Benzodiazepines antagonize cholecystokinin-induced activation of rat hippocampal neurones

Interaction of cholecystokinin and diazepam: effects on brain monoamines

An antagonism between cholecystokinin (CCK) peptides and benzodiazepines (BZD) has been described in various paradigms. We sought to determine whether CCK and BZD are also antagonistic in their effects on brain neurotransmitter levels in the rat. No effect on the noradrenergic system was induced in any brain area by CCK 8 S and diazepam alone or in combination. Administered alone, sulfated CCK octapeptide (CCK 8 S) (5 micrograms/kg ip) and diazepam (5 mg/kg ip) were found to decrease DOPAC levels in the cortex and to induce 5-hydroxy-tryptamine accumulation in the hippocampus. When administered together, these variations were no longer observed. However, a slight tendency by each substance to decrease 3-methoxy-tyramine levels in the striatum, became significant when given in association. The differences in CCK-BZD interactions observed in the striatum, cortex and hippocampus suggest that different mechanisms of action are involved. The addition of the effects occurring in the striatum might involve a GABA-ergic mechanism.

Cholecystokinin-tetrapeptide induces panic attacks in patients with panic disorder

Cholecystokinin-tetrapeptide (CCK-4) and placebo were injected to 11 panic disorder patients. CCK-4 induced a panic attack identical to spontaneous panic attacks in all patients; placebo did not induce any attacks. The role of CCK-4 in anxiety disorders is discussed.

Anxiogenic-like action of caerulein, a CCK-8 receptor agonist, in the mouse: influence of acute and subchronic diazepam treatment

Effects of caerulein, a cholecystokinin octapeptide (CCK-8) receptor agonist, on exploratory activity of mice were investigated. Exploratory and locomotor activity of animals were measured using elevated plus-maze and open field tests. The systemic administration of caerulein at non-sedative doses (100 ng/kg-1 micrograms/kg i.p.) resulted in a significant decrease in the exploratory activity of mice. This effect was completely blocked by proglumide, a CCK-8 receptor. Acute treatment with low doses (0.1-0.75 mg/kg i.p.) of diazepam did not attenuate the anxiogenic-like effect of caerulein, but at more high doses of diazepam the coadministration depressed locomotor activity in mice. After subchronic diazepam treatment (2.5 mg/kg once a day, 10 days, i.p.) tolerance was developed toward the sedative effect of diazepam, and 72 h after withdrawal of the drug the animals showed increased anxiety in the plus-maze test. 30 min after the last injection procedure the anxiogenic-like effect of caerulein (500 ng/kg i.p.) on exploration was absent in both diazepam or vehicle groups. However, 72 h after the last pretreatment injection caerulein (500 ng/kg i.p.) reduced significantly the exploratory activity in control group, whereas it was inactive after diazepam withdrawal. The results obtained in this study support the hypothesis that endogenous CCK-8 an CCK-8 receptors are involved in the neurochemistry of anxiety and the anxiolytic action of benzodiazepine tranquillizers.

Postnatal development of cholecystokinin (CCK) binding sites in the rat forebrain and midbrain: an autoradiographic study

The postnatal development of cholecystokinin (CCK) binding sites in the rat forebrain and midbrain was studied by in vitro receptor autoradiography. In the majority of structures, the densities of sites were low over the first week after birth, increased until the third week, and decreased over the fourth week to reach adult levels. However, both the rate of increase and the extent of the decrease varied in large proportions among structures. For instance, labeling in the neocortex underwent its largest increase from postnatal day 10, while this increase was already begun at day 7 in the paleocortex. On the other hand, over the fourth postnatal week, the densities could either remain roughly constant (cingulate cortex), slightly decrease (thalamic reticular nucleus), or even return to background levels (pyramidal layer of hippocampus). These different timetables may depend mostly on the differential growth of cells expressing the CCK receptor gene within the developing CNS. The absence of CCK binding sites in most of the regions during the early postnatal period precludes a major role of this peptide in the embryonic development of the rat brain. However, in some regions as the ventromedial hypothalamic nucleus, the endopyriform cortex or the medial nucleus of amygdala, 30-50% of the adult levels were already present at birth. Whether this observation reflects an earlier functional maturation of these structures or a direct participation of the corresponding CCK systems in their development remains to be established.

