Systemic cholecystokinin amplifies vago-vagal reflex responses recorded in vagal motor neurones.

Cholecystokinin (CCK) is a potent regulator of visceral functions as a consequence of its actions on vago-vagal reflex circuit elements. This paper addresses three current controversies regarding the role of CCK to control gastric function via vago-vagal reflexes. Specifically: (a) whether CNS vs. peripheral (vagal afferent) receptors are dominant, (b) whether the long (58) vs. short (8) isoform is more potent and (c) whether nutritional status impacts the gain or even the direction of vago-vagal reflexes. Our in vivo recordings of physiologically identified gastric vagal motor neurones (gastric-DMN) involved in the gastric accommodation reflex (GAR) show unequivocally that: (a) receptors in the coeliac-portal circulation are more sensitive in amplifying gastric vagal reflexes; (b) in the periphery, CCK8 is more potent than CCK58; and (c) the nutritional status has a marginal effect on gastric reflex control. While the GAR reflex is more sensitive in the fasted rat, CCK amplifies this sensitivity. Thus, our results are in stark contrast to recent reports which have suggested that vago-vagal reflexes are inverted by the metabolic status of the animal and that this inversion could be mediated by CCK within the CNS.

Cholecystokinin octapeptide exerts its therapeutic effects on collagen-induced arthritis by suppressing both inflammatory and Th17 responses.

The purpose of this study was to evaluate the potential therapeutic effect of cholecystokinin octapeptide (CCK-8) on collagen-induced arthritis (CIA), an accepted murine experimental disease model with diverse histopathological features similar to human rheumatoid arthritis (RA). CIA was induced in DBA/1J mice by immunization with chicken collagen type II (CII). CCK-8 at different doses was intraperitoneally administered daily for 1 week. Mice treated with CCK-8 at doses of 5 and 10 nmol but not 1 nmol displayed much delayed onset of CIA and significantly lower incidence and decreased severity of arthritis. CCK-8 treatment significantly reduced the production of cytokines (IL-17, IL-23, IL-6 and TNF-α) and chemokines monocyte chemoattractant protein 1 in the joints of arthritic mice or in synovial cell culture supernatant, and increased the levels of IFN-γ and TGF-ß. T cells from CCK-8 treated mice proliferated much less, produced low level of IL-17 and high levels of IFN-γ and TGF-ß. Moreover, CCK-8 treated mice showed lower levels of CII-specific IgG, particularly that of IgG2a, in sera than those from control mice. These results indicate that CCK-8 is effective in suppressing both inflammatory and Th17 responses in CIA. CCK-8 may represent a new therapeutic modality for rheumatoid arthritis.

Acupuncture for Pain Management: Molecular Mechanisms of Action.

Acupuncture reduces pain by activating specific areas called acupoints on the patient's body. When these acupoints are fully activated, sensations of soreness, numbness, fullness, or heaviness called De qi or Te qi are felt by clinicians and patients. There are two kinds of acupuncture, manual acupuncture and electroacupuncture (EA). Compared with non-acupoints, acupoints are easily activated on the basis of their special composition of blood vessels, mast cells, and nerve fibers that mediate the acupuncture signals. In the spinal cord, EA can inhibit glial cell activation by down-regulating the chemokine CX3CL1 and increasing the anti-inflammatory cytokine interleukin-10. This inhibits P38 mitogen-activated protein kinase and extracellular signal-regulated kinase pathways, which are associated with microglial activation of the C-Jun N-terminal kinase signaling pathway and subsequent astrocyte activation. The inactivation of spinal microglia and astrocytes mediates the immediate and long-term analgesic effects of EA, respectively. A variety of pain-related substances released by glial cells such as the proinflammatory cytokines tumor necrosis factor [Formula: see text], interleukin-1[Formula: see text], interleukin-6, and prostaglandins such as prostaglandins E2 can also be reduced. The descending pain modulation system in the brain, including the anterior cingulated cortex, the periaqueductal gray, and the rostral ventromedial medulla, plays an important role in EA analgesia. Multiple transmitters and modulators, including endogenous opioids, cholecystokinin octapeptide, 5-hydroxytryptamine, glutamate, noradrenalin, dopamine, [Formula: see text]-aminobutyric acid, acetylcholine, and orexin A, are involved in acupuncture analgesia. Finally, the "Acupuncture [Formula: see text]" strategy is introduced to help clinicians achieve better analgesic effects, and a newly reported acupuncture method called acupoint catgut embedding, which injects sutures made of absorbable materials at acupoints to achieve long-term effects, is discussed.

