Effect of substance P on nicotine-induced desensitization of cultured bovine adrenal chromaffin cells: possible receptor subtypes

The phenotype of migraine with unilateral cranial autonomic symptoms documents increased peripheral and central trigeminal sensitization. A case series of 757 patients

BACKGROUND

Migraine with unilateral cranial autonomic symptoms (UAS) is a putative migraine endophenotype with convincing response to trigeminal-targeted treatments that still needs a thorough characterization.

OBJECTIVE

The objective of this article is to carefully investigate the clinical phenotype of migraine with UAS in a large group of patients for more accurate migraine diagnoses, improved clinical management, and better outcome prediction.

METHODS

We studied 757 consecutive episodic and chronic migraineurs in a tertiary headache clinic with face-to-face interviews, detailing in depth their lifestyle, sociodemographic and headache characteristics.

RESULTS

Migraineurs with UAS (37.4%) differed from the general migraine population with respect to longer attack duration (OR = 2.47, p < 0.02, having >72-hour long attacks), more strictly unilateral (OR = 3.18, p < 0.001) and severe headache (OR = 1.72, p = 0.011), more frequent allodynia (OR = 3.03, p < 0.001) and photophobia (OR = 1.87, p = 0.019).

CONCLUSIONS

Migraine patients with UAS are characterized not only by symptoms due to intense peripheral trigeminal activation but also to central sensitization. Our study broadens the knowledge on the clinical and phenotypic characteristics of migraine with UAS, suggests pathophysiological implications, and supports the need for future prospective clinical studies.

Modulation of neuronal nicotinic receptor function by the neuropeptides CGRP and substance P on autonomic nerve cells

1. One classical example of how neuropeptides can affect the function of ligand-gated receptors is the modulation of neuronal nicotinic receptors (nAChRs) by substance P. The present review updates current understanding of this action by substance P and compares it with other neuropeptides more recently found to modulate nAChRs in the autonomic nervous system. 2. Calcitonin gene-related peptide (CGRP) and its N-terminal fragments have been shown to exert complex inhibitory as well facilitatory actions on nAChRs. Fragments such as CGRP(1-4), CGRP(1-5) and CGRP(1-6) rapidly and reversibly enhance agonist sensitivity of nAChRs without directly activating those receptors. Longer fragments or the full-length peptide potently inhibit responses mediated by nAChRs via an apparently competitive-type antagonism. This phenomenon differs from the substance P-induced block, which is agonist use-dependent and preferential towards large nicotinic responses. 3. It is argued that the full-length peptides CGRP and substance P might play distinct roles in the activity-dependent modulation of cholinergic neurotransmission, by inhibiting background noise in the case of CGRP or by reducing excessive excitation in the case of substance P. Hence, multiple neuropeptide mechanisms may represent a wide array of fine-tuning processes to regulate nicotinic synaptic transmission. 4. The availability of novel CGRP derivatives with a strong enhancing action on nAChRs may offer new leads for the drug design targeted for potentiation of nAChRs in the autonomic nervous system as well as in the brain, a subject of interest to counteract the deficit of the nAChR function associated with neurodegenerative diseases like Alzheimer's and Parkinson's diseases.

2003 Wolff Award: Possible parasympathetic contributions to peripheral and central sensitization during migraine

BACKGROUND

Neurologic signs of increased parasympathetic outflow to the head often accompany migraine attacks. Because increased parasympathetic outflow to the cranial cavity induces vasodilation of cerebral and meningeal blood vessels, it can enhance plasma protein extravasation and the release of proinflammatory mediators that activate perivascular nociceptors. We recently showed that activation of intracranial perivascular nociceptors induces peripheral and central sensitization along the trigeminovascular pathway and proposed that these sensitizations mediate the intracranial hypersensitivity and the cutaneous allodynia of migraine.

METHODS

The present study investigates possible parasympathetic contributions to the generation of peripheral and central sensitization during migraine by applying intranasal lidocaine to reduce cranial parasympathetic outflow through the sphenopalatine ganglion.

RESULTS

In the absence of migraine, patients were pain-free, and their skin sensitivity was normal. Their mean baseline pain thresholds were less than 15 degrees C for cold, more than 45 degrees C for heat, and more than 100 g for mechanical pressure. Their mean pain score was 7.5 of 10 (standard deviation, 1.4) during untreated migraine and 3.5 of 10 (standard deviation, 2.4) after the nasal lidocaine-induced sphenopalatine ganglion block (P <.0001). Most patients developed cutaneous allodynia during migraine, and their mean pain thresholds changed to more than 25 degrees C for cold, less than 40 degrees C for heat, and less than 10 g for mechanical pressure. Following the nasal lidocaine administration (sphenopalatine ganglion block), this allodynia remained unchanged in spite of the pain relief.

