Presence of immunoreactive calcitonin in the hypothalamus and pituitary lobes of rats

Effects of intracerebroventricular administration of calcitonin gene-related peptide (CGRP) on sex hormones and sperm quality in rats

Background

Therapeutic strategies with calcitonin gene-related peptide (CGRP) or its receptor have been investigated, but there are few studies regarding the possible harmful effects of CGRP in other body organs.

Objective

This study aimed to investigate the effect of intracerebroventricular (ICV) injection of CGRP on sex hormones and sperm quality in rats.

Methods

Twelve male rats were divided into two groups (n=6 per group). The first group (control) rats were injected with 5 µl artificial cerebrospinal fluid intra-ICV; the second group rats, 5 µl (1.5 nmol) CGRP. The levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone were measured. Epididymal sperms were used to determine the sperm parameters.

Results

The levels of testosterone, LH and FSH in CGRP group was significantly lower than in artificial cerebrospinal fluid (ACSF) group (P<0.05). The concentration and motility of sperm in CGRP group was significantly lower than in ACSF group (P<0.05). In CGRP group live spermatozoa and intact acrosome significantly reduced compared to the ACSF group (P<0.05). In addition, in CGRP group dead spermatozoa and lose acrosome significantly increased compared to the ACSF group (P<0.05).

Conclusion

ICV injection of CGRP may reduce sperm quality, probably through induction of an imbalance in FSH and LH production as well as testosterone.

Physiological consequences of space flight, including abnormal bone metabolism, space radiation injury, and circadian clock dysregulation: Implications of melatonin use and regulation as a countermeasure

Exposure to the space environment induces a number of pathophysiological outcomes in astronauts, including bone demineralization, sleep disorders, circadian clock dysregulation, cardiovascular and metabolic dysfunction, and reduced immune system function. A recent report describing experiments aboard the Space Shuttle mission, STS-132, showed that the level of melatonin, a hormone that provides the biochemical signal of darkness, was decreased during microgravity in an in vitro culture model. Additionally, abnormal lighting conditions in outer space, such as low light intensity in orbital spacecraft and the altered 24-h light-dark cycles, may result in the dysregulation of melatonin rhythms and the misalignment of the circadian clock from sleep and work schedules in astronauts. Studies on Earth have demonstrated that melatonin regulates various physiological functions including bone metabolism. These data suggest that the abnormal regulation of melatonin in outer space may contribute to pathophysiological conditions of astronauts. In addition, experiments with high-linear energy transfer radiation, a ground-based model of space radiation, showed that melatonin may serve as a protectant against space radiation. Gene expression profiling using an in vitro culture model exposed to space flight during the STS-132 mission, showed that space radiation alters the expression of DNA repair and oxidative stress response genes, indicating that melatonin counteracts the expression of these genes responsive to space radiation to promote cell survival. These findings implicate the use of exogenous melatonin and the regulation of endogenous melatonin as countermeasures for the physiological consequences of space flight.

Suppressive effect of melatonin on osteoclast function via osteocyte calcitonin

Many studies have investigated the actions of melatonin on osteoblasts and osteoclasts. However, the underlying mechanisms, especially regarding osteocyte function, remain largely unknown. Therefore, this study aimed to clarify the underlying mechanisms of melatonin action on bone tissue via osteocyte function. Chick calvariae were employed as a model. In ovo injection of melatonin (5, 50 and 500 µg) dose-dependently decreased the mRNA expression levels of cathepsin K and matrix metalloproteinase 9 (MMP9) in chick calvariae without affecting the expression levels of receptor activator of NF-κB ligand or osteoprotegerin. Surprisingly enough, the expression of calcitonin mRNA in chick calvariae was significantly raised. After 3 days of in vitro treatment of melatonin (10-7 and 10-5 M) on newly hatched chick calvariae, both calcitonin mRNA expression in calvariae and the concentration of calcitonin in cultured medium were augmented in a dose-dependent manner, coincident with the decreased mRNA expression levels of cathepsin K and MMP9. Immunohistochemical analyses revealed expression of melatonin receptors and calcitonin by osteocytes buried in bone matrix. Moreover, the mRNA expression levels of melatonin receptors, calcitonin and sclerostin (a marker of osteocyte), were strongly and positively correlated. In conclusion, we demonstrated the expression of melatonin receptors and calcitonin expression in osteocytes for the first time and suggest a new mechanism underlying the suppressive effect of melatonin on osteoclasts via upregulation of calcitonin secretion by osteocytes.

