The antagonism of bombesin in the CNS by substance P analogues

The lipid-associated 3D structure of SPA, a broad-spectrum neuropeptide antagonist with anticancer properties

[D-Arg(1), D-Trp(5,7,9), Leu(11)] substance P (SPA) belongs to a family of peptides including antagonist G and SpD that act as broad-spectrum neuropeptide antagonists at several peripheral receptors. The lipid-induced structure of these peptides may be important for the receptor interactions of these analogs. Thus we describe the tertiary structure of SPA in the presence of sodium dodecylsulfate micelles at pH 5.0, and 25 degrees C as determined from two-dimensional (1)H-NMR data recorded at 500 MHz. The resulting three-dimensional structure can be generally described as two type IV nonstandard turns around Arg(1)*, Pro(2), Lys(3), and Pro(4) and Gln(6), Trp(7)*, Phe(8), and Trp(9)* residues, respectively, inserted into the interfacial region of the micelles (the asterisks denote D-form amino acid). These turns juxtapose the N- and C-termini of SPA and may form the basis of this peptide's unique ability to inhibit peptide receptor interactions at multiple receptor types.

Capsaicin-sensitive fibers are required for the anorexic action of systemic but not central bombesin

Bombesin (BN) suppresses food intake in rats whether given centrally or systemically. Although the brain BN-sensitive receptors are known to be essential for the anorexic effect of systemic BN, the mode of communication between the gut and the brain remains unclear. This study assessed whether the anorexic effect of systemic BN is mediated humorally or via neural circuits. Afferent neurons were lesioned using capsaicin (50 mg/kg sc) on postnatal day 2, and responses to BN were assessed during adulthood. Capsaicin treatment decreased body weight gain significantly from postnatal age 4-7 wk. Peripheral BN (4-16 micrograms/kg ip) dose dependently suppressed food intake in control animals. However, this effect was completely blocked in capsaicin-treated rats. In contrast to systemic effects, feeding-suppressant effects of centrally administered BN (0.01-0.5 microgram icv) were not affected by capsaicin treatment. This research suggests that peripheral BN communicates with the brain via a neuronal system(s) whose afferent arm is constituted of capsaicin-sensitive C and/or Adelta-fibers, whereas the efferent arm of this satiety- and/or anorexia-mediating circuitry is capsaicin resistant.

Tachykinins: receptor to effector

Tachykinins belong to an evolutionarily conserved family of peptide neurotransmitters. The mammalian tachykinins include substance P, neurokinin A and neurokinin B, which exert their effects by binding to specific receptors. These tachykinin receptors are divided into three types, designated NK1, NK2 and NK3, respectively. Tachykinin receptors have been cloned and contain seven segments spanning the cell membrane, indicating their inclusion in the G-protein-linked receptor family. The continued development of selective agonists and antagonists for each receptor has helped elucidate roles for these mediators, ranging from effects in the central nervous system to the perpetuation of the inflammatory response in the periphery. Various selective ligands have shown both inter- and intraspecies differences in binding potencies, indicating distinct binding sites in the tachykinin receptor. The interaction of tachykinin with its receptor activates Gq, which in turn activates phospholipase C to break down phosphatidyl inositol bisphosphate into inositol trisphosphate (IP3) and diacylglycerol (DAG). IP3 acts on specific receptors in the sarcoplasmic reticulum to release intracellular stores of Ca2+, while DAG acts via protein kinase C to open L-type calcium channels in the plasma membrane. The rise in intracellular [Ca2+] induces the tissue response. With an array of actions as diverse as that seen with tachykinins, there is scope for numerous therapeutic possibilities. With the development of potent, selective non-peptide antagonists, there could be potential benefits in the treatment of a variety of clinical conditions, including chronic pain, Parkinson's disease, Alzheimer's disease, depression, rheumatoid arthritis, irritable bowel syndrome and asthma.

Ionophoretically applied substance P activates hamster suprachiasmatic nucleus neurons

ionophoretic ejection of substance P (SP) activated 31% and suppressed 9% of hamster suprachiasmatic nucleus (SCN) cells in vitro. Hamster SCN cells did not demonstrate variation in sensitivity to SP across the circadian phases tested. SP modulated the response of 47% of hamster SCN cells to the excitatory amino acid (EAA) agonists glutamate and N-methyl-D-aspartate (NMDA). The results indicate that SP can alter both the spontaneous and EAA-evoked firing rate characteristics of hamster SCN neurons.

A novel synthetic phyllolitorin analogue [desTrp3,Leu8]phyllolitorin inhibits scratching behavior induced by neuromedin C in rats

[DesTrp3,Leu8]phyllolitorin (DTP) (pGlu-Leu-Ala-Val-Gly-Ser-Leu-Met-NH2) was synthesized as an analogue of phyllolitorins, a new member of bombesin family, and examined if it antagonized neuromedin C (NMC)-induced scratching. DTP inhibited dose-dependently the scratching behavior by NMC (1 microgram), whereas it did not alter any element of other grooming behaviors. DTP (6 micrograms) alone was found to be neither toxic nor active in inducing both scratching and grooming, which were comparable to vehicle alone. Assuming that the scratching behavior is commonly and specifically elicited by bombesin family peptides, DTP might be classified as a new type of bombesin antagonist.

