Effects of chronic corticosterone and imipramine administration on panic and anxiety-related responses

It is known that chronic high levels of corticosterone (CORT) enhance aversive responses such as avoidance and contextual freezing. In contrast, chronic CORT does not alter defensive behavior induced by the exposure to a predator odor. Since different defense-related responses have been associated with specific anxiety disorders found in clinical settings, the observation that chronic CORT alters some defensive behaviors but not others might be relevant to the understanding of the neurobiology of anxiety. In the present study, we investigated the effects of chronic CORT administration (through surgical implantation of a 21-day release 200 mg pellet) on avoidance acquisition and escape expression by male Wistar rats (200 g in weight at the beginning of the experiments, N = 6-10/group) tested in the elevated T-maze (ETM). These defensive behaviors have been associated with generalized anxiety and panic disorder, respectively. Since the tricyclic antidepressant imipramine is successfully used to treat both conditions, the effects of combined treatment with chronic imipramine (15 mg, ip) and CORT were also investigated. Results showed that chronic CORT facilitated avoidance performance, an anxiogenic-like effect (P < 0.05), without changing escape responses. Imipramine significantly reversed the anxiogenic effect of CORT (P < 0.05), although the drug did not exhibit anxiolytic effects by itself. Confirming previous observations, imipramine inhibited escape responses, a panicolytic-like effect. Unlike chronic CORT, imipramine also decreased locomotor activity in an open field. These data suggest that chronic CORT specifically altered ETM avoidance, a fact that should be relevant to a better understanding of the physiopathology of generalized anxiety and panic disorder.

Effects of fluoxetine and imipramine in rat fetuses treated during a critical gestational period: a macro and microscopic study / Efeitos da fluoxetina e imipramina em fetos de ratas tratadas durante o período crítico da gestação: estudo macro e microscópico

OBJECTIVE: To evaluate morphological alterations in rat fetuses treated with fluoxetine and imipramine during the "critical" period of gestation. METHOD: Fifteen female rats were separated into three groups (n = 5) and treated with 10 mg/kg/day of test substances on the ninth, tenth and eleventh day of pregnancy: G1, fluoxetine; G2, imipramine hydrochloride; G3 (control), saline. On day 21, cesarean sections were performed to release the fetuses, whose bodies were weighed and macroscopically analyzed. The placenta was also weighed. The fetuses were then fixed and their encephala removed and weighed. Sections of the frontal lobe were taken for histological neuron counting. RESULTS: G1 and G2 showed the highest fetal body weight. Placental weight showed statistical differences (p < 0.01): G1 weighed more than G2 and G3. Otherwise, G2 exhibited the highest encephalon weight, statistically differing from G3 (control) and fluoxetine-treated G1 (p < 0.01). However, G1 did not statistically (p > 0.01) differ from the control group. G3 showed the highest number of neurons per area when compared to G1 and G2 (p < 0.01). CONCLUSION: The use of antidepressants in rats caused an increase in fetal weight and a decrease in the number of fetal frontal lobe neurons, thus suggesting that the use of antidepressants by pregnant women can induce depression in fetuses due to alterations in their neural development.

OBJETIVO: Avaliar as possíveis alterações ocorridas em nível macroscópico e microscópico de fetos de ratas submetidas ao tratamento com fluoxetina e imipramina durante o período "crítico" da gestação. MÉTODO: Quinze ratas, posteriormente ao acasalamento, foram divididas em três grupos experimentais (n = 5): G1, tratadas com 10mg/kg/dia de fluoxetina; G2, tratadas com 10mg/kg/dia de cloridrato de imipramina, e G3 (controle), tratadas com 10mg/kg/dia de solução fisiológica a 0,9 por cento, no 9º, 10º e 11º dias de prenhez das ratas. Posteriormente à cesária, no 21º dia de prenhez, analisou-se macroscopicamente o peso fetal e placentário. Os fetos foram fixados e houve a remoção do encéfalo para pesagem e preparação das lâminas do tecido neuronal para contagem de neurônios do lobo frontal. RESULTADOS: O G1 e G2 apresentaram maior peso fetal. O G1 apresentou maior peso placentário, diferindo do G2 e G3 (p < 0,01). De forma diferente, o G2 possuiu maior peso encefálico, diferindo do G3 e G1 (p < 0,01). G1 não diferiu estatisticamente do grupo controle (p > 0,01). O G3 exibiu maior número de neurônios, por área, do lobo frontal em relação a G1 e G2 (p < 0,01). CONCLUSÃO: A adoção dos antidepressivos causou, nos fetos, aumento de peso e redução da contagem de neurônios do lobo frontal, sugerindo que a indicação de antidepressivos às gestantes pode induzir a depressão nos fetos por alterações em seu neurodesenvolvimento.

