Heterogeneous effects of cholecystokinin on neuronal response properties in deep layers of rat barrel cortex.

Cholecystokinin (CCK) is one of the most studied neuropeptides in the brain. In this study, we investigated the effects of CCK-8s and LY225910 (CCK2 receptor antagonist) on properties of neuronal response to natural stimuli (whisker deflection) in deep layers of rat barrel cortex. This study was done on 20 male Wistar rats, weighing 230-260 g. CCK-8s (300 nmol/rat) and LY225910 (1 µmol/rat) were administered intracerebroventricularly (ICV). Neuronal responses to deflection of principal (PW) and adjacent (AW) whiskers were recorded in the barrel cortex using tungsten microelectrodes. Computer controlled mechanical displacement was used to deflect whiskers individually or in combination at 30 ms inter-stimulus intervals. ON and OFF responses for PW and AW deflections were measured. A condition-test ratio (CTR) was computed to quantify neuronal responses to whisker interaction. ICV administration of CCK-8s and LY225910 had heterogeneous effects on neuronal spontaneous activity, ON and OFF responses to PW and/or AW deflections, and CTR for both ON and OFF responses. The results of this study demonstrated that CCK-8s can modulate neuronal response properties in deep layers of rat barrel cortex probably via CCK2 receptors.

Cloning and characterization of the porcine gastrin/cholecystokinin type 2 receptor.

The gastrointestinal hormone cholecystokinin (CCK) regulates digestive processes and satiety in addition to centrally mediated effects on nociception and anxiety. CCK signals through two seven-trans-membrane receptors named the CCK-1 receptor and the CCK-2 receptor. The expression pattern and biological effects mediated by the CCK-1 and CCK-2 receptors are highly divergent. The pig is a widely used preclinical animal model in medical research, but up until recently, the porcine CCK-2 receptor was described as a pseudogene in the publicly available genomic sequence databases. Thus, it was challenging to interpret data from this animal model in studies of CCK biology and pharmacology. Here we describe an in silico prediction of the porcine CCK-2 receptor and the subsequent cloning, expression, and in vitro pharmacological characterization. We find a high degree of sequence homology with the human orthologue as well as CCK-2 receptors of other major species used in pre-clinical research. We also show that the endogenous ligands CCK-8 and Gastrin-17 bind and activate the porcine CCK-2 receptor with similar affinities and potencies as seen for the human CCK-2 receptor. We conclude that the pig has a functional CCK-2 receptor which is highly comparable to the human orthologue and therefore the pig qualifies as a valid preclinical model for the study of human CCK biology and pharmacology.

Cholecystokinin responsiveness varies across the population dependent on metabolic phenotype.

Background: Cholecystokinin (CCK) is an important satiety factor, acting at type 1 receptors (CCK1Rs) on vagal afferent neurons; however, CCK agonists have failed clinical trials for obesity. We postulated that CCK1R function might be defective in such patients due to abnormal membrane composition, such as that observed in cholesterol gallstone disease.Objective: Due to the challenges in directly studying CCK1Rs relevant to appetite control, our goal was to develop and apply a method to determine the impact of a patient's own cellular environment on CCK stimulus-activity coupling and to determine whether CCK sensitivity correlated with the metabolic phenotype of a high-risk population.Design: Wild-type CCK1Rs were expressed on leukocytes from 112 Hispanic patients by using adenoviral transduction and 24-h culture, with quantitation of cholesterol composition and intracellular calcium responses to CCK. Results were correlated with clinical, biochemical, and morphometric characteristics.Results: Broad ranges of cellular cholesterol and CCK responsiveness were observed, with elevated cholesterol correlated with reduced CCK sensitivity. This was prominent with increasing degrees of obesity and the presence of diabetes, particularly when poorly controlled. No single standard clinical metric correlated directly with CCK responsiveness. Reduced CCK sensitivity best correlated with elevated serum triglycerides in normal-weight participants and with low HDL concentrations and elevated glycated hemoglobin in obese and diabetic patients.Conclusions: CCK responsiveness varies widely across the population, with reduced signaling in patients with obesity and diabetes. This could explain the failure of CCK agonists in previous clinical trials and supports the rationale to develop corrective modulators to reverse this defective servomechanism for appetite control. This trial was registered at www.clinicaltrials.gov as NCT03121755.

