Inhibition of CRH-41 release by substance P, but not substance K, from the rat hypothalamus in vitro

Substance P: A neuropeptide involved in the psychopathology of anxiety disorders

Substance P (SP) is the most widely distributed neuropeptide in central nervous system (CNS) where it participates in numerous physiological and pathophysiological processes including stress and anxiety related behaviors. In line with this notion, brain areas that are thought to be involved in anxiety regulation contains SP and its specific NK1 receptors. SP concentration in different brain regions alters with the exposure of stressful stimulus and affected NK1 receptor binding is observed. SP is released in response to a stressor, which produces anxiogenic effects via activation of hypothalamic-pituitary-adrenal (HPA) axis, resulting in the liberation of cortisol. Moreover, SP is also involved in the activation of the sympathetic nervous system via stimulation of locus coeruleus (LC). This sympathetic surge initiates cortisol discharge by activation of HPA axis, representing the indirect anxiogenic effect of SP. Besides the aforementioned regions, SP also has an impact on other brain regions known to be involved in stress and anxiety mechanisms, including amygdala, lateral septum (LS), periaqueductal gray (PAG), ventromedial nucleus of the hypothalamus (VMH), and bed nucleus of stria terminalis (BNST). Thus, SP acts as an important neuromodulator in various brain regions in stress and anxiety response. Consistent with the above statement, SP makes a robust link in the psychopathology of anxiety disorders. As SP concentration is found elevated in stressed conditions, several studies have reported that the pharmacological antagonism or genetic depletion of NK-1 receptors results in the anxiolytic response making them a suitable therapeutic target for the treatment of stress and anxiety related disorders.

Hemokinin-1 mediates anxiolytic and anti-depressant-like actions in mice

The tachykinin NK1 receptor was suggested to be involved in psychiatric disorders, but its antagonists have failed to be effective as antidepressants in clinical trials. Hemokinin-1 (HK-1), the newest tachykinin, is present in several brain regions and activates the NK1 receptor similarly to substance P (SP), but acts also through other mechanisms. Therefore, we investigated the roles of the Tac4 gene-derived HK-1 in comparison with SP and neurokinin A (NKA) encoded by the Tac1 gene, as well as the NK1 receptor in anxiety and depression-like behaviors in mice. Mice lacking SP/NKA, HK-1 or the NK1 receptor (Tac1^-/-, Tac4^-/-, Tacr1^-/-, respectively) compared to C57Bl/6 wildtypes (WT), and treatment with the NK1 antagonist CP99994 were used in the experiments. Anxiety was evaluated in the light-dark box (LDB) and the elevated plus maze (EPM), locomotor activity in the open field (OFT) tests. Hedonic behavior was assessed in the sucrose preference test (SPT), depression-like behavior in the tail suspension (TST) and forced swim (FST) tests. FST-induced neuronal responsiveness was evaluated with Fos immunohistochemistry in several stress-related brain regions. In the LDB, Tac4^-/- mice spent significantly less, while Tacr1^-/- and CP99994-treated mice spent significantly more time in the lit compartment. In the EPM only Tac4^-/- showed reduced time in the open arms, but no difference was observed in any other groups. In the OFT Tac4^-/- mice showed significantly reduced, while Tac1^-/- and Tacr1^-/- animals increased motility than the WTs, but CP99994 had no effect. NK1^-/- consumed markedly more, while Tac4^-/- less sucrose solution compared to WTs. In the TST and FST, Tac4^-/- mice showed significantly increased immobility. However, depression-like behavior was decreased both in cases of genetic deletion and pharmacological blockade of the NK1 receptor. FST-induced neuronal activation in different nuclei involved in behavioral and neuroendocrine stress responses was significantly reduced in the brain of Tac4 ^-/- mice. Our results provide the first evidence for an anxiolytic and anti-depressant-like actions of HK-1 through a presently unknown target-mediated mechanism. Identification of its receptor and/or signaling pathways might open new perspectives for anxiolytic and anti-depressant therapies.

Mechanisms by which Stress Affects the Experimental and Clinical Inflammatory Bowel Disease (IBD): Role of Brain-Gut Axis

BACKGROUND

Stress of different origin is known to alter so called "braingut axis" and contributes to a broad array of gastrointestinal disorders including inflammatory bowel disease (IBD), irritable bowel syndrome (IBS) and other functional gastrointestinal diseases. The stressful situations and various stressors including psychosocial events, heat, hypo- and hyperthermia may worsen the course of IBD via unknown mechanism. The aims of this paper were to provide an overview of experimental and clinical evidences that stress activates the brain-gut axis which results in a mucosal mast cells activation and an increase in the production of proinflammatory cytokines and other endocrine and humoral mediators.

METHODS

Research and online content related to effects of stress on lower bowel disorders are reviewed and most important mechanisms are delineated.

RESULTS

Brain conveys the neural, endocrine and circulatory messages to the gut via brain-gut axis reflecting changes in corticotrophin releasing hormone, mast cells activity, neurotransmission at the autonomic nerves system and intestinal barrier function all affecting the pathogenesis of animal colitis and human IBD. Stress triggers the hypothalamus-pituitary axis and the activation of the autonomic nervous system, an increase in cortisol levels and proinflammatory cytokines such as tumor necrosis factor-alpha, interleukin-8, interleukin-1beta and interleukin-6.