Intracerebroventricular administration of sulphated cholecystokinin octapeptide induces anxiety-like behaviour in goldfish.

Sulphated cholecystokinin octapeptide (CCK-8s) is involved in feeding regulation as an anorexigenic neuropeptide in vertebrates. In rodents, i.c.v. administration of CCK-8s has been shown to affect not only feeding behaviour, but also psychomotor activity. However, there is still no information available concerning the psychophysiological effects of CCK-8s in goldfish. Therefore, in the present study, we examined the effect of synthetic goldfish (gf) CCK-8s on psychomotor activity in this species. Intracerebroventricular administration of gfCCK-8s at 0.1, 0.5 and 2.5 pmol g-1 body weight (BW) did not affect swimming distance (locomotor activity). Because goldfish prefer the lower to the upper area of a tank, we used this as a preference test (upper/lower test) to assess anxiety-like behaviour. Intracerebroventricular administration of gfCCK-8s at 2.5 pmol g-1 BW shortened the time spent in the upper area. The action of gfCCK-8s mimicked that of FG-7142 (the central-type benzodiazepine receptor inverse agonist, an anxiogenic agent) at 5 and 10 pmol g-1 BW. The anxiogenic-like effect of gfCCK-8s was abolished by treatment with the CCK receptor antagonist proglumide at 50 pmol g-1 BW. We also investigated the localisation of CCK/gastrin-like immunoreactivity in the goldfish brain. CCK/gastrin-like immunoreactivity was observed in the anxiety-related regions (the nucleus habenularis and the interpeduncular nucleus). These data indicate that gfCCK-8s potently affects psychomotor activity in goldfish, and exerts an anxiogenic-like effect via the CCK receptor-signalling pathway.

Non-sulfated cholecystokinin-8 increases enteric and hindbrain Fos-like immunoreactivity in male Sprague Dawley rats.

Recently, we reported that non-sulfated cholecystokinin-8 (NS CCK-8) reduces food intake by cholecystokinin-B receptors (CCK-BR). To examine a possible site of action for this peptide, and based on the fact that both NS CCK-8 and CCK-BR are found centrally and peripherally, in the current study we hypothesized that NS CCK-8 increases Fos-like immunoreactivity (Fos-LI, a neuronal activation marker) in the dorsal vagal complex (DVC) of the hindbrain and the myenteric and submucosal plexuses of the small intestine. We found that intraperitoneal NS CCK-8 (0.5 nmol/kg) increases Fos-LI in the DVC, the myenteric and the submucosal plexuses of the duodenum and the myenteric plexus of the jejunum. The findings suggest, but does not prove, a potential role for the DVC and the enteric neurons in the feeding responses evoked by NS CCK-8.

Cholecystokinin-mediated suppression of feeding involves the brainstem melanocortin system.

Hypothalamic pro-opiomelanocortin (POMC) neurons help regulate long-term energy stores. POMC neurons are also found in the nucleus tractus solitarius (NTS), a region regulating satiety. We show here that mouse brainstem NTS POMC neurons are activated by cholecystokinin (CCK) and feeding-induced satiety and that activation of the neuronal melanocortin-4 receptor (MC4-R) is required for CCK-induced suppression of feeding; the melanocortin system thus provides a potential substrate for integration of long-term adipostatic and short-term satiety signals.

miR-379 Inhibits Cell Proliferation, Invasion, and Migration of Vascular Smooth Muscle Cells by Targeting Insulin-Like Factor-1.

