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

Anxiety and the brain: Neuropeptides as emerging factors

Anxiety disorders are characterized by intense feelings of worry and fear, which can significantly interfere with daily functioning. Current treatment options primarily include selective serotonin reuptake inhibitors, benzodiazepines, non-benzodiazepine anxiolytics, gabapentinoids, and beta-blockers. Neuropeptides have shown an important role in the regulation of complex behaviours, such as psychopathology and anxiety-related reactions. Neuropeptides have a great deal of promise to advance our understanding of and ability to help people with anxiety disorders. This review focuses on the expanding role of neuropeptides in anxiety management, particularly examining the impact of substance P, neuropeptide Y, corticotropin-releasing hormone, arginine-vasopressin, pituitary adenylate cyclase-activating polypeptide, and cholecystokinin. Furthermore, the paper discusses the neuropeptides that are becoming more and more recognized for their impact on anxiety-related reactions and their potential as therapeutic targets.

The olfactory bulb: A neuroendocrine spotlight on feeding and metabolism

Olfaction is the most ancient sense and is needed for food-seeking, danger protection, mating and survival. It is often the first sensory modality to perceive changes in the external environment, before sight, taste or sound. Odour molecules activate olfactory sensory neurons that reside on the olfactory epithelium in the nasal cavity, which transmits this odour-specific information to the olfactory bulb (OB), where it is relayed to higher brain regions involved in olfactory perception and behaviour. Besides odour processing, recent studies suggest that the OB extends its function into the regulation of food intake and energy balance. Furthermore, numerous hormone receptors associated with appetite and metabolism are expressed within the OB, suggesting a neuroendocrine role outside the hypothalamus. Olfactory cues are important to promote food preparatory behaviours and consumption, such as enhancing appetite and salivation. In addition, altered metabolism or energy state (fasting, satiety and overnutrition) can change olfactory processing and perception. Similarly, various animal models and human pathologies indicate a strong link between olfactory impairment and metabolic dysfunction. Therefore, understanding the nature of this reciprocal relationship is critical to understand how olfactory or metabolic disorders arise. This present review elaborates on the connection between olfaction, feeding behaviour and metabolism and will shed light on the neuroendocrine role of the OB as an interface between the external and internal environments. Elucidating the specific mechanisms by which olfactory signals are integrated and translated into metabolic responses holds promise for the development of targeted therapeutic strategies and interventions aimed at modulating appetite and promoting metabolic health.

Photodynamic Activation of the Cholecystokinin 1 Receptor with Tagged Genetically Encoded Protein Photosensitizers: Optimizing the Tagging Patterns

Cholecystokinin 1 receptor (CCK1R) is activated photodynamically. For this to happen in situ, genetically encoded protein photosensitizers (GEPP) may be tagged to natively expressed CCK1R, but how to best tag GEPP has not been examined. Therefore, GEPP (miniSOG or KillerRed) was tagged to CCK1R and light-driven photodynamic CCK1R activation was monitored by Fura-2 fluorescent calcium imaging, to screen for optimized tagging patterns. Blue light-emitting diode irradiation of CHO-K1 cells expressing miniSOG fused to N- or C-terminus of CCK1R was found to both trigger persistent calcium oscillations-a hallmark of permanent photodynamic CCK1R activation. Photodynamic CCK1R activation was accomplished also with miniSOG fused to N-terminus of CCK1R via linker (GlySerGly)4 or 8 , but not linker (GSG)12 or an internal ribosomal entry site insert. KillerRed fused to N- or C-terminus of CCK1R after white light irradiation resulted in similar activation of in-frame CCK1R. Photodynamic CCK1R activation in miniSOG-CCK1R-CHO-K1 cells was blocked by singlet oxygen (1 O2 ) quencher uric acid or Trolox C, corroborating the role of 1 O2 as the reactive intermediate. It is concluded that photodynamic CCK1R activation can be achieved either with direct GEPP fusion to CCK1R or fusion via a short linker, fusion via long linkers might serve as the internal control.

Autonomic control of energy balance and glucose homeostasis

Neurons in the central nervous system (CNS) communicate with peripheral organs largely via the autonomic nervous system (ANS). Through such communications, the sympathetic and parasympathetic efferent divisions of the ANS may affect thermogenesis and blood glucose levels. In contrast, peripheral organs send feedback to the CNS via hormones and autonomic afferent nerves. These humoral and neural feedbacks, as well as neural commands from higher brain centers directly or indirectly shape the metabolic function of autonomic neurons. Notably, recent developments in mouse genetics have enabled more detailed studies of ANS neurons and circuits, which have helped elucidate autonomic control of metabolism. Here, we will summarize the functional organization of the ANS and discuss recent updates on the roles of neural and humoral factors in the regulation of energy balance and glucose homeostasis by the ANS.

Cutting-edge techniques should be harnessed to unravel how metabolism is modulated by a key part of the body’s nervous system. The autonomic nervous system (ANS) regulates many involuntary physiological processes, such as heart rate, breathing, and blood pressure. Scientists now believe that the ANS is involved in regulating metabolism, but its precise roles are unclear. Jong-Woo Sohn and Uisu Hyun at the Korea Advanced Institute of Science and Technology, Daejeon, Korea, reviewed understanding of how the ANS regulates energy balance, appetite, and glucose homeostasis. Recently-developed mouse models have provided insights into how ANS neurons translate neuronal and hormonal signals into commands during feeding, sending instructions to the liver, and mediating blood glucose levels. Several hormones have been identified that may act on a specific part of the ANS to influence appetite and metabolism.

Modulation of Neural Microcircuits That Control Complex Dynamics in Olfactory Networks

Neuromodulation influences neuronal processing, conferring neuronal circuits the flexibility to integrate sensory inputs with behavioral states and the ability to adapt to a continuously changing environment. In this original research report, we broadly discuss the basis of neuromodulation that is known to regulate intrinsic firing activity, synaptic communication, and voltage-dependent channels in the olfactory bulb. Because the olfactory system is positioned to integrate sensory inputs with information regarding the internal chemical and behavioral state of an animal, how olfactory information is modulated provides flexibility in coding and behavioral output. Herein we discuss how neuronal microcircuits control complex dynamics of the olfactory networks by homing in on a special class of local interneurons as an example. While receptors for neuromodulation and metabolic peptides are widely expressed in the olfactory circuitry, centrifugal serotonergic and cholinergic inputs modulate glomerular activity and are involved in odor investigation and odor-dependent learning. Little is known about how metabolic peptides and neuromodulators control specific neuronal subpopulations. There is a microcircuit between mitral cells and interneurons that is comprised of deep-short-axon cells in the granule cell layer. These local interneurons express pre-pro-glucagon (PPG) and regulate mitral cell activity, but it is unknown what initiates this type of regulation. Our study investigates the means by which PPG neurons could be recruited by classical neuromodulators and hormonal peptides. We found that two gut hormones, leptin and cholecystokinin, differentially modulate PPG neurons. Cholecystokinin reduces or increases spike frequency, suggesting a heterogeneous signaling pathway in different PPG neurons, while leptin does not affect PPG neuronal firing. Acetylcholine modulates PPG neurons by increasing the spike frequency and eliciting bursts of action potentials, while serotonin does not affect PPG neuron excitability. The mechanisms behind this diverse modulation are not known, however, these results clearly indicate a complex interplay of metabolic signaling molecules and neuromodulators that may fine-tune neuronal microcircuits.