CONCLUSION

The acute or chronic stress enhances the intestinal permeability weakening of the tight junctions and increasing bacterial translocation into the intestinal wall. An increased microbial load in the colonic tissue, excessive cytokine release and a partially blunted immune reactivity in response to stress result in its negative impact on IBD.

Blockade of tachykinin NK1/NK2 receptors in the brain attenuates the activation of corticotrophin-releasing hormone neurones in the hypothalamic paraventricular nucleus and the sympathoadrenal and pituitary-adrenal responses to formalin-induced pain in the rat

Evidence from pharmacological studies has implicated substance P (SP), a natural ligand of tachykinin NK(1) receptors which can also interact with NK(2) receptors, in the generation of pressor and tachycardic responses to stress. Using selective blockade of brain NK(1) and NK(2) receptors, we tested in conscious rats the hypothesis that SP initiates, within the neuronal brain circuits, the sympathoadrenal, hypothalamic-pituitary-adrenal (HPA) and behavioural responses to noxious stimuli. Formalin injected s.c. through a chronically implanted catheter in the area of the lower leg was used as a pain stimulus. Rats were pretreated i.c.v. with vehicle or the selective, nonpeptide antagonists of tachykinin NK(1) and NK(2) receptors, RP 67580 and SR 48968, respectively. Ten minutes thereafter, formalin was injected s.c. and the cardiovascular responses were recorded, plasma concentrations of catecholamines, adrenocorticotrophic hormone (ACTH) and corticosterone were determined and the expression of the inducible transcription factor c-Fos in the paraventricular (PVN) and supraoptic nuclei was detected to identify neurones which were activated during pain stimulation. Blockade of NK(1) and NK(2) receptors attenuated the formalin-induced increases in mean arterial pressure and heart rate, adrenaline and ACTH concentrations in plasma, and completely abolished the pain-induced c-Fos expression in corticotrophin-releasing hormone neurones localised in the parvocellular division of the PVN. The results obtained provide pharmacological evidence that tachykinins, most probably SP, act as mediators within the neuronal circuits linked to the initiation and control of the cardiovascular, sympathoadrenal, HPA and behavioural responses to pain stimuli and provide an excitatory input to corticotrophin-releasing hormone neurones in the PVN to activate the HPA axis. Our data demonstrating the inhibition of the complex response pattern to noxious stimuli and stress are consistent with the proposed anxiolytic and antidepressant activity of NK(1) and NK(2) receptor antagonists.

The effect of restraint stress on the normal colon and on intestinal inflammation in a model of experimental colitis

Stress may induce development of inflammation in animal models of colitis. The effects of restraint stress on oxidative damage and on antioxidants in the normal colonic mucosa were studied. The effect of stress on the severity of indicators of inflammation, as well as the importance of mucosal substance P (SP) as a mediator of this effect were investigated in the TNBS-colitis model. Restraint stress significantly increased malondialdehyde levels and reduced levels of low-molecular-weight-antioxidants in the normal colon. ATP and the mucosal "energy charge" decreased substantially with chronic stress. Chronic stress worsened the extent of inflammation in 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis. Mucosal SP content was not affected by exposure to chronic stress but increased after induction of colitis. The increase was greater when colitis was induced after exposure to stress. We conclude that chronic restraint stress causes oxidative damage to the normal colon and aggravates intestinal inflammation induced by TNBS. This effect may be mediated by SP.

The regulation of hypothalamic corticotropin-releasing factor release: in vitro studies

Although there are various ways in which the regulation of hypothalamic corticotropin-releasing factor (CRF) may be investigated, the most direct is by the study of CRF secretion from rat hypothalami incubated in vitro. Using this technique, we have found stimulation of secretion by noradrenaline, acetylcholine, serotonin, neuropeptide Y, and interleukins 1 and 6; inhibitory modulation was shown by GABA, substance P, atrial natriuretic peptide, opioid peptides and precursors of nitric oxide. Studies of these interactions demonstrated certain non-linear characteristics which may allow appropriate mathematical models to be devised; this may aid in our understanding of clinical disorders associated with CRF excess.

Involvement of NK1 receptors in metabolic stress markers after the central administration of substance P

Substance P (SP) is involved in the pathophysiology of several psychiatric disorders and is considered a central stress neurotransmitter. Endogenous SP does not inhibit the initial extent of the HPA axis response to restraint stress, but reduces the duration of the stress suggesting that SP plays an important role in the transition between acute and chronic stress. Stress hormones can alter metabolic functions in white adipose tissue and liver. The HPA axis is the endocrine pathway that promotes lipolysis elevating free fatty acid levels (FFA) in blood, besides indirectly causing hyperglycemia. In the present study, changes in the blood levels of stress markers in the anxiogenic-like effects of SP, as evaluated on the elevated plus-maze (EPM), were studied in adult male rats. Serum corticosterone was used as the traditional stress marker, while the plasma FFA and glucose were used as alternative anxiety/stress markers. Our findings show: (a) elevated corticosterone levels, confirming the aversive situation induced by SP (behaviorally assessed in the EPM) and indicating SP as a "chemical" stressor; (b) elevated levels of FFA and glucose, indicators of stress-induced mobilization of energy substrates, confirming the stressor effect of SP; (c) FFA levels can be used as an accurate, sensitive and reliable index of acute stress situations, including in the anxiogenic-like effect of SP, with the FFA response being as good as corticosterone as a stress marker in this case; (d) NK1 receptors involvement in the underlying mechanisms of the behavioral and metabolic effects of SP. Finally, our study indicates that some of these physiological variables are positively related to the stressor intensity.

