Autoradiographic Localization of Cholecystokinin A and B Receptors in Rat Brain Using [125I]d-Tyr25 (Nle28,31)-CCK 25 - 33S

The critical role of CCK in the regulation of food intake and diet-induced obesity

In 1973, Gibbs, Young, and Smith showed that exogenous cholecystokinin (CCK) administration reduces food intake in rats. This initial report has led to thousands of studies investigating the physiological role of CCK in regulating feeding behavior. CCK is released from enteroendocrine I cells present along the gastrointestinal (GI) tract. CCK binding to its receptor CCK1R leads to vagal afferent activation providing post-ingestive feedback to the hindbrain. Vagal afferent neurons' (VAN) sensitivity to CCK is modulated by energy status while CCK signaling regulates gene expression of other feeding related signals and receptors expressed by VAN. In addition to its satiation effects, CCK acts all along the GI tract to optimize digestion and nutrient absorption. Diet-induced obesity (DIO) is characterized by reduced sensitivity to CCK and every part of the CCK system is negatively affected by chronic intake of energy-dense foods. EEC have recently been shown to adapt to diet, CCK1R is affected by dietary fats consumption, and the VAN phenotypic flexibility is lost in DIO. Altered endocannabinoid tone, changes in gut microbiota composition, and chronic inflammation are currently being explored as potential mechanisms for diet driven loss in CCK signaling. This review discusses our current understanding of how CCK controls food intake in conditions of leanness and how control is lost in chronic energy excess and obesity, potentially perpetuating excessive intake.

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.

Presynaptically mediated effects of cholecystokinin-8 on the excitability of area postrema neurons in rat brain slices

Cholecystokinin (CCK) is a well-known gut hormone that shows anorexigenic effects via action at peripheral and central receptors. CCK is also widely distributed throughout the mammalian brain and appears to function as a neurotransmitter and neuromodulator. The area postrema is one of the circumventricular organs, located on the dorsal surface of the medulla oblongata at the caudal end of the fourth ventricle. Blood vessels in the area postrema lack a blood brain barrier, offering specific central neural elements unique access to circulating substances. Immunohistochemical studies show CCK-A receptors in the area postrema, and we reported CCK-sensitive area postrema neurons. However, the receptive mechanism of CCK in area postrema neurons still remains unexplained. We investigated the responses of area postrema neurons to agonists and antagonists of CCK receptors using whole cell and perforated patch-clamp recordings in rat brain slices. The application of CCK-8 elicited excitatory responses, such as increases in the frequency of mEPSCs (miniature excitatory postsynaptic currents), a shift toward larger amplitude mEPSCs, and increases in the frequency of action potentials. These changes were found mostly in cells not displaying the hyperpolarization-activated cation current (Ih), except for small excitatory changes in a minority of Ih-positive neurons. Tonic inward currents or an inhibitory response to CCK-8 were never seen. Analysis of the amplitude of mEPSCs before and after the administration of CCK-8 indicated the responses mediated via the presynaptic receptors. The effect of CCK-8 was abolished in the presence of CNQX (AMPA type glutamate receptor antagonist). In the presence of lorglumide (a selective CCK-A receptor antagonist), CCK-8-induced excitatory responses were inhibited. No cells responded to the administration of non-sulfated CCK-8 (CCK-8NS, a selective CCK-B receptor agonist). We conclude that CCK-8 exerts its action via presynaptic CCK-A receptors to facilitate glutamate release onto Ih-negative area postrema cells.

Enteroendocrine hormones - central effects on behavior

A number of appetite-regulating gut hormones alter behaviors linked to reward, anxiety/mood, memory and cognitive function, although for some of these (notably GLP-1 and CCK) the endogenous signal may be CNS-derived. From a physiological perspective it seems likely that these hormones, whose secretion is altered by nutritional status and by bariatric weight loss surgery, orchestrate neurobiological effects that are integrated and linked to feeding/metabolic control. Consistent with a role in hunger and meal initiation, ghrelin increases motivated behavior for food and, when food is not readily available, decreases behaviors in anxiety tests that would otherwise hinder the animal from finding food. Of the many anorexigenic signals, GLP-1 and PYY have been linked to a suppressed reward function and CCK (and possibly GLP-1) to increased anxiety-like behavior.

Cholecystokinin: an excitatory modulator of mitral/tufted cells in the mouse olfactory bulb

Cholecystokinin (CCK) is widely distributed in the brain as a sulfated octapeptide (CCK-8S). In the olfactory bulb, CCK-8S is concentrated in two laminae: an infraglomerular band in the external plexiform layer, and an inframitral band in the internal plexiform layer (IPL), corresponding to somata and terminals of superficial tufted cells with intrabulbar projections linking duplicate glomerular maps of olfactory receptors. The physiological role of CCK in this circuit is unknown. We made patch clamp recordings of CCK effects on mitral cell spike activity in mouse olfactory bulb slices, and applied immunohistochemistry to localize CCK_B receptors. In cell-attached recordings, mitral cells responded to 300 nM –1 µM CCK-8S by spike excitation, suppression, or mixed excitation-suppression. Antagonists of GABA_A and ionotropic glutamate receptors blocked suppression, but excitation persisted. Whole-cell recordings revealed that excitation was mediated by a slow inward current, and suppression by spike inactivation or inhibitory synaptic input. Similar responses were elicited by the CCK_B receptor-selective agonist CCK-4 (1 µM). Excitation was less frequent but still occurred when CCK_B receptors were blocked by LY225910, or disrupted in CCK_B knockout mice, and was also observed in CCK_A knockouts. CCK_B receptor immunoreactivity was detected on mitral and superficial tufted cells, colocalized with Tbx21, and was absent from granule cells and the IPL. Our data indicate that CCK excites mitral cells postsynaptically, via both CCK_A and CCK_B receptors. We hypothesize that extrasynaptic CCK released from tufted cell terminals in the IPL may diffuse to and directly excite mitral cell bodies, creating a positive feedback loop that can amplify output from pairs of glomeruli receiving sensory inputs encoded by the same olfactory receptor. Dynamic plasticity of intrabulbar projections suggests that this could be an experience-dependent amplification mechanism for tuning and optimizing olfactory bulb signal processing in different odor environments.

Olfaction under metabolic influences

Recently published work and emerging research efforts have suggested that the olfactory system is intimately linked with the endocrine systems that regulate or modify energy balance. Although much attention has been focused on the parallels between taste transduction and neuroendocrine controls of digestion due to the novel discovery of taste receptors and molecular components shared by the tongue and gut, the equivalent body of knowledge that has accumulated for the olfactory system, has largely been overlooked. During regular cycles of food intake or disorders of endocrine function, olfaction is modulated in response to changing levels of various molecules, such as ghrelin, orexins, neuropeptide Y, insulin, leptin, and cholecystokinin. In view of the worldwide health concern regarding the rising incidence of diabetes, obesity, and related metabolic disorders, we present a comprehensive review that addresses the current knowledge of hormonal modulation of olfactory perception and how disruption of hormonal signaling in the olfactory system can affect energy homeostasis.

