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6-Nitrodopamine (6-ND) is released by rat vas deferens and exerts a potent contractile response that is antagonized by tricyclic antidepressants and α 1 -, β 1 - and β 1 /β 2 -adrenoceptor antagonists. The release of 6-ND, noradrenaline, adrenaline and dopamine from rat isolated right atria was assessed by tandem mass spectrometry. The effects of the catecholamines were evaluated in both rat isolated right atria and in anaesthetized rats. 6-ND was the major catecholamine released from the isolated atria and the release was significantly reduced in nitric oxide synthase inhibitor L-NAME pre-treated atria or in atria obtained from L-NAME chronically treated animals, but unaffected by tetrodotoxin. 6-ND (1 pM) significantly increased the atrial frequency, being 100 times more potent than noradrenaline and adrenaline. Selective β 1 -blockers reduced the atrial frequency only at concentrations that prevented the increases in atrial frequency induced by 6-ND 1pM. Conversely, β 1 -blockade did not affect dopamine (10 nM), noradrenaline (100 pM) or adrenaline (100 pM) effect. The reductions in atrial frequency induced by the β 1 -adrenoceptor antagonists were absent in L-NAME pre-treated atria and in atria obtained from chronic L-NAME-treated animals. Tetrodotoxin did not prevent the reduction in atrial frequency induced by L-NAME or by β 1 -blockers treated preparations. In anaesthetized rats, at 1 pmol/kg, only 6-ND caused a significant increase in heart rate. Inhibition of 6-ND synthesis by chronic L-NAME treatment reduced both atrial frequency and heart rate. The results indicate that 6-ND is a major modulator of rat heart chronotropism and the reduction in heart rate caused by β 1 -blockers are due to selective blockade of 6-ND receptor., Competing Interests: Declaration of competing interest Authors declare that they have no competing interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Aims: Our previous finding demonstrates that major depressive disorder can mediate accelerated aging in rats. Desipramine is a typical tricyclic antidepressant, and can provide neuroprotection and counteract depression-like behaviors. However, whether desipramine can rescue age-related phenotypes in depressed individuals is not understood. In the present study, we investigated the physiological function of desipramine on rescuing the age-related phenotypes in these animals., Main Methods: The rats were induced by chronic mild stress paradigm, and the depression-like behaviors of rats were detected by sucrose intake test, open field test (OFT) and forced swimming test (FST). Then the depressed rats were treated by desipramine., Key Findings: Desipramine administration was effective in counteracting depression-like behaviors by increasing the sucrose solution intake, reducing the immobility time in the FST, and increasing total distance travelled and numbers of grid line crossed in the OFT. Moreover, desipramine treatment was able to reduce the oxidative damage to rat liver, and to increase the expression of telomerase reverse transcriptase (TERT), leading to correspondingly restored telomerase activity., Significance: Our findings identify that one function of desipramine may partly be to rescue age-related phenotypes in depressed individuals induced by chronic stress., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Aims: An automated experimental system applying a commercially available video image analyzer was developed for the simultaneous detection and measurement of three behavioral components; immobility, swimming (horizontal movements) and climbing (vertical movements) that occur in the murine forced swim test (FST). The system was validated using four typical antidepressants., Main Methods: System validity was confirmed by demonstrating no significant difference in 6 min time course of control group and imipramine-dosed group (30 mg/kg) between manual examinations and automated digital analysis for all the three behaviors (i.e., correlation coefficients were 0.96, 0.83 and 0.94 for immobility, swimming and climbing, respectively). The effects of acute single treatment with four antidepressants in clinical use, i.e., imipramine, desipramine, bupropion and fluvoxamine were evaluated at doses of 15, 30 and 60 mg/kg using the system., Key Findings: In 2-4 min time span analysis, all four antidepressants reduced immobility and increased climbing significantly, desipramine and bupropion increased swimming significantly, while imipramine and fluvoxamine did not., Significance: The automated experimental system enabled efficient and accurate analysis of the three murine behaviors during FST at once. Climbing could be more sensitive parameter to detect anti-depressant-like effect than immobility in this system., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Protriptyline, a tricyclic antidepressant for psychiatric disorders, can induce prolonged QT, torsades de pointes, and sudden death. We studied the effects of protriptyline on human ether-à-go-go-related gene (HERG) channels expressed in Xenopus oocytes and HEK293 cells. Protriptyline induced a concentration-dependent decrease in current amplitudes at the end of the voltage steps and HERG tail currents. The IC(50) for protriptyline block of HERG current in Xenopus oocytes progressively decreased relative to the degree of depolarization, from 142.0 microM at -40 mV to 91.7 microM at 0 mV to 52.9 microM at +40 mV. The voltage dependence of the block could be fit with a monoexponential function, and the fractional electrical distance was estimated to be delta=0.93. The IC(50) for the protriptyline-induced blockade of HERG currents in HEK293 cells at 36 degrees C was 1.18 microM at +20 mV. Protriptyline affected channels in the activated and inactivated states, but not in the closed states. HERG blockade by protriptyline was use-dependent, exhibiting a more rapid onset and a greater steady-state block at higher frequencies of activation. Our findings suggest that inhibition of HERG currents may contribute to the arrhythmogenic side effects of protriptyline.

