The behavioral effects of the calcium agonist Bay K 8644 in the mouse: antagonism by the calcium antagonist nifedipine

L-methionine and the L-type Ca2+ channel agonist BAY K 8644 collaboratively contribute to the reduction of depressive-like behavior in mice

The L-type Ca2+ channel (LTCC, also known as Cav1,2) is involved in the regulation of key neuronal functions, such as dendritic information integration, cell survival, and neuronal gene expression. Clinical studies have shown an association between L-type calcium channels and the onset of depression, although the precise mechanisms remain unclear. The development of depression results from a combination of environmental and genetic factors. DNA methylation, a significant epigenetic modification, plays a regulatory role in the pathogenesis of psychiatric disorders such as posttraumatic stress disorder (PTSD), depression, and autism. In our study, we observed reduced Dnmt3a expression levels in the hippocampal DG region of mice with LPS-induced depression compared to control mice. The antidepressant Venlafaxine was able to increase Dnmt3a expression levels. Conversely, Bay K 8644, an agonist of the L-type Ca2+ channel, partially ameliorated depression-like behaviors but did not elevate Dnmt3a expression levels. Furthermore, when we manipulated DNA methylation levels during Bay K 8644 intervention in depression-like models, we found that enhancing the expression of Dnmt3a could improve LPS-induced depression/anxiety-like behaviors, while inhibiting DNA methylation exacerbated anxiety-like behaviors, the combined use of BAY K 8644 and L-methionine can better improve depressive-like behavior. These findings indicate that DNA methylation plays a role in the regulation of depression-like behaviors by the L-type Ca2+ channel, and further research is needed to elucidate the interactions between DNA methylation and L-type Ca2+ channels.

Platelet extracellular vesicles preserve lymphatic endothelial cell integrity and enhance lymphatic vessel function

Lymphatic vessels are essential for preventing the accumulation of harmful components within peripheral tissues, including the artery wall. Various endogenous mechanisms maintain adequate lymphatic function throughout life, with platelets being essential for preserving lymphatic vessel integrity. However, since lymph lacks platelets, their impact on the lymphatic system has long been viewed as restricted to areas where lymphatics intersect with blood vessels. Nevertheless, platelets can also exert long range effects through the release of extracellular vesicles (EVs) upon activation. We observed that platelet EVs (PEVs) are present in lymph, a compartment to which they could transfer regulatory effects of platelets. Here, we report that PEVs in lymph exhibit a distinct signature enabling them to interact with lymphatic endothelial cells (LECs). In vitro experiments show that the internalization of PEVs by LECs maintains their functional integrity. Treatment with PEVs improves lymphatic contraction capacity in atherosclerosis-prone mice. We suggest that boosting lymphatic pumping with exogenous PEVs offers a novel therapeutic approach for chronic inflammatory diseases characterized by defective lymphatics.

Lymphatic-draining nanoparticles deliver Bay K8644 payload to lymphatic vessels and enhance their pumping function

Dysfunction of collecting lymphatic vessel pumping is associated with an array of pathologies. S-(-)-Bay K8644 (BayK), a small-molecule agonist of L-type calcium channels, improves vessel contractility ex vivo but has been left unexplored in vivo because of poor lymphatic access and risk of deleterious off-target effects. When formulated within lymph-draining nanoparticles (NPs), BayK acutely improved lymphatic vessel function, effects not seen from treatment with BayK in its free form. By preventing rapid drug access to the circulation, NP formulation also reduced BayK's dose-limiting side effects. When applied to a mouse model of lymphedema, treatment with BayK formulated in lymph-draining NPs, but not free BayK, improved pumping pressure generated by intact lymphatic vessels and tissue remodeling associated with the pathology. This work reveals the utility of a lymph-targeting NP platform to pharmacologically enhance lymphatic pumping in vivo and highlights a promising approach to treating lymphatic dysfunction.

Glucose regulates cyclin D2 expression in quiescent and replicating pancreatic β-cells through glycolysis and calcium channels

Understanding the molecular triggers of pancreatic β-cell proliferation may facilitate the development of regenerative therapies for diabetes. Genetic studies have demonstrated an important role for cyclin D2 in β-cell proliferation and mass homeostasis, but its specific function in β-cell division and mechanism of regulation remain unclear. Here, we report that cyclin D2 is present at high levels in the nucleus of quiescent β-cells in vivo. The major regulator of cyclin D2 expression is glucose, acting via glycolysis and calcium channels in the β-cell to control cyclin D2 mRNA levels. Furthermore, cyclin D2 mRNA is down-regulated during S-G(2)-M phases of each β-cell division, via a mechanism that is also affected by glucose metabolism. Thus, glucose metabolism maintains high levels of nuclear cyclin D2 in quiescent β-cells and modulates the down-regulation of cyclin D2 in replicating β-cells. These data challenge the standard model for regulation of cyclin D2 during the cell division cycle and suggest cyclin D2 as a molecular link between glucose levels and β-cell replication.

Voltage-dependent calcium channel and NMDA receptor antagonists augment anticonvulsant effects of lithium chloride on pentylenetetrazole-induced clonic seizures in mice

Although lithium is still a mainstay in the treatment of bipolar disorder, its underlying mechanisms of action have not been completely elucidated. Several studies have shown that lithium can also modulate seizure susceptibility in a variety of models. In the present study, using a model of clonic seizures induced with pentylenetetrazole (PTZ) in male Swiss mice, we investigated whether there is any interaction between lithium and either calcium channel blockers (CCBs: nifedipine, verapamil, and diltiazem) or N-methyl-D-aspartate (NMDA) receptor antagonists (ketamine and MK-801) in modulating seizure threshold. Acute lithium administration (5-100mg/kg, ip) significantly (P<0.01) increased seizure threshold. CCBs and NMDA receptor antagonists also exerted dose-dependent anticonvulsant effects on PTZ-induced seizures. Noneffective doses of CCBs (5mg/kg, ip), when combined with a noneffective dose of lithium (5mg/kg, ip), exerted significant anticonvulsant effects. Moreover, co-administration of a noneffective dose of either MK-801 (0.05mg/kg, ip) or ketamine (5mg/kg, ip) with a noneffective dose of lithium (5mg/kg, ip) significantly increased seizure threshold. Our findings demonstrate that lithium increases the clonic seizure threshold induced by PTZ in mice and interacts with either CCBs or NMDA receptor antagonists in exerting this effect, suggesting a role for Ca(2+) signaling in the anticonvulsant effects of lithium in the PTZ model of clonic seizures in mice.

