Substance P mechanisms of the spinal cord related to vasomotor tone in the spontaneously hypertensive rat

[Easing human pain: challenges to a novel therapeutic drug in neuropathic pain]

Pain control is very important since, even today, 20 million people suffer from neuropathic pain. Although many basic science and clinical researchers have made efforts to control pain, the mechanism of neuropathic pain is unfortunately still not fully understood. Morphine, a prototypical opioid, is a useful medicine to relieve severe pain. However, repeated or continuous use of morphine and other opioids are associated with a potential risk of analgesic tolerance, which requires an increase in dosage to maintain the same efficacy. In addition, morphine is not always effective in neuropathic pain. In this review we focus on: (1) the role of muscarinic receptors in the spinal cord and anterior cingulate cortex (ACC) in neuropathic pain, (2) how chemokine (C-C motif) ligand 1 (CCL-1) is involved in neuropathic pain, and (3) the novel mechanism of morphine tolerance. The findings in this study may cast new light on novel mechanism of neuropathic pain and development of novel clinical medicines in the future.

Upregulation of tachykinin NK-1 and NK-3 receptor binding sites in the spinal cord of spontaneously hypertensive rat: impact on the autonomic control of blood pressure

1 Effects of intrathecally (i.t.) injected tachykinin NK-1 and -3 receptor agonists and antagonists were measured on mean arterial blood pressure (MAP) and heart rate (HR) in awake unrestrained spontaneously hypertensive rats (SHR,15-week-old) and age-matched Wistar Kyoto rats (WKY). Quantitative in vitro autoradiography was also performed on the lower thoracic spinal cord of both strains and Wistar rats using specific radioligands for NK-1 receptor ([(125)I]HPP[Arg(3),Sar(9),Met(O(2))(11)]SP (3-11)) and NK-3 receptor ([(125)I]HPP-Asp-Asp-Phe-N-MePhe-Gly-Leu-Met-NH(2)). 2 The NK-1 agonist [Sar(9),Met(O(2))(11)]SP (650 and 6500 pmol) decreased MAP and increased HR in WKY. The fall in MAP was blunted in SHR and substituted by increases in MAP (65-6500 pmol) and more sustained tachycardia. The NK-3 agonist senktide (6.5-65 pmol) evoked marked increases in MAP and HR (SHR>>>WKY), yet this response was rapidly desensitized. Cardiovascular effects of [Sar(9),Met(O(2))(11)]SP (650 pmol) and senktide (6.5 pmol) were selectively blocked by the prior i.t. injection of LY303870 (NK-1 antagonist, 65 nmol) and SB235375 (NK-3 antagonist, 6.5 nmol), respectively. Antagonists had no direct effect on MAP and HR in both strains. 3 Densities of NK-1 and -3 receptor binding sites were significantly increased in all laminae of the spinal cord in SHR when compared to control WKY and Wistar rats. The dissociation constant was however not affected in SHR for both NK-1 (K(d)=2.5 nM) and NK-3 (K(d)=5 nM) receptors. 4 Data highlight an upregulation of NK-1 and -3 receptor binding sites in the thoracic spinal cord of SHR that may contribute to the hypersensitivity of the pressor response to agonists and to the greater sympathetic activity seen in this model of arterial hypertension.

Growth and neurotrophic factors regulating development and maintenance of sympathetic preganglionic neurons

The functional anatomy of sympathetic preganglionic neurons is described at molecular, cellular, and system levels. Preganglionic sympathetic neurons located in the intermediolateral column of the spinal cord connect the central nervous system with peripheral sympathetic ganglia and chromaffin cells inside and outside the adrenal gland. Current knowledge is reviewed of the development of these neurons, which share their origin with progenitor cells, giving rise to somatic motoneurons in the ventral horn. Their connectivities, transmitters involved, and growth factor receptors are described. Finally, we review the distribution and functions of trophic molecules that may have relevance for development and maintenance of preganglionic sympathetic neurons.