We studied Na(+), K(+)-ATPase activity alpha isoforms by performing ouabain inhibition curves in rat hypothalamus and mesencephalon after acute administration of desipramine to rats. In hypothalamus, Ki values for high, intermediate and low affinity populations were 0.075x10(-9) M, 0.58x10(-6) M and 0.97x10(-3) M, with isoform distribution of 55%, 28% and 17%, respectively. In mesencephalon, Ki values for high, intermediate and low affinity populations were 1.80x10(-9) M, 0.56x10(-6) M and 0.21x10(-3) M, with isoform distribution of 28%, 46% and 21%, respectively. Three hours after acute administration of 10 mg/kg desipramine to rats, Na(+), K(+)-ATPase activity in hypothalamus increased significantly 54%, 39% and 51% as assayed respectively in the absence of ouabain or in the presence of 1x10(-9) M, or 5x10(-6) M ouabain, whereas only a trend was recorded in the presence of 1x10(-3) M ouabain. In such conditions, enzyme activity in mesencephalon increased significantly 73%, 54%, 30% and 271%, respectively. Present results showed that desipramine treatment enhances the activity of Na(+), K(+)-ATPase alpha isoforms in rat hypothalamus and mesencephalon, but the extent of this increase differs according to the isoform and the anatomical area studied, suggesting a differential enzyme regulation in response to noradrenergic stimulation.

Tricyclic antidepressants have been widely used for the treatment of depression and as a therapeutic agent for the altered gastrointestinal (GI) motility of irritable bowel syndrome (IBS). The aim of this study was to clarify whether antidepressants directly modulate pacemaker currents in cultured interstitial cells of Cajal (ICC). We used the whole-cell patch-clamp techniques at 30 degrees C in cultured ICC from the mouse small intestine. Treatment of pinacidil, an ATP-sensitive K(+) channel opener, in the ICC using the current clamping mode, produced hyperpolarization of the membrane potential and decreased the amplitude of the pacemaker potentials. With the voltage clamp mode, we observed a decrease in the frequency and amplitude of pacemaker currents and increases in the resting outward currents. These effects of pinacidil on pacemaker potentials and currents were completely suppressed by glibenclamide, an ATP-sensitive K(+) channel blocker. Also, with the current clamp mode, imipramine blocked the affect of pinacidil on the pacemaker potentials. Observations of the voltage clamp mode with imipramine, desipramine and amitryptyline suppressed the action of pinacidil in the ICC. Next, we examined whether protein kinase C (PKC) and the G protein are involved in the action of imipramine on pinacidil induced pacemaker current inhibition. We used chelerythrine, a potent PKC inhibitor and GDPbetaS, a nonhydrolyzable guanosine 5-diphosphate (GDP) analogue that permanently inactivates GTP-binding proteins. We found that pretreatment with chelerythrine and intracellular application of GDPbetaS had no influence on the blocking action of imipramine on inhibited pacemaker currents by pinacidil. We conclude that imipramine inhibited the activated ATP-sensitive K(+) channels in ICC. This action does not appear to be mediated through the G protein and protein kinase C. Furthermore, this study may suggest another possible mechanism for tricyclic antidepressants related modulation of GI motility.

