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PubMed2000

Usefulness and limitations of dobutamine-atropine stress echocardiography for the diagnosis of coronary artery disease in patients with left bundle branch block. A multicentre study.

BACKGROUND: Patients with left bundle branch block exhibit abnormal septal motion which may limit the interpretation of stress echocardiograms. This study sought to assess the diagnostic value of dobutamine-atropine stress echocardiography in left bundle branch block patients. METHODS AND RESULTS: Sixty-four left bundle branch block patients (mean age 59 years, 24 men) with suspected coronary artery disease underwent dobutamine-atropine stress echocardiography and coronary arteriography. Myocardial ischaemia was defined as new or worsening wall thickening abnormalities. Coronary artery disease was quantitatively defined as a diameter stenosis >/=50% in a major epicardial artery. Rest septal motion was normal (apart from the early systolic septal notch) in 34 patients (53%) and abnormal in 30 patients (47%). Rest septal thickening was normal in 32 patients (50%) and abnormal in 32 patients (50%). All seven patients with a QRS duration >/=160 ms and an abnormal QRS axis had abnormal rest septal motion and thickening. Inter-observer agreement for ischaemia was 88%. In all but one patient disagreement was in the septum. For the anterior and posterior circulation, respectively, sensitivity was 60% (9/15) and 67% (8/12), specificity was 94% (46/49) and 98% (51/52), and accuracy was 86% (55/64) and 92% (59/64). Sensitivity for the anterior circulation tended to be better in patients with normal rest septal thickening (83% vs 44%). CONCLUSIONS: Dobutamine-atropine stress echocardiography has excellent diagnostic specificity in left bundle branch block patients with suspected coronary artery disease. In patients with abnormal rest septal thickening, however, dobutamine-atropine stress echocardiography may lack good sensitivity for detection of coronary artery disease in the anterior circulation. Left bundle branch block patients who potentially most benefit from dobutamine-atropine stress echocardiography may initially be selected by their resting electrocardiogram.

Adult↗
PubMed2001

Bisoprolol reduces cardiac death and myocardial infarction in high-risk patients as long as 2 years after successful major vascular surgery.

AIM: To assess the long-term cardioprotective effect of bisoprolol in a randomized high-risk population after successful major vascular surgery. High-risk patients were defined by the presence of one or more cardiac risk factor(s) and a dobutamine echocardiography test positive for ischaemia. METHODS: 1351 patients were screened prior to surgery, 846 patients had one or more risk factor(s), and 173 of these patients also had ischaemia during dobutamine echocardiography. One hundred and twelve patients could be randomized for additional bisoprolol therapy or standard care. Eleven patients died in the peri-operative period (up to 1 month after surgery). Randomized patients continued bisoprolol or standard care after surgery. During follow-up of 101 survivors (median 22 months, range 11-30) cardiac death or myocardial infarction was noted. No patient was lost during follow-up. Results The incidence of cardiac events during follow-up in the bisoprolol group was 12% vs 32% in the standard care group (P=0.025). Cardiac death occurred in 15 patients, nine patients in the standard care and in six in the bisoprolol group; myocardial infarction occurred in six patients, five in the standard care and one in the bisoprolol group. The odds ratio for cardiac death or myocardial infarction after surgery in high-risk patients with additional bisoprolol therapy was 0.30 (0.11-0.83). CONCLUSIONS: Bisoprolol significantly reduced long-term cardiac death and myocardial infarction in high-risk patients after successful major cardiac vascular surgery.

Adrenergic beta-Antagonists↗
PubMed2001

Coronary microvascular endothelial dysfunction in transplanted children.

