Long-term diazepam treatment produces changes in cholecystokinin receptor binding in rat brain

Antidepressant- and Anxiolytic-Like Effect of the Froriepia subpinnata Extract in the Rat: Neurochemical Correlates

BACKGROUND

The study aims to explore the potential antianxiety effect of Froriepia subpinnata, a native plant in northern Iran, and it is considered an antiflatulent, appetizing, antiseptic, antispasmodic, and diuretic. Despite its widespread use in diets and its reputation for calming effects, no prior research has specifically investigated its antianxiety properties.

METHODS

Rats were subjected to a variety of stressors for 24 days. Rats were treated with the F. subpinnata extract (100, 200, and 400 mg/kg, orally) for 14 days starting from the 10th day of stress. Then behavioral tests (elevated plus-maze, open field, sucrose preference, Morris water maze, passive avoidance) were examined. Real-time PCR was used to investigate changes in the expression of candidate genes of stress response and memory. Oxidative stress markers and corticosterone levels in serum were also measured.

RESULTS

Chronic stress reduced performance in a variety of tests of anxiety and memory, and treatment with the F. subpinnata extract dose-dependently improved the behavioral deficits caused by chronic stress. At the dose of 200 mg/kg, the F. subpinnata extract mitigated the effect of stress on the expression of several genes, such as those encoding dopamine D1 and D2 receptors, glutamate NMDA, and AMPA receptor subunits (Grin1 and Gria1, respectively), glucocorticoid and mineralocorticoid receptors, cholecystokinin (CCK) and CCKB receptor, neuropeptide Y, and the GABAA receptor alpha2 subunit. Also, the expression of two genes, TrkB and BDNF, was significantly affected by the extract, demonstrating meaningful decreasing changes. Furthermore, treatment with the extract led to a decrease in oxidative stress and an elevation in cortisol levels in stressed animals.

CONCLUSION

In this study, we provide the first evidence of the antistress and antianxiety effects of F. subpinnata extract, along with its potential procognitive impact on memory.

Cholecystokinin neurotransmission in the central nervous system: Insights into its role in health and disease

Cholecystokinin (CCK) plays a key role in various brain functions, including both health and disease states. Despite the extensive research conducted on CCK, there remain several important questions regarding its specific role in the brain. As a result, the existing body of literature on the subject is complex and sometimes conflicting. The primary objective of this review article is to provide a comprehensive overview of recent advancements in understanding the central nervous system role of CCK, with a specific emphasis on elucidating CCK's mechanisms for neuroplasticity, exploring its interactions with other neurotransmitters, and discussing its significant involvement in neurological disorders. Studies demonstrate that CCK mediates both inhibitory long-term potentiation (iLTP) and excitatory long-term potentiation (eLTP) in the brain. Activation of the GPR173 receptor could facilitate iLTP, while the Cholecystokinin B receptor (CCKBR) facilitates eLTP. CCK receptors' expression on different neurons regulates activity, neurotransmitter release, and plasticity, emphasizing CCK's role in modulating brain function. Furthermore, CCK plays a pivotal role in modulating emotional states, Alzheimer's disease, addiction, schizophrenia, and epileptic conditions. Targeting CCK cell types and circuits holds promise as a therapeutic strategy for alleviating these brain disorders.

Effects of Traumatic Stress Induced in the Juvenile Period on the Expression of Gamma-Aminobutyric Acid Receptor Type A Subunits in Adult Rat Brain

Studies have found that early traumatic experience significantly increases the risk of posttraumatic stress disorder (PTSD). Gamma-aminobutyric acid (GABA) deficits were proposed to be implicated in development of PTSD, but the alterations of GABA receptor A (GABA_AR) subunits induced by early traumatic stress have not been fully elucidated. Furthermore, previous studies suggested that exercise could be more effective than medications in reducing severity of anxiety and depression but the mechanism is unclear. This study used inescapable foot-shock to induce PTSD in juvenile rats and examined their emotional changes using open-field test and elevated plus maze, memory changes using Morris water maze, and the expression of GABA_AR subunits (γ2, α2, and α5) in subregions of the brain in the adulthood using western blotting and immunohistochemistry. We aimed to observe the role of GABA_AR subunits changes induced by juvenile trauma in the pathogenesis of subsequent PTSD in adulthood. In addition, we investigated the protective effects of exercise for 6 weeks and benzodiazepine (clonazepam) for 2 weeks. This study found that juvenile traumatic stress induced chronic anxiety and spatial memory loss and reduced expression of GABA_AR subunits in the adult rat brains. Furthermore, exercise led to significant improvement as compared to short-term BZ treatment.

Neuronal network of panic disorder: the role of the neuropeptide cholecystokinin

Panic disorder (PD) is characterized by panic attacks, anticipatory anxiety and avoidance behavior. Its pathogenesis is complex and includes both neurobiological and psychological factors. With regard to neurobiological underpinnings, anxiety in humans seems to be mediated through a neuronal network, which involves several distinct brain regions, neuronal circuits and projections as well as neurotransmitters. A large body of evidence suggests that the neuropeptide cholecystokinin (CCK) might be an important modulator of this neuronal network. Key regions of the fear network, such as amygdala, hypothalamus, peraqueductal grey, or cortical regions seem to be connected by CCKergic pathways. CCK interacts with several anxiety-relevant neurotransmitters such as the serotonergic, GABA-ergic and noradrenergic system as well as with endocannabinoids, NPY and NPS. In humans, administration of CCK-4 reliably provokes panic attacks, which can be blocked by antipanic medication. Also, there is some support for a role of the CCK system in the genetic pathomechanism of PD with particularly strong evidence for the CCK gene itself and the CCK-2R (CCKBR) gene. Thus, it is hypothesized that genetic variants in the CCK system might contribute to the biological basis for the postulated CCK dysfunction in the fear network underlying PD. Taken together, a large body of evidence suggests a possible role for the neuropeptide CCK in PD with regard to neuroanatomical circuits, neurotransmitters and genetic factors. This review article proposes an extended hypothetical model for human PD, which integrates preclinical and clinical findings on CCK in addition to existing theories of the pathogenesis of PD.