Depression of primary afferent-evoked responses by GR71251 in the isolated spinal cord of the neonatal rat

1. The pharmacological profile of GR71251, a new tachykinin receptor antagonist, and its effect on the responses evoked by stimulation of primary afferent fibres were studied in isolated spinal cord preparations of neonatal rats. Potential changes were recorded extracellularly from a lumbar ventral root (L3-L5). 2. Bath-application of substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) at 0.01-3 microM to the spinal cord induced depolarization of the ventral root in normal artificial cerebrospinal fluid (CSF). The NK1 agonist, acetyl-Arg6-septide, and the NK3 agonist, senktide, at 0.01-3 microM, also had potent depolarizing actions whereas two NK2 agonists, beta-Ala8NKA4-10 and Nle10NKA4-10, showed little depolarizing effects at 1 microM. 3. GR71251 (0.3-3 microM) caused a rightward shift of the concentration-response curves for SP, acetyl-Arg6-septide and NKA with pA2 values of 6.14, 6.75 or 6.70, respectively. The effects of GR71251 were readily reversible within 15-30 min after its removal. By contrast, GR71251 (1-5 microM) had little effect on the depolarizing responses to NKB and senktide. 4. GR71251 (1-3 microM) did not depress the depolarizing responses to bombesin, neuromedin B and gastrin-releasing peptide in normal artificial CSF. 5. Application of capsaicin to the spinal cord induced a depolarizing response, which was partially depressed by GR71251 (3-10 microM). 6. In the isolated spinal cord preparation, intense electrical stimulation of a dorsal root evoked a slow depolarizing response of the contralateral ventral root of the same segment. A similar slow ventral root depolarization was evoked by electrical stimulation of the ipsilateral saphenous nerve in an isolated spinal cord-saphenous nerve preparation. GR71251 (0.3-10 microM) dose-dependently depressed these slow ventral root potentials.7. In the spinal cord-peripheral nerve preparation, conditioning stimulation of the saphenous nerve evoked an inhibition of the muscle nerve-evoked monosynaptic reflex lasting about 20 s. The late part of the inhibition was markedly depressed by GR71251 (1-3 microM).8. The present results indicate that GR71251 is a potent and specific antagonist for tachykinin receptors in the spinal cord. The present study further provides evidence for the involvement of SP and NKA in the slow ventral root depolarization and the prolonged inhibition of monosynaptic reflex that are evoked by primary afferent stimulation.

Alpha-1 adrenoceptor subtypes in canine aorta

The present study was designed to demonstrate the existence in canine aorta of alpha 1-adrenoceptor subtypes, alpha 1High and alpha 1Low, that have different binding affinities for 3H-prazosin and to assess the binding affinity of several drugs for each subtype by a displacement experiment. A radioligand binding assay with 3H-prazosin revealed the presence of two alpha 1-adrenoceptor subtypes in the canine aorta. One of them which has a high affinity for prazosin was designated as alpha 1High (Kd: 12.40 pM, Bmax: 21.88 fmol/mg protein), and the other type was designated as alpha 1Low (Kd: 506.03 pM, Bmax: 88.22 fmol/mg protein). The pKi values of several drugs for each subtype were determined, and all drugs used in the present study, except for benoxathian and chlorethylclonidine, showed significant differences between the pKi values for alpha 1High and those for alpha 1Low. Although it is difficult to characterize each alpha 1High and alpha 1Low into alpha 1A or alpha 1B by only the displacement potency, one structural characteristic to distinguish between alpha 1High and alpha 1Low could be evaluated.

Galanin receptor antagonists M40 and C7 block galanin-induced feeding

Two peptide antagonists of the galanin receptor, M40 (galanin[1-13]-Pro-Pro-[Ala-Leu]2-Ala amide) and C7 (galanin[1-13]-spantide amide), significantly inhibited galanin-induced consumption of a palatable wet cookie mash, when microinjected intraventricularly to satiated rats. Antagonists were effective at doses equimolar to or less than the active doses of galanin. Feeding induced by an overnight fast was not significantly different in rats microinjected with saline as compared to M40 or C7, at doses which inhibited galanin-induced feeding. The activity of the chimeric compound, C7, did not appear to be linked to the properties of its C-terminal spantide-like sequence, as C7 did not induce barrel rolling at doses which inhibited galanin-induced feeding. The IC50 for displacement of 125I-[Tyr26]-porcine galanin 1-29 binding in rat hypothalamic membranes was 15 nM for M40, and 0.2 nM for C7, as compared to 0.8 nM for unlabelled porcine galanin(1-29). These two structurally different galanin antagonists, both demonstrating antagonist activity in vivo in awake, behaving rats, provide promising tools for further analyses of the functional activity of galanin in the mammalian brain.

[D-Arg1, D-Phe5, D-Trp7,9, Leu11] substance P inhibits the growth of human small cell lung cancer xenografts in vivo

We report the effect of substance P analogue, [D-Arg1, D-Phe5, D-Trp7,9, Leu11] substance P (D-Phe5SP), on the growth of human small cell lung cancer (SCLC) xenografts HC12 and ICR-SC112. Daily intraperitoneal (ip) administration (500 micrograms/day for 3 weeks) had no effect on HC12 growth rate. When administered by continuous 14-day subcutaneous (sc) infusion by osmotic minipump implanted adjacent to the tumour, D-Phe5SP 2.1 micrograms/day, caused significant inhibition (P < 0.05) of the growth of HC12 and ICR-SC112 on day 7 and day 14 compared with phosphate buffered saline (PBS)-treated controls. HC12 and ICR-SC112 tumour volume remained at 53-67% of control for 14-21 days postinfusion. D-Phe5SP 1 mg/day did not inhibit tumour growth, but dense fibrous capsules developed at the minipump outlet. Animals treated by sc infusion (but not ip) of PBS or D-Phe5SP failed to gain weight, and some groups lost weight. D-Phe5SP-treated animals had lower white blood counts than controls (not significant). These data suggest a potential clinical role for D-Phe5SP in the treatment of SCLC.

Naloxone-reversible effect of spantide on the spinally mediated behavioural response induced by neurokinin-2 and -3 receptor agonists

[D-Arg1, D-Trp7,9, Leu11]-substance P (spantide) was tested for antagonism against the licking, biting and scratching response induced by various neurokinin (NK) receptor agonists and bombesin (Bom) in mice. When co-administered with substance P (SP) intrathecally, spantide reduced the SP-induced behavioural responses in a dose-dependent manner. The duration of this antagonistic effect was approximately 30 min. Behavioural responses induced by physalaemin (Phy), [pGlu6, L-Pro9]-SP (6-11) (septide), [pGlu6, D-Pro7]-SP (6-11) (D-septide) and eledoisin (Ele) were also dose-dependently decreased by relatively small doses of spantide. Higher doses of spantide were needed to reduce the behavioural responses induced by [Sar9, Met (O2)11]-SP, neurokinin A (NK A) and neurokinin B (NK B). No significant effect of spantide was observed against the behavioural responses elicited by Bom. Pretreatment with naloxone, an opioid antagonist, resulted in a reversible effect on the behavioural reduction of NK-2 and NK-3 receptor agonists produced by spantide. However, the effect of spantide on the NK-1 receptor agonist-induced response was unchanged by naloxone. In homogenates of mouse spinal cord, competition studies confirmed that the binding of the opioid ligand [3H]naloxone was displaced by spantide with a low but measurable affinity. These results suggest that the behavioural response to NK-2 and NK-3 receptor agonists may be partially inhibited by spantide through the activation of opioid system in the mouse spinal cord.