Photodynamic Activation of Cholecystokinin 1 Receptor with Different Genetically Encoded Protein Photosensitizers and from Varied Subcellular Sites

Cholecystokinin 1 receptor (CCK1R) is activated by singlet oxygen (1O2) generated in photodynamic action with sulphonated aluminum phthalocyanine (SALPC) or genetically encoded protein photosensitizer (GEPP) KillerRed or mini singlet oxygen generator (miniSOG). A large number of GEPP with varied 1O2 quantum yields have appeared recently; therefore, in the present work, the efficacy of different GEPP to photodynamically activate CCK1R was examined, as monitored by Fura-2 calcium imaging. KillerRed, miniSOG, miniSOG2, singlet oxygen protein photosensitizer (SOPP), flavin-binding fluorescent protein from Methylobacterium radiotolerans with point mutation C71G (Mr4511C71G), and flavin-binding fluorescent protein from Dinoroseobacter shibae (DsFbFP) were expressed at the plasma membrane (PM) in AR4-2J cells, which express endogenous CCK1R. Light irradiation (KillerRed: white light 85.3 mW‧cm-2, 4' and all others: LED 450 nm, 85 mW·cm-2, 1.5') of GEPPPM-expressing AR4-2J was found to all trigger persistent calcium oscillations, a hallmark of permanent photodynamic CCK1R activation; DsFbFP was the least effective, due to poor expression. miniSOG was targeted to PM, mitochondria (MT) or lysosomes (LS) in AR4-2J in parallel experiments; LED light irradiation was found to all induce persistent calcium oscillations. In miniSOGPM-AR4-2J cells, light emitting diode (LED) light irradiation-induced calcium oscillations were readily inhibited by CCK1R antagonist devazepide 2 nM; miniSOGMT-AR4-2J cells were less susceptible, but miniSOGLS-AR4-2J cells were not inhibited. In conclusion, different GEPPPM could all photodynamically activate CCK1R. Intracellular GEPP photodynamic action may prove particularly suited to study intracellular GPCR.

NanoLuc Bioluminescence-Driven Photodynamic Activation of Cholecystokinin 1 Receptor with Genetically-Encoded Protein Photosensitizer MiniSOG

In contrast to reversible activation by agonist, cholecystokinin 1 receptor (CCK1R) is permanently activated by singlet oxygen generated in photodynamic action, with sulphonated aluminium phthalocyanine or genetically encoded mini singlet oxygen generator (miniSOG) as photosensitizer. In these works, a halogen light source was used to power photodynamic action. For possible in vivo application of photodynamic CCK1R physiology, bearing a cumbersome light-delivery device connected to an external light source by experimental animals might interfere with their behavior. Therefore, in the present work, the possibility of bioluminescence-driven miniSOG photodynamic CCK1R activation was examined, as monitored by Fura-2 calcium imaging. In parallel experiments, it was found that, after plasma membrane (PM)-localized expression of miniSOGPM in AR4-2J cells, light irradiation with blue light-emitting diode (LED) (450 nm, 85 mW·cm-2, 1.5 min) induced persistent calcium oscillations that were blocked by CCK1R antagonist devazepide 2 nM. NanoLuc was expressed bicistronically with miniSOGPM via an internal ribosome entry site (IRES) sequence (pminiSOGPM-IRES-NanoLuc). The resultant miniSOGPM-IRES-NanoLuc-AR4-2J cells were found to generate strong bioluminescence upon addition of NanoLuc substrate coelenterazine. Strikingly, coelenterazine 5 microM was found to trigger long-lasting calcium oscillations (a hallmark for permanent CCK1R activation) in perifused miniSOGPM-IRES-NanoLuc-AR4-2J cells. These data indicate that NanoLuc bioluminescence can drive miniSOGPM photodynamic CCK1R activation, laying the foundation for its future in vivo applications.

The unappreciated roles of the cholecystokinin receptor CCK(1) in brain functioning

The CCK(1) receptor is a G-protein-coupled receptor activated by the sulfated forms of cholecystokinin (CCK), a gastrin-like peptide released in the gastrointestinal tract and mammal brain. A substantial body of research supports the hypothesis that CCK(1)r stimulates gallbladder contraction and pancreatic secretion in the gut, as well as satiety in brain. However, this receptor may also fulfill relevant roles in behavior, thanks to its widespread distribution in the brain. The strategic location of CCK(1)r in mesolimbic structures and specific hypothalamic and brainstem nuclei lead to complex interactions with neurotransmitters like dopamine, serotonin, and glutamate, as well as hypothalamic hormones and neuropeptides. The activity of CCK(1)r maintains adequate levels of dopamine and regulates the activity of serotonin neurons of raphe nuclei, which makes CCK(1)r an interesting therapeutic target for the development of adjuvant treatments for schizophrenia, drug addiction, and mood disorders. Unexplored functions of CCK(1)r, like the transmission of interoceptive sensitivity in addition to the regulation of hypothalamic hormones and neurotransmitters affecting emotional states, well-being, and attachment behaviors, may open exciting roads of research. The absence of specific ligands for the CCK(1) receptor has complicated the study of its distribution in brain so that research about its impact on behavior has been published sporadically over the last 30 years. The present review reunites all this body of evidence in a comprehensive way to summarize our knowledge about the actual role of CCK in the neurobiology of mental illness.

CART in the regulation of appetite and energy homeostasis

The cocaine- and amphetamine-regulated transcript (CART) has been the subject of significant interest for over a decade. Work to decipher the detailed mechanism of CART function has been hampered by the lack of specific pharmacological tools like antagonists and the absence of a specific CART receptor(s). However, extensive research has been devoted to elucidate the role of the CART peptide and it is now evident that CART is a key neurotransmitter and hormone involved in the regulation of diverse biological processes, including food intake, maintenance of body weight, reward and addiction, stress response, psychostimulant effects and endocrine functions (Rogge et al., 2008; Subhedar et al., 2014). In this review, we focus on knowledge gained on CART's role in controlling appetite and energy homeostasis, and also address certain species differences between rodents and humans.