Modulation of acetylcholine release by cholecystokinin in striatum: receptor specificity; role of dopaminergic neuronal activity

Cholecystokinin, a neuroactive peptide functioning as a neurotransmitter and neuromodulator in the central nervous system, mediates a number of processes and is implicated in neurological and psychiatric disorders such as Parkinson's disease, anxiety and schizophrenia. Striatum is one of the brain structures with the highest concentrations of CCK in the brain, rich in CCK receptors as well. The physiological effect of CCK on cholinergic interneurons, which are the major interneurons in striatum and the modulatory interactions which exist between dopamine, acetylcholine and cholecystokinin in this brain structure are still unclear. We studied the effect of cholecystokinin octapeptide (CCK-8) on the release of acetylcholine (ACh) from striatal slices of the rat brain. CCK-8 (0.01-0.1μM) showed no statistically significant effect on the basal but enhanced dose-dependently the electrically (2Hz)-evoked release of [(3)H]ACh. When slices were preperfused with 100μM sulpiride, a selective dopamine D(2) receptor antagonist, the CCK-8 (0.01μM) effect on electrically stimulated ACh release was increased nearly 2-fold. A similar increase was observed after depletion of endogenous dopamine (DA) from nigro-striatal dopaminergic neurons with 6-hydroxydopamine (6-OHDA) (2× 250μg/animal, i.c.v.). Furthermore in the presence of dopamine (100μM) or apomorphine (10μM), the prototypical DA receptor agonist, CCK-8 (0.01μM) failed to enhance the stimulation-evoked release of [(3)H]ACh. The D(2) receptor agonist quinpirol (1μM) abolished the CCK-8 effect on electrically stimulated ACh release as well. The increase in electrically induced [(3)H]ACh release produced by 0.01μM CCK-8 was antagonized by d,l loxiglumide (CR 1505), 10μM, a non-peptide CCK-A receptor antagonist and by Suc-Tyr-(OSO3)-Met-Gly-Trp-Met-Asp-β-phenethyl-amide (GE-410), 1μM, a peptide CCK-A receptor antagonist. The antagonistic effect of GE-410 on the CCK-8-potentiated, electrically induced release of [(3)H]ACh was studied in striatum for the first time. CAM 1028 (10μM), a CCK-B receptor antagonist, also prevented the potentiating effect of CCK-8 (0.01μM) on electrically stimulated release of [(3)H]ACh. The presented results indicate that (i) CCK-8 is capable of increasing ACh elicited by field electrical stimulation in striatum; (ii) CCK-8 is more effective in its ACh-stimulating effect when dopaminergic activity in striatum is blocked i.e. CCK-8-facilitated release of electrically induced ACh from cholinergic interneurons in the striatum is under the inhibitory control of the tonic activity of dopamine from the nigrostriatal pathway; (iii) the enhancing effect of CCK-8 on electrically evoked ACh release is mediated through both CCK-A and CCK-B cholecystokinin receptors located most likely on the cell bodies of cholinergic interneurons in striatum.

Neuronal network of panic disorder: the role of the neuropeptide cholecystokinin

Panic disorder (PD) is characterized by panic attacks, anticipatory anxiety and avoidance behavior. Its pathogenesis is complex and includes both neurobiological and psychological factors. With regard to neurobiological underpinnings, anxiety in humans seems to be mediated through a neuronal network, which involves several distinct brain regions, neuronal circuits and projections as well as neurotransmitters. A large body of evidence suggests that the neuropeptide cholecystokinin (CCK) might be an important modulator of this neuronal network. Key regions of the fear network, such as amygdala, hypothalamus, peraqueductal grey, or cortical regions seem to be connected by CCKergic pathways. CCK interacts with several anxiety-relevant neurotransmitters such as the serotonergic, GABA-ergic and noradrenergic system as well as with endocannabinoids, NPY and NPS. In humans, administration of CCK-4 reliably provokes panic attacks, which can be blocked by antipanic medication. Also, there is some support for a role of the CCK system in the genetic pathomechanism of PD with particularly strong evidence for the CCK gene itself and the CCK-2R (CCKBR) gene. Thus, it is hypothesized that genetic variants in the CCK system might contribute to the biological basis for the postulated CCK dysfunction in the fear network underlying PD. Taken together, a large body of evidence suggests a possible role for the neuropeptide CCK in PD with regard to neuroanatomical circuits, neurotransmitters and genetic factors. This review article proposes an extended hypothetical model for human PD, which integrates preclinical and clinical findings on CCK in addition to existing theories of the pathogenesis of PD.

Increased cholecystokinin labeling in the hippocampus of a mouse model of epilepsy maps to spines and glutamatergic terminals

The neuropeptide cholecystokinin (CCK) is abundant in the CNS and is expressed in a subset of inhibitory interneurons, particularly in their axon terminals. The expression profile of CCK undergoes numerous changes in several models of temporal lobe epilepsy. Previous studies in the pilocarpine model of epilepsy have shown that CCK immunohistochemical labeling is substantially reduced in several regions of the hippocampal formation, consistent with decreased CCK expression as well as selective neuronal degeneration. However, in a mouse pilocarpine model of recurrent seizures, increases in CCK-labeling also occur and are especially striking in the hippocampal dendritic layers of strata oriens and radiatum. Characterizing these changes and determining the cellular basis of the increased labeling were the major goals of the current study. One possibility was that the enhanced CCK labeling could be associated with an increase in GABAergic terminals within these regions. However, in contrast to the marked increase in CCK-labeled structures, labeling of GABAergic axon terminals was decreased in the dendritic layers. Likewise, cannabinoid receptor 1-labeled axon terminals, many of which are CCK-containing GABAergic terminals, were also decreased. These findings suggested that the enhanced CCK labeling was not due to an increase in GABAergic axon terminals. The subcellular localization of CCK immunoreactivity was then examined using electron microscopy, and the identities of the structures that formed synaptic contacts were determined. In pilocarpine-treated mice, CCK was observed in dendritic spines and these were proportionally increased relative to controls, whereas the proportion of CCK-labeled terminals forming symmetric synapses was decreased. In addition, CCK-positive axon terminals forming asymmetric synapses were readily observed in these mice. Double labeling with vesicular glutamate transporter 1 and CCK revealed colocalization in numerous terminals forming asymmetric synapses, confirming the glutamatergic identity of these terminals. These data raise the possibility that expression of CCK is increased in hippocampal pyramidal cells in mice with recurrent, spontaneous seizures.

Cholecystokinin exerts an effect via the endocannabinoid system to inhibit GABAergic transmission in midbrain periaqueductal gray

Cholecystokinin modulates pain and anxiety via its functions within brain regions such as the midbrain periaqueductal gray (PAG). The aim of this study was to examine the cellular actions of cholecystokinin on PAG neurons. Whole-cell patch clamp recordings were made from rat midbrain PAG slices in vitro to examine the postsynaptic effects of cholecystokinin and its effects on synaptic transmission. Sulfated cholecystokinin-(26-33) (CCK-S, 100-300 nM), but not non-sulfated cholecystokinin-(26-33) (CCK-NS, 100-300 nM) produced an inward current in a sub-population of opioid sensitive and insensitive PAG neurons, which did not reverse over a range of membrane potentials. The CCK-S-induced current was abolished by the CCK1 selective antagonist devazepide (100 nM), but not by the CCK2 selective antagonists CI988 (100 nM, 1 μM) and LY225910 (1 μM). CCK-S, but not CCK-NS produced a reduction in the amplitude of evoked GABA(A)-mediated inhibitory postsynaptic currents (IPSCs) and an increase in the evoked IPSC paired-pulse ratio. By contrast, CCK-S had little effect on the rate and amplitude of TTX-resistant miniature IPSCs under basal conditions and when external K(+) was elevated. The CCK-S-induced inhibition of evoked IPSCs was abolished by the cannabinoid CB1 receptor antagonist AM251 (3 μM), the mGluR5 antagonist MPEP (10 μM) and the 1, 2-diacylglycerol lipase (DAGLα) inhibitor tetrahydrolipstatin (10 μM). In addition, CCK-S produced an increase in the rate of spontaneous non-NMDA-mediated, TTX-dependent excitatory postsynaptic currents (EPSCs). These results suggest that cholecystokinin produces direct neuronal depolarisation via CCK1 receptors and inhibits GABAergic synaptic transmission via action potential-dependent release of glutamate and mGluR5-induced endocannabinoid signaling. Thus, cholecystokinin has cellular actions within the PAG that can both oppose and reinforce opioid and cannabinoid modulation of pain and anxiety within this brain structure.