Potential roles for calcium-sensing receptor (CaSR) and transient receptor potential ankyrin-1 (TRPA1) in murine anorectic response to deoxynivalenol (vomitoxin).

Food contamination by the trichothecene mycotoxin deoxynivalenol (DON, vomitoxin) has the potential to adversely affect animal and human health by suppressing food intake and impairing growth. In mice, the DON-induced anorectic response results from aberrant satiety hormone secretion by enteroendocrine cells (EECs) of the gastrointestinal tract. Recent in vitro studies in the murine STC-1 EEC model have linked DON-induced satiety hormone secretion to activation of calcium-sensing receptor (CaSR), a G-coupled protein receptor, and transient receptor potential ankyrin-1 (TRPA1), a TRP channel. However, it is unknown whether similar mechanisms mediate DON's anorectic effects in vivo. Here, we tested the hypothesis that DON-induced food refusal and satiety hormone release in the mouse are linked to activation of CaSR and TRPA1. Oral treatment with selective agonists for CaSR (R-568) or TRPA1 (allyl isothiocyanate (AITC)) suppressed food intake in mice, and the agonist's effects were suppressed by pretreatment with corresponding antagonists NPS-2143 or ruthenium red (RR), respectively. Importantly, NPS-2143 or RR inhibited both DON-induced food refusal and plasma elevations of the satiety hormones cholecystokinin (CCK) and peptide YY3-36 (PYY3-36); cotreatment with both antagonists additively suppressed both anorectic and hormone responses to DON. Taken together, these in vivo data along with prior in vitro findings support the contention that activation of CaSR and TRPA1 contributes to DON-induced food refusal by mediating satiety hormone exocytosis from EEC.

Beneficial effects of the novel cholecystokinin agonist (pGlu-Gln)-CCK-8 in mouse models of obesity/diabetes.

AIMS/HYPOTHESIS: Cholecystokinin (CCK) is a rapidly degraded gastrointestinal peptide that stimulates satiety and insulin secretion. We aimed to investigate the beneficial weight-lowering and metabolic effects of the novel N-terminally modified CCK analogue, (pGlu-Gln)-CCK-8. METHODS: The biological actions of (pGlu-Gln)-CCK-8 were comprehensively evaluated in pancreatic clonal BRIN BD11 cells and in vivo in high-fat-fed and ob/ob mice. RESULTS: (pGlu-Gln)-CCK-8 was completely resistant to enzymatic degradation and its satiating effects were significantly (p < 0.05 to p < 0.001) more potent than CCK-8. In BRIN-BD11 cells, (pGlu-Gln)-CCK-8 exhibited enhanced (p < 0.01 to p < 0.001) insulinotropic actions compared with CCK-8. When administered acutely to high-fat-fed or ob/ob mice, (pGlu-Gln)-CCK-8 improved glucose homeostasis. Sub-chronic twice daily injections of (pGlu-Gln)-CCK-8 in high-fat-fed mice for 28 days significantly decreased body weight (p < 0.05 to p < 0.001), accumulated food intake (p < 0.05 to p < 0.001), non-fasting glucose (p < 0.05) and triacylglycerol deposition in pancreatic (p < 0.01), adipose (p < 0.05) and liver (p < 0.001) tissue, and improved oral (p < 0.05) and i.p. (p < 0.05) glucose tolerance and insulin sensitivity (p < 0.001). Similar observations were noted in ob/ob mice given twice daily injections of (pGlu-Gln)-CCK-8. In addition, these beneficial effects were not reproduced by simple dietary restriction and were not associated with changes in energy expenditure. There was no evidence for development of tolerance to (pGlu-Gln)-CCK-8, and analysis of histology or blood-borne markers for pancreatic, liver and renal function in mice treated with (pGlu-Gln)-CCK-8 suggested little abnormal pathology. CONCLUSIONS/INTERPRETATION: These studies emphasise the potential of (pGlu-Gln)-CCK-8 for the alleviation of obesity and insulin resistance.

Concise approach toward tetrazolo[1,5-a][1,4]benzodiazepines via a novel multicomponent isocyanide-based condensation.