In vitro effects of substance P analogue [D-Arg1, D-Phe5, D-Trp7,9, Leu11] substance P on human tumour and normal cell growth

Analogues of the neurotransmitter substance P (SP) can interact with neuropeptide receptors, and are reported to inhibit growth of small cell lung cancer cell lines (SCLC CLs). We found [D-Arg1, D-Phe5, D-Trp7,9, Leu11] substance P (D-Phe5SP) significantly inhibited DNA synthesis by 10/10 human tumour CLs; six SCLC, one N-SCLC (squamous), two ovarian and one squamous cervical carcinoma, with inhibition to 50% control levels (IC50) of 20-50 microM. There was dose dependent inhibition of colony forming efficiency (CFE) in 3/3 SCLC and 1/1 N-SCLC CL, IC50s of 0.5-6.5 microM in 5% serum. Exposure of SCLC CL HC12 to 100 microM D-Phe5SP for 1-4 h caused a progressive fall in viable cell number; surviving cells, grown in the absence of peptide, showed a decreased growth rate. During 1 week's exposure of two SCLC CLs to 20 microM D-Ph5SP, growth was slower than control cultures, while 50-100 microM completely inhibited growth. These inhibitory effects were partially reversed by increasing serum concentration from 5 to 20%, but not by SP, vasopressin, bombesin or insulin-like growth factor 1. There was some inhibition of CFE by 3/3 normal human bone marrows, IC50s of 30-80 microM, compared with 8 microM for HC12 in 20% FCS. Therefore D-Phe5SP appears to have more potent antiproliferative effects in tumour cells than normal cells, suggesting a role for this analogue in tumour treatment.

Novel selective agonists and antagonists confirm neurokinin NK1 receptors in guinea-pig vas deferens

1. This study investigated the recognition characteristics of neurokinin receptors mediating potentiation of the contractile response to field stimulation in the guinea-pig vas deferens. 2. A predominant NK1 receptor population is strongly suggested by the relative activities of the common naturally-occurring tachykinin agonists, which fall within less than one order of magnitude. This conclusion is supported by the relative activities of the synthetic NK1 selective agonists substance P methyl ester, [Glp6,L-Pro9]-SP(6-11) and delta-aminovaleryl-[L-Pro9,N-MeLeu10]- SP(7-11) (GR73632) which were 0.78, 9.3 and 120 as active as substance P, respectively. Furthermore, the NK2 selective agonist [Lys3, Gly8,-R-gamma-lactam-Leu9]-NKA(3-10) (GR64349) was active only at the highest concentrations tested (greater than 10 microM), and the NK3 selective agonist, succ-[Asp6,N-MePhe8]-SP(6-11) (senktide) was essentially inactive (10 nM-32 microM). 3. [D-Arg1,D-Pro2,D-Trp7,9,Leu11]-SP(1-11) antagonized responses to neurokinin A, neurokinin B, physalaemin, eledoisin, [Glp6,D-Pro9]-SP(6-11), GR73632 and GR64349 (apparent pKB s 5.6-6.2), but was less potent in antagonizing responses to substance P, substance P methyl ester and [Glp6,L-Pro9]-SP(6-11) (apparent pKB s less than or equal to 5.0-5.0). 4. In contrast, the recently developed NK1-selective receptor antagonist [D-Pro9[Spiro-gamma-lactam]Leu10,Trp11]-SP(1-11) (GR71251) did not produce agonist-dependent pKB estimates. Schild plot analysis indicated a competitive interaction with a single receptor population where the antagonist had an estimated overall pKB of 7.58 +/- 0.13 for the four agonists of differing subtype selectivity tested (GR73632, GR64349, substance P methyl ester and neurokinin B). This estimate is similar to that we obtained for NK1-mediated (substance P methyl ester) contraction in the guinea-pig ileum preparation (pKB= 7.86+ 0.05). 5. Tachykinin action appears not to depend on release of a number of intermediary mediators including acetylcholine, histamine or cyclo-oxygenase products, nor to involve interaction with neuronal mechanisms including alpha 2-adrenoceptor feedback, noradrenergic Uptake-I or opioid-release, since antagonism or inhibition of these mechanisms did not modify responses to tachykinins. 6. We conclude that tachykinin action in the field-stimulated guinea-pig vas deferens preparation is mediated through interaction with a predominant neurokinin NK, receptor population and this preparation can therefore be used to study NK, modulation of sympathetic neurotransmission.

Progress in the development of potent bombesin receptor antagonists

Bombesin and the mammalian-related peptides gastrin-releasing peptide (GRP), GRP and neuromedin B have been shown to have numerous actions in the CNS, gastrointestinal tract and on growth. However, the role of the peptides in various physiological processes has remained unclear because of the lack of potent antagonists. Recent in vitro studies have described four different classes of bombesin receptor antagonist, some of which are active in the nanomolar range and in vivo. Robert Jensen and David Coy describe recent insights into peptide structural determinants of biological activity. Evidence from structure-function studies have resulted in identification of some analogues that function as potent antagonists in all systems examined. Furthermore, various subtypes of bombesin receptors can now be differentiated by these various classes of antagonist.