Calcitonin is expressed in the chicken pituitary gland: influence of gonadal steroids and sexual maturation

Calcitonin (CT) is primarily produced by the thyroid C cells in mammals or by the ultimobranchial gland in chickens. CT is also expressed by the pituitary gland in rats in which it functions as a paracrine factor causing decreased lactotroph proliferation and prolactin (PRL) secretion. Gonadal steroids influence CT expression in the rat pituitary gland. However, the expression of the CT gene in the pituitary gland of chickens or of any other avian species has not previously been reported. We have tested the hypotheses that CT is expressed in the chicken pituitary gland, and that its expression is influenced by sexual maturation or in response to ovarian steroid administration. We have detected robust expression of CT cDNA in the chicken pituitary gland by reverse transcription/polymerase chain reaction (PCR). The sequence of the pituitary-derived CT cDNA is identical to that of the ultimobranchial gland. CT-immunoreactive (ir) cells have been observed throughout the anterior pituitary gland by confocal microscopy. Many of the PRL-ir cells show co-localization with CT-ir cells. Quantitative real-time PCR analysis has revealed an inverse relationship between the quantities of PRL mRNA and CT mRNA in the pituitary gland: sexually mature hens contain lower amounts of CT mRNA but larger quantities of PRL mRNA compared with sexually immature chickens. Estradiol and/or progesterone treatment of sexually immature chickens leads to a significant decrease in the quantity of pituitary CT mRNA relative to that in the vehicle-treated chickens. We conclude that pituitary CT plays an important paracrine/autocrine role in the control of lactotroph function and PRL secretion in the chicken.

Calcitonin expression in rat anterior pituitary gland is regulated by ovarian steroid hormones

Gonadotroph-derived calcitonin-like peptide (pit-CT) is a potent inhibitor of lactotroph function. We investigated the effect of ovarian hormones on pit-CT mRNA expression in the anterior pituitary (AP) gland of cycling female rats. Levels of mRNAs for pit-CT, CT receptor, prolactin (PRL), and beta-LH during 4-d estrous cycle were determined. In a second study, the effects of estrogens and progesterone on pit-CT and PRL mRNA levels were investigated. In a third group, the effect of estrogen or progesterone depletion on pit-CT mRNA expression was studied. In a fourth group, the effect of passive pit-CT immunization on PRL and LH mRNA expression was examined. Pit-CT mRNA levels varied during estrous cycle. They were highest in diestrus, but lowest in the evening of proestrus. CT-receptor mRNA levels displayed smaller fluctuations. Estrogen repletion caused a decline in pit-CT mRNA expression in ovariectomized rats, but progesterone produced a marked increase. ICI 182,780 prevented the decline of pit-CT mRNA levels during late proestrus-estrus, but RU 486 attenuated pit-CT mRNA levels. Passive CT immunization in diestrus altered PRL and LH mRNA expression, and advanced the estrus cycle. These results suggest that pit-CT mRNA expression is regulated by ovarian hormones, and depletion of pit-CT advances their estrous cycle.

Possible mechanisms of the analgesic action of calcitonin

The analgesic activity of calcitonin is well established, both through clinical observation and specific experimental investigation. The mechanism involved, however, is still unclear, and the hypotheses that have been proposed range from a simple peripheral antiinflammatory action to a direct action on specific receptors in the central nervous system. The various hypotheses are briefly reviewed and some of the supporting evidence is presented. The conclusion is that the principal mechanism of calcitonin's analgesic effect is probably a direct central action, but that this is further supported by peripheral mechanisms that may also improve bone status locally.

A pilot study of rat brain regional distribution of calcitonin, katacalcin and calcitonin gene-related peptide before and after antipsychotic treatment

In contrast to extensive determinations of calcitonin gene-related peptide (CGRP) in neural tissues, calcitonin and its carboxyl-terminal flanking peptide katacalcin (in human PDN-21) have not been systematically measured by radioimmunoassay (RIA) in discrete brain structures. Using microwave irradiation (MW), a procedure that increases the recovery of neuropeptides, we investigated by radioimmunoassay (RIA) the rat brain regional distribution of CGRP like- immunoreactivity (-LI), calcitonin-LI, and katacalcin-LI. Calcitonin-LI and katacalcin-LI were found in low concentrations in frontal cortex, occipital cortex, striatum and hippocampus. Moreover, a 4-week treatment with antipsychotic drugs altered the concentrations of the calcitonin-gene family peptides in the frontal cortex, occipital cortex, and hippocampus; the magnitude of these changes, however, was only moderate. Lastly, calcitonin-LI and katacalcin-LI baseline concentrations as well as after antipsychotic treatment were highly correlated in the frontal cortex, striatum, and hippocampus. The possible regulatory role of calcitonin gene family peptides in the central nervous system (CNS) needs to be further explored.