Brain activation pattern induced by stimulation of L-type Ca2+-channels: Contribution of CaV1.3 and CaV1.2 isoforms

Ca(V)1.2 and Ca(V)1.3, are the main dihydropyridine-sensitive L-type calcium channel isoforms in the brain. To reveal the contribution of each isoform to the neuronal activation pattern elicited by the dihydropyridine L-type calcium channel activator BayK 8644, we utilized Fos expression as a marker of neuronal activation in mutant mice (Ca(V)1.2(DHP-/-) mice) expressing dihydropyridine-insensitive Ca(V)1.2 L-type calcium channels. BayK 8644-treated wildtype mice displayed intense and widespread Fos expression throughout the neuroaxis in 77 of 80 brain regions quantified. The Fos response in Ca(V)1.2(DHP-/-) mice was greatly attenuated or absent in most of these areas, suggesting that a major part of the widespread Fos induction including most cortical areas was mediated by Ca(V)1.2 L-type calcium channels. BayK 8644-induced Fos expression in Ca(V)1.2(DHP-/-) mice indicating predominantly Ca(V)1.3 L-type calcium channel-mediated activation was noted in more restricted neuronal populations (20 of 80), in particular in the central amygdala, the bed nucleus of the stria terminalis, paraventricular hypothalamic nucleus, lateral preoptic area, locus coeruleus, lateral parabrachial nucleus, central nucleus of the inferior colliculus, and nucleus of the solitary tract. Our data indicate that selective stimulation of other than Ca(V)1.2 L-type calcium channels, mostly Ca(V)1.3, causes neuronal activation in a specific set of mainly limbic, hypothalamic and brainstem areas, which are associated with functions including integration of emotion-related behavior. Hence, selective modulation of Ca(V)1.3 L-type calcium channels could represent a novel (pharmacotherapeutic) tool to influence these CNS functions.

Design and synthesis of alkyl 7,7-dihalo-3-methyl-5-(nitrophenyl)-2-azabicyclo[4.1.0]hept-3-ene-4-carboxylates with calcium channel antagonist activity

A group of alkyl 7,7-dihalo-3-methyl-5-(2- or 3-nitrophenyl)-2-azabicyclo[4.1.0]hept-3-ene-4-carboxylates were prepared by reaction of dihalocarbenes (:CX(2), X=Br, Cl) with alkyl 2-methyl-4-(2- or 3-nitrophenyl)-1,4-dihydropyridine-3-carboxylates. In vitro calcium channel antagonist activities were determined using a guinea pig ileum longitudinal smooth muscle assay. The title compounds exhibited weaker CC antagonist activity (10(-5) to 10(-7)M range) than the reference drug nifedipine (1.4 x 10(-8)M). Structure-activity relationships showed that the position (ortho or meta) of the nitro-substituent on the C-5 phenyl ring, the size (van der Waal's radius for Br and Cl are 1.95 and 1.80A, respectively) and/or electronegativity (Cl>Br) of the C-7 geminal halogen atoms do not appear to have a significant effect on CC antagonist activity. In contrast, the effect of the alkyl ester substituent was more pronounced where compounds having a Me or Et alkyl ester group showed superior potency (IC(50) in the 10(-7)M range) relative to the reference drug nifedipine (IC(50)=1.40 x 10(-8)M). Replacement of a 2-methyl-3-methoxycarbonylvinyl moiety present in nifedipine by a bioisosteric geminal-dihalocyclopropyl moiety provided a novel class of calcium channel antagonists that do not exhibit any inotropic effect on guinea pig atria.

Design and synthesis of methyl 2-methyl-7,7-dihalo-5-phenyl-2-azabicyclo[4.1.0]hept-3-ene-4-carboxylates with calcium channel antagonist activity

A group of methyl 2-methyl-7,7-dihalo-5-(substituted-phenyl)-2-azabicyclo[4.1.0]hept-3-ene-4-carboxylates were prepared by reaction of dihalocarbenes (:CX2, X = Br, Cl) with methyl 1-methyl-4-(substituted-phenyl)-1,4-dihydropyridine-3-carboxylates. In vitro calcium channel antagonist activities were determined using a guinea pig ileum longitudinal smooth muscle assay. The title compounds exhibited weaker CC antagonist activity (10(-5)-10(-6)M range) than the reference drug nifedipine (1.4 x 10(-8)M). Structure-activity relationship studies showed that the position of a nitro substituent on the C-5 phenyl ring where the relative potency order was ortho > meta > para, and the size and/or electronegativity of the C-7 geminal-dihalo substituents (Br > Cl), were determinants of calcium channel antagonist activity. This class of compounds did not exhibit any inotropic effect on guinea pig left atria. A dihalocyclopropyl moiety is a potential bioisostere for the 2-methyl-3-methoxycarbonylvinyl moiety present in the calcium channel antagonist nifedipine.

Niguldipine impairs the protective activity of carbamazepine and phenobarbital in amygdala-kindled seizures in rats

There is evidence that some calcium (Ca(2+)) channel inhibitors enhance the protective activity of antiepileptic drugs. Since clinical trials have not provided consistent data on this issue, the objective of this study was to evaluate the interaction of a dihydropyridine, niguldipine, with conventional antiepileptics in amygdala-kindled rats. Niguldipine (at 7.5 but not at 5 mg/kg) displayed a significant anticonvulsant effect, as regards seizure and afterdischarge durations in amygdala-kindled convulsions in rats, a model of complex partial seizures. No protective effect was observed when niguldipine (5 mg/kg) was combined with antiepileptics at subeffective doses, i.e. valproate (75 mg/kg), diphenylhydantoin (40 mg/kg), or clonazepam (0.003 mg/kg). Unexpectedly, the combined treatment of niguldipine (5 mg/kg) with carbamazepine (20 mg/kg) or phenobarbital (20 mg/kg) resulted in a proconvulsive action. BAY k-8644 (an L-type Ca(2+) channel activator) did not modify the protective activity of niguldipine (7.5 mg/kg) or the opposite action of this dihydropyridine (5 mg/kg) in combinations with carbamazepine or phenobarbital. A pharmacokinetic interaction is not probable since niguldipine did not affect the free plasma levels of the antiepileptics. These data indicate that the opposite actions of niguldipine alone or combined with carbamazepine (or phenobarbital) were not associated with Ca(2+) channel blockade. The present results may argue against the use of niguldipine as an adjuvant antiepileptic or for cardiovascular reasons in patients with complex partial seizures.

Effects of dextromethorphan on the seizures induced by kainate and the calcium channel agonist BAY k-8644: comparison with the effects of dextrorphan

BAY k-8644 (an L-type Ca(2+) channel agonist of the dihydropyridine class) is recognized as a potent convulsant agent. In this study, we used BAY k-8644 to explore the effects of dextromethorphan (DM) and its major metabolite, dextrorphan (DX), on the (pro)convulsant activity regulated by calcium channels. BAY k-8644 (2 mg/kg, s.c) potentiated seizures induced in rats by kainic acid (KA) (10 mg/kg, i.p.). DM appears more efficacious than DX in attenuation of KA-induced seizures. The anticonvulsant effect of a low dose (12.5 mg/kg, s.c.) of DM was reversed by BAY k-8644 (2 mg/kg) challenge. In contrast, BAY k-8644 (1 or 2 mg/kg) did not significantly affect an anticonvulsant effect from a higher dose (25 mg/kg) of either DM or DX. Intracerebroventricular injection of BAY k-8644 (37.5 microg) significantly induced seizures in mice. DM (12.5 or 25 mg/kg) pretreatment more significantly attenuated seizures evoked by BAY k-8644 than did DX (12.5 or 25 mg/kg). Furthermore, seizure activity induced by KA or BAY k-8644 was consistent with respective activator protein-1 DNA binding activity of the hippocampus. Therefore, our results suggest that the anticonvulsant effects of the morphinans involve, at least in part, the L-type calcium channel. They also suggest that DM is a more potent anticonvulsant than DX in the KA and BAY k-8644 seizure models.