Intraperitoneal CCK and fourth-intraventricular Apo AIV require both peripheral and NTS CCK1R to reduce food intake in male rats

Apolipoprotein AIV (Apo AIV) and cholecystokinin (CCK) are secreted in response to fat consumption, and both cause satiation via CCK 1 receptor (CCK-1R)-containing vagal afferent nerves to the nucleus of the solitary tract (NTS), where Apo AIV is also synthesized. Fasted male Long-Evans rats received ip CCK-8 or fourth-ventricular (i4vt) Apo AIV alone or in combination. Food intake and c-Fos proteins (a product of the c-Fos immediate-early gene) were assessed. i4vt Apo AIV and/or ip CCK at effective doses reduced food intake and activated c-Fos proteins in the NTS and hypothalamic arcuate nucleus and paraventricular nucleus. Blockade of the CCK-1R by i4vt lorglumide adjacent to the NTS attenuated the satiating and c-Fos-stimulating effects of CCK and Apo AIV, alone or in combination. Maintenance on a high-fat diet (HFD) for 10 weeks resulted in weight gain and attenuation of both the behavioral and c-Fos responses to a greater extent than occurred in low-fat diet-fed and pair-fed HFD animals. These observations suggest that NTS Apo AIV or/and peripheral CCK requires vagal CCK-1R signaling to elicit satiation and that maintenance on a HFD reduces the satiating capacity of these 2 signals.

Acute effects on brain cholecystokinin-like concentration and anxiety-like behaviour in the female rat upon a single injection of 17β-estradiol

BACKGROUND

The neuropeptide cholecystokinin (CCK) has been implicated in the neurobiology of anxiety and panic disorders, as well as in dopamine-related behaviours. Anxiety and panic-disorders are twice as common in females compared to males, but studies of females are rare, although increasing in number. Limited studies have found that CCK fluctuates in limbic regions during the estrous cycle, and that CCK and its receptors are sensitive to estrogen.

AIM/PURPOSE

The aim of the present work was to study the acute effects of 17β-estradiol on anxiety-like behaviour and on CCK-like immunoreactivity (LI) in the female rat brain (amygdala, hippocampus, nucleus accumbens, and cingulate cortex).

METHODS

Four groups of female Sprague-Dawley rats were used: ovariectomized, ovariectomized+17β-estradiol-replacement, sham, and sham+17β-estradiol-replacement. The effect of 17β-estradiol-replacement on anxiety-related behaviour was measured in all animals on the elevated plus maze 2-24 h after injection. CCK-LI concentration was measured in punch biopsies by means of radioimmunoassay.

RESULTS

17β-estradiol decreased anxiety-like behaviour 2 h after administration in ovariectomized and sham-operated animals, as demonstrated by increased exploration of the open arms compared to respective sesame oil-treated controls. This effect was not present when testing occurred 24 h post-treatment. The rapid behavioural effect of 17β-estradiol was accompanied by changes in CCK-LI concentrations in regions of the limbic system including cingulate cortex, hippocampus, amygdala and nucleus accumbens.

CONCLUSION

Although the interpretation of these data requires caution since the data were collected from two different experiments, our results suggest that estrogen-induced anxiolytic effects may be associated with changes of the CCK-system in brain regions controlling anxiety-like behaviour.

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.

The interaction of amylin with other hormones in the control of eating

Twenty years of research established amylin as an important control of energy homeostasis. Amylin controls nutrient and energy fluxes by reducing energy intake, by modulating nutrient utilization via an inhibition of postprandial glucagon secretion and by increasing energy disposal via a prevention of compensatory decreases of energy expenditure in weight reduced individuals. Like many other gastrointestinal hormones, amylin is secreted in response to meals and it reduces eating by promoting meal-ending satiation. Not surprisingly, amylin interacts with many of these hormones to control eating. These interactions seem to occur at different levels because amylin seems to mediate the eating inhibitory effect of some of these gastrointestinal hormones, and the combination of some of these hormones seems to lead to a stronger reduction in eating than single hormones alone. Amylin's effect on eating is thought to be mediated by a stimulation of specific amylin receptors in the area postrema. Secondary brain sites that were defined to mediate amylin action - and hence potential additional sites of interaction with other hormones - include the nucleus of the solitary tract, the lateral parabrachial nucleus, the lateral hypothalamic area and other hypothalamic nuclei. The focus of this review is to summarize the current knowledge of amylin interactions in the control of eating. In most cases, these interactions have only been studied at a descriptive rather than a mechanistic level and despite the clear knowledge on primary sites of amylin action, the interaction sites between amylin and other hormones are often unknown.

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.

Effects of exogenous cholecystokinin octapeptide on acquisition of naloxone precipitated withdrawal induced conditioned place aversion in rats

Cholecystokinin octapeptide (CCK-8), a gut-brain peptide, regulates a variety of physiological behavioral processes. Previously, we reported that exogenous CCK-8 attenuated morphine-induced conditioned place preference, but the possible effects of CCK-8 on aversively motivated drug seeking remained unclear. To investigate the effects of endogenous and exogenous CCK on negative components of morphine withdrawal, we evaluated the effects of CCK receptor antagonists and CCK-8 on the naloxone-precipitated withdrawal-induced conditioned place aversion (CPA). The results showed that CCK2 receptor antagonist (LY-288,513, 10 µg, i.c.v.), but not CCK1 receptor antagonist (L-364,718, 10 µg, i.c.v.), inhibited the acquisition of CPA when given prior to naloxone (0.3 mg/kg) administration in morphine-dependent rats. Similarly, CCK-8 (0.1–1 µg, i.c.v.) significantly attenuated naloxone-precipitated withdrawal-induced CPA, and this inhibitory function was blocked by co-injection with L-364,718. Microinjection of L-364,718, LY-288,513 or CCK-8 to saline pretreated rats produced neither a conditioned preference nor aversion, and the induction of CPA by CCK-8 itself after morphine pretreatments was not significant. Our study identifies a different role of CCK1 and CCK2 receptors in negative affective components of morphine abstinence and an inhibitory effect of exogenous CCK-8 on naloxone-precipitated withdrawal-induced CPA via CCK1 receptor.

Cholecystokinin receptor-1 mediates the inhibitory effects of exogenous cholecystokinin octapeptide on cellular morphine dependence

Background

Cholecystokinin octapeptide (CCK-8), the most potent endogenous anti-opioid peptide, has been shown to regulate the processes of morphine dependence. In our previous study, we found that exogenous CCK-8 attenuated naloxone induced withdrawal symptoms. To investigate the precise effect of exogenous CCK-8 and the role of cholecystokinin (CCK) 1 and/or 2 receptors in morphine dependence, a SH-SY5Y cell model was employed, in which the μ-opioid receptor, CCK1/2 receptors, and endogenous CCK are co-expressed.

Results

Forty-eight hours after treating SH-SY5Y cells with morphine (10 μM), naloxone (10 μM) induced a cAMP overshoot, indicating that cellular morphine dependence had been induced. The CCK receptor and endogenous CCK were up-regulated after chronic morphine exposure. The CCK2 receptor antagonist (LY-288,513) at 1–10 μM inhibited the naloxone-precipitated cAMP overshoot, but the CCK1 receptor antagonist (L-364,718) did not. Interestingly, CCK-8 (0.1-1 μM), a strong CCK receptor agonist, dose-dependently inhibited the naloxone-precipitated cAMP overshoot in SH-SY5Y cells when co-pretreated with morphine. The L-364,718 significantly blocked the inhibitory effect of exogenous CCK-8 on the cAMP overshoot at 1–10 μM, while the LY-288,513 did not. Therefore, the CCK2 receptor appears to be necessary for low concentrations of endogenous CCK to potentiate morphine dependence in SH-SY5Y cells. An additional inhibitory effect of CCK-8 at higher concentrations appears to involve the CCK1 receptor.