The role of substance P in stress and anxiety responses

Substance P (SP) is one of the most abundant peptides in the central nervous system and has been implicated in a variety of physiological and pathophysiological processes including stress regulation, as well as affective and anxiety-related behaviour. Consistent with these functions, SP and its preferred neurokinin 1 (NK1) receptor has been found within brain areas known to be involved in the regulation of stress and anxiety responses. Aversive and stressful stimuli have been shown repeatedly to change SP brain tissue content, as well as NK1 receptor binding. More recently it has been demonstrated that emotional stressors increase SP efflux in specific limbic structures such as amygdala and septum and that the magnitude of this effect depends on the severity of the stressor. Depending on the brain area, an increase in intracerebral SP concentration (mimicked by SP microinjection) produces mainly anxiogenic-like responses in various behavioural tasks. Based on findings that SP transmission is stimulated under stressful or anxiety-provoking situations it was hypothesised that blockade of NK1 receptors may attenuate stress responses and exert anxiolytic-like effects. Preclinical and clinical studies have found evidence in favour of such an assumption. The status of this research is reviewed here.

NK-1 antagonist CP99994 inhibits stress-induced mast cell degranulation in rats

Mast cells are implicated in stress-induced inflammatory skin diseases such as psoriasis. Mechanisms of stress-induced mast cell degranulation however, are not entirely clear. Here we explore the role of activation of a Substance P (SP) receptor (NK-1) on mast cell degranulation upon exposure to stress in rats. A specific nonpeptide NK-1 antagonist, CP99994 was used to treat the rats either peripherally or intracerebroventricularly. Because increased SP activity in the brain may mediate the stress response, we also examined cutaneous mast cell degranulation after central injection of SP. Stress, as well as SP injected centrally, increased mast cell degranulation. Both central and peripheral injection of CP99994 prevented stress-induced mast cell degranulation. Surprisingly, the combination of stress with SP decreased mast cell degranulation, suggesting that high levels of SP may counteract the stress responses. Results in this animal model suggest that NK-1 antagonists may be used therapeutically to treat stress-induced inflammatory skin diseases; however, drug doses should be chosen carefully.

Hypothalamic response to experimental allergic encephalomyelitis: role of substance P

Adjuvant-induced arthritis (AA) is thought to be a model for experimental chronic stress that has as main features decreased adrenocorticotropin hormone (ACTH) plasma levels and a rise in median eminence content of arginine vasopressin (AVP) due to the activity of substance P. In experimental allergic encephalomyelitis (EAE), another chronic stress model, the role of substance P action is not clear. In this paper we tried to clarify the role of substance P in Lewis rats, which are susceptible to this disease. EAE was induced using myelin basic protein plus complete Freund's adjuvant injected into the hind limbs. One day later injections of an antagonist to substance P (RP 67580), saline, and substance P were administered daily for 12-14 days through a stainless steel cannula into the lateral ventricle of the brain, and then the rats were killed. The rats were divided into groups of controls, sham, diseased controls (no intracerebroventricular injections) and EAE (injected intracerebroventricularly). Plasma was used for the quantification of ACTH and corticosterone but not AVP which was assayed in hypothalamic median eminence extracts. In noninjected diseased rats the plasma levels of ACTH and corticosterone were significantly higher than in noninjected control rats, whereas the AVP concentrations in the median eminence were unchanged. The substance P antagonist did not affect the levels of these hormones in plasma or the median eminence. Substance P decreased the plasma levels of ACTH and corticosterone but did not increase the median eminence content of vasopressin. Administration of the antagonist 30 min before an equivalent dose of substance P increased the plasma levels of the two hormones, but did not change the content of AVP. Based on the lack of response to the antagonist RP 67580 we suggest that the substance P has different roles in EAE and AA at least in the later stages of EAE (after 11 days of immunization).