CONCLUSION

These findings suggest that cranial parasympathetic outflow contributes to migraine pain by activating or sensitizing (or both) intracranial nociceptors, and that these events induce parasympathetically independent allodynia by sensitizing the central nociceptive neurons in the spinal trigeminal nucleus.

Serotonin increases cytoplasmic Ca2+ concentration in PC12h cells: effect of tachykinin peptides

We report here that serotonin (5-hydroxytriptamine, 5-HT) induces an increase in intracellular Ca2+ concentration ([Ca2+]i) in rat pheochromocytoma PC12h cells, a subclone of PC12 cells, which was detected by using Ca2+ sensitive indicator dye fura-2. The [Ca2+]i increase completely disappeared when extracellular Ca2+ was chelated with excess EGTA and potently suppressed in Na+-free buffer. Nifedipine, a voltage-dependent L-type calcium channel blocker, significantly blocked the 5-HT response. Addition of another 4 mM Ca2+ to the cell suspension attenuated the [Ca2+]i increase induced by 5-HT, whereas the nicotinic action was remarkably potentiated. Furthermore, metoclopramide, a 5-HT3 receptor antagonist, inhibited the 5-HT response in a dose dependent manner. These findings suggest that the 5-HT-induced [Ca2+]i increase involves the mediation of a voltage-dependent Ca2+ channel, evoked by membrane depolarization via the activation of cation channel-type receptors, 5-HT3 receptors. We also noted the inhibitory action of tachykinin peptides on the 5-HT response, suggesting that the cell line is useful to investigate these neuromodulatory actions in the nervous system.

Uptake of [3H]dopamine in isolated chromaffin cells of the mouse: modulation by intra- and extra-adrenal peptides and other secretagogues

The effects of intra- and extra-adrenal peptides on [3H]dopamine uptake in adrenal chromaffin cells of the mouse were examined in vitro. Dopamine uptake was inhibited by acetylcholine, high potassium, reserpine, imipramine and desmethylimipramine as was in noradrenaline uptake. Among the intra-adrenal peptides, vasoactive intestinal peptide (VIP, 100 pmol/l) and neurotensin inhibited [3H]dopamine uptake by approximately 25%. Somatostatin, enkephalin, and neuropeptide Y did not cause any significant inhibition. An extra-adrenal peptide, bradykinin, inhibited the uptake while angiotensin II showed no significant effect. Intra-adrenal peptides which cause catecholamine secretion inhibit catecholamine uptake probably to extend its effect. Extra-adrenal peptide which causes catecholamine secretion also inhibits catecholamine uptake.

Exocytosis in chromaffin cells of the adrenal medulla

The chromaffin cell has been used as a model to characterize releasable components present in secretory granules and to understand the cellular mechanisms involved in catecholamine release. Recent physiological and biochemical developments have revealed that molecular mechanisms implicated in granule trafficking are conserved in all eukaryotic species: a rise in intracellular calcium triggers regulated exocytosis, and highly conserved proteins are essential elements which interact with each other to form a molecular scaffolding, ensuring the docking of granules at the plasma membrane, and perhaps membrane fusion. However, the mechanisms regulating secretion are multiple and cell specific. They operate at different steps along the life of a granule, from the time of granule biosynthesis up to the last step of exocytosis. With regard to cell specificity, noradrenaline and adrenaline chromaffin cells display different receptor and signaling characteristics that may be important to exocytosis. Characterization of regulated exocytosis in chromaffin cells provides not only fundamental knowledge of neurosecretion but is of additional importance as these cells are used for therapeutic purposes.

Novel autocrine feedback control of catecholamine release. A discrete chromogranin a fragment is a noncompetitive nicotinic cholinergic antagonist

Catecholamine secretory vesicle core proteins (chromogranins) contain an activity that inhibits catecholamine release, but the identity of the responsible peptide has been elusive. Size-fractionated chromogranins antagonized nicotinic cholinergic-stimulated catecholamine secretion; the inhibitor was enriched in processed chromogranin fragments, and was liberated from purified chromogranin A. Of 15 synthetic peptides spanning approximately 80% of chromogranin A, one (bovine chromogranin A344-364 [RSMRLSFRARGYGFRGPGLQL], or catestatin) was a potent, dose-dependent (IC50 approximately 200 nM), reversible secretory inhibitor on pheochromocytoma and adrenal chromaffin cells, as well as noradrenergic neurites. An antibody directed against this peptide blocked the inhibitory effect of chromogranin A proteolytic fragments on nicotinic-stimulated catecholamine secretion. This region of chromogranin A is extensively processed within chromaffin vesicles in vivo. The inhibitory effect was specific for nicotinic cholinergic stimulation of catecholamine release, and was shared by this chromogranin A region from several species. Nicotinic cationic (Na+, Ca2+) signal transduction was specifically disrupted by catestatin. Even high-dose nicotine failed to overcome the inhibition, suggesting noncompetitive nicotinic antagonism. This small domain within chromogranin A may contribute to a novel, autocrine, homeostatic (negative-feedback) mechanism controlling catecholamine release from chromaffin cells and neurons.

