Cholecystokinin/dopamine/GABA interactions in the nucleus accumbens: biochemical and functional correlates

The Formation and Function of the VTA Dopamine System

The midbrain dopamine system is a sophisticated hub that integrates diverse inputs to control multiple physiological functions, including locomotion, motivation, cognition, reward, as well as maternal and reproductive behaviors. Dopamine is a neurotransmitter that binds to G-protein-coupled receptors. Dopamine also works together with other neurotransmitters and various neuropeptides to maintain the balance of synaptic functions. The dysfunction of the dopamine system leads to several conditions, including Parkinson's disease, Huntington's disease, major depression, schizophrenia, and drug addiction. The ventral tegmental area (VTA) has been identified as an important relay nucleus that modulates homeostatic plasticity in the midbrain dopamine system. Due to the complexity of synaptic transmissions and input-output connections in the VTA, the structure and function of this crucial brain region are still not fully understood. In this review article, we mainly focus on the cell types, neurotransmitters, neuropeptides, ion channels, receptors, and neural circuits of the VTA dopamine system, with the hope of obtaining new insight into the formation and function of this vital brain region.

Inhibition of Geranylgeranylacetone on cholecystokinin-B receptor, BDNF and dopamine D1 receptor induced by morphine

Morphine is the pain releasing and abusing drug. Morphine leads to addiction by activating dopaminergic rewarding system consisted of the ventral tegmental area (VTA) and nucleus accumbens (NAc). Cholecystokinin (CCK) is a gut-brain neuropeptide and involved in morphine dependence. Brain-derived neurotrophic factor (BDNF) is a neurotrophin and plays roles in regulating addiction. Geranylgeranylacetone (GGA) is a medicine of protecting gastric mucosal injury and protecting neurons. Our previous study showed that GGA blocked morphine-induced withdrawal and relapse through inducing thioredoxin 1(Trx1). In this study, we investigated that whether cholecystokinin-B receptor (CCKB receptor) and BDNF were related to GGA inhibition on morphine addiction. At first, we made conditioned place preference (CPP) model and confirmed again that GGA blocked the expression of morphine-CPP in present study. Then, our results showed that morphine increased the expressions of dopamine D1 receptor, tyrosine hydroxylase (TH), CCKB receptor and BDNF in the VTA and NAc in mice, which was inhibited by GGA. These results suggest that CCK and BDNF in dopaminergic systems are associated with the role of GGA blocking morphine-CPP.

A cholecystokinin B receptor antagonist and cocaine interaction, phase I study

AIMS

RPR 102681, a cholecystokinin-B antagonist, increased dopamine (DA) release and reduced cocaine self-administration in animals. This pilot study sought to assess the safety and pharmacokinetics (PK) of co-administration of RPR 102681 and cocaine, and to confirm the DA release mechanism of RPR 102681.

METHODS

Sixteen cocaine-dependent participants were randomized to either placebo or RPR102681 at 3 ascending doses; cocaine was co-administered at steady state of RPR 102681. [¹¹ C]raclopride positron emission tomography scans were conducted at baseline and at each RPR102681 dose.

RESULTS

RPR 102681 was well tolerated, and safe to co-administer with cocaine. RPR 102681 did not alter the PK of either cocaine or its metabolite benzoylecgonine and showed no intrinsic abuse liability. There was a trend toward reduction of cocaine craving scores. In contrast to animal studies, RPR 102681 significantly increased the binding potential of [¹¹ C]raclopride in the ventral striatum (t test, P < .001) and caudate nucleus (t test, P < .0001) in a small subset of patients, suggesting that it may reduce intrasynaptic striatal DA.

CONCLUSION

Overall, this pilot study suggests that RPR 102681 would be unlikely candidate, as an agonist medication for the treatment for cocaine addiction but worth investigating further for possible role in reducing craving.

