Effects of sequential removal of rats from a group cage, and of individual housing of rats, on substance P, cholecystokinin and somatostatin levels in the periaqueductal grey and limbic regions

Substance P and its role in neural mechanisms governing learning, anxiety and functional recovery

The neurokinin Substance P (SP) is widely distributed in the central nervous system and has been extensively studied in various functional aspects. This review focuses on the behavioral relevance of SP. Here we show that SP can have memory-promoting, reinforcing and anxiolytic-like effects when administered systemically or into the nucleus basalis of the ventral pallidum. These effects seem to be mediated via the SP-preferring NK(1)receptor and differentially related to N- versus C-terminal fragments of the undecapeptide. Secondly, SP injection into the ventral pallidum can lead to increases of acetylcholine in frontal cortex and dopamine in nucleus accumbens, suggesting that the hypermnestic, positively reinforcing and anxiolytic effects observed upon basal forebrain injection of SP are mediated by activation of the nucleus accumbens-ventral pallidum circuitry. Furthermore, SP and certain SP-fragments may not only be considered to have beneficial behavioral effects in normal animals, but can also prevent lesion-induced functional deficits and improve the speed of recovery. This indicates that SP agonists might also have a neuroprotective capacity in parallel with recovery-promoting actions.

Pharmacological blockade or genetic deletion of substance P (NK(1)) receptors attenuates neonatal vocalisation in guinea-pigs and mice

The regulation of stress-induced vocalisations by central NK(1) receptors was investigated using pharmacological antagonists in guinea-pigs, a species with human-like NK(1) receptors, and transgenic NK1R-/- mice. In guinea-pigs, i.c.v. infusion of the selective substance P agonist GR73632 (0.1 nmol) elicited a pronounced vocalisation response that was blocked enantioselectively by the NK(1) receptor antagonists CP-99,994 and L-733,060 (0.1-10 mg/kg). GR73632-induced vocalisations were also markedly attenuated by the antidepressant drugs imipramine and fluoxetine (30 mg/kg), but not by the benzodiazepine anxiolytic diazepam (3 mg/kg) or the 5-HT(1A) agonist buspirone (10 mg/kg). Similarly, vocalisations in guinea-pig pups separated from their mothers were blocked enantioselectively by the highly brain-penetrant NK(1) receptor antagonists L-733,060 and GR205171 (ID(50) 3 mg/kg), but not by the poorly brain-penetrant compounds LY303870 and CGP49823 (30 mg/kg). Separation-induced vocalisations were also blocked by the anxiolytic drugs diazepam, chlordiazepoxide and buspirone (ID(50) 0.5-1 mg/kg), and by the antidepressant drugs phenelzine, imipramine, fluoxetine and venlafaxine (ID(50) 3-8 mg/kg). In normal mouse pups, GR205171 attenuated neonatal vocalisations when administered at a high dose (30 mg/kg) only, consistent with its lower affinity for the rat than the guinea-pig NK(1) receptor. Ultrasound calls in NK1R-/- mouse pups were markedly reduced compared with those in WT pups, confirming the specific involvement of NK(1) receptors in the regulation of vocalisation. These observations suggest that centrally-acting NK(1) receptor antagonists may have clinical utility in the treatment of a range of anxiety and mood disorders.

Mediators of stress effects in inflammatory bowel disease: not the usual suspects

Empirical efforts to prove or disprove an association between stress and the course of inflammatory bowel disease (IBD) have had inconsistent results. Direct study of mediators of stress-related physiological processes may clarify this important area.

METHODS

candidate mediators were selected based on evidence that they have a role in the pathophysiology of IBD. Medline searches for original articles addressing each putative mediator and psychological stress were conducted. Articles were reviewed with goals of synthesis and hypothesis generation.

RESULTS

there is evidence that substance P (SP), vasoactive intestinal protein (VIP), tumour necrosis factor alpha (TNFalpha), oxidant molecules, endogenous glucocorticoids and heat shock proteins (HSPs) are involved in the stress response.

DISCUSSION

two principles emerge which should inform efforts to investigate stress in IBD. First, stress effects are regulated by highly interdependent systems. Second, the effects of mediators are highly specific to the location of their activity, and so, investigations in IBD are likely to require direct investigation of inflamed and unaffected gut tissue.