Effects of calcium channel blockers on antidepressant action of alprazolam and imipramine

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

Effects of calcium channel blockers on antidepressant action of Alprazolam and Imipramine

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 1Tween 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

Imipramine in persistent vomiting.

A 21-year-old female presented with persistent vomiting for last 3 years. She had all the investigations done including gastroscopy but there was no abnormality detected. She was tried earlier with medicines prescribed in a medical college or a private nursing home. The cause of vomiting was thought of psychogenic. She was advised imipramine 25 mg thrice daily and responded to the treatment favourably.

Effect of Withania somnifera on forced swimming test induced immobility in mice and its interaction with various drugs.

The objective of the present study was to evaluate the antidepressant action of Withania somnifera (WS) as well as its interaction with the conventional antidepressant drugs and to delineate the possible mechanism of its antidepressant action using forced swimming model in mice. Effect of different doses of WS, fluoxetine and imipramine were studied on forced swimming test induced mean immobility time (MIT). Moreover effect of WS 100 mg/kg, i.p. was observed at different time intervals. Effect produced by combination of sub therapeutic doses of WS with imipramine (2.5 mg/kg, i.p.) as well as fluoxetine (2.5 mg/kg, i.p.) were also observed. Effect of WS (100 mg/kg, i.p.) as well as combination of WS (37.5 mg/kg, i.p.) with either imipramine (2.5 mg/kg, i.p.) or fluoxetine (2.5 mg/kg, i.p.) were observed in mice pretreated with reserpine (2 mg/kg, i.p.) and clonidine (0.15 mg/kg, i.p.). Effects of prazosin (3 mg/kg, i.p.) or haloperidol (0.1 mg/kg, i.p.) pre-treatment were also observed on WS induced decrease in MIT. WS produced dose dependent decrease in MIT. Maximum effect in MIT was observed after 30 min of treatment with WS 100 mg/kg, i.p. Combination of WS (37.5 mg/kg, i.p.) with imipramine (2.5 mg/kg, i.p.) or fluoxetine (2.5 mg/kg, i.p.) also produced significant decrease in the MIT. Clonidine and reserpine induced increase in MIT, was significantly reversed by treatment with WS (100 mg/kg, i.p.) as well as combination of WS (37.5 mg/kg, i.p.) with either imipramine (2.5 mg/kg, i.p.) or fluoxetine (2.5 mg/kg, i.p.). Pre-treatment with prazosin but not haloperidol, significantly antagonized the WS (100 mg/kg, i.p.) induced decrease in MIT. It is concluded that, WS produced significant decrease in MIT in mice which could be mediated partly through a adrenoceptor as well as alteration in the level of central biogenic amines.

Role of emotionality on inter and intrastrain variations in imipramine response. a comparative study in Balb/c and Swiss mice.

Association between emotionality and effect of imipramine on immobility time in forced swimming test was investigated in Swiss and Balb/c mice. Mice of both the strains were segregated into normal emotional (mean +/- 1SD), low emotional (> mean + 1SD) and high emotional (< mean - 1SD) based on their performance with respect to each indices of emotionality in novel arena and elevated plus maze. Baseline immobility and effect of imipramine (20 mg/kg, po) on immobility time was evaluated in these emotionally different groups of mice using forced swimming test model. Baseline immobility time of low emotional mice was found to be significantly less (P<0.01) and that of high emotional mice was found to be significantly more (P<0.01) when compared to normal emotional mice of both the strains. Immobility time after imipramine administration was found to be significantly less (P<0.05) with low emotional mice and significantly more (P<0.01) with high emotional mice when compared to normal emotional mice of both the strains.