Cholecystokinin selectively activates short axon cells to enhance inhibition of olfactory bulb output neurons

KEY POINTS

Cholecystokinin (CCK) via CCK-B receptors significantly enhances the GABA_A receptor-mediated synaptic inhibition of principal olfactory bulb (OB) output neurons. This CCK action requires action potentials in presynaptic neurons. The enhanced inhibition of OB output neurons is a result of CCK-elevated inhibitory input from the glomerular circuit. CCK modulation of the glomerular circuit also leads to potentiated presynaptic inhibition of olfactory nerve terminals and postsynaptic inhibition of glomerular neurons. Selective excitation of short axon cells underlies the CCK-potentiated glomerular inhibition.

ABSTRACT

Neuropeptides such as cholecystokinin (CCK) are important for many brain functions, including sensory processing. CCK is predominantly present in a subpopulation of excitatory neurons and activation of CCK receptors is implicated in olfactory signal processing in the olfactory bulb (OB). However, the cellular and circuit mechanisms underlying the actions of CCK in the OB remain elusive. In the present study, we characterized the effects of CCK on synaptic inhibition of the principal OB output neurons mitral/tufted cells (MTCs) followed by mechanistic analyses at both circuit and cellular levels. First, we found that CCK via CCK-B receptors enhances the GABA_A receptor-mediated spontaneous IPSCs in MTCs. Second, CCK does not affect the action potential independent miniature IPSCs in MTCs. Third, CCK potentiates glomerular inhibition resulting in increased GABA_B receptor-mediated presynaptic inhibition of olfactory nerve terminals and enhanced spontaneous IPSCs in MTCs and glomerular neurons. Fourth, CCK enhances miniature IPSCs in the excitatory external tufted cells, although neither in the inhibitory short axon cells (SACs) nor in periglomerular cells (PGCs). Finally, CCK excites all tested SACs and a very small minority of GABAergic neurons in the granule cell layer or in periglomerular cells, but not in deep SACs. These results demonstrate that CCK selectively activates SACs to engage the SAC-formed interglomerular circuit and thus elevates inhibition broadly in the OB glomerular layer. This modulation may prevent the system from saturating in response to a high concentration of odourants or facilitate the detection of weak stimuli by increasing signal-to-noise ratio.

Neuropeptide S Increases locomotion activity through corticotropin-releasing factor receptor 1 in substantia nigra of mice

Neuropeptide S (NPS), the endogenous ligand of NPS receptor (NPSR), was reported to be involved in the regulation of arousal, anxiety, locomotion, learning and memory. The basal ganglia play a crucial role in regulating of locomotion-related behavior. Here, we found that NPSR protein of mouse was distributed in the substantia nigra (SN) and globus pallidus (LGP) by immunohistochemical analysis. However, less is known about the direct locomotion-related effects of NPS in both SN and LGP. Therefore, we investigated the role of NPS in locomotion processes, using the open field test. The results showed that NPS infused into the SN (0.03, 0.1, 1nmol) or LGP (0.01, 0.03, 0.1nmol) dose-dependently increased the locomotor activity in mice. SHA 68 (50mg/kg), an antagonist of NPSR, blocked the locomotor stimulant effect of NPS in both nuleus. Meanwhile, these effects of NPS were also counteracted by the CRF1 receptor antagonist antalarmin (30mg/kg, i.p.). In addition, we found that the expression of c-Fos was significantly increased after NPS was delivered into SN. In conclusion, these results indicate that NPS-NPSR system may regulate locomotion together with the CRF1 system in SN.

Cholecystokinin A receptor (CCKAR) gene variation is associated with language lateralization

Schizophrenia is a psychiatric disorder associated with atypical handedness and language lateralization. However, the molecular mechanisms underlying these functional changes are still poorly understood. Therefore, the present study was aimed at investigating whether variation in schizophrenia-related genes modulates individual lateralization patterns. To this end, we genotyped 16 single nucleotide polymorphisms that have previously been linked to schizophrenia on a meta-analysis level in a sample of 444 genetically unrelated healthy participants and examined the association of these polymorphisms with handedness, footedness and language lateralization. We found a significant association of the cholecystokinin-A receptor (CCKAR) gene variation rs1800857 and language lateralization assessed using the dichotic listening task. Individuals carrying the schizophrenia risk allele C of this polymorphism showed a marked reduction of the typical left-hemispheric dominance for language processing. Since the cholecystokinin A receptor is involved in dopamine release in the central nervous system, these findings suggest that genetic variation in this receptor may modulate language lateralization due to its impact on dopaminergic pathways.

