alprazolam is an anxiolytic agent used primarily for short - term relief of mild to moderate anxiety and nervous tension . it has a high affinity for the gaba benzodiazepine receptor complex , and it is a full agonist for the gabaa receptor . it prevents the reuptake of noradrenaline ( na ) and 5-hydroxytryptamine ( 5-ht ) at nerve terminals . calcium antagonists have been shown to affect many different physiological processes , in particular neurotransmitter release . nifedipine mainly affects the heart and smooth muscle , causing inhibition of calcium entry associated with depolarization . verapamil enhanced the antidepressant action of alprazolam ; verapamil as an inhibitor of the cyp 450 3a4   may affect the imipramine   and alprazolam action , that are considered as substrates for cyp 450 3a4 ( 7 ) the forced swim test ( fst )   is used as a rodent model of depression . the mouse fst model has been widely used in screening antidepressants because it is simple and has been reported to be reliable across laboratories . the mouse model is more sensitive than the rat model because it produces fewer false positives . it is based on the observation that when an animal is forced to swim in a situation from which there is no escape , it will first go through a period of vigorous activity and then cease to move , other than trying to keep its head above water . immobility indicates a state of despair in which the mouse has learned that escape is impossible . fst immobility is reduced by different treatments known to be effective in depression [ 12 , 13 ] . there is a significant correlation between the potency of antidepressants in the fst and in clinical settings , but such a correlation has not been demonstrated in any other animal model of depression [ 12 , 14 ] . in this model drugs that increase central transmission of dopamine or na decrease immobility , whereas agents having the opposite effect increase immobility . the advantage of the mouse fst model is that it can readily test the possible mechanisms of antidepressant action by using specific agonists / antagonists . by augmenting or blocking antidepressant activity with agonist / antagonist receptor ligands , it is possible to detect which receptor is involved in the antidepressant effect . in this study we used behavior despair models for mental depression to investigate the effect of the calcium channel blockers , nifedipine and verapamil , on the antidepressant action of alprazolam and imipramine . these two calcium channel blockers are used in the treatment of physical illnesses that may be concurrent with depression . understanding the interaction between antidepressants and calcium channel blockers could indicate whether there is a need to modify antidepressant doses when coadministered with calcium channel blockers . the animals were housed at room temperature ( 2025c ) and a 12-h dark / light cycle . alprazolam was supplied by upjohn co. ltd , egypt , imipramine by novartis , ag , switzerland , nifedipine by bayer , ag , germany , and verapamil by weimer phara gmbh , germany . because alprazolam is not freely soluble in saline , all the drugs imipramine was given at 10 mg / kg and alprazolam at 5 mg / kg [ 18 and our unpublished results ] . one group received a single dose of 5ml / kg of 1% tween 80 ; two groups each received a single dose of the antidepressant alone ( alprazolam , 5mg / kg ; imipramine , 10mg / kg ) ; two groups each received a single dose of the calcium channel blocker ( nifedipine , 5mg / kg ; verapamil , 10mg / kg ) ; four groups each received a single dose of the calcium channel blocker followed by a single dose of the antidepressant ( with same doses used for either in the previous four groups ) . for all groups , the time of onset of immobility was measured 60 min after drug administration . we used a behavioral model of immobility first postulated by porsolt   and porsolt et al . and named the behavioral despair model . in this model , mice are forced to swim in a restricted space from which there is no escape . following an initial period of vigorous activity , the mice adopt a characteristic immobile posture with no further attempt to escape , and this reflects a state of despair or lowered mood . mice were forced to swim for four minutes in a vertical glass cylinder ( height=27 cm , diameter=16.5 cm ) containing fresh tap water at 27c and a depth of 15 cm . spss 8 software was used to determine whether the observed data were normally distributed using kolmogrov smirnov maximum deviation test for goodness of fit . if the data were normally distributed , one - way anova was applied , followed by post hoc test to compare between groups . if the data were not normally distributed , groups were compared using