Chronic nicotine treatment differentially regulates substance P and tyrosine hydroxylase immunoreactivity in substantia nigra ipsilateral to a unilateral lesion

The present study was carried out with a variety of neuroanatomical techniques to investigate the consequences of chronic continuous nicotine treatment (0.125 mg x kg(-1) x h(-1), s.c., 14 days) on the lesion-induced effects of a partial meso-diencephalic hemitransection. Both the striatonigral substance P (SP) and the nigrostriatal dopamine (DA) pathways were studied. The lesion-induced degenerative changes were most pronounced in the lateral parts of the ipsilateral substantia nigra and striatum. We have previously demonstrated that chronic nicotine infusion counteracts the lesion-induced loss of nigral tyrosine hydroxylase (TH) immunoreactive/Nissl stained DA neurons. The main finding of this study is that this phenomenon also involves changes in the striatonigral pathways. Thus, nicotine induced a disappearance of SP immunoreactive nerve terminals in substantia nigra pars compacta on the lesioned side, while it was again shown to counteract the lesion-induced disappearance of nigral TH immunoreactivity in the same animals. These data are interpreted on the basis of previous electrophysiological findings, where nicotine under similar experimental conditions counteracted the lesion-induced increase in burst firing in vivo in nigral dopamine neurons. Taken together these results indicate that nicotine may act by a reduced SP excitatory input to the nigral DA cells, which rescues them from dying. It is likely that the surviving cells are functional, since increased extracellular striatal DA levels have been observed after nicotine treatment ipsilateral to the lesion in a previous microdialysis experiment in vivo. These findings might contribute to the development of new neuroprotective therapies for patients suffering from neurodegenerative disorders such as Parkinson's disease.

Proteins from chromaffin granules promote survival of dorsal root ganglionic neurons: comparison with neurotrophins

Neurotrophins are established survival and differentiation factors for sensory dorsal root ganglionic (DRG) neurons. We have previously shown that proteins from the secretory granules of adrenal chromaffin cells have a capacity to promote the survival of cultured chick DRG neurons. Using DRG neurons from embryonic day (E) 8 chick embryos we show now that this material is (i) as effective as nerve growth factor (NGF), (ii) additive to NGF, neurotrophin-3, or -4, (iii) unlikely to be a neurotrophin, since the survival promoting effect can not be blocked by K252b, a specific inhibitor of the signal transduction pathways of neurotrophin high affinity receptors, (iv) partially blockable by antibodies to transforming growth factor-beta (TGF-beta) 1/2/3, and (v) more potent than any other out of 30 cytokines tested individually, including fibroblast growth factor (FGF)-5, epidermal growth factor (EGF), TGF-alpha, platelet-derived growth factor (PDGF)-AB, insulin-like growth factors (IGF)-I and -II, leukemia inhibitory factor (LIF), TGF-beta, glial cell line-derived neurotrophic factor (GDNF), stem cell factor, granulocyte-colony stimulating factor (G-CSF), oncostatin M, tumor necrosis factor (TNF)-alpha, and interleukins (IL)-1 through -12. We conclude that chromaffin cells, which are known to receive a sensory innervation, can provide (a) trophic factor(s), which, in addition to neurotrophins, may be relevant for the maintenance of DRG neurons.

Chemical codes of sensory neurons innervating the guinea-pig adrenal gland

Retrograde neuronal tracing in combination with double-labelling immunofluorescence was applied to distinguish the chemical coding of guinea-pig primary sensory neurons projecting to the adrenal medulla and cortex. Seven subpopulations of retrogradely traced neurons were identified in thoracic spinal ganglia T1-L1. Five subpopulations contained immunolabelling either for calcitonin gene-related peptide (CGRP) alone (I), or for CGRP, together with substance P (II), substance P/dynorphin (III), substance P/cholecystokinin (IV), and substance P/nitric oxide synthase (V), respectively. Two additional subpopulations of retrogradely traced neurons were distinct from these groups: neurofilament-immunoreactive neurons (VI), and cell bodies that were nonreactive to either of the antisera applied (VII). Nerve fibers in the adrenal medulla and cortex were equipped with the mediator combinations I, II, IV and VI. An additional meshwork of fibres solely labelled for nitric oxide synthase was visible in the medulla. Medullary as well as cortical fibres along endocrine tissue apparently lacked the chemical code V, while in the external cortex some fibre exhibited code III. Some intramedullary neuronal cell bodies revealed immunostaining for nitric oxide synthase, CGRP or substance P, providing an additional intrinsic adrenal innervation. Perikarya, immunolabelled for nitric oxide synthase, however, were too few to match with the large number of intramedullary nitric oxide synthase-immunoreactive fibres. A non-sensory participation is also supposed for the particularly dense intramedullary network of solely neurofilament-immunoreactive nerve fibres. The findings give evidence for a differential sensory innervation of the guinea-pig adrenal cortex and medulla. Specific sensory neuron subpopulations suggest that nervous control of adrenal functions is more complex than hitherto believed.