Cholecystokinin action on layer 6b neurons in somatosensory cortex

Layer 6b in neocortex is a distinct sublamina at the ventral portion of layer 6. Corticothalamic projections arise from 6b neurons, but few studies have examined the functional properties of these cells. In the present study we examined the actions of cholecystokinin (CCK) on layer 6b neocortical neurons using whole-cell patch clamp recording techniques. We found that the general CCK receptor agonist CCK8S (sulfated CCK octapeptide) strongly depolarized the neurons, and this action persisted in the presence of tetrodotoxin, suggesting a postsynaptic site of action. The excitatory actions of CCK8S were mimicked by the selective CCK(B) receptor agonist CCK4, and attenuated by the selective CCK(B) receptor antagonist L365260, indicating a role for CCK(B) receptors. Voltage-clamp recordings revealed that CCK8S produced a slow inward current associated with a decreased conductance with a reversal potential near the K(+) equilibrium potential. In addition, intracellular cesium also blocked the inward current, suggesting the involvement of a K(+) conductance, likely K(leak). Our data indicate that CCK, acting via CCK(B) receptors, produces a long-lasting excitation of layer 6b neocortical neurons, and this action may play a critical role in modulation of corticothalamic circuit activity.

Role of the amygdaloid cholecystokinin (CCK)/gastrin-2 receptors and terminal networks in the modulation of anxiety in the rat. Effects of CCK-4 and CCK-8S on anxiety-like behaviour and [3H]GABA release

The amygdala plays a key role in fear and anxiety. The intercalated islands are clusters of glutamate-responsive GABAergic neurons rich in cholecystokinin (CCK)-2 receptors which control the trafficking of nerve impulses from the cerebral cortex to the central nucleus of amygdala. In this study, the nature of the CCK-glutamate-GABA interactions within the rat rostral amygdala, and their relevance for anxiety, were studied. CCK/gastrin-like immunoreactive nerve terminals were found to be mainly restricted to the paracapsular intercalated islands and the rostrolateral part of the main intercalated island. Behaviourally, the bilateral microinjection of CCK-4 (0.043-4.3 pmol/side) or CCK-8S (4.3 pmol/side) into the rostrolateral amygdala reduced the open-arm exploration in the elevated plus-maze without affecting locomotion. In contrast, neither CCK-4 nor CCK-8S (0.043-4.3 pmol/side) had any effects in the shock-probe burying test as compared with their saline-treated controls. Biochemically, CCK-4 (0.3 and 1.5 microm), unlike CCK-8S, enhanced significantly the K(+)-stimulated release of [(3)H]GABA from amygdala slices. These effects were fully prevented by prior superfusion of the slices with either the selective CCK-2 receptor antagonist CR2945 (3 microm), or 6,7-dinitroquinoxaline-2,3(1H,4H)-dione (DNQX), 10 microm, a glutamatergic (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptor antagonist. It is suggested that CCK modulates glutamate-GABA mechanisms by acting on CCK-2 receptors via volume transmission occurring at the level of the basolateral amygdaloid nucleus and/or by synaptic or perisynaptic volume transmission in the region of the rostrolateral main and paracapsular intercalated islands, resulting in subsequent disinhibition of the central amygdaloid nucleus and anxiety or panic-like behaviour.

Cholecystokinin inhibits endocannabinoid-sensitive hippocampal IPSPs and stimulates others

Cholecystokinin (CCK) is the most abundant neuropeptide in the central nervous system. In the hippocampal CA1 region, CCK is co-localized with GABA in a subset of interneurons that synapse on pyramidal cell somata and apical dendrites. CCK-containing interneurons also uniquely express a high level of the cannabinoid receptor, CB(1), and mediate the retrograde signaling process called DSI. Reported effects of CCK on inhibitory post-synaptic potentials (IPSPs) in hippocampus are inconsistent, and include both increases and decreases in activity. Hippocampal interneurons are very heterogeneous, and these results could be reconciled if CCK affected different interneurons in different ways. To test this prediction, we used sharp microelectrode recordings from pyramidal cells with ionotropic glutamate receptors blocked, and investigated the effects of CCK on pharmacologically distinct groups of IPSPs during long-term recordings. We find that CCK, acting via the CCK(2) receptor, increases some IPSPs and decreases others, and most significantly, that the affected IPSPs can be classified into two groups by their pharmacological properties. IPSPs that are increased by carbachol (CCh-sIPSPs), are depressed by CCK, omega-conotoxin GVIA, and endocannabinoids. IPSPs that are enhanced by CCK (CCK-sIPSPs) are blocked by omega-agatoxin IVA, and are unaffected by carbachol or endocannabinoids. Interestingly, a CCK(2) antagonist enhances CCh-sIPSPs, suggesting normally they may be partially suppressed by endogenous CCK. In summary, our data are compatible with the hypothesis that CCK has opposite actions on sIPSPs that originate from functionally distinct interneurons.

Genes involved in obesity: Adipocytes, brain and microflora

The incidence of obesity and related metabolic disorders such as cardiovascular diseases and type 2 diabetes, are reaching worldwide epidemic proportions. It results from an imbalance between caloric intake and energy expenditure leading to excess energy storage, mostly due to genetic and environmental factors such as diet, food components and/or way of life. It is known since long that this balance is maintained to equilibrium by multiple mechanisms allowing the brain to sense the nutritional status of the body and adapt behavioral and metabolic responses to changes in fuel availability. In this review, we summarize selected aspects of the regulation of energy homeostasis, prevalently highlighting the complex relationships existing between the white adipose tissue, the central nervous system, the endogenous microbiota, and nutrition. We first describe how both the formation and functionality of adipose cells are strongly modulated by the diet before summarizing where and how the central nervous system integrates peripheral signals from the adipose tissue and/or the gastro-intestinal tract. Finally, after a short description of the intestinal commensal flora, rangingfrom its composition to its importance in immune surveillance, we enlarge the discussion on how nutrition modified this perfectly well-balanced ecosystem.

Centrally administered PD 140.548 N-methyl-d-glucamine prevents the autonomic responses to duodenal pain in sheep

Cholecystokinin (CCK) released in the CNS inhibits the analgesic action of exogenous opioids and may antagonize analgesia resulting from the activation of an endogenous pain inhibitory system. The aim of this study was to analyse the central action of PD 140.548 N-methyl-D-glucamine--a peptide antagonist of a specific peripheral type CCK receptor--on animal behaviour, catecholamines (CA) and cortisol concentration, as well as clinical symptoms of visceral pain induced by duodenal distension (DD). A 5 min distension of the duodenum wall, using a 10 cm long balloon filled with 40 and/or 80 ml of water (DD 40 and/or DD 80) at animal body temperature, produced a significant increase in plasma CA and cortisol levels, an increase in the heart rate, hyperventilation and other clinical symptoms (inhibition of rumen motility, bleating, teeth grinding, prostration, urination, defecation) that may be related to pain, proportionally to the degree of intestinal distension. Intracerebroventricular administration of PD 140.548 at the dose of 1 or/and 2 mg in toto 10 min before applying DD 40 completely blocked the increase in blood plasma cortisol, epinephrine (E), norepinephrine (NE) and dopamine (DA) concentration. It is suggested that the central inhibitory action of CCK antagonist on the cortisol and catecholamine release produced by visceral pain is due to the inhibition of peripheral CCK1 type receptors in the central centrifugal descending pain facilitatory system in sheep perhaps via the hypothalamic-pituitary-adrenal axis.

Estrogen and CCK1 receptor modification of mu-opioid receptor binding in the cortex of female rats

Cholecystokinin (CCK) in the nervous system has effects opposite to those of opioids. However, the mechanism by which CCK opposes the effect of opioids at the receptor or cellular level is still unknown. In the brain, distributions of CCK receptors and opioid receptors have been demonstrated to overlap. The present study was undertaken to determine the mechanism of CCK-opioid interactions in the cortex of ovariectomized rats. Furthermore, because estrogen is a powerful regulator of CCK and opioid activity, we examined whether estrogen state also modulates the interactions of these neuropeptides. mu-Opioid (MOP) receptor binding was examined in cortical membranes that were preincubated with CCK-8S and CCK receptor agonist and antagonist followed with 3H-DAMGO. Pharmacological results revealed that CCK-8S suppressed 3H-DAMGO binding in cortical membranes of ovariectomized rats. The same result was obtained using a CCK1 receptor agonist (JMV-180), whereas a CCK2 receptor agonist (CCK-4) failed to suppress 3H-DAMGO binding. Antagonism of the CCK1 receptor by JMV-179 blocked both CCK-8S and JMV-180 suppression of 3H-DAMGO binding. Furthermore, estrogen treatment to female rats resulted in a suppression of 3H-DAMGO binding in cortical membranes. These results demonstrate an estrogen regulation of the MOP receptor and a protein-protein interaction between CCK1 receptor and MOP receptor.