AIMS: To assess the response of the coronary microcirculation to acetylcholine (endothelium-dependent vasodilator) and of adenosine (endothelium-independent vasodilator) in children after heart transplantation and to verify whether endothelial dysfunction is time-dependent. METHODS AND RESULTS: We studied the endothelial function of 26 asymptomatic children previously submitted to heart transplantation, with normal transplanted hearts and epicardial coronary arteries. Ten untransplanted children served as controls. The response of coronary blood flow velocity to intracoronary infusion of acetylcholine (1.8 microg x min(-1)) and adenosine (270 microg x min(-1)) was assessed using a Doppler wire positioned in an epicardial coronary branch. In the study group, coronary blood flow velocity increased slightly during acetylcholine infusion (peak/baseline ratio=1.17+/-0.22). The ratio was inversely correlated with the length of follow-up (r=-0.50;P=0.0078). The peak/baseline ratio in control children was 1.76+/-0.73 (P<0.0002 vs. study group). After adenosine infusion, the coronary blood flow velocity peak/baseline ratio was 3.75+/-1.54 in transplanted children and 3.72+/-1.34 in controls (P=ns). CONCLUSIONS: Endothelial dysfunction in paediatric transplanted patients becomes more evident in patients with longer follow-up. This finding could prove useful in the prevention of accelerated arteriosclerosis.

Acetylcholine↗
PubMed1996

Substance P activation of enteric neurons in response to intraluminal Clostridium difficile toxin A in the rat ileum.

BACKGROUND & AIMS: Nerves have been suggested to mediate the effects of bacterial toxins in intestinal diseases. However, the mechanisms involved are unknown. This study examined endogenous substance P (SP) activation of the substance P receptor (SPR) on enteric neurons in the rat ileum after exposure to intraluminal Clostridium difficile toxin A. METHODS: After intraluminal injection of toxin A in ileal loops, tissue was examined for pathological changes by histology and for SPR activation by immunocytochemical analysis of SP-induced SPR endocytosis. RESULTS: After toxin A administration, > 70% of enteric neurons showed SPR endocytosis and became swollen with thickened dendrites. In contrast, SPRs in control rats were largely confined to the plasma membrane. Rats denervated of primary afferent fibers with neonatal capsaicin injection and animals pretreated with a nonpeptide SPR antagonist showed few endosomal SPRs, and the pathological inflammatory effects of toxin A were ablated. CONCLUSIONS: Intraluminal toxin A causes the release of SP from primary afferent neurons: this endogenous SP then acts on enteric neurons in the submucosal and myenteric plexuses. SP is the primary mediator of an axon reflex mediating neurogenic inflammation in the intestine. SPR blockade may prove to be a novel therapy used to prevent intestinal inflammation.

Animals↗
PubMed2005

The role of leukotriene B4 in Clostridium difficile toxin A-induced ileitis in rats.

BACKGROUND & AIMS: Clostridium difficile toxin A is a potent intestinal inflammatory agent that has been shown to act at least partially by neurogenic mechanisms involving activation of the transient receptor potential vanilloid 1 (TRPV1) (capsaicin) receptor. We tested the hypothesis that leukotriene B4 (LTB4) mediates the effects of toxin A via activation of the TRPV1 receptor. METHODS: Isolated rat ileal segments were pretreated with pharmacologic agents before intraluminal injection of toxin A or LTB4. After 3 hours, the treated segments were removed and inflammation was assessed by luminal fluid accumulation, myeloperoxidase activity, and histology. RESULTS: LTB4 caused ileitis similar to that caused by toxin A and antagonism of TRPV1 receptors but not LTB4 receptors inhibited LTB4-induced inflammation. LTB4 also stimulated TRPV1-mediated substance P release and pretreatment with a specific substance P-receptor antagonist blocked LTB4-induced substance P action and ileitis. Inhibition of the LTB4 biosynthetic enzyme 5-lipoxygenase inhibited toxin A-induced increases in ileal LTB4 levels and toxin A- but not LTB4-induced ileitis. CONCLUSIONS: LTB4 mediates the inflammatory effects of toxin A via activation of TRPV1 receptors.

Animals↗
PubMed2002

Simvastatin, transdermal patch, and oral estrogen-progestogen preparation in early-postmenopausal hypercholesterolemic women: a randomized, placebo-controlled clinical trial.

