Cholecystokinin-dopamine interactions

Opposite effects of CCK(B) agonists in grooming behaviour in rats: further evidence for two CCK(B) subsites

1. The hypothesis of the existence of two CCK(B) receptor subsites, CCK(B1) and CCK(B2) corresponding probably to different coupling states of CCK(B) receptors, was studied by measuring grooming behaviour in rats. 2. The B1 receptor agonist, BC197 (300 microg kg(-1), i.p.) produced a 45-50% decrease in grooming activity, which was prevented by both the CCK(B) receptor antagonists CI-988 (20 microg kg(-1) i.p.) and L-365,260 (200 microg kg(-1), i.p.). 3. In contrast, 3, 10 and 30 microg kg(-1), i.p., of the potent B2 receptor agonist, BC264, enhanced grooming (150-190%). This effect was prevented by previous injection of 75 microg kg(-1) of L-365,260 while higher doses (200 microg kg(-1), i.p.) produced only a partial antagonism. Moreover, CI-988 (20 microg kg(-1), i.p.), showed an opposite effect in potentiating the responses induced by BC264. However, 200 microg kg(-1) of CI-988 tended to suppress the increase of grooming induced by BC264. 4. The effects of BC264 were prevented by the D1 receptor (SCH 23390) and D2 receptor (sulpiride) antagonists, while those of BC197 were only antagonized by sulpiride, emphasizing the existence of a link between peptidergic (CCK) and dopaminergic systems. 5. This study brings additional evidence for the existence of the two CCK(B) receptor subsites and suggests that particular attention should be focused on the selectivity of CCK(B) receptor agonists, notably to explain the fact that some compounds such as Boc-CCK4 induce anxiogenic-like effects while others, including BC264, are devoid of these effects.

A new genetic variant in the Sp1 binding cis-element of cholecystokinin gene promoter region and relationship to alcoholism

Neuropeptide cholecystokinin (CCK) and the CCK receptors in the central nervous system mediate actions on increasing firings, anxiety, and nociceptions. Furthermore, CCK modulates the release of dopamine and dopamine-related behaviors in the mesolimbic pathway. In our study, genetic variation in the promoter and coding regions of the prepro-CCK gene were analyzed among 66 Japanese, 66 American Whites, 54 Chinese, and 41 Colombian natives. Two nucleotide sequence variants were found: a frequent mutation at nucleotide position -45 C to T involved in core sequence of Sp1 binding cis-element of the promoter region, and a C to T substitution at the 1662 position in intron 2. Analysis for the segregation study in 10 families of twins confirmed codominant heredity of two alleles. Distribution of genotypes and gene frequencies of 66 controls and 108 alcoholics in Japan presented that allelic variant T type in alcoholics was found in higher frequencies than that of controls, and distribution of these genotypes was significantly different between the both groups.

Extracellular dopamine in the anterior nucleus accumbens is distinctly affected by ventral tegmental area administration of cholecystokinin and apomorphine: data from in vivo voltammetry

The interaction of cholecystokinin (CCK) and dopamine (DA) in the mesolimbic system was investigated. The study focused on DAergic cells not containing colocalized CCK projecting from the ventral tegmental area (VTA) to the anterior nucleus accumbens (NA). Differential pulse voltammetry in pargyline pretreated and anesthetized rats was used to measure extracellular DA in the anterior NA following microinjection of apomorphine either alone or in combination with CCK-8s into the VTA. In agreement with an earlier study there was a dose-dependent increase in the DA signal in the anterior NA after microinjection of CCK-8s into the VTA. Apomorphine microinjected into the VTA produced a biphasic effect on extracellular DA in the anterior NA with an increase from basal levels of approximately 50% by 1 ng, whereas 10 ng was ineffective and 100 ng apomorphine caused a slight decrease in the DA signal. Apomorphine (1 ng) microinjected together with 1 ng CCK-8s produced an increase in the DA signal to approximately 180% of the baseline value, whereas the combination of 1 ng apomorphine and 100 ng CCK-8s was ineffective. When 100 ng apomorphine were microinjected in combination with either 1 ng or 100 ng CCK-8s, the DA signal in the anterior NA was unchanged. These results suggest that low doses of apomorphine injected into the VTA synergistically influence the effects of CCK-8s on extracellular DA in the anterior NA, whereas higher doses of apomorphine suppress the effect of CCK-8s on DAergic cells projecting to the anterior NA.

Enhancement of latent inhibition in the rat by the CCK antagonist proglumide

The behavioral paradigm of latent inhibition (LI) involves the retardation of conditioning to a stimulus when paired with reinforcement, if preexposure to that stimulus with no significant consequence has occurred. This phenomenon is believed to reflect a process of learning to ignore stimuli as irrelevant. Disruption in LI can be considered to be an attentional deficit observed in schizophrenia. The neuropeptide cholecystokinin (CCK), which coexists with dopamine (DA) in some brain regions, has been implicated in the pathophysiology of schizophrenia. The present study examined the effects of the nonselective CCK antagonist proglumide on LI (0.25, 0.5, and 1.0 mg/kg) using a conditioned suppression of drinking procedure in rats. For purposes of comparison the effects of haloperidol (0.1 mg/kg) were also investigated. Administration of 1.0 and 0.5 mg/kg, but not 0.25 mg/kg, proglumide was found to reduce suppression of drinking behavior in animals preexposed (PE) to a flashing light stimulus. These animals developed LI under conditions where preexposed control animals exhibited suppression of drinking behavior similar to that of nonpreexposed (NPE) control animals. These findings for proglumide were comparable to the effects on drinking behavior of 0.1 mg/kg haloperidol. The enhancement of LI by proglumide may be interpreted in terms of CCK dopamine interactions. Because CCK may modulate dopamine, the results reported here for proglumide strengthen the argument for the investigation of CCK-based drugs as potential antipsychotic agents.

Synthesis and evaluation of 11C-labeled nonpeptide antagonists for cholecystokinin receptors: [11C]L-365,260 and [11C]L-365,346

11C-labeled cholecystokinin (CCK) receptor antagonists, 3R(+)-N-(2,3-dihydro-1-[11C]methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepine- 3-yl)-N'-(3-methylphenyl)urea ([11C]L-365,260) and its (S)-enantiomer ([11C]L-365,346), have been synthesized and evaluated in vivo for use in CCK receptor studies with positron emission tomography (PET). Selective N-methylation of a racemic precursor with [11C]iodomethane and subsequent optical resolution of the racemate with HPLC afforded optically pure [11C]L-365,260 and [11C]L-365,346, which are selective for CCK-B (central-type) receptors and CCK-A (peripheral-type) receptors, respectively. Biodistribution studies in mice showed very low brain uptakes (<0.8% dose/gram) of the radioactivities after intravenous injections of these compounds, although that of brain CCK-B receptor-selective [11C]L-365,260 was 2-fold that of [11C]L-365,346. In peripheral organs, uptake of the radioactivity in the pancreas was the highest among the organs tested after the injection of [11C]L-365,346 and was 3-fold that of [11C]L-365,260. It was also observed that high uptake of [11C]L-365,346 in rat pancreas was significantly inhibited by a simultaneous injection with a large dose of L-365,346 (3 mg/kg). These preliminary results suggest that the nonpeptide CCK antagonist [11C]L-365,346 may be useful for probing pancreatic CCK-A receptors by PET. Owing to the very low brain permeability, however, [11C]L-365,260 may have no potential as a PET tracer for probing brain CCK-B receptors.