Effect of chlorpromazine, imipramine and lithium on MAO-A and MAO-B activity in rat brain mitochondria.

Drugs with efficacy in psychiatric disorders affect the function of central neurotransmitter amines, which are inactivated primarily by monoamine oxidase (MAO). Effect of these drugs on the two types of MAO (MAO-A and MAO-B) has been studied in rat brain. The result showed that chlorpromazine (CPZ) and imipramine (IMI) at concentrations of 1x10(-2), 5x10(-3) and 2.5x10(-3) M inhibited rat brain mitochondrial MAO-A activity in vitro by 82, 50, 39 and 86, 74, 38 %, respectively. CPZ at concentrations of 5x10(-3), 2.5x10(-3), 1x10(-3) M inhibited rat brain mitochondrial MAO-B activity in vitro by 83, 55, 39 %, respectively, while IMI at concentrations of 5x10(-4), 2.5x10(-4), 1x10(-4) M inhibited the in vitro enzyme activity by 43, 35, 21 %, respectively. Lithium at concentration of 5x10(-3) M could not either inhibit MAO-A or MAO-B in the mitochondrial fraction of rat brain.

Serotonergic mechanism in imipramine induced antinociception in rat tail flick test.

Substantial evidence has accumulated that spinally projecting serotonergic neurons modulate nociception. However, the exact receptor subtypes that mediate the antinociceptive response of serotonin within the spinal cord continue to be a subject of debate. Therefore, we explored the effect of serotonergic system on imipramine induced antinociception by using 5-Hydroxytryptamine-3 (5HT3) receptor antagonist ondansetron and 5-Hydroxytryptamine-2 (5HT2) receptor antagonist mianserine, and depletion of brain 5-Hydroxytryptamine (5HT) with p-chlorophenyl alanine (PCPA). Male wistar strain rats were pretreated with either ondansetron (0.5 mg/kg, i.p.) or mianserine (1 mg/kg, i.p.). After 15 minutes, rats received injection of imipramine (10 mg/kg). Nociception was assessed by tail-flick method. Imipramine (2 mg, 5 mg, 10 mg, and 20 mg/kg) produce antinociceptive response in the dose dependent manner. Prior treatment with 5HT3 antagonist, Ondansetron and 5HT2 antagonist, mianserine reduce the antinociceptive response of imipramine. In PCPA treated rats imipramine (10 mg/kg) failed to produce antinociception. These results indicate that the 5HT plays an important role in imipramine induced antinociception.

Antidepressant activity of Indian Hypericum perforatum Linn in rodents.

A standardised 50% aqueous ethanolic extract of Indian Hypericum perforatum (IHp) was investigated for its antidepressant activity on various experimental paradigms of depression, viz. behavioural despair (BD), learned helplessness (LH), tail suspension (TS) and reserpine-induced hypothermia (RIH) tests in rats and mice. Pilot studies indicated that single dose administration of IHp had very little or no acute behavioural effects, hence the IHp was administered orally at two dose levels (100 and 200 mg/kg, p.o.) once daily for three consecutive days, while imipramine (15 mg/kg, i.p.), a clinically used antidepressant agent, was administered acutely to rats (CF strain, 150 +/- 10 g) and mice (Wistar strain, 23 +/- 2 g) of either sex as the standard drug. Controls animals were treated similarly with equal volume of vehicle (0.3% carboxymethyl cellulose). Indian Hypericum perforatum extract showed significant antidepressant activity on all the paradigms of depression used. Thus IHp and imipramine treatments significantly reduced the immobility time in BD and TS tests. Significant reduction in escape failures was also observed in LH test. In RIH test IHp and imipramine inhibited reserpine induced hypothermia in a dose dependent manner. The observed antidepressant activity of IHp was qualitatively comparable to that induced by imipramine.

