed among the neurons of the central and peripheral nervous systems, often in close association with catecholamines. Because of its wide distribution and concentrations in selected areas of the brain, NPY is considered a putative neurotransmitter with several possible physiological effects including modulation of blood pressure, food intake and pituitary hormone release at a central level. Peripherally, the peptide seems to be involved, via direct and indirect mechanisms, in noradrenaline (NA)-mediated vasoconstriction. The ability of NPY to interact with the catecholamine transmission line may underly a possible modulatory influence of NPY on catecholamine receptor characteristics. We recently observed interaction between alpha-2 adrenergic receptors and those for NPY at the presynaptic level. Additional data from our studies in spontaneously hypertensive rats suggest that impairment of these interactions may contribute to the hypertension in this strain.

Insulin-like growth factor I shifts from promoting cell division to potentiating maturation during neuronal differentiation

SH-SY5Y neuroblastoma cells undergo neuronal differentiation and their proliferation is inhibited when they are treated with phorbol 12-myristate 13-acetate (PMA). Insulin and insulin-like growth factor I (IGF-I) are mitogens for the nontreated SH-SY5Y cells, whereas the proliferative response to such factor stimulation is lost upon differentiation, in spite of the fact that the receptors for insulin and IGF-I remain expressed and functional in the differentiated cells. Here we show that the PMA-induced differentiation of SH-SY5Y cells grown in a serum-free medium is strongly potentiated by nanomolar concentrations of IGF-I, as judged by morphology and markers for neuronal differentiation--e.g., neuropeptide tyrosine and growth-associated protein 43. Also, insulin and IGF-II potentiated the phorbol ester-induced differentiation, although less efficiently than IGF-I. Using blocking anti-receptor antibodies, it could be shown that the differentiation induced by these factors, in combination with PMA, was primarily mediated through the IGF-I receptor.

Effects of vinblastine on neuropeptide Y levels in the sympathoadrenal system, bone marrow and thrombocytes of the rat

The dose-related and time-related effects of vinblastine on tissue, platelet and plasma content of neuropeptide Y (NPY) were investigated in the rat and compared to the effects on catecholamine (CA) content. CA was quantified by HPLC with electrochemical detection and NPY-like immunoreactivity (LI) was analyzed by radioimmunoassay (RIA). Vinblastine (3.0 mg/kg, i.v.) decreased levels of both NPY-LI and CA after 48 h in the kidney, vas deferens and adrenal gland, whereas in the coeliac ganglion and bone marrow vinblastine induced an increase of NPY-LI which occurred already at a dose of 0.3 mg/kg. Also the content of NPY-LI in platelet-poor plasma and platelets as well as the decapitation-induced increase of plasma levels of noradrenaline (NA) and adrenaline (A) were attenuated by vinblastine (3.0 mg/kg). The elevation of NPY-LI content in the kidney, coeliac ganglion and bone marrow as well as the reduced levels of NPY-LI in platelets and platelet-poor plasma was observed already after 24 hours, whereas the reduction of NPY-LI and CA in the kidney and adrenal gland was present after 2 days. Vinblastine caused a biphasic effect on the content of NPY-LI in the sympathetic nerves of the kidney with an initial increase (by 120% at 24 h) followed by a decrease (by 79% at 4 days). The effect on NA-levels, however, was only a decrease. The axonal transport of NPY-LI as revealed by accumulation above a ligation of the sciatic nerve was reduced by 27% 2 days after vinblastine 3 mg/kg. The vinblastine-evoked depletion of NPY-LI and catecholamines in the kidney as well as in the adrenal was largely prevented by chlorisondamine, a nicotinic ganglionic blocking agent, suggesting that preganglionic neuronal activity was a key factor for this effect, in contrast to the influence on the coeliac ganglion cells and the megakaryocytes in the bone marrow. Furthermore, the delayed vinblastine depletion of NPY-LI in the kidney resembled the influence of surgical axotomy while reserpine caused a more rapid and complete depletion of both NPY-LI and NA. It is concluded that the multiple effects of vinblastine on sympathetic nerves, adrenal gland and megakaryocytes/thrombocytes can be monitored by analysis of NPY and be related to interference with microtubuli function and/or neuronal activation.