PURPOSE: MicroRNAs are small non-coding RNAs that play important roles in vascular smooth muscle cell (VSMC) function. This study investigated the role of miR-379 on proliferation, invasion, and migration of VSMCs and explored underlying mechanisms thereof. MATERIALS AND METHODS: MicroRNA, mRNA, and protein levels were determined by quantitative real-time PCR and western blot. The proliferative, invasive, and migratory abilities of VSMCs were measured by CCK-8, invasion, and wound healing assay, respectively. Luciferase reporter assay was used to confirm the target of miR-379. RESULTS: Platelet-derived growth factor-bb was found to promote cell proliferation and suppress miR-379 expression in VSMCs. Functional assays demonstrated that miR-379 inhibited cell proliferation, cell invasion, and migration. Flow cytometry results further showed that miR-379 induced apoptosis in VSMCs. TargetScan analysis and luciferase report assay confirmed that insulin-like growth factor-1 (IGF-1) 3'UTR is a direct target of miR-379, and mRNA and protein levels of miR-379 and IGF-1 were inversely correlated. Rescue experiments showed that enforced expression of IGF-1 sufficiently overcomes the inhibitory effect of miR-379 on cell proliferation, invasion, and migration in VSMCs. CONCLUSION: Our results suggest that miR-379 plays an important role in regulating VSMCs proliferation, invasion, and migration by targeting IGF-1.

Effects of CCK-8 and Cystathionine γ-Lyase/Hydrogen Sulfide System on Acute Lung Injury in Rats.

Acute lung injury (ALI) is mainly characterized by diffusive injuries to lung epithelium and increased permeability of alveolar-capillary membranes caused by various factors, which leads to pulmonary edema and pulmonary closure. Lipopolysaccharide (LPS), which is the main component of the cell wall of gram-negative bacteria, is one of the most important factors causing pulmonary infection and ALI. More and more reports have indicated that hydrogen sulfide (H2S) is closely correlated with ALI and has anti-inflammation function, while the specific mechanism needs further investigation. Cholecystokinin-octapeptide (CCK-8), which is an important endogenous functional fragment belonging to CCK family, participates in anti-inflammatory and anti-endotoxic shock (ES). Whether CCK-8 plays important roles in curing ALI also needs further investigation. Herein, we concluded that CCK-8 alleviated the ALI induced by LPS via regulating the catalytic activity of cystathionine γ-lyase (CSE) and the formation of H2S. This work provides new medicine-designed target for clinical doctor to prevent and cure ALI.

[The effect and mechanism of cholecystokinin octapeptide induced-gastric dysmotility on bile regurgitation during stress].