Neuroendocrine pathways in benzodiazepine dependence: new targets for research and therapy

Benzodiazepines are known to modulate the activity of the hypothalamo-pituitary-adrenocortical (HPA) axis by antagonizing the effects of corticotropin-releasing factor (CRH). Besides regulating the HPA axis CRH evolves properties of a neurotransmitter in the limbic system that is closely involved in the delivery of the emotional consequences of the stress response. At a superordinated level Neuropeptide Y (NPY) and Cholecystokinin (CCK) affect the release of CRH and modulate thereby the intensity of the physiological stress response. Benzodiazepine treatment interferes not only with the release of CRH but also with the release of NPY and CCK. Alterations in the intracortical ratio of NPY, CCK and CRH are correlated with behavioural changes like increased respectively decreased anxiety and subsequent alterations in the activity of the HPA axis. Recent research offers the possibility that the alterations of plasma levels of these neuropeptides are not only a secondary phenomenon due to drug intake, but that low levels of those neuropeptides that modulate anxiety and fear can possibly explain addiction to substances that counterbalance these deficits. Depending on the available results possible implications of NPY and CCK on benzodiazepine addiction and withdrawal symptoms are reviewed, thereby providing topics for further research.

CCK and NPY as anti-anxiety treatment targets: promises, pitfalls, and strategies

Short CCK peptides elicit panic attacks in humans and anxiogenic-like effects in some animal models, but CCK receptor antagonists have not been found clinically effective. Yet CCK overactivity appears to be involved in submissive behaviour, and CCKB receptor expression and binding are increased in suicide victims and animal models of anxiety. Preliminary data suggest that involvement of CCK and its receptor subtypes in anxiety can be better described when focusing on distinct endophenotypes, and considering environmental contingencies and confounds originating from interactions with dopamin-, opioid- and glutamatergic neurotransmission. In contrast, NPY is an anti-anxiety peptide with robust effects in various animal models when administrated into several brain regions. Studies with non-peptide antagonists selective for receptor subtypes have revealed the role of endogenous NPY in active coping. At least Y1, Y2 and Y5 receptors in various brain regions are involved, with the strongest evidence for contribution of Y1.

The neurochemical effects of anxiolytic drugs are dependent on rearing conditions in Fawn-Hooded rats

There is a vast literature examining the neurochemical effects of anxiolytics throughout the rat brain; however, although the behavioural actions of anxiolytic drugs are routinely assessed in animal models of anxiety, the majority of neurochemical studies have been performed in rats with relatively 'normal' behavioural phenotypes. Since there is significant evidence that an anxious phenotype is associated with numerous neurochemical alterations, it is feasible that the central effects of anxiolytics may vary depending on the underlying behavioural state (and corresponding neuropathology) of the experimental animal. For this reason, the aim of the present study was to examine the effect of chronic anxiolytic drug administration on the central CCK and dopamine systems in anxious (isolated from weaning) and nonanxious (group-housed) Fawn-Hooded (FH) rats. It is important to note that these studies were performed in rats with continued access to ethanol, which may affect the responses to anxiolytic treatment. Chronic anxiolytic treatment with the selective CCK-B (CCK(2)) receptor antagonist, Ci-988 (0.3 mg/kg/day ip) or diazepam (2 mg/kg/day ip), induced numerous effects throughout the central nervous system (CNS), with Ci-988 inducing significant changes in the density of dopamine D(2) receptors, and diazepam producing marked changes in both dopamine D(2) and CCK-B receptor binding density as well as preproCCK mRNA expression. Interestingly, the neurochemical effects of these anxiolytic drugs varied significantly depending on the rearing conditions of the rats, demonstrating the importance of using adequate animal models when correlating the behavioural and central effects of drugs acting throughout the CNS.

Effects of alprazolam on cholecystokinin-tetrapeptide-induced panic and hypothalamic-pituitary-adrenal-axis activity: a placebo-controlled study

Cholecystokinin-tetrapeptide (CCK-4) induces panic attacks both in patients with panic disorder (PD) and healthy volunteers. It has been shown that panic elicited by CCK-4 is improved after treatment with antidepressants. Moreover, a reduction of CCK-4-induced panic has also been demonstrated after treatment with lorazepam in single subjects and after selective GABAergic treatment with vigabatrin. Although benzodiazepines are widely used as anxiolytics, no controlled study on the effects of benzodiazepines on CCK-4-induced panic symptoms is available so far. Therefore, we investigated the effects of alprazolam and placebo on CCK-4-induced panic symptoms in a double-blind, placebo-controlled study. A total of 30 healthy subjects were challenged with 50 microg CCK-4. Out of these 30 subjects, 26 showed a marked panic response to CCK-4. Subjects were rechallenged after a 7-day interval and treated with 1 mg alprazolam or placebo 1 h prior to the second CCK-4 challenge. Panic was assessed using the acute panic inventory (API) and a DSM-IV-derived panic symptom scale (PSS). Moreover, the number of reported symptoms and self-rated anxiety and arousal were recorded. We found a significant reduction of the API and PSS scores and of the number of reported symptoms compared to placebo. Moreover, compared to placebo the CCK-4-induced ACTH and cortisol release were significantly attenuated during the CCK-4 challenge after alprazolam treatment. However, also placebo treatment reduced CCK-4-induced anxiety and HPA-axis activation to a certain extent. In conclusion, our data show that alprazolam reduces CCK-4-induced panic, which supports the hypothesis of a possible interaction between the GABA and the CCK system.