Hypothalamus-olfactory system crosstalk: orexin a immunostaining in mice

It is well known that olfaction influences food intake, and conversely, that an individual’s nutritional status modulates olfactory sensitivity. However, what is still poorly understood is the neuronal correlate of this relationship, as well as the connections between the olfactory bulb and the hypothalamus. The goal of this report is to analyze the relationship between the olfactory bulb and hypothalamus, focusing on orexin A immunostaining, a hypothalamic neuropeptide that is thought to play a role in states of sleep/wakefulness. Interestingly, orexin A has also been described as a food intake stimulator. Such an effect may be due in part to the stimulation of the olfactory bulbar pathway. In rats, orexin positive cells are concentrated strictly in the lateral hypothalamus, while their projections invade nearly the entire brain including the olfactory system. Therefore, orexin appears to be a good candidate to play a pivotal role in connecting olfactory and hypothalamic pathways. So far, orexin has been described in rats, however, there is still a lack of information concerning its expression in the brains of adult and developing mice. In this context, we revisited the orexin A pattern in adult and developing mice using immunohistological methods and confocal microscopy. Besides minor differences, orexin A immunostaining in mice shares many features with those observed in rats. In the olfactory bulb, even though there are few orexin projections, they reach all the different layers of the olfactory bulb. In contrast to the presence of orexin projections in the main olfactory bulb, almost none have been found in the accessory olfactory bulb. The developmental expression of orexin A supports the hypothesis that orexin expression only appears post-natally.

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.

Extrasynaptic neurotransmission in the modulation of brain function. Focus on the striatal neuronal-glial networks

Extrasynaptic neurotransmission is an important short distance form of volume transmission (VT) and describes the extracellular diffusion of transmitters and modulators after synaptic spillover or extrasynaptic release in the local circuit regions binding to and activating mainly extrasynaptic neuronal and glial receptors in the neuroglial networks of the brain. Receptor-receptor interactions in G protein-coupled receptor (GPCR) heteromers play a major role, on dendritic spines and nerve terminals including glutamate synapses, in the integrative processes of the extrasynaptic signaling. Heteromeric complexes between GPCR and ion-channel receptors play a special role in the integration of the synaptic and extrasynaptic signals. Changes in extracellular concentrations of the classical synaptic neurotransmitters glutamate and GABA found with microdialysis is likely an expression of the activity of the neuron-astrocyte unit of the brain and can be used as an index of VT-mediated actions of these two neurotransmitters in the brain. Thus, the activity of neurons may be functionally linked to the activity of astrocytes, which may release glutamate and GABA to the extracellular space where extrasynaptic glutamate and GABA receptors do exist. Wiring transmission (WT) and VT are fundamental properties of all neurons of the CNS but the balance between WT and VT varies from one nerve cell population to the other. The focus is on the striatal cellular networks, and the WT and VT and their integration via receptor heteromers are described in the GABA projection neurons, the glutamate, dopamine, 5-hydroxytryptamine (5-HT) and histamine striatal afferents, the cholinergic interneurons, and different types of GABA interneurons. In addition, the role in these networks of VT signaling of the energy-dependent modulator adenosine and of endocannabinoids mainly formed in the striatal projection neurons will be underlined to understand the communication in the striatal cellular networks.