Amlodipine enhances the activity of antiepileptic drugs against pentylenetetrazole-induced seizures

Amlodipine (AML), which belongs to the 1,4-dihydropyridine calcium channel antagonists, possesses pharmacological and pharmacokinetic profile that distinguishes it from other agents of this class. Pentylenetetrazole (PTZ)-induced clonic and tonic convulsions in mice were significantly reduced by administration of AML at 10 mg/kg. At this dose AML remained without influence upon the plasma level of PTZ. The ED50 value of AML against clonic seizures induced by PTZ was 5.4 mg/kg. This calcium channel antagonist (at 2.5 mg/kg) combined with ethosuximide (ETX), valproate magnesium (VPA) or phenobarbital (PB) significantly reduced their ED50 values against clonic phase of PTZ-induced seizures. AML administered alone or in combination with antiepileptic drugs (AEDs) worsened the motor performance of mice in the chimney test. However, these treatments remained without significant influence on the retention time in the passive avoidance test. Plasma levels of antiepileptics remained unchanged in the presence of AML. The results indicate that AML does not seem a good candidate for a combination therapy in epileptic patients because of its adverse potential.

The differential effects of calcium channel blockers in the behavioural despair test in mice

Various studies have shown that calcium channel blockers (CCB) affect the release of central neurotransmitters including noradrenaline (NA) and 5-hydroxytryptamine (5-HT), which are involved in depression. The behavioural despair test was used to investigate the effect of CCB on depression. The mice were treated acutely with CCB. Verapamil (5, 10, 20, and 40 mgkg(-1), i.p.) and diltiazem (10, 20, and 40 mgkg(-1), i.p.) produced a dose-dependent increase in immobility time, indicating the facilitation of depression, while nifedipine (12.5, 25, and 50 mgkg(-1), i.p.) significantly decreased the immobility time, indicating an antidepressant activity. Verapamil ( 40 mgkg(-1), i.p.) and diltiazem ( 40 mgkg(-1), i.p.) blocked the antidepressant effect of desipramine, clomipramine, mianserin, and tranylcypromine, indicating the involvement of various mechanisms in the facilitatory effect of verapamil and diltiazem on depression. The antidepressant effect of nifedipine may be attributed to the blockade of presynaptic alpha -2-receptors (autoreceptors), as nifedipine blocked the clonidine-induced facilitation of depression.

Clonidine modulates BAY K 8644-induced rat behavior and neurotransmitter changes in the brain

BAY K 8644 (methyl-1,4-dihydro-2, 6-dimethyl-3-nitro-4[2-trifluoromethyl-phenyl]-pyridine-5-carboxylate), an activator of dihydropyridine-sensitive Ca(2+) channels, injected in rats [2 mg/kg intraperitoneally (i.p.)], induces behavioral changes including ataxia, increased sensitivity to auditory stimulation, stiff tail, arched back, limb tonus and clonus, and rolling over. Neurochemical changes in the brain 45 min after application of 2 mg/kg were characterized by a significant decrease of noradrenaline in the amygdala (-27.8%, P<0.02) and piriform cortex (-16.3%, P<0.02). No significant changes of catecholamines were found in the hippocampal subregions CA1, CA3 and dentate gyrus or in the septum as compared to controls. The dopamine metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the amygdala were elevated by 60% (P<0.02) and 66.7% (P<0.02), respectively. In the septum, a 52.6% (P<0.02) increase of HVA was observed. Analysis of amino acids revealed a marked increase of gamma-aminobutyric acid (GABA) content (+50.4%, P<0.001) in the septum. Pretreatment of the rats with the alpha(2)-adrenoceptor agonist, clonidine (0.1 mg/kg i.p.), 30 min before BAY K 8644 (2 mg/kg i.p.) injection completely abolished the behavioral and neurochemical changes. The data suggest that the Ca(2+)-dependent neurotransmitter release provoked by BAY K 8644 can be modulated by stimulation of presynaptic alpha(2)-adrenoceptors. The effect of clonidine on the GABAergic system may represent an important mechanism involved in the prevention of BAY K 8644-induced behavior.

Calcium channel agonists and dystonia in the mouse

Systemic administration of the L-type calcium channel agonists +/-Bay K 8644 or FPL 64176 causes a characteristic pattern of motor dysfunction in normal C57BL/6J mice that resembles generalized dystonia. There is no associated change in the electroencephalogram, confirming that the motor disorder does not reflect epileptic seizures. However, the electromyogram reveals an increase in baseline motor unit activity with prolonged phasic discharges consistent with dystonia. The duration and severity of dystonia is dependent on the dose administered and the age of the animal at testing. The effects are transient, with the return of normal motor behavior 1-4 hours after treatment. Similar effects can be provoked by intracerebral administration of small amounts of the drugs, indicating a centrally mediated response. Dystonia can be attenuated by co-administration of dihydropyridine L-type calcium channel antagonists (nifedipine, nimodipine, and nitrendipine) but not by non-dihydropyridine antagonists (diltiazem, verapamil, and flunarizine). These results implicate abnormal function of L-type calcium channels in the expression of dystonia in this model.

Presynaptic L-type Ca(2)+ channels on excessive dopamine release from rat caudate putamen

We investigated by means of behavioral and neurochemical studies the role of the nerve terminal L-type voltage sensitive Ca(2)+ channel on dopamine (DA) release. Microinjection of Bay K 8644 (BAYK), an L-type Ca(2)+ channel stimulant, into the rat caudate putamen increased locomotor activity and rearing behavior in a dose-dependent manner, whereas injections into the amygdala had no effect. DA receptor antagonists significantly blocked BAYK-induced hyperactivity. Significant increases of extracellular DA levels were detected by microdialysis 20 min after BAYK administration into caudate putamen and then declined. This increase was influenced by tetrodotoxin, an axonal Na(+) channel blocker. Pretreatment with nimodipine and nicardipine, but not nifedipine, which are 1, 4-dihydropyridine L-type Ca(2)+ channel antagonists, administered into the caudate putamen significantly blocked BAYK-induced hyperactivity and DA efflux. These results indicate that the extraordinary DA release in the caudate putamen was mediated by extreme stimulation of the nicardipine and nimodipine-sensitive L-type Ca(2)+ channel present in the nerve terminal of striatal DA neurons.

Calcium channel activation and self-biting in mice

The L type calcium channel agonist (+/-)Bay K 8644 has been reported to cause characteristic motor abnormalities in adult mice. The current study shows that administration of this drug can also cause the unusual phenomenon of self-injurious biting, particularly when given to young mice. Self-biting is provoked by injecting small quantities of (+/-)Bay K 8644 directly into the lateral ventricle of the brain, suggesting a central effect of the drug. Similar behaviors can be provoked by administration of another L type calcium channel agonist, FPL 64176. The self-biting provoked by (+/-)Bay K 8644 can be inhibited by pretreating the mice with dihydropyridine L type calcium channel antagonists such as nifedipine, nimodipine, or nitrendipine. However, self-biting is not inhibited by nondihydropyridine antagonists including diltiazem, flunarizine, or verapamil. The known actions of (+/-)Bay K 8644 as an L type calcium channel agonist, the reproduction of similar behavior with another L type calcium channel agonist, and the protection afforded by certain L type calcium channel antagonists implicate calcium channels in the mediation of the self-biting behavior. This phenomenon provides a model for studying the neurobiology of this unusual behavior.