Effect of vasoactive intestinal peptide, bombesin and substance P on fluid secretion by isolated rat pancreatic ducts

1. We have used micropuncture techniques to study the regulation of fluid secretion by interlobular ducts isolated from the pancreas of copper-deficient rats. 2. Ducts isolated from different strains of Wistar rats exhibited quantitative differences in basal fluid secretion; however, secretion rates measured in the presence of secretin were similar. 3. Vasoactive intestinal peptide had no effect on fluid transport. 4. Bombesin stimulated fluid secretion, and this effect was abolished by removal of extracellular bicarbonate. 5. Substance P inhibited basal secretion, and that stimulated by bombesin and secretin. These inhibitory effects were partially reversed by spantide. 6. Substance P also inhibited fluid secretion stimulated by dibutyryl cyclic AMP and forskolin. This places the site of inhibition mediated by substance P at a point in the secretory mechanism distal to the generation of cyclic AMP. 7. We conclude that rat pancreatic duct cells possess receptors for bombesin and substance P, in addition to 'secretin-preferring' receptors. Since VIP had no effect on fluid transport, it is unlikely that 'VIP-preferring' receptors are present on rat duct cells.

Pharmacological properties of a C-fibre response evoked by saphenous nerve stimulation in an isolated spinal cord-nerve preparation of the newborn rat

1. An isolated spinal cord-peripheral nerve preparation of the newborn rat was developed. In this preparation it is possible to record spinal reflexes from a lumbar ventral root in response to stimulation of the ipsilateral saphenous or obturator nerve. 2. Single shock, weak intensity stimulation of the saphenous nerve induced a fast conducted compound action potential in the L3 dorsal root and a fast depolarizing response in the ipsilateral L3 ventral root. As a stronger stimulus was applied to the saphenous nerve, a slowly conducted compound action potential appeared in the dorsal root and a slow depolarizing ventral root potential (v.r.p.) in the L3 ventral root. 3. Single shock stimulation of the obturator nerve induced a rapidly conducted compound action potential in the L3 dorsal root and monosynaptic and polysynaptic reflexes, with a fast time course, in the ipsilateral L3 ventral root. 4. The slow v.r.p. evoked by saphenous nerve stimulation was depressed by the tachykinin antagonist, [D-Arg1, D-Trp7,9, Leu11] substance P (spantide), 4-16 microM. The response recovered its original shape and size 30-60 min after the removal of this antagonist. 5. The saphenous nerve-evoked slow v.r.p. was depressed by [Met5] enkephalin (0.1-1 microM), dynorphin (1-13)(0.2 microM) and morphine (1-2 microM), and these effects were reversed by naloxone (1 microM). 6. Two endogenous peptides, galanin (1-2 microM) and somatostatin (1-2.5 microM), inhibited the slow v.r.p. evoked by saphenous nerve stimulation, whereas another endogenous peptide, calcitonin gene-related peptide (0.1-0.5 microM), potentiated the slow v.r.p. The slow v.r.p. was also inhibited by gamma-aminobutyric acid (GABA, 20 microM) and muscimol (0.2 microM), and their effects were antagonized by bicuculline (1 microM). 7. The present results suggest that substance P and neurokinin A are involved in the saphenous nerve-evoked C-fibre response in the spinal cord of the newborn rat.

Localization of receptors for bombesin-like peptides in the rat brain

BN-like peptides and receptors are present in discrete areas of the mammalian brain. By radioimmunoassay, endogenous BN/GRP, neuromedin B, and ranatensin-like peptides are present in the rat brain. High-to-moderate concentrations of BN/GRP are present in the rat hypothalamus and thalamus, whereas moderate-to-high densities of neuromedin B and ranatensin-like peptides are present in the olfactory bulb and hippocampus, as well as in the hypothalamus and thalamus. While the distribution of neuromedin B and ranatensin-like peptides appears similar, it is distinct from that of BN/GRP. When released from CNS neurons, these peptides may interact with receptors for BN-like peptides. BN, GRP, ranatensin, and neuromedin B inhibit specific [125I-Tyr4]BN binding with high affinity. By use of in vitro autoradiographic techniques to detect binding of [125I-Tyr4]BN to receptors for BN-like peptides, high grain densities were found in the olfactory bulb and tubercle, the nucleus accumbens, the suprachiasmatic and paraventricular nucleus of the hypothalamus, the central medial and paraventricular thalamic nuclei, the hippocampus, the dentate gyrus, and the amygdala of the rat brain. Some of these receptors may be biologically active and mediate the biological effects of BN-like peptides. For example, when BN is directly injected into the nucleus accumbens, pronounced grooming results and the effects caused by BN are reversed by spantide and [D-Phe12]BN. Thus, the putative BN receptor antagonists may serve as useful agents to investigate the biological significance of BN-like peptides in the CNS.

Substance P analogues function as bombesin receptor antagonists and inhibit small cell lung cancer clonal growth

Human small cell lung cancer (SCLC) produces and secretes BN/GRP (bombesin/gastrin releasing peptide). Because BN stimulates the growth of SCLC cells and these cells have receptors for BN-like peptides, it is important to define agents which disrupt this self-promoting autocrine growth cycle. Here, substance P analogues were evaluated as BN receptor antagonists using SCLC cell lines. (D-Arg1, D-Pro2, D-Trp7.9, Leu11) substance P [(APTTL)SP] was one of the more potent analogues tested in inhibiting BN-like peptide receptor binding with an IC50 value of 1 microM. Micromolar concentrations of (APTTL)SP antagonized BN receptor mediated elevation of cytosolic Ca2+ levels and decreased the colony formation in soft agarose. These data suggest that SP analogues function as SCLC BN receptor antagonists and may be useful in disrupting the autocrine growth function of BN-like peptides.

