Behavioural evidence for cholecystokinin-dopamine D1 receptor interactions in the rat

The role of cholecystokinin in the induction of aggressive behavior: a focus on the available experimental data (review)

Cholecystokinin (CCK) is a neuropeptide that is (among others) reportedly involved in the pathophysiology of psychiatric disorders. The excitatory role of CCK in negative affective emotions as well as in aversive reactions, antisocial behaviors and memories, has been indicated by numerous electrophysiological, neurochemical and behavioral methodologies on both animal models for anxiety and human studies. The current review article summarizes the existing experimental evidence with regards to the role of CCK in the induction of aggressive behavior, and: (a) synopsizes the anatomical circuits through which it could potentially mediate all types of aggressive behavior, as well as (b) highlights the potential use of these experimental evidence in the current research quest for the clinical treatment of mood and anxiety disorders.

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

Background

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

Results

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

Conclusions

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

Repeated administration of methamphetamine blocked cholecystokinin-octapeptide injection-induced c-fos mRNA expression without change in capsaicin-induced junD mRNA expression in rat cerebellum

In the cerebellum, there are numerous cholecystokinin (CCK-8)-containing fibers. Since systemic CCK-8 injection-induced anxiety (psychological stress) activates the locus coeruleus cells that send mossy fiber inputs to the cerebellum, we examined whether systemic CCK-8 injections activate the rat and mouse cerebellum. First, injections of CCK-8 were found to induce c-fos mRNA expression in a vague patchy pattern that is different from single methamphetamine-induced Zebrin band-like c-fos mRNA expression, suggesting that the CCK-8 activating mossy fibers induce gene expression differently from the dopamine-containing mossy fibers in the ventral tegmental area. Second, since CCK-8 facilitates neural activity of dopamine in the midbrain, we examined whether repeated methamphetamine administration that induced behavioral sensitization had similar effects on the cerebellar CCK system. Repeated administration of methamphetamine suppressed the CCK-8-induced c-fos mRNA expression in the rat cerebellum. Third, capsaicin injections (physical stress) into a hind limb of the rat increased junD mRNA expression with no effect on c-fos mRNA expression, and repeated methamphetamine injections had no effect on the capsaicin-induced expression of junD mRNA. Fourth, either single injection of methamphetamine or CCK-8 to mice increased c-fos mRNA expression in the locus coeruleus, and so noradrenalin, but not dopamine, might interact with CCK-8-activating system. However, we considered the possibility unlikely. Thus, we conclude that repeated methamphetamine administration though dopamine selectively inhibits the c-fos mRNA expression after CCK-8 injection in the cerebellum.

The effect of a cholecystokinin agonist on masseter muscle activity in the cat

The CCK(B) agonist, pentagastrin, has been shown to induce anxiety in human subjects. Similarly, in the cat model, pentagastrin facilitates the expression of hypothalamically activated emotional behavior. Because hypothalamically mediated emotional behavior is also accompanied by increased EMG activity in the jaw muscles, these experiments were designed to examine the combined effects of administration of pentagastrin with activation of hypothalamically mediated emotional behavior upon jaw muscle EMG activity. Electrodes were carefully lowered through previously placed guide tubes overlying the hypothalamus until a behavioral site was identified. Following the establishment of a stable threshold current for eliciting an emotional behavioral response, the skin overlying the ipsilateral masseter muscle was shaved and cleaned with alcohol, and surface electrodes were attached. The EMG was recorded, amplified, digitized, and stored in a microcomputer for analysis. Mean power frequencies (MPF) and latencies for behavior were calculated for baseline prior to infusion of all drugs. Following this, the effects of intravenous administration of pentagastrin and the CCK(B) antagonist LY288513 on the MPF were determined. The infusion of the CCK(B) agonist, pentagastrin (0.77, 1.92, and 3.84 microg/kg), decreased MPF in a time-related manner. The effects of pentagastrin 1.92 microg/kg were blocked by the CCK(B) antagonist, LY288513 (6.54 microg/kg). In addition, the infusion of LY288513 alone increased MPF. These results are surprising in that pentagastrin's anxiogenic properties would appear to make it likely to facilitate motor activity, not suppress it.

The effects of CCK-4 on dopamine D1 agonist-induced grooming are blocked by a CCK(A) receptor antagonist: evidence for a novel CCK receptor subtype?

The neuropeptide cholecystokinin (CCK) has been shown to interact with dopamine in various ways, including attenuation of dopamine D1 receptor-mediated vacuous chewing and grooming. While we have demonstrated a clear role for the CCK(A) receptor in the attenuation of dopamine D1 agonist-induced vacuous chewing, studies of grooming yielded anomalous results. We examined the effects of selective CCK receptor antagonists on the attenuation of SKF 38393-induced grooming by the CCKB agonist CCK-4. Administration of SKF 38393 (5 mg/kg s.c.) to male Sprague-Dawley rats resulted in a significant increase in grooming which was reduced to control levels by CCK-4 (20 mg/kg i.p.). Pretreatment with either the CCKA receptor antagonist devazepide or the CCK(B) receptor antagonist L-365,260 significantly attenuated this effect over a range of doses (20, 100, 500 microg/kg i.p.). The suppression of dopamine D1 agonist-induced grooming by CCK-4 does not appear to reflect a non-specific effect of anxiogenesis, as it was unaffected by the anxiolytic diazepam. The CCK receptor antagonists alone were without behavioural effect. Taken together with previous studies in models of anxiety and analgesia, our findings lend further support to the hypothesis that CCK-4 may act at a novel receptor subtype.

The neurotensin antagonist SR 48692 fails to modify the behavioural responses to a dopamine D1 receptor agonist in the rat

The effects of the neurotensin antagonist SR 48692 on the behavioural responses to the dopamine D1 receptor agonist SKF 38393 were investigated in the rat. SKF 38393 (5 mg/kg s.c.) elicited vacuous chewing movements (VCMs) and grooming, which were unaffected by SR 48692 (50 micrograms/kg i.p.). The dopamine D2 receptor antagonist raclopride (0.5 mg/kg s.c.) elicited a small increase in VCMs in animals treated with SR 48692 and attenuated grooming induced by SKF 38393. These effects were not otherwise modified by SR 48692. We conclude that VCMs induced by acute administration of a dopamine D1 receptor agonist are unlikely to be dependent upon enhanced release of neurotensin in the striatum or its projections. This is contrast to the vacuous chewing response which emerges following chronic administration of neuroleptics, which is attenuated by neurotensin receptor antagonist. Thus, inasmuch as chronic neuroleptic-induced VCMs in the rat may be analogous to tardive dyskinesia in humans, the responses induced by acute administration of a D1 agonist to the rat cannot be used as a model of this disorder. Furthermore, the behavioural effects of chronic neuroleptic administration reflect more than a simple shift in the balance of D1 versus D2 receptor stimulation.