High concentration of corticosterone (Cort) 0.2 mM was incubated with PC12 cells to simulate the lesion state of brain neurons in depressive illness, it was found that the inulin-type oligosaccharides extracted from Morinda officinalis, inulin-type hexasaccharide (IHS) at the doses of 0.625, 1.25 microM or desipramine (DIM) 0.25, 1 microM protected the PC12 cells from the lesion induced by Cort. With Fura-2/AM labeling assay, DIM 0.25, 1 microM or IHS 2.5, 10 microM attenuated the intracellular Ca2+ overloading induced by Cort 0.1 mM for 48 h in PC12 cells. Using RT-PCR, treatment with Cort 0.1 mM for 48 h decreased the nerve growth factor (NGF) mRNA level in PC12 cells, IHS 5, 10 microM reversed this change. In summary, IHS attenuate the intracellular Ca2+ overloading and thereby up-regulate the NGF mRNA expression in Cort-treated PC12 cells, which may be consisted at least part of the cytopretective effect of IHS. These results also extend evidence for our hypothesis that neuroprotective action is one of the common mechanisms for antidepressants.

The present study was designed to get further insight into the mode of antidepressant action of extracts prepared from St. John's wort (SJW) and relevant active constituents. Down-regulation of central beta-adrenergic receptors (beta-AR's) has been widely considered a common biochemical marker of antidepressant efficacy. Although previous studies have reported a beta-AR down-regulation for SJW extracts, in vivo studies that compare the effects of SJW extracts with those of relevant active constituents on beta-AR density have not been done yet. We used quantitative radioligand receptor-binding-studies to examine in rats the effects of short-term (2 wks) and long-term (8 wks) administration of different SJW extracts and constituents on beta-AR binding in rat frontal cortex. The effects were compared to those of the standard antidepressants imipramine and fluoxetine. [125I]CYP binding to beta-AR was found to be decreased after short as well as after long-term treatment with imipramine (36%, 40%). Short-term treatment with fluoxetine decreased the number of beta-adrenergic receptors (17%) while long-term treatment with fluoxetine elicited an increase (14%) in beta-AR-binding. This effect was comparable to that of the lipophilic CO2 extract which decreased beta-AR-binding (13%) after two weeks and slightly increased the number of beta-AR's after 8 weeks (9%). Short-term treatment with the methanolic SJW extract decreased beta-AR-binding (14%), no effects for this extract were observed after 8 weeks. Treatment with hypericin led to a significant down-regulation (13%) of beta-AR's in the frontal cortex after 8-weeks, but not after 2 weeks, while hyperforin (used as trimethoxybenzoate, TMB), and hyperoside were ineffective in both treatment paradigms. Compared to the SJW extracts and single compounds the effect of imipramine on beta-AR-binding was more pronounced in both treatment paradigms.

In a rat forced swimming test (FS), we examined the effect of repeated injections of ACTH (adrenocorticotropic hormone) for 14 days on the decreased duration of immobility time produced by imipramine and desipramine. Both imipramine (15 and 30 mg/kg, p.o.) and desipramine (15 and 30 mg/kg, p.o.) significantly decreased the duration of immobility time in the FS. On the other hand, ACTH (100 microg/kg, i.p.) alone did not affect the duration of immobility time in FS. When ACTH (100 microg/kg, i.p.) was injected for 14 days before the 15-min swim session, it counteracted the decreased duration of immobility time induced by both imipramine and desipramine. Thus, ACTH seems to play a key role in decreasing the duration of immobility time of antidepressants in this test.