Discriminative and affective stimulus effects of dihydropyridine calcium channel modulators: relationship to antialcohol effects

Voltage-operated calcium channels (VOCCs) have been implicated in alcoholism. Thus, dihydropyridine (DHP) VOCC antagonists, such as nimodipine, reduce ethanol (EtOH) intake and preference in a variety of animal models of alcoholism. Paradoxically, the DHP VOCC agonist BAY k 8644 also demonstrates antialcohol effects in such models. The antialcohol effects of BAY k 8644 are stereoselective [the "agonistic" (-)-enantiomer being more potent than the "antagonistic" (+)-enantiomer], and are not blocked by pretreatment with nimodipine. The present review summarizes studies on the effects of DHPs in drug discrimination (DD), conditioned taste aversion (CTA), and conditioned place preference (CPP) paradigms, and discusses the possibility that the apparent antialcohol effect of these compounds is related to their discriminative and/or affective stimulus effects. In rats trained to discriminate nimodipine from vehicle, (-)-BAY k 8644 completely generalizes to the nimodipine cue; whereas, in rats trained to discriminate (-)-BAY k 8644, nimodipine completely generalizes to, and is unable to block, the (-)-BAY k 8644 cue. The same stereoselectivity is obtained for BAY k 8644 in DD paradigms and models of alcoholism. The apparent similarity of these profiles of activity suggests that a common neurobiological mechanism underlies the discriminative stimulus and antialcohol effects of DHPs. It appears unlikely, however, that the antialcohol effects of DHPs are based on substitution for, or blockade of, the EtOH cue, as these compounds were not found to generalize to, or block, the EtOH cue. Comparison of the effects of DHPs in CTA and CPP paradigms suggests that the affective stimulus effects of these compounds are dissimilar, and that the mechanism underlying the latter effects is probably not related to the mechanism underlying the antialcohol effects of DHP VOCC modulators.

"Atypical" neuromodulatory profile of glutapyrone, a representative of a novel 'class' of amino acid-containing dipeptide-mimicking 1,4-dihydropyridine (DHP) compounds: in vitro and in vivo studies

Glutapyrone, a disodium salt of 2-(2,6-dimethyl-3,5-diethoxycarbonyl-1,4-dihydropyridine-4-carboxamido)- glutaric acid, is a representative of a novel 'class' of amino acid-containing 1,4-dihydropyridine (DHP) compounds developed at the Latvian Institute of Organic Synthesis, Riga, Latvia. Conceptually, the glutapyrone molecule can be regarded as a dipeptide-mimicking structure formed by the "free" amino acid (glutamate) moiety and "crypto" (built into the DHP cycle) amino acid ("GABA") elements. Both of these amino acids are joined by the peptide bond. This compound unlike classical DHPs lacks calcium antagonistic or agonistic properties. Our previous studies revealed a profound and long-term anticonvulsant, stress-protective and neurodeficit-preventive activities of glutapyrone. In view of structural properties the role of glutamatergic mechanisms in the mediation of central effects of glutapyrone was considered. In the present study glutapyrone at the concentration range of 1 microM(-1) mM failed to effect both NMDA ([3H]TCP) and non-NMDA ([3H]KA and [3H]AMPA) receptor ligand binding in the rat cortical membranes in vitro. The compound markedly enhanced motor hyperactivity induced by the NMDA antagonist PCP and the dopamine releasing compound D-amphetamine in the rats. Glutapyrone displayed activity in a variety of animal models relevant for affective/depressive disorders in humans i.e. reserpine-induced ptosis and hypothermia, forced swimming test and open field test. These data indicate that the unusually "broad" pharmacological spectrum of glutapyrone might involve concomitant actions on multiple neurotransmitter systems, particularly, GABA-ergic and the catecholamines. It is discussed whether these functional properties are secondary to action on intracellular events, predominantly, G protein-related since glutapyrone appears to lack direct interactions with a number of receptors including ionotropic glutamate and GABA(A)/Bzd receptors.

Role of nerve terminal L-type Ca2+ channel in the brain

The microinjection of Bay K 8644 (BAYK), an L-type Ca2+ channel stimulant, into rat caudate putamen dose-dependently potentiated locomotor activity. DA receptor antagonists significantly blocked BAYK-induced hyperactivity. Striatal DA levels as detected by microdialysis increased 140 fold above steady state levels 20 min after BAYK administration into caudate putamen. This increase was not influenced by a Na+ channel blocker. Pretreatment with 1,4-dihydropyridine (DHP) L-type Ca2+ channel antagonists, but not nifedipine, into caudate putamen significantly blocked the BAYK induced-hyperactivity and DA efflux. The lowest level of intracellular DA detected by fluorohistochemistry coincided with the highest level of extracellular DA. These results indicate that the extraordinary DA release is regulated by a subtype of L-type Ca2+ channel that is present in the nerve terminal.

Effects of dihydropyridine Ca2+ channel blockers on the discriminative stimulus and the motor impairing effects of (+/-)-Bay K 8644

Functional interactions between the dihydropyridine Ca2+ channel activator, (+/-)-Bay K 8644 (methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethyphenyl )-pyridine-5-carboxylate), and several dihydropyridine L-type Ca2+ channel blockers were investigated on rotarod performance in mice and in rats trained to discriminate between (+/-)Bay K 8644 and saline. When administered alone, (+/-)-Bay K 8644 produced dose-dependent impairments of rotarod activity with an ED50 of 1.3 mg/kg. Pretreatment with nifedipine (10-30 mg/kg) produced dose-dependent rightward shifts of the (+/-)-Bay K 8644 dose-response curve. In contrast, pretreatment with several other dihydropyridine L-type Ca2+ channel blockers, including nicardipine, nimodipine, isradipine and nitrendipine, did not modify the (+/-)-Bay K 8644 dose-effect function. Rats learned to discriminate between (+/-)-Bay K 8644 (0.5 mg/kg) and saline in an average of 65 training sessions. In substitution tests, the Ca2+ channel activator engendered dose-related increases in the percentage of rats selecting the drug-associated lever with an ED50 of 0.19 mg/kg. Pretreatment with nifedipine (10 mg/kg) produced a rightward shift of the (+/-)-Bay K 8644 dose-response function. Pretreatment with nicardipine (2.5 mg/kg) only partially antagonised the training dose of (+/-)-Bay K 8644 whereas nimodipine (0.6-10 mg/kg) did not affect the (+/-)-Bay K 8644 discriminative stimulus. The results of the present study show that the behavioural effects of the dihydropyridine Ca2+ channel activator are differentially modified by dihydropyridine L-type Ca2+ channel blockers. These results may suggest that dihydropyridine blockers possess different intrinsic activities or act at different binding sites.