Conclusions

This study reveals the difference between exogenous CCK-8 and endogenous CCK effects on the development of morphine dependence, and provides the first evidence for the participation of the CCK1 receptor in the inhibitory effects of exogenous CCK-8 on morphine dependence.

Control of energy homeostasis by amylin

Amylin is an important control of nutrient fluxes because it reduces energy intake, modulates nutrient utilization by inhibiting postprandial glucagon secretion, and increases energy disposal by preventing compensatory decreases of energy expenditure in weight-reduced individuals. The best investigated function of amylin which is cosecreted with insulin is to reduce eating by promoting meal-ending satiation. This effect is thought to be mediated by a stimulation of specific amylin receptors in the area postrema. Secondary brain sites to mediate amylin action include the nucleus of the solitary tract and the lateral parabrachial nucleus, which convey the neural signal to the lateral hypothalamic area and other hypothalamic nuclei. Amylin may also signal adiposity because plasma levels of amylin are increased in adiposity and because higher amylin concentrations in the brain result in reduced body weight gain and adiposity, while amylin receptor antagonists increase body adiposity. The central mechanisms involved in amylin's effect on energy expenditure are much less known. A series of recent experiments in animals and humans indicate that amylin is a promising option for anti-obesity therapy especially in combination with other hormones. The most extensive dataset is available for the combination therapy of amylin and leptin. Ongoing research focuses on the mechanisms of these interactions.

CCK, PYY and PP: the control of energy balance

The control of food intake consists of neural and hormonal signals between the gut and central nervous system (CNS). Gut hormones such as CCK, PYY and PP signal to important areas in the CNS involved in appetite regulation to terminate a meal. These hormones can act directly via the circulation and activate their respective receptors in the hypothalamus and brainstem. In addition, gut vagal afferents also exist, providing an alternative pathway through which gut hormones can communicate with higher centres through the brainstem. Animal and human studies have demonstrated that peripheral administration of certain gut hormones reduces food intake and leads to weight loss. Gut hormones are therefore potential targets in the development of novel treatments for obesity and analogue therapies are currently under investigation.

Synergistic effect of CART (cocaine- and amphetamine-regulated transcript) peptide and cholecystokinin on food intake regulation in lean mice

Background

CART (cocaine- and amphetamine-regulated transcript) peptide and cholecystokinin (CCK) are neuromodulators involved in feeding behavior. This study is based on previously found synergistic effect of leptin and CCK on food intake and our hypothesis on a co-operation of the CART peptide and CCK in food intake regulation and Fos activation in their common targets, the nucleus tractus solitarii of the brainstem (NTS), the paraventricular nucleus (PVN), and the dorsomedial nucleus (DMH) of the hypothalamus.

Results

In fasted C57BL/6 mice, the anorexigenic effect of CART(61-102) in the doses of 0.1 or 0.5 μg/mouse was significantly enhanced by low doses of CCK-8 of 0.4 or 4 μg/kg, while 1 mg/kg dose of CCK-A receptor antagonist devazepide blocked the effect of CART(61-102) on food intake. After simultaneous administration of 0.1 μg/mouse CART(61-102) and of 4 μg/kg of CCK-8, the number of Fos-positive neurons in NTS, PVN, and DMH was significantly higher than after administration of each particular peptide. Besides, CART(61-102) and CCK-8 showed an additive effect on inhibition of the locomotor activity of mice in an open field test.

Conclusion

The synergistic and long-lasting effect of the CART peptide and CCK on food intake and their additive effect on Fos immunoreactivity in their common targets suggest a co-operative action of CART peptide and CCK which could be related to synergistic effect of leptin on CCK satiety.

Circadian rhythm drives the responsiveness of leptin-mediated hypothalamic pathway of cholecystokinin-8

Cholecystokinin (CCK) and leptin act coordinately in the brain to regulate food intake and energy balance. Recently we have reported that CCK enhances the permeability of brain barriers to leptin and we have proposed that CCK enhances energy expenditure in rats by activating in the hypothalamus the janus kinase/signal transducer and activator of transcription (JAK/STAT) signalling pathway, which is coupled to leptin receptors. Because plasma leptin concentration follows a circadian rhythm (plasma leptin concentration rise maximal values during the night, after rats start eating), we have hypothesized that the interaction between leptin and CCK should be more intense in animals receiving CCK during the night, i.e., during periods of positive energy balance. In order to further characterize the physiological relevance of the interplay between leptin and CCK we have compared the effect of diurnal vs. nocturnal administration of the C-terminal octapeptide of CCK (CCK-8) on (i) body weight and food intake, and (ii) STAT3 activation, by analyzing phosphorylated STAT3 (pSTAT3) immunostaining within the arcuate nucleus of the hypothalamus. Our results show that CCK decreases body weight and food intake only after p.m. administration. Accordingly pSTAT3 immunostaining within the hypothalamus was more intense in p.m. than in a.m.-treated animals. These data suggest that the effect of CCK on leptin pathways follows a circadian rhythm linked to the energy balance status and gives further support to the interaction between leptin and CCK.

Leptin-mediated hypothalamic pathway of cholecystokinin (CCK-8) to regulate body weight in free-feeding rats

Regulation of body weight (BW) results from the interplay between different hormonal systems acting at central and peripheral level. This study aims at characterizing the involvement of cholecystokinin (CCK) in BW and energy balance regulation. We have characterized, in free-feeding rats, the effect of CCK-8 on 1) food intake, BW, and adiposity; 2) skeletal muscle metabolism; 3) leptin signaling pathway within the arcuate nucleus of the hypothalamus; and 4) the permeability of brain barriers to leptin. We demonstrate here that CCK-8 acutely decreases BW by a mechanism partially dependent on central leptin pathways, based on the following results: 1) the effect of CCK was less intense in rats lacking functional leptin receptors (Zucker fa/fa), 2) CCK-8 facilitated the uptake of leptin from peripheral circulation to cerebrospinal fluid (CSF), 3) the concentration of leptin in CSF of rats receiving CCK was more elevated in those animals showing higher loss of BW, and 4) CCK activated leptin signaling pathways within the hypothalamus as well as phosphorylation of AMP-activated protein kinase in skeletal muscle. We also suggest that gain of BW may be linked to individual susceptibility to the effect of CCK, because we observed that in animals treated with this hormone, the increase of BW negatively correlated with leptin concentration within the CSF. Our data show that CCK has a negative impact on energy balance and suggest that CCK facilitates the access of leptin to hypothalamic areas, thus allowing leptin to act on hypothalamic targets involved in BW control.