Several of the genes in the serotonergic and the dopaminergic systems have consensus binding sites for the AP-2 transcription factor family in their regulatory regions. Imbalances in these systems have been implicated in many psychiatric disorders, including depression and bipolar affective disorder. We have made an effort to further elucidate the molecular mechanisms of drugs used for affective disorders. Recently, we analyzed the effects of chronic treatment with certain antidepressants on AP-2 in rat brain. The present study demonstrates that chronic administration of three different classes of antidepressants modulates the DNA-binding activity of AP-2 in the rat brain. Chronic administration of citalopram (10 mg/kg), imipramin (10 mg/kg) and lithium-chloride (40 mg/kg) significantly decreased DNA-binding activity of AP-2. Furthermore, citalopram (10 mg/kg) and imipramin (10 mg/kg) significantly decreased the amount of AP-2alpha protein as determined by ELISA. In addition, citalopram (10 mg/kg) significantly decreased the amount of AP-2beta protein. In contrast, chronic administration of lithium-chloride (40 mg/kg) did not affect the amount of the two AP-2 isoforms. An increased understanding of the function of transcription factors and their involvement in human disease, such as depression, could make it possible in the future to selectively modulate relevant target genes directly.

Cyclic antidepressants are still a dominating group of psychotherapeutic drugs used in the treatment of depression. One of their major side effect is salivary gland dysfunction (oral dryness, xerostomia), leading in humans to increased oral disease and dysfunction of speech, chewing, swallowing and taste. The purpose of this study was to assess the effects of the long-term administration of the tricyclic antidepressant desipramine and the reversibility of this treatment following a 15 d washout period on specific salivary proteins, composition of oral microbiota, and oral health (gingivitis) of aging female F344 rats. Total salivary proteins showed decreased concentrations with age and desipramine. Similar SDS/PAGE protein profiles appeared in all phases but in different relative amounts with age and treatment. While certain proteins maintained steady levels (lactoferrin) or decreased with age and treatment (amylase), the synthesis of proline-rich proteins, high molecular weight mucin-type glycoproteins, and lysozyme was induced with desipramine and age. The oral microbiota was significantly changed with age and the administration of the antidepressant. The incidence of gingivitis with desipramine was highest in the oldest animals, For the different parameters measured, recovery was delayed with age. These data indicate, that desipramine has profound effects on salivary protein secretion. This may partially explain the changes in microbiota and the increased incidence of gingivitis.

The effect of tricyclic antidepressant drugs amitriptyline, nortriptyline, imipramine and desipramine on synaptosomal membrane and lipid bilayer was studied using steady state and time dependent fluorescence spectroscopy of lipid specific fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH). The synaptosomal membrane was prepared from rat brain while liposomes were prepared from dimyristoyl phosphatidyl choline (DMPC) alone and a mixture of DMPC and cholesterol. Upon treatment with amitriptyline and nortriptyline a decrease was observed in the steady state anisotropy of DPH in DMPC liposomes as well as in rat brain synaptosomes. On the other hand, imipramine and desipramine did not cause any significant change. Amitriptyline and nortriptyline also decreased the steady state anisotropy of DPH in liposomes prepared from a mixture of DMPC and cholesterol. Fluorescence decay time and time dependent anisotropy of DPH in both the membranes were measured and the decay of anisotropy was analyzed using wobbling in cone model. Amitriptyline and nortriptyline treatment decreased the limiting anisotropy and order parameter, while the cone angle increased. Imipramine and desipramine did not cause significant change in these parameters. In addition to structural alterations, these drugs inhibited the activity of Na+-K+-ATPase in synaptosomal membrane, however, the decrease was more in case of amitriptyline and nortriptyline as compared to imipramine and desipramine. Our results suggest that the perturbation in membrane order caused by antidepressant drugs could depend on the net charge on the drug molecule.

