Effects of chronic antidepressant treatment on nigrostriatal and mesolimbic dopamine autoreceptors in the rat

Dopamine autoreceptors were studied by determining the effects of chronic antidepressant treatment on the ability of several doses of apomorphine to decrease 3,4-dihydroxyphenylalanine accumulation (an index of dopamine synthesis in vivo) after saline or γ-hydroxybutyric acid lactone (γ-butyrolactone). 3,4-Dihydroxyphenylalanine accumulation was measured in nigrostriatal [nucleus caudatus putamen] and mesolimbic [nucleus accumbens and tuberculum olfactorium] nerve terminals. Apomorphine decreased 3,4-dihydroxyphenylalanine accumulation in the nucleus caudatus putamen, tuberculum olfactorium and nucleus accumbens in a dose-related manner. Chronic imipramine (10 days) treatment attenuated the low and high dose apomorphine-induced decrease in 3,4-dihydroxyphenylalanine accumulation in the nucleus caudatus putamen to a greater extent than the tuberculum olfactorium or nucleus accumbens. In γ-butyrolactone-treated animals chronic treatment with imipramine, amitriptyline or bupropion (10 days) attenuated the low dose apomorphine effect in the nucleus caudatus putamen, but not the tuberculum olfactorium or nucleus accumbens. Only 2 days of imipramine treatment had no effect on the apomorphine-induced decrease in 3,4-dihydroxyphenylalanine accumulation in the nucleus caudatus putamen with or without γ-butyrolactone treatment. These data suggest that chronic treatment with three antidepressants produces dopamine autoreceptor subsensitivity in nigrostriatal neurons more than mesolimbic neurons and that this effect is not seen with short-term imipramine treatment.     

Characteristics of the combined action of melatonin and imizin on the structure of forced swimming and the circadian rhythm

Acute administration of melatonin (10 mg/kg) produced a depressed effect on the mice behavior. But it's injection after chronic imipramine (10 mg/kg/day, 2 weeks) potentiated antidepressant ability and shortened the duration of immobility in the structure of swimming. In rats, which had a high amplitude of circadian rest-activity rhythm, melatonin produced imipramine effect on circadian mobility, but potentiated antidepressant action in animals with low initial level of locomotor activity.     

Absence of noxious effects of selected neuroleptics in dominant-lethal mutagenesis assay.

In a dominant-lethal assay in mice the following tricyclic neuroleptics were tested: prothiaden, imipramine, oxyprothepin decanoate and docloxythepin. No dominant-lethal effect was induced by these neuroleptics, even when administered at doses many times as great as clinical doses. The reduced percentages of pregnancies, in females who had copulated with males receiving docloxythepin, observed during and immediately after its administration, were directly connected with marked sedation induced in the males by this neuroleptic.     

Effect of imipramine hydrochloride on the activity of gamma-aminobutyric acid transaminase in regions of the rat brain

The effect of intraperitoneal injection of imipramine hydrochloride on the activity of gamma-aminobutyric acid transaminase was determined in three regions of the rat brain.The cerebral hemispheres did not show a significant change in the activity of gamma-aminobutyric acid transaminase. Cerebellum and brain stem, both, however, showed a very significant decrease in the activity of the enzyme at 15 and 30 minutes after drug administration. At 90 minutes after drug administration, the activity of gamma-aminobutyric acid transaminase had returned to nearly control values.     

Induction of behavioral supersensitivity to apomorphine by DFP treatment

The effect of DFP, a long-acting inhibitor of acetylcholinsterase, on apomorphine-induced climbing behavior, was tested in mice. Twelve hours following the intraperitoneal administration of a single dose of DFP, animals demonstrated a significant increase in apomorphine-induced climbing behavior. This effect was not observed twenty-four hours following DFP pretreatment. These results suggest that acute administration of a cholinomimetic agent, may produce behavioral supersensitivity to dopamine agonists.     

