Cholecystokinin octapeptide levels in rat brain are changed after subchronic neuroleptic treatment

The potential role of cholecystokinin in schizophrenia: review and update

The role of the neuropeptide cholecystokinin in schizophrenia has been widely explored because of its modulating action on midbrain dopamine neurons. The recent discovery of more specific receptor subtype cholecystokinin antagonists should be considered as potential treatment for schizophrenia with fewer side effects. This paper reviews cholecystokinin/dopamine interactions in animal and human studies. Clinical trials with cholecystokinin agonists and antagonists in schizophrenia are updated.

Viral Delivery of GDNF Promotes Functional Integration of Human Stem Cell Grafts in Parkinson's Disease

Dopaminergic neurons (DAns), generated from human pluripotent stem cells (hPSCs), are capable of functionally integrating following transplantation and have recently advanced to clinical trials for Parkinson's disease (PD). However, pre-clinical studies have highlighted the low proportion of DAns within hPSC-derived grafts and their inferior plasticity compared to fetal tissue. Here, we examined whether delivery of a developmentally critical protein, glial cell line-derived neurotrophic factor (GDNF), could improve graft outcomes. We tracked the response of DAns implanted into either a GDNF-rich environment or after a delay in exposure. Early GDNF promoted survival and plasticity of non-DAns, leading to enhanced motor recovery in PD rats. Delayed exposure to GDNF promoted functional recovery through increases in DAn specification, DAn plasticity, and DA metabolism. Transcriptional profiling revealed a role for mitogen-activated protein kinase (MAPK)-signaling downstream of GDNF. Collectively, these results demonstrate the potential of neurotrophic gene therapy strategies to improve hPSC graft outcomes.

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.

Chemical identity of 5-HT2A receptor immunoreactive neurons of the rat septal complex and dorsal hippocampus

Brain 5-HT2A receptors have been implicated in various behavioural and physiological processes including hippocampus-dependent learning and memory. To clarify the cellular localization and chemical identity of 5-HT2A receptor-immunoreactive (-ir) neurons in the rat septal complex and dorsal hippocampus, an immunofluorescence histochemical study was performed using a monoclonal antibody to the 5-HT2A receptor. Pretreatment with colchicine increased the number of 5-HT2A receptor-ir cell bodies, indicating that the 5-HT2A receptor protein undergoes microtubule-dependent anterograde transport in axons and dendrites. 5-HT2A receptor immunoreactivity was detected in septal cholinergic neurons, identified with an antiserum to the vesicular acetylcholine transporter (VAChT), and in GABAergic cell bodies in the medial septum/diagonal band of Broca, identified with antisera to glutamic acid decarboxylase (GAD) and the calcium-binding protein parvalbumin. In the dorsal hippocampus, 5-HT2A receptor immunoreactivity was demonstrated in cells located in the pyramidal cell layer (CA1-3) throughout the Ammon's horn and in the granular cell layer of the dentate gyrus. Furthermore, 5-HT2A receptor immunoreactivity was present in most hippocampal interneurons identified by the presence of GAD65, parvalbumin, calbindin D-28k, somatostatin and neuropeptide Y. In contrast, 5-HT2A receptor immunoreactivity was present in only a few interneurons containing cholecystokinin and calretinin immunoreactivity. The results suggest that serotonin acting on 5-HT2A receptors can modulate hippocampal functions via direct actions on hippocampal glutamatergic principal cells and indirectly via actions on hippocampal interneurons with different phenotypes as well as GABAergic and cholinergic septohippocampal neurons.

Effects of chronic olanzapine and haloperidol differ on the mouse N1 auditory evoked potential

Auditory evoked potentials have been used in a variety of animal models to assess information-processing impairments in schizophrenia. Previous mouse models have primarily employed a paired click paradigm to assess the transient measures of auditory gating. The current study uses stimulus trains at varied interstimulus intervals (ISI) between 0.25 and 8 s in mice to assess the effects of chronic olanzapine and haloperidol on auditory processing. Data indicate that olanzapine increases the amplitude of the N40, P80, and P20/N40 components of the auditory evoked potential, whereas haloperidol had no such effect. The ISI paradigm also allowed for an evaluation of several components of the mouse evoked potential to assess those that display response properties similar to the human P50 and N100. Data suggest that the mouse N40 displays an ISI response relationship that shares characteristics with the human N100, whereas the P20 appears more consistent with the human P50 across the ISI range evaluated in this task. This study suggests that olanzapine may help improve N100 impairments seen in schizophrenia, while haloperidol does not.

Effects of antipsychotic drugs on cholecystokinin and preprotachykinin (substance P) mRNA expression in the rat hippocampal formation

To assess the involvement of substance P (SP) and cholecystokinin (CCK) in the effects of antipsychotic drugs, preprotachykinin-A (PPT-A) and CCK mRNA expression was studied in the hippocampal formation using in situ hybridisation following 21 daily i.p. injections with the typical antipsychotic drug haloperidol (1 mg/kg) and the atypical drug clozapine (15 mg/kg). PPT-A mRNA levels were increased in the hippocampal CA3 subregion and in the entorhinal cortex after haloperidol, whereas a decrease was observed in the CA1 after clozapine. CCK mRNA levels increased in the CA1, the entorhinal cortex and in hilus, following both haloperidol and clozapine. It is suggested that earlier findings of increased SP levels in the hippocampal formation of schizophrenics may be a consequence of haloperidol treatment and that reduced hippocampal CCK and CCK mRNA levels found earlier in schizophrenics do not result from antipsychotic drug treatment. These results are consonant to the hypothesis that increased cortical CCK transmission may be beneficial in the treatment of psychosis.

Body weight gain induced by antipsychotic drugs: mechanisms and management

Long-term administration of typical and atypical antipsychotic drugs (AP) induces excessive weight gain which afflicts up to 50% of patients, impairs health and interferes with treatment compliance. Basic and clinical research has shown that AP may affect body weight through diverse mechanisms. Increased appetite is probably related to the interaction of AP with neuronal receptors to dopamine, serotonin and histamine. Additional metabolic-endocrine disruption of weight regulation may be related to the effects of AP-induced hyperprolactinaemia on gonadal-adrenal steroids and insulin sensitivity. In humans, programmed physical activity, dietary restriction, anorectic agents, and drugs that counteract hyperprolactinaemia have been shown to be successful in a limited number of studies. Two novel strategies could expand the available therapeutic options. First, in preclinical experiments in female rats the estradiol antagonist/agonist drug tamoxifen or estradiol itself have been shown to completely prevent the obesity provoked by the AP sulpiride, and to induce an endocrine-metabolic milieu that seems to counteract AP-induced obesity. Secondly, it has also been shown that oral antihyperglycaemic agents such as metformin may decrease body weight and counteract insulin resistance and hyperinsulinaemia which is correlated with several metabolic abnormalities in obese subjects. Lastly, estradiol replacement, tamoxifen and/or antihyperglycaemic agents are not devoid of significant side-effects, and these drugs have not been tested in obese psychiatric patients. Therefore, further research is needed before their clinical use may be recommended.