The influence of neuropeptide Y and norepinephrine on ovulation in the rat ovary

Neuropeptide Y (NPY) was measured in tissue extracts from ovaries of rats treated with pregnant mare serum gonadotropin (PMSG). The extracted NPY-immunoreactive material was identical to synthetic human NPY with regard to size and hydrophobicity as evaluated by gel filtration and high performance liquid chromatography. The concentration of NPY was related to the estrous cycle and a maximum was observed in relation to the endogenous luteinizing hormone (LH) peak. NPY immunoreactivity was demonstrated by immunohistochemistry to be localized within nerve fibers supplying blood vessels and follicles. The increase in the NPY content could not be related to accumulation around specific ovarian structures. Employing an in vitro set-up, NPY (10(-7) M) was unable to induce ovulation and did not increase the ovulation rate in LH-stimulated ovaries. The combination of NPY (10(-7) M) and NE (10(-7) M) did not significantly increase the number of ovulations compared to that induced by NE (10(-7) M) alone. In conclusion, NPY content in the ovary is related to the estrous cycle, but NPY does not seem to have any direct effect on the ovulatory process.

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.

Neuropeptide Y and tyrosine hydroxylase mRNA levels in the locus coeruleus show similar increases after reserpine treatment

In situ hybridisation histochemistry was used to study the effect of intra-peritoneal reserpine administration on messenger RNA (mRNA) levels in the locus coeruleus (LC) of the rat. 48h after injection, levels of mRNA encoding tyrosine hydroxylase (TH) and neuropeptide Y (NPY) in the LC increased to approximately 250% of control values (p less than 0.05). The level of beta-tubulin mRNA was unaffected by reserpine administration. The similar and selective increase in TH and NPY mRNA in the LC following reserpine administration suggests that NPY may play a role in the neurotransmitter function of this catecholaminergic nucleus.

Neuropeptide Y upregulates the adhesiveness of human endothelial cells for leukocytes

The nervous system and the autonomic system in particular have been associated with stress-induced changes in host resistance to infections and inflammatory reactions. Since a key step in initiation of inflammation is adhesion of leukocytes to the endothelium, we hypothesized that neuron-derived factors might be involved in this process. Neuropeptide Y (NPY), a 36-amino acid neuropeptide that is colocalized and released with norepinephrine from sympathetic nerves, has already been implicated in inflammatory reactions via modulation of histamine release from mast cells. This study was undertaken to examine the potential role of NPY in proinflammatory processes via modulation of endothelium-leukocyte interaction. NPY (0.01-10 microM) increased the adhesion of 51Cr-labeled human neutrophils or the human monocytic U937 cell line to human umbilical vein endothelial cells in a dose- and time-dependent manner. The stimulation of human umbilical vein endothelial cell adhesiveness occurred as early as 30 minutes and lasted over 48 hours. The increase of leukocyte adhesion to human umbilical vein endothelial cells by NPY was not inhibited by protein synthesis inhibitor cycloheximide, nor was it associated with expression of intercellular adhesion molecule-1 on human umbilical vein endothelial cells; in contrast, strong expression of intercellular adhesion molecule-1 was induced by tumor necrosis factor alpha and lipopolysaccharide endotoxin. These data suggest that neuron-derived factors such as NPY may serve as modulators of not only the neuromuscular unit but also the interaction of endothelial cells with leukocytes. In this capacity, the sympathetic nervous system might play an important role in the regulation of proaggregatory and hemostatic activity of microvessels.

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.

Innervation of the guinea pig spleen studied by electron microscopy

The innervation of the guinea pig spleen was investigated by electron microscopy. Unmyelinated nerve fibers in the capsulotrabecular and arterial systems were found to contain large and small granular and small agranular synaptic vesicles in their terminals and are thought to be sympathetic adrenergic in nature. They influence the contraction of the smooth muscle cells by diffusion innervation in these systems. These nerve terminals were also scattered in both the red and the white pulp. Pulp nerves wrapped by Schwann cells were further enclosed by myofibroblastic reticular cells. This condition revealed that the pulp nerves pass through the connective-tissue spaces of the reticular fibers, which contain elastic fibers, collagenous fibrils, and lamina densa-like materials of the usual basement laminae. One of the target cells for the pulp nerves is considered to be the myofibroblastic reticular cell in the reticular meshwork. Neurotransmitter substances released from the naked adrenergic nerve terminals travel through the reticular fibers and may play a role, by both close association innervation and diffusion innervation, in the contraction of reticular cells to expose the reticular fibers. At the exposed sides, connective-tissue elements of the reticular fibers are bathed with blood plasma, and the included naked nerve terminals, devoid of Schwann cells but with basement laminae of these cells, face free cells at some distance or are in close association with free cells, especially lymphocytes, macrophages, and plasma cells. The close ultrastructural relationship between the naked adrenergic nerve terminals and immunocytes strongly suggests that there is an intimate relationship between the immune system and the sympathetic nervous system through both close association innervation and diffusion innervation. Thus splenic adrenergic nerves of the guinea pig may play a triple role in 1) contraction of smooth muscle cells to regulate blood flow in the organ, 2) induction of the exposure of reticular fibers by contraction of the reticular cells in order to form a close relationship of the nerve terminals with the immunocytes, and 3) subsequent neuroimmunomodulation of the immunocytes.