The acute and the chronic effects of imipramine on the spontaneous motility in chick embryos

The effect of imipramine on the spontaneous motility and development of chick embryos was studied from the 4th to the 19th day of incubation. On acute administration (a single dose of 12.5 of 25 mg/kg egg weight), imipramine already induced significant depression of spontaneous motility in 11-day embryos--an effect which increased significantly after the 15th day of incubation. The similar effect of imipramine in spinal embryos testifies to its direct action on the spinal cord and draws attention to certain details of the role of supraspinal structures of the CNS in the acute effect of imipramine. The chronic administration of imipramine showed that it had an almost 100% lethal effect from 4th to the 7th day of incubation. Between the 8th and the 10th day it caused longlasting depression of spontaneous motility. When it was administered between the 11th and 16th day of incubation, no significant effect on the development of spontaneous motor activity was found in chick embryos.     

Effect of combined treatment with imipramine and metyrapone on the immobility time, the activity of hypothalamo-pituitary-adrenocortical axis and immunological parameters in the forced swimming test in the rat.

Major depression is frequently associated with the hyperactivity of the hypothalamic-pituitary-adrenocortical axis, and glucocorticoid synthesis inhibitors have been shown to exert antidepressant action. The aim of the present study was to examine the effect of joint administration of metyrapone (50 mg/kg) and imipramine (5 and/or 10 mg/kg) on immobility time, plasma corticosterone concentration, the weight of spleens and thymuses and the proliferative activity of splenocytes in rats subjected to the forced swimming test--an animal model of depression. Metyrapone alone (50 mg/kg) reduced the immobility time of rats in the forced swimming test and decreased plasma corticosterone level, but did not change immunological parameters. Joint administration of metyrapone and imipramine (5 and 10 mg/kg) produced a more pronounced antidepressant-like effect than either of the drugs given alone. The forced swimming procedure significantly increased the proliferative activity of splenocytes, that parameter being reduced only by co-administration of metyrapone and imipramine. Joint administration of metyrapone and imipramine inhibited to a similar extend the corticosterone level as did treatment with metyrapone alone (about twofold); however, the plasma corticosterone level in animals treated with metyrapone and the higher dose of imipramine did not differ from the concentration of this steroid in control, not-stressed rats. The obtained results indicate that metyrapone potentiates the antidepressant-like activity of imipramine and exerts a beneficial effect on the stress-induced increase in plasma corticosterone concentration and the proliferative activity of splenocytes. These finding suggest that a combination of metyrapone and an antidepressant drug may be useful for the treatment drug-resistant depression and/or depression associated with a high cortisol level.     

Adrenaline in various organs of the rat: its origin, location and diurnal fluctuation

In order to examine the origin and location of adrenaline in peripheral organs of mammals, adrenaline and noradrenaline were measured in several organs of the rat after adrenalectomy, guanethidine treatment and imipramine injection. One week after bilateral adrenalectomy, adrenaline disappeared almost completely from the heart, spleen and submaxillary gland. Chronic administration of guanethidine caused decreases in both noradrenaline and adrenaline in the peripheral organs. Injection of imipramine induced a reduction of adrenaline concentration in the spleen and submaxillary gland. It is considered that adrenaline in the peripheral organs of mammals is mostly derived from the adrenal gland and that circulating adrenaline is taken up by sympathetic nerve endings in the organs. The adrenaline content of the peripheral organs increased after electric foot-shock and changed according to the time of day. The peak of the circadian rhythm appeared about 6 hours after the peak of the urinary adrenaline rhythm. These findings suggest that adrenaline in body organs plays some role in the responses of the sympathetic nervous system to stressful conditions or even to daily activities.     

Hemodynamic and cardiac actions of trazodone and imipramine in the anesthetized dog.

The relative cardiovascular effects of trazodone and imipramine were compared in two open-chest, anesthetized dog models. Trazodone lowered arterial blood pressure (0.3 mg/kg), slowed heart rate (3 mg/kg) and reduced myocardial contractile force (3–10 mg/kg) following i.v. administration. Low i.v. doses (0.05–0.15 mg/kg) of imipramine increased arterial blood pressure and heart rate, presumably as a consequence of its known anticholinergic properties and/or effects on neuronal catecholamine re-uptake mechanisms. Subsequent to administration of 1.5 and 5 mg/kg, however, the vascular and myocardial depressant effects of imipramine were evident. Trazodone (1–10 mg/kg, i.v.), unlike imipramine, effected a substantial level of $\text{alpha}$-adrenergic blockade $\text{vs.}$ a fixed challenge dose of norepinephrine, although less than that associated with phentolamine. Both trazodone and imipramine reduced aortic flow although $\text{via}$ different mechanisms. The reduction following administration of trazodone resulted from a decrease in heart rate whereas imipramine depressed aortic flow by lowering stroke volume.     