Cholecystokinin enhances GABAergic inhibitory transmission in basolateral amygdala

The neuropeptide cholecystokinin (CCK) is anxiogenic in studies of human and animal behavior. As the amygdala formation has been implicated in generation of emotional states such as anxiety, we tested the effect of CCK on spontaneous synaptic events in the basolateral amygdala (BLA) using whole cell patch recordings in rat brain slice preparation. We found that CCK increased the frequency of spontaneous inhibitory postsynaptic potentials (sIPSPs) and currents (sIPSCs). This effect was blocked by the fast sodium channel blocker tetrodotoxin (TTX), indicating that the CCK effect is likely mediated by direct excitation of GABAergic interneurons. The CCK(B) receptor subtype antagonist, CR2945, blocked the CCK effect, while CCK4, a specific CCK(B) agonist, increased sIPSC frequency. We hypothesize that these actions may underlie the anxiogenic effects of CCK observed in behavioral studies.

CCK2 receptor nullification attenuates lipopolysaccharide-induced sickness behavior

Systemic infection produces a highly regulated set of responses such as fever, anorexia, adipsia, inactivity, and cachexia, collectively referred to as sickness behavior. Although the expression of sickness behavior requires immune-brain communication, the mechanisms by which peripheral cytokines signal the brain are unclear. Several mechanisms have been proposed for neuroimmune communication, including the interaction of cytokines with peripheral nerves. A critical role has been ascribed to the vagus nerve in mediating sickness behavior after intraperitoneally delivered immune activation, and converging evidence suggests that this communication may involve neurochemical intermediaries afferent and/or efferent to this nerve. Mice lacking functional CCK2/gastrin receptors (CCK2KO) and wild-type (WT) controls were administered LPS (50, 500, or 2,500 μg/kg; serotype 0111:B4; ip). Results indicate a role for CCK2 receptor activation in the initiation and maintenance of LPS-induced sickness behavior. Compared with WT controls, CCK2KO mice were significantly less affected by LPS on measures of body temperature, activity, body weight, and food intake, with the magnitude of effects increasing with increasing LPS dose. Although activation of CCK2 receptors at the level of the vagus nerve cannot be excluded, a possible role for these receptors in nonvagal routes of immune-brain communication is suggested.

Modulatory effect of CCK-8S on GABA-induced depolarization from rat dorsal root ganglion

CCK is a brain-gut peptide that is abundantly distributed in both gastrointestinal tract and mammalian brain. The sulfated octapeptide fragment of cholecystokinin (CCK-8S) has been shown to be involved in numerous physiological functions such as behavior, anxiety, learning/memory processes and neuropathic pain. CCK-8S is one of the strongest endogenous anti-opioid substances and suppresses opioid peptides-mediated 'pre-synaptic inhibition' of gamma-aminobutyric acid (GABA) release. Here we provide evidence that CCK-8S modulates GABA-evoked membrane depolarization in rat dorsal root ganglion (DRG) neurons using intracellular recording technique. Bath application CCK-8S-induced membrane depolarization in most of the rat DRG neurons. The depolarization was blocked by prolumide but not LY225910. Pretreatment with CCK-8S suppressed the GABA-evoked depolarization in a concentration-dependent manner. The CCK-8S inhibition was also time-dependent and reached the peak at about 2 min. The inhibitory effect of CCK-8S was strongly suppressed by pre-incubation of CCK-B receptor antagonist LY225910, phospholipase C inhibitor U73122, protein kinase C inhibitor chelerythrine and calcium chelator BAPTA-AM, respectively. The protein kinase A inhibitor H-89 did not affect CCK-8S effect. The results suggest that CCK-8S inhibits GABA-A receptor function by activation of CCK-B receptor followed by activation of intracellular PLC-Ca(2+)-PKC cascade. Thus, CCK-8S might enhance nociceptive information transmission through inhibition of the "pre-synaptic inhibition" evoked by GABA, which may explain its role in modulation of primary sensory information (especially pain).

Neuronal excitability in the periaqueductal grey matter during the estrous cycle in female Wistar rats

Extracellular recordings were made from output neurons in the dorsal half of the periaqueductal gray matter (dPAG) in urethane-anesthetized female Wistar rats. All the neurons were quiescent. A basal level of firing was therefore induced by continuous iontophoretic application of D,L-homocysteic acid (DLH). In the presence of the GABA(A) receptor antagonist bicuculline methiodide (BIC 0-30 nA) the DLH-induced firing increased further, revealing the presence of ongoing GABAergic inhibitory tone on the recorded neurons. The BIC-induced increase in firing rate was significantly greater in neurons recorded during estrus (Est) and late diestrus (LD) compared with proestrus (Pro) and early diestrus (ED) suggesting that GABAergic tone was lower in Est and LD. I.v. injection of the panicogenic cholecystokinin (CCK)(B) receptor agonist pentagastrin (PG, 40 microg kg(-1)) produced an increase in firing rate in 12/17 (70%) of neurons tested in the dPAG. Iontophoretic application of PG (10-30 nA) also produced a current-related increase in firing rate in 73.6% of the neurons tested. The excitatory response was reduced during application of the selective CCK(B) receptor antagonist beta-[2-([2-(8-azaspiro[4.5]dec-8-ylcarbonyl)-4,6-dimethylphenyl]amino)-2-oxoethyl]-(R)-napthalenepropanoic acid (CR2945) (60 nA, n=6). The PG-evoked increase in firing rate was significantly greater in neurons recorded during Est and LD compared with during Pro and ED. Juxtacellular labeling with neurobiotin in eight neurons revealed multipolar cells 12-44 microm diameter with up to six primary dendrites. In three of eight neurons, a filled axon was present and coursed without branching toward the perimeter of the periaqueductal gray matter (PAG). The estrous cycle-related change in responsiveness to BIC and PG suggests that the panic circuitry in the PAG may become more responsive to panicogenic agents during estrus and late diestrus as a consequence of a decrease in the intrinsic level of inhibitory GABAergic tone. The findings may have implications for understanding the neural processes that underlie the development of premenstrual dysphorias in women.

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.

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.

Determination of target cells for cholecystokinin in the porcine pancreas

The cholecystokinin (CCK) family of peptides and receptors is present throughout the brain and gastrointestinal tract including pancreatic tissue. The expression of these molecules in the gut and pancreas is species-specifically regulated and the role of CCK in porcine pancreatic islet hormone secretion is still a matter of discussion. Therefore, in this study we have determined the cell-type specific localization of and its high affinity CCKA-receptor in islet cells using immunohistochemical techniques. Serial sectioning followed by double-immunostaining of methanol/acetic acid-fixed, paraffin-embedded pancreatic tissues were performed with antibodies against CCK, CCKA-receptor, glucagon and somatostatin. To determine whether CCK specific mRNA is locally expressed, total RNA was isolated, transcribed to cDNA and analysed with specific primer for CCK gene expression. Our results clearly show that CCK and the CCKA-receptor coexist in glucagon--but not in somatostatin-producing cells. Moreover our RT-PCR experiments demonstrate that there is no local gene expression of CCK in the porcine pancreas. Our results provide evidence that, in the porcine species, blood-borne CCK binds specifically to the CCKA-receptor and may thereby modulate the glucose homeostasis via a direct action on A-cells.