Behavioral analysis indicates benzodiazepine-tolerance mediated by the benzodiazepine binding-site at the GABA(A)-receptor

1. GABA(A)-receptor induced changes in locomotion and anxiety-like behaviors were studied in rats using an open-field and an elevated plus-maze. Acute and chronic doses of the benzodiazepine diazepam without and in combination with the GABA uptake inhibitor SKF-89976A were investigated. 2. Fifty-six male rats of the strain PVG/OlaHsd (PVG; 180-200 g body wt) were used to assess the influence of the benzodiazepine binding-site to the development of tolerance. Rats were divided into six groups: The first receiving saline (0.9%), the second and third diazepam (10.0 mg/kg) daily for 23 days with or without an acute challenge of 2.0 mg/kg diazepam. The fourth group received diazepam (10.0 mg/kg) daily and acutely SKF-89976A (15.0 mg/kg) plus diazepam and the fifth and sixth group received acute treatment with diazepam (2.0 mg/kg) or SKF-89976A (15.0 mg/kg). 3. Under chronic treatment with diazepam the animals became tolerant to acute doses of diazepam in activity and anxiety-related behaviors. Acute treatment with SKF-89976A increased exploration. Parameters expressing anxiolytic-like behaviors were increased, too, but not all of them significantly. In diazepam tolerant animals SKF-89976A produced anxiolytic-like behaviors 4. We conclude that the BZ- and not the GABA-binding site at the GABA(A)-receptor is involved in the development of BZ-tolerance.

The inability of CCK to block (or CCK antagonists to substitute for) the stimulus effects of chlordiazepoxide

To further examine the relationship between cholecystokinin (CCK) and GABA, the present study assessed the ability of the CCK-A antagonist devazepide and the CCK-B antagonist L-365,260 to substitute for the stimulus effects of chlordiazepoxide (CDP), as well as the ability of CCK-8s to block these effects, in female Long-Evans rats within the conditioned taste aversion baseline of drug discrimination learning. Both devazepide and L-365,260 failed to substitute for the discriminative stimulus properties of CDP, and CCK-8s failed to block its stimulus effects. The benzodiazepine diazepam did substitute for, and the benzodiazepine antagonist flumazenil did block, the stimulus effects of CDP. This suggests that the lack of substitution for, or antagonism of, CDP by the CCK antagonists and CCK-8s, respectively, was not due to the inability of the present design to assess such effects. Possible bases for the current findings, e.g., necessity of an anxiogenic baseline, drug and receptor specificity, as well as the dose-response nature of the interaction, were discussed. Given that a relationship between CCK and GABA has been reported in other designs, the present results suggest that such a relationship may be preparation specific.

Diazepam and buspirone alter neuropeptide Y-like immunoreactivity in rat brain

Neuropeptide Y-like immunoreactivity (NPY-LI) was investigated in naIve Sprague-Dawley rats subjected to acute, subchronic (7 days) or chronic (21 days) intraperitoneal treatment with diazepam (1 or 3 mg/kg once daily) or buspirone (1.5 or 5 mg/kg twice daily). NPY-LI was determined by radioimmunoassay in the amygdala, nucleus accumbens, hypothalamus and frontal cortex 24 h after the last dose of the drugs. Amygdala NPY-LI decreased after acute diazepam (3 mg/kg) or buspirone (1.5 mg/kg) and increased after subchronic treatment with both doses of diazepam and after chronic buspirone (1.5 mg/kg) treatment. Both diazepam and buspirone given in subchronic and chronic doses decreased NPY-LI levels in the nucleus accumbens. Hypothalamic NPY-LI changed only after chronic treatment: it decreased after diazepam and increased after buspirone (5 mg/kg). NPY-LI content in the frontal cortex decreased after subchronic diazepam (3 mg/kg) treatment and slightly increased after buspirone. The study has shown that both diazepam and buspirone affect NPY-LI levels in rats. These results suggest that the NPY system in the amygdala and nucleus accumbens is implicated in the anxiolytic effects of the drugs studied.

Tolerance to acute anxiolysis but no withdrawal anxiogenesis in mice treated chronically with 5-HT1A receptor antagonist, WAY 100635

Anxiolytic-like activity in the mouse elevated plus-maze has recently been demonstrated for a range of compounds varying in degree of selectivity as 5-HT1A receptor antagonists. As tolerance and dependence liability are among the major clinical disadvantages of benzodiazepine therapy, the present study examined the effects of acute drug challenge on the plus-maze profiles of mice following daily treatment for 20 days with saline, chlordiazepoxide (CDP; 10.0 mg/kg) or the selective 5-HT1A receptor antagonist, WAY 100635 (0.1-1.0 mg/kg). To assess the development of physical dependence (withdrawal anxiogenesis), the study incorporated independent groups of animals tested on the maze 24 h after the final dose. Challenge with CDP or WAY 100635 produced behavioural changes indicative of anxiety reduction in mice that had received daily handling/saline for 20 days, thereby demonstrating that the chronic injection regimen per se had not compromised the acute efficacy of either agent. The absence of a similar response to acute drug challenge in mice treated chronically with CDP or WAY 100635 suggested the development of tolerance to the acute anxiolytic effects of both compounds under present test conditions. Despite these observations, however, no signs of enhanced anxiety were evident 24 h following discontinuation of chronic treatment with either compound. In a further experiment, the absence of withdrawal anxiogenesis at 24 h was replicated and extended to discontinuation periods of 36 and 48 h for both drugs. Although present results show that tolerance develops to the acute anxiolytic effects of CDP and WAY 100635 in the murine plus-maze, they also suggest that enhanced anxiety is not an inevitable consequence of abrupt cessation of chronic treatment with either compound.