Neurokinin-1 receptors and spinal cord control of blood pressure in spontaneously hypertensive rats

In this study we examined blood pressure and heart rate responses to intrathecal administration of a synthetic NK1-receptor agonist, H2N-(CH2)4-CO-Phe-Phe-Pro-NmeLeu-Met-NH2 (GR 73,632), in spontaneously hypertensive rats (SHR) and their progenitor strain, the Wistar-Kyoto rat (WKY). Sodium pentobarbitone anaesthetised rats with implanted intrathecal catheters were paralysed (pancuronium dibromide) and artificially ventilated. Injection of GR 73,632 at the T9 spinal level evoked dose-dependent increases in mean arterial pressure (MAP) in WKY and SHR. SHR had a lower MAP response threshold than WKY but increase in response with increasing dose was less in SHR than WKY. Biphasic blood pressure responses at high doses were observed in both strains. Prior administration of the NK1-receptor antagonist (3 aR,7aR)-7,7-diphenyl-2-[1-imino-2(methoxyphenyl)ethyl] perhydroisoindol-4-one (RP 67,580) significantly reduced the pressor response in WKY but not SHR. The depressor response was not attenuated in either strain.

Distribution and co-localization of 5-hydroxytryptamine, thyrotropin-releasing hormone and substance P in the cat medulla

This study demonstrates the co-existence of three neurochemicals in ventral medullary neurons of the cat utilizing fluorescence immunohistochemistry. Neurons containing 5-hydroxytryptamine, thyrotropin-releasing hormone and substance P were identified within the rostrocaudal extent of the medulla, specifically within the raphe pallidus and raphe magnus and in the reticular formation of the ventrolateral medulla in the nucleus paragigantocellularis lateralis. Within the raphe pallidus the majority of 5-hydroxytryptamine-containing neurons were co-localized with thyrotropin-releasing hormone and substance P. However, in the raphe magnus the majority of stained neurons contained 5-hydroxytryptamine and thyrotropin-releasing hormone but were devoid of substance P. In the ventrolateral medulla two major populations of neurons were identified rostral to the inferior olivary nuclei, one containing 5-hydroxytryptamine and thyrotropin-releasing hormone, while a more lateral group contained substance P alone. More caudally, at the level of the inferior olives, the majority of 5-hydroxytryptamine-containing cells also displayed immunoreactivity for thyrotropin-releasing hormone and substance P. A consistent finding in both the ventromedial and ventrolateral regions of the medulla was a population of 5-hydroxytryptamine-containing cells which did not stain for either thyrotropin-releasing hormone or substance P. The functional role of co-localized neurochemicals remains unknown but co-existence of neurotransmitter substances in medullary neurons may allow for specific and multiple actions in the spinal cord.

Substance P immunoreactive boutons form synapses with feline sympathetic preganglionic neurons

In this study, the relationship between substance P-immunoreactive boutons and antidromically activated sympathetic preganglionic neurons was examined by light and electron microscopy. Sympathetic preganglionic neurons in the T2-T4 spinal segments of the cat were identified by intracellular recording and antidromic activation from the corresponding white ramus. Neurons were filled with lucifer yellow and then stained to reveal, simultaneously, substance P and lucifer yellow immunoreactivity. All of the neurons examined with the light microscope (n = 13) received appositions from substance P-immunoreactive boutons. Appositions were found on all parts of the neuron, including the somata, dendrites, and axon initial segment. In most cases (11/13) few close appositions were seen; however, two neurons received large numbers of appositions from substance P-immunoreactive boutons. On one neuron, 16 substance P-immunoreactive varicosities that were identified as being closely apposed at the light microscope level were serially sectioned and examined with the electron microscope. Of these 16 varicosities, eight either directly contacted the neuron or formed morphologically identifiable synapses. The remaining eight varicosities were separated from the neuron by thin glial processes. Two other sympathetic preganglionic neurons that were examined ultrastructurally also received substance P-immunoreactive synapses and close contacts. These findings suggest that substance P-containing nerve fibres could affect all sympathetic preganglionic neurons but are likely to be important in regulating the activity of only a small proportion of these neurons.