Dependence of the effects of tripeptide MIF and lithium chloride on the degree of supersensitivity of dopamine receptors of the brain

The desensitizing effects of MIF and lithium in respect to supersensitive striatal DA receptors in rats with unilateral lesion of the nigro-striatal pathway by 6-hydroxydopamine were revealed. Two groups of 6-hydroxydopamine-denervated rats were selected by their qualitative responsiveness to apomorphine-induced rotational behavior. It was found, that MIF and lithium (subchronic administration) did not modify behavioral supersensitivity in the highly sensitive group which showed two-peak rotational pattern in response to 0.05 mg/kg apomorphine, which was converted into a single-peak rotational pattern by haloperidol. On the contrary, administration of MIF and lithium for 21 days inhibited the apomorphine-induced rotations to 54 and 65% respectively in the less supersensitive group, which showed a single peak rotational pattern to apomorphine. Moreover, haloperidol showed the high antagonistic potency in these animals. These results suggest, that MIF and lithium might not exert desensitizing effects in the presence of high degree of supersensitivity of the striatal DA receptors, which is probably involved, for example, in the phenomenon of persistent tardive dyskinesia.     

Reversal by cholecystokinin of apomorphine-induced inhibition of dopamine release in the nucleus accumbens of the rat

In vivo electrochemical techniques were used to study the effects of the sulfated (CCK8-S) and unsulfated (CCK8-US) forms of cholecystokinin octapeptide on apomorphine-induced inhibition of dopamine (DA) release in the nucleus accumbens of the anesthetized rat. A dose-dependent inhibition of DA release was observed with intravenous (i.v.) injections of apomorphine. CCK8-S administered i.v. at the nadir of the apomorphine-induced inhibition of DA release produced a transient and dose-dependent increase followed by a prolonged decrease in DA release CCK8-US was ineffective in altering apomorphine's inhibitory effects on DA release. The CCK receptor antagonist proglumide injected i.v. 10 min after apomorphine administration had no effect on apomorphine-induced inhibition of DA release, but blocked the effects of CCK8-S on this inhibition. Given that apomorphine may inhibit DA release by a direct hyperpolarizing action on DA neurons, the observation that CCK8-S temporarily reverses apomorphine-induced effects and further inhibits DA release suggests that CCK8-S exerts its inhibitory effects via a process of depolarization block in DA neurons. These findings indicate that apomorphine and CCK8-S may inhibit DA release in vivo by opposite effects on DA cell membrane potentials and suggest that endogenously released CCK may serve to modulate mesolimbic DA neurotransmission.     

Effect of estrogens on apomorphine-induced circling behavior in the rat.

The effect of administration of estrogens parenterally for 1 week was tested on apomorphine-induced circling in a group of castrated female rats with a lesion of the left entopednucluar nucleus. We observed a significant decrease in the number of turns per minute in estrogen-treated animals as compared with controls. Our tentative explanation is that estrogens decrease the sensitivity of dopamine receptors in the striatum.     

Assessment of Noradrenaline and 5-Hydroxytryptamine Uptake in Intact Rat Brain

A method for the measurement of 3H-monoamine [noradrenaline (NA) and 5-hydroxytryptamine (5-HT)] uptake into intact brain following intracerebroventricular injection is described. Most of the accumulated monoamine was associated with nerve terminals (synaptosomes). Radioactivity in the synaptosomal fraction was retained by 0.45-micron filters and was osmotically sensitive, features indicative of accumulation within particles rather than binding to membranes. [3H]5-HT associated with synaptosomes was reduced in animals pretreated with the neurotoxin 5,7-dihydroxytryptamine, in parallel with a reduction in endogenous 5-HT levels. Oral administration of tricyclic antidepressants including clomipramine, desipramine, and imipramine inhibited the synaptosomal accumulation of 3H-monoamines. Overall, the features of the accumulation of 3H-monoamines, after intracerebroventricular administration, displayed many of the characteristics expected of a physiological monoamine reuptake system.     

