Nitrendipine decreases benzodiazepine withdrawal seizures but not the development of benzodiazepine tolerance or withdrawal signs

L-Type Calcium Channel Blockers: A Potential Novel Therapeutic Approach to Drug Dependence

This review describes interactions between compounds, primarily dihydropyridines, that block L-type calcium channels and drugs that cause dependence, and the potential importance of these interactions. The main dependence-inducing drugs covered are alcohol, psychostimulants, opioids, and nicotine. In preclinical studies, L-type calcium channel blockers prevent or reduce important components of dependence on these drugs, particularly their reinforcing actions and the withdrawal syndromes. The channel blockers also reduce the development of tolerance and/or sensitization, and they have no intrinsic dependence liability. In some instances, their effects include reversal of brain changes established during drug dependence. Prolonged treatment with alcohol, opioids, psychostimulant drugs, or nicotine causes upregulation of dihydropyridine binding sites. Few clinical studies have been carried out so far, and reports are conflicting, although there is some evidence of effectiveness of L-channel blockers in opioid withdrawal. However, the doses of L-type channel blockers used clinically so far have necessarily been limited by potential cardiovascular problems and may not have provided sufficient central levels of the drugs to affect neuronal dihydropyridine binding sites. New L-type calcium channel blocking compounds are being developed with more selective actions on subtypes of L-channel. The preclinical evidence suggests that L-type calcium channels may play a crucial role in the development of dependence to different types of drugs. Mechanisms for this are proposed, including changes in the activity of mesolimbic dopamine neurons, genomic effects, and alterations in synaptic plasticity. Newly developed, more selective L-type calcium channel blockers could be of considerable value in the treatment of drug dependence. SIGNIFICANCE STATEMENT: Dependence on drugs is a very serious health problem with little effective treatment. Preclinical evidence shows drugs that block particular calcium channels, the L-type, reduce dependence-related effects of alcohol, opioids, psychostimulants, and nicotine. Clinical studies have been restricted by potential cardiovascular side effects, but new, more selective L-channel blockers are becoming available. L-channel blockers have no intrinsic dependence liability, and laboratory evidence suggests they reverse previously developed effects of dependence-inducing drugs. They could provide a novel approach to addiction treatment.

Benzodiazepine-induced hippocampal CA1 neuron α-amino-3-hydroxy-5-methylisoxasole-4-propionic acid (AMPA) receptor plasticity linked to severity of withdrawal anxiety: differential role of voltage-gated calcium channels and N-methyl-D-aspartic acid receptors

Withdrawal from 1-week oral administration of the benzodiazepine, flurazepam (FZP) is associated with increased alpha-amino-3-hydroxy-5-methylisoxasole-4-propionic acid (AMPA) receptor (AMPAR) miniature excitatory postsynaptic currents (mEPSCs) but reduction of N-methyl-D-aspartic acid (NMDA) receptor (NMDAR)-evoked (e)EPSCs in hippocampal CA1 neurons. A positive correlation was observed between increased AMPAR-mediated mEPSC amplitude and anxiety-like behavior in 1-day FZP-withdrawn rats. These effects were disrupted by systemic AMPAR antagonist administration (GYKI-52466, 0.5 mg/kg, intraperitoneal) at withdrawal onset, strengthening the hypothesis that CA1 neuron AMPAR-mediated hyperexcitability is a central component of a functional anatomic circuit associated with the expression of withdrawal anxiety. Abolition of AMPAR current upregulation in 2-day FZP withdrawn rats by GYKI-52466 injection also reversed the reduction in NMDAR-mediated eEPSC amplitude in CA1 neurons from the same rats, suggesting that downregulation of NMDAR function may serve a protective, negative-feedback role to prevent AMPAR-mediated neuronal overexcitation. NMDAR antagonist administration (MK-801, 0.25 mg/kg intraperitoneally) had no effect on modifying increased glutamatergic strength or on withdrawal anxiety, whereas injection of an L-type voltage-gated calcium channel antagonist, nimodipine (10 mg/kg, intraperitoneally) averted AMPAR current enhancement and anxiety-like behavior, suggesting that these manifestations may be initiated by a voltage-gated calcium channel-dependent signal transduction pathway. An evidence-based model of likely cellular mechanisms in the hippocampus contributing to benzodiazepine withdrawal anxiety was proposed implicating regulation of multiple CA1 neuron ion channels.