Clozapine decreases neuropeptide Y-like immunoreactivity and neuropeptide Y mRNA levels in rat nucleus accumbens

The aim of this study was to evaluate the effect of acute, subchronic (14 days) and chronic (28 days) intraperitoneal (i.p.) administration of clozapine (10 or 25 mg/kg) on neuropeptide Y (NPY) system activity in the nucleus accumbens of the rat. NPY-like immunoreactivity (NPY-LI) decreased 24 h after subchronic clozapine while NPY mRNA after both acute and subchronic clozapine treatment. NPY-LI levels were also reduced 8 days after cessation of chronic lower-dose treatment. Subchronic (14 days) administration of the 5-HT2A antagonist ketanserin (1 mg/kg i.p.) or the dopamine D2/D3 antagonist (+/-) sulpiride (100 mg/kg i.p.) reduced NPY-LI levels, whereas the dopamine D1-like antagonist SCH 23390 (0.5 mg/kg i.p.), dopamine D4 antagonist L-745,870 (1 mg/kg per os), and alpha1-adrenergic antagonist prazosin (0.2 mg/kg i.p.) had no effect. There were no significant differences between the ketanserin-induced decrease in NPY-LI levels and the effects of the following two-drug combinations: ketanserin and SCH 23390, ketanserin and L-745,870, and ketanserin and prazosin. The study has shown that clozapine reduces NPY system activity in the rat nucleus accumbens. It seems that the action of clozapine is partly mediated by blockade of 5-HT2A and D2/D3 dopaminergic receptors.

Effects of acute or long-term treatment with chlorpromazine, haloperidol or sulpiride on neuropeptide Y-like immunoreactivity concentrations in the nucleus accumbens of rat

The effects of acute, subchronic ( 14 days) or chronic (28 days) intraperitoneal (i.p.) administration of chlorpromazine (2 or 10 mg/kg), haloperidol (0.5 or 2 mg/kg) or sulpiride (50 or 100 mg/kg) on the neuropeptide Y (NPY) system in the rat nucleus accumbens were studied. NPY-like immunoreactivity (NPY-LI) decreased in a dose- and time-dependent manner, and was the lowest after haloperidol. NPY-LI levels increased 8 days after withdrawal of chronic drugs treatment. Acute administration of haloperidol reduced NPY mRNA, while Subchronic treatment did not change it. Subchronic i.p. administration of the dopamine D1-like antagonist SCH 23390 (1 mg/kg) reduced NPY-LI levels but the alpha1-adrenergic antagonist prazosin (0.2 mg/kg) had no effect. The effect of sulpiride coadministered with SCH 23390 was greater than that of SCH 23390 alone, while prazosin coadministered with sulpiride insignificantly reduced the effect of sulpiride. The dopamine D2/D3 agonist quinpirole given as a single injection (3 mg/kg) did not alter NPY-LI content by itself but antagonized the chlorpromazine-induced decrease and attenuated the haloperidol-induced decrease. Our findings indicate that the accumbens NPY system is markedly affected by the antipsychotics studied, and suggest that their effects may be in part mediated by blockade of D2-like (D2, D3) and D1 dopaminergic receptors.

Abnormal cholecystokinin mRNA levels in entorhinal cortex of schizophrenics

Limbic cortical regions, including anterior cingulate cortex (ACC), prefrontal cortex (PFC) and entorhinal cortex (ERC), have been implicated in the neuropathology of schizophrenia. Glutamate projection neurons connect these limbic cortical regions to each other, as well as to the terminal fields of the striatal/accumbens dopamine neurons. Subsets of these glutamate projection neurons, and of the GABA interneurons in cortex, contain the neuropeptide cholecystokinin (CCK). In an effort to study the limbic cortical glutamate projection neurons and GABA interneurons in schizophrenia, we have measured CCK mRNA with in situ hybridization histochemistry in postmortem samples of dorsolateral (DL)PFC, ACC and ERC of seven schizophrenics, nine non-psychotic suicides and seven normal controls. CCK mRNA is decreased in ERC (especially layers iii vi) and subiculum in schizophrenics relative to controls. Cellular analysis indicates that there is a decrease in density of CCK mRNA in labelled neurons. In so far as ERC CCK mRNA is not reduced in rats treated chronically with haloperidol, this decrease in schizophrenics does not appear to be related to neuroleptic treatment. In contrast, in DLPFC, where schizophrenics do not differ from normals, the suicide victims have elevated CCK mRNA (especially in layers v and vi), and increased cellular density of CCK mRNA, relative to both normals and schizophrenics. These results lend further support for the involvement of ERC and hippocampus in schizophrenia, suggesting that neurons that utilize CCK may be particularly important. Similarly, an increase in CCK mRNA levels in the PFC of suicides adds to a growing body of evidence implicating this structure in this pathological state. In so far as CCK is co-localized with GABA or glutamate in cortical neurons, both of these neuronal populations need to be studied further in schizophrenia and suicide.

Cholecystokinin messenger RNA deficit in frontal and temporal cerebral cortex in schizophrenia

No consistent markers of pathology have been established yet in schizophrenia, although abnormalities in frontal and temporal structures are indicated from positron emission tomography (PET) studies. We have used in situ hybridization to investigate functional changes focusing on the quantitation of cholecystokinin (CCK) mRNA, whose product has been shown to be depleted in schizophrenia. CCK mRNA and G(o) alpha-subunit mRNA were measured in eight schizophrenic and eight control subjects matched for age and postmortem delay. The study revealed a marked decrease in CCK mRNA of 83% in frontal cortex (BA10) and 63% in superior temporal cortex (BA22) in schizophrenia with no change in G(o) alpha-subunit mRNA in either region. This study was extended to a further series of eight patients to determine the reproducibility of this effect and to quantitate laminar changes in CCK mRNA. Quantitation of CCK mRNA in inner cortical layers (layer V/VI) was carried out in frontal and temporal cortex in comparison with G(o) alpha-subunit mRNA, which is also concentrated in this region; this study showed a similar selective decrease in CCK mRNA in frontal and temporal cortex of 47% and 51%, respectively. A confirmatory decrease in CCK mRNA was also obtained by slot blot analysis of CCK mRNA in tissue extracts of frontal cortex by reference to levels of beta-tubulin mRNA, CCK mRNA:beta-tubulin mRNA was significantly decreased (67%) in schizophrenic tissue compared to control tissue. There was no significant correlation of CCK mRNA loss with neuroleptic treatment or duration of illness.