OBJECTIVE: To illustrate the existence of bile regurgitation under stress condition, and explore the possible effects and related mechanism of changes of cholecystokinin octapeptide (CCK-8) on stress-induced bile regurgitation in rats. METHODS: (1) Changes in plasma CCK-8 and gastric bile concentration were measured by using radioimmunoassay while simultaneously calculating gastric ulcer index and intragastric pH; (2) Each isolated gastric strips were suspended in a tissue chamber to record the contractile responses by polyphysiograph; (3) The responsiveness of gastric smooth muscle cells (SMCs) to sulfated cholecystokinin octapeptide (CCK-8S) were examined using fura-2-loaded microfluorimetric measurement of intracellular calcium concentration ([Ca(2+)] i); (4) The current of L-type calcium channels (I(CaL)) of SMCs were recorded by patch-clamp techniques. RESULTS: (1) Compared with the normal control, plasma CCK-8 [from (2.23 +/- 0.88) pmol/L to (10.80 +/- 3.82) pmol/L] and gastric bile concentration [from (37.93 +/- 23.76) micromol/L to (1316.00 +/- 197.36) micromol/L] significantly increased during the stress (P < 0.01) and both simultaneously reached the peak at the time point of 2 h after stress; ulcer index (from 0.62 +/- 0.23 to 32.01 +/- 16.11) and intragastric pH (from 1.06 +/- 1.20 to 5.29 +/- 1.25) apparently increased (P < 0.01); (2) Significant changes to CCK-8S were found in the mean contractile amplitude and frequency of circular muscle and longitudinal muscle of gastric antrum and pylorus; (3) CCK-8S-evoked significant increase in [Ca(2+)] i [from (65.8 +/- 7.4) nmol/L to (472.1 +/- 35.6) nmol/L, P < 0.01] could be suppressed by CCK-A receptor antagonist; whereas a small but significant increases were still elicited by CCK-8S under condition of the removal of extracellular calcium; (4) CCK-8S-intensified calcium current I(Ca-L) [from (-56.42 +/- 6.57) pA to (-88.54 +/- 5.71) pA, P < 0.01)] apparently inhibited by respective administration of nifedipine, Ca(2+)-ATPase inhibitors or calcium dependent chloride channel blocker (P < 0.01). CONCLUSIONS: Gastric mucosal damage induced by bile regurgitation is closely connected with gastric antrum and pylorus dysmotility evoked by CCK-8 during the stress. CCK-8S-evoked [Ca(2+)] i increase in gastric antrum and pylorus SMC depends on the release of intracellular calcium stores which activates L-type voltage-dependent calcium channels through the activation of calcium dependent chloride channels.

Activation of Nesfatin-1-Containing Neurones in the Hypothalamus and Brainstem by Peripheral Administration of Anorectic Hormones and Suppression of Feeding via Central Nesfatin-1 in Rats.

Peripheral anorectic hormones, such as glucagon-like peptide (GLP)-1, cholecystokinin (CCK)-8 and leptin, suppress food intake. The newly-identified anorectic neuropeptide, nesfatin-1, is synthesised in both peripheral tissues and the central nervous system, particularly by various nuclei in the hypothalamus and brainstem. In the present study, we examined the effects of i.p. administration of GLP-1 and CCK-8 and co-administrations of GLP-1 and leptin at subthreshold doses as confirmed by measurement of food intake, on nesfatin-1-immunoreactive (-IR) neurones in the hypothalamus and brainstem of rats by Fos immunohistochemistry. Intraperitoneal administration of GLP-1 (100 µg/kg) caused significant increases in the number of nesfatin-1-IR neurones expressing Fos-immunoreactivity in the supraoptic nucleus (SON), the area postrema (AP) and the nucleus tractus solitarii (NTS) but not in the paraventricular nucleus (PVN), the arcuate nucleus (ARC) or the lateral hypothalamic area (LHA). On the other hand, i.p. administration of CCK-8 (50 µg/kg) resulted in marked increases in the number of nesfatin-1-IR neurones expressing Fos-immunoreactivity in the SON, PVN, AP and NTS but not in the ARC or LHA. No differences in the percentage of nesfatin-1-IR neurones expressing Fos-immunoreactivity in the nuclei of the hypothalamus and brainstem were observed between rats treated with saline, GLP-1 (33 µg/kg) or leptin. However, co-administration of GLP-1 (33 µg/kg) and leptin resulted in significant increases in the number of nesfatin-1-IR neurones expressing Fos-immunoreactivity in the AP and the NTS. Furthermore, decreased food intake induced by GLP-1, CCK-8 and leptin was attenuated significantly by pretreatment with i.c.v. administration of antisense nesfatin-1. These results indicate that nesfatin-1-expressing neurones in the brainstem may play an important role in sensing peripheral levels of GLP-1 and leptin in addition to CCK-8, and also suppress food intake in rats.