Neurobiology of panic disorder

Various provocative agents, including sodium lactate, carbon dioxide (CO2), caffeine, yohimbine, serotoninergic agents, and cholecystokinin (CCK), have been utilized as panicogenics in studies on healthy volunteers as well as in panic disorder patients. An overview of the utilization of these agents to study the neurobiology of panic disorder is presented. The possible roles of several neurotransmitters and neuromodulators in the etiology of panic disorder and in the actions of drugs used in its treatment are also discussed.

Effect of central and peripheral administrations of cholecystokinin-tetrapeptide on panic-like reactions induced by stimulation of the dorsal periaqueductal grey area in the rat

Administration of cholecystokinin-tetrapeptide (CCK-4) triggers panic attacks in humans, but it is not known whether CCK-4 acts in the brain to produce this effect. Panic-like reactions (flight and tachycardia) induced in rats by injecting D, L-homocysteic acid (DLH) into the dorsal periaqueductal grey area (DPAG), were used as an animal model to investigate this issue. CCK-4 (2 micrograms) infused into the DPAG did not change these panic-like reactions. The DLH-induced tachycardia was prolonged by intracerebroventricular injection of CCK-4 (40 or 4 micrograms); however, the DLH-induced flight behavior was not changed by similar central injections of CCK-4 (40, 4, or 0.4 micrograms). Peripheral injection of t-butoxycarbonyl (BOC)-CCK-4 (40 micrograms) potentiated the flight behavior, but did not alter the tachycardia response. It was concluded that CCK tetrapeptide potentiates panic-like behaviors by acting on a peripheral target or on a circumventricular area of the brain. In contrast, increased brain CCK-4 prolongs tachycardia by acting in the brain at a level distinct from the DPAG.

Anxiogenic-like effect of the neuropeptide Y Y1 receptor antagonist BIBP3226: antagonism with diazepam

The effect of the novel non-peptide neuropeptide Y Y1 receptor antagonist BIBP3226, N2-(diphenylacetyl)-N-[(4-hydroxy-phenyl)-methyl]-D-arginine amide, on exploratory behaviour of rats in the elevated plus-maze was studied. BIBP3226 (0.5 and 5 micrograms, i.c.v.) induced an anxiogenic-like effect at the higher dose tested. This effect was antagonised by diazepam (0.5 mg/kg). The anxiogenic-like effect of BIBP3226 was not related to a decrease in general locomotor activity. These findings support the hypothesis that neuropeptide Y Y1 receptor subtype is involved in anxiety regulation.

Cholecystokinin in anxiety

Cholecystokinin (CCK) plays an important role in both the alimentary tract and the central nervous system (CNS). At present it seems to be the most abundant neuropeptide in the CNS. This paper reviews the CCK neuronal system and its interactions with gamma-aminobutyric acid (GABA) and serotonin (5-hydroxytryptamine; 5-HT). In addition, its putative role in anxiety will be discussed on the basis of animal data and studies in healthy volunteers and panic disorder patients. According to these investigations, the CCK4 challenge test fulfills most criteria for an ideal panicogenic agent and evidence has been found that CCKB receptor antagonists might possess anxiolytic properties in man.

L-364,718 and L-365,260, two CCK antagonists, have no affinity for central benzodiazepine binding sites in chickens

It has recently been demonstrated that L-365,260, a CCK-B antagonist in mammals, causes an increase in food intake in chickens. In contrast, L-364, 718, a CCK-A antagonist in mammals, shows this effect only at very high dose levels. It has been shown that L-365,260 has very low affinity for chicken CCK receptors. Thus, the mechanism of action of L-365,260 remains unknown. As L-365,260 is a benzodiazepine derivative, one may hypothesize that it would be acting on benzodiazepine binding sites. The aims of this work were to establish the existence of benzodiazepine binding sites in the chicken brain, and to check the possibility that L-365,260 was acting on these receptors, determining the affinity of L-364,718 and L-365,260 for them. We have found specific binding for tritiated flunitrazepam (a benzodiazepine agonist) ([3H]-flunitrazepam) in chicken brain membranes. A single binding site was detected with a Kd of 3.58 +/- 0.97 nM and a Bmax of 451.6 +/- 23.3 fmol/mg protein L-365,260 and L-364,718 exhibited very low affinity for these binding sites (Ki = 1.17 x 10(-6) +/- 0.16 x 10(-6) M and Ki > 10(-5) M, respectively). Thus, these results demonstrate that the increase in food intake caused by L-365,260 in the chicken is not due to a direct action on benzodiazepine receptors. Other possible explanations for its effect are discussed.

The behavioural and neuronal effects of the chronic administration of benzodiazepine anxiolytic and hypnotic drugs

Benzodiazepine anxiolytic and hypnotic drugs are some of the most widely prescribed drugs in the Western world. Despite this fact, the mechanisms that underlie the development of tolerance to, and dependence upon, benzodiazepines are poorly understood. The aim of this review is to summarize and critically evaluate the experimental evidence relating to the chronic behavioural and neuronal effects of benzodiazepines. Behavioural studies in animals generally indicate that tolerance gradually develops to the muscle relaxant, ataxic, locomotor and anticonvulsant effects of benzodiazepines. The evidence relating to the development of tolerance to the anxiolytic effects of benzodiazepines is less clear. The literature on the possible mechanisms of benzodiazepine tolerance and dependence is large, highly complex and difficult to interpret. The effect of chronic benzodiazepine treatment varies enormously as a function of the benzodiazepine used and the treatment schedule employed. Many studies have demonstrated a down-regulation of benzodiazepine binding sites, although affinity is usually unchanged. The evidence relating to the number and affinity of GABAA binding sites is unclear. Some studies suggest that chronic benzodiazepine administration results in a reduction in the number of Cl- channels associated with the GABAA receptor complex, although it is not clear that the efficacy of the GABA binding site in operating the Cl- channel necessarily changes. There is, however, substantial evidence to support the hypothesis that chronic benzodiazepine treatment results in a reduction in the coupling between the GABAA and benzodiazepine binding sites (the "functional uncoupling hypothesis"). Although some electrophysiological studies suggest that chronic benzodiazepine treatment results in a subsensitivity to GABA, this effect seems to be highly area-specific.