Neuroendocrine pharmacology of stress

Exposure to hostile conditions initiates responses organized to enhance the probability of survival. These coordinated responses, known as stress responses, are composed of alterations in behavior, autonomic function and the secretion of multiple hormones. The activation of the renin-angiotensin system and the hypothalamic-pituitary-adrenocortical axis plays a pivotal role in the stress response. Neuroendocrine components activated by stressors include the increased secretion of epinephrine and norepinephrine from the sympathetic nervous system and adrenal medulla, the release of corticotropin-releasing factor (CRF) and vasopressin from parvicellular neurons into the portal circulation, and seconds later, the secretion of pituitary adrenocorticotropin (ACTH), leading to secretion of glucocorticoids by the adrenal gland. Corticotropin-releasing factor coordinates the endocrine, autonomic, behavioral and immune responses to stress and also acts as a neurotransmitter or neuromodulator in the amygdala, dorsal raphe nucleus, hippocampus and locus coeruleus, to integrate brain multi-system responses to stress. This review discussed the role of classical mediators of the stress response, such as corticotropin-releasing factor, vasopressin, serotonin (5-hydroxytryptamine or 5-HT) and catecholamines. Also discussed are the roles of other neuropeptides/neuromodulators involved in the stress response that have previously received little attention, such as substance P, vasoactive intestinal polypeptide, neuropeptide Y and cholecystokinin. Anxiolytic drugs of the benzodiazepine class and other drugs that affect catecholamine, GABA(A), histamine and serotonin receptors have been used to attenuate the neuroendocrine response to stressors. The neuroendocrine information for these drugs is still incomplete; however, they are a new class of potential antidepressant and anxiolytic drugs that offer new therapeutic approaches to treating anxiety disorders. The studies described in this review suggest that multiple brain mechanisms are responsible for the regulation of each hormone and that not all hormones are regulated by the same neural circuits. In particular, the renin-angiotensin system seems to be regulated by different brain mechanisms than the hypothalamic-pituitary-adrenal system. This could be an important survival mechanism to ensure that dysfunction of one neurotransmitter system will not endanger the appropriate secretion of hormones during exposure to adverse conditions. The measurement of several hormones to examine the mechanisms underlying the stress response and the effects of drugs and lesions on these responses can provide insight into the nature and location of brain circuits and neurotransmitter receptors involved in anxiety and stress.

Review on the influence of stress on immune mediators, neuropeptides and hormones with relevance for inflammatory bowel disease

Stress has long been postulated to influence the progression of inflammatory bowel disease (IBD). Our current understanding of the relationship between stress and IBD is still limited, and hence explanation for the occurrence of relapses has remained largely speculative. Stress affects the immune system, the neuroendocrine system and the intestinal epithelia. Stress induces the release of pro-inflammatory Th1 cytokines and neuropeptides, such as tachykinins. Thereby, stress may induce alterations of the intestinal epithelium via the interaction of the neuroendocrine and immune system and may induce relapses of IBD. The present review focuses on this network and highlights the role of distinct mediators and mechanisms, i.e. neurotransmitters, hormones and immune cells, which are involved in the response to stress on the one hand, and contribute to the onset, progression or relapses of IBD on the other.

Stress and inflammatory disease: widening roles for serotonin and substance P

Serotonin has been implicated in mediating the hypothalamo-pituitary-adrenal (HPA) axis response to stress and is an important therapeutic target for a number of psychiatric disorders including depression. The neurokinin substance P has been shown to inhibit stress-induced HPA axis activity and we have demonstrated that endogenous substance P is able to reduce the duration of the HPA axis response to stress suggesting an important role in the termination of the stress response. This may be important in controlling the transition from acute to chronic stress and substance P has recently attracted attention as a potential antidepressant.In addition to these central effects, serotonin and substance P are considered to be pro-inflammatory agents. Despite being implicated in mediating inflammation there have been few studies investigating the effects of manipulations of serotonergic or substance P systems on chronic inflammatory disease. Treatment of rats with adjuvant-induced arthritis(AA), a model of chronic inflammatory stress, with a substance P antagonist specific for the NK1 receptor subtype resulted in a reduction in hind paw inflammation suggesting substance P may influence inflammation. We have noted that depletion of whole body serotonin and selective central depletion of serotonin results in a decrease in the severity of inflammation in rats with adjuvant arthritis. Furthermore, treatment with a selective serotonin reuptake inhibitor results in an earlier onset and increased severity of inflammation in adjuvant arthritis, confirming a pro-inflammatory role for serotonin. Serotonin is also present in the immune tissues and concentrations in the spleen fall following the development of inflammation in adjuvant arthritis. Concentrations of serotonin are significantly higher in normal female spleen than in males, and this may underlie the greater predisposition of females to certain autoimmune diseases.There is increasing evidence of a role for transmitters such as serotonin and substance P,both centrally and peripherally, in mediating a wide variety of inflammatory and psychiatric disorders. A better understanding of the mechanisms of action of these transmitters and the development of suitable drugs targeting specific receptor subtypes has great potential to impact on clinical practice in the near future. The purpose of this review is to consider the separate roles of serotonin and substance P in relation to HPA axis stress responses, in the context of a model of chronic inflammatory disease, highlighting novel directions of current research for each of these transmitters.

Substance P is involved in terminating the hypothalamo- pituitary-adrenal axis response to acute stress through centrally located neurokinin-1 receptors

The neurokinin substance P (SP) has been previously shown to inhibit basal hypothalamo-pituitary-adrenal (HPA) axis activity. This study was designed to investigate the effects of central injection of the specific neurokinin-1 receptor antagonist RP67580 on the HPA axis response to acute restraint stress. In non-restrained rats injected with RP67580, plasma ACTH and corticosterone levels were elevated at 30 and 60 min compared to rats injected with vehicle, but there were no differences between vehicle and RP67580 groups at 4h. In restrained rats injected with vehicle, plasma ACTH and corticosterone levels were significantly elevated at 30 min and 60 min following initiation of the stress but had returned to basal levels at 4h. In restrained rats injected icv with RP67580, plasma corticosterone and ACTH levels were significantly elevated at 30 min and 60 min, with no significant differences compared to the restraint stressed vehicle-injected group. However, in the RP67580-injected group, corticosterone and ACTH levels remained significantly elevated at 4h following onset of restraint compared to those in the restraint stressed vehicle-injected group. Corticotrophin-releasing factor mRNA levels in the parvocellular subdivision of the paraventricular nucleus of the hypothalamus and POMC mRNA levels in the anterior pituitary were significantly increased in the stressed group 4h following injection with RP67580 compared to the stressed group injected with vehicle alone. These data show that endogenous SP does not inhibit the initial magnitude of the HPA axis response to restraint stress, but does act through neurokinin-1 receptors at a central level to reduce the duration of the response to stress. This suggests that SP may be an important central agent controlling the transition between acute and chronic stress.