A novel and efficient method for the synthesis of heteroannulated [1,4]benzodiazepines via an isocyanide-based multicomponent reaction is reported. The tetrazolo[1,5-a][1,4]benzodiazepines were obtained by a facile azide Ugi five-center four-component reaction (U-5C-4CR) using ketones, sodium azide, ammonium chloride, and corresponding isocyanide. The aforementioned tetrazolodiazepines represent a notable class of compounds with proven platelet aggregation inhibitory and cholecystokinin agonist activities.

Does the panic attack activate the hypothalamic-pituitary-adrenal axis?

Realizou-se levantamento bibliográfico no indexadorMEDLINE, através das palavras-chave "cortisol" e "panic", sem limite de tempo, restringindo-se a sereshumanos e à localização das palavras-chave no título e no resumo. Foram excluídos artigos de revisão e relatos de caso, estudos sobre alterações ocorridas entre dois ataques, e os que tratavam de outras doenças psiquiátricas ou de sujeitos sadios, quando não comparados com pacientes de pânico. Os resultados mostraram que ataques de pânico naturais ou provocados pelos agentes panicogênicos seletivos, lactato de sódio e dióxido de carbono, não ativam o eixo hipotálamo-pituitária-adrenal (HPA). Agonistas do receptor de colecistocinina B elevam os hormônios de estresse, quer haja ataque de pânico ou não, parecendo ativar diretamente o eixo HPA. O antagonista benzodiazepínico flumazenil não eleva o nível dos hormônios de estresse, porém não induz ataques de pânico de modo consistente. Agentes farmacológicos que produzem ansiedade em pacientes de pânico e em voluntários saudáveis elevam o nível dos hormônios de estresse, entre estes o antagonista a2-adrenérgico ioimbina, os agentes serotonérgicos 1-(m-clorofenil) piperazina (mCPP) e fenfluramina, bem como o agente psicostimulante cafeína. Portanto, o ataque de pânico não parece ativar o eixo HPA, ao contrário da ansiedade antecipatória.

Does the panic attack activate the hypothalamic-pituitary-adrenal axis?

A bibliographic search has been performed in MEDLINE using cortisol and panic as key-words, occurring in the title and/or in the abstract. Human studies were selected, with no time limit. The following publications were excluded: review articles, case reports, panic attacks in disorders other than panic disorder, and studies on changes that occurred in-between panic attacks. The results showed that real-life panic attacks as well as those induced by selective panicogenic agents such as lactate and carbon dioxide do not activate the hypothalamic-pituitary-adrenal (HPA) axis. Agonists of the colecystokinin receptor B, such as the colecystokinin-4 peptide and pentagastrin, increase stress hormones regardless of the occurrence of a panic attack and thus, seem to activate the HPA axis directly. The benzodiazepine antagonist flumazenil does not increase stress hormones, but this agent does not reliably induce panic attacks. Pharmacological agents that increased anxiety in both normal subjects and panic patients raised stress hormone levels; among them are the alpha2-adrenergic antagonist yohimbine, the serotonergic agents 1-(m-chlorophenyl) piperazine (mCPP) and fenfluramine, as well as the psychostimulant agent caffeine. Therefore, the panic attack does not seem to activate the HPAaxis, in contrast to anticipatory anxiety.

Effects of secretagogues and bile acids on mitochondrial membrane potential of pancreatic acinar cells: comparison of different modes of evaluating DeltaPsim.