Influences of CCK-8 on expressions of apoptosis-related genes in prefrontal cortex neurons of morphine-relapse rats.

In order to elucidate the influences of CCK-8 on expressions of apoptosis-related genes, Bax, Bcl-2 and Caspase-3, of prefrontal cortex neurons in morphine-relapse rats, an effective, successful morphine-relapse-rat model using the conditioned place preference (CPP) under CCK-8 (0.01, 0.1 and 1.0µg, i.c.v) intervention was established. The prefrontal cortexes were made into slices with the cellular plasmas immunohistochemically stained. The expressions of Bax, Bcl-2, Caspase-3 of neurons were evaluated through their scores, and each corresponding ratio of Bax and Bcl-2 (Bax/Bcl-2) was also computed. The results showed that the expression of Bcl-2 was very weak and those of Bax and Caspase-3 were hardly seen in group normal saline; the expressions of Bax and Caspase-3 were strong and that of Bcl-2 was weak in group morphine and compared to group normal saline, there were significant differences (P<0.05); the expressions of Bax, Caspase-3 and the ratios of Bax/Bcl-2 have a gradually-decreased trend in the sequence of group 0.01µg, group 0.1µg and group 1.0µg, but the expression of Bcl-2 has an opposite trend in the same sequence, and compared to group morphine, there were significant differences (P<0.05) excluding group 0.01µg. So we draw a conclusion that CCK-8 (0.1 and 1.0µg, i.c.v) could protect neurons of prefrontal cortex through up-regulating the expression of Bcl-2, down-regulating those of Bax and Caspase-3 and reducing Bax/Bcl-2 ratio in the model of morphine-relapse rats.

Contribution of CCK1 receptors to cardiovascular and respiratory effects of cholecystokinin in anesthetized rats.

The study investigated the share of vagal input at infra- and supra-nodosal level and the contribution of CCK1 and CCK2 receptors to the cardiorespiratory responses produced by an intravenous injection of sulfated cholecystokinin octapeptide (CCK-8) in anesthetized rats. This compound administered intravenously at a dose of 50µg/kg induced short-lived decline in tidal volume and respiratory rate resulting in depression of minute ventilation. Midcervical vagotomy had no effect on CCK-8-evoked ventilatory changes, whereas supranodosal denervation abolished slowing down of breathing. Cardiovascular response to CCK challenge was characterized by a transient decrease followed by an augmentation in the mean blood pressure (MAP) in the intact animals. Vagotomy performed at both levels abrogated the declining phase of MAP. Blood pressure changes were associated with decreased heart rate present in all neural states. All cardiovascular and respiratory effects were antagonized by pre-treatment with devazepide-CCK1 receptors' antagonist, whereas CI988-antagonist of CCK2 receptors was ineffective. In conclusion, our results indicate that CCK-8 modulates slowing down of respiratory rhythm via CCK1 receptors located in the nodose ganglia (NG) and depresses tidal volume via central CCK1 dependent mechanism. CCK-8-evoked decline in blood pressure may be due to activation of vagal afferents, whereas pressor responses seem to be mediated by an activation of CCK1 receptors in the central nervous system. Bradycardia was probably induced by the direct action of CCK-8 on the heart pacemaker cells.

Vagal afferent-dependent cholecystokinin modulation of visceral pain requires central amygdala NMDA-NR2B receptors in rats.