Variations in plasma levels of substance P and effects of a specific substance P antagonist of the NK(1) receptor on preovulatory LH and FSH surges and progesterone secretion in the cycling cynomolgus monkey

These studies investigated the role of substance P (SP) in the regulation of the hypothalamic-pituitary-ovarian axis in cynomolgus monkeys with normal menstrual cycles. Plasma concentrations of SP were determined in blood samples taken every morning in normally menstruating cynomolgus monkeys throughout the menstrual cycle. There was a significant decreasing linear trend of SP during the follicular phase (cycle day -13 to day 0) and a significant inverse relationship between SP plasma values and plasma 17beta-estradiol (E(2)) values from day -13 to day 0 of the adjusted cycle. Correspondingly, SP area under the curve was significantly greater during the follicular phase than the luteal phase. In a second experiment, plasma concentrations of E(2), luteinizing hormone (LH), follicle-stimulating hormone (FSH) and progesterone and length of cycles were measured after five daily intragastric administrations (10 mg/kg) of an NK(1) receptor (SP receptor) antagonist (RPR 100893; 10 mg/kg) initiated after serum E(2) concentrations had exceeded 125 pg/ml. There was a statistically significant reduction in the amplitude (41% of control) and the area under the curve (37% of control) of the preovulatory LH surge. In addition, there was a reduction of the duration of the LH surge (3 +/- 0.1 days in controls vs. 2.1 +/- 0.2 days in treated animals). The present results show for the first time that there are significant variations in plasma levels of SP, with a strong negative correlation with serum levels of E(2) during the follicular phase of the cynomolgus monkey, and that endogenous SP has a potentiating role in the interactive hypothalamo-anterior-pituitary mechanisms which lead to the preovulatory LH and FSH surges during the menstrual cycle in the monkey.

Ultradian rhythm of basal corticosterone release in the female rat: dynamic interaction with the response to acute stress

The present study investigated the dynamic regulation of the hypothalamo-pituitary-adrenal axis and its significance to acute stress responsiveness in the female rat. An automated, frequent blood-sampling technique allowed the circadian rhythm of corticosterone to be resolved into a series of pulses. These were equally distributed (mean interval, 50.9 +/- 3.7 min) throughout the 24-h cycle, but their magnitude varied significantly, being higher between 1800-2200 h (137 +/- 9 ng/ml) than between 0600-1000 h (75 +/- 17 ng/ml). This pattern of release indicates continuous, but variable, activity of the axis throughout the day. The pulsatile ultradian rhythm suggested alternate periods of secretion and inhibition, which were found to have a profound effect on the corticosterone responses to acute stress. Noise stress (10 min, 114 decibels) evoked a transient increase in corticosterone, which reached a maximum (377 +/- 87 ng/ml) 20 min after onset. However, within this group (n = 26) the response varied depending on the underlying basal activity. When stress coincided with a rising (secretory) phase of a pulse, corticosterone concentrations rose to 602 +/- 150% of mean basal concentrations (P < 0.001). In contrast, when stress coincided with a falling (nonsecretory) phase of a pulse, a significantly smaller response, no greater than a basal pulse, was evoked. Thus, the alternate periods of secretion and inhibition generating basal hypothalamo-pituitary-adrenal activity are an important determinant of responses to acute stress.

Role of tachykinins in the regulation of the hypothalamo-pituitary-adrenal axis

Tachykinins are a family of neuropeptides, which act by binding to three main subtypes of G protein-coupled receptors, named NK1, NK2 and NK3. Tachykinins are contained in both nerve fibers and secretory cells of the hypothalamo-pituitary-adrenal (HPA) axis, and evidence indicates that they take part in the functional control of it. Tachykinins involved in this function include substance P (SP), neuropeptide K and its derivative neurokinin A (NKA), and neurokinin B, which preferentially bind to NK1, NK2 and NK3 receptors, respectively. NK1 agonists exert an inhibitory effect on the hypothalamo pituitary CRH/ACTH system, while NK2 and perhaps NK3 agonists stimulate it, thereby controlling the secretion and growth of the adrenal cortex via circulating ACTH. Intra-adrenal tachykinins may also affect the cortex function. Their direct action on adrenocortical cells is doubtful and probably pharmacologic in nature, but several investigations suggest that tachykinins indirectly stimulate the cortex by acting on medullary chromaffin cells, which in turn exert a paracrine control on adrenocortical cells. SP enhances aldosterone production of zona glomerulosa by eliciting catecholamine secretion; neuropeptide K and NKA raise glucocorticoid production of zonae fasciculata and reticularis through the activation of the intramedullary CRH/ACTH system. The relevance of these effects of tachykinins under basal conditions is questionable, although there are indications that SP is involved in the maintenance of a normal growth and steroidogenic capacity of rat zona glomerulosa, and that SP and NKA play an important role in the stimulation of the adrenal growth during the fetal life. In contrast, evidence has been provided that the role of tachykinins, and especially of SP, could become very relevant under paraphysiological (e.g., physical or inflammatory stresses) or pathological conditions (e.g., ACTH-secreting pituitary tumors), when an excess of steroid-hormone production has to be counteracted.