Spinal cord substance P mediates the inhibition of gastric acid secretion induced by electrical stimulation of the preoptic area

A possible role of spinal substance P (SP) in the mediation of signals to inhibit gastric acid secretion by central activation of the sympatho-adrenomedullary system was examined in urethane-anesthetized rats. Intrathecal (i.t.) administration of SP (1-10 nmol) inhibited vagally induced acid output. I.t. administration of spantide, a SP receptor antagonist, reduced the inhibitory effect of 3 nmol SP. I.t. administration of spantide (0.1-1 nmol) blocked the inhibition of vagally induced gastric acid output evoked by electrical stimulation of the preoptic area. Atropine, hexamethonium, phentolamine, propranolol, DL-para-chlorophenylalanine (PCPA) and 5,7-dihydroxytryptamine (5,7-DHT) were without effect. Repeated i.t. administration of 10 nmol SP produced desensitization to the SP-induced inhibitory response on gastric acid output. In these animals, electrical stimulation of the preoptic area did not inhibit vagally induced gastric acid output. These results suggest that electrical stimulation of the preoptic area excites SP-containing neurons in the spinal cord, and a resultant sympatho-adrenomedullary system-mediated inhibition of gastric acid secretion occurs.

Role of central tachykinin peptides in cardiovascular regulation in rats

The mechanisms of action of tachykinin peptides thought to be involved in central cardiovascular regulation were examined. Intracerebroventricular injections (i.c.v.) of tachykinin peptides caused dose-dependent increases in blood pressure and heart rate. The pressor responses to substance P (SP) (10 micrograms, i.c.v.) and neurokinin A (NKA) (10 micrograms, i.c.v.) were blocked by peripheral administration of pentolinium or phentolamine, and partially attenuated by adrenalectomy. In contrast, the only initial pressor response to the neurokinin B (NKB) analogue senktide (10 micrograms, i.c.v.) was blocked by pentolinium or phentolamine. The pressor response to senktide was inhibited by pretreatment with a vasopressin V1 receptor antagonist (d(CH2)5OMe(Tyr)AVP) (10 micrograms/kg, i.v.), and senktide (10 micrograms, i.c.v.) caused an increase in plasma vasopressin level. However, the vasopressin antagonist did not influence the SP- and NKA-induced pressor responses. These results suggest that central SP and NKA increase the blood pressure and heart rate via sympathetic nerve activity, whereas central NKB increases the blood pressure mainly via release of vasopressin from the hypothalamus.

Characterization of tachykinin receptors in endothelial cells of porcine artery

The binding of iodine-labeled Bolton-Hunter substance P (125I-BHSP) to porcine endothelial cell membranes was examined. The endothelial cells had a single high-affinity binding site with a dissociation constant of 0.10 nM, and a maximum number of binding sites of 52.2 fmol/mg protein. The relative potencies of various tachykinins to displace the binding of 47 pM 125I-BHSP suggested that endothelial cells of porcine aorta contain the NK-1 subtype of tachykinin receptor. A GTP analogue, guanyl-5'-yl imidodiphosphate, induced marked reduction in the number of 125I-BHSP binding sites suggesting that these binding sites are coupled with GTP-binding protein.

Central pressor actions of neurokinin B: increases in neurokinin B contents in discrete nuclei in spontaneously hypertensive rats

The regional distributions of neurokinin B-like immunoreactivity and substance P-like immunoreactivity in the central nervous system in spontaneously hypertensive rats (SHRs) and normotensive Wistar Kyoto rats (WKYs) were examined. The distribution of neurokinin B-like immunoreactivity in WKYs was not exactly the same as that of substance P-like immunoreactivity. The neurokinin B-like immunoreactivity contents of the supraoptic nucleus of the hypothalamus and the caudal part of the nucleus tractus solitarii were higher in SHRs than in WKYs. Injections of selective neurokinin B receptor peptides, senktide (suc-[Asp6,Me-Phe8]-substance P6-11) and [Pro7]-neurokinin B, into the lateral brain ventricle of the normotensive rats caused dose-dependent increases in the blood pressure, and blockade of peripheral vascular vasopressin receptors reduced these pressor responses, but did not affect the substance P-induced pressor response. These findings suggest that the novel tachykinin peptide, neurokinin B has an important role in central pressor action in rats.