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.

Effect of sulpiride on somatostatin receptors, somatostatin-like immunoreactivity and modulation of adenylyl cyclase activity in the rat brain

The present study investigates the effects of the administration of an intracerebroventricular (i.c.v.) dose of 500 micrograms/rat of the neuroleptic (-) sulpiride on somatostatin-like immunoreactivity (SSLI) levels, 125I-Tyr11-SS binding to its specific receptors, SS-modulated adenylyl cyclase (AC) activity and the pertussis toxin (PTX) substrates measured by toxin-catalysed ADP ribosylation of the alpha-subunits from G-proteins. (-) Sulpiride significantly decreased the SSLI levels in the frontoparietal cortex at 30 min but was without effect on the SSLI concentration in the striatum. This decrease had disappeared within 24 hr. The administration of (-) sulpiride produced a significant increase in the number of 125I-Tyr11-SS receptors and a significant reduction in their affinity at 30 min after injection in the striatum without affecting the frontoparietal cortex. The effects of the (-) sulpiride injection had disappeared after 24 hr. This change in SS binding was not due to a direct effect of (-) sulpiride on these receptors since no effect on binding was produced by high concentrations of (-) sulpiride (10(-5) M) when added in vitro. No significant differences were seen in either brain region for the basal or the forskolin (FK)-stimulated AC enzyme activities in the control and (-) sulpiride groups. In the (-) sulpiride group, the capacity of SS to inhibit FK-stimulated AC in the frontoparietal cortex was significantly higher than in the control group with no significant difference in the striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential induction of neurotensin and c-fos gene expression by typical versus atypical antipsychotics

Precise neural mechanisms underlying the pathophysiology and pharmacotherapy of psychotic disorders remain largely unknown. Present studies investigated the effects of various antipsychotic drugs on expression of the gene encoding the purported endogenous antipsychotic-like peptide neurotensin (NT) in striatal regions of the rat brain. The results demonstrate that several clinically efficacious antipsychotic drugs selectively and specifically increase expression of NT/neuromedin N (NT/N) mRNA in the shell of the nucleus accumbens, a region of the forebrain associated with limbic systems. On the other hand, only typical antipsychotics that cause a high incidence of acute motor side effects increased the expression of NT/N mRNA in the dorsolateral striatum, an extrapyramidal region primarily involved in motor control. In addition, it appears that distinct mechanisms may be involved in the effects of antipsychotics on NT/N gene expression in the dorsolateral striatum versus the accumbal shell. Thus neuroleptic-induced increases in NT/N mRNA expression in the dorsolateral striatum were preceded by a rapid and transient activation of c-fos mRNA, whereas none of the antipsychotics affected c-fos mRNA expression in the accumbal shell. The anatomical characteristics of NT/N gene expression induced by typical versus atypical antipsychotics raise the possibility that increased activity of specific NT neurons may contribute to the therapeutic effects (NT neurons in the accumbal shell) or motor side effects (NT neurons in the dorsolateral striatum) of these drugs.

Changes at cholecystokinin receptors induced by long-term treatment with diazepam and haloperidol

Fourteen days administration of haloperidol (1 mg/kg daily) prevented the motor depressant effect of caerulein (an agonist at cholecystokinin receptors, 15 micrograms/kg) and the antagonistic effect of caerulein (100 micrograms/kg) against (+)-amphetamine (5 mg/kg) induced hyperlocomotion in mice. The antiaggressive effect of caerulein (40 micrograms/kg) in saline-treated mice was replaced by increased aggressiveness after long-term haloperidol and diazepam (5 mg/kg daily) treatment. The anticonvulsant effect of caerulein (125 micrograms/kg) against picrotoxin (10 mg/kg) induced seizures was abolished after 14 days diazepam, but not after haloperidol, treatment. The above described changes in the mouse behaviour are probably related to the development of subsensitivity at CCKA receptors, whereas the CCKB receptor subtype becomes more sensitized to the action of caerulein after long-term haloperidol and diazepam treatment.

Expression of the Proneurotensin Gene in the Rat Brain and Its Regulation by Antipsychotic Drugs

In this chapter, we have presented evidence for several potential levels of interaction of NT/N gene products with dopaminergic systems of the brain. We have focused on one manifestation of this interaction related to the effects of antipsychotic drugs on expression of the NT/N gene in two anatomically discrete populations of neurons. It appears that certain antipsychotic drugs can dramatically increase expression of this gene in the dorsolateral striatum by blocking dopamine D2 receptors, perhaps by increasing expression of the gene encoding the transcriptional regulator fos. In addition, a second group of NT cells in the shell region of the nucleus accumbens also respond to these drugs by increasing NT/N gene expression. Several other peptides have been suggested to respond to treatment with antipsychotic drugs. However, there are some important differences with respect to their effects on the NT cells we have studied. The most important of these is the differential responsiveness of the DLSt and nucleus accumbens NT neurons to typical and atypical antipsychotics. We showed that all antipsychotic drugs tested increased NT/N mRNA gene expression in the accumbens, a region thought to be involved in dopaminergic disturbances underlying psychosis. However, only the typical neuroleptics that have a high propensity to induce acute extrapyramidal motor side effects influenced NT/N gene expression in the dorsolateral striatum, a structure importantly involved in regulation of motor functions. We hypothesize, therefore, that NT/N-expressing neuronal systems in the nucleus accumbens may mediate some or all of the antipsychotic effects, whereas those in the dorsolateral striatum may be involved in motor effects of neuroleptic drugs. Thus, examination of the effects of these drugs on these neuronal populations will not only clarify their mechanism of action, but in addition may provide a useful "screening" assay for new drugs with enhanced antipsychotic activity, but reduced propensity to induce the debilitating extrapyramidal side effects that are a major cause of patient noncompliance. Future studies will focus on the effects of antipsychotic drugs on NT neurons in clinically relevant models of chronic administration, and on the molecular events involved in their effects on expression of the NT/N gene in the brain.