Neuropeptide K and neurokinin A stimulate CRH and ACTH release by rat adrenal medulla in vitro

Tachykinins are a family of peptides that are able to modulate the activity of the hypothalamo-pituitary CRH-ACTH system. Mammalian tachykinins include neurokinin A (NKA), neurokinin B (NKB), neuropeptide K (NPK), and substance P (SP). We investigated by RIA the effects of tachykinins on the release of CRH and ACTH by rat adrenal medulla in vitro. NKA and NPK concentration-dependently enhanced the release of both CRH and ACTH, NPK being more active than NKA. NKB exerted only a minor stimulatory action exclusively on CRH release, and SP was ineffective. The stimulatory effect of both NKA and NPK on ACTH release was blocked by the CRH receptor antagonist alpha-helical-CRH, thereby suggesting that the increase in ACTH secretion is consequent to the stimulation of CRH release. These findings indicate that NKA and NPK are stimulators not only of the central (hypothalamo-pituitary), but also of the peripheral (intramedullary) branch of the CRH-ACTH system.

The possible role of endogenous substance P in the modulation of the response of rat pituitary-adrenal axis to stresses

The role played by endogenous substance P (SP) in the regulation of hypothalamo-pituitary-adrenal (HPA) axis was investigated in the rat. Normal and ether-stressed (2 min ether-vapor inhalation) or cold-stressed (20 min at 4 degrees C) animals were given a bolus subcutaneous injection of 100 nmol spantide (SPA) a specific antagonist of SP; their blood concentrations of ACTH, aldosterone (ALDO) and corticosterone (B) were measured by specific RIA, 1, 2 or 4 h after the injection. SPA did not evoke significant changes in the basal plasma levels of the three hormones. Ether and cold stresses markedly raised the blood concentrations of ACTH, ALDO and B, being maximal response observed after 1 or 2 h. SPA notably enhanced the responses of the three hormones to ether stress. SPA magnified ALDO and B responses to cold stress, but it notably depressed ACTH one. In light of these findings, it may be concluded that (i) endogenous SP does not affect basal activity of rat HPA axis, but it exerts an inhibitory action on its response to the stresses, especially the ether-inhalation one: and (ii) different mechanisms are involved in the cold and ether stress-induced activation of the HPA axis.

Neuroendocrine immune responses to inflammation: the concept of the neuroendocrine immune loop

The neuroendocrine and immune responses to inflammatory stress represents an integrated circuit whose basis is reviewed in this chapter. Pro-inflammatory cytokines such as IL-1 beta, TNF-alpha and IL-6 released from inflammatory foci initiate local anti-inflammatory mechanisms and travel via the blood stream to the brain where they trigger a variety of neuroendocrine counter-regulatory mechanisms. There is therefore an important neuroendocrine-immune loop in which stimulatory signals are received by the neural systems from inflammatory foci. These signals are transduced by the hypothalamus which initiates a complex hormonal cascade reaction aimed at modulating inflammation and returning the organism to normal physiological homeostasis once the trigger has been neutralized. Abnormalities in this cross-talk can profoundly influence the susceptibility to developing chronic inflammatory disease. Thus, in conclusion, the neuroendocrine-immune loop has important pathophysiological implications for disease processes.

Peripheral mononeuropathy affects hypothalamic and splenocyte beta-endorphin levels but not immune function in the rat

Beta-endorphin and substance P levels were measured in the hypothalamus of rats 14 days after chronic constriction injury of right sciatic nerve. Furthermore, beta-endorphin concentrations in splenocytes, phytoemoagglutinin-induced proliferation of splenocytes, and natural killer activity were assessed. We observed a significant increase of beta-endorphin and substance P hypothalamic levels, and a significant decrease of beta-endorphin concentrations in the immune cells. In contrast, the peripheral mononeuropathy did not affect the immune function. This study presents a picture of central and peripheral peptide changes consistent with a painful condition, but different from what previously observed in rats which underwent peripheral nerve deafferentation or stressful conditions.

Effects of neurokinin-A on the rat hypothalamo-pituitary-adrenal axis

The effects of neurokinin-A (NKA) on the rat hypothalamo-pituitary-adrenal (HPA) axis were studied in vivo and in vitro. A subcutaneous injection of 1 or 3 nmol/100 g NKA did not alter plasma ACTH concentration. The lower dose of NKA evoked a transient rise in plasma corticosterone (B) concentration (PBC) at 30 min, and did not change plasma aldosterone (ALDO) concentration (PAC). The higher dose of NKA increased PBC at 30 and 60 min, and PAC at 30, 60 and 120 min. NKA did not affect basal ALDO secretion of dispersed zona glomerulosa (ZG) cells, but it markedly enhanced basal B production by dispersed zona fasciculata/reticularis (ZF/R) cells (minimal and maximal effective concentrations were 10(-9) M and 10(-6) M). Video-imaging analysis showed that 10(-6) M NKA increased intracellular Ca2+ concentration in dispersed ZF/R cells, but not in ZG ones. These findings indicate that NKA exerts a stimulatory action on the rat adrenal secretory activity, which is independent of any effect on the pituitary ACTH release: the B secretagogue action seems to be due to a direct effect of NKA on ZF/R cells, while the ALDO secretagogue action is not direct. but probably mediated by factor(s) other than ACTH.