Capsaicin-sensitive afferents and blood pressure regulation during pentobarbital anaesthesia in the rat

(1) Maintenance of blood pressure was investigated during induction of pentobarbital anaesthesia in rats after elimination of capsaicin-sensitive afferent neurons (capsaicin-denervated rats) as compared to vehicle-treated controls. The catecholamine content of heart and adrenals and the rise in blood pressure following electrical excitation of the spinal adrenergic nerves (pithed rat preparation) was also compared between both groups. (2) Capsaicin-denervated rats and their controls had equal amounts of catecholamines in heart and adrenals as well as equal pressor responses to electrical stimulation of spinal sympathetic nerves, thus excluding an influence of capsaicin on efferent pathways. In the state of consciousness, both groups showed the same blood pressure. (3) In capsaicin-denervated rats and in their controls, pentobarbital-induced anaesthesia (50 mg/kg i.p.) was characterized by a decline in blood pressure during the first 6 min. In the controls, this fall in blood pressure was followed by a slow compensatory rise to a level slightly higher than before anaesthesia, and this level was maintained during the following 60 min. This compensation was completely absent in capsaicin-denervated rats, indicating a role for capsaicin-sensitive nerves in this mechanism. An injection of pentobarbital (50 mg/kg i.p.) in pithed rats reduced the pressor response to electrical stimulation of spinal sympathetic nerves by about 40% in capsaicindenervated rats and in their controls. This inhibitory effect of pentobarbital might be involved in the initial fall in blood pressure in intact animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Substance P receptors in the human spinal cord: decrease in amyotrophic lateral sclerosis

The distribution of substance P receptors was examined by autoradiography at all levels of the human postmortem spinal cord using the ligand [125I]Bolton-Hunter substance P. Adjacent sections were used to localize substance P-like immunoreactivity by a radioimmunohistochemical technique. In the control spinal cord substance P-like immunoreactivity was found to be highly concentrated in the superficial layers of the dorsal horn, intermediolateral cell columns and lamina X, while lower levels of immunoreactivity were observed in other areas of the grey matter of the spinal cord. In contrast, high densities of substance P binding sites were localized not only to the substantia gelatinosa of the dorsal horn but also to other regions of the grey matter of the spinal cord, particularly in the area of the preganglionic sympathetic neurons in the intermediolateral cell column and in the region of the somatic motor neurons of the ventral horn. In 5 cases of amyotrophic lateral sclerosis we found a marked reduction of substance P binding, especially in the ventral horn associated with the loss of motor neurons. These results suggest a postsynaptic localization of substance P receptors to the motor neurons of the ventral horn in the human spinal cord and a role for substance P in the function of motor neurons.

Intraspinal substance P-containing projections to the sympathetic preganglionic neuropil in pigeon, Columba livia: high-performance liquid chromatography, radioimmunoassay and electron microscopic evidence

The present study uses quantitative and electron microscopic methods to investigate the hypothesis that intraspinal substance P-sympathetic preganglionic neuron circuitry exists in vertebrates. Radioimmunoassay and high-performance liquid chromatography were used to: (1) characterize the chemical nature of the substance P-like immunoreactivity in the sympathetic preganglionic neuropil; and (2) quantify the relative contributions of brain stem, primary sensory and intraspinal neurons to the substance P content within the sympathetic preganglionic neuropil. Electron microscopic observations on the localization of substance P-like immunoreactivity within the preganglionic neuropil caudal to complete thoracic spinal cord transections are also reported. High-performance liquid chromatographic analyses demonstrate that pigeon substance P-like immunoreactivity co-migrates with synthetic substance P, suggesting that the substance P-like material is authentic substance P content within the sympathetic preganglionic neuropil. Electron microscopic observations on the localization of substance P-like immunoreactivity within the preganglionic neuropil caudal to complete preganglionic cell column (inclusive of intermediate spinal laminae V and VII as well as preganglionic neurons located within nucleus intercalatus spinalis); (2) cutting the dorsal rootlets entering the last cervical (C14) and first two thoracic (T1, T2) spinal segments resulted in massive depletion of substance P content in dorsal horn of T1, but no detectable losses within the preganglionic cell column or ventral horn of T1; and (3) total mid-thoracic (T3-4) spinal cord transection significantly depleted the substance P content in the preganglionic cell column (T3-4) as well as in the dorsal (T1-4) and ventral horns (T2-4). Ultrastructural examination of the sympathetic preganglionic neuropil caudal to spinal transections (survival times of 3-14 days) revealed the presence of numerous, intact, normal appearing substance P-like immunoreactive terminals. Immunolabeled terminals formed asymmetric contacts on medium-sized and small caliber dendrites. Extensive degeneration was evident in this material as well. The ultrastructural features of degenerating processes were distinctive and quite dissimilar in appearance from those exhibiting substance P-like immunoreactive staining. No evidence for damage-induced sequestration of substance P-like material into glial elements was found. The above observations are consistent with earlier findings in rat and pigeon, and provide new quantitative and qualitative evidence to support the hypothesis that intraspinal substance P-containing interneurons contribute t