Types of cholecystokinin-containing periglomerular cells in the mouse olfactory bulb

The periglomerular cells (PG) of the olfactory bulb (OB) are involved in the primary processing and the refinement of sensory information from the olfactory epithelium. The neurochemical composition of these neurons has been studied in depth in many species, and over the last decades such studies have focused mainly on the rat. The increasing use of genetic models for research into olfactory function demands a profound characterization of the mouse olfactory bulb, including the chemical composition of bulbar interneurons. Regarding both their connectivity with the olfactory nerve and their neurochemical fate, recently, two different types of PG have been identified in the mouse. In the present report, we analyze both the synaptology and the chemical composition of specific PG populations in the murine olfactory bulb, in particular, those containing the neuropeptide cholecystokinin. Our results demonstrate the existence in the mouse of non-GABAergic PG and that these establish synaptic contacts with the olfactory nerve within the glomeruli. Based on previous classifications, we propose that this population would constitute a new subtype of type 1 mouse PG. In addition, we demonstrate the partial coexistence of cholecystokinin with the calcium-binding proteins neurocalcin and parvalbumin. All these findings add further data to our knowledge of the synaptology and neurochemistry of mouse PG. The differences observed from other rodents reflect the neurochemical heterogeneity of PG in the mammalian OB.

Hormones in the naso-oropharynx: endocrine modulation of taste and smell

Olfaction and gustation are important sensory modalities for locating food and for determining which foodstuffs to ingest. It is becoming apparent that there is a strong link between olfaction, gustation and metabolic control. Because endocrine signaling in the naso-oropharynx is likely to influence food intake, satiety and general metabolic control, it is important to examine some of the major hormones that play an integral part in energy homeostasis. Here, we provide an overview of the main endocrine factors known to be present in the naso-oropharynx and discuss their functional roles in maintaining metabolic function. Gaining a greater appreciation of how flavor perception is linked to peripheral metabolism could lead to novel therapeutic strategies for obesity and lifestyle-related diseases.

Cholecystokinin-2 receptors modulate freezing and escape behaviors evoked by the electrical stimulation of the rat dorsolateral periaqueductal gray

Systemic injection of the cholecystokinin type 2 (CCK(2)) receptor agonist CCK-4 evokes panic attacks in humans and facilitates the expression of a panic-related defensive behavior, escape, in rats. Given the prominent role attributed to the dorsal periaqueductal gray (dPAG) in the pathophysiology of panic, this midbrain area has been assumed to be one of the key regions mediating these effects of CCK-4. However, only a few studies have directly investigated the role of dPAG CCK(2) receptors in the regulation of panic-related behaviors. Even more disappointingly, the results of these investigations have been far from conclusive. In the present study we further addressed this issue by evaluating the effect of the intra-dorsolateral periaqueductal gray (dlPAG) injection of CCK-4 on two panic-related defensive behaviors, freezing and escape, evoked in male Wistar rats by the electrical stimulation of the dlPAG. The effects of CCK-4 (0.005-0.5 microg/0.2 microl) were compared to those caused by the local microinjection of the CCK(2) receptor antagonist LY225910 (0.001-1.0 microg/0.2 microl). The results showed that whereas CCK-4 facilitated the expression of both freezing and escape behaviors, LY225910 had the opposite effect. Pretreatment with an ineffective dose of LY225910 prevented the panicogenic-like effect of CCK-4. These results strengthen the view that CCK(2) receptors located in the dlPAG are involved in the regulation of panic-related behaviors and may mediate the effect of CCK-4 on panic.

Cholecystokinin is necessary for the expression of morphine conditioned place preference

There is evidence that the neuropeptide cholecystokinin (CCK) is important for the rewarding effects of drugs of abuse. However, less is known regarding the role of CCK in drug seeking and craving. The present study investigated whether the CCK(B) antagonist L-365, 260 could block morphine-induced drug seeking using the conditioned place preference paradigm and whether the dopaminergic reward pathway contributes to the effect of L-365, 260 on expression of morphine place preference. We found that systemic administration of the CCK(B) antagonist L-365, 260 attenuates the expression of morphine-induced drug seeking as assessed using conditioned place preference (CPP) and shows that this effect is mediated by CCK(B) receptors in the anterior nucleus accumbens (NAcc). Additionally, we demonstrate that this effect is dependent on D(2) receptor activation in the anterior nucleus accumbens (NAcc). These results indicate that endogenous CCK modulates the incentive-salience of morphine-associated cues and suggest that CCK antagonists may be useful in the treatment of drug craving.