Sudden darkness induces a high activity-low anxiety state in male and female rats

The effects of sudden darkness on spontaneous motor activity in an open field and performance in an elevated plus-maze (EPM) were assessed in adult male and female rats. In the open field test, sudden darkness increased total locomotion, locomotion in central squares, rearing frequency (RF), and diminished defecation units (DU). In the dark, total locomotion remained elevated during the 20-min test period, while in the light total locomotion decreased significantly after the fourth minute, in both sexes. All the effects of sudden darkness in the open field test were more pronounced in female rats. In the EPM, sudden darkness increased the number of entries into the open arms, total entries, percentages of entries into the open arms, and time spent in the open arms. The changes were more significant in female than in male rats. These results show that sudden darkness increases general motor activity and suggest it diminishes habituation, fear, and anxiety. The results also suggest that this behavioral shift is sexually differentiated. Sudden darkness emerges as an experimental tool to simultaneously test physiologically-induced increases in spontaneous motor activity and decreases in anxiety.

A disrupted cholecystokinin A receptor gene induces diabetes in obese rats synergistically with ODB1 gene

Otsuka Long-Evans Tokushima fatty (OLETF) rats develop hyperglycemia, hyperinsulinemia, and mild obesity, which are characteristic of human non-insulin-dependent diabetes mellitus. We have shown that two recessive genes, ODB1 mapped on the X chromosome and ODB2 mapped on chromosome 14, are involved in the induction of the diabetes in OLETF rats. Recently we found that OLETF rats are the naturally occurring cholecystokinin type A receptor (CCKAR) gene knockout rats. In this study, we focused on the genotype of CCKAR gene and the ODB1 gene in regulation of glucose homeostasis in the F2 cross of the OLETF rats. Relatively high plasma glucose levels were observed in the F2 offspring with the homozygously disrupted CCKAR gene. A synergistic effect for increasing plasma glucose levels in F2 rats between disrupted CCKAR gene and the ODB1 gene was shown. The CCKAR gene was found to map very close to ODB2 by a linkage analysis using microsatellite markers. These results suggest that CCKAR gene maintains normoglycemia in rats.

Social isolation increases cholecystokinin mRNA in the central nervous system of rats

To investigate cholecystokinin (CCK) mRNA changes induced by social isolation rats were isolated in single cages soon after weaning for 30 days. They were then sacrificed and their brains removed for in situ hybridization (ISH) study. Control animals were housed in groups of 6 per cage for the same period. ISH was performed using a 32P-labelled oligonucleotide probe complementary to CCK-8 mRNA and the results analysed by computerized densitometry. They showed a significant increase (from 59.5-152.3%) in CCK mRNA expression in the basolateral amygdala, cortex, CA1, dorsal raphe nucleus, geniculate body and ventral tegmental area of isolated rats. These results suggest that social isolation may influence CCK gene expression.

Disrupted cholecystokinin type-A receptor (CCKAR) gene in OLETF rats

OLETF rats develop hyperglycemia, hyperinsulinemia and mild obesity, which is characteristic of human non-insulin-dependent diabetes mellitus (NIDDM). We cloned and sequenced the cholecystokinin type-A receptor (CCKAR) gene in the rats. Comparing the DNA sequences of the OLETF CCKAR gene and LETO CCKAR gene, normal gene, we found a deletion in the OLETF gene, 6847 bases in length, which was flanked by two 3-base-pair direct repeats (5'-TGT-3') at positions -2407/-2405 and 4441/4443, numbered according to the LETO gene sequence, one of which was lost. The promoter region, the first and second exons were missing in the mutant. The region upstream and downstream of the deletion, including exons 3, 4 and 5, was conserved between the two strains, and did not contain any base changes. We found that the gene mapped to chromosome 14 in rats. OLETF rats are the naturally occurring knockout animals with the homozygously disrupted CCKAR gene.

Spontaneous preference for ethanol in naive rats is influenced by cholecystokinin A receptor antagonism

Naive adult male Wistar rats free to choose between water or 10% ethanol (v/v) spontaneously became water-preferring (WP) rats, as they drank mainly water (approximately 35 ml per day), or alcohol-drinking (ED) rats, as they also drank a significant amount of ethanol (approximately 14 ml per day). The selective CCKA receptor antagonist L-364,718 at doses selective for the CCKA receptor (5 micrograms/kg, IP) halved the consumption of alcohol of the ED rats without modifying their total liquid in-take. In contrast, the CCKB antagonists L-365,260 or GV150013 were without effect when used at doses selective for the CCKB receptor. These data indicate that the CCK system could be involved in the modulation of alcohol intake. In particular, they suggest that CCKA receptors could play a role in the ethanol preference.

Role of different neurotransmitter systems in the cholecystokinin octapeptide-induced anxiogenic response in rats

The possible involvement of different neurotransmitter systems in the anxiogenic action of cholecystokinin octapeptide sulphate ester (CCK-8) was investigated in rats. Intracerebroventricularly (i.c.v.) administered CCK-8 induced an anxiogenic response in an elevated plus-maze test. Pretreatment with dopaminergic, muscarinergic acetylcholine receptor blockers and an opiate receptor antagonist blocked the anxiogenic response to CCK-8. The alpha and beta adrenoreceptor, the GABA receptor and the 5-hydroxytryptamine (5-HT) receptor blockers were not able to modulate the 'anxiogenic-like' effect of CCK-8. The results suggest that the anxiogenic effects of CCK-8 are mediated via different neurotransmitters and the anxiogenic action can be prevented by receptor blockers to these transmitters.