The long-term effect of d-amphetamine (AMPH) on the induction of oxidative stress was examined in vivo in the rat brain. In this study, 2,3-dihydroxybenzoic acid (2,3-DHBA) and malonaldehyde (MDA) were used as the index of the hydroxyl radical and lipid peroxidation, respectively. The levels of 2,3-DHBA, MDA and dopamine (DA) in striatal homogenates were examined 7 days following injection of a single large dose of AMPH (7.5 mg/kg, i.p.) in rats pretreated with desipramine (10 mg/kg, i.p.), an agent that inhibits the metabolism of AMPH. Our results showed that 2,3-DHBA and MDA levels were significantly increased by AMPH, whereas DA and its metabolites, DOPAC and HVA were depleted in the striatum. Pretreatment with the glutamate NMDA receptor subtype antagonist MK-801 (1 mg/kg, i.p.) attenuated the increases of 2,3-DHBA and MDA, and provided partial protection against the long-lasting loss of DA produced by AMPH. Overall, the results demonstrate that AMPH could induce sustained production of free radical and oxidative damage, and lead to DA terminal degeneration in the striatum of the rat.

Under normal metabolic conditions glucose is an important energy source for the mammalian brain. Positron Emission Tomography studies of the central nervous system have demonstrated that tricyclic antidepressant medications alter cerebral metabolic function. The mode by which these drugs perturb metabolism is unknown. In the present study the interactions of tricyclic antidepressants with the GLUT1 glucose transport protein is examined. Amitriptyline, nortriptyline, desipramine, and imipramine all inhibit the influx of 3-O-methyl glucose into resealed erythrocytes. This inhibition is observed with drug concentrations in the millimolar range. All four antidepressants also noncompetitively displace cytochalasin B binding to GLUT1. The K(I) for this displacement ranges from 0.56 to 1.43 millimolar. This value is in a range greater than that associated with clinical doses and this effect may not be directly applicable to side effects observed with normal use. The observed interaction of these drugs with GLUT1 may reflect an affinity for other glucose-transport or glucose-binding proteins, and may possibly contribute to tricyclic antidepressant toxicity.

The effects of tianeptine, a novel and unusual tricyclic antidepressant drug, on tail-flick and hot-plate tests, which are two thermal analgesia evaluating methods, have been investigated in mice. Tianeptine (5 and 10 mg/kg), para-chlorophenylalanine (pCPA) (100 mg/kg) and a combination of pCPA and tianeptine (10 mg/kg) or saline were injected to mice intraperitoneally. pCPA (100 mg/kg) was injected 24 h before tianeptine or saline treatment when it was combined with tinaeptine (10 mg/kg) or tested alone. The tail-flick latencies and hot-plate reaction times of the mice were measured between 15th and 180th minutes following injections. Tianeptine (10 mg/kg) exhibited a significant antinociceptive activity that could be measured by both tests as compared to groups which were treated with saline or pCPA alone between 15th and 180th min of the observation period. The lower dose of tianeptine (5 mg/kg) or pCPA (100 mg/kg) did not produce any significant changes on tail-flick latency or hot-plate reaction time of the mice. However, pretreatment with pCPA completely blocked the antinociceptive effect induced by tianeptine (10 mg/kg) in both tests used in the present study. Furthermore, tianeptine (10 mg/kg) did not cause any significant impairment effects on rotarod performance of the mice. Our results suggested that tianeptine has a prominent thermal antinociceptive activity in mice and that increased serotonergic activity may be responsible for the analgesic effect of tianeptine.

In the present study we observed that lipopolysaccharide (LPS) administration provoked a characteristic reduction in body weight gain, food consumption, saccharin (but not water) consumption and nocturnal locomotor activity. It has been previously suggested that the ability of LPS to suppress the consumption of, and preference for, a palatable solution such as saccharin without altering water consumption, may represent an anhedonic response. The results of the present study demonstrate that chronic treatment with the tricyclic antidepressant (TCA) desipramine (7.5 mg/kg; i.p.) prevented LPS-induced anorexia, loss of body weight, the antidipsogenic effect and hypoactivity. In contrast, chronic treatment with the antidepressants paroxetine (7.5 mg/kg; i.p.) and venlafaxine (10 mg/kg; i.p.) failed to alter any of the LPS-induced behavioural responses. Furthermore, chronic treatment with desipramine (and to a lesser extent paroxetine) reduced the consumption of, and preference for, saccharin suggesting that these antidepressant treatments induce an "anhedonic" response in their own right. In conclusion, chronic desipramine treatment attenuated LPS-induced depressive-like behavioural symptoms in the rat. However, chronic treatment with paroxetine and venlafaxine did not significantly alter LPS-induced behavioural responses. The results of the present study support the hypothesis that TCA's may exert part of their anti-depressive efficacy through their effects on the immune system. However, this property does not appear to be shared by newer antidepressants which possess a better side effect profile than the TCA's. The suppressive effect of TCA's on proinflammatory cytokine secretion is discussed as a mechanism by which these agents alter LPS-induced behavioural responses.