Inhibition of salmon calcitonin on secretion of progesterone and GnRH-stimulated pituitary luteinizing hormone

The effects of salmon calcitonin (sCT) on the production of progesterone and secretion of luteinizing hormone (LH) were examined in female rats. Diestrous rats were intravenously injected with saline, sCT, human chorionic gonadotropin (hCG), or hCG plus sCT. Ovariectomized (Ovx) rats were injected with saline or sCT. In the in vitro experiments, granulosa cells and anterior pituitary glands (APs) were incubated with the tested drugs. Plasma LH levels of Ovx rats were reduced by sCT injection. Administration of sCT decreased the basal and hCG-stimulated progesterone release in vivo and in vitro. 8-Bromo-cAMP dose dependently increased progesterone production but did not alter the inhibitory effect of sCT. H-89 did not potentiate the inhibitory effect of sCT. Higher doses of 25-hydroxycholesterol and pregnenolone stimulated progesterone production and diminished the inhibitory effects of sCT. sCT did not decrease basal release of LH by APs, but pretreatment of sCT decreased gonadotropin-releasing hormone (GnRH)-stimulated LH secretion. These results suggested that sCT inhibits progesterone production in rats by preventing the stimulatory effect of GnRH on LH release in rat APs and acting directly on ovarian granulosa cells to decrease the activities of post-cAMP pathway and steroidogenic enzymes.

Effect of calcitonin on the activity of ANG II-responsive neurons in the rat subfornical organ

In addition to the well-documented ability of calcitonin to lower blood calcium levels, blood-borne calcitonin may also affect neurons located outside the blood-brain barrier, e.g., in the subfornical organ (SFO), where numerous receptors for this peptide have been described. In an in vitro preparation of the rat SFO, calcitonin activated 61% of 36 neurons, only 1 neuron was inhibited, and the remainder were unresponsive. All but two of the neurons excited by 10(-7) M calcitonin were also stimulated by 10(-7) M ANG II. The threshold concentration for the excitatory effects of calcitonin was 10(-9) M and was thus similar to ANG II. Like ANG II, subcutaneous injection of calcitonin stimulated water intake, although to a lower extent. These results suggest that blood-borne calcitonin could stimulate drinking by its excitatory effect on neurons in the SFO. Calcitonin, which is released during food intake, might be involved in prandial drinking, which is presently considered an acquired behavior.

Purification of calcitonin-like peptides from rat brain and pituitary

Accumulating evidence supports the existence of nonthyroidal calcitonin (CT)-like peptides, more similar to fish CTs, which may act as endogenous regulators of CT receptors in brain and other tissues. In this study, we have carried out large-scale extractions from Sprague-Dawley rat brain diencephalon and pituitary, and purified a novel, biologically active, CT-like peptide from pituitary. Monitoring of the calcitonin-like activity of the peptides from rat brain and pituitary required different detection systems. While the brain CT cross-reacted with C-terminally directed salmon CT-specific antisera, the pituitary CT did not. However, the pituitary CT was biologically active, exhibiting specific interaction with CT receptors to activate adenylate cyclase. Conventional chromatographic techniques were employed to purify the CT-like peptides. Although the brain CT was not purified to homogeneity, size exclusion chromatography revealed the presence of multiple molecular weight forms of immunoreactive CT. Of these, only the lowest molecular weight form was biologically active. Purification from the pituitary resulted in the isolation of a biologically active peptide with a mass of 3267 Da. This mass differs from the mass of both salmon and thyroid-derived rat CT. Initial amino acid sequencing of the pituitary CT indicated that it was N-terminally blocked. Following aminopeptidase digestion, a unique six amino acid sequence, EKSQSP, was identified. Elucidation of the amino acid composition provided supporting evidence that the peptide was novel and was consistent with a full length peptide of approximately 30 amino acids. These data support the existence of novel, nonthyroidal, CTs which are potential regulators of CT receptor-mediated functions.