BACKGROUND: Cholecystokinin (CCK), a gut hormone that is released during feeding, exerts gastrointestinal effects in part through vagal pathway. It is reported to be a potential trigger for increased postprandial visceral sensitivity in healthy subjects and, especially in patients with irritable bowel syndrome. NR2B-containing N-methyl-d-aspartate (NMDA) receptors in the central amygdala (CeA) participate in pain modulation. Systemically administered CCK activates the CeA-innervating neurons. Here, we investigated whether CCK modulation of visceral sensitivity is mediated through CeA NMDA-NR2B receptors and whether this modulation involves vagal pathway. METHODS: We first examined the visceromotor response (VMR) to colorectal distention (CRD) following i.p. injection of CCK octapeptide (CCK-8) in a rat model. Next, the NR2B antagonist ifenprodil and the NR2A antagonist NVP-AAM077 were microinjected into the CeA before systemic CCK injection. NR2B phosphorylation was detected by Western blot. To down-regulate NR2B gene expression, NR2B-specific small interfering RNA (siRNA) was delivered into CeA neurons by electroporation. In addition, the effects of functional deafferentation by perivagal application of capsaicin and pretreatment with the CCK1 receptor antagonist devazepide were investigated. KEY RESULTS: CCK-8 increased VMR to CRD in a dose-dependent manner. This effect was blunted by intra-CeA administration of ifenprodil (but not NVP-AAM077) and was accompanied by phosphorylation of NR2B subunits in the CeA. CCK failed to increase VMR to CRD in NR2B siRNA-treated rats. Perivagal capsaicin application and pretreatment with devazepide prevented CCK-induced pronociception and CeA NR2B phosphorylation. CONCLUSIONS & INFERENCES: The pronociception induced by systemic CCK, which is vagal afferent-dependent, requires activation of CeA NMDA-NR2B receptors.

Cholecystokinin does not stimulate prosomatostatin-derived peptides in man.

In man, plasma cholecystokinin (CCK) and somatostatin-28 (S-28) levels increase after ingestion of a mixed meal. Both peptides originate from the gastrointestinal tract. In supra- and periphysiological doses, CCK stimulates the release of somatostatin-14 from in vitro pancreatic islets and gastric cells and increases circulating somatostatin-like immunoreactivity in dogs, leading to the conjecture that CCK regulates somatostatin-like immunoreactivity secretion. Nonetheless, whether CCK is responsible in part for the meal-induced rise in S-28 in man has not been established. Therefore, the present study was designed to determine if CCK, at both physiological and supraphysiological concentrations, increases the circulating levels of prosomatostatin (proS)-derived peptides in humans. On 3 separate days, five healthy men ate a mixed liquid meal or received iv infusions of CCK at rates of 18 or 38 pmol/kg.h. Plasma levels of pro-S-derived peptides, including pro-S, S-14, S-13, S-28, and CCK, were measured. Basal CCK levels averaged 0.9 +/- 0.1 pmol/L and increased after the meal to a peak level of 5.4 +/- 1.5 pmol/L and averaged 3.1 +/- 1.2 pmol/L over 90 min. The mean basal levels of pro-S, S-14, and S-13, measured collectively, was 6.1 +/- 0.4 pmol/L eq S14 and was unaltered by food intake. The S-28 level was 6.7 +/- 0.6 pmol/L and rose to a zenith of 13.1 +/- 3.3 pmol/L by 90 min. Infusion of CCK at 18 and 38 pmol/kg.h produced steady state plasma CCK levels of 4.1 +/- 1.1 and 9.9 +/- 1.5 pmol/L, respectively. Basal levels of pro-S-derived peptides were unaltered during the infusion of either the low or high dose of CCK. We conclude that CCK by itself is not a physiological signal to the release of pro-S-derived peptides in man.

CSF cholecystokinin octapeptide in patients with bulimia nervosa and in normal comparison subjects.

Cholecystokinin octapeptide (CCK-8) appears to modulate appetitive behavior, and in rodents, anxiety-related behavior. The authors studied CCK-8 in patients with bulimia nervosa. CSF concentrations of CCK-8 were measured in 11 drug-free female patients with DSM-III-R-defined bulimia nervosa and in 16 normal subjects. The bulimic patients had significantly lower levels of CCK-8 than the comparison subjects. CCK-8 concentrations were inversely correlated with scores on the anger-hostility, anxiety, and interpersonal sensitivity subscales of the SCL-90-R. They were not significantly correlated with age, percentage of standardized average body weight, or mean weekly frequency of binge eating or vomiting. The results indicate that central CCK-8 abnormalities may play a role in the pathophysiology of bulimia nervosa.