Immunologically induced sympathectomy of preganglionic nerves by antibodies against acetylcholinesterase: increased levels of peptides and their messenger RNAs in rat adrenal chromaffin cells

Systemic administration of murine monoclonal acetylcholinesterase antibodies to rats has been shown to cause selective degeneration of sympathetic preganglionic neurons. In the present study rats were subjected to a single i.v. injection of these acetylcholinesterase antibodies, or to normal IgG or saline for control. Exophthalmos, piloerection and eyelid-drooping (ptosis) were observed within 1 h after administration of the antibodies. Rats were killed at different time-points after antibody administration, and the adrenal glands were analysed by means of indirect immunohistochemistry and in situ hybridization histochemistry. As soon as 3 h after the antibody treatment, a marked increase in the number of chromaffin cells expressing mRNA encoding, respectively, enkephalin, calcitonin gene-related peptide, galanin, neurotensin and substance P was seen. At 12 h the peptide mRNA levels were still elevated and there was a concomitant increase in the number of peptide-immunoreactive cells. All peptide levels remained high for at least 48 h; however, 77 days after the antibody treatment only enkephalin-immunoreactive cells could be encountered. A disappearance of acetylcholinesterase- and enkephalin-immunoreactive cells could be encountered. A disappearance of acetylcholinesterase- and enkephalin-positive fibers was already seen 3 h after the antibody treatment, and after 24 h no fibers were encountered. In contrast, up until 48 h there was no apparent change in the number or intensity of immunofluorescent fibers expressing calcitonin gene-related peptide, galanin, neurotensin or substance P. However, 77 days after the antibody treatment the number of calcitonin gene-related peptide- and substance P-immunoreactive fibers was increased as compared to controls. In addition, reappearance of acetylcholinesterase- and enkephalin-immunoreactive fibers was seen 77 days after antibody administration, although their number was still low as compared to controls. Double-labeling immunohistochemistry revealed that the chromaffin cells expressing peptides after the antibody treatment preferentially were adrenaline storing cells (noradrenaline-negative). The majority of these cells expressed only one peptide. Both surgical transection of the splanchnic nerve as well as treatment with acetylcholine receptor antagonists mimicked the effects seen after the acetylcholinesterase-antibody treatment, although changes were less pronounced. The present results show that interruption of splanchnic transmission induces fast, marked, and selective increases in peptide expression in rat adrenal chromaffin cells.

Functional studies with substance P analogues: effects of N-terminal, C-terminal, and C-terminus-extended analogues of substance P on nicotine-induced secretion and desensitization in cultured bovine adrenal chromaffin cells

Substance P (SP) and SP analogues, including C-terminal, N-terminal, and C-terminus-extended analogues, have been investigated for their ability to modulate nicotine-induced secretion from bovine adrenal chromaffin cells in culture. Secretion was monitored by measuring the release of endogenous catecholamines by electrochemical detection following separation on HPLC and the release of endogenous ATP with an on-line luciferin-luciferase bioluminescence technique. SP is known to have the following two effects on nicotine-induced secretion of catecholamines (see Livett and Zhou, 1991): inhibition of the nicotinic response and protection against nicotinic desensitization. Secretion induced by 10(-5) M nicotine was inhibited 70-80% by SP, SP-methyl ester, and the C-terminus-extended analogue SP-Tyr12-NH2, 65% by (Ala3)SP-NH2, 45% by the C-terminal analogue SP(4-11), and 20 and 5% by the N-terminal analogues SP(1-7) and SP(1-5), respectively, when these peptides were present at 3 x 10(-5) M concentrations. The order of potency was SP = SP-methyl ester = SP-Tyr12-NH2 > (Ala3)SP-NH2 > SP(4-11) > SP(1-7) > SP(1-5). SP, SP-methyl ester, and (Ala3)SP-NH2 protected against nicotinic desensitization by 40-55%, and SP(4-11) protected by 20% (all at 3 x 10(-5) M). In contrast, the N-terminal analogues SP(1-7) and SP(1-5) and the C-terminus-extended analogue SP-Tyr12-NH2 at 3 x 10(-5) M did not protect against nicotinic desensitization. Cyclo-SP(3-9), Ac-SP(3-9)-NH2, SP(3-9), and SP(3-6) had neither inhibitory nor facilitatory effects on secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effects of beta-amyloid peptides on nicotine-induced Ca2+ influx in PC12h cells in culture