Decreased cholecystokinin levels in cerebrospinal fluid of patients with adult chronic hydrocephalus syndrome

Cholecystokinin (CCK) levels were measured in cerebrospinal fluid (CSF) of patients with adult chronic hydrocephalus syndrome (ACHS) (n = 16) and compared with levels from a control group (n = 11). The CSF concentration of CCK in the ACHS group (0.79 +/- 0.53 fmol/mL) was significantly reduced (p = .002) with respect to the controls (1.55 +/- 0.54 fmol/mL). As CCK-8, the most prevalent from of CCK in the central nervous system, has been demonstrated to play a significant role in several physiological and behavioral actions, the reduced octapeptide values found in ACHS could be involved in the disturbances associated with this disorder. Continuous monitoring of intracranial pressure (ICP) demonstrated different ICP profiles in ACHS. We found that all patients with abnormal ICP records except one showed CCK values under the detection limit. Three of the 4 patients with normal ICP had CCK levels within the normal range. These preliminary studies could evidence that ICP alterations are responsible for part of the loss of brain neuropeptide levels in ACHS.

Mouse cholecystokinin type-A receptor gene and its structural analysis

The mouse cholecystokinin type-A receptor (CCK(A)R) gene was cloned and sequenced, and the exon/intron boundaries were determined by cDNA cloning. The gene, approximately 10 kb in length, contains the entire coding region, and consists of five exons. The deduced amino acid sequence was homologous with that of other species, with the exception of an additional DNA sequence encoding 7 amino acids in exon 5. A region of the 5' end of exon 2 appeared to be alternatively spliced, and generated an isoform shorter by 52 bases. The shorter isoform may encode an 48 amino acid open reading frame due to frameshift of translation. These two mRNA isoforms were expressed equally in the mouse gallbladders.

Distribution of cholecystokinin immunoreactivity in the BALB/c mouse forebrain: an immunocytochemical study

The present study describes cholecystokinin (CCK) immunoreactivity (CCK-IR) distribution in the brains of control and colchicine-treated mice. In the brains of control mice, the CCK-IR strongly revealed numerous axons and terminals. Perikarya exhibiting a faint to moderate immunoreactivity were also observed in areas such as cortices, hippocampus, amygdala, septum, and thalamus. The colchicine treatment did not seem to notably affect the brain CCK-IR innervation, but resulted in profound changes of the perikaryal staining. Indeed, the regions, which contained numerous moderately stained perikarya in the control animals, exhibited after colchicine treatment immunoreactive perikarya intensely stained but only in moderate number. This feature obviously appeared in the cortex in which, in addition to strongly stained perikarya, colchicine induced the appearance of numerous CCK-IR hillocks. In the lateral amygdala and thalamus of colchicine-treated animals, the somatic immunoreactivity was considerably decreased. The regions, such as paraventricular hypothalamic nucleus and bed nucleus of the stria terminalis, which in the control animals did not exhibit any stained perikaryon, showed a high number of strongly stained cell bodies after colchicine treatment. This study, mapping the mouse forebrain CCK-IR, demonstrated a wide distribution of this peptide. Moreover, CCK-IR is spontaneously visible in neurons of untreated mouse in some brain areas previously shown in the rat to exhibit CCK mRNA, but no clear perikaryal CCK-IR even after colchicine treatment.

Persistence of the releasable pool of CCK in the rat nucleus accumbens and caudate-putamen following lesions of the midbrain

Previous studies have identified populations of dopamine neurons in the midbrain that colocalize cholecystokinin some of which project to the nucleus accumbens and caudate-putamen. The contribution of dopamine-colocalized peptide to the total releasable pool of cholecystokinin in these brain regions was investigated using microdialysis. Dopamine, dihydroxyphenylacetic acid and cholecystokinin immunoreactive levels in dialysates of the posterior medial nucleus accumbens and medial caudate-putamen were determined following 6-hydroxydopamine lesions of the ventral tegmental area and substantia nigra or transection of the medial forebrain bundle. An 89-99% depletion in basal extracellular dihydroxyphenylacetic acid and an 87-99% decrease in veratridine-evoked extracellular dopamine levels was observed in the nucleus accumbens and caudate-putamen, 4 weeks after 6-hydroxydopamine lesion. No statistically significant difference was observed between lesioned and control animals in the basal or veratridine-evoked extracellular level of cholecystokinin immunoreactivity in either region. Similarly, transection of the medial forebrain bundle failed to significantly deplete the releasable pool of cholecystokinin immunoreactivity in the nucleus accumbens or caudate nucleus despite 89-99% depletions of dopamine and its metabolite. These data suggest that midbrain dopamine or non-dopaminergic cells are not the primary source of releasable cholecystokinin in the posterior medial nucleus accumbens and medial caudate-putamen measured by microdialysis.

Pretreatment with neurokinin substance P but not with cholecystokinin-8S can alleviate functional deficits of partial nigrostriatal 6-hydroxydopamine lesion

The neuropeptide substance P (SP) has been implicated in the control of various neuro-behavioral functions including reinforcement and learning processes. It also exerts neurotrophic and regenerating effects in vitro and in vivo. A previous study indicated a potential therapeutic effect of SP in rats with partial 6-hydroxydopamine lesions of the nigrostriatal dopamine system when SP was administered after the lesion. The purpose of the present study was to determine whether prelesion treatment with SP would also interact with the effects of unilateral 6-hydroxydopamine lesion of the substantia nigra. Thus, SP (50 micrograms/kg) was administered i.p. on 8 consecutive days prior to unilateral lesion of the substantia nigra. Furthermore, we investigated the effects of prelesion treatment with cholecystokinin-8S (CCK; 1 microgram/kg), another neuropeptide, which is closely related to dopaminergic neurons, and which also can have neurotrophic and neuroprotective functions. Our results show that animals with partial neostriatal dopamine depletions (residual dopamine levels of more than 10%) did not show turning asymmetries when pretreated with SP, whereas animals pretreated with vehicle exhibited an initial ipsiversive asymmetry from which they recovered. In contrast, behavioral asymmetries were most pronounced in animals which had been pretreated with CCK. These peptide treatments did not affect the degree of neostriatal dopamine depletion; however, dihydroxyphenylacetic acid/dopamine ratios were enhanced in the neurostriatum of animals with partial dopamine damage after SP- and CCK-pretreatment, and in the ventral striatum of SP-pretreated animals. These data provide evidence that prelesion treatment with SP, but not with CCK, can alleviate functional deficits induced by a partial nigro-striatal dopamine lesion. This effect may be related to enhanced ventral striatal dopamine activity and/or to the peptide's known effects on learning, motivation, and emotion.

Effects of chronic lithium and electroconvulsive stimuli on cholecystokinin mRNA expression in the rat brain

This study compares the effect of lithium (Li+) and electroconvulsive stimuli (ECS), two treatments commonly used in the treatment of affective disorders, on CCK mRNA expression in the rat brain. Two groups of rats receiving either 4 week Li+ or vehicle food supplementation and two groups receiving 6 ECS or 6 sham ECS during 2 weeks were studied. A significant decrease in CCK mRNA levels was seen in the caudate putamen both after Li+ as compared to vehicle and ECS as compared to sham ECS, 27 and 25%, respectively. A small (10%), yet significant, decrease was also seen in the inner entorhinal cortex after Li+. The results indicate that both Li+ and ECS inhibit CCK synthesis in the caudate putamen and are consistent with other findings of presumed decreased dopaminergic action in this part of the brain following these treatments.