In this study, we investigated the effects of secretagogues and bile acids on the mitochondrial membrane potential of pancreatic acinar cells. We measured the mitochondrial membrane potential using the tetramethylrhodamine-based probes tetramethylrhodamine ethyl ester and tetramethylrhodamine methyl ester. At low levels of loading, these indicators appeared to have a low sensitivity to the uncoupler carbonyl cyanide m-chlorophenylhydrazone, and no response was observed to even high doses of cholecystokinin. When loaded at high concentrations, tetramethylrhodamine methyl ester and tetramethylrhodamine ethyl ester undergo quenching and can be dequenched by mitochondrial depolarization. We found the dequench mode to be 2 orders of magnitude more sensitive than the low concentration mode. Using the dequench mode, we resolved mitochondrial depolarizations produced by supramaximal and by physiological concentrations of cholecystokinin. Other calcium-releasing agonists, acetylcholine, JMV-180, and bombesin, also produced mitochondrial depolarization. Secretin, which employs the cAMP pathway, had no effect on the mitochondrial potential; dibutyryl cAMP was also ineffective. The cholecystokinin-induced mitochondrial depolarizations were abolished by buffering cytosolic calcium. A non-agonist-dependent calcium elevation induced by thapsigargin depolarized the mitochondria. These experiments suggest that a cytosolic calcium concentration rise is sufficient for mitochondrial depolarization and that the depolarizing effect of cholecystokinin is mediated by a cytosolic calcium rise. Bile acids are considered possible triggers of acute pancreatitis. The bile acids taurolithocholic acid 3-sulfate, taurodeoxycholic acid, and taurochenodeoxycholic acid, at low submillimolar concentrations, induced mitochondrial depolarization, resolved by the dequench mode. Our experiments demonstrate that physiological concentrations of secretagogues and pathologically relevant concentrations of bile acids trigger mitochondrial depolarization in pancreatic acinar cells.

Analysis of strain difference in behavior to Cholecystokinin (CCK) receptor mediated drugs in PVG hooded and Sprague-Dawley rats using elevated plus-maze test apparatus.

This study investigated the behavioral mechanisms underlying the anxiogenic, or anxiolytic mediated effects of CCK(2) receptor mediated agonist (CCK-4) and antagonist drugs (LY225910, LY288513, CR2945) in PVG hooded and Sprague-Dawley (SD) rats using the elevated plus maze test apparatus. In addition, the effects of a CCK(1) antagonist (CR1409) were investigated for its possible mediation in anxiety behavior between PVG hooded and SD rats. PVG hooded rats treated with CCK-4, decreased the time spent in the open arm and increased the time spent in the closed arm and correspondingly showed increase in the number of entries in the open arms while the number of entries in closed arm was insignificant, whereas SD rats decreased the time spent in the closed arm, while other parameters remained insignificant. PVG hooded rats administered with various CCK(2) antagonists (LY225910, LY288513, and CR2945) significantly increased the time spent in the open arm and correspondingly decreased the time spent in the closed arm, while the number of entries in the open or closed arm was insignificant, in contrast, SD rats failed to show any reliable significance. PVG hooded rats administered with the CCK(1) antagonist (CR1409), failed to show any reliable significance, in contrast, SD rats significantly increased the time spent in the open arm. The strain differences observed in this study suggests that CCK plays mainly as a neuromodulator, in which the various CCK(2) antagonists may not affect baseline anxiety state, but instead they modulate heightened states of anxiety through differential effects of CCK(1)/CCK(2) receptors.

Effect of peripheral cholecystokinin receptor agonists on c-Fos expression in brain sites mediating food consumption in rats.

Peripheral cholecystokinin (CCK) elicits satiety by acting on hypothalamic nuclei. The anoretic effect of CCK is mediated by the vagus nerve and involves brainstem areas receiving vagal inputs, such as the nucleus tractus solitarius (NTS) and the area postrema (AP). This work aims to analyze, by measuring c-Fos expression, the effect of selective CCK receptor agonists on brain areas involved in food-intake/satiety process. We observed that SR-146,131, a CCK(1)R agonist, increased c-Fos expression in NTS and AP as well as in some hypothalamic nuclei. CCK-4, a CCK(2)R agonist which does not cross the blood-brain barrier (BBB), only was effective in the hypothalamus. Our data show that the activation of the brainstem is not a requisite to obtain a hypothalamic effect of peripheral CCK and suggest that CCK-4 may indirectly stimulate hypothalamic areas endowed with BBB, without previous activation of neither NTS nor AP.

Effect of intraperitoneal mRNA antisense-oligodeoxynucleotides to cholecystokinin on anxiety-like and learning behaviors in rats: association with pre-experimental stress.