Death related to midazolam overdose during endoscopic retrograde cholangiopancreatography

We report a midazolam-related death that occurred during endoscopic retrograde cholangiopancreatography (ERCP). The acute intoxication due to midazolam overdose was confirmed by high-pressure liquid chromatography (HPLC) analysis of the blood samples taken from the patient in the intensive care unit (2.8 microg/ml) and postmortem (2.4 microg/ml). The case strongly emphasizes the necessity of the precautions that should be taken when midazolam is intravenously administered.

NMDA receptor antagonists potently suppress the spontaneous withdrawal signs induced by discontinuation of long-term diazepam treatment in Fischer 344 rats

The present study investigated the effects of the NMDA receptor antagonists dizocilpine (MK-801) and ifenprodil on the appearance of diazepam withdrawal signs caused by discontinuation of long-term diazepam treatment using a drug-admixed food (DAF) method in Fischer 344 rats. The total withdrawal score was significantly decreased by after-withdrawal treatment with dizocilpine or ifenprodil. Dizocilpine, in particular, markedly suppressed the motor withdrawal signs and body weight loss, while ifenprodil suppressed the motor and emotional withdrawal signs. Furthermore, the decrease in the food intake during withdrawal (anorexia) was significantly reduced by dizocilpine, but not by ifenprodil. These behavioral results indicated that the activation of NMDA receptors during withdrawal may play an important role in the appearance of withdrawal signs (in particular motor withdrawal signs) caused by discontinuation of chronic diazepam treatment, and that inhibitory agents for NMDA receptors may be effective in alleviation of the appearance of benzodiazepine withdrawal signs.

Influence of certain calcium-channel blockers on some aspects of lorazepam-dependence in mice

The effect of acute and chronic treatments of the calcium-channel blockers, isradipine, diltiazem and flunarizine in protecting against lorazepam dependence has been demonstrated in mice. Dependence was induced by twice-daily administration of lorazepam (1 mg kg-1) for 10 days, doubling the dose during the next 10 days. Withdrawal symptoms and changes in the noradrenaline, dopamine and 5-hydroxytryptamine content of different regions of the brain were observed after either 24-h withdrawal or flumazenil administration. Isradipine inhibited lorazepam withdrawal symptoms, the effect being accompanied in the 24-h withdrawal group by significant decreases in the noradrenaline and dopamine content of the thalamus and hypothalamus and in the noradrenaline content of the mid-brain. In the flumazenil-treated group isradipine produced significant decreases in mid-brain noradrenaline and dopamine levels and in the dopamine content of the thalamus and hypothalamus. Diltiazem did not, on the other hand, afford significant protection against lorazepam withdrawal symptoms and did not induce any significant change in the neurotransmitters studied. Flunarizine significantly inhibited lorazepam withdrawal symptoms, an effect accompanied by significant reduction in noradrenaline and dopamine levels in the thalamus and hypothalamus. Dopamine was also significantly reduced in the cerebral cortex. Similar effects were produced in the flumazenil-treated group, and the noradrenaline content was reduced in the medulla, pons and cerebellum. It was concluded that isradipine and flunarizine might be of value in ameliorating lorazepam withdrawal symptoms.

Behavioral measures of anxiety during opiate withdrawal

Heightened anxiety is a major component of the withdrawal syndromes associated with ethanol and sedative hypnotic medications. Because of similarities between the opiate and sedative-hypnotic withdrawal syndromes as well as data implicating heightened noradrenergic tone with opiate withdrawal, we investigated changes in anxiety measures identified by plus-maze and social interaction testing during opiate withdrawal. Because Sprague Dawley rats had very low levels of entry into plus-maze open arms, further studies were conducted using the Long-Evans strain. Long-Evans rats received continuous infusions of morphine sulfate at 44 mg/kg per day delivered by osmotic pump over 7 days while control animals received inert implants. During the first 3 days of withdrawal, the number and time of entries into open and closed arms of a plus-maze was recorded. Both social and aggressive behaviors were scored durings pairings of groups of two socially naive animals. Body weight was significantly reduced in morphine-treated animals prior to and during withdrawal. Both the number of entries into open plus-maze arms and the time spent in open areas increased over the 3 days of testing. However, no difference in plus-maze activity was detected between morphine-treated and control subjects. On the third day of withdrawal, social interaction time was greater in pairs of withdrawn and control subjects compared to pairs of two control subjects. In conclusion, behavioral measures of anxiety are not increased during opiate withdrawal.