In this paper, we show the importance of intracellular calcium (Ca2+) signaling systems in the pathophysiology of mood disorders based on our recent work. Patients with affective disorders appear to have an enhanced intracellular Ca2+ rise in response to serotonin. We have observed effects of antidepressant drugs on intracellular Ca2+ signaling in rat cultured neuronal cells and glioma cells, and found that acute application of several classes of antidepressant drugs inhibited intracellular Ca2+ signaling and Ca2+-related signaling. It is important to investigate the role of intracellular Ca2+ signaling system for an understanding of the pathophysiology of affective disorders.

The effects of desipramine and fluoxetine were examined on rat hepatic tryptophan-2,3-dioxygenase activity in the presence or absence of exogenous melatonin. Male Wistar rats were treated intraperitoneally over 8 days. The antidepressants were also administered individually and their impact on the enzyme noted. Desipramine reduced basal hepatic tryptophan-2,3-dioxygenase activity in the liver while fluoxetine had no observable effect. However, fluoxetine also prevented the hemin induced elevation in total enzyme activity. Exogenous melatonin (0.25mg/kg/day) for 8 days counteracted the inhibitory effects of both desipramine and fluoxetine at concentrations of 2.5mg/kg/day. Total enzyme activity was restored when melatonin was administered in combination with either drug. The experimental findings indicate that there is chemical antagonism at the surface of the enzyme between melatonin and the antidepressants that abolishes the observed inhibitory effects of the administered compounds.

Tramadol is a clinically-effective, centrally-acting analgesic. This drug is a racemic mixture of two enantiomers, each one displaying different mechanisms: (+)tramadol displays opioid agonist properties and inhibits serotonin reuptake while (-)tramadol inhibit preferentially noradrenaline reuptake. The action of tramadol on the monoaminergic reuptake is similar to that of antidepressant drugs. Therefore, we have examined the effects of (+/-)tramadol, (+)tramadol and (-)tramadol in a test predictive of antidepressant activity, the forced swimming test in mice. Both (+/-)tramadol and its (-) enantiomer displayed a dose-dependent reduction on immobility; while the effect induced by the (+) enantiomer was not significant. Inhibition of noradrenaline synthesis, but not of serotonin synthesis, was capable of blocking the effect of (+/-)tramadol. The alpha-adrenoceptor antagonist phentolamine, as well as the alpha2-adrenergic antagonist yohimbine, and the beta-adrenoceptor blocker propranolol countered the immobility-reducing action of (+/-)tramadol. Moreover, neither the serotoninergic blocker methysergide nor the opioid antagonist naloxone antagonized the effect of (+/-)tramadol. Our results show that (+/-)tramadol and (-)tramadol have antidepressant-like effect in mice, probably mediated by the noradrenergic system rather than the serotoninergic or opioidergic ones.

In the last few years, considerable evidence has appeared concerning the importance of the opioid systems in the action mechanism of some antidepressant drugs. This action mechanism could be mediated through the inhibition of the enzymes responsible for enkephalin degradation. In this sense, imipramine treatment in vivo increases the enkephalin levels, and this effect is enhanced by inhibitors of enkephalin-degrading enzymes. The present work shows the effects in vitro of imipramine and its active metabolite desipramine on the activities of two membrane-bound enkephalin-degrading aminopeptidases present in rat brain. Imipramine and desipramine in vitro do not affect the aminopeptidase M activity, but they reversibly inhibits the aminoeptidase MII. The enzyme kinetic analysis shows that this enzyme molecule has two different binding sites for each drug, which exert a mixed type enzyme inhibition.