Cholecystokinin-2 receptors couple to cAMP–protein kinase A to depress excitatory synaptic currents in rat nucleus accumbens in vitro

We recently reported that the activation of cholecystokinin-2 receptors depress evoked excitatory postsynaptic currents (EPSCs) in nucleus accumbens (NAc) indirectly through γ-aminobutyric acid (GABA) acting on γ-aminobutyric acid-B (GABAB) receptors. Here, we determined the second messenger system that couples cholecystokinin-2 receptors to the observed synaptic depression. Using in vitro forebrain slices of rats and whole-cell patch recording, we tested the hypothesis that cholecystokinin-2 receptors are coupled to cAMP and protein kinase A signaling pathway. Cholecystokinin-8S induced inward currents and depressed evoked EPSCs. Forskolin, an activator of adenylyl cyclase and rolipram that is an inhibitor of phosphodiesterase type IV, independently increased EPSC amplitude and blocked the inward current and synaptic depression induced by cholecystokinin-8S. Furthermore, the membrane-permeable cAMP analog, 8-bromo-cAMP, blocked the cholecystokinin-8S effects. H89, a protein kinase A inhibitor, also blocked cholecystokinin-8S effects. However, depression of the evoked EPSC by baclofen, a GABABreceptor agonist, was not blocked by H89 or forskolin. These findings indicate that cholecystokinin-2, but not GABAB, receptors are coupled to the adenylyl cyclase – cAMP – protein kinase A signaling pathway in the NAc to induce inward currents and cause synaptic depression.

Cortical sources of CRF, NKB, and CCK and their effects on pyramidal cells in the neocortex

In order to investigate how neuropeptide transmission can modulate the neocortical network, we mapped the expression of neurokinin (NK) B, cholecystokinin (CCK), and corticotropin-releasing factor (CRF) and their receptors to neuronal types using patch-clamp and single-cell reverse transcription-polymerase chain reaction in acute slices of rat neocortex. Classification of neurons by unsupervised clustering based on the analysis of multiple electrophysiological and molecular properties disclosed 3 GABAergic interneuron clusters and 1 pyramidal cell cluster. The 3 neuropeptides were expressed in a cluster of interneurons characteristically expressing vasoactive intestinal peptide. CRF was additionally found in a cluster containing almost exclusively somatostatin-expressing interneurons, whereas CCK was present in all clusters. The respective receptors of these peptides, NK-3, CCK-B, and CRF-1, were essentially expressed in pyramidal cells. At -60 mV, pyramidal cells were weakly depolarized by each of these peptides. When pyramidal neurons were maintained to about 5 mV below spike threshold, depolarization induced by each peptide resulted in a long-lasting action potential discharge. Neuropeptide effects were prevented by selective antagonists of NK-3, CCK-B, and CRF-1 receptors. These results suggest that pyramidal neurons are the primary target of NKB, CCK, and CRF in the neocortex. They further indicate that specific interneuron types coordinate the release of these peptides and can induce a long-lasting increase of the excitability of the neocortical network.

Cholecystokinin and endogenous opioid peptides: interactive influence on pain, cognition, and emotion

It is well documented that stressful life experiences contribute to the etiology of human mood disorders. Cholecystokinin (CCK) is a neuropeptide found in high concentrations throughout the central nervous system, where it is involved in numerous physiological functions. A role for CCK in the induction and persistence of anxiety and major depression appears to be conspicuous. While increased CCK has been associated with motivational loss, anxiety and panic attacks, an increase in mesocorticolimbic opioid availability has been associated with coping and mood elevation. The close neuroanatomical distribution of CCK with opioid peptides in the limbic system suggests that there may be an opioid-CCK link in the modulation and expression of anxiety or stressor-related behaviors. In effect, while CCK induces relatively protracted behavioral disturbances in both animal and human subjects following stressor applications, opioid receptor activation may change the course of psychopathology. The antagonistic interaction of CCK and opioid peptides is evident in psychological disturbances as well as stress-induced analgesia. There appears to be an intricate balance between the memory-enhancing and anxiety-provoking effects of CCK on one hand, and the amnesic and anxiolytic effects of opioid peptides on the other hand. Potential anxiogenic and mnemonic influences of site-specific mesocorticolimbic CCK and opioid peptide availability, the relative contributions of specific CCK and opioid receptors, as well as the time course underlying neuronal substrates of long-term behavioral disturbances as a result of stressor manipulations, are discussed.

Cholecystokinin and Adrenal‐Cortex Secretion

Cholecystokinin, or CCK, is a 33-amino acid peptide, originally considered a gut hormone, that acts via two subtypes of receptors, named CCK1-R and CCK2-R. CCK, along with its receptors, has been subsequently localized in the central nervous system, where it exerts, among other fuctions, antiorexinogenic actions. In this survey, we describe findings indicating that CCK, similar to other peptides modulating food intake (e.g., neuropeptide Y, leptin, and orexins), is also able to regulate the function of the hypothalamo-pituitary-adrenal axis, acting on both its central and peripheral branches. CCK stimulates aldosterone secretion via specific receptors (CCK1-Rs and CCK2-Rs in rats, and CCK2-Rs in humans) located in zona glomerulosa cells and coupled to the adenylate cyclase-dependent signaling cascade; and enhances glucocorticoid secretion from zona fasciculata-reticularis cells via an indirect mechanism mainly involving the CCK2-R-mediated stimulation of corticotropin-releasing hormone-dependent ACTH release.

Stomach-brain communication by vagal afferents in response to luminal acid backdiffusion, gastrin, and gastric acid secretion

Vagal afferents play a role in gut-brain signaling of physiological and pathological stimuli. Here, we investigated how backdiffusion of luminal HCl or NH(4)OH and pentagastrin-stimulated acid secretion interact in the communication between rat stomach and brain stem. Rats were pretreated intraperitoneally with vehicle or appropriate doses of cimetidine, omeprazole, pentagastrin, dexloxiglumide (CCK(1) receptor antagonist), and itriglumide (CCK(2) receptor antagonist) before intragastric administration of saline or backdiffusing concentrations of HCl or NH(4)OH. Two hours later, neuronal activation in the nucleus of the solitary tract (NTS) and area postrema was visualized by c-Fos immunohistochemistry. Exposure of the rat gastric mucosa to HCl (0.15-0.5 M) or NH(4)OH (0.1-0.3 M) led to a concentration-dependent expression of c-Fos in the NTS, which was not related to gender, gastric mucosal injury, or gastropyloric motor alterations. The c-Fos response to HCl was diminished by cimetidine and omeprazole, enhanced by pentagastrin, and left unchanged by dexloxiglumide and itriglumide. Pentagastrin alone caused an omeprazole-resistant expression of c-fos, which in the NTS was attenuated by itriglumide and prevented by dexloxiglumide but in the area postrema was reduced by dexloxiglumide and abolished by itriglumide. We conclude that vagal afferents transmit physiological stimuli (gastrin) and pathological events (backdiffusion of luminal HCl or NH(4)OH) from the stomach to the brain stem. These communication modalities interact because, firstly, acid secretion enhances afferent signaling of gastric acid backdiffusion and, secondly, gastrin activates NTS neurons through stimulation of CCK(1) receptors on vagal afferents and of CCK(2) receptors on area postrema neurons projecting to the NTS.