Effects of a unilateral 6-hydroxydopamine lesion and prolonged L-3,4-dihydroxyphenylalanine treatment on peptidergic systems in rat basal ganglia

The effect of a unilateral 6-hydroxydopamine (6-OHDA) lesion of the medial forebrain bundle or of a sham lesion on the neuropeptide content of the striatum and substantia nigra was investigated with or without 6 months L-3,4-dihydroxyphenylalanine (L-DOPA; 200 mg/kg per day) plus carbidopa (25 mg/kg per day) treatment. [Met5]- and [Leu5]enkephalin, substance P (SP), neurotensin (NT) and cholecystokinin (CCK) were measured by a combined HPLC/RIA method. Neurotensin levels were increased in the striatum, and [Leu5]enkephalin, and SP levels were reduced in the substantia nigra as a consequence of the lesion, while the levels of other peptides were unaltered. Administration of L-DOPA to sham-operated rats bilaterally increased SP levels in striatum and substantia nigra, and [Met5]enkephalin and CCK content in substantia nigra. L-DOPA treatment of 6-OHDA-lesioned rats increased [Met5]- and [Leu5]enkephalin and CCK levels in the striatum ipsilateral to the lesion but not on the intact side. In the substantia nigra, the lesion-induced decrease in [Leu5]enkephalin and SP was reversed by L-DOPA treatment, [Met5]enkephalin and CCK levels ipsilateral to the lesion were further enhanced, and there was an increase in NT ipsilateral to the lesion. Cryptic [Met5]- and [Leu5]enkephalin increased in the ipsilateral striatum following an 6-OHDA lesion. L-DOPA treatment did not alter cryptic enkephalin levels or the lesion-induced increase in cryptic [Met5]enkephalin, while cryptic [Leu5]enkephalin was further increased in lesioned animals given L-DOPA. These results suggest that the pattern of change in basal ganglia peptides in Parkinson's disease is not due solely to the destruction of the nigrostriatal pathway, the drug treatment of the disease or a combination of these factors.

Dopaminergic regulation of cholecystokinin mRNA content in rat striatum

The nigrostriatal dopaminergic activity was pharmacologically changed to assess whether dopamine (DA) regulates cholecystokinin (CCK) mRNA steady state in rat striatum. Cocaine and benztropine, two dopaminergic agonists known to induce DA release and to block its re-uptake, produced a time dependent increase in CCK mRNA content in rat striatum. A significant increase in striatal CCK mRNA was observed 8 h after a single injection of cocaine (15 mg/kg, i.p.) or benztropine (15 mg/kg, i.p.) whereas a two-fold increase was observed after a daily treatment for one week with these two dopaminergic agonists. Cocaine and benztropine failed to change CCK mRNA content in the cerebral cortex. Haloperidol, a dopaminergic receptor blocker, injected at 1 mg/kg, i.p., daily for 7 days, decreased CCK mRNA content in striatum but not in the cerebral cortex. Moreover, haloperidol blocked the effect of cocaine and benztropine, suggesting that the stimulation of striatal dopaminergic receptors is necessary for the induction of CCK biosynthesis. The neurotoxin 6-hydroxydopamine injected into the medial forebrain bundle, elicited a 50% decrease in striatal CCK mRNA, supporting the hypothesis that DA tonically regulates CCK biosynthesis in postsynaptic neurons. To characterize the dopaminergic receptor subtype involved in this regulation, BHT 920, a specific D2 receptor agonist and SKF 38393, a specific D1 receptor agonist were used. While one week treatment with BHT 920 (1 mg/kg, i.p.) increases striatal CCK mRNA content, SKF 38393 (3 mg/kg, i.p.) failed to change this parameter. These data suggest that the increase of striatal CCK mRNA is mediated by the activation of the D2 receptor subtype.

Isocratic reverse-phase HPLC separation and RIA used in the analysis of neuropeptides in brain tissue

A reverse-phase, high-performance liquid chromatographic (HPLC) method was employed to separate and characterise five neuropeptides from complex mixtures, with important advantages over methods employed earlier using combined HPLC-RIA studies. Peptides were separated using 0.5M pyridine-0.5M formic acid buffer, pH 4, containing propan-l-ol 14% (met-enkephalin, leu-enkephalin, neurotensin) or 20% (CCK-8-S, substance P) at a flow rate of 1.0 ml/min. Isocratic conditions, and volatile solvents, resulted in a highly reproducible method, producing samples in a form designed for subsequent RIA. The application and importance of the procedure is demonstrated by comparison of the measurements of apparent peptide levels in crude brain extracts with those of authentic peptides as determined after HPLC purification.

The regional distribution of thyrotropin releasing hormone, leu-enkephalin, met-enkephalin, substance P, somatostatin and cholecystokinin in the rat brain and pituitary

There was no apparent difference in the regional distribution of neuropeptides in the brain of male and female rats. The highest levels of immunoreactive leu-enkephalin, TRH, substance P and somatostatin were found in the hypothalamus, while the striatum and the cerebral cortex had the highest concentrations of met-enkephalin and cholecystokinin respectively. The lowest concentrations of these were found in the cerebellum. Enkephalins (cerebral cortex), substance P (cerebral cortex and brain stem), and somatostatin (brain stem and striatum) showed higher level in the female while enkephalin and substance P contents in the anterior pituitary were higher in the male.

Effects of ceruletide and haloperidol on the hypothalamo-pituitary beta-endorphin system and brain beta-endorphin contents in the rat: with special reference to effects of ceruletide in chronically haloperidol-treated rats

Subcutaneous (sc) administration of 200 micrograms/kg ceruletide (CER), a decapeptide chemically related CCK-8, and 5 mg/kg haloperidol (HLP) to rats increased the plasma immunoreactive beta-endorphin (ir-beta-END) level. The combined injection of CER and haloperidol caused higher plasma ir-beta-END levels than either drug alone. High plasma ir-beta-END levels returned to control levels on the 2nd day. Prior intraperitoneal (ip) administration of a CCK receptor antagonist, L-364,718 (3 mg/kg), but not proglumide (400 mg/kg, ip), inhibited CER-induced, but not HLP-induced, elevation in plasma ir-beta-END levels. The dopamine agonist, bromocriptine (1 mg/kg, ip) decreased plasma ir-beta-END levels, but had not effect on CER-induced elevation in plasma ir-beta-END levels, whereas bromocriptine-induced reduction in plasma ir-beta-END levels was antagonised by HLP. CER injection to chronically HLP-treated rats caused a greater elevation of plasma ir-beta-END levels compared to saline-injected rats. In contrast to the acute experiment, plasma ir-beta-END levels remained elevated over a period of 24 h. In the acute experiment, CER, HLP or the combined treatment with these two drugs had no effect on ir-beta-END contents in the pituitary gland and brain. In the chronic experiment, HLP increased the adenohypophyseal and septal ir-beta-END contents and decreased the hippocampal ir-beta-END contents 24 h after the final HLP injection. CER caused a small reduction only in the hippocampal ir-beta-END contents of CER-injected rats 15 min after injection. When determined on the 2nd day, however, the increases in the adenohypophyseal and septal ir-beta-END contents and the decrease in the hippocampal ir-beta-END contents observed in CER-injected rats were of the same magnitude as those of rats not given the CER injection. These findings indicate that CER stimulates the release of ir-beta-END from the adenohypophysis through CCK-A receptors and that elevated plasma ir-beta-END levels is partly involved in some behavioural effects induced by CER. Furthermore, sustained elevation of plasma ir-beta-END levels after a single injection of CER to chronically HLP-treated rats may explain its long-lasting therapeutic and behavioural effects.