Neuropeptide Y: an overview of central distribution, functional aspects, and possible involvement in neuropsychiatric illnesses

Neuropeptide Y (NPY) was first discovered and characterized as a 36-amino-acid peptide neurotransmitter in 1982. It is widely distributed in the central nervous system, with particularly high concentrations within several limbic and cortical regions. A number of co-localizations with other neuromessengers such as noradrenaline, somatostatin, and gamma-aminobutyric acid have been demonstrated. A large number of physiological and pharmacological actions of NPY have been suggested. Recent clinical data also suggest the involvement of NPY in several neuropsychiatric illnesses, particularly in depressive and anxiety states. This article gives a comprehensive review of central distribution of NPY and its receptors, co-localizations and interactions with other neuromessengers, genetic aspects, pharmacological and physiological actions, influence on neuroendocrine functions, and possible involvement in various neuropsychiatric illnesses.

Neuropeptide Y (NPY) in human nasal mucosa

Neuropeptide Y (NPY), a potent vasoconstrictor peptide found in sympathetic neurons, was analyzed in human inferior turbinate nasal mucosal tissue. NPY content determined by radioimmunoassay was 3.13 +/- 0.79 pmol/g tissue (n = 6) in mucosa extracted with ethanol-acetic acid. NPY-immunoreactive nerves were found around small muscular arteries, arterioles, arteriovenous anastomoses, and as free fibers near arteriolar and venous vessels. They formed a plexus around the arterial vessels, and were also present between vascular smooth muscle cells. Few NPY fibers were present near glands or the epithelium. [125I]NPY binding sites were localized by autoradiography to small muscular arteries, arterioles, and a few venous sinusoids. In explant culture experiments, 4 microM NPY did not stimulate release of [3H]glucosamine-labeled glycoconjugates or lactoferrin (a product of serous cells) from nasal mucosal fragments. Degradation of NPY by a tissue homogenate was rapid (t1/2 = 13.5 +/- 2.3 min). The degradation was inhibited by thiorphan and phosphoramidon, inhibitors of neutral endopeptidase activity. NPY released from sympathetic neurons may play a role as a constrictor of arterial vessels and regulate vasomotor tone in the human nasal mucosa.

Pharmacology of noradrenaline and neuropeptide tyrosine (NPY)-mediated sympathetic cotransmission

Pharmacological and physiological aspects for neuropeptide Y (NPY) and noradrenaline (NA) cotransmission have been studied in the peripheral sympathetic nervous control of blood vessels, heart, spleen and vas deferens. NPY coexists with NA in large dense cored vesicles and is released compared to NA mainly upon high frequency stimulation or strong reflex sympathetic activation. NPY release is inhibited via prejunctional alpha-2 adrenoceptors and adenosine receptors but facilitated by angiotensin II or beta-receptor activation. NPY exerts prejunctional inhibitory actions on both NA and NPY release, enhances the vasoconstrictor effect of NA and evokes potent, long-lasting vasoconstriction. Specific receptor mechanisms for NPY exist at both the pre- and postjunctional levels; a large amidated C-terminal portion of NPY is necessary for receptor binding, inhibition of cyclic AMP formation and vasoconstrictor effects. Denervation results in supersensitivity for both NA and NPY-evoked vasoconstriction. Reserpine pretreatment is associated with depletion of NA as well as NPY; the effect on NPY is entirely dependent on an intact nerve activity. Reserpine treatment combined with preganglionic denervation depletes NA by 99% while NPY levels are maintained intact. The characteristic appearance of the nerve stimulation evoked vasoconstrictor response with a high correlation to NPY outflow after reserpine treatment, suggests that NPY may be involved as a transmitter in a variety of vascular beds. NPY-synthesis in ganglia seems to be regulated by nicotinic receptor activity; secondary stimulation by eg reserpine stimulates and nicotine antagonists decrease NPY-synthesis. Many classical pharmacological agents including guanethidine, clonidine, yohimbine, angiotensin II, nicotine and desipramine influence NPY release. A complex interplay therefore seems to occur at both the pre- and postjunctional levels of transmission for the classical transmitter NA and the coexisting peptide NPY, creating a great diversity of chemical signalling potential.