Anabolic-androgenic steroids affect the content of substance P and substance P(1-7) in the rat brain

The effects of intramuscular (i.m.) injections of nandrolone decanoate (15 mg/kg/day), an anabolic-androgenic steroid, on the levels of substance P (SP) and on its N-terminal fragment SP(1-7) were examined in the male rat brain by radioimmunoassay. The results demonstrated that the SP immunoreactivity in amygdala, hypothalamus, striatum, and periaqueductal gray was significantly enhanced, whereas the concentration of the N-terminal fragment SP(1-7) was enhanced in the nucleus accumbens and in periaqueductal gray. In the striatum the steroid induced a decrease in the content of SP(1-7). The relevance of these peptides in connection with anabolic-androgenic steroid-induced aggression is discussed.

Conditioned fear-induced changes in neuropeptide Y-like immunoreactivity in rats: the effect of diazepam and buspirone

The study aimed to investigate the influence of conditioned fear, produced in the passive avoidance test, on neuropeptide Y-like immunoreactivity (NPY-LI) and the effect of anxiolytics on NPY-LI in frightened rats. Rats avoided the dark chamber, where they were previously subjected to electric footshock, and they exhibited increased numbers of defecations and gastric ulcers. Moreover, they showed increased NPY-LI in the amygdala, nucleus accumbens and hypothalamus, and decreased NPY-LI in the frontal cortex. Diazepam (1 or 3 mg/kg) and buspirone (1.5 or 5 mg/kg) dose-dependently inhibited passive avoidance and decreased the numbers of defecations, and they also decreased the number of gastric ulcers. Diazepam reversed while buspirone only attenuated the fear-induced changes in NPY-LI in all regions studied. In the amygdala, the effect of diazepam was dose-dependent. The effect of diazepam on both behaviour and NPY-LI was antagonized by flumazenil (15 mg/kg). Apart from supporting the role of the NPY system in fear and anxiety, the results of this study suggest that NPY is involved in the anxiolytic effects of diazepam and buspirone and that the effect of diazepam is mediated by benzodiazepine receptors.

Effect of neurokinin-I receptor antagonists on the function of 5-HT and noradrenaline neurons

Substance P antagonists have been proposed to be a new class of antidepressants. The present study aimed to determine the effect of the selective non-peptide rat neurokinin-1 (NK1) receptor antagonists WIN 51,708 and CP-96,345 on the firing activity of rat dorsal raphe serotonin (5-HT) and locus coeruleus noradrenaline (NA) neurons. While WIN51,708 (2mg/kg, i.v.) and CP-96,345 (0.15 mg/kg, i.v.) did not modify the firing activity of 5-HT and NA neurons, both antagonists attenuated the suppressant effect of the alpha2-adrenoceptor agonist clonidine on the firing activity of both types of neurons. In contrast, the responsiveness of 5-HT neurons to the i.v. administration of the 5-HT autoreceptor agonist LSD and the 5-HT1A receptor agonist 8-OH-DPAT remained unchanged. These findings suggest that NK1 receptor antagonists affect markedly the NA system via an attenuation of the function of alpha2-adrenoceptors on the cell body of NA neurons and, consequently, may also modulate 5-HT neurotransmission.

Anxiolytic-like effects in rats produced by ventral pallidal injection of both N- and C-terminal fragments of substance P

Prior studies have shown that the neurokinin substance P (SP) has anxiolytic-like effects when administered into the nucleus basalis (NB) area of the rat ventral pallidum. The present work was performed to examine whether the anxiolytic effects of SP in the nucleus basalis can be assigned its amino (N)- or carboxy (C)-terminal moiety. Using the elevated plus-maze model of anxiety in combination with unilateral injection of N-terminal SP(1-7) or C-terminal SP(7-11) into the NB region, we found that the treatment with either SP-fragment increased the number of entries into and time spent on the open arms as well as excursions into the end of the open arms, indicative of an anxiolytic-like profile. Furthermore, the effective doses of SP(1-7) (0.67 ng) and SP(7-11) (0.45 ng) were equimolar to the dosage of the whole SP molecule (1 ng), which was effective to reduce anxiety. Thus, the results support earlier findings that ventral pallidal injection of SP has anxiolytic-like effects and provide new evidence that fragments of SP, representing the N- and C-terminal domain of the peptide can reduce fear-parameters at a concentration similar to that of the parent peptide.