Effect of haloperidol on immunoreactive neuropeptide Y in rat cerebral cortex and basal ganglia

To clarify the dopaminergic regulation of neuropeptide Y (NPY) neurons, the effect of haloperidol on NPY in basal ganglia and the cerebral cortex of the rat brain was investigated by sensitive radioimmunoassay and immunocytochemistry using antiserum against rat NPY. After repeated intraperitoneal injections of haloperidol (5 mg/kg) for 6 days, the content of immunoreactive NPY was significantly decreased in the caudate-putamen, but significantly increased in the lateral prefrontal cortex. After treatment for 21 days, the content of immunoreactive NPY in the caudate-putamen remained significantly low, but the extent of change in the lateral prefrontal cortex diminished. In the medial prefrontal cortex, piriform cortex, parietal cortex and nucleus accumbens, no significant changes were found after treatment for either 6 or 21 days. These findings were compatible with those obtained by immunocytochemistry using the same antiserum: an increase of immunoreactive fibers and terminals in the lateral prefrontal cortex and their decrease in the caudate-putamen. However, in the nucleus accumbens the density of immunoreactive fibers and terminals was decreased in the rostral portion, but not in the caudal portion after haloperidol treatment for 6 and 21 days. These findings suggest that dopaminergic afferents region-specifically regulate dopamine-sensitive NPY neurons in the rat brain.

Similar behavioral and biochemical effects of long-term haloperidol and caerulein treatment in albino mice

Behavioral and biochemical experiments on male albino mice have revealed similar effects after the cessation of repeated (15 days) haloperidol (0.5 mg/kg daily IP) and caerulein (0.1 mg/kg daily SC) treatment. Tolerance developed to the action of muscimol (a GABA-A agonist, 1 mg/kg IP), caerulein (a CCK-8 agonist, 15 micrograms/kg SC) and flumazenil (a benzodiazepine antagonist, 10 mg/kg IP). Muscimol and caerulein were not able to suppress the motor activity of mice after 15 days treatment with haloperidol and caerulein. Flumazenil, which increased motor activity in saline-treated animals, also failed to affect activity after extended haloperidol or caerulein treatment. In contrast, the motor excitation induced by amphetamine (an indirect dopamine agonist, 3 mg/kg IP) was increased after haloperidol or caerulein administration. In radioligand binding studies the density of dopamine-2-receptors in striatum, opioid receptors in mesolimbic structures, and benzodiazepine and GABA-A receptors in brainstem was significantly elevated after long-term haloperidol or caerulein treatment. Simultaneously, the number of CCK-8, benzodiazepine and GABA-A receptors in cerebral cortex was decreased. It is probable that CCK-8-ergic mechanisms are involved closely in the action of repeated haloperidol treatment. CCK-8 seems to modulate the action of haloperidol through altering the sensitivity of dopamine, opioid, GABA-A and benzodiazepine receptors.

Tyrosine hydroxylase and cholecystokinin mRNA levels in the substantia nigra, ventral tegmental area, and locus ceruleus are unaffected by acute and chronic haloperidol administration

1. The studies described herein were designed to test the hypothesis that a neuroleptic, haloperidol, may alter the level of expression of the tyrosine hydroxylase and cholecystokinin genes in discrete brain regions. 2. In situ hybridization was employed to quantitate changes in concentration of mRNA for tyrosine hydroxylase and cholecystokinin in the ventral tegmental area, substantia nigra, and locus ceruleus after acute or chronic treatment with haloperidol or vehicle. 3. Haloperidol had no effect on the level of tyrosine hydroxylase or cholecystokinin mRNAs, in the ventral tegmentum, substantia nigra, or locus ceruleus, at either 3 or 19 days of drug administration. 4. These data suggest that haloperidol administration does not alter the level of tyrosine hydroxylase or cholecystokinin mRNAs in midbrain dopamine neurons of the rat.

In vivo studies on the enhancement of cholecystokinin release in the rat striatum by dopamine depletion

The release of cholecystokinin-8-like (CCK) immunoreactivity from the rat striatum has been studied in vivo using brain microdialysis. A basal efflux of CCK-like immunoreactivity was not detectable in the majority of experiments. Intrastriatal infusion of veratrine (100 micrograms/ml) increased striatal dialysate levels of CCK-like immunoreactivity above detection limits, representing an overflow into the interstitial fluid. High concentrations of potassium caused similar but less consistent effects. Extracellular dopamine depletion using alpha-methyl-p-tyrosine or reserpine also increased the dialysate content of CCK-like immunoreactivity. In contrast, inhibition of peptidases reported to hydrolyse CCK in vitro did not affect either basal or evoked efflux of CCK-like immunoreactivity. These data demonstrate that CCK-like immunoreactivity may be released from neuronal elements within the striatum by depolarizing stimuli in vivo, and suggest that increased overflow of CCK-like immunoreactivity is associated with dopamine depletion.

A mechanism for the involvement of colocalized neuropeptides in the actions of antipsychotic drugs

Evidence has accumulated to implicate neuropeptides localized within midbrain dopamine neurons (cholecystokinin, neurotensin, acetylcholinesterase) in synaptic transmission, mental disease, and pharmacotherapy. We suggest a means by which antipsychotic drugs alter the dynamics between dopamine and colocalized peptides: the intrinsic ability of these agents to stimulate dopamine neuronal activity while blocking dopamine receptors modulates the ratio of catecholaminergic to peptidergic transmission within the mesotelencephalic system. Imbalances of peptide and dopamine cotransmission and their modulation by neuroleptics may be relevant to the pathogenesis and pharmacotherapy of schizophrenia.

Cholecystokinin binding sites in the rat forebrain: effects of acute and chronic methamphetamine administration

Using the in vitro quantitative receptor autoradiographical technique, changes in the binding parameters of [propionyl-3H] propionylated CCK-8 [( 3H]pCCK-8) binding sites in the rat forebrain were investigated following acute and chronic administration of methamphetamine (MAP). The (Kd)app values of [3H]pCCK-8 binding sites in the frontal medial cortex and anterior cingulate cortex were significantly reduced after a single injection of 4mg/kg MAP. On the other hand, chronic treatment (14 days) with MAP at this dose significantly decreased the Bmax value of [3H]pCCK-8 binding sites in the anterior cingulate cortex accompanied by supersensitivity of locomotor effects to MAP. These findings suggest that dopamine (DA) neurons in these two regions are functionally related to intrinsic CCK-containing cortical neurons, and that CCK subsensitivity, perhaps due to an alteration in DA transmission, is involved in MAP sensitization. These findings may be relevant to the DA hypothesis of schizophrenia.