Synthetic beta-amyloid peptides and the neuropeptide substance P (SP) were examined for their ability to modulate nicotinic response in PC12h cells, a subclone of PC12 cells, SP, beta A1-40 and its peptide fragment beta A25-35-NH2 significantly inhibited an increase in cytoplasmic calcium concentrations ([Ca2+]i) induced by nicotine in a dose-dependent manner. Furthermore, beta A1-40 was found to inhibit the [Ca2+]i increase induced by depolarization with a high concentration of potassium. These findings show that both beta A1-40 and beta A25-35-NH2 may mimic the function of SP on inhibition of nicotinic response through different mechanisms.

An amyloid peptide, beta A4 25-35, mimics the function of substance P on modulation of nicotine-evoked secretion and desensitization in cultured bovine adrenal chromaffin cells

The amyloid protein (beta A4) is found in the CNS of patients with Alzheimer's disease; however, the pathogenic role of this protein is not known. In the present study, a peptide fragment of beta A4 (beta A4 25-35; Gly-Ser-Asn-Lys-Gly-Ala-Ile-Ile-Gly-Leu-Met-NH2), which contains the conserved C-terminal sequence of substance P (X-Gly-Leu-Met-NH2), and the neuropeptide substance P (SP) were examined for their ability to modulate nicotine-evoked secretion from cultured bovine adrenal chromaffin cells. Secretion of the released endogenous catecholamines was monitored by electrochemical detection after separation by HPLC. Secretion induced by 10(-5) M nicotine was inhibited by SP and beta A4 25-35. The IC50 of SP and beta A4 25-35 was 3 x 10(-6) and 3 x 10(-5) M, respectively. SP and beta A4 25-35 both protected against nicotine receptor desensitization. However, beta A4 25-35 was approximately 10-fold less effective than SP in its protective effect. The present work shows that beta A4 25-35 can mimic the modulatory actions of SP on the nicotinic response of cultured bovine chromaffin cells, i.e., inhibition of the nicotinic response and protection against nicotinic desensitization. These modulatory actions may be associated with changes in nicotinic receptor levels reported to occur in Alzheimer's disease.

Two classes of binding sites for [3H]substance P in rat cerebral cortex

The binding characteristics of [3H]substance P ([3H]SP) were investigated in membranes prepared from rat cerebral cortex. Binding of [3H]SP reached equilibrium after 50 min at 25 degrees C and was saturable at 8 nM. Saturation data could be resolved into high affinity (equilibrium dissociation constant, Kd, 0.22 nM) and low affinity sites (Kd, 2.65 nM). The low affinity sites were more numerous than the high affinity sites, with a ratio of 4:1. The non-hydrolyzable GTP analogue GppNHp had no effect on binding, indicating that the high and low affinity sites are not guanine nucleotide-regulated states of the same (NK-1) receptor. The low affinity sites are unlikely to represent NK-3 receptors since coincubation with the selective NK-3 receptor agonist senktide did not alter the biphasic nature of [3H]SP binding. The rank order of potency for inhibition of [3H]SP (2 nM) binding was SP > or = [Sar9, Met(O2)11]-SP > or = physalaemin >> SP(3-11) > NP gamma = [Ala3]-SP > or = SP(4-11) > or = NPK > or = SP(5-11) > or = NKB approximately NKA >> SP(1-9), compatible with binding to an NK-1 site. N-terminal fragments and non-amidated analogues were ineffective competitors for [3H]SP binding. However, competition data for several peptides including substance P (SP) and the NK-1 selective agonist [Sar9, Met(O2)11]-SP could be resolved into two components.(ABSTRACT TRUNCATED AT 250 WORDS)

Tumor necrosis factor modulates the inactivation of catecholamine secretion in cultured sympathetic neurons

Cytokines exert multiple effects on cellular functions. We studied the effects of cytokines on the calcium-dependent release of catecholamines in cultured neurons from neonatal rat superior cervical ganglia. Incubation of sympathetic neurons with recombinant human interleukin-1 beta (0.14-0.7 nM) or recombinant human tumor necrosis factor-alpha (1 nM) for 24-48 h had no effect on the baseline spontaneous release and the initial K(+)-evoked [3H]norepinephrine release, compared with untreated cells. A repeat K(+)-induced depolarization after 6 min resulted in a decrease of [3H]norepinephrine secretion to 69 +/- 5.8% (n = 11) of the initial secretion in recombinant human tumor necrosis factor-treated cells, but not in control cells. The secretory response was restored when the interval between the two K+ challenges was increased to 10 min. We conclude that the diminished secretory response to a repeat stimulus in recombinant human tumor necrosis factor-treated superior cervical ganglia neurons is due to a prolonged recovery from inactivation of secretion in these cells.