The role of dopamine D2 receptor in the behavioral effects of imipramine--study with the use of antisense oligonucleotides.

Antisense strategies have a potential to specifically block the production of a given protein, e.g. receptor subtype, thus may help to uncover its behavioral and/or biochemical function. In the present study we demonstrated the utility of this approach for studying the role of dopamine D2 receptors in the anti-immobility effect of imipramine in the forced swimming test. Following intracerebroventricular (i.c.v.) administration of phosphorothioate oligonucleotide complementary to mRNA encoding for dopamine D2 receptors (D2 antisense ODN; 1 nmol/1 microl H2O, twice a day for 5 days) to the rats, the decrease in the locomotor activity (shortened total distance travelled and decrease in vertical activity, without differences in the stereotypic movements of animals), as well as the decrease of specific binding of [3H]raclopride in the striatum and limbic forebrain were observed. At the same time, i.c.v. administration of D2 antisense ODN reversed the effect of imipramine in the forced swimming test, what may indicate that the dopamine D2 receptors play a significant role in the behavioral anti-immobility effects of imipramine.     

Effects of the Binding of Imipramine to Erythrocytes and Plasma Proteins on Its Transport Through the Rat Blood-Brain Barrier

Brain extraction of a tricyclic antidepressant, imipramine, was investigated using the carotid injection technique in the rat. The extent to which drug binding to plasma proteins and erythrocytes could inhibit the brain extraction was measured. Equilibrium dialysis showed that imipramine is highly bound to human serum albumin (HSA), alpha 1-acid glycoprotein (AAG), lipoproteins, and erythrocytes. The free dialyzable drug fraction was inversely related to the protein concentration. Despite this degree of binding, no significant reduction in the brain extraction of the drug was observed in the presence of HSA, lipoprotein, or erythrocytes. Only AAG reduced the brain transport of this drug in a ratio related to the protein concentration. However, the rat brain extraction was higher than expected from the in vitro measurement of the dialyzable fraction. These data indicate that the amount of circulating imipramine available for penetration in brain exceeds widely the dialyzable fraction of the drug as measured in vitro.     

Pharmacokinetics of imipramine are affected by age and sex in rats

Chronic treatment with the antidepressant imipramine (IMI) leads to accumulation of imipramine's major metabolite desmethylimipramine (DMI) in the brain. Juvenile, young and middle-aged female rats, as well as juvenile and young male rats were treated chronically with imipramine (14 days) and analyzed 24 hours later for levels of IMI and DMI in the hypothalamus-preoptic area (HPA) and serum. Older animals of both sexes showed higher levels of DMI than juvenile animals, in both the HPA and serum. Females also had higher DMI levels than males at comparable ages. Analysis of IMI and DMI levels at intervals after a single imipramine injection suggested that the initial metabolism of imipramine is slower in older animals and in females (compared to males). The results indicate that age and gender alter the initial metabolism of imipramine, leading to enhanced accumulation of metabolites during chronic treatment in older animals and in female rats, compared to younger rats and males, respectively.     

Simultaneous catalepsy and apomorphine-induced stereotypic behavior in mice

Intraventricular administration of haloperidol or chlorpromazine produces catalepsy and blocks apomorphine-induced stereotypic behavior. Low intraventricular doses of domperidone, sulpiride and spiperone, equally cataleptogenic as haloperidol or chlorpromazine, augment rather than diminish stereotypic behavior produced by subsequent apomorphine treatment. The resultant stereotypic behavior continues even while the animal is in a rigid cataleptic posture and is marked by persistent gnawing and licking. Prior to the induction of catalepsy and after recovery from it, mice display the entire range of typical apomorphine-induced behavior including sniffing, climbing, gnawing, and licking. This animal model may be related to the clinical observation of the coexistence of tardive dyskinesia and drug-induced Parkinsonism in individual patients.     

Do imipramine and dihydroergosine possess two components--one stimulating 5-HT1 and the other inhibiting 5-HT2 receptors?