Effects of diltiazem, a Ca2+ channel blocker, on naloxone-precipitated changes in dopamine and its metabolites in the brains of opioid-dependent rats

The effects of diltiazem, an L-type Ca2+ channel blocker, on naloxone (an opioid receptor antagonist)-precipitated withdrawal signs and changes in extracellular levels of dopamine (DA) and its metabolites in various brain regions of morphine (a mu-opioid receptor agonist) or butorphanol (a mu/delta/kappa mixed opioid receptor agonist) dependent rats were investigated using high performance liquid chromatography fitted with an electrochemical detector (HPLC-ED). Rats were rendered opioid-dependent by continuous intracerebroventricular (i.c.v.) infusion with morphine (26 nmol/microliters per h) or butorphanol (26 nmol/microliters per h) for 3 days. The expression of physical dependence produced by these opioids, as evaluated by naloxone (5 mg/kg. i.p.)-precipitated withdrawal signs, was reduced by concomitant infusion of diltiazem (10 and 100 nmol/microliters per h). Under the same condition, naloxone decreased the levels of: DA in the cortex, striatum, and midbrain; 3,4-dihydroxyphenylacetic acid (DOPAC) in the cortex, striatum, limbic areas, and midbrain: and homovanilic acid (HVA) in the striatum, limbic areas, and midbrain regions. In animals rendered dependent on butorphanol, the results obtained were similar to those of morphine-dependent rats except for the changes in DOPAC levels. Furthermore, concomitant infusion of diltiazem and opioids blocked the decreases in levels of DA, DOPAC, and HVA in a dose-dependent manner. These results suggest that the augmentation of intracellular Ca2+ mediated through L-type Ca2+ channels during continuous opioid infusion results in a decrease in extracellular levels of DA and its metabolites in some specific regions, which are intimately involved in the expression of withdrawal syndrome precipitated by naloxone.

Ca2+ channel blocker, diltiazem, prevents physical dependence and the enhancement of protein kinase C activity by opioid infusion in rats

The influence of an L-type Ca2+ channel blocker, diltiazem [(2S-cis)-3-(acetyloxy)-5-[2-(dimethylamino)-ethyl]-2,3-dihydro-2- (4- methoxyphenyl)-1,5-benzothiazepin-4(5H)-one], on the behavioral signs of naloxone (opioid receptor antagonist)-precipitated withdrawal syndrome and the enhancement of protein kinase C activity in the pons/medulla regions of rats rendered dependent on morphine (mu-opioid receptor agonist) or butorphanol (mu/delta/kappa mixed opioid receptor agonist) was investigated. The expression of physical dependence produced by continuous intracerebroventricular (i.c.v.) infusion of morphine (26 nmol/microliters per h) or butorphanol (26 nmol/microliters per h) for 3 days, as evaluated by naloxone (5 mg/kg, i.p.)-precipitated withdrawal signs, was dose dependently attenuated by concomitant infusion of diltiazem (10 and 100 nmol/microliters per h). Furthermore, diltiazem (100 nmol/microliters per h) completely inhibited the enhancement of cytosolic protein kinase C activity in the pons/medulla regions in rats rendered dependent by continuous infusion with morphine or butorphanol. These results suggest that the augmentation of intracellular Ca2+ concentration mediated through L-type Ca2+ channels during continuous opioid infusion leads to the enhancement of cytosolic protein kinase C activity in the pons/medulla region which is intimately involved in the development and/or expression of physical dependence on opioids.

Role of L-type calcium channels on yohimbine-precipitated clonidine withdrawal in vivo and in vitro

This study was designed to elucidate the possible participation of L-type calcium channels in the expression of clonidine-withdrawal precipitated by yohimbine in clonidine-dependent animals. Mice implanted for 5 days with osmotic minipumps containing the alpha 2-adrenoceptor agonist clonidine showed symptoms of a withdrawal syndrome (jerks, headshakes, defecations and weight loss) when yohimbine, an alpha 2-adrenoceptor antagonist, was injected. Similarly, isolated rat ilea incubated with clonidine in vitro showed a withdrawal contracture when yohimbine was added to the organ bath. The effects of L-type calcium channel blockers (verapamil and diltiazem) and the stimulant Bay K 8644 on these two different types of withdrawal responses were evaluated. A dose-dependent decrease in yohimbine-precipitated clonidine withdrawal in vivo was observed when verapamil (10-40 mg/kg, s.c. and 120 micrograms/mouse, i.c.v.) or diltiazem (5-20 mg/kg, s.c. and 160 micrograms/mouse, i.c.v.) were administered to mice dependent on clonidine. No effect was found after Bay K 8644 (0.5-5 mg/kg, s.c. and 1-5 micrograms/mouse) was injected under these conditions. In vitro, both verapamil (0.1-5 microM) and D-cis-diltiazem (1-50 microM) concentration-dependently reduced the height of the yohimbine-precipitated withdrawal contracture in rat ileum incubated with clonidine. Furthermore, the effect of diltiazem was stereospecific, as D-cis-diltiazem 10 microM markedly inhibited clonidine withdrawal, whereas the same concentration of L-cis-diltiazem had no effect. In contrast, the calcium channel stimulant Bay K 8644 (0.1-1 microM) increased the height of the ileum withdrawal contracture.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Ca2+ channel blockers on physical dependence on diazepam in mice