An analogue of substance P with broad receptor antagonist activity

[DPro4,DTrp7,9,10]Substance P-4-11 functions as a substance P receptor antagonist in several different systems. Because some analogues of substance P can function as receptor antagonists for bombesin as well as substance P, we tested [DPro4,DTrp7,9,10]substance P-4-11 for its ability to modify the interaction of various pancreatic secretagogues with their receptors in dispersed acini from guinea pig pancreas. [DPro4,DTrp7,9,19]Substance P-4-11 did not stimulate amylase secretion and did not alter the stimulation of amylase secretion caused by secretin, vasoactive intestinal peptide, calcitonin gene-related peptide or carbachol, but did inhibit the stimulation of amylase secretion caused by substance P, bombesin or cholecystokinin. With substance P, bombesin and cholecystokinin, [DPro4,DTrp7,9,10]substance P-4-11 caused a parallel rightward shift in the dose-response curve for stimulation of amylase secretion with no change in the maximal response. Schild plots of these results gave straight lines with slopes that were not significantly different from unity. [DPro4,DTrp7,9,10]Substance P-4-11 inhibited binding of 125I-labeled substance P, 125I-[Tyr4]bombesin and 125I-cholecystokinin octapeptide over the same range of concentrations as that in which it inhibited biologic activity of each of these peptides. Half-maximal inhibition of binding of 125I-substance P occurred with 4 microM, of 125I-[Tyr4]bombesin with 17 microM and of 125I-cholecystokinin octapeptide with 5 microM. With each radiolabeled peptide the value of Ki for inhibition of binding by [DPro4,DTrp7,9,10]substance P-4-11 was not significantly different from the corresponding value of Ki calculated from the appropriate Schild plot. The present results indicate that [DPro4,DTrp7,9,10]substance P-4-11 is a competitive antagonist at receptors for substance P, for bombesin and for cholecystokinin. Thus, these receptors must share a common peptide recognition mechanism even though they interact with agonists that have no obvious structural similarity.

In vivo motor effects of substance P on the rat urinary bladder

Intravesical pressure recordings of the urinary bladder in anesthetized rats were performed and the role of substance P (SP) in the motor control of this organ was evaluated. Regional injection of SP (0.4 nmoles i.a.) into the superior vesical artery elicited a prompt bladder contraction; this motor response was dosedependent. The detrusor contraction could be completely inhibited by a SP-analogue, (D-Pro2, D-Trp7,9)-SP (45-90 nmoles i.a.). Furthermore, the detrusor contraction evoked by preganglionic stimulation of the pelvic nerves was partially inhibited by the same antagonist in a higher dose (65% reduction at a total dose of 150-300 nmoles). The contractile response to SP (0.5 nmoles i.a.) was also significantly reduced after blockade of muscarinic receptors with atropine (50% reduction at 1 mg/kg i.a.) or after ganglionic blockade with hexamethonium (75% reduction at 25 mg/kg i.v. + 50 mg/kg hr i.a.). Immunocytochemical studies demonstrated the occurrence of SP-immunopositive nerve terminals in the detrusor part of the rat urinary bladder. Based on these findings it is suggested that SP may act as a neurotransmitter/modulator in this organ. The mechanism of action for SP on the detrusor seems to be complex and may involve ganglionic transmission via both types of cholinoceptors as well as direct activation of smooth muscle.

Bombesin-induced grooming in the golden hamster

Lateral cerebroventricular injection of the peptide bombesin (0.01-1.0 micrograms) promptly elicited excessive grooming and scratching behaviors in home-caged male and female golden hamsters. Bombesin-induced grooming persisted throughout a 60-min observation period at doses of 0.1-1.0 micrograms. Grooming with forepaws and mouth was more consistently increased than hindleg scratching behaviors. Dependence of this neuropeptide effect on grooming on muscarinic cholinergic activity was assessed by injecting scopolamine (0.001-1 mg/kg) intraperitoneally 15 min prior to 0.1 microgram bombesin. Excessive grooming induced by centrally administered bombesin was abolished by 0.1 and 1 mg/kg scopolamine, although basal level of grooming was not significantly affected. The findings indicate a cross-species generality of the dependence of bombesin-induced grooming on muscarinic cholinergic activity, and species-specific differences among rodents in the components of excessive grooming elicited by bombesin.

Effects of substance P analogues on spinal dorsal horn neurons

The effects of iontophoretically applied (D-Pro2, D-Phe7, D-Trp9)-SP and (D-Pro2, D-Trp7,9)-SP on the spontaneous and evoked activity of functionally identified cat spinal dorsal horn neurons have been investigated in vivo by means of extracellular single unit recording technique. In addition, the rat spinal cord slice preparation has been used to study the actions of (D-Pro2, D-Trp7,9)-SP and (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-SP on the resting membrane potential of dorsal horn neurons and also on their responses to dorsal root stimulation and exogenous SP application. We have observed that both (D-Pro2, D-Phe7, D-Trp9)-SP and (D-Pro2, D-Trp7,9)-SP produced an excitation of about 15% of all neurons tested and had a weak antagonistic effect against SP in the cat spinal cord. (D-Pro2, D-Trp7,9)-SP suppressed the SP-induced excitation in 63% of examined cells. In addition, depression of the glutamate-induced excitation and spontaneous activity was evident in 10% and 19% of the cat dorsal horn neurons tested, respectively. In the spinal cord slice preparation (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-SP proved to be a more potent antagonist of the SP-induced depolarization and the dorsal root-elicited slow depolarization, if compared with (D-Pro2, D-Trp7,9)-SP.

Localization of tachykinin binding sites (NK1, NK2, NK3 ligands) in the rat brain

A comparative autoradiographic analysis of the distribution of tachykinin binding sites was made on brain serial sections using several ligands. (1) 3H-SP, 125I-BHSP and 3H-physalaemin labeled identical binding sites (NK1 type). (2) 3H-NKB, 125I-BHE and 3H-eledoisin also labeled identical sites (NK3 type). (3) 125I-BHNKA preferentially labeled NK3 binding sites, the distribution of 125I-BHNKA binding sites being identical to that of 3H-NKB or 125I-BHE binding sites. (4) The distributions of 3H-SP and 3H-NKB binding sites were markedly different. (5) A very low density of labeling was found with 3H-NKA or 125I-NKA, and these binding sites were distributed only in areas rich in either 3H-SP or 3H-NKB binding sites. (6) Particular efforts were made to look for the presence of tachykinin binding sites in the substantia nigra, since this structure is particularly rich in SP and NKA and contains functional tachykinin receptors of the NK1 and NK2 types as suggested by physiological studies. Confirming previous reports, low or very low labeling was observed in the substantia nigra with 3H-SP or 125I-BHSP and 3H-NKB or 125I-BHE. Similar results were found with 3H-NKA, 125I-NKA or 125I-BHNKA. In conclusion, our data do not provide evidence yet for the existence of NK2 binding sites in the rat brain.

