Central actions of calcitonin on body temperature and intestinal motility in rats: evidence for different mediations

Central administration of aminoprocalcitonin inhibits food intake and stimulates the hypothalamic-pituitary-adrenal axis in rats via the corticotrophin-releasing factor system

Aminoprocalcitonin (N-PCT), a neuroendocrine peptide derived from procalcitonin, reduces food intake and body weight when administered centrally in rats. We have recently shown that N-PCT is expressed in brain areas known to be involved in energy homeostasis, including the paraventricular nucleus (PVN) of the hypothalamus, which contains a prominent population of corticotrophin-releasing factor (CRF)-synthesising neurones. CRF plays a pivotal role in the regulation of the hypothalamic-pituitary adrenal (HPA) axis and food intake. However, little is known about functional interactions of N-PCT and CRF. In the present study, we found endogenous N-PCT protein in the rat PVN. We also showed N-PCT immunoreactivity in PVN co-localised with NeuN, a neuronal marker, or glial fibrillary acidic protein, an astrocyte marker. Double staining immunohistochemistry revealed that N-PCT co-localised with CRF in parvocellular neurones of the PVN. Intracerebroventricular N-PCT administration increased CRF mRNA and content in the hypothalamus, suggesting that N-PCT stimulates the HPA axis and suppresses food intake and body weight via CRF-dependent pathways. In keeping with this, i.c.v. co-injection of D-Phe-CRF(12-41), a CRF receptor antagonist, significantly attenuated N-PCT-induced reduction in food intake and body weight in a dose-dependent manner. Furthermore, i.c.v. administration of N-PCT increased plasma adrenocorticotrophic hormone and corticosterone concentrations and induced the expression of Fos protein, a marker of neuronal activity, in parvocellular CRF neurones. These data collectively support the hypothesis that N-PCT inhibits food intake and body weight and stimulates the HPA axis via CRF-mediated pathways.

In vitro autoradiographic localization of the calcitonin receptor isoforms, C1a and C1b, in rat brain

In this study the distribution of the calcitonin receptor isoforms, C1a and C1b, were mapped in rat brain using in vitro autoradiography and manipulation of their different pharmacological specificities. While salmon calcitonin binds to both receptors with high affinity, only the C1a receptor interacts with human calcitonin. Thus, the distribution of C1a specific binding sites was mapped using [125I]human calcitonin. The C1b receptors were mapped using [125I]salmon calcitonin in the presence of unlabelled human calcitonin and rat amylin, displacing binding of [125I]salmon calcitonin to C1a and C3 (amylin) sites, respectively. The distribution of C1a and C1b receptors was found to predominantly overlap. Brain regions displaying C1a, but little or no C1b, binding sites included the nucleus of the solitary tract, area postrema and the intermediate lobe of the pituitary. Although there were no nuclei expressing exclusively C1b receptors, parts of the mesencephalic and pontine reticular formation, and the thalamic paraventricular nucleus were enriched in C1b receptors relative to the density of C1a receptors in other brain regions. These data indicate that the relative expression of the two receptor isoforms, although predominately parallel, is not uniform in the rat brain.

Extensive brain mapping of calcitonin-induced anorexia

The purpose of this study was to compare the localization in the brain of calcitonin-induced anorexia to the distribution of calcitonin binding sites (as described by others). We, thus, performed an extensive mapping of brain structures to determine those involved in calcitonin-induced anorexia. A significant anorexia is found after injection of calcitonin (15 ng in 0.3 microliters) into several brain areas. Forebrain: lateral septum, lateral part of the anterior commissure, and bed nucleus of the stria terminalis; hypothalamus: floor of the anterior part of the hypothalamus, paraventricular nucleus and adjacent perifornical area; thalamus: nucleus reuniens, an area internal to the mamillo-thalamic tract, and medial geniculate body; other areas: amygdala, lateral hippocampus, and central gray. No significant effect is found in the following areas: forebrain: nucleus accumbens, striatum, and medial septum; hypothalamus: lateral, ventro-medial, dorso-medial, and posterior nuclei; thalamus: centro-medial nucleus, lateral part of the zona incerta, and lateral geniculate body; hippocampus: dorsal and ventral parts; midbrain: central tegmentum, ventral tegmental area, and substantia nigra. When these results are compared to the distribution of calcitonin binding sites in the brain, two types of discrepancies are found. The first is the absence of effect in areas containing receptors: these areas may be involved in calcitonin-induced behaviors other than food intake. The second is the occurrence of anorexia in areas where no receptors are found: this finding is not easy to explain and raises some speculative hypotheses. In conclusion, calcitonin is active to decrease food intake in several brain areas, the strongest effect occurring in the paraventricular/perifornical area.(ABSTRACT TRUNCATED AT 250 WORDS)

Medial diencephalic sites involved in calcitonin-induced hyperthermia and analgesia

Calcitonin is a peptide hormone which can act centrally to decrease food intake and locomotor activity, and increase body temperature and nociceptive thresholds. In a previous study we showed that the brain sites involved in the food intake and locomotion decreases were mostly the paraventricular nucleus, the perifornical area and the preoptic area above the optic chiasma. We now study the diencephalic sites involved in calcitonin-induced increases in body temperature and nociceptive thresholds. Salmon calcitonin (15 ng in 0.3 microliters) was injected in several diencephalic sites, and the effects on body temperature and nociceptive thresholds compared with a saline injection. The results show that the sensitive sites are the dorsomedial nucleus of the hypothalamus, the preoptic area and the centromedial nucleus of the thalamus, and not the paraventricular nucleus and adjacent perifornical area. Therefore, different kinds of central effects of calcitonin can be differentiated on an anatomical basis.