mann - whitney two samples ( non  matched ) u test . administration of imipramine , alprazolam , or nifedipine separately produced a significant delay in the onset of immobility compared to the control group . the combined administration of alprazolam and nifedipine produced a significant delay in the onset of immobility compared to either alprazolam treated mice or the control group . the effect of imipramine on the onset of immobility ( delay ) was potentiated by the administration of nifedipine(table 1 ) . effects of nifedipine on the onset of immobility by alprazolam and imipramine using the behavior despair model of depression . b : p  0.05 compared to group treated with alprazolam + nifedipine . c : p  0.05 compared to group treated with imipramine+nifedipine . administration of verapamil , alprazolam or imipramine produced a significant delay in the onset of immobility compared to the control group . our findings demonstrate that verapamil significantly delays the onset of immobility produced by alprazolam ( table 2 ) . effects of verapamil on the onset of immobility produced by alprazolam or imipramine using the behavior despair model of depression . the values are expressed as mean  s.e.m . a : p0.05 compared to control group treated with tween 80-treated . administration of imipramine , alprazolam , or nifedipine separately produced a significant delay in the onset of immobility compared to the control group . the combined administration of alprazolam and nifedipine produced a significant delay in the onset of immobility compared to either alprazolam treated mice or the control group . the effect of imipramine on the onset of immobility ( delay ) was potentiated by the administration of nifedipine(table 1 ) . effects of nifedipine on the onset of immobility by alprazolam and imipramine using the behavior despair model of depression . b : p  0.05 compared to group treated with alprazolam + nifedipine . c : p  0.05 compared to group treated with imipramine+nifedipine . administration of verapamil , alprazolam or imipramine produced a significant delay in the onset of immobility compared to the control group . our findings demonstrate that verapamil significantly delays the onset of immobility produced by alprazolam ( table 2 ) . effects of verapamil on the onset of immobility produced by alprazolam or imipramine using the behavior despair model of depression . the values are expressed as mean  s.e.m . a : p0.05 compared to control group treated with tween 80-treated . it has been suggested that calcium channel inhibitors may have antidepressant properties , and that calcium may play an important role in affective disorders . voltage - dependent calcium channel antagonists have been reported to produce antidepressant - like effects in rodents [ 2628 ] . interruption of the ca - calmodulin - nos - guanylyl cyclase subcellular signaling pathway at any point produces antidepressant - like effects . in our study , this antidepressant action could have been mediated by 5-ht1a activation , whereby nifedipine reduced 5-ht uptake . serotonin may activate calcium influx through calcium channels by activation of 5-ht receptors , which are insensitive to nifedipine , in neuronal cells . the increase in calcium influx is through 5-ht3 receptors [ 31 , 33 ] , the 5-ht3 receptor being a ligand - gated ion channel activated by the neurotransmitter serotonin . receptors of this subtype have been localized to several regions of the brain , they appear to be involved in many neuronal functions , and to mediate antidepressant effects . in glial cells , it has been suggested that the pharmacology of l - type ca - channel blockers overlaps with that of 5-ht2 receptor antagonists . nifedipine may produce an antidepressant action through gabaa activation , which leads to the release of na that produces an antidepressant effect . this may be gaba acting on second inhibitory interneurons ( as in direct and indirect pathways of extrapyramidal systems ) . nifedipine may also produce its antidepressant effect by increasing the release of intracellular calcium through gabaa receptors   and na [ 39 , 40 ] . the central antidepressant effect of nifedipine may be mediated through an interaction , with novel modulatory sites on gabaa receptors , that is not through picrotoxin , flumazenil or zn sites . nifedipine may exert an antidepressant action by decreasing the ability of vesicles to re - uptake na . nifedipine may block calcium uptake through potential operated ( k ) channels or through receptor operated ( 5-ht ) channels . moreover , verapamil showed an antidepressant- like effect as it delayed the onset of immobility in the swimming maze . studies have shown that verapamil modulates the action of antidepressant