Hormone replacement therapy (HRT) seems to have a favorable influence on the plasma lipid profile. Only a few investigations have examined the effects of HRT versus hepatic hydroxymethyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors. We compared the relative effects of different hypolipidemic strategies on lipoproteins and coagulative parameters in women with recent-onset spontaneous menopause. In this 24-week, placebo-controlled trial, 60 consecutive healthy women aged >/= 45 years, with amenorrhea from 6 to 60 months (mean, 1.9 +/- 1.4 years), serum follicle stimulating hormone (FSH) greater than 40 U/L, and slight to moderate hypercholesterolemia (low-density lipoprotein-cholesterol [LDL-C] 160 to 250 mg/dL, high-density lipoprotein-cholesterol [HDL-C] < 75 mg/dL, and triglycerides < 200 mg/dL) were enrolled and randomized to dietetic advice (placebo group), simvastatin 10 mg, 0.625 mg of conjugated equine estrogen (CEE), or 50 microg estrogen transdermal patch (ETP). In the latter 2 cases, the progestative nomegestrol was added to estrogens (days 17 to 28 of the cicle). Lipoprotein parameters were evaluated after separating very-low-density lipoproteins (VLDLs) by ultracentrifugation, while fasting glucose and insulin, homocysteine, and hemocoagulative parameters were determined in plasma. Fifty-four patients completed the trial. Total cholesterol (TC) and LDL-C significantly decrased in the simvastatin (-62 mg/dL [-20%] and -72 mg/dL [-30%], respectively), CEE (-42 mg/dL [-13%] and -45 mg/dL [-18%]), and ETP (-30 mg/dL [-10%] and -26 mg/dL [-11%]) groups compared to baseline, but only simvastatin showed an effect significantly superior to diet alone. Apolipoprotein (Apo) B was decreased by simvastatin (-25%, P <.001) and by CEE (-10%, P <.05); again, simvastatin was more effective than either diet or ETP. Triglyceride concentration and VLDL-C were unmodified by treatments. HDL-C and Apo A-I significantly increased in the simvastatin group (+18% and +8%, respectively), while HDL-C was unmodified by both HRT regimens and Apo A-I was reduced by ETP treatment (-17%); lipoprotein[a] (Lp[a]) was decreased by both HRTs (-38%, P <.05, and -22%, P =.07, for CEE and ETP, respectively). Among coagulative parameters, plasminogen activator inhibitor-1 (PAI-1) was significantly reduced by CEE (-29%, P <.05) but not ETP treatment (+16%, P = not significant), while fibrinogen, antithrombin, and homocysteine were unaffected by therapy. Thus, HRT, particularly CEE, seems well tolerated and moderately effective in improving the lipid pattern and, perhaps, the coagulative/fibrinolytic balance in postmenopausal hypercholesterolemic women; it may represent a therapeutic option in slightly dyslipidemic subjects. Statins are preferred in case of more severe disease.

Administration, Cutaneous↗
PubMed2001

The N-terminal domain of substance P is required for complete homologous desensitization but not phosphorylation of the rat neurokinin-1 receptor.

The agonist activity of substance P (SP) is a function of the C-terminal domain of the peptide. A C-terminal SP fragment (SP(6-11)) and analog (septide) and neurokinin A (NKA; a related tachykinin with a divergent N-terminal amino acid sequence) were found to be full neurokinin-1 receptor (NK-1R) agonists, but were not able to desensitize the receptor maximally as much as SP. Substance P caused 95.6 +/- 0.9% maximal desensitization of the NK-1R whereas SP(6-11), septide, and NKA(only)caused 74 +/- 3.5, 50.6 +/- 8, and 71.5 +/- 4.4% maximal desensitization, respectively (mean +/- SEM; P < 0.001 vs SP). When a series of SP C-terminal fragment peptides were tested for their NK-1R desensitizing activity, it was found that SP(5-11)and SP(6-11)caused significantly less maximal NK-1R desensitization than SP. SP N-terminal fragment peptides had no effect on the ability of SP(6-11)to compete with(3)H-SP binding, generate an IP(3)response, or cause NK-1R desensitization when tested with or without SP(6-11). SP, SP(6-11), septide, and NKA all maximally stimulated 8-9-fold increases in NK-1R phosphorylation. When attached to the C-terminal domain of SP responsible for NK-1R binding and agonism, the N-terminus of SP is responsible for 25-50% of homologous desensitization and this may occur via a mechanism other than NK-1R phosphorylation.