Cholecystokinin activates CCKB receptors to excite cells and depress EPSCs in the rat rostral nucleus accumbens in vitro

The peptide cholecystokinin (CCK) is abundant in the rat nucleus accumbens (NAc). Although it is colocalized with dopamine (DA) in afferent terminals in this region, neurochemical and behavioural reports are equally divided as to whether CCK enhances or diminishes DA's actions in this nucleus. To better understand the role of this peptide in the physiology of the NAc, we examined the effects of CCK on excitatory synaptic transmission and tested whether these are dependent on DA and/or other neuromodulators. Using whole-cell recording in rat forebrain slices containing the NAc, we show that sulphated CCK octapeptide (CCK-8S), the endogenously active neuropeptide, consistently depolarized cells and depressed evoked excitatory postsynaptic currents (EPSCs) in the rostral NAc. It caused a reversible, dose-dependent decrease in evoked EPSC amplitude that was accompanied by an increase in the decay constant of the EPSC but with no apparent change in paired pulse ratio. It was mimicked by unsulphated CCK-8 (CCK-8US), a CCK(B) receptor-selective agonist, and blocked by LY225910, a CCK(B) receptor-selective antagonist. Both CCK-8S and CCK-8US induced an inward current with a reversal potential around -90 mV that was accompanied by an increase in input resistance and action potential firing. The CCK-8S-induced EPSC depression was slightly reduced in the presence of SCH23390 but not in the presence of sulpiride or 8-cyclopentyltheophylline. By contrast, it was completely blocked by CGP55845, a potent GABA(B) receptor-selective antagonist. These results indicate that CCK excites NAc cells directly while depressing evoked EPSCs indirectly, mainly through the release of GABA.

Suckling-induced activation of neuronal input to the dorsomedial nucleus of the hypothalamus: possible candidates for mediating the activation of DMH neuropeptide Y neurons during lactation

Activation of the neuropeptide Y (NPY) neuronal system in the dorsomedial nucleus of the hypothalamus (DMH) during lactation in the rat is in part due to neural impulses arising from the suckling stimulus. However, the afferent neuronal input to the DMH that is activated during lactation and is responsible for activation of NPY neurons is currently unknown. Previously, using cFos as a marker for neuronal activation, we identified several brain areas in the lactating animals that were activated by the suckling stimulus. Thus, the objective of the present study was to determine if any of these suckling activated areas project directly to the DMH. The retrograde tracer, fluorogold (FG), was injected into the DMH on day 4 postpartum. FG-injected lactating rats were then deprived of their eight-pup litters on day 9 postpartum, and 48 h later, the pups were returned to the females to reinitiate the suckling stimulus for 90 min and induce cFos expression. The animals were then perfused and the brains were subjected to double-label immunohistochemistry to visualize both FG- and cFos-positive cells. Substantial numbers of FG/cFos double-labeled cells were found in forebrain regions, including the preoptic area, lateral septal nucleus, ventral subiculum, and supramammillary nucleus, and in brainstem regions, including the lateral parabrachial nucleus, periaqeductal gray, and ventrolateral medulla. In conclusion, these areas are potentially important candidates for mediating the activation of the NPY neuronal system in the DMH during lactation.

Regulation of cholecystokinin release from central nerve terminals

The high abundance of the cholecystokinin octapeptide in various brain regions is expressed by involvement of this neuropeptide in diverse brain functions. This peptide is mostly, if not always, co-localized with classic transmitters in central nerve terminals. Since the functions of the coexisting transmitters are often different, differential regulation of their release is obvious. This differentiation is realized by differences in presynaptic localization, release dynamics, and calcium regulation. In addition, CCK release is locally modulated by receptors, kinases and phosphatases. The regulatory mechanisms of CCK release are placed into physiological perspective.

Comparative analysis of the central CCK system in Fawn Hooded and Wistar Kyoto rats: extended localisation of CCK-A receptors throughout the rat brain using a novel radioligand

The neuropeptide cholecystokinin has been implicated in the actions of a number of central processes including anxiety and reward. For this reason, the aim of the present study was to compare the density of CCK-A and -B receptors and the mRNA encoding preproCCK throughout the brains of an alcohol-preferring (Fawn Hooded) rat strain with that of a non-alcohol-preferring (Wistar Kyoto) strain of rat. Our study revealed significant differences with regard to the central CCK system of the FH compared to the WKY rat, including differences in CCK-A receptor binding throughout the dorsal medulla, and altered CCK-B binding density throughout the cerebral cortex and reticular nucleus of the thalamus. The most striking result, given the altered behavioural phenotype of the FH rat, was the 33% lower density of CCKmRNA measured throughout the ventral tegmental area of the FH rat when compared to the WKY. This study also reports on a protocol to utilise a novel radioligand, [125I]-D-Tyr-Gly-A-71378, for autoradiographic detection of CCK-A receptors throughout the rat brain. As previously reported, CCK-A receptors were located throughout the area postrema, interpeduncular nucleus and nucleus tractus solitarii; however, binding to CCK-A receptors was also visualised throughout the medial pre-optic area, the arcuate nucleus and the circumventricular regions of the ventral hypothalamus, regions known to contain CCK-A receptors but which were previously undetectable using autoradiography in rat brain.

Direct visualization of cholecystokinin subtype2 receptors in rat central nervous system using anti-peptide antibodies

The cholecystokinin receptor, subtype 2 (CCK(2)R), is considered, based on receptor autoradiography, to be the predominant receptor for this peptide transmitter in the mammalian central nervous system. To directly visualize the CCK(2)R we utilized a convenient and sensitive immunohistochemical procedure using antipeptide receptor antibodies raised in rabbits against unique portions of the carboxyl tail and third intracellular loop of the CCK(2)R. Antibodies were characterized by ELISA and Western blotting, and used for immunohistochemistry in rat brain sections. Studies with both antibodies revealed a widespread topographic distribution of CCK(2)R-like immunoreactivity (CCK(2)R-LI) in regions such as cortex, olfactory bulb, nucleus accumbens, septum, striatum, hippocampus, basolateral amygdala, habenula, hypothalamus, thalamus, ventral mesencephalon, inferior colliculus, parabrachial nucleus, pontine nucleus, supercolliculus, red nucleus, subcommisural and occulomotor nucleus, area postrema, solitary, olivary, cochlear, cuneate and trigeminal nuclei and spinal cord dorsal horn in agreement with the results of previous receptor autoradiography.

Altered cholecystokinin binding site density in the supraoptic nucleus of morphine-tolerant and -dependent rats

The processes underlying the development of neuronal tolerance to and dependence upon opiates are not yet fully understood. To evaluate a possible role for cholecystokinin (CCK) in these processes, quantitative receptor autoradiography and in situ hybridisation histochemistry were used to study both the density and distribution of sulphated CCK octapeptide (CCK8S) binding sites and preproCCK peptide mRNA levels within the dorsal (oxytocin neurone-rich) supraoptic nuclei of rats given an intracerebroventricular (i.c.v.) infusion of morphine over 5 days, which is known to induce tolerance and dependence in mechanisms regulating oxytocin neurones. Specific CCK8S binding was significantly increased in the supraoptic nuclei of both morphine-dependent and salt-loaded (2% sodium chloride to drink for 48 h) rats compared to their respective controls (P < 0.05). In situ hybridisation histochemistry revealed no difference in preproCCK mRNA levels within supraoptic neurones of (i.c.v.) morphine-treated compared with either i.c.v. vehicle-treated or untreated control animals. These results suggest that CCK receptor mechanisms involved in the control of magnocellular oxytocin neurone activation are upregulated during chronic morphine treatment, and this may favour increased sensitivity to CCK, thereby offsetting the inhibitory actions of morphine, contributing to tolerance and perhaps to the withdrawal excitation characteristic of dependence.