Substance P modulates the time course of nicotinic but not muscarinic catecholamine secretion from perfused adrenal glands of rat

1. Substance P (SP) and acetylcholine (ACh) are contained within the splanchnic nerve terminals in the adrenal gland and can be released in response to stress. In the rat, the release of aCh brings about secretion of catecholamines (CA) by acting on nicotinic and muscarinic receptors on the adrenal chromaffin cells. 2. In the present study, we have used a rat isolated adrenal gland preparation to investigate the effects of SP, perfused at different concentrations, on CA secretion evoked by 10(-5) M nicotine and 10(-4) M muscarine. 3. In the first 10 min stimulation period (S1), in the absence of SP, nicotine (10(-5) M) evoked substantial and equal secretion of noradrenaline (NA) and adrenaline (Ad). In a second 10 min stimulation period (S2), carried out 18 min after S1, the nicotinic response was desensitized. In contrast, the muscarinic response, which preferentially evoked Ad secretion in S1 (Ad/NA: 8.7/1), was well maintained in S2. 4. SP present in S1 had no effect on desensitization of the subsequent nicotinic response in S2. 5. At low concentrations (10(-7)-10(-10) M), SP changed the time course of nicotine-induced CA secretion during S1 by enhancing CA secretion in the first 4 min and inhibiting CA secretion thereafter. The maximal effect occurred at 10(-9) M SP. 6. At a higher concentration (10(-5) M), SP inhibited total nicotinic CA secretion throughout S1 and produced a biphasic secretion of CA (depressed in the presence of SP and enhanced after wash out of SP). Pre-exposure of adrenal glands to SP (10-' to 10- M) for 10min produced marked inhibition of the nicotine-induced CA secretion. 7. In contrast to the effect of SP on the nicotinic response, SP from 10- to 10-SM had no effect on muscarinic CA secretion. 8. This difference in sensitivity of the nicotinic and muscarinic responses to SP points to a diversity of mechanisms available for control of adrenal catecholamine secretion. In addition to the ability of SP to increase or decrease the total amount of adrenal CA secretion, dependent on the concentration of SP, the present study shows that SP can change the time-course of nicotinic CA secretion. These results with the rat adrenal gland perfused in vitro suggests both a quantitative and temporal role for SP as a novel modulator of adrenal CA secretion.

Capsaicin-sensitive sensory neurons are involved in the plasma catecholamine response of rats to selective stressors

1. The effect of capsaicin pre-treatment on adrenal catecholamine (CA) secretion in response to stress is controversial. In earlier experiments performed under pentobarbitone anaesthesia, the release of CA in response to stress was complicated by the effects of the barbiturate anaesthesia. 2. In the present study we have used conscious freely moving rats with indwelling cannulae to study the effect of neonatal capsaicin pre-treatment on the plasma CA response to different types of stressors (swimming stress, hypovolaemic stress, immobilization stress and cold stress). 3. After swimming for 20 min, plasma noradrenaline (NA) levels increased by 8-fold and adrenaline by 2-fold in control rats. The increase in plasma NA levels in the capsaicin group was attenuated at 10 min of swimming compared with the vehicle group (P < 0.05). 4. With hypovolaemic stress, there were no differences in plasma CA levels, blood pressure and heart rate between the capsaicin group and the vehicle group. There were also no differences in plasma CA levels after immobilization stress between the two groups. 5. With cold stress, plasma NA levels increased 5-fold and adrenaline levels by 3-fold over basal at 45 min in the vehicle pre-treated rats. This increase was not observed in the capsaicin group. 6. Immunoreactive substance P was depleted by only 68% in the splanchnic nerve following capsaicin pre-treatment. If the remaining 32% was biologically active substance P then it could account for the maintenance of the response to hypovolaemic and immobilization stress. However, it might be possible that the responses to hypovolaemic and immobilization stresses could be attenuated if a more complete depletion were achieved. 7. These results in conscious rats indicate that capsaicin-sensitive sensory neurons are required for plasma CA response to selective stressors. They are required for CA output in response to cold stress and to the early phase of swimming stress, but not to hypovolaemic stress and immobilization stress.