Animals↗
PubMed1990

Spinal bone loss and ovulatory disturbances.

BACKGROUND: Osteoporosis develops in women with estrogen deficiency and amenorrhea who lose bone at an accelerated rate. It is not known to what extent bone loss differs between ovulatory women with regular menstrual cycles who are training intensely and those who are sedentary. METHODS: We measured the density of cancellous spinal bone from the 12th thoracic vertebra to the 3rd lumbar vertebra by quantitative computed tomography on two occasions one year apart in 66 premenopausal women 21 to 42 years of age. All the women had two consecutive ovulatory cycles immediately before entering the study. Twenty-one women were training for a marathon, 22 ran regularly but less intensively, and 23 had normal levels of activity. The lengths of the women's menstrual cycles and luteal phases, diet, exercise levels, and hormonal levels were also determined. We defined ovulatory disturbances as anovulatory cycles and cycles with short luteal phases. RESULTS: The mean (+/- SD) spinal bone density in the 66 women decreased 3.0 +/- 4.8 mg per cubic centimeter per year (2.0 percent per year) (P less than 0.001). Amenorrhea did not develop in any woman during the year of observation (only 2.7 percent of the cycles were greater than 36 days long). Ovulatory disturbances occurred in 29 percent of all cycles, however. Bone loss was strongly associated with these disturbances (r = 0.54, 24 percent of the variance). The 13 women who had anovulatory cycles lost bone mineral at a rate of 6.4 +/- 3.8 mg per cubic centimeter per year (4.2 percent per year). The women training for a marathon had menstrual cycles similar to those of the women in the other two groups. CONCLUSION: Decreases in spinal bone density among women with differing exercise habits correlated with asymptomatic disturbances of ovulation (without amenorrhea) and not with physical activity.

Adult↗
PubMed1999

The effect of bisoprolol on perioperative mortality and myocardial infarction in high-risk patients undergoing vascular surgery. Dutch Echocardiographic Cardiac Risk Evaluation Applying Stress Echocardiography Study Group.

BACKGROUND: Cardiovascular complications are the most important causes of perioperative morbidity and mortality among patients undergoing major vascular surgery. METHODS: We performed a randomized, multicenter trial to assess the effect of perioperative blockade of beta-adrenergic receptors on the incidence of death from cardiac causes and nonfatal myocardial infarction within 30 days after major vascular surgery in patients at high risk for these events. High-risk patients were identified by the presence of both clinical risk factors and positive results on dobutamine echocardiography. Eligible patients were randomly assigned to receive standard perioperative care or standard care plus perioperative beta-blockade with bisoprolol. RESULTS: A total of 1351 patients were screened, and 846 were found to have one or more cardiac risk factors. Of these 846 patients, 173 had positive results on dobutamine echocardiography. Fifty-nine patients were randomly assigned to receive bisoprolol, and 53 to receive standard care. Fifty-three patients were excluded from randomization because they were already taking a beta-blocker, and eight were excluded because they had extensive wall-motion abnormalities either at rest or during stress testing. Two patients in the bisoprolol group died of cardiac causes (3.4 percent), as compared with nine patients in the standard-care group (17 percent, P=0.02). Nonfatal myocardial infarction occurred in nine patients given standard care only (17 percent) and in none of those given standard care plus bisoprolol (P<0.001). Thus, the primary study end point of death from cardiac causes or nonfatal myocardial infarction occurred in 2 patients in the bisoprolol group (3.4 percent) and 18 patients in the standard-care group (34 percent, P<0.001). CONCLUSIONS: Bisoprolol reduces the perioperative incidence of death from cardiac causes and nonfatal myocardial infarction in high-risk patients who are undergoing major vascular surgery.

Adrenergic beta-Antagonists↗
PubMed1986

Evidence for a common evolutionary origin of brain and pancreas cholecystokinin receptors.