Effects of sulphated cholecystokinin octapeptide (CCK-8) on the dorsal motor nucleus of the vagus

Sulphated cholecystokinin octapeptide (CCK-8) was applied by superfusion (2.1 x 10(-7) to 4.2 x 10(-6) M) to neurons of the dorsal motor nucleus of the vagus (DMV) in slice preparations of the rat medulla oblongata. Intracellular recordings show 23 of 54 (43%) neurons to be depolarized and the depolarization to be associated with an increase in membrane input resistance; 6 of 54 (11%) neurons were hyperpolarized and the hyperpolarization was associated with a decrease in membrane input resistance. Both effects were dose-dependent, reversible and persisted after blockade of synaptic transmission by Ca2+ free/high Mg2+ solution. On the other hand, nonsulphated CCK-8, a nonactive analogue of CCK-8, had no effect. These data show that vagal neurons in the DMV have receptors for CCK-8 and that CCK-8 may modulate vagal output mainly by increasing neuronal excitability.

Autoradiographic demonstration of the antagonism of anthramycin and diazepam against cholecystokinin in the mouse brain using the [14C]-2-deoxyglucose method

Effects of diazepam (DZP), a synthetic benzodiazepine drug, and anthramycin (ATM), a benzodiazepine antitumor antibiotic produced by a certain species of streptomyces, on the uptake of 2-deoxy-D-[14C]-glucose (2-DG) in mouse brain neurons with or without cholecystokinin were examined. 2-DG uptake in neurons was evaluated by using an autoradiographic technique. The sulfated octapeptide CCK (CCK8) was injected intracisternally; DZP and ATM, intraperitoneally; and 2-DG, intravenously to mice. Autoradiograms prepared from the slices of the brain were converted to false color images. CCK8 (1 microgram/mouse) markedly stimulated the 2-DG uptake in neurons in the various regions of the brain, but the stimulative effects of CCK8 was almost completely suppressed after an intraperitoneal administration of 1.0 mg/kg of DZP or 0.5 mg/kg of ATM. Since it has been previously shown that these doses of DZP and ATM almost completely reversed the antinociception produced by 1 microgram/mouse of CCK8, the present results on the 2-DG uptake in the mouse brain are considered to further support the antagonism between CCK8 and DZP or ATM in the central nervous system.

Effects of cholecystokinin and pentagastrin on rat hippocampal neurones maintained in vitro

Extracellular and intracellular recordings from CA1 neurones of rat hippocampal slices were undertaken to assess the relative potencies of cholecystokinin fragments. The CCK peptides displayed a large variability in their effects on extracellularly recorded population spikes. Intracellular recordings from CA1 neurones revealed a more consistent excitant action of these compounds. The C-terminal octapeptide CCK-8S, the tetrapeptide CCK-4 and pentagastrin were all found to be agonists when applied to hippocampal CA1 neurones maintained in vitro. Repeated application of the peptide fragments to the same cell resulted in a loss of activity. Neurones pre-treated with a CCK peptide showed no response to an application of a second, different, CCK fragment indicative of receptor cross-desensitization. Depolarisations induced by the excitatory amino acid L-glutamate remained unaffected by peptide application. These data suggest that the CCK fragments are agonists at rat CA1 neurones and share a common mode of action distinct from that of the excitatory amino acid L-glutamate.