Antidepressant-like effects of CCK(B) receptor antagonists: involvement of the opioid system

RB 101 (N-[(R,S)-2-benzyl-3-[(S)-2-amino-4-methylthiobutyldithio]-1-oxopr opyl]-L -phenylalaninebenzyl ester), a systemically active inhibitor of enkep halin catabolism, has been shown to elicit antidepressant-like effects in mice, both in the forced-swimming and in the conditioned suppression of the mobility tests. The same type of response has been also observed following administration of the cholecystokinin CCK(B) receptor antagonist L-365,260 ((3R)-(+)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepin -3-yl)-3 -methylphenylurea). In terestingly, the delta-opioid receptor antagonist naltrindole (17-cyclopropylmethyl-6,7-dehydro-4,5alpha-epoxy-3,14-dihydroxy-6, 7,2'-3'-indolomorphinan) blocks the effect of both RB 101 and L-365,260 in the conditioned suppression of the motility test. In this work we have investigated the involvement of the opioid system in the antidepressant response to the CCK(B) receptor antagonist L-365,260 in the forced-swimming test in mice. The effect of L-365,260 was decreased by the delta-opioid receptor antagonist naltrindole. Furthermore, the CCK(B) receptor agonist, BC 264 (Boc-Tyr(OSO3H)-gNle-mGly-Trp-(NMe)Nle-Asp-Phe-NH2), blocked the antidepressant-like effect of RB 101 while CCK-8 (H-Asp-Tyr(OSO3H)-Met-Gly-Trp-Met-Asp-Phe-NH2) enhanced the effect of this drug, probably through stimulation of central CCK(A) receptors, since the CCK(A) receptor antagonist devazepide ((3S)-(-)-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepin++ +-3-yl)-1H-indole-2 -carboxamide) abolished the CCK-8-induced potentiation of the RB 101 effect. In addition, RB 101 enhanced the effect of L-365,260. Such an effect was blocked by the delta-opioid receptor antagonist naltrindole. These data further support the involvement of opioid receptors in the antidepressant-type effect induced by CCK(B) receptor blockers and support the hypothesis of a regulatory role of CCK in the activity of the endogenous opioid system. As in other experimental paradigms, CCK(A) and CCK(B) receptor stimulation appears to have opposite effects in modulating opioidergic activity.

Association of enkephalin catabolism inhibitors and CCK-B antagonists: a potential use in the management of pain and opioid addiction

The overlapping distribution of opioid and cholecystokinin (CCK) peptides and their receptors (mu and delta opioid receptors; CCK-A and CCK-B receptors) in the central nervous system have led to a large number of studies aimed at clarifying the functional relationships between these two neuropeptides. Most of the pharmacological studies devoted to the role of CCK and enkephalins have been focused on the control of pain. Recently the existence of regulatory mechanisms between both systems have been proposed, and the physiological antagonism between CCK and endogenous opioid systems has been definitely demonstrated by coadministration of CCK-B selective antagonists with RB 101, a systemically active inhibitor, which fully protects enkephalins from their degradation. Several studies have also been done to investigate the functional relationships between both systems in development of opioid side-effects and in behavioral responses. This article will review the experimental pharmacology of association of enkephalin-degrading enzyme inhibitors and CCK-B antagonists to demonstrate the interest of these molecules in the management of both pain and opioid addiction.

Modulation of neurotransmitter release by cholecystokinin in the neostriatum and substantia nigra of the rat: regional and receptor specificity

The effect of cholecystokinin peptides on the release of dynorphin B, aspartate, glutamate, dopamine and GABA in the neostriatum and substantia nigra of the rat was investigated using in vivo microdialysis. Sulphated cholecystokinin-8S in the dialysis perfusate (1-100 microM) induced a concentration-dependent increase in extracellular dynorphin B and aspartate levels, both in the neostriatum and substantia nigra. Striatal dopamine levels were only increased by 100 microM of cholecystokinin-8S, while in the substantia nigra they were increased by 10-100 microM of cholecystokinin-8S. Extracellular GABA and glutamate levels were increased following 100 microM of cholecystokinin-8S only. Striatal cholecystokinin-8S administration also produced a significant increase in nigral dynorphin B levels. Local cholecystokinin-4 (100 microM) produced a moderate, but significant, increase of extracellular dynorphin B and aspartate levels in the neostriatum and substantia nigra. No effect was observed on the other neurotransmitters investigated. A 6-hydroxydopamine lesion of the nigrostriatal dopamine pathway did not affect the increases in dynorphin B and aspartate levels produced by local administration of cholecystokinin-8S. Basal extracellular GABA levels were increased significantly in both the neostriatum and substantia nigra ipsilateral to the lesion. Nigral glutamate and aspartate levels were also increased in the lesioned substantia nigra, but in the lesioned neostriatum aspartate levels were decreased. The cholecystokinin-B antagonist L-365,260 (20 mg/kg, s.c.), but not the cholecystokinin-A antagonist L-364,718 (devazepide; 20 mg/kg, s.c.), significantly inhibited the effect of cholecystokinin-8S on striatal dynorphin B and aspartate levels. In the substantia nigra, however, the effect of cholecystokinin-8S on dynorphin B and aspartate levels was inhibited to a similar extent by both L-365,260 and L-364,718. Pretreatment with L-364,718, but not with L-365.260, prevented the increase in nigral dopamine levels produced by nigral cholecystokinin-8S administration. Taken together, these results suggest that cholecystokinin-8S modulates dynorphin B and aspartate release in the neostriatum and substantia nigra of the rat via different receptor mechanisms. In the neostriatum, the effect of cholecystokinin-8S on dynorphin B and aspartate release is mediated via the cholecystokinin-B receptor subtype, while in the substantia nigra, cholecystokinin-8S modulates dynorphin B and aspartate release via both cholecystokinin-A and cholecystokinin-B receptor subtypes. Cholecystokinin-8S modulates dopamine release mainly in the substantia nigra, via the cholecystokinin-A receptor subtype.