Characterization of somatostatin- and cholecystokinin-immunoreactive periglomerular cells in the rat olfactory bulb

Periglomerular cells (PG) are interneurons of the olfactory bulb (OB) that modulate the first synaptic relay of the olfactory information from the olfactory nerve to the dendrites of the bulbar principal cells. Previous investigations have pointed to the heterogeneity of these interneurons and have demonstrated the presence of two different types of PG. In the rat OB, type 1 PG receive synaptic contacts from the olfactory axons and are gamma-aminobutyric acid (GABA)-ergic, whereas type 2 PG do not receive synaptic contacts from the olfactory axons and are GABA immunonegative. In this study, we analyze and characterize neurochemically a group of PG that has not been previously classified either as type 1 or type 2. These PG are immunoreactive for the neuropeptides somatostatin (SOM) or cholecystokinin (CCK). By using double immunocytochemistry, we demonstrate that neither the SOM- nor the CCK-immunoreactive PG contain GABA immunoreactivity, which is a neurochemical feature of type 1 PG. Moreover, they do not contain the calcium-binding proteins calbindin D-28k and calretinin, which are neurochemical markers of the type 2 PG. Electron microscopy demonstrates that the dendrites of the SOM- and CCK-containing PG are distributed in the synaptic and sensory subcompartments of the glomerular neuropil and receive synaptic contacts from the olfactory axons. Therefore, they should be included in the type 1 group rather than in the type 2. Altogether, these data indicate that the SOM- and the CCK-containing PG may constitute a group of GABA-immunonegative type 1 PG that has not been previously described. These results further extend the high degree of complexity of the glomerular circuitry.

CCK-8 prevents the development of kindling and regulates the GABA and NPY expression in the hippocampus of pentylenetetrazole (PTZ)-treated adult rats

Neuronal loss and irreversible brain damage often cause the worsening of symptoms and the decreased efficacy of pharmacological treatment occurring in epileptic patients and animal models of kindling. Recently we reported that the neurotransmitter/neuromodulatory peptide Cholecystokinin-8 (CCK-8) is able to induce the structural and functional neuronal recovery of chemical- and surgical-induced lesions when i.p. injected in rodents. The present study therefore, was aimed at verifying the hypothesis that treatment with a CCK-8 dose having a neuroprotective action might affect brain alterations and the development of kindling in adult rats receiving the convulsant agent pentylenetetrazole (PTZ). Compared to rats receiving Saline prior to PTZ, which manifested clonic-tonic seizures (Class 5 behavioural change scale) after three weeks of treatment, rats pre-treated with CCK-8 showed an improvement of behavioural score exhibiting myoclonus and occasionally tonic seizures (Class 3/4). This decreased susceptibility to develop convulsions was associated with the recovery of PTZ-induced reduction of ChAT levels in forebrain and GABA/GAD expression in the hippocampus. Furthermore, NPY immunoreactivity distribution and NPY mRNA levels were also increased in the hippocampus of rats receiving CCK-8 injection before each PTZ treatment. These data indicate that CCK-8 possesses the ability to prevent and/or suppress the convulsant effects of PTZ by stimulating the synthesis of neurotransmitters/peptides involved in the inhibition of hippocampal hyper-excitability. Our findings suggest that CCK-8 may have anticonvulsant and neuroprotective properties that merit further investigation.

Reduced effects of amphetamine on prepulse inhibition of startle in gastrin-deficient mice

The present study was aimed at investigating the role of gastrin in startle, startle habituation and prepulse inhibition (PPI). There were no significant differences between gastrin knockout mice and their wildtype controls in any of these baseline parameters. The disruption of PPI by treatment with 5 mg/kg of amphetamine was absent in gastrin knockout mice. However, a higher dose of amphetamine disrupted PPI in both genotypes. Similarly, treatment with the dopamine receptor agonist, apomorphine, the N-methyl-D-aspartate receptor antagonist, MK-801, and the serotonin-1A receptor agonist, 8-hydroxy-di-propylaminotetralin (8-OH-DPAT) modulated PPI similarly in gastrin knockout mice and wildtype controls. These data suggest a role of gastrin in the brain in modulating dopamine release in areas involved in PPI.