Concentration of carbon dioxide, interstitial pH and synaptic transmission in hippocampal formation of the rat

1. Interstitial pH (pHo) was measured with ion-selective microelectrodes in the fascia dentata of rats anaesthetized with urethane, while CO2 levels were controlled by varying pulmonary ventilation and CO2 content of inspired air. In the CA1 sector of hippocampal tissue slices in vitro pHo was similarly measured and altered by varying CO2 in the gas phase, or by adding HCl or NaOH to the artificial cerebrospinal fluid (ACSF) of the bath, or by changing the concentration of HCO3-. 2. Orthodromically evoked compound action potentials ('population spikes') were depressed in hypercapnia and increased in hypocapnia. In the fascia dentata of intact brains the population spike of the granule cells varied on average by more than 40% of control amplitude for each 0.1 change of pHo. In the CA1 zone of tissue slices in vitro, the change of population spike amplitude was approximately 30% per pH change of 0.1 caused by altered CO2 or HCO3- concentration, but only about 15% per pH change of 0.1 when HCl or NaOH were administered. 3. In anaesthetized rats the focal synaptic potential (FEPSP) evoked by a given stimulus intensity was weakly influenced by varying [CO2]; in tissue slices weak effects on FEPSP were inconsistent. In hippocampus both in situ and in vitro the population spike triggered by a given magnitude of FEPSP increased in hypocapnia and decreased in hypercapnia. This suggests that the main effect of CO2 is on the electric excitability of postsynaptic cells, with minor or no effect on transmitter release and on the interaction of the transmitter with its receptors. 4. Hypercapnia of anaesthetized rats was usually associated with a slight increase of [K+]o in the fascia dentata. Tissue [Ca2+]o changed little and not consistently. Neither of these two ions, nor concomitant changes of blood pressure or tissue partial pressure of oxygen, (Pt, O2), could account for the effects of pH on neuronal excitability. 5. The results show that increasing the extracellular concentration of H+ ions has a moderately depressant effect on the firing threshold of hippocampal neurones. The more powerful effects of elevated [CO2] and of lowered [HCO3-] may probably be explained by a direct effect on the neuronal membrane. The brain, by regulating breathing, controls its own excitability.

Substance P antagonists block carbachol-induced "boxing" behavior at a site of coexistence in the rat prefrontal cortex

A cholinergic projection from the dorsolateral tegmentum to the medial anterior cortex has previously been shown to contain substance P and corticotropin releasing factor. Behavioral analysis of acetylcholine, substance P and corticotropin releasing factor microinjected into the medial anterior cortex revealed a seizure-related "boxing" behavior elicited by carbachol, which was potentiated by coinjection with substance P and antagonized by coinjection with corticotropin releasing factor. We now report that two antagonists of substance P receptors, [D-Pro2, D-Phe7, D-Trp9]-substance P and [D-Pro2, D-Trp7,9]-substance P, attenuate "boxing" behavior when coinjected with carbachol. Neither antagonist produced observable behavioral effects when microinjected alone. An analog of substance P, [pGlu,5, MePhe,8 Sar9]-substance P (5-11) potentiated carbachol-induced "boxing" at doses similar to naturally-occurring substance P. Monoclonal and polyclonal antisera against substance P were not effective antagonists of carbachol-induced "boxing." The ability of substance P antagonists to block carbachol-induced "boxing" has two major implications: (1) endogenous substance P may be modulating endogenous acetylcholine in the tegmental-cortical pathway; and (2) substance P antagonists may provide a new avenue for the development of antiepileptic drugs.

(D-Phe12) bombesin and substance P analogues function as central bombesin receptor antagonists

The potency of synthetic bombesin (BN) analogues with D-Phe12 substitutions and substance P analogues was investigated in the rat CNS. (D-Phe12,Leu14)BN, (D-Phe12)BN and (Tyr4,D-Phe12)BN inhibited binding to rat brain slices with IC50 values of approximately 2 microM. Similarly, spantide inhibited binding to rat brain slices with an IC50 value of 1.5 microM. Spantide inhibited specific (125I-Tyr4)BN binding as a result of decreased rate of association, whereas the rate of dissociation was unaffected. Neither the (D-Phe12)BN analogues nor the substance P analogues inhibited specific binding of 125I-VIP to rat brain slices. Central administration of BN (0.5 micrograms) induced grooming and suppressed feeding and resting. (Tyr4, D-Phe12)BN (5 micrograms) antagonized the behavioral effects of BN. Although spantide (2 micrograms) also antagonized many of the BN effects, it had intrinsic effects and hence the behavioral antagonism was not specific. These data suggest that although both (D-Phe12)BN and substance P analogues may function as central BN receptor antagonists, the (D-Phe12)BN analogues may be functionally the more useful class of antagonists.

Substance P antagonists and analgesia: a review of the hypothesis

This review focused entirely on the hypothesis that a substance P/neurokinin antagonist should have, and the experimental evidence examining whether they do have, analgesic/antinociceptive properties. Such a hypothesis is reasonable considering the wealth of evidence implicating substance P in the nociceptive process and the demonstration that antibodies to substance P produce or potentiate antinociception. However, despite the availability of several putative antagonists, their pharmacological purity, specificity and selectivity are questionable. Thus, the investigator may not have, as yet, the appropriate tool drug with which to work. Much of the information concerning these points is generated utilizing in vitro (referring to isolated tissue preparations) bioassay tests which may not adequately reflect nor predict their pharmacology in the CNS. Differences in species responsiveness further complicate experimental design and interpretation. Apart from these factors, the choice of test or tests becomes an important consideration. What test, if any, adequately and appropriately reflects the endogenous physiological activity of substance P in nociception and predicts clinically useful activity of an antagonist? Several different models have been described and I have emphasized that conclusions based on a single model should be interpreted with caution. If the ultimate intent of the study is to further define the role of substance P in nociception, then most of the models discussed are adequate. However, if the intent is to demonstrate that a substance P/neurokinin antagonist should have therapeutically useful analgesic activity, it is incumbant on the investigator to demonstrate that, in their model, substance P release is a primary event, the resultant analgesia correlates to the occupancy of the neurokinin receptor by antagonist (ultimately important for all conclusions) and that the model adequately reflects activity of known analgesics in clinical use (validation of the model). In conclusion, given the complexities and contradictions of existing information, the hypothesis that a substance P/neurokinin antagonist should have analgesic/antinociceptive properties remains to be proven.