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)

Calcitonin inhibits testosterone and luteinizing hormone secretion through a mechanism involving an increase in cAMP production in rats

Effects of calcitonin peptides, including human calcitonin (hCT), salmon calcitonin (sCT), and calcitonin gene-related peptide (CGRP), on the secretion of testosterone and luteinizing hormone (LH) in male rats were studied. Male rats were injected intravenously with human chorionic gonadotropin (hCG), calcitonin peptides, or hCG plus calcitonin peptides. Blood samples were collected at several intervals following hormone challenge. In an in vitro experiment, testis blocks were incubated with hCG (0, 0.05, 0.5, or 5 IU/ml) or hCG (0.5 IU/ml) plus calcitonin peptides (0-10(-9) or 10(-6) M) at 34 degrees C for 30 minutes. Both medium and plasma samples were extracted by ether and analyzed for testosterone by radioimmunoassay (RIA). The concentration of calcium in each plasma sample was measured by an automatic calcium analyzer. The anterior pituitary gland (AP) was incubated with or without calcitonin peptides (0-10 nM) at 37 degrees C for 30 minutes. They were then incubated with gonadotropin releasing hormone (GnRH, 10 nM) for a further 30 minutes. The concentration of LH in AP medium was measured by RIA. The accumulation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in both testicular tissues and APs were measured by RIA. A single intravenous injection of calcitonin peptides decreased the basal and hCG-stimulated levels of plasma testosterone gradually from 60 to 180 or 360 minutes after challenge. The plasma calcium was not altered by the injection of calcitonin peptides and/or hCG. Administration of calcitonin peptides in vitro resulted in a dose-dependent inhibition of both basal and hCG-stimulated release of testosterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcitonin induces a decreased Na+ conductance in identified neurons of Aplysia

The ionic mechanism of the effect of extracellularly ejected calcitonin (CT) on the membrane of identified neurons R9 and R10 of Aplysia was investigated with voltage-clamp, micropressure ejection, and ion substitution techniques. Micropressure-ejected CT caused a marked hyperpolarization in the unclamped neuron. Heat-inactivated CT was without effect. Clamping the same neuron at its resting potential level (-60 mV) and re-ejecting CT with the same dose produced a slow outward current (Io(CT), 30-40 sec in duration, 4-6 nA in amplitude) associated with a decrease in input membrane conductance. Io(CT) was decreased by depolarization and increased by hyperpolarization. The extrapolated reversal potential of Io(CT) was approximately +10 mV. Io(CT) was sensitive to changes in the external Na+ concentration but not to changes in K+, Ca2+, and Cl- concentrations. Micropressure-ejected forskolin produced a slow outward current, which, like the current to CT, was associated with a decrease in input membrane conductance, and was sensitive to changes in the external Na+ concentration. Io(CT) was prolonged by bath-applied isobutylmethylxanthine (IBMX) but was not affected by 1-oleoyl-2-acetylglycerol (OAG) and calphostin C. Neither superfusion of the neuron with nordihydroguaiaretic acid (NDGA) nor superfusion with indomethacin caused any changes in Io(CT). These results suggest that extracellular CT can induce a slow outward current associated with a decrease in Na+ conductance, mediated by a receptor-controlled increase in intracellular cyclic adenosine 3',5'-monophosphate.

Biologically active salmon calcitonin-like peptide is present in rat brain

Although high densities of calcitonin (CT) receptors and potent CT-induced actions occur within the rat central nervous system, the physiological ligand for central receptors remains unidentified. This study identifies a salmon CT (sCT)-like peptide in extracts of rat brain. Aliquots of 1 M HCl brain extracts were reconstituted in 0.01 M acetic acid and assayed for sCT-like immunoreactivity using a radioimmunoassay (RIA) based on a guinea pig anti-sCT antibody (detection limit 0.1 ng). The assay was less than 0.1% cross-reactive with human CT, porcine CT, rat calcitonin gene-related peptide (CGRP)-I and human CGRP-I. Extracts of diencephalon revealed sCT-like activity (30-120 ng/g wet weight), while extracts from cortex, cerebellum and medulla oblongata did not contain detectable activity. Reverse-phase HPLC analysis demonstrated co-elution with synthetic sCT. Further, the peak material was active in 4 CT bioassay systems; (1) stimulation of cAMP production in UMR 106-06 cells and (2) T47D cells, (3) inhibition of 125I-sCT binding in UMR 106-06 cells and (4) inhibition of 125I-sCT binding in sheep brain membranes. The bioactivity of material in these assays was similar to that estimated through the RIA. The results identify, for the first time, the presence of sCT-like material in the rat brain and constitutes the first demonstration of biologically active sCT-like material from brain extracts. Salmon CT-like peptide may represent the endogenous ligand for central CT receptors.

