Dopaminergic agents affected neuronal transmission of cholecystokinin in the rat brain

Changes in cholecystokinin mRNA expression in methamphetamine-induced behavioral sensitization

Neuropeptide cholecystokinin (CCK) mRNA was measured in the rat brain subchronically treated with methamphetamine (MAP). Male Wistar rats were injected daily with MAP (3 or 6 mg/kg, i.p., once a day) or saline for 14 days. Progressive reinforcement was observed in MAP-induced stereotyped behaviors. After 7 or 14 days of discontinuation, the rats were decapitated and the brains were prepared for Northern blot analysis using 32P-labeled cDNA probes. Northern blot analysis revealed that the levels of CCK mRNA in the frontal cortex and the hippocampus of 3 or 6 mg/kg MAP-treated rats were significantly decreased, compared to the saline-treated controls. These findings indicate that the alteration in CCK mRNA levels in the frontal cortex and the hippocampus of MAP-treated rats persisted for at least 2 weeks and might be involved in the expression of MAP-induced long-lasting behavioral sensitization (reverse tolerance).

Circadian rhythms of dopamine and cholecystokinin in nucleus accumbens and striatum of rats--influence on dopaminergic stimulation

The concentrations of cholecystokinin (CCK) and dopamine (DA) were determined in the nucleus accumbens (anterior, posterior) and striatum of rats every 2 h during a period of 24 h. For both substances, a circadian rhythm was found, which was best fitted by a dominant 24-h period superimposed by the second (12 h) and fourth (6 h) harmonics. The rhythms in CCK and DA were negatively correlated because of a difference in phase position by approximately 3 h. A dominant DA peak was found in the light phase coinciding with a trough in CCK and vice versa in the dark phase. Based on these data, CCK and DA were determined in rats treated with gamma-butyrolactone (GBL; inhibitor of DA release) or thyrotropin-releasing hormone (TRH; stimulator of DA release) at 0900 h or 1300 h to study a putative time-dependency in drug effects. After GBL treatment, CCK as well as DA increased by up to 200% whereas TRH administration led to a rather complex alteration, inasmuch as CCK was increased or decreased, depending on circadian time, whereas the rhythmic pattern in DA remained relatively unaffected. Comparing the drug effects obtained at 0900 h with the response seen at 1300 h revealed significant quantitative as well as qualitative differences. The results demonstrate that the neurotransmission system investigated changed its level of activity depending on time of day. No changes were obtained that convincingly may be ascribed to colocalization of DA and CCK. It is concluded that the chronobiological data indicate a close interaction of CCK and DA in various areas of the rat brain, independent of colocalization.

Pre-synaptic dopaminergic control mechanisms for CCK-8 like immunoreactivity in the rat medial frontal cortex

In order to study the control mechanism of cholecystokinin (CCK) contents of the rat brain mediated by pre-synaptic receptors in dopamine (DA) neurons, R(+) and S(-) compounds of 3-(3-hydroxyphenyl)-N-n-propylpiperidine (3-PPP), which are selective pre-synaptic dopaminergic agents, were administered in rats at low and high doses. CCK-8-like immunoreactivity (CCK-8 LI) was measured in the medial frontal cortex. In another experiment, a neurotoxin, N-methyl-D-aspartic acid (NMDA) was used to degenerate efferent CCK neurons and CCK interneurons of the medial frontal cortex, followed by an intraperitoneal administration of apomorphine hydrochloride (APO) to study the effect on CCK-8 LI via the pre-synaptic DA receptor. According to the results of these experiments, CCK-8 LI was increased in the medial frontal cortex in response to the stimulation of pre-synaptic DA receptor, suggesting a control of CCK-8 release, at least in part, by the pre-synaptic DA receptor.

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.

Sources of neostriatal cholecystokinin in the cat

The objective of this study was to determine the sources of cholecystokinin within the neostriatum of the cat. Cholecystokinin-immunoreactive cells and fibers were detected by means of the peroxidase antiperoxidase immunohistochemical technique. This method was combined with intrastriatal injections of the retrograde marker horseradish peroxidase conjugated with wheat-germ agglutinin to survey the possible afferent sources of cholecystokinin to the feline neostriatum. Intrinsic, apparently aspiny cholecystokinin-immunoreactive neurons organized in a pericapsular pattern were found within both the caudate and putamen of the cat. In addition, both thalamostriatal and mesostriatal projections containing cholecystokinin were observed. These results indicate that cholecystokinin within the neostriatum of the cat arises from both intrinsic and extrinsic sites.

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.

In vivo release of cholecystokinin-like immunoreactivity in rat frontal cortex under freely moving conditions

Release of cholecystokinin-like immunoreactivity (CCK-LI) was measured in rat medial prefrontal cortex in vivo by brain dialysis and enzyme immunoassay under freely moving condition. Perfusion of 50 mM K+ resulted in the increase of CCK-LI in the dialysate. The data on high-performance liquid chromatography (HPLC) of the dialysate showed that the increase of the CCK-LI was mainly due to the increase of CCK octapeptide sulfate itself. In the preliminary experiments, we applied this brain dialysis method for determination of CCK-LI release with drug treatment. After treatment with sulpiride (i.p.), a D2 dopamine receptor antagonist, a significant increase of CCK-LI was observed, indicating that this brain dialysis technique is applicable to detect change in the level of CCK-LI release after a certain drug treatment.