Tolerance to the ataxic effects of diazepam in guinea pig is not associated with a reduced sensitivity of GABAA receptors in the vestibular nucleus

Some studies have suggested that drug tolerance observed following repeated benzodiazepine exposure may be associated with the development of a subsensitivity to gamma-aminobutyric acid (GABA) in dorsal raphe and hippocampal neurons. In other areas such as the substantia nigra such subsensitivity has not been found. The aim of the present study was to determine whether tolerance develops to the ataxic effects of diazepam on the righting reflex following low (i.e. 2 mg/kg i.p.), multiple daily doses and, if so, whether it is correlated with the development of a subsensitivity of medial vestibular nucleus neurons to the selective GABAA receptor agonist, isoguvacine. Guinea pigs which received i.p. vehicle injections three times daily for 5 days, or single daily doses of 2 or 6 mg/kg diazepam, showed increased righting reflex latencies in response to a 6 mg/kg diazepam challenge dose. However, guinea pigs which received 2 mg/kg diazepam i.p., three times daily for 5 days, exhibited minimal or no ataxia when given the same diazepam challenge dose, indicating the development of tolerance. Brain stem slices including the medial vestibular nucleus were removed from guinea pigs which had received the same diazepam and vehicle three times daily injection schedules, and recordings were made from single neurons during superfusion of isoguvacine. Although medial vestibular nucleus neurons from animals which received chronic diazepam administration showed smaller decreases in firing rate in response to 10(-8) M isoguvacine, the difference was not statistically significant compared to neurons from animals which received vehicle treatment or acute diazepam treatment. Resting activity was also similar between the diazepam and vehicle groups, in contrast to a previous study which had shown hyperexcitability in medial vestibular nucleus cells from animals which had received single daily injections for up to 60 days. These results suggest that, in contrast to studies which have employed single daily doses, tolerance to the ataxic effects of diazepam on the righting reflex occurs rapidly with divided daily doses. However, this tolerance is not correlated with significant changes in the sensitivity of GABAA receptors on medial vestibular nucleus neurons.

The effects of long-term, low-dose diazepam treatment on the guinea pig righting reflex and medial vestibular nucleus neuronal activity

Guinea pigs received a 2 mg/kg IP injection of diazepam, or an equivalent volume of vehicle, daily for 28-60 days. To determine whether tolerance developed to the ataxic effects of diazepam on the righting reflex, daily righting reflex latency (RRL) measurements were made before and 20, 30, and 40 min following the diazepam or vehicle injection for 28 days. Analyses of the RRLs for individual animals indicated that a significant decrease in RRL over time (indicating tolerance) occurred in only one out of nine animals receiving diazepam and in none of the vehicle animals. Medial vestibular nucleus (MVN) neurons in brain stem slices from animals receiving chronic diazepam treatment had a significantly higher average firing rate than those from vehicle controls. These results suggest that: a) long-term treatment with single 2 mg/kg daily IP injections of diazepam does not result in tolerance to diazepam's ataxic effects on the righting reflex in the majority of animals; b) this form of diazepam treatment may, nonetheless, induce a hyperactivity of brain stem MVN neurons that may be consistent with the occurrence of a withdrawal syndrome.

Effects of the CCKB antagonist L-365, 260 on benzodiazepine withdrawal-induced hypophagia in rats

The effect of the selective CCKB antagonist L-365, 260 on chlordiazepoxide (CDP) withdrawal-induced hypophagia was assessed in two related studies in rats pretreated for 21 days with CDP at doses escalated from 10 to 30 mg/kg per day (b.i.d). L-365, 260 was studied at doses from 0.001 to 10 mg/kg (b.i.d). There was no evidence that L-365, 260 at any dose alleviated CDP withdrawal-induced hypophagia. These data contrast with reports that CCKB antagonists alleviate behavioural benzodiazepine (BZ) withdrawal symptoms considered to be indicative of "anxiogenesis". Presumably, such positive effects of CCKB antagonists are due to "functional antagonism", with enhanced anxiety during BZ withdrawal being attenuated by anxiolytic actions of CCKB antagonists. Collectively, studies with CCKB antagonists and other agents involving a number of different BZ withdrawal signs suggest that BZ withdrawal is a heterogeneous syndrome, with various different underlying mechanisms. CCKB antagonists appear to alleviate only a subset of possible BZ withdrawal signs.

On the significance of cholecystokinin receptors in panic disorder

Interest in the biological aspects of panic disorder has been focussed mainly on the noradrenergic and serotonergic systems in the brain. Recently evidence has been found that Cholecystokinin (CCK) receptors in the Central Nervous System (CNS) may be involved in panic disorders. This hypothesis is based on the results of animal electrophysiological studies, animal models of anxiety and on challenge test using CCK fragments in humans. In this review, the studies evaluating the putative involvement of CCK, and especially CCK-B receptors, in panic disorder will be discussed.