The effects of Ca2+ channel blockers on the development of physical dependence on diazepam were examined in mice. Co-administration of flunarizine (T-type Ca2+ channel sensitive blocker), but not of either nifedipine or diltiazem (L-type Ca2+ channel sensitive blockers), with diazepam significantly suppressed the hypersensitivity to FG 7142 following chronic treatment with diazepam. The hypersensitivity to FG 7142 may reflect benzodiazepine withdrawal convulsions. These results suggest that flunarizine, but not nifedipine or diltiazem, may suppress the development of physical dependence on diazepam, and that T-type Ca2+ channels in the brain, rather than L-type Ca2+ channels, may be involved in the development of physical dependence on diazepam.

Raised [3H]-5-HT release and 45Ca2+ uptake in diazepam withdrawal: inhibition by baclofen

The effect of diazepam withdrawal (2 mg/kg/day) on release of [3H]-5-hydroxytryptamine(5-HT) and [14C]-GABA from rat cortical and hippocampal slices was studied. No changes in [14C]-GABA release (basal, K(+)-evoked, uptake) from slices of either region were observed. Similarly, all parameters of [3H]-5-HT release were unchanged in cortical slices. However, during diazepam withdrawal, depolarised [3H]-5-HT release from hippocampal slices was raised with no changes in basal release or uptake into the slices being found. This increase could be prevented by in vivo administration of 1 mg/kg baclofen--this dose having no significant effect on [3H]-5-HT release from hippocampal slices of control rats. To further investigate this effect, 45Ca2+ uptake into hippocampal synaptosomes was examined and found to be increased during withdrawal. This was blocked by in vitro addition of 10 microM (-)baclofen, which had no effect on 45Ca2+ uptake in controls. Inhibition of 45Ca2+ uptake by (-)baclofen was also enhanced in nonwithdrawn diazepam-treated rats, but not in rats treated acutely with diazepam. The results from both studies indicate that chronic diazepam treatment increases neuronal sensitivity to baclofen. These results are discussed with reference to the anxiogenic state during diazepam withdrawal and a recent report of reversal of this behaviour by baclofen.

Effect of peripheral administration of cinnarizine and verapamil on the abstinence syndrome in diazepam-dependent rats

The effects of two calcium channel blockers (verapamil and cinnarizine) were evaluated on diazepam withdrawal symptoms. Rats were made diazepam dependent by chronic treatment with daily injections of the drug, 20 mg/kg IP for 3 weeks. On abrupt termination of the drug, animals showed withdrawal hyperactivity that was assessed by autonomic, behavioural and motor signs. The peak effect was seen 3 days after the withdrawal of diazepam. On IP administration, verapamil and cinnarizine (10, 20 and 40 mg/kg) given on eight occasions at an interval of 12 h reversed the withdrawal-induced increase in spontaneous motor activity. Cinnarizine in higher doses (20 and 40 mg/kg) was found to be effective in suppressing the behavioural signs but verapamil did not show any protective effect against startle response and irritability. These results suggest that modulation of the calcium influx in the CNS might influence withdrawal.

Smithkline Beecham Prize for Young Psychopharmacologists: A review of the relationship between calcium channels and psychiatric disorders

The symptoms and etiology of most major psychiatric disorders probably represent an underlying disturbance of neurotransmitter function. Understanding the mechanisms which control neurotransmitter function, and in particular neurotransmitter release, is therefore of considerable importance in determining the appropriate pharmacological treatment for these disorders. Calcium entry into neurons triggers the release of a wide range of neurotransmitters and recently our understanding of the mechanisms which control neuronal calcium entry has increased considerably. Neuronal calcium entry occurs through either voltage-sensitive or receptor-operated calcium channels. This article reviews the different subtypes of calcium channel, with particular reference to their structure; drugs which act upon them; and the possible function of the subtypes identified to date. In addition, it reviews the potential role of calcium channel antagonists in the treatment of a wide range of psychiatric disorders, and concludes that these drugs may have an increasing therapeutic role particularly in the treatment of drug dependence, mood disorders and Alzheimer's disease.