Long-term benzodiazepine treatment reduces neuronal responsiveness to cholecystokinin: an electrophysiological study in the rat

Acute benzodiazepine administration has been reported to antagonize the effect of cholecystokinin both in the periphery and in the central nervous system. A two-week treatment with either diazepam (5 mg/kg per day) or flurazepam (15 mg/kg per day) markedly reduced the excitatory effect of microiontophoretically applied sulphated cholecystokinin octapeptide-(26-33) on rat CA3 hippocampal pyramidal neurons but not that of acetylcholine. In view of the sustained anxiolytic activity of benzodiazepines that contrasts with their transient sedative effect, the present results suggest that the reduction of neuronal responsiveness to cholecystokinin by these drugs might be related to their anxiolytic property.

Electrophysiology of benzodiazepine receptor ligands: multiple mechanisms and sites of action

Electrophysiology of BZR ligands has been reviewed from different points of view. A great effort was made to critically discuss the arguments for and against the temporarily leading hypothesis of the mechanism of action of BZR ligands, the GABA hypothesis. As has been discussed at length in the present article, an impressive body of electrophysiological and biochemical evidence suggests an enhancement of GABAergic inhibition in CNS as a mechanism of action of BZR agonists. Biochemical data even indicate a physical coupling between GABA recognition sites and BZR which, together with the effector site build-up by Cl- channels, form a supramolecular GABAA/BZR complex. By binding to a specific site on this complex, BZR agonists allosterically increase and BZR inverse agonists decrease the gating of GABA-linked Cl- channels, whereas BZR antagonists bind to the same site without an appreciable intrinsic activity and block the binding and action of both agonists as well as inverse agonists. While this model is supported by many electrophysiological experiments performed with BZR ligands in higher nanomolar and lower micromolar concentrations, it does not explain much controversial data from animal behavior and, more importantly, is not in line with electrophysiological effects obtained with low nanomolar BZ concentrations. The latter actions of BZR ligands in brain slices occur within a concentration range compatible with concentrations of BZ observed in CSF fluid, which would be expected to be found in the biophase (receptor level) during anxiolytic therapy in man. Enhanced K+ conductance seems to be a suitable candidate for this effect of BZR ligands. This direct action on neuronal membrane properties may underlie the many electrophysiological observations with extremely low systemic doses of BZR ligands in vivo which demonstrated a depressant effect on spontaneous neuronal firing in various CNS regions. Skeletomuscular spasticity and epilepsy are two neurological disorders, where both the enhanced GABAergic inhibition and increased K+ conductance may contribute to the therapeutic effect of BZR agonists, since electrophysiological and behavioral studies strongly support GABA-dependent as well as GABA-independent action of BZR ligands elicited by low to intermediate doses of BZ necessary to evoke anticonvulsant and muscle relaxant effects. Somewhat higher doses of BZR ligands, inducing sedation and sleep, lead perhaps to the only pharmacologically relevant CNS concentrations (ca. 1 microM) which might be due entirely to increased GABAergic inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of adenosine in the central actions of the benzodiazepines

1. Evidence is presented which indicates that the central actions of the benzodiazepines cannot be fully accounted for by assuming an action only at the GABAA-Cl- channel supramolecular complex. 2. The hypothesis is presented, together with supporting evidence, that inhibition of adenosine uptake can account for many of the actions of the benzodiazepines. 3. New findings showing that Ro 15-1788 and Ro 5-4864 have both potentiative and antagonistic interactions with adenosine are discussed. 4. The proconvulsant beta-carbolines are shown to be adenosine antagonists. 5. The concept that benzodiazepine action may involve several mechanisms is presented.