Substance P enhances desensitization of the nicotinic response in bovine chromaffin cells but enhances secretion upon removal

A fundamental process in neurosecretion is desensitization, or a declining response to a stimulus. The response of chromaffin cells to continuous nicotinic stimulation, secretion of catecholamines, desensitizes within a few minutes. The neuropeptide substance P (SP) has been reported to prevent desensitization in culture dish experiments and to enhance desensitization in patch clamp studies. In the present study, these contradictory responses have been demonstrated and the apparent contradictions resolved. We have measured catecholamine secretion by on-line electrochemical detection in a constant-pressure flow system. Isolated chromaffin cells cultured on quartz plates were stimulated with the nicotinic agonist 1,1-dimethyl-4-phenylpiperazinium (DMPP) in the presence and absence of SP. SP inhibited secretion and increase the rate of desensitization compared with stimulation by DMPP alone. However, when the cells were stimulated a second time with DMPP alone immediately after 5-min stimulation with SP + DMPP, the rate of desensitization was markedly lower than the control. Removal of SP after a desensitizing stimulation with SP + DMPP caused a slow secondary release of catecholamine in response to the continued stimulation with DMPP. The kinetic analysis of the secretory response shows that the primary response to SP is enhanced desensitization, but that upon removal of SP the response to DMPP desensitizes less rapidly. We suggest that SP protects some receptors from nicotinic desensitization while holding them in an inactive state, and that upon removal of SP these receptors can slowly respond to DMPP.

Role of capsaicin-sensitive neurons in catecholamine secretion from rat adrenal glands

Sensory fibres innervate the adrenal medulla but their function is not known. In the present study, we have used the sensory neurotoxin capsaicin to evaluate the effect of capsaicin sensitive sensory fibres on catecholamine (CA) secretion from isolated perfused rat adrenal glands. CA secretion in response to 1 and 10 min electrical field stimulation of adrenal nerve terminals was significantly attenuated in the adrenal glands of adult rats pretreated as neonates with capsaicin and was frequency dependent, being more pronounced at the higher frequencies of stimulation (5 to 30 Hz) than at the low (0.3, 1 Hz) frequencies. Perfusion of control rat adrenal glands with capsaicin did not evoke CA secretion, but did increase CA secretion in response to perfusion with nicotine. Perfusion with capsaicin for 30 min (but not for 4 min) reduced the CA secretory response to subsequent nerve stimulation. The results suggest that capsaicin sensitive sensory neurons innervating the adrenal medulla are involved in the regulation of adrenal CA secretion evoked by electrical stimulation of adrenal nerve terminals.

Substance P has biphasic effects on catecholamine secretion evoked by electrical stimulation of perfused rat adrenal glands in vitro

The adrenal medulla is innervated by the splanchnic nerve which contains substance P-immunoreactive fibres originating in the dorsal root ganglia but whose function in the adrenal medulla is not known. In the present study, we have examined the effect of exogenous substance P on catecholamine secretion and [3H]-choline overflow evoked by field stimulation of the perfused rat adrenal gland. Substance P had biphasic effects on catecholamine secretion evoked by field stimulation: at the lower concentrations (10(-7)-3 x 10(-6) M), substance P facilitated catecholamine secretion whereas at higher concentrations (3 x 10(-5) M), substance P inhibited catecholamine secretion. The effects of substance P were long-lasting: substance P at all concentrations present during the second of three 6-min stimulations increased catecholamine secretion during the third stimulation. The enhancement of catecholamine secretion by substance P during field stimulation was not blocked by atropine but was substantially blocked by hexamethonium plus atropine. Substance P at all concentrations inhibited the evoked [3H]-choline overflow with a maximal inhibition of 60% (at 10(-6) M). In the absence of stimulation, substance P (10(-7)-3 x 10(-5) M) had no effect on the basal catecholamine secretion or basal [3H]-choline overflow. These results indicate that substance P has modulatory effects on adrenal catecholamine secretion and [3H]-choline overflow evoked by electrical stimulation. Presynaptically, substance P inhibits transmitter overflow from cholinergic nerve terminals and post-synaptically substance P has biphasic effects on catecholamine secretion dependent on the substance P concentration. These results suggest a functional role for substance P-containing fibres innervating the adrenal medulla.