Cholecystokinin octapeptide increases spontaneous glutamatergic synaptic transmission to neurons of the nucleus tractus solitarius centralis

Cholecystokinin (CCK) is released from enteroendocrine cells after ingestion of nutrients and induces multiple effects along the gastrointestinal tract, including gastric relaxation and short-term satiety. We used whole cell patch-clamp and immunohistochemical techniques in rat brain stem slices to characterize the effects of CCK. In 45% of the neurons of nucleus tractus solitarius subnucleus centralis (cNTS), perfusion with the sulfated form of CCK (CCK-8s) increased the frequency of spontaneous excitatory currents (sEPSCs) in a concentration-dependent manner (1-300 nM). The threshold for the CCK-8s excitatory effect was 1 nM, the EC(50) was 20 nM, and E(max) was 100 nM. The excitatory effects of CCK-8s were still present when the slices were preincubated with tetrodotoxin or bicuculline or when the recordings were conducted with Cs(+) electrodes. Pretreatment with the CCK-A receptor antagonist, lorglumide (1 microM), antagonized the effects of CCK-8s, whereas perfusion with the CCK-B preferring agonist CCK-8 nonsulfated (CCK-ns, 1 microM) did not affect the frequency of sEPSCs. Similarly, pretreatment with the CCK-B receptor antagonist, triglumide (1 microM), did not prevent the actions of CCK-8s. Although the majority (i.e., 76%) of CCK-8s unresponsive cNTS neurons had a bipolar somata shape and were TH-IR negative, no differences were found in either the morphological or the neurochemical phenotype of cNTS neurons responsive to CCK-8s. Our results suggest that the excitatory effects of CCK-8s on terminals impinging on a subpopulation of cNTS neurons are mediated by CCK-A receptors; these responsive neurons, however, do not have morphological or neurochemical characteristics that automatically distinguish them from nonresponsive neurons.

In vitro analysis of the effects of cholecystokinin on rat brain stem motoneurons

Using whole cell patch clamp in thin brain stem slices, we tested the effects of cholecystokinin (CCK) on identified gastric-projecting neurons of the rat dorsal motor nucleus of the vagus (DMV). Perfusion with the sulfated form of CCK octapeptide (CCK8s, 30 pM-300 nM, EC50 approximately 4 nM) induced a concentration-dependent inward current in 35 and 41% of corpus- and antrum/pylorus-projecting DMV neurons, respectively. Conversely, none of the fundus-projecting DMV neurons responded to perfusion with CCK8s. The CCK8s-induced inward current was accompanied by a 65 +/- 17% increase in membrane input resistance and reversed at 90 +/- 4 mV, indicating that the excitatory effects of CCK8s were mediated by the closure of a potassium conductance. Pretreatment with the synaptic blocker TTX (0.3-1 microM) reduced the CCK8s-induced current, suggesting that a portion of the CCK8s-induced current was mediated indirectly via an action on presynaptic neurons apposing the DMV membrane. Pretreatment with the selective CCK-A receptor antagonist lorglumide (0.3-3 microM) attenuated the CCK8s-induced inward current in a concentration-dependent manner, with a maximum inhibition of 69 +/- 12% obtained with 3 microM lorglumide. Conversely, pretreatment with the selective CCK-B antagonist triglumide did not attenuate the CCK8s-induced inward current; pretreatment with triglumide (3 microM) and lorglumide (1 microM) attenuated the CCK8s-induced current to the same extent as pretreatment with lorglumide alone. Immunohistochemical experiments showed that CCK-A receptors were localized on the membrane of 34, 65, and 60% of fundus-, corpus-, and antrum/pylorus-projecting DMV neurons, respectively. Our data indicate that CCK-A receptors are present on a subpopulation of gastric-projecting neurons and that their activation leads to excitation of the DMV membrane.

Cholecystokinin modulates migration of gonadotropin-releasing hormone-1 neurons

Expression of the brain-gut peptide cholecystokinin (CCK) in the developing olfactory-gonadotropin-releasing hormone-1 (GnRH-1) neuroendocrine systems was characterized, and the function of CCK in these systems was analyzed both in vivo and in vitro. We present novel data demonstrating that CCK transcript and protein are expressed in sensory cells in the developing olfactory epithelium and vomeronasal organ, with both ligand and receptors (CCK-1R and CCK-2R) found on olfactory axons throughout prenatal development. In addition, migrating GnRH-1 neurons in nasal regions express CCK-1R but not CCK-2R receptors. The role of CCK in olfactory-GnRH-1 system development was evaluated using nasal explants, after assessing that the in vivo expression of both CCK and CCK receptors was mimicked in this in vitro model. Exogenous application of CCK (10(-7) m) reduced both olfactory axon outgrowth and migration of GnRH-1 cells. This inhibition was mediated by CCK-1R receptors. Moreover, CCK-1R but not CCK-2R antagonism caused a shift in the location of GnRH-1 neurons, increasing the distance that the cells migrated. GnRH-1 neuronal migration in mice carrying a genetic deletion of either CCK-1R or CCK-2R receptor genes was also analyzed. At embryonic day 14.5, the total number of GnRH-1 cells was identical in wild-type and mutant mice; however, the number of GnRH-1 neurons within forebrain was significantly greater in CCK-1R-/- embryos, consistent with an accelerated migratory process. These results indicate that CCK provides an inhibitory influence on GnRH-1 neuronal migration, contributing to the appropriate entrance of these neuroendocrine cells into the brain, and thus represent the first report of a developmental role for CCK.

Cholecystokinin modulation of locomotor behavior in rats is sensitized by chronic amphetamine and chronic restraint stress exposure

DA release in the nucleus accumbens (NAcc) is a critical substrate mediating locomotor behavior. Cholecystokinin (CCK) is co-localized with dopamine (DA) in up to 90% of mesolimbic DA neurons. We have previously shown that while CCKA receptor antagonists generally do not affect locomotor behaviors, systemic administration of a CCKA receptor antagonist attenuates amphetamine (AMPH)-induced locomotion in animals previously treated chronically with AMPH, suggesting that chronic stimulant pretreatment may sensitize CCK systems. The present studies examined this issue by testing the effects of CCKA antagonists on AMPH- and novel environment-induced locomotor activity following two manipulations which are known to alter mesolimbic system function: Chronic AMPH administration and chronic restraint stress (RS). Additionally, CCK immunoreactivity in the mesolimbic system following these manipulations was examined using immunohistochemistry. Results indicated that intra-NAcc microinjections of the selective CCKA receptor antagonist PD-140548 attenuated AMPH-induced and novel environment-induced locomotion only in animals which had previously been exposed to chronic AMPH or chronic RS pretreatment. However, chronic AMPH and chronic RS did not produce detectable changes in the number of CCK-immunostained neurons in the ventral tegmental area (VTA) or substantia nigra (SN), or in CCK levels in any of the subregions of the NAcc. Together, these results suggest that the role of endogenous CCK in the modulation of locomotor behaviors is sensitized following chronic psychostimulant or chronic RS exposure. However, this sensitization does not appear to be accompanied by changes in the overall basal levels of CCK or in the number of CCK-positive cells within the mesoaccumbens system.