Effects of cholecystokinin-receptor agonists on cortical 5-HT release in guinea pigs on the X-maze

Exposure of guinea pigs to the elevated plus maze (X-maze), an animal model of anxiety, causes an increase of extracellular serotonin (5-HT) in the lateral prefrontal cortex monitored by microdialysis. The neuropeptide cholecystokinin (CCK) plays a role in the modulation of anxiety. To compare the roles of CCK receptors, the effects of the CCK-A receptor agonist A-71378, the CCK-A/B receptor agonist CCK-8S and the CCK-B receptor agonist BOC-CCK-4 on anxiety-related behavior and the 5-HT release in the prefrontal cortex were determined. None of the drugs changed the behavior of the guinea pigs and the cortical 5-HT release under resting conditions in the familiar home cage. A-71378 and CCK-8S had no effect on the behavior on exposure to the X-maze whereas BOC-CCK-4 induced an 'anxious' behavior. The results suggest that 'anxious' behavior induced by CCK is associated with selective CCK-B receptor stimulation. A-71378 inhibited the rise in 5-HT on exposure to the X-maze. CCK-8S had no effect and the anxiogenic BOC-CCK-4 potentiated the rise in 5-HT on the X-maze. Both CCK receptors mediate changes in 5-HT release under aversive conditions, but not in a resting state. The results suggest a receptor subtype-specific influence of CCK on behavior and 5-HT activity under aversive conditions.

Effects of the CCK(A) receptor antagonists SR 27897B and PD140548 on baroreflex function in conscious rats

Since the cardiovascular effects of cholecystokinin (CCK) seem to particularly involve the A ('peripheral') subtype of CCK (CCK[A]) receptor, we examined the actions of two novel, highly selective CCK(A) receptor antagonists, PD140548 (N-alpha-methyl-N[(tricyclo[3.3.1.1(3,7)]dec-2-yloxy)carbony l]-L-tryptophyl]-D-3-(phenylmethyl)-beta-alanine) and SR 27897B (1-[[2-(4-(2-chlorophenyl)thiazol-2-yl)aminocarbonyl]acetic acid) on CCK-induced alterations in blood pressure and heart rate, and on the baroreceptor reflex in the conscious, instrumented rat. CCK (2 microg, i.v.) produced a pressor response and biphasic effects on heart rate involving an initial bradycardia followed by a pronounced tachycardia. Administration of PD140548 (10 mg/kg, i.v.) and SR 27897B (0.6 mg/kg, i.v.) significantly inhibited the pressor effects of CCK (35 and 47%, respectively), whilst reversing the bradycardic responses to a tachycardia. The CCK(A) receptor antagonists had different effects on the baroreceptor heart rate reflex since only PD140548 caused a significant increase in the gain or sensitivity of the reflex. This effect of PD140548 on gain is likely to occur via a central mechanism and may reflect the increased lipophilicity of PD140548 relative to SR 27897B. Overall, these investigations provide new evidence for the involvement of the CCK(A) receptor in cardiovascular regulation.

Cholecystokinin (CCK-8) modulates vesicular release of excitatory amino acids in rat hippocampal nerve endings

The modulation of endogenous amino acid transmitter release by the sulphated octapeptide cholecystokinin (CCK-8S) was investigated in purified rat hippocampal synaptosomes. In the presence of extracellular Ca2+, CCK-8S increased the basal release of glutamate, but not of aspartate and GABA. In addition, CCK-8S dose-dependently increased the KCl-evoked Ca2+-dependent release of both glutamate and aspartate to about 1.4-fold at concentrations > or = 0.5 microM. CCK-8S did not change the KCl-evoked Ca2+-dependent GABA release, not even in the presence of the GABA uptake carrier blocker N-(4,4-diphenyl-3-butenyl)-3-piperidine carboxylic acid 89976-A (SK&F89976-A; 10 microM). The CCKB receptor antagonist L365,260 (1 microM) blocked the CCK-8S-induced release of glutamate by 70%, and of aspartate by 100%. In conclusion, CCK stimulates exocytosis of excitatory amino acids in rat hippocampus by activating a low-affinity presynaptic CCK receptor, presumably of the B-subtype. However, CCK does not modulate the release of GABA, which has been reported to be colocalized with this peptide.

Cortical 5-HT-CCK interactions and anxiety-related behaviour of guinea-pigs: a microdialysis study

Serotonin (5-HT) and cholecystokinin (CCK) are involved in the development of anxiety. There are only few data suggesting interactions between CCK and 5-HT under aversive conditions. In our study the cholecystokinin tetrapeptide (CCK-4) (10 microg/kg) induced 'anxious' behaviour and potentiated the increase of 5-HT release on the elevated plus maze (X-maze). The 'anxiolytic' 5-HT1A agonist 8-hydroxy-2-(di-n-propyl amino) tetralin (8-OH-DPAT; 0.3 mg/kg) reduced basal 5-HT and the increase in 5-HT release on the X-maze. 8-OH-DPAT given simultaneously with CCK-4, blocked the effects of CCK-4. The results demonstrate an interaction between CCK and 5-HT1A mechanisms via the influence on cortical 5-HT release.

Histochemistry in rat brain and spinal cord with an antibody directed at the cholecystokininA receptor

Various neurobiological evidence indicates that A-subtype cholecystokinin (CCKA) receptors are widely distributed through the mammalian neuroaxis despite the sparse localization found by receptor autoradiography. To address this paradox, immunohistochemistry has been performed in rat brain and spinal cord using an antibody directed at a portion of the amino terminal sequence of the CCKA receptor. Immunoreactivity, visualised using diaminobenzidine, was widely and topographically distributed being most concentrated in medulla and spinal cord. Many forebrain areas contained specifically labelled neurones, notably the nucleus accumbens, septum, stria terminalis, habenula, substantia nigra, ventral tegmental area and lateral geniculate nucleus. In medulla, heavily labelled perikarya were found in parabrachial and trigeminal nuclei, while in spinal cord immunoreactivity was localized in dorsal horn. Localization of immunoreactivity was consistent with the reported distribution of CCKA receptor-mediated mechanisms. Our observations represent the first attempt to describe the localization of the CCKA receptor in brain using immunohistochemistry and support its wide functional involvement in the central nervous system.

On the distribution of cholecystokinin B receptors in monkey brain

In view of recent evidence for a role for the B subtype of cholecystokinin (CCKB) receptor in panic and anxiety, the distribution of CCKB receptors in the forebrain of a Rhesus macaca monkey was examined by receptor autoradiography employing [125I]D-Tyr25(Nleu28,31)-CCK25-33S. CCKB receptors were widely and topographically distributed in cortex. Other structures with notable labelling included the basal ganglia, presubiculum, amygdala, mamillary bodies, cerebellar cortex and pineal gland. The distribution of CCKB receptors further supports roles for this peptide in behavioural processes.

Electrophysiological studies of the cholecystokininA receptor antagonists SR27897B and PD140548 in the rat isolated nodose ganglion

With increased interest in the pharmacology of cholecystokininA (CCKA) receptors, including their trophic and mitogenic effects, the actions of two new non-peptide CCKA receptor antagonists, PD140548 and SR 27897B, were investigated in a convenient model system, the rat isolated nodose ganglion. CCK (1 nM-1 microM) caused concentration-dependent depolarisations when superfused over the nodose ganglion at 37 degrees C as measured by a silicone grease gap technique, and both CCKA antagonists caused significant rightward shifts in the concentration response curve to CCK. SR 27897B (3 and 10 nM) caused 7.9- and 17.9-fold shifts in the CCK concentration-response curve and the apparent-log KB values for each concentration of antagonist were calculated to be 9.36 and 9.23. Further experiments with PD140548 (30 and 100 nM) yielded shifts of 2.9- and 12.5-fold from which -log KB values were determined to be 7.80 and 8.06. Overall SR 27897B was significantly more efficacious than PD140548. Thus, the isolated nodose ganglion preparation allows a functional assessment of CCKA-mediated responses, with the results indicating that both SR 27897B and PD140548 are efficacious CCKA receptor antagonists.

Neurochemical modulation of cardiovascular control in the nucleus tractus solitarius

The central control of cardiovascular function has been keenly studied for a number of decades. Of particular interest are the homeostatic control mechanisms, such as the baroreceptor heart-rate reflex, the chemoreceptor reflex, the Bezold-Jarisch reflex and the Breuer-Hering reflex. These neurally-mediated reflexes share a common termination point for their respective centrally-projecting sensory afferents, namely the nucleus tractus solitarius (NTS). Thus, the NTS clearly plays a critical role in the integration of peripherally initiated sensory information regarding the status of blood pressure, heart rate and respiratory function. Many endogenous neurochemicals, from simple amino acids through biogenic amines to complex peptides have the ability to modulate blood pressure and heart rate at the level of the NTS. This review will attempt to collate the current knowledge regarding the roles of neuromodulators in the NTS, the receptor types involved in mediating observed responses and the degree of importance of such neurochemicals in the tonic regulation of the cardiovascular system. The neural pathway that controls the baroreceptor heart-rate reflex will be the main focus of attention, including discussion of the identity of the neurotransmitter(s) thought to act at baroafferent terminals within the NTS. In addition, this review will provide a timely update on the use of recently developed molecular biological techniques that have been employed in the study of the NTS, complementing more classical research.