5-(Tryptophylamino)-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-Based Cholecystokinin Receptor Antagonists: Reversal of CCK1 Receptor Subtype Selectivity toward CCK2 Receptors

With the aim of reversing selectivity or antagonist/agonist functionality in the 5-(tryptophylamino)-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-derived potent and highly selective CCK(1) antagonists, a series of 4-benzyl and 4-methyl derivatives have been synthesized. Whereas the introduction of the benzyl group led, in all cases, to complete loss of the binding affinity, the incorporation of the methyl group gave a different result depending on the stereochemistry of the 1,3-dioxoperhydropyrido[1,2-c]pyrimidine scaffold. Thus, the introduction of the methyl group into the (4aS,5R)-diastereoisomers, giving a (4S)-configuration, produced a 3-fold increase in the CCK(1) binding potency and selectivity. However, the same structural manipulation in the opposite (4aR,5S)-stereochemistry, leading to a (4R,4aR,5S)-configuration, produced reversal of the selectivity for CCK(1) to the CCK(2) receptors. The replacement of the Boc group at the tryptophan moiety by a 2-adamantyloxycarbonyl group also contributed to that reversal. The resulting compounds displayed moderate CCK(2) antagonist activity in rat and human receptors, and a very small partial agonist effect on the production of inositol phosphate in COS-7 cells transfected with the wild-type human CCK(2) receptor.

The biochemical bases of the placebo effect

A great variety of medical conditions are subject to the placebo effect. Although there is mounting evidence to suggest that the placebo effect is related to the expectation of clinical benefit, little is still known about the biochemical bases underlying placebo responses. Positron emission tomography studies have recently shown that the placebo effect in Parkinson's disease, pain, and depression is related to the activation of the limbic circuitry. The observation that placebo administration induces the release of dopamine in the ventral striatum of patients with Parkinson's disease suggests a link between the placebo effect and reward mechanisms. In addition to Parkinson's disease, the placebo-reward model may also apply to other disorders. However, the relative contribution of the different neurotransmitters and neuropeptides that are known to be involved in modulating the activity of the limbic system may be disease-specific. Thus, while the placebo-induced clinical benefit observed in Parkinson's disease would mostly reflect the release of dopamine in the dorsal striatum, the activation of opioid and serotonin pathways could be particularly implicated in mediating placebo responses encountered in pain and depression, respectively.

Mother-Infant Interactions in Rats Lacking CCKA Receptors

Mediation of mother-infant interactions by the brain-gut peptide cholecystokinin (CCK) was examined by observing behavior of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, which lack functional CCKA receptors because of a genetic abnormality. OLETF (n = 10) and control (Long-Evans Tokushima Otsuka [LETO] n = 10) dams interacted with 1 pup of each line on Postpartum Days 6-9. OLETF pups received more body and anogenital licking and emitted substantially more ultrasonic vocalizations than LETO pups. OLETF dams carried pups less frequently and showed a nursing position more frequently than LETO dams. No significant Pup X Dam Line interactions or line differences in dams' activity were detected. The results provide convergent validity to previous pharmacological studies implicating CCK mediation of both infant and maternal behavior.

Regulation of gene expression and cocaine reward by CREB and ΔFosB

DeltaFosB (a truncated form of FosB) and CREB (cAMP response element binding protein) are transcription factors induced in the brain's reward pathways after chronic exposure to drugs of abuse. However, their mechanisms of action and the genes they regulate remain unclear. Using microarray analysis in the nucleus accumbens of inducible transgenic mice, we found that CREB and a dominant-negative CREB have opposite effects on gene expression, as do prolonged expression of DeltaFosB and the activator protein-1 (AP-1) antagonist DeltacJun. However, unlike CREB, short-term and prolonged DeltaFosB induction had opposing effects on gene expression. Gene expression induced by short-term DeltaFosB and by CREB was strikingly similar, and both reduced the rewarding effects of cocaine, whereas prolonged DeltaFosB expression increased drug reward. Gene expression after a short cocaine treatment was more dependent on CREB, whereas gene expression after a longer cocaine treatment became increasingly DeltaFosB dependent. These findings help define the molecular functions of CREB and DeltaFosB and identify clusters of genes that contribute to cocaine addiction.