Early postnatal development of cholecystokinin-immunoreactive structures in the visual cortex of the cat.

The early postnatal development of cholecystokinin-immunoreactive (CCK-ir) neurons was analyzed in visual areas 17 and 18 of cats aged from postnatal day 0 to adulthood. Neurons were classified mainly by axonal criteria. According to their chronology of appearance neurons are grouped into three neuronal populations. The first population consists of five cell types which appear perinatally in areas 17 and 18. Four of them have axons terminating in layer VI. Neurons with columnar dendritic fields of layers IV and V display a conspicuous dendritic arborization with the long dendrites always arranged parallel to each other. This way they form a vertically oriented dendritic column. The neurons differentiate at around P 2 and are present until the end of the second postnatal week. They disappear possibly by degeneration and cell death. Multipolar neurons of layer VI have long dendrites and axonal domains of up to 800 micron in diameter. Three percent of these neurons send out two axons instead of only one. Neurons differentiate at P 0 and the cell type persists into adulthood. Bitufted to multipolar neurons of layer V constitute a frequent type; 10% of these cells issue two axons. They differentiate at P 2 and the type survives into adulthood. Bitufted to multipolar neurons of layers II/III appear at P 2 and send their axons into layer VI. So, early postnatally an axonal connection from superficial cortical layers to layer VI is established. The cell type persists into adulthood. The fifth cell type of the first population is constituted by the neurons of layer I with intralaminar axons which differentiate at P 2. Although they derive from the early marginal zone, the cell type survives into adulthood. The second population consists of two cell types which appear around the end of the second and during the third postnatal week in areas 17 and 18. Multipolar neurons of layer II have horizontally or obliquely arranged basket axons which, during the second postnatal month, form patches of high fiber and terminal density along the layer I/II border. Neurons with descending main axons issuing horizontal and oblique collaterals of layers II-IV form broad axonal fields. The third population in area 17 is constituted by three cell types: Bitufted neurons with axons descending in form of loose bundles of layers II/III differentiate during the fifth postnatal week. Small basket cells of layers II/III with locally restricted axonal plexuses and somewhat larger basket cells of layer IV appear during the sixth and seventh week.(ABSTRACT TRUNCATED AT 400 WORDS)

Cholecystokinin-8 and nerve growth factor: two endogenous molecules working for the upkeep and repair of the nervous system.

Cholecystokinin-8 (CCK-8), the small peptide initially described as a gastric factor involved in the regulation of feeding behavior, is today recognized as one of the most abundant neurotransmitters/ neuropeptides in brain and is an important signal factor for the peripheral and central nervous systems. In the past twenty years, many studies have focused on possible clinical applications of this peptide and its receptor ligands in psychiatric diseases and gastrointestinal pathologies. Recently it has been suggested that CCK-8 may also have a neuroprotective role, thus opening a new field of interest around the physiology and the pharmacology of this neuropeptide and its receptors. It has been demonstrated that CCK-8 counteracts neuronal deficit following chemical or surgical lesions in both the central and peripheral nervous systems and that Nerve Growth factor (NGF) is involved in the CCK-induced recovery process. By using selective CCK receptor antagonists it has been demonstrated that CCK-8, when injected intraperitoneally, has the ability to stimulate NGF synthesis in brain and peripheral organs by a mechanism that involves the activation of CCK receptors. As has been widely reported, NGF is an essential survival and differentiative factor for selective neuronal populations of the PNS and CNS and plays a role in the events of degeneration and repair of the nervous system in diseases with different etiologies, e.g. neurodegenerative and autoimmune diseases as well as diabetes-associated pathologies. The possibility of using NGF in therapy has been evaluated and systemic and intracerebral NGF treatment have been tested in patients and animal models. Although the results of these studies are encouraging, the difficulty to predict and/or eliminate the side effects of NGF/NGF antibody treatment has made it difficult to fully evaluate the potential of the beneficial effects. In this context recent results obtained in our laboratories may offer a new prospective for the pharmacological approaches to the diseases associated with altered NGF production and functions. The data of our recent observations on NGF and CCK-8 is covered in this review.