Discovery of the antidepressant and anti-emetic efficacy of substance P receptor (NK1) antagonists

The development of small-molecule antagonists of the substance P (SP)-preferring tachykinin NK1 receptor during the past decade represents an important opportunity to exploit these molecules as novel therapeutic agents. On the basis of its anatomical localization and function, SP has been implicated in diverse pathophysiologies; of these, diseases of the CNS have been examined in the greatest detail. Although SP is best known as a pain neurotransmitter, it also controls vomiting and various behavioural, neurochemical and cardiovascular responses to stress. Recent clinical trials have confirmed the efficacy of NK1 receptor antagonists to alleviate depression and emesis but, surprisingly, not pain. Thus, multiple clinical trials, targeted to appropriate patient populations, are necessary to define the therapeutic potential of novel neurotransmitter ligands.

Effects of formalin pain on hippocampal c-Fos expression in male and female rats

Immediate early genes are crucial intermediates in a cascade linking membrane stimulation to long-term alterations of neuronal activity. In the present experiment, we performed immunohistochemistry for c-Fos to determine the effects of persistent pain on cells of the hippocampus of male and female rats. Animals were subcutaneously injected with formalin (50 microl, 10%) and perfused: 2 h later, time 2; 24 h later, time 24; 24 h later after 20 min of the open-field test, time 24/OF. Controls were left undisturbed. In control, c-Fos was higher in females than in males in all hippocampal fields. In males at time 2, formalin increased c-Fos in the dentate gyrus (DG) and CA3 fields; at time 24, c-Fos returned to the control level; at time 24/OF, c-Fos was higher than in control in the DG, but not in the other fields. In the formalin-treated females at time 2 and at time 24, c-Fos levels were lower, or tended to be lower, than in control in all hippocampal fields; at time 24/OF, c-Fos levels in the DG were higher than in control and in males. In conclusion, persistent pain had different effects on c-Fos in the hippocampal subfields, depending on the time after treatment and the sex of the subject.

Distinct mechanism for antidepressant activity by blockade of central substance P receptors

The localization of substance P in brain regions that coordinate stress responses and receive convergent monoaminergic innervation suggested that substance P antagonists might have psychotherapeutic properties. Like clinically used antidepressant and anxiolytic drugs, substance P antagonists suppressed isolation-induced vocalizations in guinea pigs. In a placebo-controlled trial in patients with moderate to severe major depression, robust antidepressant effects of the substance P antagonist MK-869 were consistently observed. In preclinical studies, substance P antagonists did not interact with monoamine systems in the manner seen with established antidepressant drugs. These findings suggest that substance P may play an important role in psychiatric disorders.

Effect of individual versus group caging on the incidence of pituitary and Leydig cell tumors in F344 rats: proposed mechanism

Recently, an increase in pituitary tumor (pars distalis adenoma) incidence, and decrease in testicular interstitial cell tumor incidence, has been noted in F344 rats, in 2 year National Toxicology Program dermal and inhalation studies. One of the factors that may have contributed to this correlation is the difference in housing protocols. Rats in inhalation and dermal toxicity studies are singly caged, in contrast to other types of studies in which rats are group-caged, such as dosed-feed, dosed-water, or gavage studies. We propose that stress, related to individual caging, particularly among males, directly impairs testosterone synthesis and produces Leydig cell atrophy which leads to a feedback increase in the synthesis of luteinizing hormone by the anterior pituitary. This is followed by anterior pituitary cell functional hypertrophy, hyperplasia, and eventually neoplasia. It is known that individual caging of male rats produces a stress response associated with increased serum corticosteroids. The testicular interstitial cells (Leydig cells) have specific receptors for the glucocorticoid hormones. The Leydig cell enzyme 11-beta-hydroxysteroid dehydrogenase (11-beta-HSD) inactivates gluococorticoids; however, prolonged stress depletes this enzyme, enabling the gluococorticoids to impair steroidogenesis and eventually to lead to compensatory pituitary proliferations, including neoplasms.