RATIONALE: Cholecystokinin and its analogs generate anxiety in humans and measurable anxiety-like behaviors in rats. Cholecystokinin receptor blockers have been reported to have variable effects in the treatment of anxiety disorders. We demonstrated that intracerebroventricular administration of Cholecystokinin-antisense oligodeoxynucleotides (ASODN) for 3 days significantly diminished anxiety-like behavior in rats. OBJECTIVE: This study was designed to examine the effects of peripheral (intraperitoneal) administration of Cholecystokinin-ASODN on anxiety-like and learning behaviors in rats, in general and in a pre-experiment stress paradigm. METHODS: In the first study Cholecystokinin-ASODN was injected intraperitoneally to rats five times at 24-h intervals. Control groups received injections of either a scrambled oligodeoxynucleotide (ScrODN) or vehicle. On the sixth day, the rats were assessed in the elevated plus-maze paradigm and in the Morris water maze. In the second study, rats were pre-exposed to a cat for 10 min as a model for psychological stress, and then treated with intraperitoneal Cholecystokinin-ASODN and tested in both paradigms. RESULTS: The results show that for intact rats, intraperitoneal Cholecystokinin-ASODN significantly increased anxiety-like behavior and impaired retention performance in the Morris water maze, compared to both control groups. In stressed rats, Cholecystokinin-ASODN reduced anxiety-like behaviors in the plus-maze and improved performance in the water maze compared with controls. CONCLUSIONS: These results indicate that the anxiolytic effect of intraperitoneal Cholecystokinin-ASODN may be dependent on the baseline endogenous level of stress (i.e., on the Cholecystokinin levels). Basal endogenous levels of Cholecystokinin, as well as exogenous dosage of Cholecystokinin agonists and/or anxiolytic agents, appear to play an important role in the expression and/or control of anxiety-related behaviors in rats.

Neuroendocrine control of intestinal mucosal mast cells under physiological conditions.

Mast cells are involved in the pathogenesis of both allergies to food and inflammatory bowel disorders. In addition, there are several lines of evidence suggesting that mucosal mast cells also respond to intraluminal stimuli. Our aim was to identify neuroendocrine stimuli that could modify mucosal mast cell activity in the rat. Anaesthetized rats were prepared for duodenal perfusion and mast cell activation was measured by analysis of RMCP II concentration in the duodenal perfusate. Either buffered saline solution or a 5% ovalbumin hydrolysate (OVH) solution was infused into the duodenum. Subdiaphragmatic vagotomy or afferent ablation by intraluminal treatment with capsaicin diminished RMCP II concentration in basal conditions and significantly reduced the response to OVH, which in control animals induced a three-fold increase of the protease. The noradrenergic blockers phentholamine and propranolol significantly diminished RMCP II concentration in basal conditions and completely blocked the response to OVH. Intravenous infusion of cholecystokinin-related peptides also induced a response of mast cells. However, the response was different depending on the peptide. CCK-8 induced a slight increase of RMCP II, whereas both CCK-33 and gastrin induced a significant decrease in mast cell activity. These results show that intraluminal content modulates mucosal mast cell activity by complex mechanisms involving both nervous and endocrine pathway.

Functional neuroanatomy of the ventral striopallidal GABA pathway. New sites of intervention in the treatment of schizophrenia.

Microdialysis was employed to investigate the dopamine, cholecystokinin (CCK) and neurotensin receptor regulation of ventral striopallidal GABA transmission by intra-accumbens perfusion with selective receptor ligands and monitoring local or ipsilateral ventral pallidal GABA release. In the dual probe studies intra-accumbens perfusion with the dopamine D1 and D2 receptor agonists SKF28293 and pergolide had no effect on ventral pallidal GABA, while both the D1 and D2 receptor antagonists SCH23390 and raclopride increased ventral pallidal GABA release. In contrast, intra-accumbens CCK decreased ventral pallidal GABA release and this was reversed by local perfusion with the CCK2 receptor antagonist PD134308 but not the CCK1 receptor antagonist L-364,718. In a single probe study intra-accumbens neurotensin increased local GABA release, which was strongly potentiated when the peptidase inhibitor phosphodiepryl 08 was perfused together with neurotensin. In addition, the neurotensin receptor antagonist SR48692 counteracted this phosphodiepryl 08 induced potentiated increased in GABA release. Taken together, these findings indicate that mesolimbic dopamine and CCK exert a respective tonic and phasic inhibition of ventral pallidal GABA release while the antipsychotic activity associated with D1 and D2 receptor antagonists may be explained by their ability to increase ventral striopallidal GABA transmission. Furthermore, the findings suggest that CCK2 receptor antagonists and neurotensin endopeptidase inhibitors may be useful antipsychotics.