Cholecystokinin: Corelease with dopamine from nigrostriatal neurons in the cat

Halothane-anaesthetized cats were implanted with push-pull cannulae to demonstrate the in vivo release of cholecystokinin-like immunoreactivity (CCK-LI) in the substantia nigra and the ipsilateral caudate nucleus. The spontaneous and the calcium-dependent potassium-evoked release of CCK-LI were observed in both structures. In addition, the local application of tetrodotoxin (10-6 M) reduced the spontaneous release of the peptide. 6-OHDA lesions made in the substantia nigra pars compacta led to a complete destruction of nigrostriatal dopaminergic neurons. CCK-LI levels were not affected in the caudate nucleus but were reduced substantially in the substantia nigra. The activation of dopaminergic cells induced by the nigral application of alpha-methyl-para-tyrosine (10-4 M) stimulated the release of CCK-LI and dopamine in the ipsilateral caudate nucleus, whilst opposite effects were seen in the substantia nigra. Similar results were obtained when dopaminergic transmission was blocked in the caudate nucleus suggesting that the evoked release of CCK-LI by the alpha-methyl-para-tyrosine treatment originates from dopaminergic nerve terminals and not from other CCK-LI containing fibres in response to released dopamine. Dopamine (10-7 M) as well as the D1 agonist SKF 38393 (10-5 M) stimulated CCK-LI release when applied into the caudate nucleus while the D2 agonist, LY 171555 (10-6 M) slightly reduced peptide release. The local application of cholecystokinin-8 sulfate (CCK-8S) (10-8 M, for 30 min) into the substantia nigra pars compacta increased the firing rate of dopaminergic cells and stimulated the release of newly synthesized 3H-dopamine from dendrites and nerve terminals. These results suggest, but do not definitively prove, that, in the cat, CCK-LI and dopamine are coreleased from nigrostriatal mixed dopaminergic/CCK-LI neurons and that CCK-LI released from dendrites is, like dopamine, involved in the regulation of the activity of these cells.

Apomorphine affects cholecystokinin content via preferentially D1 or D2 dopamine receptor according to the regions of the rat brain

Cholecystokinin octapeptide-like immunoreactivity (CCK-8IR) was measured in several regions of the rat brain after the intraperitoneal administration of apomorphine, SKF-38393 (D1 agonist), LY-171555 (D2 agonist). In the medial prefrontal cortex and striatum, apomorphine and SKF 3839 decreased CCK-8IR. In the anterior and posterior nucleus accumbens, on the other hand, the inhibitory effect of apomorphine was mimicked by LY-171555. These results suggest that apomorphine affects CCK-8IR via either the D1 dopamine (DA)-receptor or D2 DA-receptor according to the brain region.

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.

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.

Regional effects of apomorphine on rat brain cholecystokinin-8 like immunoreactivity following electrolytic lesions of the ventral tegmental area

After bilateral electrocoagulation of the ventral tegmental area (VTA) of rats, apomorphine (APO) was administered intraperitoneally to study the effect on the cholecystokinin-8 like immunoreactivity (CCK-8 IR) in the medial prefrontal cortex, the anterior and posterior part of the nucleus accumbens and the corpus striatum. In the medial prefrontal cortex and the posterior part of the nucleus accumbens, CCK-8 IR was markedly decreased by lesioning of the VTA. Then recovery of CCK-8 IR was noted in the APO treated rats following electrolytic lesioning of the VTA. This recovery corresponds to the response of CCK neurons not originating in the VTA or CCK interneurons to APO via DA receptors. In the anterior part of the nucleus accumbens and the corpus striatum, no significant decrease in CCK-8 IR was noted even following lesioning of the VTA. APO administration following the lesioning, however, resulted in a marked increase in CCK-8 IR in the anterior part of the nucleus accumbens and the corpus striatum. According to this result, in these sites, very few CCK neurons originating in the VTA exist and CCK neurons originating in sites other than the VTA or CCK interneurons react on APO via DA receptors.

The chronic administration of dopamine antagonists and methamphetamine changed the [3H]-cholecystokinin-8 binding sites in the rat frontal cortex

The specific cholecystokinin (CCK) binding in the slide-mounted tissue sections of the rat frontal cortex was measured with [3H]-CCK-8. The binding was saturable, reversible, high in affinity, and inhibited by caerulein. The chronic administration of dopamine (DA) antagonists and methamphetamine (MAP) showed a tendency to increase the [3H]-CCK-8 binding sites (Bmax) in the frontal cortex. Long-term treatments with DA antagonists led to the depletion of CCK-8 and may have caused an observed proliferation of CCK-8 receptors in the frontal cortex.