Effect of calcitonin on the alcohol drinking of rats

Previous work has shown that calcitonin inhibits eating by rats and that it affects several neurotransmitter systems suspected to play a role in alcohol consumption. The present study was an initial test of whether calcitonin does affect voluntary alcohol consumption by male Wistar rats with prolonged alcohol experience. Calcitonin (20 IU/kg) or saline was injected subcutaneously on 10 consecutive days when the rats (n = 20) had continual access to 10% (v/v) ethanol solution, and to food and water. Using a cross-over design, the effects of 40 IU/kg calcitonin vs. saline were then examined in a second 10-day treatment period. Similar patterns of effects were obtained with both calcitonin doses, but the patterns differed with alcohol, food, and water intake. Alcohol drinking showed biphasic changes with both doses, producing highly significant Treatment x Day interactions (p < 1E-10 and p = 6E-7): it was significantly reduced on the first day of calcitonin treatment and significantly increased on the last few days. Food intake was reduced on all calcitonin days although most markedly on the first. Water drinking was not altered on the first calcitonin day, but was greatly increased on the second, then gradually returned toward the baseline. In a second experiment, the animals were switched to 1 hr of alcohol access per day, and calcitonin (20 IU/kg) was administered periodically to one group 4 hr before the alcohol access. Alcohol drinking was significantly reduced in all cases when the calcitonin injection was preceded by at least 1 day without calcitonin.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcitonin-immunoreactive cells are present in the brains of some cyclostomes

In the brains of four species of cyclostomes (two species each of lampreys and hagfishes), immunoreactive calcitonin-producing cells (iCT cells) were located immunohistochemically by the peroxidase-antiperoxidase method using anti-salmon calcitonin antiserum. In the case of both the adults and the ammocoetes of the brook lamprey (Lampetra reissneri) which lives in freshwater throughout its life, iCT cells were found in two distinct areas: in the pars ventralis hypothalami of the diencephalon and in the torus semicircularis of the mesencephalon. The iCT cells in the diencephalon are classified as bipolar nerve cells, and those in the mesencephalon are classified as multipolar nerve cells. In both the anadromous and catadromous arctic lamprey (Lampetra japonica), iCT cells were present only in the diencephalon, and those were bipolar nerve cells. There seemed to be no differences in the numbers and the immunostainability of the iCT cells, despite the different environments inhabited by the lampreys. In the hagfishes (Eptatretus burgeir and Paramyxine atami) that inhabit seawater throughout their lives, iCT cells were also found only in the diencephalon, although they were very few in number and exhibited poor immunostainability.

Cells showing immunoreactivity for calcitonin or calcitonin gene-related peptide (CGRP) in the central nervous system of some invertebrates

In the central nervous system of some species of several invertebrate phyla, including land planarians (Platyhelminthes), ribbon worms (Nemertina), slugs (Mollusca), polychaetes, earthworms and leeches (Annelida), pill bugs (Arthropoda), and beard worms (Pogonophora), salmon calcitonin-immunoreactive cells and rat calcitonin gene-related peptide (CGRP)-immunoreactive cells were found by immunohistochemistry. These immunoreactive cells were located in the region surrounding the neuropile, although the sizes of the cells varied according to species. Some of them were round or polygonal and regarded as apolar nerve cells because of their lack of cytoplasmic processes, whereas others were spindle-shaped or elongated, being comparable with unipolar nerve cells because of extension of their cytoplasmic processes in the direction of the neuropile. In some cases, it was noted that the cytoplasmic processes had complicated branches or formed loop-like structures at their ends. These observations suggest that a calcitonin-like or CGRP-like substance is extensively present in invertebrates as well as vertebrates.

Central nervous system binding sites for calcitonin and calcitonin gene-related peptide

Alternative splicing of the primary RNA transcript of the calcitonin gene leads to the generation of two distinct peptides, calcitonin (CT) and calcitonin gene-related peptide (CGRP). These peptides share only limited sequence homology and generally subserve different biological functions through their own distinct binding sites, which differ in specificity and distribution. Additionally, a binding site with high-affinity binding for both peptides that has a restricted pattern of distribution has been identified. The present article reviews the biochemical and morphological characteristics of centra CT and CGRP binding sites.

The effects on anterior pituitary hormone secretion of salmon calcitonin in healthy volunteers

The reports of the effect of calcitonin on pituitary function are confusing and often refer to uncontrolled studies. We have now carried out a double-blind placebo-controlled trial of intravenous and subcutaneous salmon calcitonin on anterior pituitary function in 17 healthy volunteers. Visual analogue scores for the nausea and vomiting seen after salmon calcitonin correlated with the rise in ACTH and, secondarily, cortisol. Calcitonin had no effect on growth hormone, prolactin, thyrotrophin, luteinizing hormone or follicle stimulating hormone. It is concluded that the stimulation of ACTH secretion following a single dose of salmon calcitonin is probably the result of the stress of nausea rather than a direct effect on the pituitary.