Novel CCK-B receptor agonists: diketopiperazine analogues derived for CCK4 bioactive conformation

Recently, we proposed a CCK-B agonist bioactive conformation characterized by an 'S' shape of the peptidic backbone which was derived from structure-activity relationships and conformational analysis of CCK4 (Trp-Met-Asp-Phe-NH2) analogues. Using this template, we report here the synthesis of cyclic CCK4 analogues which contain, in place of the Trp-Met dipeptide, a diketopiperazine moiety resulting from a cyclization between Nle and N-substituted (D)Trp residues and coupled with a small linker to Asp-Phe-NH2. Some of these compounds displayed good affinities and selectivities for the CCK-B receptor. The results are discussed in terms of size, hydrophobicity and spatial orientation of the side-chains on the diketopiperazine ring. The most potent ligand exhibited potent and full CCK-B receptor agonist properties in promoting the hydrolysis of inositol phosphates (EC50 = 8 nM) in CHO cells, stably transfected with the rat brain CCK-B receptor. This compound was also shown to be a potent selective CCK-B/gastrin receptor agonist since, it increased gastric acid secretion measured in anesthetized rats on i.v. administration. These compounds provide a rigid template for the design of non-peptide CCK-B agonists, by modification of the remaining peptide moiety.

Decrease in exploratory behavior in naturally occurring cholecystokinin (CCK)-A receptor gene knockout rats

We recently found a specific strain of rats (Otsuka Long Evans Tokushima Fatty; OLETF rats) lacking cholecystokinin (CCK)-A receptor because of a genetic abnormality. Since CCK is an abundant neurotransmitter peptide in the brain, we examined whether these animals exhibit any behavioral abnormalities by conducting open-field tests. OLETF rats showed hypolocomotor activity and a decrease in the incidence of rearing in open-field tests. CCK release from the synaptosomes, and levels of CCK and CCK-B receptor mRNAs were the same as those observed in normal rats. It is suggested that the decreased exploration in OLETF rats may be due to the lack of CCK-A receptor.

Evidence for a differential cholecystokinin-B and -A receptor regulation of GABA release in the rat nucleus accumbens mediated via dopaminergic and cholinergic mechanisms

In the present study we characterized the cholecystokinin receptor regulation of (i) the dopamine D2 agonist binding sites in striatal sections including the nucleus accumbens and (ii) GABA and dopamine release in the central part of the rat nucleus accumbens, by combining the in vitro filter wipe-off and the in vivo microdialysis techniques. In the binding study we demonstrate that sulphated cholecystokinin octapeptide (1 nM) increased (219 +/- 30%) the KD value of the D2 agonist [3H]N-propylnorapomorphine binding sites in sections from the striatum including the accumbens. This effect was counteracted by the cholecystokinin-B antagonist PD134308 (50 nM). In a parallel study using microdialysis in the central nucleus accumbens, we found that local perfusion with sulphated cholecystokinin octapeptide (1 microM) induced an increase in GABA (135 +/- 7%) and dopamine (146 +/- 8%) release which was unaffected by the cholecystokinin-A antagonist L-364,718 (10 nM). In contrast, when the cholecystokinin-B antagonist PD134308 (10 nM) was co-perfused with the peptide it prevented the increase in dopamine and decreased GABA release (-24 +/- 2%). This reduction was counteracted by the addition to the perfusate medium of the cholecystokinin-A antagonist or the cholinergic muscarinic M2 receptor antagonist AF-DX 116 (0.1 microM). Taken together, these data demonstrate that the facilitation by sulphated cholecystokinin octapeptide of GABA and dopamine release in the central accumbens probably reflects an inhibitory effect of the peptide on both pre- and postsynaptic D2 receptors, mediated via cholecystokinin-B receptor activation. In addition, for the first time we provide evidence for a differential cholecystokinin-A and -B receptor-mediated regulation of GABA transmission in the central accumbens, where the cholecystokinin-B receptor exerts a dominant excitatory influence while the cholecystokinin-A receptor mediates an inhibition of GABA release via a local muscarinic M2 receptor.

Impairment of stress adaptive behaviours in rats by the CCKA receptor antagonist, devazepide

1. Cholecystokinin (CCK) is released during stress both in limbic and hypothalamic areas suggesting that CCK could participate in modulating neuroendocrine as well as behavioural responses to stress. 2. In this study we have examined the effect of CCK receptor antagonists on the retention of the immobility response to a forced-swim stress in rats. In this test, rats are forced to swim during 15 min (conditioning period) and 24 h later, the duration of immobility is measured during a period of 5 min (re-test period). During the conditioning period rats display a period of vigorous activity, followed by progressive inactivity. During the re-test period rats remain 70-80% of the time in an immobile posture. 3. The CCKA receptor antagonist, devazepide (MK-329) but not the CCKB receptor antagonist, L-365,260, administered s.c. immediately before the conditioning period, decreased the duration of acquired immobility during the re-test period. The effect of devazepide was prevented by cholecystokinin octapeptide (CCK-8; 40 micrograms kg-1, s.c) as well as by the selective glucocorticosteroid GII receptor agonist, dexamethasone (30 micrograms kg-1, s.c.) 4. Neither corticosterone nor ACTH plasma levels measured both after the re-test period and after the conditioning period were modified by devazepide treatment. 5. The results suggest a role for CCK in the behavioural adaptation to stress and indicate a relationship between CCK systems and glucocorticoids in the neuronal mechanisms involved in the acquisition of adaptive behaviours to stress.

Immunohistochemical studies of mesolimbic dopaminergic neurons in Fischer 344 and Lewis rats

Previous work has shown that the inbred Lewis and Fischer 344 rat strains differ in several behavioral measures related to mesolimbic dopamine function. Moreover, the ventral tegmental area (VTA) of the Lewis rat has been shown to contain higher levels of tyrosine hydroxylase compared to that of the Fischer rat by blot immunolabeling procedures. To investigate structural correlates of this biochemical difference, an immunohistochemical study of VTA dopaminergic neurons in these two strains was undertaken. Results show that the density and total number of tyrosine hydroxylase-positive neurons in the VT 4 of the Lewis rat is about 50% of that found in the Fischer rat. In contrast, examination of the substantia nigra in the same sections revealed no differences in the density and number of tyrosine hydroxylase-positive cells between these strains. Fischer-Lewis strain differences were also evident for cholecystokinin immunoreactivity in the VTA, with much lower levels seen in the Lewis rat, consistent with the known colocalization of this neuropeptide in many VTA dopamine neurons. The finding of 50% fewer tyrosine hydroxylase-positive neurons in the VTA of the Lewis rat, along with our earlier results showing 45% higher levels of tyrosine hydroxylase by blot immunolabeling, would suggest much higher levels of tyrosine hydroxylase per VTA neuron in this strain. However, no obvious strain difference in the cellular intensity of tyrosine hydroxylase immunoreactivity could be detected by immunohistochemistry. Finally, the density of VTA dopamine neurons was assessed in 1-week-old Fischer and Lewis rats. In contrast to the results obtained for adult animals, no difference in the number of tyrosine hydroxylase-positive neurons was apparent in these young animals, indicating that the Fischer-Lewis strain difference in VTA dopamine neurons appears later in postnatal development. These anatomical findings shed new light on the differences in the mesolimbic dopamine system between Fischer and Lewis rats that may contribute to the behavioral differences exhibited by these animals.