Evidence for antiaggressive property of some calcium channel blockers

The effect of calcium channel blockers on foot shock induced (aggression (FSA) were studied in mice. Verapamil, (10, 20 and 40 mg kg-1 i.p.) diltiazem (20 and 40 mg kg-1 i.p.) and nifedipine (25 and 50 mg kg-1 i.p.) significantly reduced fighting episodes. Diltiazem and nifedipine blocked the amphetamine induced facilitation of FSA, while verapamil blocked both amphetamine as well as physostigmine induced facilitation of FSA. These findings suggest that calcium channel blockers possess antiaggressive activity, which may be attributed to decrease in central dopaminergic and/or cholinergic mechanism.

Ca2+ channel blockade and the antielectroshock activity of NMDA receptor antagonists, CGP 40116 and CGP 43487, in mice

Nicardipine, nifedipine and flunarizine showed anticonvulsive activity (reflected by significant elevations of the seizure threshold for tonic hindlimb extension) in doses of 20, 20 and 15 mg/kg, respectively. In combination studies, CGP 40116 [D-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid] or its methyl ester derivative (CGP 43487) was administered in a constant dose of 0.25 and 3.5 mg/kg, respectively. At these doses both competitive NMDA receptor antagonists were able to elevate significantly the convulsive threshold. Nicardipine, nifedipine, and flunarizine were administered at maximal doses (or lower) not affecting the convulsive threshold (15, 15 and 10 mg/kg, respectively). The protective activity of CGP 40116 and CGP 43487 was dose dependently potentiated by all three Ca2+ channel inhibitors. The combined treatment caused motor impairments (evaluated in the chimney test) and long-term memory deficits (measured in the passive avoidance task) similar to these produced by CGP 40116 or CGP 43487 alone. Our results indicate that nicardipine, nifedipine and flunarizine significantly potentiate the protective activity, but not the adverse effects, of CGP 40116 and CGP 43487 in mice.

Behavioral and analgesic effects induced by administration of nifedipine and nimodipine

Evidence exists that calcium antagonists can have effects on neural function. The aim of this work is to analyze the effect of two dihydropyridines, nifedipine and nimodipine, administered for 11 days on the behavior and pain sensitivity of rats. Nociception was tested using the tail electric stimulation test, and behavior parameters using a holeboard. Our results show that chronic administration of nifedipine or nimodipine induces analgesia that can be evaluated by tail withdrawal. However, neither the vocalization nor the vocalization after discharge were modified, so the analgesia may be mediated by spinal mechanisms. Rats treated with nifedipine or nimodipine exhibited a dose-dependent tendency to avoid the center of the field without modification of other parameters, suggesting an increased emotivity in the rats. This conclusion is supported by the fact that anxiogenic or anxiolytic drugs modify the pattern of locomotion without significant changes in other parameters related with the motility. The results from this study suggest the view of a complex mechanism of action underlying nifedipine- and nimodipine-mediated behavioral effects.

Drugs acting on calcium channels modulate the diuretic and micturition effects of dexmedetomidine in rats

The purpose of this study was to assess the effects of calcium channel antagonist, verapamil, and agonist, Bay K 8644, on the alpha 2-adrenoceptor agonist, dexmedetomidine-induced (300 micrograms kg-1 subcutaneously) diuresis and overflow incontinence, in rats. Ultrasonography study revealed that verapamil (2.5 mg kg-1 subcutaneously) or Bay K 8644 (0.5 mg kg-1 intraperitoneally) coadministrations delayed dexmedetomidine-induced bladder filling and significantly prolonged the latency of urination (P < 0.05). Bay K 8644 decreased relative bladder volume and stopped continuous urination from dexmedetomidine, whereas verapamil had neither effect. However, none of the drugs eliminated the overflow incontinence. Dexmedetomidine alone increased the hourly and total (for 4 hours) urine volume. Bay K 8644 (0.5 or 1 mg kg-1) dose-dependently decreased the diuretic effect of dexmedetomidine (P < 0.01). Verapamil (0.5, 1 or 2.5 mg kg-1) dose-dependently decreased urine volume in the first hour (P < 0.01), and thereafter potentiated the diuretic effect of dexmedetomidine. Simultaneous determinations of mean arterial blood pressure (MAP) and urine output after dexmedetomidine and the highest dose of verapamil coadministration demonstrated a significant correlation between these variables (r = 0.537; P < 0.001). MAP of 100 mmHg or less was associated with a urine output significantly lower (P < 0.001) than that at higher pressures. Thus, hypotension during the first hour after dexmedetomidine-verapamil may explain the transient reduction in urination during this period. We conclude that modulation of calcium channel affects dexmedetomidine actions on both urine formation and micturition. Since both alpha 2-adrenoceptor agonists and calcium channel blockers have frequently been used for antihypertensive therapy and as adjuvant drugs during anesthesia, these interactions may have some practical importance.

Antidystonic effects of L-type Ca2+ channel antagonists in a hamster model of idiopathic dystonia

The effects of selective L-type Ca2+ channel antagonists on severity of dystonia were investigated in a mutant hamster model of idiopathic generalized dystonia. Nimodipine and diltiazem significantly decreased the severity of dystonia. Nimodipine was more potent in this respect and did not cause any behavioral side effects. The present data therefore suggest that Ca2+ channel antagonists could be useful in the treatment of idiopathic dystonia. The antidystonic effect of diltiazem and nimodipine may be based on their antidopaminergic action. However, the lack of significant effects of the L-type channel agonist (+/-)-BAY k-8644 (1-5 mg/kg; methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoro-methylphenyl) -pyridine-5-carboxylate)) on severity of dystonia may indicate that voltage-gated Ca2+ channels are not critically involved in the pathophysiology of dystonia in mutant hamsters.

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)

The Ca2+ channel agonist Bay K 8644 induces central respiratory depression in cats, an effect blocked by naloxone

We analyzed the respiratory effects induced by the Ca2+ channel agonist Bay K 8644 and its enantiomers, Bay R 5417 and Bay R 4407, applied to the ventral medullary surface of cats. Bay K 8644 (10 to 100 micrograms) and Bay R 5417 (50 to 200 micrograms) elicited a dose-dependent respiratory depression. Naloxone (0.1 mg/kg), but not D-naloxone, reversed these effects, indicating that an endogenous opioid mechanism was involved. Bay R 4407 (100 micrograms) was ineffective. The respiratory depressant effects induced by Bay K 8644 and its (-) enantiomer were a consequence of their agonist properties on the L-type Ca2+ channel, since (1) the activity of Bay K 8644 was stereospecific, and (2) nimodipine prevented the effect. We suggest that potent activation of Ca2+ channels or other mechanisms by high doses of Ca2+ agonists elicits the release of endogenous opioid peptides in medullary respiration-related structures.