Antagonism of calcitonin-induced anorexia by chronic, but not acute, tricyclic antidepressants in the rat

Intraperitoneal or intracerebral injections of calcitonin in the rat produce several behavioral and hormonal effects which have some analogies with the human depressive syndrome. To determine if calcitonin effects are sensitive to antidepressant drugs, the ability of antidepressants and other psychotropic drugs to interact with calcitonin-induced anorexia was tested. The results show that chronic treatments (21 days) with tricyclic, or with tetracyclic, antidepressants significantly tend to neutralize the anorectic effect of calcitonin. Other antidepressants and other psychotropic drugs had no significant effect. The acute administration (24 h) of clomipramine did not antagonize the effect of calcitonin, and even significantly enhanced it. These results allow the author to propose the effects of calcitonin in the rat as a new animal model of depression, and to raise the hypothesis that a possible mechanism of action of tricyclic antidepressant treatments is to counteract the effects of certain brain peptides.

Role of central prostaglandin E2 in the regulation of gastric acid secretion in the rat

The central action of prostaglandin E2 (PGE2) on gastric acid secretion was investigated in rats by comparing the effects of intracisternal (i.ci.) and i.v. administration of PGE2 and the influence of i.ci. injection of indomethacin on acid secretion and PGE2 generation in the brain and stomach. I.ci. injections of PGE2 (1-10 micrograms) or the stable analog, 16,16-dimethyl PGE2, (0.01-0.1 micrograms) induced a dose dependent inhibition of baclofen-stimulated gastric acid secretion by 0-82% and by 7-87% respectively. I.v. infusion of PGE2 also induced a dose related inhibition of baclofen-stimulated acid secretion, but 10 fold higher doses were required. I.ci. or i.v. injection of indomethacin in doses ranging from 50 to 500 micrograms/rat, produced a similar dose dependent inhibition of the PGE2 generation in both the gastric mucosa and brain cortex measured 1 h post injection. I.ci. injection of indomethacin (500 micrograms) increased within 10 min acid secretion with a peak response at 20-30 min; 60-120 min post injection, when prostaglandin synthesis was inhibited by 90%, basal and baclofen-stimulated acid output were not altered. These results further establish that PGE2 acts in the brain to inhibit vagally stimulated gastric acid secretion in rats, and do not support a tonic inhibitory influence of endogenous brain PGE2 in the regulation of gastric acid secretion. In addition, these data showed that indomethacin injected i.ci. at 500 micrograms does not induce a selective inhibition of prostaglandin synthesis in the brain.

Central nervous system action of peptides to influence gastrointestinal motor function

The central action of peptides to influence GI motility in experimental animals is summarized in Table 1. TRH stimulates gastric, intestinal, and colonic contractility in rats and in several experimental species. A number of peptides including calcitonin, CGRP, neurotensin, NPY, and mu opioid peptides act centrally to induce a fasted MMC pattern of intestinal motility in fed animals while GRF and substance P shorten its duration. The dorsal vagal complex is site of action for TRH-, bombesin-, and somatostatin-induced stimulation of gastric contractility, and for CCK-, oxytocin- and substance P-induced decrease in gastric contractions or intraluminal pressure. The mechanisms through which TRH, bombesin, calcitonin, neurotensin, CCK, and oxytocin alter GI motility are vagally mediated. An involvement of central peptidergic neurons in the regulation of gut motility has recently been demonstrated in Aplysia, indicating that such regulatory mechanisms are important in the phylogenesis. Alterations of the pattern of GI motor activity are associated with functional changes in transit. TRH is so far the only centrally acting peptide stimulating simultaneously gastric, intestinal, and colonic transit in various animals species. Opioid peptides acting on mu receptor subtypes in the brain exert the opposite effect and inhibit concomitantly gastric, intestinal, and colonic transit. Bombesin and CRF were found to act centrally to inhibit gastric and intestinal transit and to stimulate colonic transit in the rat. The antitransit effect of calcitonin and CGRP is limited to the stomach and small intestine. The delay in GI transit is associated with reduced GI contractility for most of the peptides except central bombesin that increases GI motility. Nothing is known about brain sites through which these peptides act to alter gastric emptying and colonic transit. Regarding brain sites influencing intestinal transit, TRH-induced stimulation of intestinal transit in the rat is localized in the lateral and medial hypothalamus and medial septum. The periaqueductal gray matter is a responsive site for mu receptor agonist- and neurotensin-induced inhibition of intestinal transit. The neural pathways from the brain to the gut whereby these peptides express their stimulatory or inhibitory effects on GI transit is vagal dependent with the exception of calcitonin. It is not known whether the vagally mediated inhibition of GI transit by these peptides results from a decrease activity of vagal preganglionic fibers synapsing with excitatory myenteric neurons or an activation of vagal preganglionic neurons synapsing with inhibitory myenteric neurons. The lack of specific antagonists for these peptides has hampered the assessment of their physiological role.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcitonin binding site distribution in the cat central nervous system: a wider insight of the peptide involvement in brain functions