drugs that downregulate  adrenergic systems . it has a similar final effect as  blockers , and shares this effect with antidepressant drugs . working on different types of calcium entry , verapamil blocks the prejunctional 2 receptors , which leads to an increase in na release [ 4548 ] . verapamil may have direct catecholamine- releasing effects , as it interacts with catecholamine storage vesicles in a way that reduces their ability to take up and store catecholamine , and thereby increasing na release from sympathetic nerves . verapamil has no effect on na - induced increase in calcium influx , which means that there are verapamil- sensitive and verapamil - insensitive calcium channels . verapamil enhances atp response , which is released along with na from the motor nerves ; atp may indeed be a co - transmitter [ 51 , 52 ] . suggested that atp induces na release from sympathetic neurons via its action on a subclass of the nicotinic cholinoceptor , because this effect was blocked by nicotinic receptor antagonists . it also increases calcium influx to the cells via calcium channel - activated na receptors and potential - dependent slow calcium- channels activated by na - induced membrane depolarization . na stimulates calcium chloride conductance , leading to opening of voltage - gated calcium channels . verapamil inhibits 5-ht uptake by a mechanism that does not involve alteration in calcium fluxes ( 56 ) , which leads to enhancement of 5-ht release ; verapamil produces competitive inhibition of a 5-ht carrier and inhibits na - dependent uptake of 5-ht [ 58 , 59 ] , which is competitively inhibited by imipramine . it also facilitates the release of large amounts of k+-induced 5-ht in the hippocampus synaptosomatic sites . it also activates 5-ht3 presynaptic receptors , inducing calcium influx [ 62 , 63 ] , which triggers the release of calcium from intracellular stores and leads to increased calcium in both the cytoplasm and nucleus . it also increases chloride channel activity by acting on the 5-ht1c receptor [ 65 , 66 ] . it has been suggested that the increased [ ca ] activates chloride channels ( cl ) , causing an efflux of chloride and subsequent depolarization of the cell membrane ; this leads to the opening of voltage- gated calcium channels [ 67 , 68 ] . cl currents can be activated separately by ca release from intracellular stores ( in response to external application of caffeine or na ) and by ca influx through voltage - dependent ca channels . activation of cl channels by ca release produces a membrane depolarization that is required for an enhanced opening of voltage - dependent ca channels in response to noradrenaline in venous smooth muscle . it was concluded that extracellular chloride is essential for contraction in afferent arterioles after activation of voltage - dependent calcium channels . verapamil can not modify calcium - dependent fractions of gaba release induced by high k depolarization . presynaptic action of zn in the hippocampus increases the release of gaba in the synaptic cleft . zinc enhances gaba release by potentiating ampa / kaiate receptors in the hippocampus region , followed by a decrease in presynaptic glutamate release . the nmda receptor gates two inhibitory sites for zinc , one is voltage dependent   and the other is not [ 7476 ] . calcium channels may play two roles in the regulation of depolarization - induced gaba release . first , they permit depolarization - induced influx of calcium , which then promotes gaba release . second , they influence gaba release through a mechanism that does not involve external calcium . it has been proposed that calcium channels serve to permit an influx of na , which in turn promotes calcium - independent gaba release through an influence on the high affinity gaba transport system . blockage of choline uptake may play a role in the antidepressant - like effect of verapamil . flumazenil did not antagonize the antidepressant effects of alprazolam or imipramine , while these effects were blocked by picrotoxin . enhanced 5-ht release in the hippocampus , exhibited by the atypical benzodiazepine , alprazolam , but not by the typical benzodiazepine , diazepam , may underlie the antidepressant activity of alprazolam . it has been suggested that some of the neuronal stabilizing effects of benzodiazepine receptors may be mediated by the regulation of ca conductance , as benzodiazepine binding sites regulate voltage - sensitive cachannels in brain membranes . benzodiazepines and calcium channel inhibitors cause significant inhibition of adenosine transport ; hence , this potentiates adenosine action at the concentration required to induce effects through occupation of their respective , specific high - affinity sites . benzodiazepine ( clonazepam , flunitrazepam , and diazepam ) binding sites regulate voltage - sensitive ca channels in brain membranes , and it has been suggested that some of the neuronal stabilizing effects of benzodiazepine receptors may be mediated by the regulation of ca conductance . diazepam had no effect on the immobility time in the swimming maze , but antagonized the antidepressant effect of imipramine . this means that both alprazolam and imipramine produce antidepressant effects through voltage - sensitive ca channels . benzodiazepines act as ca - channel antagonists ; this antagonism may not be related to their antidepressant action [ 85 , 86 ] . imipramine can inhibit presynaptic reuptake of the biogenic amines , serotonin , and na to produce an antidepressant action [ 8789 ] . imipramine may increase calcium release from intracellular stores   by increasing na concentrations through inhibiting its uptake by pre - synaptic sites , through gabaa receptor activation . this may lead to increased calcium influx through voltage - gated calcium channels , which ultimately depend on the chloride transport system , or by depolarization due to an increase in the external potassium concentrations . it was suspected that this might lead to calcium influx through voltage activated calcium channels . nifedipine blocks l - type calcium channels activation which is due gabaa receptor activation - mediated depolarization [ 94 , 95 ] , which may not play a role in the antidepressant action . imipramine produces an inhibition of the peak threshold calcium current , which probably decreases the maximum available calcium conductance . it was suggested that imipramine acts by interfering with the influx of extracellular calcium , through both the receptor- operated and voltage - gated calcium channels , but does not affect the release of calcium from intracellular storage sites [ 97 , 98 ] . in the present study we showed that verapamil has an antidepressant - like effect in the mouse swimming maze model . treatment with verapamil combined with alprazolam or imipramine produces an additive antidepressant effect , possibly because verapamil has an antidepressant - like effect , but the mechanism is not understood yet . either imipramine or nifedipine produced a delay in the onset of immobility of 75% and 81% , respectively , compared to the control . combining nifedipine with imipramine led to a delay of 73% in the onset of immobility compared to the control ; which is less than the additive effect . this observation could be explained by the fact that nifedipine has its own antidepressant action mechanism but also blocks the imipramine mechanism that depends on l - type calcium channel activation . this study showed that nifedipine possesses antidepressant properties . combining nifedipine with alprazolam produced an additive antidepressant effect , indicating that different mechanisms were involved .
alprazolam is effective as an anxiolytic and in the adjunct treatment of depression . in this study , 
 the effects of calcium channel antagonists on the antidepressant action of alprazolam and imipramine were investigated . 
 a forced swimming maze was used to study behavioral despair in albino mice . 
 mice were divided into nine groups ( n = 7 per group ) . 
 one group received a single dose of 1% tween 80 ; two groups each received a single dose of the antidepressant alone ( alprazolam or imipramine ) ; two groups each received a single dose of the calcium channel blocker ( nifedipine or verapamil ) ; four groups each received a single dose of the calcium channel blocker followed by a single dose of the antidepressant ( with same doses used for either in the previous four groups ) . 
 drug administration was performed concurrently on the nine groups . 
 our data confirmed the antidepressant action of alprazolam and imipramine . 
 both nifedipine and verapamil produced a significant antidepressant effect ( delay the onset of immobility ) when administered separately . 
 verapamil augmented the antidepressant effects of alprazolam and imipramine ( additive antidepressant effect ) . 
 this may be due to the possibility that verapamil might have antidepressant - like effect through different mechanism . 
 nifedipine and imipramine combined led to a delay in the onset of immobility greater than their single use but less than the sum of their independent administration . 
 this may be due to the fact that nifedipine on its own might act as an antidepressant but blocks one imipramine mechanism that depends on l - type calcium channel activation . combining nifedipine with 
 alprazolam produced additional antidepressant effects , which indicates that they exert antidepressant effects through different mechanisms .