Cholecystokinin (CCK) assays.

Cholecystokinin (CCK) is a peptide that acts as a peripheral hormone and as a central neurotransmitter. To date, two distinct receptors have been identified for CCK using structural and operational criteria; CCK1 and CCK2 (formerly CCKA and CCKB, respectively). In addition, there is the gastrin receptor found in the stomach which has a high structural similarity to the CCK2 receptor, but which displays a different pharmacology. This unit presents two methods for the quantification of selective agonists and antagonists at CCK1 receptors and an assay for CCK2 receptors. In the first tissue, the guinea-pig ileum longitudinal muscle with myenteric plexus, both CCK1 and CCK2 receptors are present in the same preparation. Each receptor is distinguished in this assay using selective agonists and antagonists against the unwanted receptor subtype. The second preparation, the guinea-pig gallbladder, is a classical preparation for studying CCK1 receptor-active compounds in the absence of CCK2 sites.

The effect of a cholecystokinin agonist on masseter muscle activity in the cat.

The CCK(B) agonist, pentagastrin, has been shown to induce anxiety in human subjects. Similarly, in the cat model, pentagastrin facilitates the expression of hypothalamically activated emotional behavior. Because hypothalamically mediated emotional behavior is also accompanied by increased EMG activity in the jaw muscles, these experiments were designed to examine the combined effects of administration of pentagastrin with activation of hypothalamically mediated emotional behavior upon jaw muscle EMG activity. Electrodes were carefully lowered through previously placed guide tubes overlying the hypothalamus until a behavioral site was identified. Following the establishment of a stable threshold current for eliciting an emotional behavioral response, the skin overlying the ipsilateral masseter muscle was shaved and cleaned with alcohol, and surface electrodes were attached. The EMG was recorded, amplified, digitized, and stored in a microcomputer for analysis. Mean power frequencies (MPF) and latencies for behavior were calculated for baseline prior to infusion of all drugs. Following this, the effects of intravenous administration of pentagastrin and the CCK(B) antagonist LY288513 on the MPF were determined. The infusion of the CCK(B) agonist, pentagastrin (0.77, 1.92, and 3.84 microg/kg), decreased MPF in a time-related manner. The effects of pentagastrin 1.92 microg/kg were blocked by the CCK(B) antagonist, LY288513 (6.54 microg/kg). In addition, the infusion of LY288513 alone increased MPF. These results are surprising in that pentagastrin's anxiogenic properties would appear to make it likely to facilitate motor activity, not suppress it.

Inhibition by CCK of ascending contraction elicited by mucosal stimulation in the duodenum of the rat.

CCK released by intraluminal stimuli modifies duodenal activity contributing to a decrease in gastric emptying. However, the neural mechanisms by which CCK controls motility are not well known. The aim of this study was to investigate the interaction between CCK and the enteric nervous system through the study of the effects of CCK-8 on ascending excitation. Anaesthetized Sprague-Dawley rats were prepared with a strain-gauge sutured to the duodenum wall. An electrode holder was placed in the duodenum lumen to elicit ascending contraction. Electrical field stimulation of the duodenal mucosa (4 Hz, 0.6 ms, 30 V) induced an ascending excitation which was blocked by hexamethonium (10 mg kg-1; n=5) and atropine (0.3 mg kg-1; n=5), but enlarged by L-NNA (10(-5) mol kg-1; n=5). CCK-8 (3 ¿ 10(-9) mol kg-1 10 min-1) blocked ascending excitation and an inhibition of the induced phasic activity was observed instead (n=18). Individually, none of the CCK receptor antagonists (L-364 718 and L-365 260) (3 ¿ 10(-7) mol kg-1; n=6 each) blocked the inhibition of ascending excitation induced by CCK-8. However, simultaneous infusion of both antagonists abolished CCK-8 effect on electrical stimulation (n=5). Similarly, none of the CCK-8 agonists (A-71623, A-71378, gastrin) modified the ascending excitation. In contrast, the simultaneous infusion of A-71623 and CCK-4 (n=4) induced an effect similar to CCK-8. In conclusion, CCK-8 blocked ascending contraction elicited by electrical field stimulation of duodenal mucosa by means of simultaneous activation of CCK-A and CCK-B receptors.