Evidence that endogenous substance-P (SP) is involved in the maintenance of the growth and steroidogenic capacity of rat adrenal zona glomerulosa

A 7-day intraperitoneal infusion with the specific SP antagonist magnitude of D-Pro4,D-Trp7,9-SP4-11 (SP-A; 0.3 nmol.kg-1.min-1) significantly lowered plasma aldosterone (ALDO) concentration and caused atrophy of adrenal zona glomerulosa (ZG) and its parenchymal cells. Dispersed ZG cells from SP-A-infused rats displayed a marked decrease in both their basal and maximally agonist-stimulated ALDO production. The simultaneous infusion of rats with SP (0.03 nmol.kg-1.min-1) completely annulled all these effects of SP-A. The plasma levels of ACTH and corticosterone, and the morphology of adrenal zona fasciculata were not affected by SP-A or SP-A plus SP infusion. These findings suggest that endogenous SP is specifically involved in the positive control of growth and secretion of the rat ZG.

Adrenal medulla is involved in the aldosterone secretagogue effect of substance P

Substance P (SP) increased aldosterone secretion of rat adrenal slices, but not of isolated zona glomerulosa cells, and this effect was annulled by two specific antagonist of SP (SP-A). Both tissue preparations displayed an aldosterone secretory response to isoprenaline (IP) that was blocked by l-alprenolol (AL). AL reversed the aldosterone response of adrenal slices to IP, SP, or IP plus SP, whereas SP-A only suppressed that to SP. Quarters of adrenocortical autotransplants, which are completely deprived of chromaffin cells, showed an aldosterone response to IP, but not to SP. These findings suggest that the mechanism underlying the aldosterone secretagogue action of SP probably involves the stimulation of catecholamine release by adrenal medulla chromaffin cells.

Metabolic stability of some tachykinin analogues to cell-surface peptidases: roles for endopeptidase-24.11 and aminopeptidase N

The metabolism of several tachykinin antagonists by membrane peptidases has been examined. [beta Ala8]NKA(4-10) was not stabilized against degradation by endopeptidase-24.11 and this was the major activity in renal brush border membranes hydrolyzing this peptide. The antagonist MEN 10263 was much more resistant to hydrolysis by endopeptidase-24.11, although hydrolysis of the C-terminal Leu-Phe bond was detectable. Three other tachykinin receptor antagonists (MEN 10208, MEN 10207, and MEN 10376), by virtue of D-Trp substitutions, were rendered resistant to endopeptidase-24.11 but were still susceptible to aminopeptidase action. These studies provide further insight into design features necessary to produce metabolically stable peptide analogues.

Neuropeptide K enhances glucocorticoid release by acting directly on the rat adrenal gland: the possible involvement of zona medullaris

Neuropeptide K (NPK), a member of the kassinin-like tachykinin family, is contained in the rat hypothalamus and is known to stimulate pituitary ACTH release. The intraperitoneal bolus administration of NPK dose-dependently enhanced corticosterone blood level not only in intact rats, but also in hypophysectomized/ACTH replaced animals. NPK did not affect corticosterone secretion of dispersed rat adrenocortical cells; however, it concentration-dependently raised basal corticosterone production by decapsulated adrenal quarters (including both cortical and medullary tissues). Minimal and maximal effective concentrations were 10(-9) and 10(-8) M, respectively. 10(-8) M NPK potentiated corticosterone response of adrenal quarters elicited by 10(-12) M ACTH, but not that evoked by higher concentrations of ACTH. The direct corticosterone secretagogue effect of 10(-8) M NPK is annulled by 10(-6) M alpha-helical-CRH or corticotropin-inhibiting peptide, competitive inhibitors of CRH and ACTH, respectively. In light of these findings, the hypothesis is advanced that NPK exerts a direct stimulatory action on adrenocortical secretion and that the mechanism underlying this effect of NPK may involve the activation of the intra-medullary CRH/ACTH system.

Nitric oxide modulates the release of corticotropin-releasing hormone from the rat hypothalamus in vitro