Gastrointestinal effects of diazepam-withdrawal are linked to activation of central cholecystokinin-ergic pathways in rats

The influence of flumazenil-precipitated diazepam withdrawal on intestinal myoelectric activity and colonic transit was evaluated, in diazepam-dependent rats. Administered intraperitoneally, flumazenil (15 mg kg-1) induced a strong stimulation of the duodenal spiking activity lasting 197 +/- 20 min, and accelerated colonic transit corresponding to a significantly (P < 0.05) increased value of the geometric centre (3.52 +/- 0.23 vs 2.44 +/- 0.1 for the control). Both devazepide and L365260 administered intracerebroventricularly at a dose of 10 micrograms kg-1 abolished the flumazenil-induced withdrawal effect on the duodenum, whereas at a lower dose (1 microgram kg-1) only L365260 was able to antagonize this effect. In the same way, devazepide, loxiglumide and L365260 suppressed the effect of precipitated withdrawal on colonic transit when administered intracerebroventricularly at a dose of 10 micrograms kg-1, whereas similar blockade was obtained at a dose of 5 micrograms kg-1 with L365260, and 10 ng kg-1 with PD135-158. It is concluded that in rats precipitated diazepam-withdrawal altered intestinal motility and colonic transit and that these effects are mediated by central release of cholecystokinin (CCK) or activation of CCK-ergic neurons.

Benzodiazepine/cholecystokinin interactions at functional CCK receptors in rat brain

1. The effects of benzodiazepines on cholecystokinin (CCK) responses produced following activation of CCKB receptors by pentagastrin in the ventromedial hypothalamus (VMH) or CCKA receptors by CCK-8S in the dorsal raphe of the rat brain in vitro have been investigated. 2. The benzodiazepine agonist, flurazepam, at high concentrations, blocked pentagastrin-induced excitations in the rat VMH yielding an equilibrium constant (Ke) value of 12.5 microM. 3. In the rat dorsal raphe, where activation of CCKA receptors leads to neuronal depolarization, flurazepam also produced a weak block of the CCK response. 4. Flurazepam blocked CCK responses but not carbachol-induced excitations of VMH neurones. The inhibition of CCK responses by flurazepam was not blocked by the benzodiazepine antagonist, flumazenil. 5. These data suggest that flurazepam is a weak antagonist at central CCKB receptors. 6. At central CCKA receptors, flurazepam blocked CCK-8S responses but the inhibition was not competitive, with a reduction in the peak CCK-8S obtainable in the presence of flurazepam. These results suggest that flurazepam acts at a site other than the CCKA receptor itself to block CCK responses in the dorsal raphe.

Rapid tolerance to the depressive effects of diazepam on guinea pig motor control using divided doses

The effects of acute and chronic IP injections of diazepam on the guinea pig righting reflex latency (RRL) were measured using an automated measurement system known as a "tolerometer." Single IP injections of 2.0, 6.0, 18.0, and 20.0 mg/kg diazepam significantly increased the RRL compared to no injection (naive animals), diazepam vehicle injections, or 1.0 mg/kg diazepam injections. The effects of chronic IP injection schedules on the RRL were compared: 18 or 20 mg/kg in a single, once daily injection for 5 days; 6 mg/kg in a single, once daily injection for 5 days; and 6 mg/kg, three times a day, for 5 days. Neither 20, 18, nor 6 mg/kg/day for 5 days resulted in significant tolerance to the depressive effects of diazepam on the righting reflex. By contrast, when 6 mg/kg was administered three times a day for 5 days, tolerance developed by the third day of treatment. There were no differences between the three groups in the amount of exposure to the measurement apparatus or the testing situation. These results support the view that species like guinea pig and rat that metabolise diazepam rapidly, develop tolerance more quickly if diazepam is administered in divided doses or by continuous release; this may be because the duration of the occupation of CNS benzodiazepine recognition sites is a critical factor in the development of tolerance.

Pentagastrin induced panic attacks: enhanced sensitivity in panic disorder patients

The effects of pentagastrin, a synthetic analogue of the cholecystokinin tetrapeptide (CCK4), were studied in 15 patients with panic disorder and 15 healthy controls. Three different intravenous dosages of pentagastrin (0.1, 0.3 and 0.6 microgram/kg) and saline were investigated. Subjects were randomly allocated to two of the four treatment groups and tested on two separate occasions, 1 week apart, using an unbalanced double-blind incomplete block design. The mean panic rate with pentagastrin was 55% (12/22) for patients and 5% (1/22) for controls. None of the subjects panicked with saline. The frequency of panic attacks between the three pentagastrin doses in patients was not different. One control subject had a panic-like attack at the highest dose of pentagastrin. These findings concur with previous studies on the panicogenic effect of CCK4 and pentagastrin and suggest a greater sensitivity for CCK receptor agonists in patients suffering from panic disorder than in healthy controls.

Quantification of the depressive effects of diazepam on the guinea pig righting reflex

The effects of 5 mg/kg/day diazepam (IP for 21-39 days) on righting reflex latency (RRL) and neuronal activity in the medial vestibular nucleus (MVN) were investigated in guinea pigs. Diazepam treatment increased the RRL relative to vehicle-injected controls (p < 0.05, ANOVA); although the average RRL in the diazepam-treated animals did decrease over time, this decrease was not statistically significant and therefore evidence of tolerance was not obtained. MVN slices were removed from diazepam-treated animals and recordings were made from MVN neurons in vitro. The average resting activities for MVN neurons in slices from diazepam-treated animals and uninjected animals from a previous study were not significantly different.

Biological actions of cholecystokinin

Cholecystokinin (CCK) has emerged as an important mammalian neuropeptide, localized in peripheral organs and in the central nervous system. This review presents an overview of the molecular aspects of CCK peptides and CCK receptors, the anatomical distribution of CCK, the neurophysiological actions of CCK, release of CCK and effects of CCK on release of other neurotransmitters, and the actions of CCK on digestion, feeding, cardiovascular function, respiratory function, neurotoxicity and seizures, cancer cell proliferation, analgesia, sleep, sexual and reproductive behaviors, memory, anxiety, and dopamine-mediated exploratory and rewarded behaviors. Human clinical studies of CCK in feeding disorders and panic disorders are described. New findings are presented on potent, nonpeptide CCK antagonists, selective for the two CCK receptor subtypes, which demonstrate that endogenous CCK has biologically important effects on physiology and behavior.