Hormonal regulation of adult sympathetic neurons: the effects of castration on neuropeptide Y, norepinephrine, and tyrosine hydroxylase activity

Previous studies utilizing the hypogastric ganglia (HG) have indicated that gonadal steroids exert organizational and activational effects on noradrenergic biochemistry. Bilateral castration of male rodents at birth prevents the normal maturation of tyrosine hydroxylase (T-OH) activity in the HG; castration during adulthood results in a progressive decline in T-OH activity. Testosterone replacement corrects both the ontogenetic and adult functional alterations in the neurotransmitter-synthesizing enzyme. The present studies in adult male rats extend these previous observations and asked the question whether gonadal steroids regulate the neurotransmitters neuropeptide Y (NPY) and norepinephrine (NE) in the HG. Adult rodents were castrated and ganglia T-OH, NPY, and NE were examined at various time points after surgery. All three indices of sympathetic neuron biochemistry declined following castration, but they exhibited different profiles. It appears that hormones may affect enzyme activity and neurotransmitter pools differently within neurons. Testosterone replacement therapy fully restored T-OH activity, and NPY and NE levels in the HG. These studies extend the activational role of testosterone in regulating sympathetic neuron neurotransmitter and neuropeptide levels as well as neurotransmitter-synthesizing enzymes.

Effects of neuropeptide Y and noradrenaline on uterine artery blood pressure and blood flow velocity in the pregnant guinea-pig

Neuropeptide Y (NPY) coexists with noradrenaline (NA) in many peripheral sympathetic nerves. Since it has been found that patients with preeclampsia have elevated myometrial levels of both NPY and NA, we have examined the effects of NPY and NA on blood pressure and blood flow velocity in the uterine artery of the term pregnant guinea-pig (n = 7). We found that NPY (10-1000 pmol) significantly increased local blood pressure, with increases ranging from 15.4% (P less than 0.05) to 46.4% (P less than 0.001) as compared to control. NA (10-1000 pmol) had similar effects, increasing local blood pressure (5%-57.5% (P less than 0.01]. NPY had no significant effect on uterine blood flow velocity as measured by pulsed Doppler ultrasound, whereas NA (10-1000 pmol) decreased local uterine blood flow velocity (5.9%-30.2% (P less than 0.05]. The effect of NPY on blood pressure was phentolamine-resistant, indicating that it is not alpha-adrenoceptor-mediated. The results indicate that NPY and NA have significant pressor effects in the local uterine circulation during pregnancy in the guinea-pig.

Neuropeptide Y is released together with noradrenaline from the human heart during exercise and hypoxia

The myocardial release of neuropeptide Y-like immunoreactivity (NPY-LI) and noradrenaline (NA) during exercise with and without arterial hypoxia was measured in 18 healthy men by arterial (a) and coronary sinus (cs) catheterization. Exercise was performed in the supine position on a cycle ergometer at a load, selected to produce a heart rate during air breathing of 120 beats min-1. Coronary sinus blood flow (CSBF) was measured and a and cs samples for NPY-LI, NA, oxygen and lactate analyses were taken at rest and after 6 min exercise. The inspiratory gas was then switched to 15% (n = 8) or 12% (n = 10) oxygen in nitrogen, exercise continued at the same load and measurements repeated after 6 min. At rest no significant release and during normoxic exercise a very small myocardial release of NPY-LI and NA was detected. During hypoxia compared to normoxia the cardiac NPY-LI release increased four-fold and the NA net release doubled at the same time as the arterial NPY-LI remained unaltered or only slightly increased. Both the NPY-LI and the NA net release from the heart correlated with the heart rate and the arterial but not the cs oxygen tension. The NPY-LI release was correlated with the NA net release. The findings suggest that arterial hypoxia stimulates cardiac NPY together with NA release which derives from local sympathetic nerves. The release from the heart seems to be greater than from other tissues.