Substance P increases catecholamine secretion from perfused rat adrenal glands evoked by prolonged field stimulation

1. We have studied the effect of substance P (SP) on catecholamine (CA) secretion evoked by prolonged field stimulation from the perfused rat adrenal gland in vitro. 2. Previous studies show that SP has an inhibitory effect on the nicotinic response in a number of different tissue preparations. In the present study, we found that SP at concentrations from 10(-7) to 10(-6) M markedly increased CA secretion evoked by prolonged high-frequency field stimulation but not that evoked by low-frequency field stimulation. 3. In the absence of field stimulation SP by itself had no direct effect on CA secretion. This indicates that SP acts as a neuromodulator rather than a neurotransmitter to increase CA secretion from the adrenal medulla. 4. The nicotinic receptors were still functional following a period of prolonged field stimulation (120 min) because CA secretion was markedly increased in response to the nicotinic agonist dimethylphenylpiperazinium (DMPP). 5. Capsaicin pre-treatment reduced CA secretion evoked by prolonged field stimulation and the facilitatory action of SP on CA secretion lasted longer in these capsaicin-pre-treated rats than in controls, indicating that SP-containing capsaicin-sensitive fibres innervating the adrenal medulla may be involved in the regulation of CA secretion. 6. In parallel with the increase in CA secretion, 3H overflow from the splanchnic nerve pre-labelled with [3H]choline was also increased by SP. The increase in CA secretion by SP lasted longer than the increase in 3H overflow. These results suggest that SP facilitates CA secretion from the adrenal gland at two levels: (1) pre-synaptically by facilitating ACh release from splanchnic nerve terminals, and (2) post-synaptically by modulating the nicotinic secretory response by protection against nicotinic desensitization of secretion. 7. The present studies provide further evidence that endogenous SP in the splanchnic nerve may modulate CA secretion during stress.

A novel substance P binding site in bovine adrenal medulla

Radioligand binding techniques were used to characterize the substance P (SP) binding site on membranes prepared from bovine adrenal medullae. 125I-labelled Bolton-Hunter substance P (BHSP), which recognises the C-terminally directed, SP-preferring NK1 receptor, showed no specific binding. In contrast, binding of [3H]SP was saturable (at 6 nM) and reversible, with an equilibrium dissociation constant (Kd) 1.46 +/- 0.73 nM, Bmax 0.73 +/- 0.06 pmol/g wet weight and Hill coefficient 0.98 +/- 0.01. Specific binding of [3H]SP was displaced by SP greater than neurokinin A (NKA) greater than SP(3-11) approximately SP(1-9) greater than SP(1-7) approximately SP(1-4) approximately SP(1-6), with neurokinin B (NKB) and SP(1-3) very weak competitors and SP(5-11), SP(7-11) and SP(9-11) causing negligible inhibition (up to 10 microM). This potency order is quite distinct from that seen with binding to an NK1 site, a conclusion confirmed by the lack of BHSP binding. It appears that Lys3 and/or Pro4 are critical for binding, suggesting an anionic binding site. These data suggest the existence of an unusual binding site which may represent a novel SP receptor. This site appears to require the entire sequence of the SP molecule for full recognition.

Vasoactive intestinal peptide stimulates proenkephalin A mRNA expression in bovine adrenal chromaffin cells

The effects of vasoactive intestinal peptide (VIP) and substance P (SP) on the amount of proenkephalin A (ProEnk A) mRNA in cultures of bovine adrenal chromaffin cells were examined. Exposure of chromaffin cells to 5 microM VIP for 24 h produced a significant elevation in ProEnk A mRNA. The stimulatory effect of VIP could be abolished by the presence of the calcium channel blocker D600 or actinomycin D but was not affected by the nicotinic antagonist hexamethonium. The results suggest that VIP may induce transcription of ProEnk A mRNA by a Ca2+-dependent, non-cholinergic mechanism. By contrast, SP (5 microM) had no effect on the amount of ProEnk A mRNA. Since VIP is found in nerve terminals and the ganglion cells within the adrenal medulla, this peptide could be an endogenous regulator of adrenal enkephalin gene expression.

Mammalian tachykinins modulate the nicotinic secretory response of cultured bovine adrenal chromaffin cells

We have studied the modulatory actions of two members of the tachykinin family (neurokinin A and B) on endogenous catecholamine (CA) secretion from cultured adrenal chromaffin cells. Their ability to modulate the nicotinic response was compared to that of substance P (SP). Both neurokinin A and neurokinin B were found to have two distinct actions similar to SP, on nicotine-induced CA release: (1) an inhibitory action at low nicotine concentrations; and (2) a protective action against desensitization by high nicotine concentrations. However, on a molar basis, the efficacy of neurokinin A or B to modulate the nicotinic response (both inhibition or protection) was 30 times less than SP. We have also tested the ability of a SP antagonist (D-Arg1-D-Pro2-D-Trp7,9-Leu11-SP) to antagonize the modulatory actions of SP on the nicotinic response. The results suggest the possibility that SP's actions on the bovine adrenal chromaffin cells might be mediated through two receptor subtypes of two different affinities.