Concurrent treatment with verapamil prevents diazepam withdrawal-induced anxiety, in the absence of altered calcium flux in cortical synaptosomes

Rats, chronically treated with diazepam (4 mg/kg/day) for 28 days, displayed increased anxiety when tested in the elevated plus-maze, 42 hr after the last dose. This anxiogenic withdrawal response was entirely prevented by the concurrent administration of the calcium channel antagonist, verapamil. No anxiolytic effect of chronic administration of verapamil was observed in vehicle-treated rats. To investigate the possibility that increased calcium function in nerve terminals might underlie diazepam withdrawal-induced anxiety, the uptake by cortical synaptosomes of 45Ca2+ was studied. Both fast (3-sec) and slow (60-sec) phase uptake were measured. No changes in basal (5 mM), potassium-stimulated (55 mM) or net uptake were observed during either fast or slow phase uptake. It is concluded that increased calcium influx in nerve terminals in the cortex does not underlie the anxiogenic effect of withdrawal of the benzodiazepine but that further studies must be carried out in other regions of the brain.

Chronic dihydropyridine treatment can reverse the behavioural consequences of and prevent adaptations to, chronic ethanol treatment

1. Chronic treatment with the dihydropyridine calcium channel antagonist, nitrendipine, given concurrently with ethanol, prevented the ethanol withdrawal syndrome in mice, even though the chronic nitrendipine treatment was stopped 24 h or 48 h before the withdrawal testing. 2. This effect was seen in two strains of mice with different methods of ethanol administration. Nitrendipine was effective when given for two weeks but not after only two days' treatment. 3. Two other dihydropyridine calcium antagonists, nimodipine and PN 200-110, given chronically with ethanol, also prevented the withdrawal syndrome. The tests were again made 24 h after the last administration of dihydropyridine. 4. The chronic nitrendipine treatment also prevented the rise in the number of central dihydropyridine binding sites that occurs on chronic ethanol administration. 5. Chronic administration of nitrendipine alone did not cause any withdrawal behaviour. 6. Chronic nitrendipine treatment did not affect the seizure threshold to bicuculline in mice that were not given ethanol. 7. Whole brain concentration measurements showed that the effects were not due to residual nitrendipine in the CNS at the time of withdrawal testing or to differences in central ethanol concentrations during the treatment. 8. It is suggested that the results provide evidence for a functional role for dihydropyridine-sensitive calcium channels in ethanol dependence.

A calcium channel antagonist stereoselectively decreases ethanol withdrawal hyperexcitability but not that due to bicuculline, in hippocampal slices

1. Extracellular recordings were made from CA1 area of isolated hippocampal slices of the mouse after chronic ethanol administration in vivo, with orthodromic stimulation of the Schaffer collateral/commissural fibres. 2. The (+)-isomer of the calcium channel antagonist PN 200-110 (isradipine) significantly decreased all the recorded signs of hyperexcitability in the slices during ethanol withdrawal. These included increased paired pulse potentiation and decreases in the thresholds for elicitation of single and multiple population spikes. 3. The (-)-isomer of PN 200-100 did not affect ethanol withdrawal hyperexcitability in the slices. 4. Neither isomer of PN 200-110 affected the field potentials in slices from control animals. 5. The gamma-aminobutyric acid (GABA) antagonist, bicuculline, lowered thresholds for eliciting population spikes in hippocampal slices from untreated animals. The active, (+)-isomer of PN 200-110 did not affect this action of bicuculline in hippocampal slices from untreated animals. 6. The stereoisomerism of the action of PN 200-110 on ethanol withdrawal hyperexcitability in the hippocampal slice was therefore the same as that seen in blockade of calcium channels. The results suggested that ethanol withdrawal hyperexcitability recorded in the isolated hippocampal slice involved increased activity of voltage-sensitive calcium channels.

The role of neuronal calcium channels in dependence on ethanol and other sedatives/hypnotics

This review discusses the importance of neuronal calcium currents in dependence on ethanol, barbiturates, benzodiazepines and opiates. The main sections describe the actions of ethanol on control of intracellular calcium and on calcium and calcium-dependent conductance mechanisms. In particular, the effects of both acute and chronic ethanol treatment on dihydropyridine-sensitive, voltage-dependent, calcium channels are described. The later sections cover the effects of barbiturates, benzodiazepines and opiates on these systems. The conclusions suggest that dihydropyridine calcium channel antagonists may offer a new therapeutic approach to the treatment of ethanol and opiate dependence.