An evolutionary basis for the distinct forms of cholecystokinin (CCK) receptors in the mammalian brain and pancreas was examined. The brains and pancreases of ratfish, frog, snake, and chicken contained saturable, high-affinity binding sites for iodinated porcine CCK-33. In the ectothermic species, the brain and pancreas CCK receptors exhibited nearly the same relative specificities for various CCKs and gastrins. Sulfated CCK-8 and sulfated gastrin-17 were the most potent while their nonsulfated analogs and gastrin-4 were less potent. By contrast, in the chicken, the specificities of brain and pancreas CCK receptors closely resembled their mammalian counterparts. We conclude that brain and pancreas CCK receptors with new specificities for binding CCKs and gastrins evolved at the level of the divergence of endotherms (birds and mammals) from reptiles. We propose that the prior evolution of gastrin provided the selection pressure for these changes. The endotherm pancreas receptor arose in evolution by narrowing its requirement for the position of a sulfated tyrosine residue in its ligands from either the sixth or seventh position from the carboxyl terminus to the seventh position only. The endotherm brain receptor arose in evolution by losing its requirement for a sulfated ligand and by transferring its high-affinity binding domain from the tyrosine residue in the carboxyl termini of CCK and gastrin to the carboxyl-terminal tetrapeptide active site common to CCKs and gastrins.

Animals↗
PubMed1988

Receptor binding sites for substance P, but not substance K or neuromedin K, are expressed in high concentrations by arterioles, venules, and lymph nodules in surgical specimens obtained from patients with ulcerative colitis and Crohn disease.

Several lines of evidence indicate that tachykinin neuropeptides [substance P (SP), substance K (SK), and neuromedin K (NK)] play a role in regulating the inflammatory and immune responses. To test this hypothesis in a human inflammatory disease, quantitative receptor autoradiography was used to examine possible abnormalities in tachykinin binding sites in surgical specimens from patients with inflammatory bowel disease. Surgical specimens of colon were obtained from patients with ulcerative colitis (n = 4) and Crohn disease (n = 4). Normal tissue was obtained from uninvolved areas of extensive resections for carcinoma (n = 6). In all cases, specimens were obtained less than 5 min after removal to minimize influences associated with degradation artifacts and were processed for quantitative receptor autoradiography by using 125I-labeled Bolton-Hunter conjugates of NK, SK, and SP. In the normal colon a low concentration of SP receptor binding sites is expressed by submucosal arterioles and venules and a moderate concentration is expressed by the external circular muscle, whereas SK receptor binding sites are expressed in low concentrations by the external circular and longitudinal muscle. In contrast, specific NK binding sites were not observed in any area of the human colon. In colon tissue obtained from ulcerative colitis and Crohn disease patients, however, very high concentrations of SP receptor binding sites are expressed by arterioles and venules located in the submucosa, muscularis mucosa, external circular muscle, external longitudinal muscle, and serosa. In addition, very high concentrations of SP receptor binding sites are expressed within the germinal center of lymph nodules, whereas the concentrations of SP and SK binding sites expressed by the external muscle layers are not altered significantly. These results demonstrate that receptor binding sites for SP, but not SK or NK, are ectopically expressed in high concentrations (1000-2000 times normal) by cells involved in mediating inflammatory and immune responses. These data suggest that SP may be involved in the pathophysiology of inflammatory bowel disease and might provide some insight into the interaction between the nervous system and the regulation of inflammation and the immune response in human inflammatory disease.

Autoradiography↗
PubMed1989

Substance P receptor binding sites are expressed by glia in vivo after neuronal injury.