Subarachnoid and epidural calcitonin in patients with pain due to metastatic cancer

Nine patients with metastatic cancer who had pain refractory to traditional treatments received a subarachnoid injection of salmon calcitonin. Eight of the nine patients reported pain relief after subarachnoid injection varying from 1 hr to 5 days. Four of the responding patients subsequently received an epidural injection of salmon calcitonin, and two of these patients reported pain relief. Although many patients experienced pain relief, nausea and vomiting appeared to be a significant side effect, occurring in seven out of nine patients.

Ionostatic control of food intake in the domestic fowl

It has been suggested that there is ionostatic control of food intake in which calcium, acting in the hypothalamus, alters food intake. This study was conducted to determine the effects of intracerebroventricular (ICV) injections of calcium on food and water intake in both broiler and Leghorn cockerels. The ICV injection of 50, 100, or 150 mM CaCl2 had no significant affect on food or water intake in Leghorn cockerels. In broilers, the ICV injection of 50 mM CaCl2 significantly increased food intake. This effect appeared to be due to Ca++ as equivalent amounts of Cl- given as NaCl had no effect on food intake nor did isosmotic solutions of NaCl. The effect of Ca++ on water intake in broilers is equivocal as it increased water intake in one experiment while decreasing it in another. Whereas these results support the hypothesis of a role for calcium in food intake regulation in broilers, they do not support the existence of a specific ionostatic control mechanism.

Anatomical mapping of the rat hypothalamus for calcitonin-induced anorexia

The primary physiological function of calcitonin, a peptide hormone secreted by the thyroid gland, is to modulate plasma calcium concentrations. Calcitonin also has several effects on the central nervous system including an inhibition of feeding behavior. In the present study synthetic salmon calcitonin (15 ng in 0.3 microliter) was found to produce a marked suppression of eating when infused in several hypothalamic areas. The greatest inhibition was produced by infusions into the paraventricular nucleus of the hypothalamus, the perifornical area and several areas on the floor of the hypothalamus. A less marked inhibition of eating was produced by infusions in the nucleus accumbens. Infusions in the olfactory tubercule, the ventrolateral hypothalamus, the medial forebrain bundle and the posterior nucleus of the hypothalamus had no effect. It is concluded that the anorectic effects of calcitonin on the central nervous system are mediated by several hypothalamic and extrahypothalamic sites.

Calcitonin as a feeding suppressant: localization of central action to the cerebral III ventricle

Calcitonin suppresses food and water intake. To further study this effect of calcitonin, rats were subjected to various intra-cerebroventricular (ICV) applications of calcitonin. The results show: (1) Intra-third ventricular (III-ICV) infusion of calcitonin dose-dependently decreased food intake with short- and long-term effects; (2) Potency was decreased by using non-siliconized materials; (3) Potency decreased with age of rats; (4) Infusion into the aqueduct and cisterna magna decreased short- and long-term food intake less than III-ICV administration; (5) Aqueduct obstruction did not affect feeding suppression by III-ICV calcitonin. Aqueduct obstruction did not affect dipsogenic response to III-ICV infusion of angiotensin II; (6) Results of water intake and food to water intake ratios suggest a greater calcitonin effect on food intake than on water intake. The evidence suggests that the hypothalamus is a main locus for suppression of food intake by ICV administered calcitonin.

Calcitonin-induced anorexia in rats: evidence for its inhibitory action on lateral hypothalamic chemosensitive neurons

Effects of a synthetic derivative of eel calcitonin, [Asu1,7]ECT on feeding behavior, and its direct action on the neuronal activity of lateral hypothalamic area (LHA) were studied in rats. Food intake was significantly reduced in a dose-dependent manner after intra-third ventricular injection of [Asu1,7]ECT (0.2-1.0 U/rat). The neuronal activity of LHA neurons, especially the glucose-sensitive neurons, was inhibited by electrophoretic application of [Asu1,7]ECT. The inhibition was accompanied by a hyperpolarization of the membrane by about 5-7 mV with an increase in the membrane resistance (5.0-8.7%). This effect was also shown to be independent of noradrenergic or serotonergic mechanisms. Phosphodiesterase inhibitors, such as 3-isobutyl-1-methylxanthine and papaverine augmented the inhibitory response, whereas nicotinic acid blocked it. These results suggest that the anorexia caused by [Asu1,7]ECT is mediated through a direct inhibition of chemosensitive neuronal activity in the LHA, caused by an increase in the intracellular level of cyclic 3',5'-adenosine monophosphate.