Changes in neuropeptide levels after brain damage in rats

The physiological and pathophysiological roles of neuropeptides are still not clear. The aim of our study was to detect long lasting changes of vasoactive-intestinal peptide (VIP), somatostatin (SOM) and substance P (SP) contents in the rat cerebral cortex and hippocampus after brain lesion. The experiments were performed on groups of adult male Wistar rats. The first group consisted of animals with unilateral ablation of the sensorimotor cortex performed at the age of 60 days. The second group was a control one (rats of the same age but with an intact brain). Both groups of animals were sacrificed at the age of 90-105 days and radioimmunoassay was used to determine amounts of VIP, SOM and SP. The mean values of VIP levels were decreased significantly only in contralateral cortical areas, while there was an increase of SP in lesioned animals. Our results suggest that descrete changes in neuropeptide levels occur during restorative processes after brain lesion.

Effects of acute systemic treatment with the 5 HT-uptake blocker alaproclate on tissue levels and release of substance P in rat periaqueductal grey

The effects of acute systemic treatment with alaproclate, a serotonin uptake blocker on regional brain tissue levels of substance P, neurokinin A and cholecystokinin were studied in the rat. The peptide levels of all three peptides were increased (23-35%) in the rat periaqueductal grey 60 min after treatment with alaproclate (20 mumol/kg peroral, p.o.), compared to controls. In the cingulate cortex, the tissue levels of substance P and cholecystokinin were increased (19-32%) after subcutaneous (s.c.) treatment with alaproclate, compared to controls. Higher tissue levels of all three peptides (20-38%) in the periaqueductal grey, and lower levels of substance P and cholecystokinin in the cingulate cortex were found following saline s.c. compared to saline p.o., probably due to different degrees of stress. In microdialysis experiments, a s.c. injection of either saline (2 ml/kg), alaproclate (20 mumol/kg) or morphine (3 mg/kg) was found to slowly increase the substance P release in the periaqueductal grey. Experiments with the selective 5-HT neurotoxin, 5,7-dihydroxytryptamine indicated no neuronal co-existence of substance P and serotonin in the periaqueductal grey and cingulate cortex. In conclusion, acute treatment with the serotonin uptake blocker alaproclate increases both the tissue level and the release of substance P in the periaqueductal grey.

Clomipramine and clonazepam increase cholecystokinin levels in rat ventral tegmental area and limbic regions

Recent reports suggest that a cholecystokinin (CCK)-related dysfunction may be a target by which drugs can modulate anxiety and panic disorders. In the present study, effects of subchronic (14 days) treatment with the monoamine uptake inhibitors nortriptyline (30 mumol/kg per day), amitriptyline (29 mumol/kg per day), clomipramine (32 mumol/kg per day) and alaproclate (39 mumol/kg per day), as well as with the benzodiazepine clonazepam (0.25 mumol/kg per day), on rat brain levels of CCK- and substance P-like immunoreactivity, were compared. The drugs were administered by continuous s.c. infusion using implanted osmotic pumps. The plasma concentrations of the monoamine uptake inhibitors were similar after 1 and 2 weeks of treatment, indicating that steady-state plasma levels had been reached during the first week. Treatment with clomipramine or clonazepam increased the CCK-like immunoreactivity level in the ventral tegmental area (by 64.4 +/- 28.8% and 105.1 +/- 28.8%, respectively) and in the cingulate cortex (by 30.3 +/- 10.1% and 36.0 +/- 11.8%, respectively) (P < 0.05 or P < 0.01). Clomipramine also significantly increased the CCK-like immunoreactivity level in the periaqueductal grey by 85.1 +/- 29.7%. Neither nortriptyline nor amitriptyline or alaproclate produced any significant alterations in the CCK- or substance P-like immunoreactivity levels in the areas examined. The present results may suggest that an altered utilization of CCK in limbic circuits could be of importance for the well documented clinical effect of clomipramine and clonazepam in panic disorders.