Anticonvulsant properties of calcium channel blockers in mice: N-methyl-D-,L-aspartate- and Bay K 8644-induced convulsions are potently blocked by the dihydropyridines

Ten calcium channel blockers were evaluated in mice after intraperitoneal (i.p.) administration for prevention of seizures induced by various convulsants. The dihydropyridines (class II calcium antagonists, i.e., nisoldipine, nitrendipine, nicardipine, nifedipine, and nimodipine) selectively prevented seizures elicited by administration of pentylenetetrazol (PTZ), N-methyl-D,L-aspartate (NMDLA) and the dihydropyridine calcium channel agonist BAY K 8644. With regard to prevention of NMDLA-induced seizures and the subsequent mortality, these compounds were similar in potency to the noncompetitive NMDA receptor antagonist MK801. Unlike MK801 (IC50 = 0.014 microM), the dihydropyridines did not inhibit in vitro binding of MK801 to synaptic membrane fractions prepared from rat cerebrohippocampal tissue. The dihydropyridines did not influence seizures elicited by maximal electroshock (MES). Flunarizine (diphenyl-alkylamine, class IV) was selectively active in the MES test, considerably less potent against NMDLA-induced convulsions/mortality, exhibited weak noncompetitive NMDA antagonism in vitro (IC50 = 28 microM), and was inactive in the PTZ and BAY K 8644 testing paradigms. Diltiazem, a class III benzothiazepine, possessed relatively weak broad spectra of activity against MES, PTZ, NMDLA, and BAY K 8644 test situations. It was inactive in vitro as a noncompetitive NMDA antagonist. The class I compound verapamil (phenylalkylamine) displayed only moderate inhibition of NMDLA-evoked seizures/mortality. Prenylamine (class V) was moderately active against convulsions produced by MES and NMDLA while retaining a degree (IC50 = 16 microM) of noncompetitive NMDA antagonism. Lidoflazine (class VI) was inactive in all tests. The Ca2+ channel blockers and MK801 were inconsistent in their ability to prevent bicuculline (BIC)-elicited convulsions.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium agonists and antagonists of the dihydropyridine type: effect on nicotine-induced antinociception and hypomotility

The influence of a calcium agonist (BAYK 8644) and several calcium channel blockers on nicotine-induced antinociception was investigated in mice. The effect of nicotine was sharply increased by BAYK 8644. This potentiation by BAYK 8644 was blocked by pretreating the animals with nifedipine at 2 and 10 mg/kg. The calcium channel antagonists, nifedipine and nimodipine at doses that had no effect on tail-flick time, reduced significantly the antinociception induced by nicotine (1.5 mg/kg, s.c.). However, the effect of verapamil on nicotine was not significant. These results indicate that DHP calcium channels (type L-channel) play a role in some of the pharmacological effects of nicotine, particularly, locomotor activity and antinociception.

Effect of Bay K 8644 on the synthesis and metabolism of dopamine and 5-hydroxytryptamine in various brain areas of the rat

The effects of Bay K 8644 (1, 2 and 4 mg kg-1, i.p.) on the synthesis and metabolism of dopamine and 5-hydroxytryptamine (5-HT) in rat brain after m-hydroxybenzylhydrazine administration were studied. Bay K 8644 (2 and 4 mg kg-1, i.p.) caused an increase in the synthesis of both dopamine in the striatum and 5-HT in the midbrain and striatum, measured as the accumulation of 3,4-dihydroxyphenylalanine (dopa) and 5-hydroxytryptophan, respectively. Moreover, Bay K 8644 at the dose of 4 mg kg-1 increased the turnover of dopamine in the striatum and of 5-HT in midbrain and striatum. These neurochemical changes were antagonized by the calcium channel antagonist nimodipine (10 mg kg-1, i.p.). It is concluded that dihydropyridine receptors may mediate the brain region-specific changes in the dopaminergic and 5-HT-ergic neurotransmission which occur following activation of neuronal calcium channels.

Facilitation of shuttle-box avoidance behaviour in mice treated with nifedipine in combination with amphetamine

The dihydropyridine calcium channel antagonist nifedipine, tested in mice of CD-1, C57BL/6 and DBA/2 strains, at doses of 2.5, 5 and 10 mg/kg IP, had no significant effect on shuttle-box avoidance acquisition. Nifedipine also failed to affect performance retention in CD-1 mice subjected to a one-trial passive avoidance task (step-through). While ineffective alone, nifedipine strongly enhanced the shuttle-box avoidance facilitating action of amphetamine (1 and 2 mg/kg IP) in low performing CD-1 mice. The results indicate that although calcium channel blockers do not affect learning in avoidance paradigms in normal animals, they can interfere with the effects of other centrally acting drugs. Calcium antagonists might interfere with neuronal changes induced by amphetamine, but at present it is difficult to explain the strong avoidance facilitation produced by combinations of nifedipine and amphetamine. A possibility that the action of nifedipine on cerebral circulation is involved in the amphetamine-nifedipine interaction cannot be excluded.

Effects of antiepileptic drugs, calcium channel blockers and other compounds on seizures induced by activation of voltage-dependent L calcium channel in DBA/2 mice

1. The convulsant activity of the calcium voltage L-channel agonist Bay k 8644 was studied in genetically epilepsy prone DBA/2 mice. 2. Seizures were induced by intracerebroventricular injection of Bay k 8644. 3. These seizures were reversed by some calcium channel blockers such as dihydropyridines, some excitatory amino acid antagonists such as 2-amino-7-phosphonoeptanoate and CPPene, 2-chloro-adenosine, some anticonvulsant drugs such as magnesium valproate, diazepam and clonazepam and two kappa opioid agonists (U-50488H and U-54494A). 4. The remaining antiepileptic drugs (carbamazepine, phenytoin, phenobarbital and trimethadione) were ineffective in this respect. Other anticonvulsant compounds such as dizocilpine (MK 801), ketamine and drugs enhancing GABAergic transmission did not significantly affect the clonic phase of the seizures induced by Bay k 8644. 5. These results show that Bay k 8644 seizures are relatively resistant to some anticonvulsant compounds. The role of some neurotransmitters on seizures induced by Bay k 8644 is discussed.

The effects of chronic treatment with the dihydropyridine, Bay K 8644, on hyperexcitability due to ethanol withdrawal, in vivo and in vitro

1. The effects of chronic treatment with the dihydropyridine, Bay K 8644, were studied on the ethanol withdrawal syndrome, in vivo and in vitro. 2. Addition of racemic Bay K 8644 to the drinking mixture, throughout the chronic ethanol treatment, decreased the behavioural excitability seen during ethanol withdrawal in vivo. 3. All the signs of hyperexcitability in field potentials in the isolated hippocampal slice, caused by ethanol withdrawal, were decreased by the chronic administration of Bay K 8644. 4. These effects resembled those previously reported for chronic administration of calcium channel antagonists; racemic Bay K 8644 has both calcium channel activating and antagonist properties. 5. Measurement of brain levels of Bay K 8644 at the end of the chronic treatment showed that the compound reached micromolar concentrations during the treatment, but none could be detected in the tissues at the time of the above measurements. 6. It is possible that the results might be explained by predominance of the calcium channel antagonist properties of this compound, owing to the high central concentrations achieved during the treatment. Tolerance to the calcium channel activating properties of Bay K 8644 may also have occurred during the chronic treatment.