We have investigated altered association of tubulin dimers interacting with G proteins and modulating adenylyl cyclase (AC) as a result of long-term amitriptyline (AMT) treatment. Gpp(NH)p-stimulated, but not basal or manganese-stimulated, AC activity was significantly augmented in cortex membranes prepared from rats chronically treated with AMT. The enhancement of AC activity by Gpp(NH)p-liganded tubulin (tubulin-Gpp(NH)p) was significantly higher in chronically AMT-treated rats than in control rats. Moreover, in cortex membranes from controls, tubulin-Gpp(NH)p prepared from chronically AMT-treated rats was more effective to activate AC activity than tubulin-Gpp(NH)p from controls. Immunoblotting and photoaffinity guanine nucleotide binding procedures showed no significant differences in the amount and the function of G proteins between controls and AMT-treated groups. It is suggested that long-term AMT treatment causes alteration in the functional interaction between tubulin and G protein, and this modification may participate in enhanced coupling of Gs to the catalytic subunit of AC induced by the chronic antidepressant treatment.

One subtype of imidazoline receptors (IR1) is similar to alpha 2-adrenoceptors (alpha 2 AR) based on their high affinity for clonidine and related imidazoline compounds. On the other hand, IR1 possess low affinity for norepinephrine (NE) and other catecholamines. Imidazoline receptors have also been found to be over-expressed in plasma membranes from platelets and brain tissues of depressed patients. Over-expression of IR1 in platelet membranes of depressed patients became normalized after various antidepressant treatment to the patients. Herein, the prototypic antidepressant, imipramine (IMI), has been studied in regard to its treatment effects on [125I]p-iodoclonidine binding to both alpha 2 AR and IR1 in rat brainstem membranes. No effects of chronic IMI treatment were found on brainstem alpha 2 AR binding sites (Bmax and/or KD parameters unchanged) after 25 days of daily injections (i.p. IMI 20 mg/kg/day). However, IMI induced a decrease in the density (Bmax measured under NE mask) of brainstem IR1 sites, with no change in KD. Downregulation of IR1 sites was dose-dependent (minimal effective dose of i.p. IMI was 10 mg/kg/day) and time-dependent (> 16 days of treatment). These results implicate brainstem IR1 in the chronic effects of antidepressants.

Imipramine is an effective antidepressant agent that blocks the reuptake of monoamines. In order to understand some of its basic mechanisms of action, we investigated the effects of chronic imipramine administration (10 mg/kg, i.p.; 21 days) on the alpha-2 receptor population of several brain sites. Alpha-2 receptor density was estimated by in vitro autoradiography using [3H]Idazoxan. The densitometric analysis revealed a decreased receptor density in the A2 region of the tractus solitarius (20%) and locus coeruleus (16%). No changes were observed in the amygdala, pyriform cortex, periacueductal gray and the bed nucleus of the stria terminalis. These results suggest that chronic imipramine treatment selectively modulates the alpha-2 receptor population localized in the brain stem norepinephrine-rich nuclei and not in the population present on limbic structures innervated by noradrenergic terminal projections. The possible physiological consequences of this selective modulation of alpha-2 receptors are discussed.

Systemic administration of 4-Aminopyridine at a dose of 4 mg/kg (4-AP) induces hypothermia in mice. Scopolamine (ED50 = 0.26 mg/kg) and two tricyclic antidepressants, desipramine (ED50 = 1.82 mg/kg) and IM/P/3/4 (ED50 = 8.95 mg/kg) completely antagonize 4-AP-induced hypothermia, whereas minaprine (0.1-0.25 mg/kg), a non-tricyclic antidepressant, reverts only 45% of the maximal effect of 4-AP. Oxotremorine at a dose of 0.05 mg/kg (OXO) induces a hypothermic effect comparable to that of 4-AP. Scopolamine (ED50 = 0.011 mg/kg) completely reverts OXO-induced hypothermia whereas desipramine and IM/P/3/4 never produce more than 60% of antagonism over a wide range of doses. Minaprine does not affect OXO-induced hypothermia. These results suggest that the interaction of antidepressants with cholinergic function occurs mainly at the pre-synaptic level.