Brain CCK-B receptors mediate the suppression of dopamine release by cholecystokinin

The sulfated octapeptide of cholecystokinin (CCK-8S) and CCK fragments were administered to mice to determine the subtype and central versus peripheral location of the CCK receptor that modulates dopamine release in the neostriatum. Dopamine release was decreased when unsulfated CCK (CCK-8U) or the butoxycarbonyl tetrapeptide of CCK (t-boc-CCK-4) was infused into the brain ventricles but not when injected subcutaneously. These CCK fragments bind to the brain-type (CCK-B) but not alimentary-type (CCK-A) receptor. Centrally or peripherally administered CCK-8S also lowered dopamine release and this action was not blocked by the selective CCK-A receptor antagonist, L 364,718. The increase in dopamine release following amphetamine administration was attenuated by central injections of t-boc-CCK-4, CCK-8U, or CCK-8S, and this action of CCK-8S was not prevented by L 364,718. These data are the first to demonstrate that CCK-B receptors in brain mediate the suppression of dopamine release by cholecystokinin, especially when release is augmented. CCK-B receptor agonists should be useful for the treatment of psychiatric conditions that result from hyperactive dopamine neurons.

Effects of short- and long-term haloperidol administration and withdrawal on regional brain cholecystokinin and neurotensin concentrations in the rat

The effects of oral administration of the neuroleptic, haloperidol, on regional brain concentrations of cholecystokinin (CCK) and neurotensin were examined in the rat. Both short-term (3 weeks) and long-term (8 months) haloperidol administration increased the concentration of CCK in the substantia nigra. While short-term administration significantly increased the concentration of CCK in the ventral tegmental area and decreased the concentration of CCK in the cortex, including the medial prefrontal cortex, these effects were not observed following long-term drug administration. In contrast, long-term, but not short-term, haloperidol administration decreased the concentration of CCK in the olfactory tubercle. Withdrawal from long-term haloperidol did not alter CCK concentrations in any of the brain regions examined. Short-term haloperidol administration significantly increased the concentration of neurotensin in the caudate-putamen. Both short- and long-term administration increased the concentration of neurotensin in the nucleus accumbens, but only the increased following long-term administration reached statistical significance. Withdrawal from long-term haloperidol administration slightly decreased the concentrations of neurotensin in the caudate-putamen and nucleus accumbens. These results indicate that dopamine receptor blockade can affect both CCK- and neurotensin-containing neural systems. Furthermore, these two neuropeptides are affected differently depending upon the duration of haloperidol administration and withdrawal from this drug. The results raise the possibility that chronic administration of haloperidol may be toxic to some neurotensin-containing neurons in the basal ganglia.

Cholecystokinin receptor subtypes and neuromodulation

The sulfated octapeptide of cholecystokinin (CCK-8S) and CCK fragments have been administered to mice to determine the subtype and location of the CCK receptor that modulates the release of dopamine (DA) in brain. 1. Centrally (i.c.v.) or peripherally (s.c.) administered CCK-8S lowers DA release, and to a lesser extent, metabolism, in the neostriatum and olfactory tubercle. 2. DA release is decreased when the CCK-B selective compounds, unsulfated CCK-8 (CCK-8U) or the butoxycarbonyl tetrapeptide of CCK (t-boc-CCK-4), are given i.c.v. but not when injected s.c. 3. The increase in DA release following amphetamine administration is attenuated by i.c.v. but not s.c. injections of t-boc-CCK-4 or CCK-8U and by CCK-8S given via either route. 4. None of the s.c. actions of CCK-8S are prevented by the CCK-A receptor antagonist, L 364,718. CCK-B receptors in brain mediate the suppression by CCK of basal and augmented DA release. CCK-B receptor agonists may be useful for the treatment of psychiatric conditions that result from excessive DA release.

Chronic neuroleptic-induced mouth movements in the rat: suppression by CCK and selective dopamine D1 and D2 receptor antagonists

Fluphenazine decanoate (25 mg/kg IM every 3 weeks x 6) resulted in spontaneous vacuous chewing mouth movements and jaw tremor in male Sprague-Dawley rats. These movements could be suppressed by the selective D1 or D2 dopamine antagonists SCH 23390 (0.5 mg/kg) and raclopride (0.5 mg/kg), respectively, and by CCK-8S (50 micrograms/kg). Fluphenazine-induced mouth movements were unaffected by the selective CCK antagonist MK-329, and by a dose of physostigmine (50 micrograms/kg) sufficient to stimulate mouth movements in placebo treated rats. Scopolamine (0.1 mg/kg) suppressed spontaneous mouth movements in placebo-treated rats, but the effect on fluphenazine-induced mouth movements was not significant. A higher dose of scopolamine (0.5 mg/kg) did suppress the neuroleptic-induced mouth movements, but also induced hyperactivity, characterized by increased sniffing and grooming. These findings indicate that mouth movements resulting from the chronic administration of neuroleptics to the rat may serve as a useful pharmacological model of tardive dyskinesia in the human, and suggest that a relative increase of D1 activity as well as impaired CCK function may contribute to the pathogenesis of this disorder.

CCK-8 injected into the nucleus accumbens attenuates the supersensitive locomotor response to apomorphine in 6-OHDA and chronic-neuroleptic treated rats

Postsynaptic dopamine-cholecystokinin (CCK) interactions in the nucleus accumbens were studied in two behavioral preparations of DA receptor supersensitivity: chronic-neuroleptic treated and 6-hydroxydopamine (6-OHDA) denervated rats. Subcutaneous (SC) injections of apomorphine (APO; 0.15 mg/kg) in experiment 1 produced marked hyperlocomotion in rats following 12 days of pretreatment with cis-[Z]-flupenthixol (2 mg/kg; twice per day). Bilateral intra-accumbens (N.Acc.) microinjections of CCK-8 (2 ng and 2 micrograms) reliably reduced APO-stimulated hyperlocomotion. An intermediate CCK dose (20 ng) was without effect. No change in APO responsivity following chronic vehicle treatment was observed and the baseline APO response was not altered by CCK at any dose. Denervation of mesolimbic dopamine (DA) terminals by intra-N.Acc. injections of 6-hydroxydopamine (6-OHDA; 8 micrograms/side) in experiment 2 similarly resulted in intense locomotor hyperactivity after APO stimulation (0.1 mg/kg; SC). Bilateral intra-N.Acc. injections of CCK-8 (1, 10, 100 ng, and 1 micrograms) significantly attenuated the supersensitive locomotor response to APO. As in experiment 1, CCK produced "biphasic" dose-response effects with strong attenuation that persisted throughout the entire 60-min test at both high (1 microgram) and low (1 ng) doses. Intermediate CCK doses (10 and 100 ng) produced only short-term reductions in activity. Hypomotility induced by APO in SHAM-lesioned rats was not effectively reversed by CCK treatments. CCK had no effect on unstimulated baseline locomotor activity in either 6-OHDA or SHAM-lesioned rats. These results provide further evidence that CCK-8 modulates mesolimbic DA activity by functionally opposing the postsynaptic effects of DA in the region of the nucleus accumbens.