Social isolation of rats increases the density of cholecystokinin receptors in the frontal cortex and abolishes the anti-exploratory effect of caerulein

The role of cholecystokinin (CCK) receptors in the development of anxiety caused by social isolation of rats was studied using the elevated plus-maze and receptor binding techniques. The isolation of male Wistar rats significantly reduced their exploratory activity in the elevated plus-maze compared with that of rats kept in groups of four. Caerulein (0.1-5 micrograms/kg s.c.), an agonist at CCK receptors, only at the highest dose (5 micrograms/kg) significantly decreased the exploratory behaviour of rats housed in groups, but not in the isolated rats. By contrast, small doses of caerulein (0.1-0.5 microgram/kg) even tended to increase the behavioural activity of isolated rats in the plus-maze test. In parallel to the behavioural changes, isolation of the rats increased the number of [3H]pCCK-8 binding sites in the frontal cortex, but not in the other forebrain structures (the mesolimbic area, striatum and hippocampus). Isolation did not affect the density of benzodiazepine receptors in the frontal cortex. In conclusion, the isolation of rats for 7 days produced anxiogenic-like effect on the behaviour of rats and increased the number of CCK receptors in the frontal cortex without affecting benzodiazepine receptors.

Release of cholecystokinin in the central nervous system

The octapeptide cholecystokinin (CCK) is one of the most abundant neuropeptides of the central nervous system. A number of features (for instance heterogeneity of the regional distribution, subcellular localization at the nerve terminal level, calcium-dependent release upon nervous tissue depolarization) support the candidacy of CCK as a neurotransmitter. The reported co-existence of CCK and dopamine in some meso-limbic neurons has led to speculation that the neuropeptide may interact with the catecholamine in neuropsychopathologies linked to dopamine dysfunctions, like schizophrenia. Data from the experimental animals have so far generated conflicting results. It should be noted that the interactions between CCK and dopamine, and, in particular, the effects of CCK and dopamine on each other release, both in vitro and in vivo, have been poorly investigated and would require special attention. Evidence is accumulating that CCK may participate in the expression of anxiety. Indeed antagonists at the central CCK receptors exhibit anxiolytic activity in the laboratory animal. An interesting linkage appears to exist in the brain between 5-hydroxytryptamine (5-HT) and CCK. Activation of 5-HT3 receptors was found to increase CCK release from rat cortical or nucleus accumbens synaptosomes. Interestingly, antagonists at 5-HT3 receptors appear to possess anxiolytic activity. Recent studies carried out in conscious unrestrained rats show that the calcium-dependent, tetrodotoxin-sensitive release of CCK-like immunoreactivity evoked in the rat frontal cortex by veratrine infusion can be inhibited by submicromolar concentrations of 5-HT3 receptor antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional changes in neuropeptide levels after 5,7-dihydroxytryptamine-induced serotonin depletion in the rat brain

The levels of five neuropeptides (substance-P, somatostatin, cholecystokinin octapeptide, methionine-enkephalin and dynorphin) were examined in the brain and the spinal cord of rats 2 weeks after intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT). 5,7-DHT injection caused a significant reduction of the serotonin level in all regions of the brain. The level of each neuropeptide except dynorphin significantly increased in specific regions of the brain after 5,7-DHT treatment without any decrease in their levels in any region. Since, coexistence and interaction between classical neurotransmitters and neuropeptides in the same neurons have been reported, both are indispensable for evaluating pathophysiological state of the brain function associated with abnormal neural transmission. The present findings together with previous reports suggest that neuropeptides act as neurotransmitters and compensate for the impaired function of the serotonergic systems.

Benzodiazepines increase preprocholecystokinin messenger RNA levels in rat brain

Using in situ hybridisation, the effects of acute and chronic diazepam administration and diazepam withdrawal on preprocholecystokinin (CCK) mRNA levels in discrete regions of rat brain were determined. In cerebral cortex and a subpopulation of hippocampal neurones, CCK mRNA levels were increased after a single injection of diazepam and 24 h after withdrawal from chronic diazepam treatment, but not after chronic diazepam treatment. These results show that, in some neuronal groups, CCK mRNA expression is regulated by benzodiazepines, although there is no clear link between CCK mRNA levels and anxiety state.

Anti-exploratory effect of N-methyl-D-aspartate in elevated plus-maze. Involvement of NMDA and CCK receptors

N-Methyl-D-aspartate (NMDA, 20 mg/kg) produced a clear decrease in mouse exploration in open parts of an elevated plus-maze. Paradoxically, 40 mg/kg NMDA did not modify the behavior of the mice in the plus-maze. NMDA at a dose of 80 mg/kg again depressed the exploratory activity of mice, but this effect was accompanied with tremor and compulsive tail biting. The 'anti-exploratory' dose of NMDA (20 mg/kg) increased, whereas the 'tremorigenic' dose (80 mg/kg) significantly decreased the number of cholecystokinin (CCK) binding sites in the mouse cerebral cortex. The competitive NMDA antagonist (+/-)-CPP (2.5-5 mg/kg) and the non-competitive antagonist MK-801 (0.25 mg/kg) antagonized the anti-exploratory effect of NMDA (20 mg/kg). The tricyclic antidepressant imipramine (5 mg/kg, but not 1 or 10 mg/kg) also attenuated the inhibition of exploratory activity induced by NMDA. Of three CCK receptor antagonists tested, the unselective CCK antagonist proglumide (1 mg/kg, but not 0.1 and 10 mg/kg) significantly opposed the anti-exploratory action of NMDA. The selective CCK antagonists L-365,260 (1 microgram/kg) and devazepide (1 microgram/kg) were evidently weaker antagonists of NMDA. Furthermore, 10 micrograms/kg of L-365,260, a CCK-B receptor antagonist, and 1 mg/kg of devazepide, a CCK-A receptor antagonist, even tended to augment the effect of NMDA in the plus-maze. The results of the present study seem to give some support to the notion that not only NMDA receptors, but also CCK-ergic mechanisms are involved in the modulation of anti-exploratory action of NMDA in the elevated plus-maze.