The mechanisms by which imipramine and dihydroergosine stimulate the 5-HT syndrome in rats and inhibit the head-twitch response in rats and mice were studied. Imipramine- and dihydroergosine-induced stimulation of the 5-HT syndrome was inhibited stereoselectively by propranolol, a high affinity ligand for 5-HT1 receptor sites, but not by ritanserin, a specific 5-HT2 receptor antagonist. (-)-Propranolol potentiated the inhibitory effect of imipramine, but not of dihydroergosine on the head-twitch response, while ritanserin was without effect. Neither imipramine nor dihydroergosine were able to stimulate the 5-HT syndrome in the animals pretreated with p-chlorophenylalanine. As expected, 8-OH-DPAT, a selective 5-HT1A receptor agonist, stimulated, and 5-HT1B agonists CGS 12066B and 1-(trifluoromethylphenyl)piperazine (TFMPP) failed to stimulate the 5-HT syndrome induced in rats by pargyline and 5-HTP administration. A higher dose of ritanserin inhibited the syndrome. While 8-OH-DPAT alone produced all behavioral components of the 5-HT syndrome, dihydroergosine or imipramine alone even at very high doses never produced tremor or a more intensive forepaw padding as seen when these drugs were given in combination with pargyline and 5-HTP. A single administration of (-)-propranolol also inhibited the head-twitch response. This effect lasted in mice longer than after ritanserin administration. In in vitro experiments dihydroergosine expressed approximately twenty-fold higher affinity for 3H-ketanserin binding sites than imipramine. The results suggest that imipramine and dihydroergosine possess two components--one stimulating the 5-HT syndrome in rats by a presynaptic, presumably 5-HT1A-mediated mechanism, and the other inhibiting 5-HT2 binding sites.     

Hypoaminoacidemia caused by imipramine but not by clenbuterol is dissociable from hyperglycemia and hyperinsulinemia

The effects of the tricyclic antidepressant imipramine (20 mg/kg) and the beta-adrenoceptor agonist clenbuterol (0.5 mg/kg) on the serum concentrations of tyrosine, tryptophan, glucose and insulin were compared 30 min after intraperitoneal injection. The drugs had nearly identical effects on serum tyrosine, which was reduced to 73% of control by both drugs, and on tryptophan, which was reduced to 72% by imipramine and to 66% by clenbuterol. In contrast, whereas clenbuterol raised serum glucose to 174% and insulin to 379% of control, imipramine had no significant effects on either glucose or insulin. The results clearly demonstrate that the effects of imipramine on blood amino acid levels are dissociable from effects on glucose and insulin. We conclude, therefore, that hypoaminoacidemia caused by imipramine is not mediated by stimulating insulin release.     

Relationship between levels and uptake of serotonin and high affinity [3H]imipramine recognition sites in the rat brain

High affinity [3H]imipramine binding, endogenous levels of serotonin and noradrenaline, and serotonin uptake were determined in brain regions of rats with selective destruction of serotonergic neurons by 5,7-dihydroxytryptamine (5,7-DHT), of adrenergic neurons by 6-hydroxydopamine (6-OHDA), and of rats treated with reserpine. Neonatal treatment with 5,7-DHT resulted in a significant decrease of both serotonin levels and density (Bmax) of high affinity [3H]imipramine binding sites in the hippocampus. In contrast, an elevation of serotonin levels and an increase in Bmax of [3H]imipramine binding were noted in the pons--medulla region. No changes were observed in the noradrenaline content in either of these regions. Intracerebral 6-OHDA lesion produced a drastic suppression of noradrenaline levels in cerebral cortex but failed to alter the binding affinity (KD) or density (Bmax) of [3H]imipramine recognition sites. A single injection of reserpine (2.5 mg/kg) resulted in marked depletion of both serotonin (by 57%) and noradrenaline (by 86%) content and serotonin uptake (by 87%) in the cerebral cortex but had no significant influence of the parameters of high affinity [3H]imipramine binding in this brain region. The results suggest that high affinity [3H]imipramine binding in the brain is directly related to the integrity of serotonergic neurons but not to the magnitude of the uptake or the endogenous levels of the transmitter, and is not affected by damage to noradrenergic neurons or by low levels of noradrenaline.