Specific neuroanatomical and neurochemical correlates of locomotor and grooming effects of bombesin

Experiments characterized the behavioral effects of bombesin (BN) administered systemically (1-8 micrograms/kg; IP) or centrally at the nucleus tractus solitarius (NTS) and the nucleus accumbens (NA) (0.0001-1.0 microgram/0.5 microliter). The role of dopaminergic system(s) in the mediation of BN-induced behavioral effects in rat was also investigated. Locomotor activity was quantitated with the aid of microprocessor controlled infrared beam grid systems while grooming related behaviors were simultaneously collected by an observer using time-sampling procedures over a 60 min period. Locomotor stimulation appeared to be specific to BN administration at the NA whereas the elicitation of grooming appeared to be specific to BN administration at the NTS. The dopaminergic system(s) appeared to play a significant role in the mediation of the effects of BN administered intra NA but not intra NTS.

Specific neuroanatomical and neurochemical correlates of grooming and satiety effects of bombesin

Experiments characterized the behavioral effects of bombesin (BN) administered systemically (1-8 micrograms/kg; IP) or centrally at the nucleus tractus solitarius (NTS) and the nucleus accumbens (NA) (0.0001-1.0 microgram/0.5 microliter). The role of dopaminergic system(s) in the mediation of BN-induced behavioral effects in rats was also investigated. In the "satiety" paradigm, grooming and eating behaviors were monitored in 5-hr-food-deprived rats trained to take a portion of their daily food intake over the 20 min observation period. The elicitation of grooming and satiety appeared to be specific to BN administration at the NTS but not the NA. The dopaminergic system(s) did not appear to mediate the behavior effects of BN intra NTS. The BN-induced grooming profile appeared to be paradigm independent although the baseline grooming profile was not. At the NTS, a dissociation of BN-induced grooming and satiety was evident on the basis of time-course and dose-effect. The similarity of the time-course of satiety induced by BN injected at the NTS and IP suggested that BN may mediate a physiological satiety signal at the NTS. Furthermore, since BN induced satiety 10(4) more potently and 20% more efficaciously intra NTS than IP, the NTS may be a critical site for the action of BN on satiety.

Pharmacological examination of cholecystokinin (CCK-8)-induced contractile activity in the rat isolated pylorus

The actions of cholecystokinin (CCK) in the production of a satiety-like state have been suggested to be mediated via receptors for CCK which are located in the pylorus. We investigated the actions of CCK and other pharmacological agents upon the isolated rat pylorus in vitro. We used the change in isometric tension of the tissue preparation (contraction amplitude) as the measure of the effects of the pharmacological agents. Cholecystokinin COOH-terminal octapeptide (CCK-8) was observed to elicit contraction in a dose-dependent manner, with the half-maximal dose (ED50) in the vicinity of 1 nM. Rapid desensitization to CCK was observed. The contraction amplitude was atropine-independent, and was not significantly antagonized by a wide variety of other pharmacological agents. The Na+-channel blocker tetrodotoxin was without effect upon contractile amplitude, as was the K+-channel blocker 4-aminopyridine, except at very high concentrations. Neurotensin, bombesin, and the substance P and bombesin antagonist spantide all elicited contraction in the isolated tissue; neurotensin had a similar potency to CCK-8 and bombesin was 10-15-fold less potent than CCK-8. Unsulfated CCK-8 was at least 170-fold less potent than sulfated CCK-8 and tetragastrin was at least 500-fold less potent than CCK-8. These results suggest that pyloric CCK receptors, which appear to have a pharmacological profile typical of peripheral CCK receptors, may have a physiological role in the peptidergic control of gastric emptying in the rat.

A tachykinin antagonist inhibits gastric emptying and gastrointestinal transit in the rat

The effect of a substance P antagonist, [D-Pro2, D-Trp7,9]-substance P (SPA), on gastric emptying and gastrointestinal transit in the rat was studied in order to elucidate a possible physiological role of endogenous substance P and other tachykinins in gastrointestinal motility. SPA was given by intraperitoneal injection concurrently with the intragastric administration of a test meal containing charcoal and 51Cr. Examination 15 min after the test meal showed that SPA (0.13-1.3 mumol kg-1) inhibited gastric emptying and gastrointestinal transit in a dose-dependent manner. The inhibitory effect of SPA on gastric emptying and gastrointestinal transit remained unchanged after pretreatment of rats with mepyramine (8.7 mumol kg-1) plus cimetidine (19.8 mumol kg-1) or with guanethidine (67 mumol kg-1). Since a full examination of SPA as a specific tachykinin antagonist was not possible in vivo, SPA was also tested on circular muscle strips from the rat gastric corpus in vitro. Submaximal contractions in response to bombesin or bethanechol were not reduced by SPA (50 microM), whereas those in response to substance P were inhibited. The results suggest that SPA inhibits gastric emptying and gastrointestinal transit by interfering with the action of tachykinins released from enteric nerves and that endogenous tachykinins are involved in the regulation of gastrointestinal motility.

Substance P antagonists in substantia nigra are anticonvulsant

Bilateral intranigral microinfusion of antagonist analogs of substance P significantly attenuated convulsions induced by maximal electroshock or intravenous bicuculline in rats. Infusions of substance P antagonists placed adjacent to the substantia nigra in the vicinity of the lateral hypothalamus were without anticonvulsant action. Our data indicate an as yet undescribed role for substance P antagonists in the regulation of seizure susceptibility, and provide additional evidence that decreasing the activity of substantia nigra outputs is anticonvulsant.