Autonomic, sensory, and motor dysfunction following intrathecal administration of three substance P antagonists

Antagonists of the putative peptide neurotransmitter substance P have been found to produce pronounced cardiovascular effects when administered into the spinal subarachnoid space. These previous studies have not, however, provided any direct evidence that these effects result from interaction with substance P receptors. The present study was designed to characterize the modification of cardiovascular function resulting from administration of these compounds, and evaluate their effects on the integrity of spinal cord function. Intrathecal administration of two substance P antagonists produced a depressor response accompanied by a reduction of hindquarter vascular resistance. Following administration of a substance P antagonist, the integrated cardiovascular responses to electrical stimulation of the renal afferent nerves and ventrolateral medulla were markedly attenuated. Intrathecal administration to conscious rats of three substance P antagonists led to a variety of sensory and motor dysfunctions, including loss of spontaneous motor function, responsiveness to mechanical and thermal stimuli, and bladder function. No such effects were produced by administration of substance P, luteinizing hormone releasing hormone (LHRH), or LHRH antagonist. These effects from administration of a substance P antagonist were associated with a dose-dependent necrosis of spinal cord tissue. The necrosis may be secondary to ischemia since pretreatment with the vasodilator adenosine significantly delayed or blocked the sensory and motor dysfunctions. This conclusion was supported by the demonstration that cerebrovascular smooth muscle (pial vessels) was constricted by a SP antagonist. Taken together, these data suggest that substance P antagonists appear to non-specifically block transmission in the spinal cord, by mechanisms which may involve reduction of blood flow to the spinal cord.

Altered levels of neuropeptides in the medulla and spinal cord of spontaneously hypertensive rats

1. Spontaneously hypertensive rats (SHR) are useful for investigating the possible pathophysiological and neurochemical basis of human essential hypertension. 2. The accepted pathogenic mechanism of hypertension in SHR is an increased central sympathetic drive which results in an increased peripheral resistance. 3. The neurochemical basis of the increased sympathetic drive is unknown. The observation that there are reduced levels of neuropeptides (vasoactive intestinal peptide, neuropeptide Y, cholecystokinin octapeptide, neurotensin and calcitonin gene related peptide) in the spinal cord in SHR rats compared with age and gender matched Wistar-Kyoto normotensive rats could provide a basis for understanding the mechanism of hypertension in SHR.

Regional distribution of substance P- and thyrotrophin-releasing hormone-like immunoreactivity and indoleamines in the rabbit spinal cord

The distribution of thyrotrophin-releasing hormone (TRH), substance P, and the indoleamines [5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA)] has been examined in selected regions of the thoracic and lumbar spinal cord of the rabbit using sensitive radioimmunoassays for the first two and HPLC with electrochemical detection for the indoleamines. The levels of TRH- and substance P-like immunoreactivity (TRH-I and SP-I, respectively) were greatest in the ventral and dorsal grey matter, respectively. The level of TRH-I in most thoracic regions was greater than that in equivalent lumbar regions, but the only segmental difference in SP-I was in the ventral grey matter, where the lumbar segment contained more immunoreactivity. 5-HT and 5-HIAA were more evenly distributed than either peptide and showed no segmental variation in levels in equivalent regions, but the ventral grey matter contained significantly higher levels of 5-HT and had a greater 5-HT/5-HIAA ratio than all other regions. The absolute levels and the overall distribution of SP-I, TRH-I, and indoleamines in the thoracolumbar cord of the rabbit was very similar to that previously reported in both rats and humans, and the possible functional role of the peptides and indoleamines in spinal neurones is discussed.