Cholecystokinin antagonists: pharmacological and therapeutic potential

Cholecystokinin (CCK) is a regulatory peptide hormone, predominantly found in the gastrointestinal tract, and a neurotransmitter present throughout the nervous system. In the gastrointestinal system CCK regulates motility, pancreatic enzyme secretion, gastric emptying, and gastric acid secretion. In the nervous system CCK is involved in anxiogenesis, satiety, nociception, and memory and learning processes. Moreover, CCK interacts with other neurotransmitters in some areas of the CNS. The biological effects of CCK are mediated by two specific G protein coupled receptor subtypes, termed CCK(1) and CCK(2). Over the past fifteen years the search of CCK receptor ligands has evolved from the initial CCK structure derived peptides towards peptidomimetic or non-peptide agonists and antagonists with improved pharmacokinetic profile. This research has provided a broad assortment of potent and selective CCK(1) and CCK(2) antagonists of diverse chemical structure. These antagonists have been discovered through optimization programs of lead compounds which were designed based on the structures of the C-terminal tetrapeptide, CCK-4, or the non-peptide natural compound, asperlicin, or derived from random screening programs. This review covers the main pharmacological and therapeutic aspects of these CCK(1) and CCK(2) antagonist. CCK(1) antagonists might have therapeutic potential for the treatment of pancreatic disorders and as prokinetics for the treatment of gastroesophageal reflux disease, bowel disorders, and gastroparesis. On the other hand, CCK(2) antagonists might have application for the treatment of gastric acid secretion and anxiety disorders.

Molecular mechanisms and therapeutical implications of intramembrane receptor/receptor interactions among heptahelical receptors with examples from the striatopallidal GABA neurons

The molecular basis for the known intramembrane receptor/receptor interactions among G protein-coupled receptors was postulated to be heteromerization based on receptor subtype-specific interactions between different types of receptor homomers. The discovery of GABAB heterodimers started this field rapidly followed by the discovery of heteromerization among isoreceptors of several G protein-coupled receptors such as delta/kappa opioid receptors. Heteromerization was also discovered among distinct types of G protein-coupled receptors with the initial demonstration of somatostatin SSTR5/dopamine D2 and adenosine A1/dopamine D1 heteromeric receptor complexes. The functional meaning of these heteromeric complexes is to achieve direct or indirect (via adapter proteins) intramembrane receptor/receptor interactions in the complex. G protein-coupled receptors also form heteromeric complexes involving direct interactions with ion channel receptors, the best example being the GABAA/dopamine D5 receptor heteromerization, as well as with receptor tyrosine kinases and with receptor activity modulating proteins. As an example, adenosine, dopamine, and glutamate metabotropic receptor/receptor interactions in the striatopallidal GABA neurons are discussed as well as their relevance for Parkinson's disease, schizophrenia, and drug dependence. The heterodimer is only one type of heteromeric complex, and the evidence is equally compatible with the existence of higher order heteromeric complexes, where also adapter proteins such as homer proteins and scaffolding proteins can exist. These complexes may assist in the process of linking G protein-coupled receptors and ion channel receptors together in a receptor mosaic that may have special integrative value and may constitute the molecular basis for some forms of learning and memory.

CCK-nitric oxide interaction in rat cortex, striatum and pallidum

We have chosen to study the effects of both nitric oxide (NO) and cholecystokinin neuromodulatory systems in some motor structures that are frequently involved in excitotoxic phenomena. In particular, 7-nitroindazole, a selective inhibitor of neuronal NO synthase, was administered in control and sulfated cholecystokinin octapeptide-treated rats. Cortical surface, striatal and pallidal depth bioelectric activities were examined through Fast Fourier Transform analysis. Cortical and pallidal recordings revealed an increase of rapid standard rhythms after the inhibition of neuronal NO synthase; in contrast, striatal depth recordings showed a marked increase of slow standard rhythms. All these effects were completely abolished by chronic pre-treatment with sulfated cholecystokinin octapeptide. The results suggest a functional co-operation between cholecystokinin and NO systems in the modulation of the bioelectric activity of all the motor structures examined, and the possibility of preventing excitotoxic damages induced by an anomalous balance between excitatory and inhibitory neurotransmitters in these areas.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