Effects of cholecystokinin peptides and GV 150013, a selective cholecystokininB receptor antagonist, on electrically evoked endogenous GABA release from rat cortical slices.

The effects of cholecystokinin (CCK) agonists and antagonists on spontaneous and electrically evoked endogenous GABA release from rat cerebral cortex slices were evaluated. Neither the nonselective and CCK(B)-selective receptor agonists CCK-8S (3-1,000 nM) and CCK-4 (3-1,000 nM), respectively, nor the selective CCK(B) and CCK(A) receptor antagonists GV 150013 (3-30 nM) and L-364,718 (10-100 nM), respectively, significantly affected spontaneous GABA release. CCK-8S (1-1,000 nM) and CCK-4 (1-1,000 nM) increased the electrically (5 and 10 Hz)-evoked GABA release. On the contrary, GV 150013 (10 and 30 nM) significantly decreased the electrically evoked GABA release only when the slices were stimulated at the higher 10 Hz frequency. The CCK-8S- and CCK-4-induced increases in electrically evoked GABA release were counteracted by GV 150013, but not by L-364,718. Furthermore, GV 150013 at 3 nM shifted to the right the CCK-4 concentration-response curve, whereas at the higher 10 nM concentration it dramatically flattened the curve. Finally, in cortical slices obtained from rats chronically treated with GV 150013, the concentration-response curve of CCK-4 was shifted to the left and the peak effect of the peptide was significantly higher than that observed in naive animals. These results suggest that CCK increases electrically evoked, but not spontaneous, endogenous GABA release from rat cortical slices, possibly by activating local CCK(B) receptors. In addition, chronic treatment with the novel CCK(B) receptor antagonist GV 150013 leads to an enhanced responsiveness of cortical slices to CCK-4 application.

Localization of CCK receptors in thalamic reticular neurons: a modeling study.

In an earlier experimental study, intracellular recording suggested that cholecystokinin (CCK) suppresses a K+ conductance in thalamic reticular (RE) neurons, yet the reversal potential of the CCK response, revealed using voltage clamp, was hyperpolarized significantly relative to the K+ equilibrium potential. Here, biophysical models of RE neurons were developed and used to test whether suppression of the K+ conductance, gK, can account for the CCK response observed in vitro and also to determine the likely site of CCK receptors on RE neurons. Suppression of gK in model RE neurons can reproduce the relatively hyperpolarized reversal potential of CCK responses found using voltage clamp if the voltage clamp becomes less effective at hyperpolarized potentials. Three factors would reduce voltage-clamp effectiveness in this model: the nonnegligible series resistance of the voltage-clamp electrode, a hyperpolarization-activated mixed cation current (Ih) in RE neurons, and the dendritic location of CCK-sensitive K+ channels. Although suppression of gK in the dendritic compartments of model RE neurons simulates both the magnitude and reversal potential of the CCK response, suppression of gK in just the somatic compartment of model RE neurons fails to do so. Thus the model predicts that CCK should effectively suppress K+ conductance RE neuron dendrites and thereby regulate burst firing in RE neurons. This may explain the potent effects of CCK on intrathalamic oscillations in vitro.

Long-term effects of CCK-agonist and -antagonist on food intake and body weight in Zucker lean and obese rats.

The present study evaluates long-term effects of the CCK-agonist caerulein and the CCK-A antagonist loxiglumide in obese and lean Zucker rats. Caerulein and loxiglumide altered food intake neither in obese nor in lean rats. By as yet unknown mechanisms, however, weight increase was accelerated by loxiglumide and reduced by caerulein in obese and lean rats. Caerulein increased pancreatic weight only in lean but not in obese rats. Thus, obese rats show a resistance of pancreatic CCK-A receptors. The failure of CCK-agonist and -antagonist to alter food intake suggests that this CCK-resistance is not responsible for obesity in the genetically altered rats.