Interaction between N-methyl-D-aspartate receptor antagonists and imipramine in shock-induced depression.

In the past few years, literature has accumulated describing manifestation of seizures following administration of certain antidepressants. Such reports are of particular importance because depression is a frequent psychiatric problem associated with epilepsy. Therefore, in the view of the fact that NMDA receptor antagonists have been reported to reduce behavioural deficits and have been shown to be anticonvulsant, it was considered imperative to study their antidepressant effect using shock-induced depression model in mice. Presentation of inescapable foot shock significantly reduced ambulation and rearing in the open field arena and increased immobility duration in the FST. Pretreatment with imipramine, MK 801 and ketamine significantly prevented the effect of shock. Also, the combination of imipramine with either of the NMDA antagonists antagonised the effect of shock. Haloperidol, prazosin and ketanserin pretreatment modified the effect of these agents. These findings suggest an antidepressant effect of the NMDA receptor antagonists, and a complexity of neurotransmitter mechanisms, which are responsible for the occurrence of behavioural effects in shock-induced depression model.

Chronic imipramine treatment-induced changes in acetylcholinesterase (EC 3.1.1.7) activity in discrete rat brain regions

Cholinergic as well as monoaminergic neurotransmission seems to be involved in the etiology of affective disorders. Chronic treatment with imipramine, a classical antidepressant drug, induces adaptive changes in monoaminergic neurotransmission. In order to identify possible changes in cholinergic neurotransmission we measured total, membrane-bound and soluble acetylcholinesterase (Achase) activity in several rat brain regions after chronic imipramine treatment. Changes in Achase activity would indicate alterations in acetylcholine (Ach) availability to bind to its receptors in the synaptic cleft. Male rats were treated with imipramine (20 mg/kg, ip) for 21 days, once a day. Twenty-four hours after the last dose the rats were sacrificed and homogenates from several brain regions were prepared. Membrane-bound Achase activity (nmol thiocholine formed min(-1) mg protein(-1) after chronic imipramine treatment was significantly decreased in the hippocampus (control = 188.8 + 19.4, imipramine = 154.4 + 7.5, P<0.005) and striatum (control = 850.9 + 59.6, imipramine = 742.5 + 34.7, P<0.005). A small increase in total Achase activity was observed in the medula oblongata and pons. No changes in enzyme activity were detected in the thalamus or total cerebral cortex. Since the levels of Achase seem to be enhanced through the interaction between Ach and its receptors, a decrease in Achase activity may indicate decreased Ach release by the nerve endings. Therefore, our data indicate that cholinergic neurotransmission is decreased after chronic imipramine treatment which is consistent with the idea of an interaction between monoaminergic and cholinergic neurotransmission in the antidepressant effect of imipramine.

Influence of antidepressant drugs on learning and memory paradigms in mice.

Effect of antidepressant drugs (amitriptyline, imipramine and fluoxetine) on cognitive functions, impaired by the muscarinic antagonist scopolamine were investigated in mice. The changes in learning and memory tasks were studied using transfer latency on elevated plus maze and employing number of descents in passive avoidance paradigms. Amitriptyline and imipramine showed significant memory impairment. They also potentiated scopolamine-induced memory deficit in a significant way. Amitriptyline and imipramine impair cognitive function possibly due to their anticholinergic properties. Fluoxetine, a newer antidepressant, however showed no effect on learning and memory. It significantly reversed the scopolamine-induced memory impairment in both the tests. Fluoxetine with no anticholinergic property may prove to be a better drug in endogenous depression in elderly patients.

GABAergic agents modify imipramine analgesia.