Immunoreactive calcitonin in brain regions and pituitary of sheep

In this study we have investigated the presence of immunoreactive calcitonin in the central nervous system and pituitary of sheep. The calcitonin concentrations were determined radioimmunologically by two different antibodies. We have demonstrated calcitonin in extracts of areas of the central nervous system, whole pituitary, thyroid gland and plasma of 21 sheep. The concentrations were (ng/g wet weight, mean values +/- SE): thyroid 16.0 +/- 4.4, pituitary 2.03 +/- 0.34, reticular formation 1.64 +/- 0.25, substantia nigra 1.53 +/- 0.46, dentate nucleus 1.11 +/- 0.27, putamen 1.05 +/- 0.35, hippocampus 0.97 +/- 0.17, fornix 0.96 +/- 0.15, anterior thalamus 0.92 +/- 0.28, mammillary body 0.88 +/- 0.12, cerebellum 0.86 +/- 0.09, caudate nucleus 0.84 +/- 0.11, posterior hypothalamus 0.83 +/- 0.19, epiphysis 0.75 +/- 0.25, thalamus centralis 0.71 +/- 0.10, almond nucleus 0.69 +/- 0.16, medulla oblongata 0.67 +/- 0.15, anterior hypothalamus 0.66 +/- 0.20, precentral gyrus 0.66 +/- 0.16, globus pallidus 0.63 +/- 0.31, postcentral gyrus 0.36 +/- 0.08 and plasma (ng/ml) 0.058 +/- 0.013. Our results demonstrate that immunoreactive calcitonin is present in the central nervous system (CNS) of sheep, compatible with a neurotransmitter function for this hormone.

Calcitonin and calcitonin gene-related peptide alter the excitability of neurons in rat forebrain

Individual neurons in the hypothalamus, thalamus, cortex, and other forebrain areas of urethane-anesthetized, male rats were iontophoretically tested for their membrane sensitivity to salmon calcitonin (CT), human CT, and CT gene-related peptide (CGRP). Extracellular recording of unit activity revealed that depression of neuronal firing was the predominant effect of iontophoretically applied salmon CT (35 of 74 cells tested). Few neurons responded to salmon CT with an increase in firing rate (N = 3). When CGRP was iontophoretically applied a pattern of response resembling that of salmon CT was observed. CGRP was predominantly inhibitory and excited those neurons whose firing rate was increased by salmon CT. Inhibition was also the predominant effect of human CT. However, no neurons were excited by human CT. The results clearly demonstrate that a subpopulation of neurons with membrane sensitivity to salmon CT, human CT, and CGRP are present in the rat forebrain. This finding suggests that modulation of neuronal activity may underlie the behavioral and biochemical effects of these peptides when administered centrally. Endogenous CGRP and CT-like peptides in rat brain may be capable of regulating these events as neurotransmitters or neuromodulators.

Novel peptides from the calcitonin gene: expression, receptors and biological function

Calcitonin gene products include calcitonin and its carboxyl-terminal flanking peptide (in man PDN-21), and calcitonin gene-related peptide (CGRP). Alternative splicing of the initial gene transcripts results in the production of two distinct messenger RNA encoding precursors of CGRP and of calcitonin. CGRP messenger RNA is the predominant transcription product of the calcitonin gene in neural tissues, but it is also present in the pituitary and the C-cells of normal thyroid glands and in medullary thyroid carcinoma. Immunoreactive CGRP has, moreover, been recognized around blood vessels of the heart. Calcitonin and PDN-21 are cosecreted from thyroid C-cells, but they are also found in the brain and pituitary. CGRP receptors are present in the brain and the heart, and calcitonin receptors in bone and kidney cells and in the hypothalamus. Calcitonin administered peripherally and in vitro inhibits bone resorption and stimulates renal 1.25-dihydroxycholecalciferol production. CGRP used in the same manner has potent cardiovascular effects (vasodilation, hypotension, positive chronotropic and inotropic action in the heart). Intracerebroventricular administration of CGRP raises the blood pressure, and both CGRP and calcitonin inhibit gastric acid secretion and food intake. The distinct but overlapping effects of calcitonin and CGRP raise important regulatory and functional issues.