CCKB receptors mediate CCK-8S-induced activation of dorsal hippocampus CA3 pyramidal neurons: an in vivo electrophysiological study in the rat

The sulphated octapeptide C-terminal fragment of cholecystokinin (CCK-8S) is present in high concentration in the mammalian brain, where it acts via two types of receptor denoted CCKA and CCKB. In the dorsal hippocampus, CCK-8S exerts a potent excitatory effect on pyramidal neurons. The present electrophysiological study was undertaken to determine which CCK receptor type mediates this neuronal activation. Using in vivo extracellular unitary recordings of CA3 pyramidal hippocampal neurons, we compared the effect of SNF-8702, a potent selective CCKB receptor agonist, to that of CCK-8S, and assessed the effects of selective CCKA and CCKB antagonists. CCK-8S and SNF-8702, microiontophoretically applied on the same neurons produced a similar degree and pattern of activation. Both CCK-8S- and SNF-8702-induced activations were suppressed by the microiontophoretic application of the CCKB antagonist CI-988, but not by that of the CCKA antagonist SR 27897. CCK-8S-induced activation was not significantly modified by the intravenous administration of the CCKA antagonists devazepide and SR 27897. However, it was reduced by the CCKB antagonist PD 135158, administered intravenously or intracerebroventricularly, and by the intravenous administration of the CCKB antagonist L-365,260. The intravenous administration of PD 135158 also reduced SNF-8702-induced activations. These results indicate that CCKB receptors mediate CCK-8S-induced activation of rat CA3 pyramidal neurons.

Cholecystokinin-induced release of dopamine in the nucleus accumbens of the spontaneously hypertensive rat

Changes in dopamine neurotransmission in the nucleus accumbens of the spontaneously hypertensive rat (SHR) may be involved in the pathogenesis of hypertension. This investigation tested the hypothesis that the sulfated octapeptide cholecystokinin (CCK8S) induced release of dopamine is greater in the SHR than in its normotensive control, the Wistar-Kyoto rat (WKY). Dopamine and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were sampled using microdialysis in the caudal half of the nucleus accumbens of 10-week-old anesthetized SHRs and WKYs. Samples were collected in the following order: 3 baseline, 3 CCK8S (10 mumol/l), and 3 postdrug samples. The samples were then analyzed using high pressure liquid chromatography with electrochemical detection. CCK8S increased dopamine and DOPAC levels in both the SHR and WKY with a larger increase in basal dopamine in the SHR (greater than 200%). Perfusion of the nucleus accumbens with 1 mumol/l of CCK8S or the nonsulfated form of CCK8 (CCK8US, 10 mumol/l) produced no significant increase in the release of dopamine in the SHR. These results indicate that CCK8S-induced release of dopamine in the nucleus accumbens is greater in the SHR. Changes in CCK8S neurotransmission/receptor function may be responsible for the alterations in dopaminergic function of the SHR and the pathogenesis of hypertension.

Characterization of a serine peptidase responsible for the inactivation of endogenous cholecystokinin in human brain

Depolarization of slices of human cerebral cortex releases cholecystokinin-8 immunoreactivity, only a fraction of which is recovered in intact immunoreactive form in the medium. This suggests that extensive hydrolysis takes place during short incubations. In the presence of diisopropylfluorophosphate, a serine reagent, the recovery is nearly doubled, however, consistent with the involvement of a serine peptidase activity. The latter was characterized by assessing the protective effects of a series of serine protease inhibitors belonging to the families of peptide chloromethylketones or boronic acids. The relative potency of these inhibitors was similar to corresponding values previously found with rat brain slices indicating that a similar serine peptidase activity is responsible for endogenous cholecystokinin inactivation in the two species.

Chromosomal localization of the gastric and brain receptors for cholecystokinin (CCKAR and CCKBR) in human and mouse

Receptors for cholcystokinin (CCK) can be pharmacologically classified into at least two distinct subtypes, CCKAR and CCKBR. In an effort to determine whether the CCKA and CCKB receptors may be associated with certain CNS or gastrointestinal diseases, we have localized and compared the human and mouse chromosomal loci encoded by the CCKAR and CCKBR genes. The gene encoding the CCKA receptor maps to a syntenic region of human chromosome 4 and mouse chromosome 5. The CCKB receptor gene, on the other hand, resides on a syntenic region of human chromosome 11 and distal mouse chromosome 7. Localization of the CCK receptors with two dopamine receptors, DRD5 (4p15.1-p15.3) and DRD4 (11p15), provides the interesting possibility of coinvolvement in neuropsychiatric or CNS illnesses.

Further studies on the role of cholecystokinin-A and B receptors in secretion of anterior pituitary hormones in male rats

We compared the effects of unselective cholecystokinin (CCK) agonists (caerulein and CCK-8s) and a CCKB agonist CCK-4 on the secretion of thyrotropin (TSH), growth hormone (GH) and prolactin (PRL) in male rats. The subcutaneous (s.c.) administration of caerulein and CCK-8s suppressed dose-dependently TSH and GH levels. In contrast, when given into the 3rd brain ventricle (i.c.v.) caerulein dose-dependently elevated the GH levels. Next the importance of the afferent vagal nerves was studied in the action of caerulein and CCK-4. Subdiaphragmatic vagotomy itself decreased cold-stimulated TSH levels but abolished the suppressing effect of intraperitoneal (i.p.), and apparently also that of the i.c.v. caerulein. GH and PRL levels were altered neither by vagotomy nor caerulein. CCK-4 did not affect hormone levels. Atropine and butylscopolamine (i.p.) themselves did not alter TSH, PRL or GH secretion in intact rats. Neither did they reverse the effect of caerulein on TSH. In conclusion, CCKA receptors dominate in TSH and CCKB receptors in GH regulation. CCKA receptors in the gastrointestinal tract, related to the nervus vagus are mediating the inhibitory effect of caerulein upon TSH secretion but inhibition of GH secretion does not depend on the nervus vagus. CCKB receptors in the brain stem or near the 3rd brain ventricle are responsible for stimulation of GH secretion.