Changes in hypothalamic cholecystokininA and cholecystokininB receptor subtypes and associated neuropeptide expression in response to salt-stress in the rat and mouse

This study demonstrates cholecystokinin receptor plasticity in response to salt-loading in the rat and mouse hypothalamus. It identifies, for the first time, the cholecystokinin receptor subtypes involved, firstly by receptor autoradiography and secondly by in situ hybridization. Both species showed increases in hypothalamic [125I]Bolton Hunter-cholecystokinin-8 binding. Co-incubation with the specific cholecystokininA and cholecystokininB antagonists, devazepide and CI-988, indicated that in the rat cholecystokininB receptor binding markedly increased, with a small increase in cholecystokininA receptor binding. In the mouse the response was comprised solely of cholecystokininA receptors. In situ hybridization studies were carried out on a range of peptide messenger ribonucleic acids after salt-loading. In the rat large increases in hypothalamic gene expression were detected for oxytocin, vasopressin, corticotrophin-releasing factor and preprocholecystokinin. In the mouse only vasopressin messenger ribonucleic acid increased, whilst hypothalamic oxytocin, preprocholecystokinin and corticotropin-releasing factor remained unchanged. However, corticotrophin-releasing factor messenger ribonucleic acid increased in the mouse amygdala. In situ hybridization was performed using oligonucleotide probes specific for either the cholecystokininA or cholecystokininB receptor messenger ribonucleic acid, and this showed good agreement with the receptor autoradiography. CholecystokininB receptor expression was upregulated in the rat hypothalamus along with a small but significant increase in cholecystokininA receptors. In the mouse only cholecystokininA receptor expression was increased. In addition to these molecular changes rats lost about 25% of their body weight during six days of salt-challenge, whilst mice continued to grow in line with controls. This work demonstrates differential changes in cholecystokinin receptor subtype binding between the rat and the mouse. It represents the first report of differential changes in cholecystokininA and cholecystokininB receptor messenger ribonucleic acids within the brain, and shows that cholecystokinin receptors within the rodent hypothalamus are capable of plastic responses to chronic osmotic stress.

Effects of administration of cholecystokinin into the VTA on DA overflow in nucleus accumbens and amygdala of freely moving rats

The carboxyterminal octapeptide of cholecystokinin (CCK-8) coexists with dopamine (DA) in mesolimbic neurons of the ventral tegmental area (VTA). In the present study, in vivo microdialysis in freely moving rats was used to assess the relative effects of sulfated CCK-8 (CCK-8S), unsulfated CCK-8 (CCK-8US) and CCK tetrapeptide (CCK-4), focally injected into the VTA, on DA overflow in two mesolimbic DA/CCK-8S terminal regions, the nucleus accumbens and the amygdala. Consistent with electrophysiological findings, microinjection of CCK-8S, but not CCK-8US or CCK-4, elicited increases in DA overflow in both terminal regions. In the absence of anatomical evidence of CCK-containing fibers in the VTA region, it seems reasonable to conclude that the modulation of terminal DA overflow by CCK-8S through actions at the somatodendritic region represents a form of autoregulation of these cells. Whereas CCK-8US and CCK-4 are preferential CCK-B receptor agonists, CCK-8S binds non-selectively to CCK-A and CCK-B receptors. Thus, these results implicate CCK-A receptors in the stimulatory effects of CCK-8S on VTA DA neurons.

Expression of cholecystokinin mRNA in corticothalamic projecting neurons: a combined fluorescence in situ hybridization and retrograde tracing study in the ventrolateral thalamus of the rat

Cholecystokinin (CCK), a well-known neuroactive peptide, has been observed in the axon endings within the thalamic reticular nucleus and the adjacent ventrolateral nucleus of the thalamus. The origin of this CCK innervation remains undefined. In this study, a fluorescence in situ hybridization (FISH) technique was used in conjunction with latex microsphere retrograde tracing to investigate whether cortical neurons may provide a source of CCK afferents to the ventrolateral thalamic nucleus. Rhodamine latex beads were injected into the ventrolateral thalamic nucleus of adult male rats to retrogradely label corticothalamic cells. After 7 days, tissues were processed for FISH using a 24-base oligonucleotide probe complementary to the 3' coding region of rat preprocholecystokinin mRNA. It was found that CCK transcripts are expressed in about 80% of identified corticothalamic projecting neurons. We therefore conclude that the descending cortical projections to the ventrolateral thalamus may provide an important source of CCK innervation to this region of the brain.

The influence of 5-hydroxytryptamine re-uptake blockade on CCK receptor antagonist effects in the rat elevated zero-maze

In this study, the elevated zero-maze model of anxiety was used to investigate CCK receptor antagonist effects on the behaviour of male Lister-hooded rats and to demonstrate, by administering antagonists in the presence or absence of selective 5-hydroxytryptamine (5-HT) re-uptake inhibitors, the involvement of 5-HT in the mediation of these effects. Devazepide, a selective CCKA receptor antagonist, L-365,260 (3R(+)-N-2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepin- 3-yl-N1- (3-methyl-phenyl)urea) or CI-988 (4-([2-[[3-(1H-indol-3-yl)-2-methyl-1- oxo-2-[[(tricyclo[3.3.1.1.(3.7)]-dec-2-yloxy)-carbonyl]-amin o]- propyl]-amino]-1-phenylethyl]-amino)-4-oxo-[R-(R*,R*)]-butanoate- N-methyl-D-glucamine), both selective CCKB receptor antagonists, were administered 30 min prior to testing. Behavioural analysis during testing included measures of risk-assessment behaviours (e.g. stretched-attend posture) in addition to time spent on the open quadrants. Devazepide induced significant anxiolytic effects, whereas CI-988 produced inconsistent results and L-365,260 was ineffective. When administered simultaneously with the 5-HT re-uptake inhibitors zimelidine or Wy 27587 (N-[[[1-[(6- fluoro-2-naphthalenyl)methyl]-4-piperidinyl]amino] carbonyl]-3-pyridine carboxamide methyl sulphonate salt), the significant anxiolytic effect induced by devazepide was dose-dependently and significantly attenuated. Zimelidine and Wy27587 had little effect alone on zero-maze behaviour at the lower of two doses given. These data show that the elevated zero-maze, in conjunction with the analysis of 'risk-assessment' behaviours, is an anxiety model which is sensitive to the anxiolytic effects of CCK receptor antagonism.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholecystokinin blockade of emotional stress- and CRF-induced colonic motor alterations in rats: role of the amygdala

Intracerebroventricular (i.c.v.) injection of corticotropin-releasing factor (CRF) and emotional stress (ES) induce stimulation of colonic motility in rats, an effect blocked by i.c.v. injection of CCK-8s. This study examined in rats the contribution of the central nucleus of the amygdala (CA) in the blocking effect of CCK-8s on ES and CRF-induced colonic hypermotility. CRF (500 ng/kg, i.c.v.) induced a 73.5% increase in colonic spike burst frequency. Bilateral infusions of 1, 5, 10 and 20 ng/kg of CCK-8s in the CA region 10 min prior to CRF i.c.v. injection reduced, in a dose related manner, the CRF-induced stimulation of colonic motility. A 109% increase in colonic spike burst frequency was observed in rats placed in a test cage in which they had previously received electric footshocks (ES). CCK-8s and A-71623, a selective CCK-A receptor agonist, (10, 25 and 50 ng/kg) infused bilaterally into the CA, 30 min before ES, significantly reduced this stimulatory effect, while CCK-4 and A-63387, a selective CCK-B receptor agonist (10, 25 and 50 ng/kg), had no effect on such a response. CA lesions by ibotenic acid did not affect ES-induced increase in colonic spike activity. However, CCK-8s (50 ng/kg) microinfused into CA lesioned rats was unable to block the ES-induced stimulation of colonic motility, while CCK-8s i.c.v. injected (100 ng/kg) is still active on the colonic response to ES. These results suggest that CA is a site of interaction of CCK-8s with CRF to block the colonic response to stress and that these effects involve the CCK-A receptor subtype.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding of cholecystokinin, bombesin and muscarine to neurons and astrocytes in explant cultures of rat central nervous system: autoradiographic and immunohistochemical studies