Inhibition of non-dopamine cells in the ventral tegmental area by benzodiazepines: relationship to A10 dopamine cell activity

Previous electrophysiological studies have demonstrated that non-dopaminergic (non-DA) neurons within the substantia nigra pars reticulata (SNR) are extremely sensitive to the inhibitory effects of GABA and GABA-mimetic drugs, including benzodiazepines, whereas dopaminergic (DA) neurons in the substantia nigra pars compacta (SNC) are less sensitive to these compounds and may be influenced indirectly by SNR neurons. The interactions between A10 DA and non-DA neurons within the adjacent ventral tegmental area (VTA) are not as well characterized. In the present experiments, single unit recording and microiontophoretic techniques were used to determine the effects of benzodiazepines on DA and non-DA neurons in the VTA of chloral hydrate anesthetized rats. Diazepam, administered intravenously (i.v.), potently inhibited non-DA, SNR-like cells within the VTA. The effects of diazepam on A10 DA cells were more variable than those observed on non-DA, SNR-like cells in this region, but 77% of such cells showed moderate to marked excitation. Both of these effects were reversed by the benzodiazepine antagonist Ro 15-1788; on many cells, this agent produced marked rebound effects beyond the original basal firing rates. However, when administered alone, Ro 15-1788 exerted no effect on either cell population. Microiontophoretic administration of the benzodiazepines chlordiazepoxide and flurazepam resulted in marked inhibition of non-DA SNR-like cells, but produced either mild inhibition or no effect on A10 DA cells; excitation of DA cells was never observed even though the same neuron was excited by i.v. diazepam. These findings suggest that benzodiazepines act directly upon non-DA, SNR-like cells in the VTA to produce inhibition of activity and a disinhibition of A10 DA cells. This relationship makes it unlikely that benzodiazepines would enhance feedback inhibition of DA cells following neuroleptic administration. In fact, when administered following haloperidol, i.v. diazepam failed to reverse haloperidol-induced increases of A10 DA cell firing; if anything, diazepam further depolarized the cell. If antipsychotic drugs produce their clinical effects, in part, by inducing depolarization inactivation of DA cells, then benzodiazepines might be a useful adjunctive therapy in the treatment of schizophrenia.

Long-term antidepressant treatment reduces neuronal responsiveness to flurazepam: an electrophysiological study in the rat

Long-term administration of various types of antidepressant drugs has been recently reported to reduce the density of benzodiazepine receptors in the rat CNS. In the present study, using the microiontophoretic technique, the effect of flurazepam application on cholecystokinin-induced activation of hippocampal pyramidal neurons was assessed in rats treated with the antidepressants desipramine, trimipramine and citalopram, and the antipsychotic chlorpromazine, for 3 weeks. All 3 antidepressant drugs, but not chlorpromazine, reduced the efficacy of flurazepam. A two-week treatment with desipramine produced a similar effect, whereas a one-week treatment with this drug failed to alter the effect of flurazepam. These results constitute further evidence that long-term antidepressant treatment down-regulates benzodiazepine receptors.

Beta-carbolines selectively antagonize the cholecystokinin action in isolated guinea-pig gallbladder muscle

Two beta-carbolines, methyl beta-carboline-3-carboxylate (beta-CCM) and ethyl beta-carboline-3-carboxylate (beta-CCE), caused the parallel shift of the dose-response curve for cholecystokinin (CCK) in isolated guinea-pig gallbladder muscle. The Schild plot regarding the parallel shift in the dose-response curves had a regression line with a slope of 1.03 and a pA2 value of 5.17 for beta-CCE, while the method of van Rossum gave a pA2 value of 5.24 for beta-CCE and 5.53 for beta-CCM. Both the beta-carbolines protected CCK receptors in the gallbladder muscle from alkylation by dibenamine, but beta-CCM did not protect acetylcholine receptors from dibenamine alkylation. These results suggest that beta-CCM and beta-CCE, so-called inverse agonists of benzodiazepines (BZP), antagonize the CCK action in the gallbladder muscle in a competitive manner, and the antagonism takes place at CCK receptor sites. No spare receptors for CCK were found in the guinea-pig gallbladder muscle.