In vitro studies have demonstrated that glia can express functional receptors for a variety of neurotransmitters. To determine whether similar neurotransmitter receptors are also expressed by glia in vivo, we examined the glial scar in the transected optic nerve of the albino rabbit by quantitative receptor autoradiography. Receptor binding sites for radiolabeled calcitonin gene-related peptide, cholecystokinin, galanin, glutamate, somatostatin, substance P, and vasoactive intestinal peptide were examined. Specific receptor binding sites for each of these neurotransmitters were identified in the rabbit forebrain but were not detected in the normal optic nerve or tract. In the transected optic nerve and tract, only receptor binding sites for substance P were expressed at detectable levels. The density of substance P receptor binding sites observed in this glial scar is among the highest observed in the rabbit forebrain. Ligand displacement and saturation experiments indicate that the substance P receptor binding site expressed by the glial scar has pharmacological characteristics similar to those of substance P receptors in the rabbit striatum, rat brain, and rat and canine gut. The present study demonstrates that glial cells in vivo express high concentrations of substance P receptor binding sites after transection of retinal ganglion cell axons. Because substance P has been shown to regulate inflammatory and immune responses in peripheral tissues, substance P may also, by analogy, be involved in regulating the glial response to injury in the central nervous system.

Animals↗
PubMed1992

Reversible in vitro growth of Alzheimer disease beta-amyloid plaques by deposition of labeled amyloid peptide.

The salient pathological feature of Alzheimer disease (AD) is the presence of a high density of amyloid plaques in the brain tissue of victims. The plaques are predominantly composed of human beta-amyloid peptide (beta A4), a 40-mer whose neurotoxicity is related to its aggregation. Radioiodinated human beta A4 is rapidly deposited in vitro from a dilute (less than 10 pM) solution onto neuritic and diffuse plaques and cerebrovascular amyloid in AD brain tissue, whereas no deposition is detectable in tissue without performed plaques. This growth of plaques by deposition of radiolabeled beta A4 to plaques is reversible, with a dissociation half-time of approximately 1 h. The fraction of grey matter occupied by plaques that bind radiolabeled beta A4 in vitro is dramatically larger in AD cortex (23 +/- 11%) than in age-matched normal controls (less than 2%). In contrast to the human peptide, rat/mouse beta A4 (differing at three positions from human beta A4) does not affect the deposition of radiolabeled human beta A4. beta A4 has no detectable interaction with tachykinin receptors in rat or human brain. The use of radioiodinated beta A4 provides an in vitro system for the quantitative evaluation of agents or conditions that may inhibit or enhance the growth or dissolution of AD plaques. This reagent also provides an extremely sensitive method for visualizing various types of amyloid deposits and a means for characterizing and locating sites of amyloid peptide binding to cells and tissues.

Aged↗
PubMed1992

A functional domain in the heavy chain of scatter factor/hepatocyte growth factor binds the c-Met receptor and induces cell dissociation but not mitogenesis.

We recently found that scatter factor (SF), a cell motility factor with a multimodular structure, is identical to hepatocyte growth factor (HGF), a potent mitogen of various cell types. SF/HGF is the ligand of the c-Met receptor tyrosine kinase. Here we used transient expression of naturally occurring and in vitro mutagenized cDNAs of SF/HGF to delineate the protein domains necessary for biological activity and binding to the c-Met receptor. (i) A single-chain SF/HGF resulting from the destruction of the protease cleavage site between heavy and light chain (Arg-494--> Gln) was largely inactive, indicating that proteolytic cleavage is essential for acquisition of the biologically active conformation. (ii) A SF/HGF splice variant encoding a protein with a 5-amino acid deletion in the first kringle domain was as highly active as the wild-type molecule. (iii) The separately expressed light chain (with serine protease homology) was inactive in all assays tested. (iv) The separate heavy chain as well as a naturally occurring splice variant consisting of the N terminus and the first two kringle domains bound the c-Met receptor, stimulated tyrosine auto-phosphorylation, and induced scattering of epithelial cells but not mitogenesis. These data indicate that a functional domain in the N terminus/first two kringle regions of SF/HGF is sufficient for binding to the Met receptor and that this leads to the activation of the downstream signal cascade involved in the motility response. However, the complete SF/HGF protein seems to be required for mitogenic activity.

Amino Acid Sequence↗
PubMed1994

Direct observation of substance P-induced internalization of neurokinin 1 (NK1) receptors at sites of inflammation.