Reversal of tolerance to morphine but no potentiation of morphine-induced analgesia by antiserum against cholecystokinin octapeptide.

Tolerance to morphine analgesia was induced in rats by chronic treatment with morphine (5-30 mg/kg, t.i.d. for 6 days). Intracerebroventricular (i.c.v.) injection of antiserum against cholecystokinin octapeptide (CCK-8) reversed tolerance to morphine by 50% (P less than 0.001). Intrathecal (ith) injection of the CCK-8 antiserum produced a similar, although less marked, reversal of tolerance to morphine. Rats made tolerant to analgesia induced by morphine developed a cross tolerance to electroacupuncture-induced analgesia. This cross tolerance was also reversed by the CCK-8 antiserum by more than 50% (P less than 0.001). Intracerebroventricular or intrathecal injection of the CCK-8 antiserum per se produced no significant changes in the basal level of the latency of the tail flick response, nor did it affect the analgesia induced by morphine in naive rats. The results suggest that prolonged activation of opioid receptors may trigger the CCK-8 system in the central nervous system to exert a negative feedback control, which may constitute one of the mechanisms for the development of tolerance to opioids.

In vivo sulfation of cholecystokinin octapeptide. Possible interactions of the two forms of cholecystokinin with dopamine in the brain.

In most laboratories CCK-8(s) has been found to be the biologically active form of CCK-8 in the CNS. The role of CCK-8(ns) has scarcely been investigated and is poorly understood. CCK-8(s) exerts a transmitter and/or modulator role in this projection. CCK-8(ns), on the other hand, profoundly affects DA-ergic neurotransmission in the nigrostriatal DA-ergic projection. The octapeptide modulates the turnover and release of DA from this neuron population. DA-mediated behavioral reactions are also modulated by CCK-8(ns). We should emphasize that the biological importance of CCK-8(ns) in the CNS has hitherto generally been neglected. Our results point to the equivalence of CCK-8(s) and CCK-8(ns) in the CNS in most biological tests. In some cases the latter compound is the more potent one. In most of these tests the C-terminal fragment (tetragastrin = CCK-4) also proved to be active. It is most likely that a brain receptor population exists which can bind both forms of CCK-8 and even CCK-4. Nevertheless, the CNS could contain binding sites which bind only CCK-8(s) as a ligand. We have found that an unidentified sulfotransferase of the brain can sulfate CCK-8(ns) and thereby provide a ligand for the special receptors of CCK-8(s). It is likely that CCK modulates the turnover and release of DA, and vice versa. Theoretically, different biochemical mechanisms could exist for interactions between CCK octapeptides and DA. We have focused our investigations on the enzymic sulfation-desulfation processes of both CCK-8 and DA and have devised a hypothetical model for the possible interactions. Both CCK-8(ns) and DA could be sulfated in vivo, this enzymic reaction generally requiring active sulfate (PAPS). These two compounds could compete for the limited pool of PAPS, and thus CCK-8 and DA could mutually regulate their levels in the same cell by influencing one of the metabolic (DA) or synthetic (CCK-8(s)) pathways. CCK-8(s) also might provide the O-sulfate group for DA by enzymic transformation, and, conversely, DA-O-sulfate may sulfate CCK-8(ns) in a similar way. These trans-sulfation processes could also mutually determine the concentrations of DA and CCK-8 co-existing in one cell. Experiments to prove these models are planned.