Synaptic connections, axonal and dendritic patterns of neurons immunoreactive for cholecystokinin in the visual cortex of the cat

A subpopulation of gamma-aminobutyric acid (GABA) containing neurons was reported to contain cholecystokinin-immunoreactive material in the visual cortex of cat [Somogyi et al., J. Neurosci. (1984) 4, 2590-2603]. In the present study pre-embedding immunocytochemistry was used to identify which of the several types of presumed GABAergic nonpyramidal cells in areas 17 and 18 contain cholecystokinin immunoreactivity. Most of the cholecystokinin-immunoreactive somata were found in layers II-III, they were less frequent in layers I and VI, and relatively rare in layers IV and V. The distribution and density of the axon terminals resembled that of the cell bodies. Two well defined types of cholecystokinin-immunoreactive neuron were distinguished: (1) double bouquet cells in layers II-III with vertically projecting axons, and (2) small basket cells with local axons either restricted to layers II-III, or descending to layer V. Additional cholecystokinin-positive cells showed features of bitufted or multipolar neurons in layers II-VI and horizontal cells in layer I, but these cells could be defined less well due to partial staining. Cholecystokinin-immunoreactive dendrites were found to run horizontally in layer I for several hundred micrometers. Some of the cholecystokinin-immunoreactive cells in layer VI had very long dendrites ascending radially up to layer III, as did their axons. A few cholecystokinin-immunoreactive cells appeared to have two axons and this was confirmed by electron microscopy. All cholecystokinin-immunoreactive neurons and terminals were separated from the basal lamina of blood vessels by glial endfeet. Random samples of boutons from each layer as well as identified terminals traced to their origin from local neurons were examined in the electron microscope. All of the boutons established symmetrical (type II) synaptic contacts with dendritic shafts, spines or somata. Quantitative electron microscopy of the postsynaptic targets of double bouquet cells and small basket cells demonstrated clear differences between these two types of neuron; basket cells having a higher proportion of their terminals in synaptic contact with somata. The findings that several distinct types of cortical neurons, as defined by their synaptic connections, contain cholecystokinin-immunoreactive material and that identified axons of all examined neurons form type II synaptic contacts suggests that the majority, if not all cholecystokinin-positive boutons forming type II contacts originate from local cortical cells. The distribution of targets postsynaptic to cholecystokinin-positive neurons is compared to those of cells labelled by other methods.

Design of potent, orally effective, nonpeptidal antagonists of the peptide hormone cholecystokinin

We describe the design and synthesis of nonpeptidal antagonists of the peptide hormone cholecystokinin. Several of these compounds have high specificity and nanomolar binding affinity and are active after oral administration. To our knowledge, the design of such agents has not previously been accomplished for any peptide hormone. The structural similarities between these synthetic compounds and the anxiolytic 1,4-benzodiazepines are noted, and the potential of this structural feature for future design of ligands for other peptide hormone receptors is discussed.

Effects of benzodiazepines on responses of guinea-pig ileum and gall-bladder and rat pancreatic acini to cholecystokinin

Bradwejn and De Montigny have recently shown that benzodiazepines selectively inhibit excitation of hippocampal neurones by cholecystokinin (CCK). We show here that lorazepam and chlordiazepoxide selectively inhibit the nerve-mediated response of ileal longitudinal muscle to CCK, but have no effect on the direct stimulation of gall-bladder muscle or pancreatic acini by this peptide. Lorazepam (1 and 10 microM) and chlordiazepoxide (0.1 and 1 microM) inhibited responses of guinea-pig ileum, but not gall-bladder to CCK. Responses of both tissues to acetylcholine (ACh) were unaffected and lorazepam (10 microM) did not inhibit ileal responses to neurotensin, 5-hydroxytryptamine and substance P which act entirely or in part by stimulating myenteric nerves. Chlordiazepoxide (1 and 10 microM) did not inhibit CCK-stimulated amylase release from dispersed rat pancreatic acini. Higher concentration of the same drugs and diazepam (1 and 10 microM) which has high affinity for benzodiazepine receptors on gastrointestinal muscle, inhibited responses of ileum and gall-bladder to both CCK and acetylcholine.