Cloning and expression of the rabbit gastric CCK-A receptor

Cholecystokinin stimulates pancreatic zymogen secretion by binding with high affinity to a receptor on the pancreatic acinar cell. This receptor has been cloned and shown to be a CCK-A subtype. CCK also stimulates pepsinogen secretion from the gastric chief cell with high affinity. Using polymerase chain reaction with primers from the known sequence of the rat pancreatic CCK-A receptor cDNA, we prepared a 600 bp product from rat and rabbit stomach cDNA. From Southern analysis these represented a fragment of a gastric CCK-A receptor. PCR was then used to amplify a rabbit lambda ZAP II gastric epithelial cDNA library with the same primers, and the product was identified by sequencing as representing a CCK-A receptor fragment. When this PCR product was used to screen the library, ten positive clones were identified in a screening of 4.10(5) plaques, and several of these were sequenced. All had essentially the same sequence contained within 2 of these clones consisted of 427 amino acids and was 92% homologous (87% identity) to the known rat pancreatic CCK-A sequence but only 43% homologous to the gastric CCK-B sequence. The cDNA was subcloned into a pcDNA1 expression vector and transiently expressed in the human embryonic kidney cell line, HK 293. The responses of intracellular Ca2+ in these transfected cells to CCK and gastrin were monitored using video imaging. On the average 40% of the cells responded to CCK-8 by a transient elevation of [Ca2+]i followed by a steady state plateau. CCK was a high and gastrin a low affinity ligand for this signal, corresponding to the actions of these ligands on pepsinogen secretion from chief cells and somatostatin release from D cells. Hence from sequence and second messenger responses, the clone represents the CCK-A receptor presumably responsible for pepsinogen secretion by gastric chief cells and somatostatin release from gastric D cells.

Pharmacological properties of ureido-acetamides, new potent and selective non-peptide CCKB/gastrin receptor antagonists

We present here the pharmacological properties of 3 ureido-acetamide members of a novel family of non-peptide cholecystokinin-B (CCKB) receptor antagonists. RP 69758 (3-(3-[N-(N-methyl N-phenyl-carbamoylmethyl) N-phenyl-carbamoylmethyl] ureido)phenylacetic acid), RP 71483 ((E)-2-[3-(3-hydroxyiminomethyl phenyl) ureido] N-(8-quinolyl) N-[(1,2,3,4-tetrahydro 1-quinolyl)carbonylmethyl]acetamide) and RP 72540 ((RS)-2-[3-(3-[N-(3-methoxy phenyl) N-(N-methyl N-phenyl-carbamoylmethyl) carbamoylmethyl] ureido) phenyl] propionic acid) displayed nanomolar affinity for guinea-pig, rat and mouse CCKB receptors labelled with [3H]pCCK-8 or with the selective CCKB receptor ligand [3H]pBC264. RP 69758 and RP 72540 showed selectivity factors in express of 200 for CCKB versus CCKA receptors. All three compounds had also high affinity for gastrin binding sites in the stomach. The ureido-acetamides behaved as potent antagonists of CCK-8-induced neuronal firing in rat hippocampal slices in vitro, a functional model of brain CCKB receptor mediated responses. RP 69758 is also a potent gastrin receptor antagonist in vivo that dose dependently inhibits gastric acid secretion induced by i.v. injection of pentagastrin in the rat. None of the three ureido-acetamides, at concentrations up to 1 microM, significantly blocked CCK-8-evoked contractions of the guinea-pig ileum in vitro, a CCKA receptor bioassay. In ex vivo binding studies, i.p. administration of RP 69758 and RP 72540 resulted in a dose-dependent inhibition of [3H]pCCK-8 binding in mouse brain homogenate. However, the relative penetration of these ureido-acetamides into the forebrain after peripheral administration was below 0.01%. RP 71483 did not appear to cross the blood-brain barrier in quantities sufficient to prevent [3H]pCCK-8 binding at low doses, a property that makes it suitable for the exploration of the peripheral versus central origin of the behavioural effects observed following systemic administration of CCK. RP 69758, RP 71483 and RP 72540 are highly potent and selective non-peptide CCKB receptor antagonists which are useful tools to explore the physiological functions of CCKB receptors.

Selective non-peptide ligands for an accommodating peptide receptor. Imidazobenzodiazepines as potent cholecystokinin type B receptor antagonists

A series of imidazobenzodiazepines, non-peptide antagonists of the peptide hormone cholecystokinin (CCK), are described. Derived by chemical modification of the benzodiazepine ring system embedded within the CCK-B antagonist L-365,260, these compounds display CCK-B/CCK-A selectivity and some analogs have receptor binding affinities in the subnanomolar range. This group of novel imidazobenzodiazepines, among which N-[(2S,4R)-methyl-6-phenyl-2,4-dihydro-1H-imidazo[1,2- alpha][1,4]benzodiazepin-4-yl]-N'-[3-methylphenyl]-urea (12) is the principal compound, expands the structural diversity of the collection of non-peptide CCK-B antagonists and will be useful in further delineating the function of CCK in the central nervous system.

Distribution of cholecystokinin receptors in the bovine brain: a quantitative autoradiographic study

Quantitative in vitro receptor autoradiography was used to study the distribution of cholecystokin receptors in the bovine brain. [125I]Bolton-Hunter cholecystokinin octapeptide binding was described in whole hemisphere sagittal and coronal sections using cholecystokinin octapeptide, devazepide and L-365,260 as competitors to identify the subtypes. High levels of cholecystokinin receptors were found in the cortex, where they presented a laminar distribution which varied from area to area. The basal ganglia, the caudate nucleus, nucleus accumbens and putamen presented high to moderate levels of cholecystokinin binding, whereas only very low labelling was found in the globus pallidus. Cholecystokinin binding was present in all portions of the bovine hippocampus; high levels were found in the dentate gyrus, CA1 subfield of Ammon's horn, subiculum and presubiculum. Moderate to high levels were also found in the amygdala, inferior colliculus and olfactory tract, while most of the hypothalamic and thalamic nuclei exhibited very low or no cholecystokinin binding. Low cholecystokinin binding was uniformly distributed across cell layers of the bovine cerebellar cortex. Competition of [125I]Bolton-Hunter cholecystokinin octapeptide binding in the cortex, nucleus accumbens, caudate nucleus, hippocampus, cerebellum and brainstem was much greater in the presence of L-365,260 than devazepide, thereby suggesting that the majority of cholecystokinin receptors in these regions are of the cholecystokinin-B subtype. The results of this study, when compared to distribution profiles in other mammalian species, provide further evidence for species differences in the distribution of cholecystokinin receptors in the brain. The results also support the possible interaction between cholecystokinin and dopaminergic systems in areas of the brain containing dopaminergic terminals, such as the frontal cortex, nucleus accumbens, caudate-putamen and olfactory tubercle.