The Vogel conflict test: procedural aspects, gamma-aminobutyric acid, glutamate and monoamines

A multitude of mechanisms are involved in the control of emotion and in the response to stress. These incorporate mediators/targets as diverse as gamma-aminobutyric acid (GABA), excitatory amino acids, monoamines, hormones, neurotrophins and various neuropeptides. Behavioural models are indispensable for characterization of the neuronal substrates underlying their implication in the etiology of anxiety, and of their potential therapeutic pertinence to its management. Of considerable significance in this regard are conflict paradigms in which the influence of drugs upon conditioned (trained) behaviours is examined. For example, the Vogel conflict test, which was introduced some 30 years ago, measures the ability of drugs to release the drinking behaviour of water-deprived rats exposed to a mild aversive stimulus ("punishment"). This model, of which numerous procedural variants are discussed herein, has been widely used in the evaluation of potential anxiolytic agents. In particular, it has been exploited in the characterization of drugs interacting with GABAergic, glutamatergic and monoaminergic networks, the actions of which in the Vogel conflict test are summarized in this article. More recently, the effects of drugs acting at neuropeptide receptors have been examined with this model. It is concluded that the Vogel conflict test is of considerable utility for rapid exploration of the actions of anxiolytic (and anxiogenic) drugs. Indeed, in view of its clinical relevance, broader exploitation of the Vogel conflict test in the identification of novel classes of anxiolytic agents, and in the determination of their mechanisms of action, would prove instructive.

Reactivation of cocaine conditioned place preference induced by stress is reversed by cholecystokinin-B receptors antagonist in rats

The effects of different cholecystokinin (CCK) receptor antagonists (devazepide and L365,260) on cocaine or stress-induced reactivation of cocaine conditioned place preference (CPP) were investigated in rats. After receiving alternate injection of cocaine (10 mg/kg) and saline for 8 consecutive days, the rats spent more time in the drug-paired side (cocaine CPP) on day 9. These animals did not show cocaine CPP on day 31 following saline-paired training daily from days 10 to 30 (21-day extinction). However, a single injection of cocaine (10 mg/kg) or 15 min of intermittent footshock could reinstate CPP on day 32 with significant more time spent in the drug-paired side in comparison with that on day 0. Systemic injection of CCK-A receptor antagonists, devazepide (0.1 and 1 mg/kg, i.p.), 30 min before cocaine priming, significantly attenuated cocaine-induced reinstatement of CPP, while CCK-B receptor antagonist, L365,260 (0.1 and 1 mg/kg, i.p.), did not show a similar effect. In contrast, pretreatment with L365,260 (0.1 and 1 mg/kg, i.p.) but not devazepide (0.1 and 1 mg/kg, i.p.) significantly blocked stress-induced reinstatement of CPP. In another experiment, CCK-A or B receptor antagonists were infused into nucleus accumbens or amygdala to determine which brain area are involved in the role of different CCK receptors in stress or drug-induced relapse to cocaine seeking. The results show that infusion of the devazepide (10 microg) into the nucleus accumbens significantly inhibited the cocaine-induced reinstatement of CPP, while infusion of devazepide (1 and 10 microg) into amygdala did not affect cocaine-induced reactivation of CPP. Interestingly, infusion of L365,260 (1 and 10 microg) into both nucleus accumbens or amygdala significantly attenuated or blocked stress-induced reinstatement of CPP. These findings demonstrate that CCK-A and B receptor have different roles in relapse to drug craving and further suggest that the brain areas involved in the CCK receptors on reinstatement of drug seeking are not identical. CCK-B receptor antagonists might be of some value in the treatment and prevention of relapse to stress-induced to drug craving following long-term detoxification.