Cholecystokinin antagonism by benzodiazepines in the food intake in mice

Three benzodiazepines, chlordiazepoxide, diazepam and flurazepam, were demonstrated to reverse the suppressed food intake in mice in response to cholecystokinin octapeptide (CCK8). CCK8 (200 ng) was administered intracisternally, and the benzodiazepines intraperitoneally at doses of 0.1 to 1 mg/kg. The three benzodiazepines slightly depressed the feeding by themselves, but significantly reversed the satiety effects of CCK8. Naloxone (2 mg/kg) decreased the food intake but failed to reverse the CCK8 satiety action. The benzodiazepines were considered to antagonize the satiety action of CCK8 in the central nervous system through unknown mechanisms.

Multiple treatment potentiates the anticonvulsive activity of cholecystokinin octapeptides

The dose-response curves for the anticonvulsive activity of sulfated and nonsulfated cholecystokinin octapeptide (CCK-8-SE and CCK-8-NS) against picrotoxin-induced (6 mg/kg SC) seizures were assessed either following or without pretreatment with a single high dose of CCK-8-SE or CCK-8-NS, to examine acute tolerance to the effect after IP injections in mice. As CCK-8-SE or CCK-8-NS pretreatment, a 1.6 mumole/kg dose was injected 2 hr prior to the second injection. No acute tolerance to the anticonvulsive activity was demonstrated, and CCK-8-NS pretreatment significantly potentiated its own anticonvulsive activity. Chronic (8-day) daily treatment with a 0.16 mumole/kg dose of CCK-8-SE or CCK-8-NS antagonized seizures by picrotoxin, presumably in a cumulative manner. To investigate the interactions of CCK octapeptides with other anticonvulsive agents, picrotoxin-induced seizures were antagonized with several doses of diazepam following or without acute, high-dose pretreatment with CCK-8-SE or CCK-8-NS. The two octapeptides only slightly modified the activity of diazepam: CCK-8-SE pretreatment displayed a tendency to antagonize it, while CCK-8-NS pretreatment to potentiate it. The results suggest that multiple treatment with CCK-8 induces sensitization of CCK receptors mediating anticonvulsive activity.

Effects of PK 8165, a partial benzodiazepine receptor agonist, on cholecystokinin-induced activation of hippocampal pyramidal neurons: a microiontophoretic study in the rat

Benzodiazepines (BZD) have been reported to suppress cholecystokinin-8S (CCK-8S)-induced activation. PK 8165, a ligand of BZD receptors, is an anxiolytic devoid of sedative and anticonvulsant effects. PK 8165, applied microiontophoretically or administered i.v. at low doses, suppressed CCK-8S-induced activation of hippocampal pyramidal neurons, whereas, at high doses it antagonized the effect of microiontophoretic applications of flurazepam. These results indicate that PK 8165 acts as a mixed agonist-antagonist at BZD receptors and suggest that the suppression of CCK-8S-induced activation by BZD might be related to their anxiolytic property rather than to their sedative or anticonvulsant activity.

Caerulein and its analogues: neuropharmacological properties

The decapeptide from the frog Hyla caerulea, caerulein (caerulein diethylammonium hydrate, ceruletide, CER) is chemically closely related to the C-terminal octapeptide of cholecystokinin (CCK-8). Like CCK-8, CER and some of its analogues produce many behavioural effects in mammals: inhibition of intake of food and water; antinociception; sedation; catalepsy; ptosis, antistereotypic, anticonvulsive and tremorolytic effects; inhibition of self-stimulation. Effects of CER in man comprise sedation, satiety, changes in mood, analgesia and antipsychotic effects. A modulation of central dopaminergic functions appears to be one possible mechanism of CER and its analogues. A common denominator for all effects of CER is, at present, not evident.