Different modifications of the dopamine metabolism in the core and shell parts of the nucleus accumbens following CCK-A receptor stimulation in the shell region

After the injection of CCK8 into the posterior N. Acc. of rats DA, DOPAC HVA contents were determined from punches of the anterior and posterior N. Acc. and VTA. CCK8 (20 pmol/side) modified these levels only in the posterior N. Acc. and these responses were inhibited by the CCK-A antagonist devazepide. Five min after treatment, DA, DOPAC and HVA were increased in the N. Acc.shell and 10 min later they were decreased in the N. Acc.core. These data suggest that in these regions CCK8 could both abolish the influence of DA from the core on the transmission of motor information and favor that of DA from the shell on emotional-like responses.

The CCKB receptor antagonist, L-365,260, elicits antidepressant-type effects in the forced-swim test in mice

Selective CCKA and CCKB receptor agonists and antagonists were used to study the involvement of endogenous cholecystokinin in the behavioural changes that occur in mice in the forced-swimming test (Porsolt's test). The CCKB receptor antagonist, L-365,260 ((3R)-(+)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4- benzodiazepin-3-yl)-3-methylphenylurea), but not the CCKA receptor antagonist, devazepide ((3S)-(-)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepin -3-yl)- 1H-indole-2-carboxamide), elicited an antidepressant-type response (a decrease in the duration of immobility) that was suppressed by previous treatment with either CCK-8 (H-Asp-Tyr(OSO3H)-Met-Gly- Trp-Met-Asp-Phe-NH2) or the selective CCKB receptor agonist BC-264 (Boc-Tyr(SO3H)-gNle-mGly-Trp-N(Me)-Nle-Asp-Phe- NH2). The L-365,260 effect was also prevented by the dopamine receptor antagonist, SCH-23,390 (a dopamine D1-selective receptor antagonist: R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl- 2,3,4,5-tetrahydro-1H-3-benzazepine) and sulpiride (a dopamine D2-selective receptor antagonist: (-)-5-(aminosulfonyl)-N-[(1-ethyl-2-pyrrolidinyl) methyl]-2-metoxybenzamide). On the other hand, co-administration of subthreshold doses of L-365,260 and nomifensine (an atypical antidepressant that selectively blocks dopamine re-uptake mechanisms, 1,2,3,4-tetrahydro-2-methyl-4-phenyl-8-isoquinolinamine) led to a potent antidepressant-type response. These results indicate that blocking of CCKB receptors could result in an increase of extracellular dopamine contents in some brain areas involved in depression and suggest a potential use of CCKB receptor antagonists, alone or combined with antidepressants, in the treatment of depressive syndromes.

Repeated administration of MDMA down-regulates preprocholecystokinin mRNA expression but not tyrosine hydroxylase mRNA expression in neurones of the rat substantia nigra

The effect of repeated administration of 3,4-methylenedioxymethamphetamine (MDMA) on the expression of tyrosine hydroxylase and preprocholecystokinin (CCK) messenger RNAs in substantia nigra was examined by in situ hybridisation histochemistry. Sections hybridised with 35S-labelled oligonucleotides were subjected to computerised image analysis to determine the density of silver grains above positively labelled cells as an index of steady state mRNA levels. In the substantia nigra pars compacta, CCK mRNA levels were significantly reduced in drug-treated animals 24 h and at 2 weeks after the last dose of MDMA (10 mg/kg i.p., twice daily for 4 days). In the same animals, MDMA caused no change in the level of tyrosine hydroxylase mRNA in this brain region. The results show that MDMA can produce changes in dopamine neurones. Furthermore, since tyrosine hydroxylase and cholecystokinin are co-expressed in substantia nigra pars compacta, these results suggest that the expression of the tyrosine hydroxylase and CCK genes are regulated independently.

Pentagastrin infusions in patients with panic disorder. II. Neuroendocrinology

Cholecystokinin (CCK) has well-documented anxiogenic effects in animals and normal people, and panicogenic effects in patients with panic disorder, but little is known about its neuroendocrine profile. We examined neuroendocrine responses to intravenous infusions of pentagastrin, a selective CCK-B receptor agonist, in 10 patients with panic disorder and 10 normal control subjects. Pentagastrin potently activated the hypothalamic-pituitary-adrenal (HPA) axis, but did not release growth hormone or any of several vasoactive peptides (neurokinin A, substance P, vasoactive intestinal peptide). The HPA axis response was unrelated to increases in symptoms. Panic patients did not differ from controls in neuroendocrine responses to the CCK agonist. Differential sensitivity to novelty stress accounted for the only patient-control differences in neuroendocrine profiles. The data suggest that CCK may help modulate normal HPA axis activity, but its anxiogenic effects are unrelated to its stimulatory effects on the HPA axis. Pentagastrin provides a safe and readily available probe for further study of CCK receptor systems in humans.

CCK-8-evoked cationic currents in substantia nigra dopaminergic neurons are mediated by InsP3-induced Ca2+ release

Our recent study demonstrated that by activating CCK-A receptors, CCK-8 excites substantia nigra (SN) dopaminergic (DA) neurons via increasing a non-selective cationic conductance. In the present study, we further studied the molecular mechanism by which CCK-8 induces cationic currents in SN DA neurons. CCK-8-evoked inward currents were inhibited by the intracellular perfusion of GDP-beta-S (1 mM). In DA neurons internally perfused with GTP-gamma-S (0.5 mM), the inward currents produced by CCK-8 became irreversible. Pretreating DA neurons with 500 ng/ml pertussis toxin (PTX) did not significantly affect the ability of CCK-8 to induce cationic currents. Intracellular application of heparin (2 mg/ml), an inositol 1,4,5-trisphosphate (InsP3) receptor antagonist, and buffering intracellular calcium with the Ca(2+)-chelator BAPTA (10 mM) suppressed CCK-8-evoked cationic currents. Dialyzing DA neurons with protein kinase C (PKC) inhibitors, staurosporine and PKC(19-31), failed to prevent CCK-8 from generating cationic currents. It is concluded that PTX-insensitive G-proteins mediate CCK-8-induced enhancement of cationic conductance of SN DA neurons. The coupling mechanism via G-proteins is likely to involve the generation of InsP3, and subsequent InsP3-evoked Ca2+ release from the intracellular store results in activating the non-selective cationic conductance.

Nucleus accumbens dopamine-CCK interactions in psychostimulant reward and related behaviors

The present paper provides an overview of dopamine (DA) and cholecystokinin (CCK) mechanisms that contribute to psychostimulant reward-related behaviors. Three different behavioral paradigms are focused on: intravenous psychostimulant reward, psychostimulant-induced locomotor activity, and psychostimulant-induced feeding. Based on evidence derived from these different behavioral paradigms, this paper reviews data indicating that nucleus accumbens CCK and DA play an important role in mediating reward. Neurobiological mechanisms are proposed to explain the functional relationship between CCK and DA in the nucleus accumbens.