The benzodiazepine antagonist flumazenil blocks the effects of CCK receptor agonists and antagonists in the elevated plus-maze

Peripheral administration of the unsulphated cholecystokinin octapeptide (CCK-8us) led to an anxiogenic-like action in the elevated plus-maze model of anxiety in rats. Devazepide and L-365,260 showed potent anxiolytic-like effects at similar doses. The fact that devazepide is 1000 times more potent as a CCK-A receptor antagonist than L-365,260, whereas the two compounds are nearly equipotent at the CCK-B receptor subtype, suggests that CCK-B rather than CCK-A receptors are involved in these effects. Similar results were obtained in mice using the two-compartment test. In the elevated plus-maze, the benzodiazepine antagonist, flumazenil, which was inactive when given alone, significantly antagonized the anxiogenic-like activity of CCK-8us and the anxiolytic-like effects of devazepide and L-365,260. These results suggest a complex interaction between benzodiazepine and CCK receptor mechanisms in the regulation of anxiety states.

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.

The antagonism of benzodiazepine withdrawal effects by the selective cholecystokininB receptor antagonist CI-988

The ability of a selective cholecystokininB (CCKB) receptor antagonist, CI-988, to block benzodiazepine withdrawal effects was examined in mice. The discontinuation of twice daily administration of diazepam (1 mg kg-1, i.p.) induced withdrawal anxiogenesis and a proconvulsant effect. In contrast, no such effects were seen following withdrawal from similar administration of CI-988. However, CI-988 dose-dependently (0.001-1.0 mg kg-1, s.c.) antagonized both the anxiogenesis and the proconvulsant effect following diazepam-withdrawal.

Age-related differences of cholecystokinin receptor binding in the rat brain

1. Cholecystokinin and benzodiazepine receptor binding was evaluated in 2-, 9- and 18-month old rats in the brain regions where cholecystokinin octapeptide and gamma-aminobutyric acid are known to coexist in common nerve cells (frontal cortex, hippocampus). 2. There was a regionally selective alteration of hippocampal 3H-CCK-8 binding in the oldest age group, if compared to both young and adult animals. Non-linear regression analysis of binding data revealed significantly lower apparent number of binding sites (Bmax), and twofold (but not statistically significantly) higher binding affinity for the radiolabelled ligand. No differences between any age groups in 3H-flunitrazepam binding to benzodiazepine receptors were found. 3. The results suggest that changes in cholecystokinin receptor characteristics might contribute to the behavioural impairments in aged rats.

Alterations in brain cholecystokinin receptors in suicide victims

Cholecystokinin (CCK) and benzodiazepine receptor binding characteristics were analyzed in the brain tissue samples from 19 suicide victims and 23 control cases. In the frontal cortex, significantly higher apparent number of CCK receptors and affinity constants were found in the series of suicide victims. These differences between suicides and controls were present in similar proportions when the suicide cases with depressive syndrome or violent or non-violent means of self-killing were compared to matched controls. However, when the samples were split into subgroups consisting of persons either below or over the age of 60 years, significant differences in the CCK receptor characteristics in the frontal cortex were observed only between younger suicides and controls. Furthermore, the younger suicide victims had a higher density of CCK receptors in the cingulate cortex, whereas in older suicides the value was lower as compared to age-matched controls. No difference in benzodiazepine receptor binding was found between control and suicide groups. The results of this investigation suggest that CCK-ergic neurotransmission is linked to self-destructive behaviour, probably through its impact on anxiety and adaptational deficits.

The CCK-A and CCK-B receptor antagonists, devazepide and L-365,260, enhance morphine antinociception only in non-acclimated rats exposed to a novel environment

Devazepide, a potent CCK-A receptor antagonist, and L-365,260, a selective CCK-B receptor antagonist, have been introduced as pharmacologic tools for differentiating the physiologic roles of CCK-A and CCK-B receptor subtypes. In the present study, we tested the effects of devazepide and L-365,260, on morphine antinociception in rats using the thermal sensorimotor tail flick test. Both devazepide and L-365,260 significantly enhanced the antinociceptive action of morphine, but only in rats that had not been acclimated to the laboratory environment or habituated to investigator handling. When tested with fully acclimated animals, devazepide and L-365,260 had no effect whatsoever; they neither enhanced nor attenuated morphine-induced antinociception. These observations indicate that the effects of devazepide and L-365,260, CCK antagonists, on morphine antinociception appear to be dependent on the animal's response to a new environment or to the stress induced by an unaccustomed experimental paradigm.

Cholecystokinin-induced anxiety: how is it reflected in studies on exploratory behaviour?

Central cholecystokinin (CCK)-ergic neurotransmission has been implicated in the genesis of negative emotions. Most animal studies on the neurochemical background of CCK-induced anxiety have, up to date, exploited exploratory activity paradigms. The interaction of CCK with GABAergic inhibitory neurotransmission, mediated probably through CCK-B receptors, could be the neurochemical substrate for anxious type of exploratory behaviour. However, the CCK-A and CCK-B receptor-mediated interactions of this neuropeptide with mesencephalic dopaminergic regulation of motivation for locomotor activity have the potential to interfere with the behavioural outcome from routine exploratory activity tests. Systemic treatment with CCK receptor antagonists is likely to influence both GABA- and dopamine-linked CCK-ergic neurotransmission, and therefore their effects in exploratory activity tests should be interpreted with caution.