Early events elicited by bombesin and structurally related peptides in quiescent Swiss 3T3 cells. II. Changes in Na+ and Ca2+ fluxes, Na+/K+ pump activity, and intracellular pH

The amphibian tetradecapeptide, bombesin, and structurally related peptides caused a marked increase in ouabain-sensitive 86Rb+ uptake (a measure of Na+/K+ pump activity) in quiescent Swiss 3T3 cells. This effect occurred within seconds after the addition of the peptide and appeared to be mediated by an increase in Na+ entry into the cells. The effect of bombesin on Na+ entry and Na+/K+ pump activity was concentration dependent with half-maximal stimulation occurring at 0.3-0.4 nM. The structurally related peptides litorin, gastrin-releasing peptide, and neuromedin B also stimulated ouabain-sensitive 86Rb+ uptake; the relative potencies of these peptides in stimulating the Na+/K+ pump were comparable to their potencies in increasing DNA synthesis (Zachary, I., and E. Rozengurt, 1985, Proc. Natl. Acad. Sci. USA., 82:7616-7620). Bombesin increased Na+ influx, at least in part, through an Na+/H+ antiport. The peptide augmented intracellular pH and this effect was abolished in the absence of extracellular Na+. In addition to monovalent ion transport, bombesin and the structurally related peptides rapidly increased the efflux of 45Ca2+ from quiescent Swiss 3T3 cells. This Ca2+ came from an intracellular pool and the efflux was associated with a 50% decrease in total intracellular Ca2+. The peptides also caused a rapid increase in cytosolic free calcium concentration. Prolonged pretreatment of Swiss 3T3 cells with phorbol dibutyrate, which causes a loss of protein kinase C activity (Rodriguez-Pena, A., and E. Rozengurt, 1984, Biochem. Biophys. Res. Commun., 120:1053-1059), greatly decreased the stimulation of 86Rb+ uptake and Na+ entry by bombesin implicating this phosphotransferase system in the mediation of part of these responses to bombesin. Since some activation of monovalent ion transport by bombesin was seen in phorbol dibutyrate-pretreated cells, it is likely that the peptide also stimulates monovalent ion transport by a second mechanism.

A centrally elicited respiratory stimulant effect by bombesin in the rat

The effects of the tetradecapeptide bombesin on respiratory regulation in the rat were studied using a whole body plethysmographic model. Application of the peptide was made intracerebroventricularly (i.c.v.) as well as via microinjections into specific brainstem areas. I.c.v. injection (0.1-5 micrograms) resulted in a dose-dependent increase in tidal volume while respiratory frequency was decreased only at higher doses. The respiratory duty cycle remained unchanged while the respiratory drive was significantly increased. The respiratory effects were blunted by bilateral section of the tenth cranial nerve. Studies employing the occluded breath technique indicated a change in the threshold to afferent vagal signals while the time-setting for inspiration remained unchanged. Similar ventilation changes were elicited when the peptide was injected into the area of the nucleus ambiguous but not in several other areas of the brainstem. Such bombesin sensitive areas are consistent with a recent immunohistochemical study describing a dense pattern of immunoreactive somata in this area of the brainstem. The ventilatory stimulant effect seems to depend on an intact afferent vagal innervation.

Spantide: failure to antagonize bombesin-induced stimulation of gastrin secretion in dogs

Spantide ([d-Arg1, d-Trp7,9, Leu11] substance P) was shown to function not only as a substance P receptor antagonist but also as a bombesin receptor antagonist. This study examined the effects of spantide on intravenous bombesin-induced stimulation of gastrin and acid secretion. Dogs were infused with spantide (1 or 10 nmol kg 1 hr 1) or saline and bombesin (60 pmol kg-1 hr-1), and the gastric acid and plasma gastrin responses were monitored. Spantide did not significantly modify gastrin or gastric acid secretion induced by bombesin. It is concluded that spantide may not be a useful bombesin antagonist for in vivo studies.

Effects of bombesin on behavior

This report describes the influence of bombesin on the gross behavior of goldfish, frogs, mice, rats, guinea pigs, rabbits, chicks, pigeons and monkeys. Goldfish, frogs, chicks and pigeons were overtly unaffected by bombesin given centrally and/or peripherally. Mice, rats, guinea pigs, rabbits and monkeys responded quickly to intracerebroventricular (i.c.v.) and/or intrathecal (i.th.) administration of bombesin by displaying a range of behaviors suggestive of altered skin sensation. In mice, bombesin was essentially equipotent as a scratch inducer by i.c.v. and i.th. routes (A50 = 0.010-0.019 microgram) but 6800 times less potent i.p. In rats, bombesin-induced grooming and scratching behaviors were shown to be qualitatively different from those associated with ACTH-(1-24) and thyrotropin releasing hormone. Spantide and [D-Arg1, D-Pro2, D-Trp7,9, Leu11]substance P (both at 0.20, 0.50 and 0.80 microgram i.c.v.), two proposed bombesin receptor antagonists, did not markedly influence bombesin-induced scratching or hypothermia in rats.

Centrally-mediated bombesin effects on gastrointestinal motility

Administration of bombesin into the lateral cerebral ventricle (i.c.v.) of rats results in a dose-related delay in gastric emptying and small intestinal transit. Recordings of intestinal intraluminal pressure in this species show that the i.c.v. peptide produces a dose-related increase in the frequency of duodenal contractions, and a complex inhibitory/excitatory jejunal effect at low and high doses, respectively. Intrathecal (i.th.) or i.c., but not intraperitoneal (i.p.), bombesin produces a dose-related slowing of gastrointestinal and colonic transit in mice. I.c.v. bombesin is 13.5 and 3406 times more potent in inhibition of gastrointestinal transit than when given by the i.th. or i.p. routes, respectively. Similarly, the i.c.v. peptide is 1.54 and over 11000 times more potent in slowing mouse colonic transit than when given by the i.th. or i.p. routes, respectively. The substance P analogue, D-Arg1, D-Pro2, D-Trp7,9, Leu11-Substance P (DAPTL-SP)(a reported bombesin antagonist in vitro) was not effective in blocking the gastrointestinal transit effects of the peptide in vivo. Transection of the spinal cord at the level of the second thoracic vertebra (T2) eliminates the gastrointestinal and colonic effects of i.th., but not i.c.v. bombesin. Thus, bombesin can affect motor function of the gut via activity within the brain or spinal cord of rats and mice; the activity of the peptide when given at the supraspinal level depends on an intact vagus nerve and adrenal-pituitary axis, while the activity of the peptide given at the spinal level appears to depend on the integrity of ascending spinal-supraspinal pathways.