Studies on the cardiovascular effects produced by the spinal action of two substance P analogues in the rat: evidence for a central catecholaminergic mechanism

The effects of two substance P (SP) analogues, [D-Trp7,9,10]SP (ana1) and [D-Pro4,Lys6,D-Trp7,9,10,Phe11]SP-(4-11) (ana2) on mean arterial pressure (MAP) and heart rate (HR) were measured following intrathecal administration at one of three spinal cord levels in rats anaesthetized with sodium pentobarbital. Following an initial increase, a profound and long-lasting fall in MAP and HR occurred when 6.5 nmol of either ana1 or ana2 was injected at T1-T3 or T8-T10. Only transient changes in MAP and a slight increase in HR was observed after injection of either peptide at L2-L4. The profound and long-lasting hypotension and bradycardia induced by ana1 were not significantly altered after intravenous injection of hexamethonium, phentolamine, propranolol, atropine, diphenhydramine, cimetidine, methysergide, naloxone or morphine. However, the biphasic effect of ana1 on MAP was prevented by the intrathecal administration of prazosin and yohimbine, suggesting that a central catecholaminergic mechanism including alpha 1- and alpha 2-adrenergic receptors is involved. The latter treatment did not prevent the tachycardia which occurred when the bradycardia was blocked, indicating that different mechanisms mediate the spinal action of ana1 on MAP and HR. Finally, cervical transection of the spinal cord eliminated the profound and long-lasting depressor effect of ana2, suggesting that a supraspinal mechanism is involved in this cardiovascular response.

Microinjection of kainic acid into the rostral ventrolateral medulla causes hypertension and release of neuropeptide Y-like immunoreactivity from rabbit spinal cord

Microinjections of kainic acid were made into the pressor area of the rostral ventrolateral medulla oblongata of anaesthetized rabbits, in the region of the C1 adrenaline-containing neurons. Over the 65 min following the microinjection, there was a significant increase in blood pressure, as well as an increase in the release of neuropeptide Y-like immunoreactivity into the spinal subarachnoid space. These data provide evidence for a functional bulbospinal neuropeptide Y-containing projection which may be responsible for mediating the pressor effects of stimulation of the rostral ventrolateral medulla.

Substance P given intrathecally at the spinal T9 level increases arterial pressure and heart rate in the rat

Administration of 10 micrograms of substance P intrathecally at the spinal T9 level of the unanaesthetized and the anaesthetized rat provoked an increase in arterial pressure and an increase in heart rate. Both cardiovascular responses began within 1-2 min of administration, and the peak of each occurred at 4-10 min. In the anaesthetized rat, which gave rise to the bulk of the responses reported, peak arterial pressure was ca 20 mm Hg greater than pre-administration levels, and peak heart rate was greater by ca 50 beats per min. Similar administration of vehicle failed to alter either parameter. Arterial pressure and heart rate in substance P-treated rats were significantly different from those in vehicle-treated rats up to 15-20 min after administration. Pretreatment with the sympathetic ganglion blocker, hexamethonium (10 mg/kg, i.v.), prevented the responses to intrathecal administration of substance P. Pretreatment with [D-Pro2, D-Phe7, D-Trp9]-substance P, an analogue with antagonist properties in the central nervous system, blocked both responses to substance P but failed to alter similar responses provoked by intrathecal administration of angiotensin II. Pretreatment with vehicle had no effect on responses to substance P or to angiotensin II. The antagonist also had partial agonistic effects. Both arterial pressure and heart rate were transiently increased, but this effect was reversed within 6 min; in the case of heart rate, values returned to the pre-application level but arterial pressure fell to a ca 15 mm Hg below this level. These results demonstrate a pharmacologically specific excitatory effect of substance P on spinal mechanisms controlling sympathetic output to the vessels and the heart; this output can be either via the adrenal medullae or via nerve pathways to the vessels and the heart. Our results also support the possibility that dysfunction of substance P systems at the spinal level may underly some models of hypertension and may be involved in some cases of essential hypertension in man, as well as in autonomic dysfunction associated with some neurological disorders.

An increase in the sympathoadrenal medullary function in stroke-prone spontaneously hypertensive rats under anesthetized and resting conditions

Sympathoadrenal medullary functions were investigated in stroke-prone spontaneously hypertensive rats (SHR-SP) and in control normotensive Wistar-Kyoto rats (WKY) under halothane-anesthetized and resting conditions. The mean frequency of the spontaneous efferent activity of a single adrenal sympathetic nerve fiber was 1.08 +/- 0.11 impulses/s in WKY and 2.82 +/- 0.24 imp/s in SHR-SP, indicating a much higher level in SHR-SP than in WKY. The secretion rates of both adrenaline and noradrenaline from the adrenal gland were higher in SHR-SP than in WKY. The secretion rates of adrenaline and noradrenaline in WKY were 16.8 +/- 3.0 and 1.70 +/- 0.09 ng/kg X min, respectively, while those in SHR-SP were 36.7 +/- 3.9 and 2.56 +/- 0.18 ng/kg X min, respectively.