Cholecystokinin system in striatal-nigral neuronal networks: infusion of quinolinic acid into rat striatum

Unilateral infusions of quinolinic acid (QUIN) into the rat striatum led to an increase in cholecystokinin octapeptide sulfate-like immunoreactivity (CCK8S-LI) in the striatum and substantia nigra 4 days later. These changes were suppressed by the injection of gamma-aminobutyric acid into substantia nigra 30 min before sacrifice. Intraperitoneal administration of haloperidol 40 min before sacrifice also suppressed the effect of QUIN on CCK. These results suggest that nigrostriatal dopaminergic neurons regulate CCK neurons via presynaptic sites in the striatum, and also that striatonigral GABAergic neurons interact with CCK neurons in the substantia nigra.

The colocalization of cholecystokinin and tyrosine hydroxylase mRNAs in mesencephalic dopaminergic neurons in the rat brain examined by in situ hybridization

The colocalization of cholecystokinin and tyrosine hydroxylase mRNAs was studied with a cellular resolution in the mesencephalic dopaminergic neurons of the rat brain by in situ hybridization using synthetic oligonucleotides. An extensive colocalization of cholecystokinin-expressing cells, greater than that seen previously by immunohistochemistry, was found in the ventral tegmental area and in the substantia nigra pars compacta. We observed in these regions that cholecystokinin and tyrosine hydroxylase mRNAs coexisted in the same neurons but not all dopamine cells expressed cholecystokinin mRNA. 6-Hydroxydopamine-induced destruction of mesostriatal dopaminergic neurons resulted in a complete loss of cholecystokinin and tyrosine hydroxylase mRNA expression throughout the substantia nigra pars compacta, indicating that all cholecystokinin expressing cells are 6-hydroxydopamine-sensitive. While increased enkephalin mRNA expression in the striatum ipsilateral to the lesion was detected, no change of cholecystokinin mRNA expression was observed in any forebrain on the lesioned side, suggesting that cholecystokinin expression in the forebrain is not under dopaminergic control. These results show the usefulness of the in situ hybridization approach for the precise localization of cells in rat brain which express mRNAs for cholecystokinin and tyrosine hydroxylase and for the study of the effects of neurotoxic lesions on these cells.

Cholecystokinin attenuates basal and drug-induced increases of limbic and striatal dopamine release

Subcutaneous administration to mice of the sulfated octapeptide of cholecystokinin (CCK; 0.2-1 mg/kg) lowered dopamine release and metabolism in the caudate-putamen and frontal cortex in a dose- and time-related manner. Twelve-fold higher doses of CCK were required to lower dopamine release and metabolism in the olfactory tubercle. Amphetamine-induced increases in dopamine release but not metabolism in the caudate-putamen and olfactory tubercle were attenuated in a dose-related manner by CCK. Increases in dopamine release and metabolism following haloperidol were also attenuated by CCK. These data are consistent with the potential antipsychotic action of CCK receptor agonists. CCK appears to be a suppressor of striatal, limbic and cortical dopamine release, especially when release is augmented.

Dopamine, GABA, cholecystokinin and opioids in neuroleptic-induced tardive dyskinesia

The long-term administration of neuroleptics causes tardive dyskinesia, which closely resembles levodopa-induced dyskinesias, and is brought about through complex mechanisms which are ill-defined. It is generally believed that the pathogenesis of tardive dyskinesia relates closely to the chronic blockade of dopamine receptor sites and that its pathophysiology results from a hypersensitivity of dopamine receptor sites. In the therapeutic management of neuroleptic-induced tardive dyskinesia, in addition to reserpine and lithium, diazepam, baclofen, or gamma-vinyl-gamma-aminobutyric acid have also been advocated. However, the reported beneficial effects of diazepam and GABA-mimetic agents in ameliorating the symptoms of tardive dyskinesia may occur through a mechanism which does not necessarily link transmission involving both dopamine and GABA. The presence of high concentrations of both cholecystokinin and opioids in the striatum also suggests that these peptides not only may influence dopaminergic transmission, but that they may also be relevant to the psychopathology of schizophrenia and to the therapeutic effects of neuroleptics. Indeed, the acute and chronic administration of neuroleptics alters the levels of cholecystokinin and opioids and their receptors in several brain regions including the striatum. However, neuroleptics also alter the biochemical integrity of neurotensin, neuropeptide Y, substance P and somatostatin, which may also play a role in the overall expression of the neuroleptic-induced extrapyramidal reactions.

The use of cholecystokinin in schizophrenia: a review

Cholecystokinin (CCK) is a peptide originally isolated from the gut. It has been investigated as a candidate treatment for schizophrenia on the assumption that the illness is associated with an imbalance between CCK and dopamine in the mesolimbic dopamine system. Many of the studies to assess the efficacy of CCK used open designs and are prone to observer bias and over-optimistic reporting. Most of the studies used CCK as an adjunct to standard neuroleptic treatment and are too small to be able to demonstrate extra efficacy above that of the active compound. Only three out of ten studies using CCK or placebo as an adjunct to neuroleptics reported limited efficacy. Of the 14 placebo-controlled reports only three were in drug-free patients. These were unfortunately too small, or too brief, to draw valid conclusions of efficacy. A summary of these data suggests that although 500 patients have received CCK, its efficacy in the treatment of schizophrenia has not been properly tested.

Differential effects of antipsychotic drugs on the neurotensin concentration of discrete rat brain nuclei

The present study mapped the topographic distribution of, and the effect of neuropharmacologically distinct antipsychotic drugs on, the concentration of neurotensin (NT) in the rat brain at the level of discrete nuclei or areas. The chronic administration of either haloperidol or clozapine increased the concentration of NT-like immunoreactivity (NT-LI) in the nucleus accumbens and decreased it in the medial prefrontal and cingulate cortex and in the interstitial (bed) nucleus of the stria terminalis. In contrast, the prolonged administration of haloperidol, but not clozapine, increased the concentration of NT-LI in the anterior caudate nucleus and posterior caudate-putamen. The concentration of NT-LI in the great majority of the rat brain nuclei examined was unaffected by the chronic administration of either antipsychotic drug. This pattern of pharmacological response distinguishes NT from all other neuropeptides which have been shown to be influenced by prolonged antipsychotic drug administration. These findings suggest that the functional information imparted to NT-containing cells by neuronal dopamine (DA) release, as inferred from the consequences of receptor blockade, varies remarkably between different populations of DA neurons and further implicate NT as a neuroanatomically-selective neurochemical substrate of the adaptive responses mediating the therapeutic and motoric side effects of antipsychotic drugs.