There is now considerable evidence that nitric oxide (NO) is an important neuroregulatory agent, but there has been very little investigation of the possible role of NO in neuroendocrine mechanisms. We have previously shown that acute rat hypothalamic explants can be used to study the regulation of hypothalamic neuropeptide release, and we have now utilised this experimental approach to investigate the putative involvement of NO in the control of the principal corticotropin-releasing hormone, CRH. We studied the direct effects of the NO precursor L-arginine (L-ARG), as well as the NO donors molsidomine and sodium nitroprusside, on both the basal and stimulated release of CRH; the stimuli used were non-specific depolarisation with potassium chloride (KCl) and the specific cytokine, interleukin-1 beta (IL-1 beta; 100 U/ml). L-ARG was tested in each experimental condition with and without contemporaneous addition of its competitive antagonist NG-monomethyl-L-arginine (L-NMMA). IL-1 beta-induced CRH release was also investigated in the presence of D-arginine (D-ARG), which is not active as a precursor to NO, and ferrous hemoglobin (Hb), a substance which is a potent inactivator of NO. None of the NO precursors (L-ARG, molsidomine, sodium nitroprusside) or antagonists (L-NMMA or Hb) was able to affect basal CRH release. However, L-ARG 10 and 100 microM were found to significantly inhibit the release of CRH induced by 40 mM KCl; CRH fell to 45% of its stimulated level at the higher dose of L-ARG. This effect was attenuated in the presence of L-NMMA at a ten-fold higher dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Substance P inhibits the release of anterior pituitary adrenocorticotrophin via a central mechanism involving corticotrophin-releasing factor-containing neurons in the hypothalamic paraventricular nucleus

Chronic osmotic stimulation influences the hypothalamo-adenohypophysial axis by inhibiting the synthesis of hypothalamic corticotrophin-releasing factor (CRF-41) and subsequently the secretion of basal and adrenalectomy-elevated adrenocorticotrophin from the adenohypophysis. In the present study, we used a substance P antagonist to test the hypothesis that this inhibition is mediated centrally by substance P or other tachykinins. In control rats and rats given 2% saline to drink for 12 days, intracerebroventricular administration of a substance P antagonist elevated plasma adrenocorticotrophin and corticosterone levels. Using quantitative in situ hybridization histochemistry, it was also demonstrated that CRF mRNA increased in the medial parvocellular division of the paraventricular nucleus of saline-treated as well as control rats 6 h after intracerebroventricular administration of the antagonist, while vasopressin mRNA in the medial parvocellular division of the paraventricular nucleus was increased in the control animals only. These results provide evidence that central endogenous substance P has an inhibitory influence over the synthesis and release of CRF-41 both under normal conditions and during a chronic osmotic stimulus.

Preprotachykinin A gene expression in distinct hypothalamic and brain stem regions of the rat is affected by a chronic osmotic stimulus: a combined immunohistochemical and in situ hybridization histochemistry study

Chronic osmotic stimulation influences the hypothalamoadenohypophysial axis by inhibiting the synthesis of corticotrophin releasing factor (CRF-41) in the parvocellular subdivision of the paraventricular nucleus (PVN) and, subsequently, the secretion of adrenocorticotrophin (ACTH) from the adenohypophysis. Using quantitative in situ hybridization histochemistry, we have investigated the effect of chronic osmotic stimulation on preprotachykinin A (PPT-A) mRNA levels in a number of brain areas known to send substance P-containing projections to the medial parvocellular part of the PVN. Chronic osmotic stimulation increased PPT-A gene expression in the lateral hypothalamic area, the arcuate nucleus, the catecholaminergic brain stem areas A2, C1, and C2, although PPT-A mRNA levels in the bed nucleus of the stria terminalis, the medial preoptic nucleus, the caudate-putamen, and the A1 were unaffected by chronic osmotic stimulation. In addition, immunohistochemical staining of substance P-immunoreactive elements contained within the same areas was carried out on colchicine-treated animals. Generally, those areas responding to the osmotic stimulus with increased PPT-A mRNA synthesis showed increased numbers of substance P-immunoreactive perikarya, suggesting that increased levels of mRNA are associated with increased peptide synthesis. These results provide evidence that central endogenous substance P contained in brain regions projecting to the paraventricular nucleus could have an inhibitory influence over the synthesis of CRF-41 during a chronic osmotic stimulus.

Osmotic regulation of substance P and neurokinin A peptide content and substance P binding sites in distinct hypothalamic nuclei of the rat

Quantitative receptor autoradiography using Bolton-Hunter iodinated substance P (SP) was used to localize specific sites in the rat hypothalamus. The amount of SP and neurokinin A (NkA) in extracts from discrete areas of the hypothalamus was measured using specific radioimmunoassays. A high density of SP binding sites was observed in the perimeter of the magnocellular paraventricular and supraoptic nuclei, while the magnocellular nuclei themselves possessed a low receptor density. In control animals, the number of SP binding sites was also low in the arcuate nucleus and the median eminence. Substance P and NkA peptide concentrations were highest in the paraventricular nucleus (PVN), decreasing in the following order: arcuate nucleus (Arc) greater than median eminence (ME) greater than supraoptic nucleus (SON) greater than subfornical organ (SFO). In animals given 340 mmol/l NaCl instead of tap water to drink for 12 days, significant increases in the number of SP binding sites occurred in the medial parvocellular subdivision of the PVN, periamygdaloid cortex, medial preoptic nucleus, Arc, and ME, but other hypothalamic areas were unaffected. In saline-treated animals, significant increases in SP and NkA peptide concentrations were observed in the ME, while in the SFO only the concentration of NkA increased significantly. In the SON, substance P and neurokinin A levels were doubled, whereas in the PVN and Arc no changes in peptide levels were observed. Chronic osmotic stimulation is associated with lowered circulating levels of adrenocorticotropin releasing hormone (ACTH), and the present data further substantiate the hypothesis that hypothalamic tachykinin-containing neuronal terminals are centrally involved in the inhibition of anterior pituitary ACTH release observed during chronic osmotic stimulation.