Immunolocalization of CCK1R in rat brain using a new anti-peptide antibody

An antibody directed at the carboxy tail of the cholecystokinin-1 receptor (CCK1R) was characterized by ELISA and Western blotting. Immunohistochemistry established that CCK1R-like immunoreactivity (CCK1R-LI) was widely and topographically distributed through the neuroaxis, appearing relatively higher in rhi- and diencephalon, and intense in both neuronal somata (cytoplasmic) and processes. CCK1R-LI was found in new loci, but also in areas previously identified by receptor autoradiography, electrophysiology and in situ hybridization of CCK1R mRNA. The widespread distribution of CCK1R has implications for the functional roles of these receptors in brain. The high titre and low background seen with this new antiserum makes it of great value for cell and tissue research.

Characterization of the role of endogenous cholecystokinin on the activity of the paraventricular nucleus of the hypothalamus in rats

Activation of the hypothalamic-pituitary-adrenal axis by fasting seems to involve cholecystokinin (CCK) receptors. This work aims to characterize the role of endogenous CCK in the activity of the paraventricular nucleus (PVN) of the hypothalamus during food withdrawal. We investigated, by c-Fos immunohistochemistry, the effect of CCK1 and CCK2 receptor antagonists (SR-27,897 and L-365,260, respectively) on c-Fos levels expression induced by food deprivation. Under our conditions, the number of cells expressing c-Fos was reduced both by SR-27,897 and L-365,260 in food-deprived rats. To investigate the importance of glucose availability, we studied the effect of CCK receptor antagonists on c-Fos synthesis induced by the glucose antimetabolite 2-deoxyglucose. In these animals, only SR-27,897 decreased c-Fos expression in the PVN. Our results indicate that the effect of CCK antagonists is mainly perceptible when glucose availability decreases, and suggest that CCK-ergic inputs could drive the activity of the PVN under fasting/low glucose conditions.

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.

Enterostatin inhibition of dietary fat intake is dependent on CCK-A receptors

Enterostatin, a pentapeptide released from the exocrine pancreas and gastrointestinal tract, selectively inhibits fat intake through activation of an afferent vagal signaling pathway. This study investigated if the effects of enterostatin were mediated through a CCK-dependent pathway. The series of in vivo and in vitro experiments included studies of 1) the feeding effect of peripheral enterostatin on Otsuka Long Evans Tokushima Fatty (OLETF) rats lacking CCK-A receptors, 2) the effect of CCK-8S on the intake of a two-choice high-fat (HF)/low-fat (LF) diet, 3) the effects of peripheral or central injection of the CCK-A receptor antagonist lorglumide on the feeding inhibition induced by either central or peripheral enterostatin, and 4) the ability of enterostatin to displace CCK binding in a 3T3 cell line expressing CCK-A receptor gene and in rat brain sections. The results showed that OLTEF rats did not respond to enterostatin (300 microg/kg ip) in contrast to the 23% reduction in intake of HF diet in Long Evans Tokushima Otsuka (LETO) control rats. CCK (1 microg/kg ip) decreased the intake of the HF diet in a two-choice diet regime with a compensatory increase in intake of the LF diet. Peripheral injection of lorglumide (300 microg/kg) blocked the feeding inhibition induced by either near-celiac arterial or intracerebroventricular enterostatin, whereas intracerebroventricular lorglumide (5 nmol icv) only blocked the response to intracerebroventricular enterostatin but not to arterial enterostatin. Enterostatin did not bind on CCK-A receptors because neither enterostatin nor its analogs VPDPR and beta-casomorphin displaced [3H]L-364,718 from CCK-A receptors expressed in 3T3 cells or the binding of 125I-CCK-8S from rat brain sections. The data suggest that both the peripheral and central responses to enterostatin are mediated through or dependent on peripheral and central CCK-A receptors.

Modulation of visceral hyperalgesia by morphine and cholecystokinin from the rat rostroventral medial medulla

Using a model of visceral nociception, we examined whether cholecystokinin (CCK) acts as an anti-opioid peptide in the rat rostral ventromedial medulla (RVM). Because such interaction may be affected by inflammation, rats with and without inflamed colons were studied. The visceromotor response to noxious colorectal distension (CRD), quantified electromyographically, was recorded before and after intra-RVM administration of CCK, CCK receptor antagonists, and morphine. Either 50% ethanol/saline (vehicle) or 2,4,6-trinitrobenzenesulfonic acid (TNBS), which inflames the colon, was instilled into the colon 5 days before experiments. Intra-RVM morphine dose-dependently attenuated responses to CRD in intracolonic vehicle-treated rats. In TNBS-treated rats with inflamed colons, responses to CRD were significantly increased and 0.3, 3.0 and 6.0 microg doses of intra-RVM morphine reduced responses to control (i.e. were anti-hyperalgesic); the greatest dose tested (30 microg) further reduced responses to 40% control. In intracolonic vehicle-treated rats, intra-RVM pre-treatment with a selective CCK(B) (but not CCK(A)) receptor antagonist dose-dependently and significantly enhanced the effect of a low dose of morphine. Intra-RVM CCK-8 peptide enhanced responses to CRD in intracolonic vehicle-treated, but not TNBS-treated rats. Intra-RVM naloxone was without effect in intracolonic vehicle-or TNBS-treated rats, suggesting an absence of tonic opioid activity in RVM. These results document a CCK-opioid interaction in RVM, suggesting that colon inflammation leads to tonic activity at CCK(B) receptors in RVM.

What we know and what we need to know about the role of endogenous CCK in psychostimulant sensitization

The unique distribution of CCK and its receptors and its co-localization with dopamine makes it ideally situated to pay a role in dopamine-mediated reward and psychostimulant sensitization. A number of studies support the hypothesis that CCK acting through the CCK 1 and CCK 2 receptors is an endogenous modulator of dopamine neurotransmission. Behavioral studies with CCK antagonists and CCK 1 receptor mutant rats support a role for endogenous CCK in behavioral sensitization to psychostimulants. CCK microdialysis studies in the nucleus accumbens (NAC) have demonstrated that extracellular CCK is increased in the NAC by psychostimulants, providing neurochemical evidence that CCK could be involved in the behavioral response to psychostimulants. A model for how CCK may be acting in multiple brain regions to foster sensitization is presented and the gaps in our knowledge about the role of CCK in psychostimulant sensitization are described.

Some aspects on the anatomy and function of central cholecystokinin systems

The distribution of some cholecystokinin (CCK) systems in the rat brain is reviewed focusing on mesencephalic dopamine neurones which coexpress CCK and, in particular, on cortico-striatal CCK neurones which probably have glutamate as their co-transmitter. Functional studies based on the effect of several CCK(B) antagonists on phencyclidine-induced motility suggest that CCK is involved in locomotor behaviour causing inhibition in phencyclidine-treated habituated rats. In contrast, in unhabituated rats CCK stimulates exploratory behaviour. These effects may be related to the cortico-striatal CCK/glutamatergic pathway. Moreover, these studies provide evidence for endogenous release of a neuropeptide with behavioural consequences.