Comparison between short- and long-term haloperidol administration on somatostatin and substance P concentrations in the rat brain

Neuroleptics influence a variety of putative neurotransmitters in the basal ganglia, including somatostatin and substance P. Most studies have been performed in animals after only 3 or 4 weeks of neuroleptic administration and have seldom examined the effects of withdrawal. To understand better the effects of haloperidol on neuropeptide systems, the effects of short-term (3 weeks) and long-term (8 months) administration, as well as withdrawal from long-term administration of haloperidol, on somatostatin and substance P concentrations were examined in the rat. Short-term haloperidol significantly decreased the concentrations of somatostatin in the caudate-putamen, nucleus accumbens, and ventral tegmental area, and decreased the concentration of substance P in the substantia nigra and the nucleus accumbens. However, long-term administration only decreased the concentration of somatostatin in the nucleus accumbens. In addition, a slight reduction in the concentration of substance P in the medial prefrontal cortex was detected after long-term treatment. After withdrawal from long-term haloperidol administration the concentrations of these peptides did not differ from control values in any of the brain regions examined. These results confirm that dopamine receptor blockade can affect the somatostatin and substance P systems in the basal ganglia and indicate that during long-term administration (8 months) tolerance develops to some of the effects that are observed after shorter (3 weeks) treatment periods.

Dopaminergic agents affected neuronal transmission of cholecystokinin in the rat brain

In order to study the interaction between cholecystokinin (CCK) and dopamine (DA), we prepared an anti-CCK-8 antibody with low cross reactivity, and observed effects of administered various dopaminergic agents on CCK-immunoreactivity (CCK-IR) in discrete brain regions of rats. CCK-8 IR (boiling water extraction) and CCK-33 IR (acetic acid extraction) were also measured in the same sample. A single administration of haloperidol decreased the CCK-8 IR in the corpus striatum and that of racemic sulpiride significantly decreased the CCK-8 IR in the frontal cortex and the limbic system. In contrast, a single administration of apomorphine or methamphetamine increased the CCK-8 IR in the same regions. These findings suggest that an acute response of the CCK system to administered dopaminergic agents may be due to a change in the rate of release of CCK-8, but not to a change in its synthesis in areas in which DA neurons originating in the midbrain innervate. After chronic administration of racemic sulpiride or methaphetamine, CCK-8 IR in various brain regions exhibited a tendency close to that of control.

An analysis of cholecystokinin-induced increase in acetylcholine output from cerebral cortex of the rat

The effect of colecystokinin (CCK-8) on the release of ACh from the cerebral cortex was studied in urethane-anaesthetized rats with the cortical cup technique. The increase in output of ACh brought about by the administration of CCK-8 1.5 micrograms/kg (i.p.) was prevented by pretreatment with haloperidol (1 mg/kg i.p.) and by lesions of the nucleus basalis magnocellularis and substantia nigra but it was reduced only slightly by bilateral vagotomy. Conversely, none of the treatments abolished the decrease in output of ACh brought about by CCK-8 at a dose of 10 micrograms/kg (i.p.). Local injection of CCK-8 into the nucleus basalis had no effect. Therefore, CCK-8 appears to increase cortical cholinergic activity by indirectly stimulating the cholinergic neurones of the nucleus basalis through dopaminergic neurones.

Striatal lesions and transplants demonstrate that cholecystokinin receptors are localized on intrinsic striatal neurones: a quantitative autoradiographic study

Considerable evidence supports the existence of modulatory interactions between cholecystokinin and dopamine in the striatum. In order to explore further the nature of such interactions, the anatomical localization of CCK receptors in rat striatum was investigated autoradiographically following selective lesions. Infusion of 6-hydroxydopamine into the medial forebrain bundle had no effect on striatal CCK receptor content. In contrast, destruction of striatal cell bodies with ibotenic acid or quinolinic acid markedly reduced the number of striatal [125I]CCK-8 binding sites. CCK receptor levels were restored to normal following transplantation of neonatal striatal tissue into rats previously treated with ibotenic acid. These results suggest that CCK receptors are located primarily on intrinsic striatal neurones and not on nigrostriatal afferent fibres.

Characterization of [3H]cholecystokinin octapeptide binding to mouse brain synaptosomes: effects of neuroleptics

The presence of high concentrations of both dopamine and cholecystokinin (CCK) in the striatum and in various limbic structures suggests that the CCK may not only influence dopaminergic transmission, but it also may be relevant to the psychopathology of schizophrenia and to the therapeutic effects of neuroleptics. By using a synaptosomal fraction isolated from the mouse cerebral cortex and [propionyl-3H]CCK8-sulphate ([3H]CCK8S) as a ligand, a single binding site for [3H]CCK8 with a KD value of 1.04 nM and a Bmax value of 42.9 fmol/mg protein was identified. The competitive inhibition of [3H]CCK8S binding by related peptides produced an order of potency of CCK8-sulphated (IC50 = 5.4 nM) greater than CCK8-unsulfated (IC50 = 40 nM) and greater than CCK4 (IC50 = 125 nM). The regional distribution of [3H]CCK8S binding in the mouse brain was highest in the olfactory bulb (34.3 +/- 5.6 fmol/mg protein) greater than cerebral cortex greater than cerebellum greater than olfactory tubercle greater than striatum greater than pons-medulla greater than mid brain greater than hippocampus greater than hypothalamus (12.4 +/- 2.1 fmol/mg protein). The repeated administration of haloperidol (2.5 mg/kg/tid) increased the binding of [3H]CCK8S in cerebral cortex from 31.8 +/- 1.7 to 38.9 +/- 5.2 fmol/mg protein. The varied distribution of CCK8S receptors may signify nonuniform functions for the octapeptide in the brain.

Age-related decreases in the concentration of Met- and Leu-enkephalin and neurotensin in the basal ganglia of rats

Previous studies using radioimmunoassay procedures have failed to show age-related changes in the concentration of Met- and Leu-enkephalin or neurotensin in rat basal ganglia. In contrast, using a combined high-pressure liquid chromatography (HPLC)-radioimmunoassay (RIA) technique we now report considerable decreases in the levels of these neuropeptides in areas of basal ganglia of 22 months old-compared to 3 months-old male Wistar rats. The concentration of Met-enkephalin was greatly reduced in the striatum and nucleus accumbens, but not in substantia nigra, of old compared to young animals. There was a similarly large decrease in Leu-enkephalin content in striatum of old rats with less marked decreases occurring in both the nucleus accumbens and substantia nigra. Neurotensin levels in the striatum and substantia nigra were greatly reduced in old rats, with a less marked decrease in the nucleus accumbens.