Calcitonin (CT) binding site distribution has been studied in the cat CNS. The autoradiographic analyses of [125I]-eelCT (ECT) binding showed high density of silver grains in the mesencephalic PAG, in the raphe nuclei and in the dorsal horns, laminae I, IV, V, and VI, where ECT may act to inhibit nociceptive transmission. Other binding-rich areas included the caudatus, the amygdala, the hypothalamus, the substantia nigra, the locus coeruleus and the formatio reticularis mesencephalica. Medium to low density was seen, amongst other areas in the cortex piriformis, the hippocampus, the medial and intralaminar thalamus and the tractus spino-thalamicus. ECT binding site distribution revealed essentially homologous locations in the cat and rat CNS. At difference, the presence of binding in the piriform cortex and in discrete thalamic nuclei suggests a widespread involvement of ECT in a variety of central functions in addition to what already demonstrated.

Potent CNS action of calcitonin to inhibit cysteamine-induced duodenal ulcers in rat

Intracisternal injection of calcitonin (0.01-5 micrograms) dose dependently prevented the development of duodenal ulcers induced by cysteamine in female rats. By contrast, intravenous infusion of the peptide at a dose 50 times higher than an effective intracisternal dose, had no effect. Intracisternal injection of calcitonin increased by three fold the generation of 6-keto-PGF1 alpha, the stable hydrolysis product of PGI2, in the duodenal mucosa. These studies demonstrated that calcitonin acts within the brain to potently suppress duodenal ulcers induced by cysteamine. The mechanisms of the antiulcer effect may involve changes in prostaglandin generation along with alterations of gastrointestinal secretion and motility associated the central injection of calcitonin. Growing evidence suggests that salmon calcitonin may act as a neuromodulator or neurotransmitter in the central nervous system. Specific binding sites have been demonstrated for calcitonin in the hypothalamus, brain stem and dorsal horn of the spinal cord using homogenate and membrane preparations or in vitro autoradiography methods. The peptide injected into the cerebrospinal fluid (CSF) produces a wide spectrum of biological effects including analgesia, hyperthermia, changes in pituitary hormone release, decrease in food and water intake, locomotor activity, and blood pressure. Numerous studies also demonstrated that calcitonin acts within the brain to markedly influence gastrointestinal secretory and motor function in rats and dogs and gastric ulceration in rats. In particular, intracisternal injection of salmon calcitonin was found very potent to selectively inhibit gastric ulcers elicited by stress, aspirin and central thyrotropin-releasing factor but not by necrotizing agents. In the present study, we further investigated the antiulcer effect of salmon calcitonin using the well established cysteamine experimental model to induce duodenal ulcers in rats. Part of this work has been reported in abstract form.

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC and related agents: II

Antipyretics, in particular acetaminophen, aspirin and ibuprofen, constitute the single most important class of drugs used therapeutically for an effect on body temperature. Hallucinogens exert prominent actions on the central nervous system, and it is not surprising that, like so many other centrally-acting agents, they too often affect temperature. This compilation primarily covers the considerable amount of data published from 1981 through 1985 on the interactions of these drugs and thermoregulation, but data from many earlier papers not included in a previous compilation are also tabulated. The effects of agents not classically considered as antipyretics on temperatures of febrile subjects are also covered. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent.

Effects of calcitonin and CGRP alone or in combination on food intake and forestomach (reticulum) motility in sheep

The effects of intracerebroventricular (ICV) and intravenous (IV) administration of calcitonin and calcitonin gene-related peptide (CGRP) on feeding behavior and reticular motility were investigated in sheep. ICV calcitonin at a dose of 2 to 200 mU/kg reduced, in a dose-related manner, the immediate (0-60 min) food intake. The daily food intake was also significantly (p less than 0.05) decreased for doses up to 20 mU/kg, and the frequency of reticular contractions during the first hour of eating was decreased by 27.9%. Calcitonin at the highest IV dose (200 mU/kg) did not affect feeding behavior or reticular motility. In contrast, CGRP given ICV did not affect the first 3 hour period of food intake, while a significant increase (27.8%) in daily food intake was observed at a dose of 20 ng/kg despite immediate inhibitory effects on reticular frequency. No effect on feeding behavior and forestomach motility was noticed for a 25 times higher dose IV administered. Furthermore, CGRP given ICV (100 ng/kg) did not antagonize the immediate anorectic effects of calcitonin (200 mU/kg), although it delayed commencement of rumination and partially restored the daily food intake. These results suggest that calcitonin and CGRP play opposite roles in the central control of food intake in sheep, probably by acting on different brain structures, yet have a similar effect on reticular motility.