Effects of some calcium antagonists upon the activity of common antiepileptic compounds on sound-induced seizures in DBA/2 mice

1. Flunarizine (2.65 mumol/kg, i.p.) and nimodipine (5.25 mumol/kg, i.p.) potentiated the anticonvulsant properties of phenytoin, phenobarbital and valproate against audiogenic seizures in DBA/2 mice. 2. Diltiazem (5.25 mumol/kg, i.p.) was able to potentiate the antiseizure activity of phenytoin but was not effective against the anticonvulsant action of phenobarbital and valproate. 3. Verapamil (5.25 mumol/kg, i.p.) was unable to potentiate the anticonvulsant properties of all antiepileptic drugs studied. 4. Bay K 8644 (1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluorophenyl)-pyridine- 5-carboxylic acid), a calcium agonist at a dose of 2.65 mumol/kg, i.p., induced a reduction of anticonvulsant potency of phenytoin, phenobarbital and valproate. 5. None of the calcium antagonists used significantly increased the plasma levels of antiepileptic compounds or significantly affected the body temperature changes induced by anticonvulsant drugs. 6. It may be concluded that some calcium antagonists enhance the anticonvulsant properties of some antiepileptic drugs against audiogenic seizures. A pharmacokinetic interaction does not seem responsible for these effects.

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.

Neuropsychopharmacological studies of a Ca2+ channel blocker on the modulation of brain Ca2+ mobilization of spontaneously hypertensive rats under mild stress

The psychotropic effects of a calcium channel blocker (Ca antagonist) were examined in behavioral studies following changes in 45Ca2+ influx in synaptosomal fractions of brain tissues using spontaneously hypertensive rats (SHR). Under a novel circumstance utilizing 85-dB noise, SHR demonstrated hyperactivity and a significant increase in 45Ca2+ uptake into synaptosomal fractions of frontal cortex (FC) and hippocampus. Such hyperactivity may be caused not only be seeking behavior but also by stress-induced anxiety. Such hyperactivity was significantly blocked after 10 days of repeated administration of diazepam (DZP), tandospirone (SM-3997; SM), a 5-HT1A anxiolytic, and nitrendipene (Nit), a Ca antagonist. Moreover, repeated administration of DZP, SM and Nit reduced the maximum binding density of 3H-PN200-110 and reduced the 45Ca2+ uptake in FC of SHR. In hippocampus, midbrain, hypothalamus and striatum, the increased ratio of 45Ca2+ uptake was reduced after repeated administration of Nit or SM. These results suggest that the hyperactivity induced by this novel circumstances was reduced by DZP, SM and Nit and may be attributed to inhibition of voltage-dependent Ca channel activities in FC. In addition, Nit may induce anti-anxiety through the modulation of Ca2+ mobilization in the central nervous system.

The effect of dihydropyridine calcium channel agents on 5-HT metabolism in the CNS of the rat

The effects of dihydropyridines on the levels of 5-hydroxytryptamine (5-HT) and 5-hydroxy-3-indole acetic acid (5-HIAA) in the spinal cord and various brain regions of the rat have been studied. Nimodipine, nitrendipine and nifedipine (10 mg kg-1), nisoldipine (5 mg kg-1), and BAY K8644 (0.2 and 2 mg kg-1) were administered i.p. 1 h before killing. The administration of nifedipine and nitrendipine increased 5-HT turnover in all of the areas studied except for the spinal cord. Nisoldipine increased 5-HT turnover in midbrain, hippocampus and cortex, while the effect of nimodipine was restricted to midbrain. BAY K8644 at 2 mg kg-1 produced the same effects as nifedipine and nitrendipine; however, at low doses (0.2 mg kg-1), this compound increased 5-HT turnover only in midbrain and medulla oblongata. These results indicate that both dihydropyridine calcium channel agonist and antagonists are able to activate the 5-HT-ergic system in the central nervous system of the rat in-vivo. Therefore, it seems likely that such effects could be due to indirect actions or to interactions of the compounds with receptors other than the voltage-sensitive calcium channels.

Iminodipropionitrile-induced dyskinesia in mice: striatal calcium channel changes and sensitivity to calcium channel antagonists

Administration of 3,3'-iminodipropionitrile (IDPN) (1 g/kg, i.p. for 3 days) in mice leads to the development of a characteristic syndrome consisting of lateral and vertical head and neck movements, hyperactivity, random circling, increased locomotor activity, and increased startle response. Nifedipine, verapamil, and diltiazem (10 mg/kg) inhibited significantly the symptoms of IDPN-induced dyskinesia. However, there was no change in the affinity (KD) or the density of PN 200-110 binding sites (Bmax) in whole brains of IDPN-treated mice. Similarly, the K(+)-depolarization-dependent Ca2+ uptake in synaptosomes from whole brain, cortex, or striatum was not altered following IDPN treatment. However, IDPN caused a significant increase in the Bmax value (from 157 +/- 7 fmol/mg to 237 +/- 31 fmol/mg in control and treated groups, respectively) of PN 200-110 binding to the striatum without change of KD value (38 +/- 4.7 pM versus 33 +/- 1.6 pM). IDPN also caused a slight but significant decrease in the KD value (from 68 +/- 10.1 pM to 45 +/- 4.5 pM in control and treated groups, respectively), without significant change of Bmax value (563 +/- 51 fmol/mg versus 485 +/- 41 fmol/mg) of PN 200-110 binding to the cortex. IDPN did not alter omega-conotoxin binding in whole brain, striatum, or cortex. The behavioral effects of chronic IDPN treatment as inhibited by L-type calcium channel antagonists and this may be associated with the observed increase in striatal L-type calcium channels.

Differential interactions between benzodiazepines and the dihydropyridines, nitrendipine and Bay K 8644

The effects of the dihydropyridine calcium antagonist, nitrendipine and the calcium channel activator, Bay K 8644, have been compared on the anaesthetic, ataxic and anticonvulsant effects of benzodiazepines. Possible interactions between the peripheral benzodiazepine receptor antagonist, PK11195, and the classical benzodiazepines were also examined. Nitrendipine considerably potentiated the anaesthetic effects of benzodiazepines and increased their ataxic effects but had no effect on the anticonvulsant actions. Clonazepam did not produce anaesthesia, at doses up to 1 g kg-1 or when given with nitrendipine. When given alone, nitrendipine did not cause general anaesthesia. Nitrendipine did not appear to alter the metabolism of midazolam. The calcium channel activator, Bay K 8644, reduced the anaesthetic potency of midazolam and, when given alone, produced ataxia. It did not significantly alter central concentrations of midazolam. The "peripheral" benzodiazepine antagonist, PK11195, did not affect the ataxic or anaesthetic actions of benzodiazepines. These results suggest that dihydropyridine-sensitive calcium channels may be more important to the general anaesthetic than to the anticonvulsant actions of benzodiazepines. The "peripheral" benzodiazepine site did not appear to play a role in either of these properties.

The effects of dihydropyridine calcium channel modulators on pentylenetetrazole convulsions

The effects of low doses of dihydropyridine (DHP) calcium channel antagonists nimodipine, nifedipine, (-)-R-202-791, and amlodipine, the DHP calcium channel agonist BAY K 8644 were investigated on clonic convulsions to pentylenetetrazole (PTZ) in mice. Nimodipine (2-20 mg/kg) produced a dose-dependent increase in the onset time for convulsions, but did not decrease the number of mice convulsing. Nifedipine, amlodipine (10 mg/kg) and BAY K 8644 (2 mg/kg) also produced an increase in the onset time for convulsions. (-)-R-202-791 (10 mg/kg) was without effect on clonic convulsions to PTZ. BAY K 8644 increased the number of mice dying from tonic-extension convulsions to PTZ. Nimodipine did not affect convulsions elicited by strychnine. Thus, low doses of DHP calcium antagonists possess anticonvulsant properties which are structurally dependent, while DHP calcium channel activators may act to promote convulsions. These observations suggest and support previous evidence that DHP receptors are important modulatory sites for the convulsive state.