The cellular localization of binding sites for the gastrointestinal peptides [3H]cholecystokinin and [125I]bombesin as well as the cholecystokininB-antagonist [3H]L-365,260 was investigated in explant cultures of rat cortex, cerebellum, brainstem and spinal cord using autoradiographic techniques. Many neurons in cortical, brainstem and spinal cord cultures revealed intense labelling of the radioligands whereas cerebellar neurons showed only little binding. In addition to neurons, binding sites for these peptides were also observed on astrocytes. Labelling of glial cells in cerebellar cultures was usually weaker than in the other CNS areas studied, suggesting a certain specialization of astrocytes in various brain regions. By means of combined immunohistochemical and autoradiographic techniques it was demonstrated that many neurons and astrocytes which expressed binding sites for [3H]cholecystokinin, [3H]L-365,260 and [125I]bombesin were also immunostained by the monoclonal muscarinic receptor antibody M 35 providing evidence for a co-localization of peptidergic and cholinergic receptors on the membrane of these cells. Our autoradiographic findings suggesting the presence of receptors for cholecystokinin and bombesin on astrocytes are supported by electrophysiological studies demonstrating that both peptides induce a hyperpolarization of glial cells.

Effects of cholecystokinin tetrapeptide and sulfated cholecystokinin octapeptide in rat models of anxiety

The effects of the acutely administered cholecystokinin (CCK) agonists CCK tetrapeptide (BOC-CCK-4) and sulfated CCK octapeptide (CCK-8S) were examined in four animal models of anxiety in rats. In the elevated plus maze, BOC-CCK-4 reduced the time spent in the open arms and the number of entries into the open arms. BOC-CCK-4 but not the anorectic acting CCK-8S increased the suppression of feeding in a conflict paradigm based on novelty suppressed feeding in hungry rats. In the two-compartment black-and-white box, BOC-CCK-4 decreased the time spent and locomotor activity in the white compartment. In the ultrasound vocalization test, using rat pups separated from the mother, BOC-CCK-4 increased the number of distress calls. No evidence was found for inducing anxiety-like behaviour by CCK-8S.

Effects of BOC-CCK-4 and L 365.260 on cortical 5-HT release in guinea-pigs on exposure to the elevated plus maze

The elevated plus maze is a well-established model of anxiety, with previous results showing that guinea-pigs handled daily from birth exhibit behaviour in this test similar to rats. In the present microdialysis study exposure of the guinea-pig to the elevated plus maze increased extracellular 5-HT in the lateral prefrontal cortex. The CCK-B receptor agonist BOC-CCK-4 (10 micrograms/kg) produced 'anxious' behaviour and potentiated the rise in 5-HT observed on exposure to the X-maze. The basal release of cortical extracellular 5-HT was not affected by BOC-CCK-4. Pretreatment with the selective CCK-B antagonist L 365.260 (100 micrograms/kg) antagonized both the 'anxious' behaviour and the neurochemical changes induced by BOC-CCK-4 while L 365.260 alone produced 'anxiolytic' behaviour, decreased basal extracellular 5-HT and prevented the increase in extracellular 5-HT seen when the guinea-pigs were exposed to the X-maze. Our results show that CCK-B receptor stimulation and blockade induce changes in central extracellular 5-HT levels associated with 'anxious' and 'anxiolytic' behaviour, respectively.

CCK antagonists: pharmacology and therapeutic interest

CCK was first identified and characterized in the digestive tract where it is known to be a factor involved in the control of gut motility. Later, CCK and CCK receptors were identified in regions of the central nervous system that are associated with the control of emotion, motivation and sensory processing. The recent discovery and development of CCK-receptor antagonists having selective affinity for either CCKA or CCKB receptors has led to a better understanding of the functional role of CCK and its binding sites in the brain and periphery. Some of these compounds are being examined in man for their therapeutic usefulness in mental as well as in digestive disorders. This review will highlight the results from both basic and clinical investigations that have examined the effects of selective CCK receptor ligands. The focus will be on the central nervous system pharmacology of CCK antagonists and the involvement of CCK in gastrointestinal and colonic motility.

Electrophysiological and autoradiographical evidence for cholecystokinin A receptors on rat isolated nodose ganglia

The sulphated octapeptide, cholecystokinin (CCK-8S), is believed to be a neurotransmitter of vagal sensory neurones, and here the presence of functional receptors for CCK-8S in the rat vagus nerve has been investigated by electrophysiological and autoradiographic techniques. CCK-8S caused concentration-dependent depolarizations when superfused over the rat isolated nodose ganglion at 37 degrees C as measured by a silicone grease gap technique. Concentration-response curves to CCK-8S were shifted to the right by low concentrations of the CCKA receptor antagonist, Devazepide, but not by the CCKB receptor antagonist, L-365,260, data which indicate that receptors were of the CCKA subtype. Consistent with this notion, the CCKB agonist, unsulphated CCK-8, was without effect until high concentrations (> 1 microM) were used. A synthetic analogue of CCK-8S, D-Tyr25(Nle28,31)-CCK 25-33S, which has been reported to be more stable and peptidase-resistant than CCK-8S, was equipotent with CCK-8S in depolarizing the nodose ganglion. When D-Tyr25(Nle28,31)-CCK 25-33S was labelled with 125I, it bound to tissue sections of nodose ganglion. By light microscopic autoradiography, silver grains were found to be highly localized over cell bodies of vagal sensory neurones. An excess of CCK-8S inhibited binding as did Devazepide, but not L-365,260, confirming that binding sites were CCKA subtype receptors. These results indicate the existence of functional CCKA receptors in the nodose ganglion and strengthen the case for the involvement of vagal sensory neurones in gastric emptying and satiety.

Inhibition of A9 and A10 dopamine cells by the cholecystokinin-B antagonist LY262691: mediation through feedback pathways from forebrain sites

The diphenylpyrazolidinone cholecystokinin-B (CCK-B) antagonist LY262691 has been shown to decrease the number of spontaneously active dopamine (DA) cells in the ventral tegmental area (A10) and substantia nigra (A9) of the anesthetized rat. In the present study, we examined the localization of the receptors mediating these effects of LY262691 on A9 and A10 DA cells. In one group of anesthetized rats, the effects of systemic administration of LY262691 on the number of spontaneously active A9 or A10 DA cells was determined using extracellular, single-unit recordings after radio frequency lesions were placed in the nucleus accumbens, caudate-putamen, or medial prefrontal cortex. Lesions of the caudate-putamen blocked the effects of systemically administered LY262691 on the number of spontaneously active A9, but not A10, DA cells. Conversely, lesions of the n. accumbens blocked the effects of systemically administered LY262691 on A10, but not A9, DA cells. Lesions of the medial prefrontal cortex blocked the effects of systemically administered LY262691 on both A9 and A10 DA cells. In a separate group of anesthetized rats, the number of spontaneously active A9 or A10 DA cells was determined after LY262691 was microinjected into the n. accumbens, caudate-putamen, or medial prefrontal cortex. Microinjection of LY262691 into the caudate-putamen led to a significant decrease in the number of spontaneously active A9, but not A10, DA cells. Conversely, microinjection of LY262691 into the n. accumbens or medial prefrontal cortex led to a significant decrease in the number of spontaneously active A10, but not A9, DA cells.(ABSTRACT TRUNCATED AT 250 WORDS)