Substance P (SP) can cause plasma leakage at sites of inflammation by binding to neurokinin type 1 (NK1) receptors on the surface of endothelial cells. Internalization after ligand binding could reduce the number of NK1 receptors on the cell surface and thus participate in the desensitization and resensitization of the inflammatory response to SP. By using an antibody to the receptor, we directly observed SP-induced internalization of NK1 receptors into endosomes in endothelial cells of postcapillary venules in the rat tracheal mucosa. In the absence of SP, an average of 15 immunoreactive endosomes were present per endothelial cell. After an intravenous injection of SP, the number of immunoreactive endosomes peaked at 107 per cell at 3 min and gradually returned to the baseline by 120 min. In parallel experiments we observed that when cultured cells transfected with the NK1 receptor were exposed to rhodamine-SP and an antibody to an extracellular Flag epitope of the NK1 receptor, the SP was internalized with the receptor antibody. Both in the cultured cells and in the endothelial cells of intact animals, the prompt SP-induced internalization was accompanied by rapid, long-lasting desensitization to SP. These studies suggest that internalization of NK1 receptors by endothelial cells may be one of the mechanisms that limit the amount of plasma leakage at sites of inflammation.

Animals↗
PubMed1994

Synaptic relationship between substance P and the substance P receptor: light and electron microscopic characterization of the mismatch between neuropeptides and their receptors.

Light microscopic studies have demonstrated significant mismatches in the location of neuropeptides and their respective binding sites in the central nervous system. In the present study we used an antiserum raised against a synthetic peptide corresponding to the carboxyl-terminal tail of the substance P (SP) receptor (SPR) to further explore the relationship between a neuropeptide and its receptor. Light microscopy revealed an excellent correlation between the patterns of SPR immunoreactivity and of 125I-labeled SPR-binding sites in the central nervous system. The SPR appeared to be exclusively expressed by neurons; in fact, the SPR decorates the somatic and dendritic surface of neurons, producing Golgi-like images. Electron microscopic analysis in cortex, striatum, and spinal cord revealed that approximately 70% of the surface membrane of immunoreactive neurons is SPR laden. Simultaneous electron microscopic labeling of SP and SPR demonstrated significant mismatch at the synaptic level. Although some SP terminals contacted SPR-immunoreactive membrane, no more than 15% of the SPR-laden membrane apposed synaptic terminals. These results suggest that in contrast to more "classical" central and peripheral nervous system synapses, wherein the receptor immediately apposes the site of neurotransmitter storage and release, much of the surface of SPR-expressing neurons can be targeted by SP that diffuses a considerable distance from its site of release.

Animals↗
PubMed1995

Rapid endocytosis of a G protein-coupled receptor: substance P evoked internalization of its receptor in the rat striatum in vivo.

Studies on cultured cells have shown that agonists induce several types of G protein-coupled receptors to undergo internalization. We have investigated this phenomenon in rat striatum, using substance P (SP)-induced internalization of the SP receptor (SPR) as our model system. Within 1 min of a unilateral striatal injection of SP in the anesthetized rat, nearly 60% of the SPR-immunoreactive neurons within the injection zone display massive internalization of the SPR--i.e., 20-200 SPR+ endosomes per cell body. Within the dendrites the SPR undergoes a striking translocation from the plasma membrane to endosomes, and these dendrites also undergo a morphological reorganization, changing from a structure of rather uniform diameter to one characterized by large, swollen varicosities connected by thin fibers. In both cell bodies and dendrites the number of SPR+ endosomes returns to baseline within 60 min of SP injection. The number of neurons displaying substantial endosomal SPR internalization is dependent on the concentration of injected SP, and the SP-induced SPR internalization is inhibited by the nonpeptide neurokinin 1 receptor antagonist RP-67,580. These data demonstrate that in the central nervous system in vivo, SP induces a rapid and widespread SPR internalization in the cell bodies and dendrites and a structural reorganization of the dendrites. These results suggest that many of the observations that have been made on the internalization and recycling of G protein-coupled receptors in in vitro transfected cell systems are applicable to similar events that occur in the mammalian central nervous system in vivo.

Analysis of Variance↗