Localization of salmon calcitonin binding sites in rat brain by autoradiography

The regional distribution of [125I]salmon calcitonin (sCT) binding sites was examined in rat brain by receptor autoradiography. Dense specific labeling was recognized over the hypothalamus, preoptic and accumbent nuclei, amygdala, zona incerta, interpeduncular nucleus, periventricular gray and the reticular formation. Intermediate binding was seen over the arcuate and supramamillary nuclei and substantia nigra, and no binding in the neocortex, cerebellum, thalamus, basal ganglia and mamillary bodies. The well defined topographical distribution strongly indicates physiological roles for sCT in the mammalian brain.

Pituitary immunoreactive calcitonin-like material: lack of evidence for cross-reactivity with pro-opiomelanocortin

In mammals, calcitonin (CT) is synthesized, stored, and secreted by intrathyroidal C cells. Several reports have suggested the presence of immunoreactive CT in the pituitary gland. We have studied the rat pituitary gland using a radioimmunoassay for CT and have also found immunoreactive CT-like material. Assay of extracts of whole rat pituitary glands was performed using a radioimmunoassay for human CT, which gave identical dilution curves with synthetic human CT (hCT), synthetic rat CT (rCT), and mouse and rat thyroid extracts, but not with a variety of other pituitary and hypothalamic peptides. Immunoreactive CT (iCT) content of extracts of whole pituitary glands ranged from 6 to 72 pg/mg wet weight of tissue (60-840 pg/whole pituitary gland), whereas iCT was not measureable (less than 5 pg/mg tissue) in similar extracts of hypothalamus and cerebral cortex. Gel filtration studies of pituitary extracts showed a peak of iCT, which eluted with 125I-rCT and diluted in parallel with rCT. To investigate whether the pituitary iCT was related to pro-opiomelanocortin, extracts of ACTH-producing AtT20/D16 cells from mice, which contain the ACTH precursor in large quantities, were examined and no iCT was found. Immunohistochemical studies of rat pituitary glands with peroxidase-antiperoxidase and immunofluorescent techniques showed positive staining for CT in cells in the pars anterior, but not in the pars intermedia of pars nervosa; this staining was not eliminated when the antiserum was absorbed with CT under conditions that completely obliterated staining of rat thyroid glands. Double staining demonstrated essentially two distinct populations of cells, one positive for CT and another positive for ACTH, with less than 1% of the cells positive for both ACTH and CT. Immunoreactive CT-like material was present in the pituitary glands of rats thyroparathyroidectomized 18 days before they were killed, but was diminished. Biosynthetic labeling in vitro of rat pituitary glands with 3H-leucine showed incorporation into prolactin; there was no incorporation into CT. No in vitro secretion of iCT by whole rat pituitary glands either basally or after high K+ stimulation was observed. We conclude that: (1) a substance that has certain immunologic and size characteristics of CT is present in minute amounts in the pituitary gland of rats; (2) this material is not a part of the ACTH precursor; and (3) positive immunohistochemical staining in pituitary glands may not be specific for authentic CT.

Salmon calcitonin in lizard brain: a possible neuroendocrine transmitter

Calcitonin is a polypeptide which until recently was thought to be concerned primarily with the control of body calcium. Recent studies carried out with radioimmunoassay have demonstrated the presence of this peptide in brain and we have carried out an immunohistochemical study showing the presence of high concentrations of calcitonin in the nerve varicosities and terminals of the hypothalamus and in particular the median eminence of the lizard Lacertus muralis. The distribution of this calcitonin, which cross-reacted with anti-salmon calcitonin, suggests that this polypeptide and/or its flanking peptides may function as a neuroendocrine neurotransmitter.

Ability of calcitonins to alter food and water consumption in the rat

Synthetic salmon calcitonin (sCT) given SC (30 MRC U/kg) or ICV (1.4 U, 300 ng) inhibited 24-hr food consumption in the rat by 50-100%. Furthermore, ICV doses of sCT ranging from 75 ng (0.35 U) to 300 ng (1.4 U) lowered both food and water intake in a dose-dependent manner. Use of various forms of CT give an apparent order of potency of salmon greater than porcine greater than or equal to human with sCT being at least 40 fold more potent than the mammalian forms. Measurement of food and water intake over a brief (30-90 min) period showed that ICV sCT was effective in reducing food and water consumption regardless of whether it had been given 1, 12, or 23 hr previously. Daily administration of sCT for 5 days caused marked suppression of food and water intake for 2 days; thereafter, consumption returned toward normal, becoming equivalent to vehicle injected controls by day 3 or 4 despite continued daily injections of sCT. The results show that CT can act centrally to modify certain types of behavior and are of special interest since CT-like peptides have been described in the pituitary and hypothalamus and since CT receptors have been reported in hypothalamic and other brain regions.