Genetic components of ethanol responses

A powerful technique for determining the role of a particular neurotransmitter in mediating a response to ethanol (EtOH) is the analysis of selectively bred lines of animals. Lines selected for sensitivity and resistance to an EtOH effect differ principally in gene frequencies for genes affecting the selected response. Hence, other differences between the lines are likely due to pleiotropic actions of those genes. We discuss behavioral pharmacological experiments in two sets of selected lines. Withdrawal Seizure-Prone (WSP) and -Resistant (WSR) mouse lines were selected for severe and minimal handling-induced convulsions (HIC), respectively, after withdrawal from chronic EtOH inhalation. The HIC is also elevated after acute administration of low doses of convulsant drugs. WSP mice were found to be more sensitive than WSR mice to many such drugs. There was no apparent specificity of such effects to any particular neurotransmitter system. Thus, genetic determination of a behavioral response to EtOH in this case cannot be traced to the influence of a single neurotransmitter system. COLD and HOT mice were selectively bred to show severe and mild hypothermia, respectively, after acute EtOH administration. COLD mice are also more sensitive to a number of other alcohols, barbiturates, and other general central nervous system depressants. When tested for sensitivity to a number of drugs with specific effects on neurotransmitter systems, COLD and HOT mice did not differ in sensitivity to drugs affecting dopaminergic, alpha-adrenergic, or nicotinic acetylcholinergic systems. COLD mice were more sensitive, however, to opioid and serotonergic drugs. Thus, analysis of these selected lines was successful in identifying particular neurotransmitters which may be important in EtOH-induced hypothermia.

Anticonvulsant effects of dihydropyridine Ca2+ antagonists in electrocortical shock seizures

The dihydropyridine calcium antagonists nimodipine (NMD), PN200-110, and nicardipine were compared with phenytoin (PHT) as potential anticonvulsants in electrocortical shock (ECS)-induced seizures in the white New Zealand rabbit. Before treatment, seizure duration ranged from 43.8 +/- 5.1 to 49.6 +/- 5.2 s with an ECS stimulus of 10-V, 100-Hz, 0.1-ms pulses for 5 s. Each drug was administered into the right internal intracarotid artery 2 min before the ECS. A cumulative nimodipine dose of 440 micrograms/kg decreased seizure discharge to 6.6 +/- 5.0 s (p less than 0.001), whereas a total dose of 1.0 mg/kg PN200-110 was required to achieve a similar effect. Nicardipine was ineffective. A cumulative dose of 7 mg/kg phenytoin was required to suppress seizure discharge. These results indicate that Ca2+ channels modulated by dihydropyridines play a facilitating role in ECS-induced seizures. We propose that the anticonvulsant effects of nimodipine and PN200-110 are due to inhibition of neuronal calcium L-channels. Dihydropyridine Ca2+ antagonists that penetrate the blood-brain barrier (BBB) and bind to neuronal tissue may emerge as a novel class of anticonvulsants.

Effects of dihydropyridine calcium channel antagonists in ethanol withdrawal; doses required, stereospecificity and actions of Bay K 8644

The effects of dihydropyridine calcium channel antagonists, and the calcium channel activator, Bay K 8644, were examined on the convulsive behaviour induced by handling in mice following withdrawal from chronic ethanol inhalation. Nimodipine and nitrendipine and PN 200-110 significantly decreased the convulsive behaviour, after intraperitoneal doses of the same order of magnitude as have been found by others to be required for displacement of radiolabelled dihydropyridine in the CNS. The (+) isomer of PN 200-110 was effective, but the (-) isomer, which is ineffective in vitro, had no significant action. Bay K 8644 prevented the actions of nimodipine against the ethanol withdrawal syndrome. The behavioural ratings after nimodipine plus Bay K 8644 were significantly higher than after vehicle treatment. Bay K 8644 alone, when given to naive mice, caused convulsive behaviour resembling that seen in withdrawal from chronic ethanol treatment, but when given during ethanol withdrawal did not significantly increase the behavioural signs.

Anticonvulsant properties of some calcium antagonists on sound-induced seizures in genetically epilepsy prone rats

1. The anticonvulsant activity of calcium channel antagonists, was studied after intraperitoneal or oral administration in genetically epilepsy prone rats (GEPR). 2. Flunarizine, dihydropyridines and HA 1004, administered intraperitoneally, were the most potent compounds. Diltiazem, prenylamine, perhexiline, verapamil and methoxyverapamil, given intraperitoneally, were able to reduce the incidence of the tonic phase but were completely ineffective in preventing clonic and running phases of sound-induced seizures in GEPR. Similar anticonvulsant activity was observed when these compounds were administered orally. 3. After intracerebroventricular administration of some of the hydrosoluble calcium antagonists studied, the anticonvulsant effects were similar to those observed after systemic administration. 4. The systemic administration of Bay K 8644, a dihydropyridine analogue, having the ability to stimulate calcium entry into cells produced a dose-dependent increase in clonic and tonic convulsions and other epileptic phenomena, which were prevented by pretreatment with nimodipine or nitrendipine. 5. The possible role of purinergic, excitatory amino acid, GABA-benzodiapine mechanisms as well as the role of Ca2(+)-calmodulin and calcium channel binding sites on the anticonvulsant effects of some calcium antagonists are discussed.

Calcium channel blockers: effect on morphine-induced hypermotility

Acute morphine treatment has been shown to cause a uniform calcium depletion in various brain regions and to evoke hypermotility in mice. On the other hand, it has been reported previously that calcium channel blockers reduce the behavioral stimulation induced by different methods in mice, and it is known that these drugs increase the morphine analgesia and reduce the abstinence syndrome. The effect of calcium channel blockers, nifedipine and diltiazem, on the morphine- and amphetamine-induced hypermotility were evaluated. Mice activity was measured with photocell motility meters. The results show that neither nifedipine nor diltiazem decrease significantly the motility in control and amphetamine-treated mice; however, when they were administered to morphine-treated mice the hypermotility was significantly reduced. The mechanism responsible for this interference is still unknown.

Central neurochemical effects of dihydropyridine calcium antagonists

Recent advances in central dihydropyridine (DHP)-binding sites are reviewed. DHP-binding sites are pre-synaptically and post-synaptically localized in the brain. The functional role of post-synaptic sites is still unknown, whereas pre-synaptic sites seem to contribute to the control of calcium uptake and of neurotransmitter release. DHP-binding sites may be modualated in physiological (age, sex) and pathological events (hypertension, ischaemia, neurological diseases) or after drug treatments (alcohol, morphine, etc.). The reviewed data suggest new therapeutic implications of DHP calcium channel antagonists in the treatment of other diseases and of drug withdrawal syndrome.