Localization of substance P-like immunoreactive fibers in the thoracic spinal cord of guinea pig

A dorsal-horn fiber system is revealed in the thoracic spinal cord of guinea pig by means of substance P immunocytochemistry. This system has repeated craniocaudal and/or caudo-cranial extensions and possesses five main components: a superficial network, situated beneath the dorsolateral surface of the spinal cord. This network is connected with the dorsal root fibers and the accumulations of substance P-like immunoreactive (SP-LI) fibers in the Lissauer's tract; an accumulation of SP-LI fibers in the Lissauer's tract at the border of the dorsal horn; two collateral SP-LI fascicles (one lateral and one medial) emerging from the SP-LI fiber accumulation in the Lissauer's tract; a transversal fascicle running through laminae III-V, and an SP-LI network in the region of the lateral spinal cord nucleus. These components of the dorsal-horn fiber system show widespread connections with ipsi- and contralateral spinal cord areas, connecting them in cranio-caudal and/or caudo-cranial directions. The SP-LI dorsal-horn system has close relationship with groups of preganglionic sympathetic cells in the intermediate zone of the spinal cord, respective with the vegetative network of this zone. It is suggested that some fibers of the dorsal-horn system that originate from dorsal-root ganglia may represent primary sensory or visceral afferents. It is likely that the dorsal-horn fiber system and the vegetative network of the thoracic spinal cord may represent the morphological basis for the integration of the central and peripheral vegetative nervous systems, and the somatic and vegetative nervous system.

Distribution of substance K (neurokinin A) in the brain and peripheral tissues of rats

The regional distribution of substance P (SP) and substance K (SK) in the central nervous system and peripheral tissues of rats was studied. High levels of SK-like immunoreactivity (SK-LI) and of SP-like immunoreactivity (SP-LI) were found in the substantia nigra, nucleus tractus solitarius and nucleus habenula. Neonatal treatment of rats with capsaicin caused a significant decrease in the SK-LI content in the submaxillary gland, but capsaicin had no effect on SK-LI content in any area of the brain. These observations suggest that SK in the brain and peripheral tissues may have significant physiological roles.

Substance K, a novel tachykinin injected bilaterally into the ventral tegmental area of rats increases behavioral response

Novel tachykinins such as substance K and neuromedin K have been identified in the mammalian CNS. Bilateral injections of substance K and related peptides as well as of substance P into the dopamine cell body area of the ventral tegmental area caused dose-dependent increases in locomotor activity and rearing, in rats. As this behavior was blocked by the pretreatment with haloperidol (0.1 mg/kg, i.p.), the activation of dopaminergic systems may be involved in the hypermotility induced by the administration of substance K.

LH-RH analogue acts as substance P antagonist by inhibiting spinal cord vasomotor responses

Intrathecal injections of the luteinizing hormone-releasing hormone (LH-RH) analogue, [D-pGlu1-D-Phe2-D-Trp3,6]-LH-RH caused dose-dependent decreases in mean arterial blood pressure in anesthetized rats similar to those seen with [D-Pro4-D-Trp7,9]-substance P4-11. Similarly, intrathecal injections of either peptide reversed the pressor response elicited by application of kainic acid on the ventral surface of the medulla oblongata. Both analogues also had similar IC50 values (approximately 10(-5) M) for the inhibition of specific [3H]substance P binding in tissue-sections of the intermediolateral cell column. However, the LH-RH analogue failed to block substance P (SP)-induced contractions of the isolated guinea pig ileum and did not affect tail-flick withdrawal time in a thermal nociceptive test, whereas the SP analogue acted as an antagonist in both of these bioassays. These results suggest that [D-pGlu1-D-Phe2-D-Trp3,6]-LH-RH may act as an antagonist which can inhibit the sympathetic vasomotor outflow and potentially be a substance P-physalaemin (SP-P) receptor antagonist in the central nervous system but without effect on peripheral SP-P receptors.