The influence of GABA agonists and antagonists on analgesic activity of imipramine (IMA, 20 mg/kg, ip) was studied using the hotplate method. Administration of GABAA receptor agonist muscimol (1 mg/kg, ip), GABAB receptor agonist baclofen (3 mg/kg, ip) or GABA-T inhibitor aminooxyacetic acid (25 mg/kg, ip) increased the analgesic effect of IMA. On the other hand pretreatment of GABAA receptor antagonist bicucukline (2 mg/kg ip), GABAB receptor antagonist delta-amino-n-valeric acid (50 mg/kg, ip) or GABA synthesis inhibitor thiosemicarbazide (50 mg/kg, ip) attenuated the IMA analgesia. These results suggest that the analgesic action of IMA may be mediated by functional alteration of a central GABAergic mechanism and/or subsequent stimulation of GABA receptors.

Parasympatholytic activity of psychoactive drugs in rat brain mitochondria.

Chlorpromazine, imipramine and amphetamine at a concentration of 0.66, 1.33 and 13.3 x 10(4) M in vitro inhibited acetyl cholinesterase activity by 16, 23 and 31% respectively in rat brain mitochondria. No change in enzyme activity was induced by these drugs in vivo. There is little cholinergic facilitation through acetylcholinesterase inhibition in the presence of psychoactive drugs.

Psychoactive drug induced alteration of tryptamine tetrazolium reductase activity in rat brain.

The psychoactive drugs imipramine, chlorpromazine and lithium chloride inhibit tryptamine tetrazolium reductase activity in vitro by 68, 60 and 33% respectively at a concentration of 1 x 10(-3) M while amphetamine negligibly inhibits the enzyme activity. No change in enzyme activity is observed in vivo.

Regional differences in the levels of biogenic amines and their metabolites in rat brain after tricyclic antidepressant treatments

Changes in the levels of biogenic amines in different brain regions and the cerebrospinal fluid in rats were measured after acute or chronic treatment with tricyclic antidepressants. After single or 3 weeks' treatment with imipramine or desipramine, blocks of tissues were obtained from seven regions of the brain (frontal cortex, corpus striatum, hippocampus, thalamus, hypothalamus, substantia nigra and cerebellum) immediately after collection of the cerebrospinal fluid (CSF) from the cisterna magna. The concentrations of biogenic amines and their metabolites (norepinephrine, epinephrine, dopamine, 5-hydroxytryptamine (5-HT), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA)) in brain tissues and the CSF were measured using the high performance liquid chromatography-electrochemical detection system (HPLC-ECD). Treatment with desipramine or imipramine caused major alterations in the concentrations of central norepinephrine or 5-HT and its metabolite, respectively. Brain regional responses were variable according to the kind of tricyclic antidepressants and the duration of treatment. It is noteworthy that chronic treatment with both desipramine and imipramine caused altered hippocampal concentrations of norepinephrine and/or 5-HT and its metabolites. Striatal DOPAC concentrations were also changed after acute or chronic treatment with both drugs. These results suggest that tricyclic antidepressants altered neurotransmission according to the brain region, and the hippocampal norepinephrine and 5-HT and/or the striatal dopamine may have a significant role for the expression of antidepressant action of tricyclic antidepressants.

Changes in the sensitivities of dopamine receptors to chronic treatment with imipramine & haloperidol in rats.

Apomorphine induced locomotor activity was studied in Wistar rats treated with imipramine and haloperidol with the help of automated measuring devices. The control rats showed a biphasic response of hypomotility and sedation to low dose apomorphine, and hypermotility to high dose apomorphine. In chronic imipramine-treated rats, the hypomotility and sedative response to low dose apomorphine challenge was significantly attenuated (P less than 0.05), as compared to saline treated controls. A similar response was observed in the chronically haloperidol treated rats (P less than 0.01). However, there were no significant differences in motility responses to high dose apomorphine challenge between the control and experimental groups. These results suggest that presynaptic dopamine auto receptors may not be involved in mediating the loss of response to low dose apomorphine by chronic imipramine treatment. Imipramine being predominantly a monoamine uptake inhibitor and haloperidol a potent postsynaptic D-2 blocker, some indirect mechanisms may be involved in the loss of response to low dose apomorphine challenge.