Oestrogen modulates cholecystokinin: opioid interactions in the nervous system

Responses of the nervous system to introceptive and extroceptive inputs depend upon the state of the brain. Oestrogen has the ability to modulate brain state and dramatically alter interactions among neural circuits to influence an organism's responses to given stimuli. Cholecystokinin (CCK) and endogenous opioid peptides (EOP) have a wide and parallel distribution in the nervous system. Their reciprocal interactions regulate a diverse physiology including reproduction, cortical function and nociception. The actions of CCK and EOP are diametrically opposed, in many regions. For example, when opioids inhibit reproductive behaviour or nociception, CCK facilitates. Because oestrogen is a powerful regulator of the expression of CCK and EOP, we examined whether oestrogen-state also modulated the interactions of these neuropeptides. In this paper we present new data and review previous work that demonstrates oestrogen modulation of functional CCK-opioid interactions that regulate reproductive behaviour, cortical function and nociception.

Cholecystokinin-8 induces intracellular calcium signaling in cultured myenteric neurons from neonatal guinea pigs

The responsiveness of cultured myenteric neurons to cholecystokinin (CCK-8) was examined using fura-2-based digital microfluorimetric measurement of intracellular calcium ([Ca(2+)](i)). CCK-8 (10(-10)-10(-6)M) evoked concentration-dependent increases in percentage of neurons responding (8-52%) and delta[Ca(2+)](i) (76-169 nM). Gastrin (1 microM) also induced an increase in [Ca(2+)](i) in 29+/-6% of neurons (delta[Ca(2+)](i): 71+/-3 nM). L-364,718, an antagonist for the CCK-A receptor, blocked [Ca(2+)](i) response to CCK-8. Removal of extracellular calcium eliminated CCK-induced [Ca(2+)](i) increments, as did the addition of the calcium channel inhibitors nickel (1mM) and lanthanum (5mM). Nifedipine (1-50 microM) dose-dependently attenuated CCK-caused [Ca(2+)](i) responses. CCK evokes [Ca(2+)](i) signaling in myenteric neurons by the influx of extracellular calcium, likely through L-type calcium channels.

Cocaine treatment increases extracellular cholecystokinin (CCK) in the nucleus accumbens shell of awake, freely moving rats, an effect that is enhanced in rats that are behaviorally sensitized to cocaine

Cholecystokinin (CCK) is co-localized with dopamine, is known to modulate dopamine neurotransmission and is involved in behavioral sensitization to psychostimulants. To better understand its role, CCK was measured by microdialysis in the nucleus accumbens (NAC) shell in response to cocaine in drug-naive rats and in rats that are behaviorally sensitized to cocaine. Basal extracellular levels of CCK in drug-naive rats were 0.17 pg/20 min fraction, while in cocaine-sensitized rats, they were significantly higher (0.56 pg). Treating drug-naive rats with cocaine caused a significant increase in CCK to 0.58 pg. Cocaine treatment of cocaine-sensitized rats increased CCK to 0.98. When analyzed as a function of time after cocaine treatment, these increases were sustained and were significantly different from CCK levels of saline-treated rats. In cocaine-sensitized rats, CCK levels following cocaine treatment were also significantly higher than levels in drug-naive animals receiving a single injection of cocaine. These results provide evidence for an activation of the mesolimbic and/or cerebral cortical CCK system in response to repeated cocaine administration. These results provide a neurochemical basis for an important role of CCK (via modulation of dopamine neurotransmission) in expression of cocaine sensitization.

Decreased haloperidol-induced potentiation of zif268 mRNA expression in the nucleus accumbens shell and the dorsal lateral striatum of rats lacking cholecystokinin-A receptors

Evidence suggests that endogenous cholecystokinin (CCK), a neuropeptide that modulates brain dopamine function, may contribute to the therapeutic and motor effects of antipsychotic drugs via activation of CCK-A receptors in the mesolimbic and nigrostriatal pathways, respectively. To determine if CCK modulates the effects of antipsychotic drugs through CCK-A receptors, we measured the haloperidol-induced zif268 mRNA response in the nucleus accumbens (NA) shell, NA core, and dorsal lateral striatum (DLS) in Otsuka Long Evans Tokushima Fatty (OLETF) rats that lack CCK-A receptors due to a spontaneous mutation. OLETF rats and normal Long Evans rats were treated with subcutaneous (s.c.) injections of saline or haloperidol (2 mg/kg). In situ hybridization was performed and zif268 mRNA expression was quantified. The haloperidol-induced expression of zif268 mRNA was significantly decreased in the DLS (P < 0.01) and the NA shell (P < 0.05), but not in the NA core, in OLETF rats compared to LETO rats. These data suggest that CCK-A receptor mechanisms may contribute to the therapeutic and the extrapyramidal motor effects associated with antipsychotic drug treatment.

PYY inhibits CCK-stimulated pancreatic secretion through the area postrema in unanesthetized rats

Peptide YY (PYY) inhibits CCK-8-secretin-stimulated pancreatic secretion in vivo. To investigate whether CCK-8-secretin-stimulated pancreatic secretion is mediated through a vago-vagal pathway and whether PYY inhibits this pathway through the area postrema (AP), chronic pancreatic, biliary, and duodenal catheters were implanted in AP-lesioned (APX) or sham-operated rats. The effects of APX on pancreatic secretion stimulated by bethanechol, pancreatic juice diversion (PJD), or CCK-8-secretin, were tested, with and without background PYY infusion, in unanesthetized rats. APX reduced basal pancreatic secretion by 15-20% (P < 0.01). APX had no effect on bethanechol-stimulated secretion and potentiated protein secretion stimulated by PJD (396 vs. 284%) and exogenous CCK-8-secretin. In sham-operated rats, background PYY potently inhibited CCK-8-secretin-stimulated pancreatic fluid (1.8 vs. 48.2%) and protein secretion (3.7 vs. 45.8%) but potentiated fluid (52.9 vs. 43.1%) and protein (132.9 vs. 68.9%) secretion in APX rats. Our findings demonstrate that PYY inhibits CCK-8-secretin-stimulated pancreatic secretion through an AP-dependent mechanism in sham-operated rats. The AP also contributes to basal pancreatic secretion.

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.

CCK/dopamine interactions in Fawn-Hooded and Wistar-Kyoto rat brain

The aim of this study was to compare the actions of CCK neuropeptides within the nucleus accumbens (N.Acc) of alcohol preferring (Fawn-Hooded, FH) and alcohol nonpreferring (Wistar-Kyoto, WKY) rats. CCK-8S (30-300 nM) facilitated the K(+) stimulated release of [(3)H]dopamine (DA) from N.Acc prisms in both rat strains, whereas CCK-4 (30 nM-1 microM) caused a significant decrease of evoked [(3)H]DA in the FH rat only. A scattered distribution of CCK-A and -B receptor immunopositive varicose fibers were visualized throughout the N.Acc of both rat strains along with a topographic distribution of CCK receptor positive cells throughout the ventral mesencephalon.