The antinociceptive effect of acutely and chronically (every brain elimination half-life time) administered metapramine, a tricyclic antidepressant without anticholinergic or cardiotoxic effects, was studied in three different pain tests. In the hot plate test, its action was more potent when jumping was used as a pain parameter (acute ED50 = 19 +/- 3 mg/kg, i.p.) than when pain was assessed by licking of forepaws (only 20 mg/kg, i.p. was weakly active). Five chronic doses of 15 mg/kg were as active in the tail-flick test as an acute dose of 20 mg/kg (only active dose). Metapramine was more effective in the PBQ-induced writhing test after acute (ED50 = 9.9 +/- 0.1 mg/kg, i.p.) and chronic administration. A significant linear correlation was found between the effect in this test and plasma and overall brain levels of metapramine. No correlation was observed with levels of its three desmethylated metabolites. The usefullness of using a well-defined pattern of administration based on pharmacokinetic parameters and the involvement of monoaminergic mechanisms and of some metabolites of metapramine are discussed.

Effect of desipramine (given i.p. 30 min prior to the tracer injection) on the in vivo binding of 3H-SCH23390 and 3H-N-methylspiperone (3H-NMSP) in mouse striatum was studied. The ratio of radioactivity in the striatum to that in the cerebellum at 15 min after i.v. injection of 3H-SCH23390 or 45 min after injection of 3H-NMSP were used as indices of dopamine D1 or D2 receptor binding in vivo, respectively. In vivo binding of D1 and D2 receptors was decreased in a dose-dependent manner by acute treatment with desipramine (DMI). A saturation experiment suggested that the DMI-induced reduction in the binding was mainly due to the decrease in the affinity of both receptors. No direct interactions between the dopamine receptors and DMI were observed in vitro by the addition of 1 mM of DMI into striatal homogenate. Other antidepressants such as imipramine, clomipramine, maprotiline and mianserin also decreased the binding of dopamine D1 and D2 receptors. The results indicated an important role of dopamine receptors in the pharmacological effect of antidepressants.

The effects of the new tricyclic antidepressant tianeptine were investigated on dopaminergic (DAergic) metabolism in the anteromedian prefrontal cortex and the nucleus accumbens of the rat. DAergic metabolism was assessed by the measurement of DOPAC, the main presynaptic metabolite of dopamine, using in vivo voltammetry in rats ventilated with halothane (0.5-0.75% in air). Acute treatment with tianeptine (10 mg/kg, 20 mg/kg) only increased significantly DOPAC levels in the anteromedian prefrontal cortex. After chronic treatment with tianeptine (15 days, 2 times/day) the increases in DOPAC levels in this structure were altered and less pronounced with the 20 mg/kg dose. Previous studies led to suggest that both acute and chronic effects on DAergic terminals in the anteromedian prefrontal cortex may be involved in the therapeutic action of this new antidepressant.

Chronic (4 days or more) administration of imipramine or mianserin, but not atropine, leads to an extinction in muricidal behavior in the rat. Moreover, receptor binding assays revealed that there is a significant decline in the number of beta-adrenergic, but not serotonin2, receptors in the frontal cortex at the onset of the behavioral modification. While the antidepressants also induced receptor binding changes in nonmuricidal control animals, the pattern of these changes differed from that observed in the muricidal subjects suggesting that the receptor modification was, to some extent, trait-dependent. These findings indicate that, with the muricidal model, chronic rather than acute drug treatment may be a more selective test for antidepressant efficacy. In addition, the data suggest that a decline in brain beta-adrenergic receptors may be causily related to the behavioral modification.

The antidepressants mianserin and amoxapine, and the neuroleptic loxapine caused significant decreases in the number of rat frontal cortex S2-serotonergic receptors after a single acute injection. The affinity of serotonin for this site was also decreased after acute mianserin. Daily injections of loxapine and amoxapine for 2, 7 or 28 days resulted in decreased receptor density but no change in Kd. Down-regulation of S2 sites by mianserin was not dependent on endogenous serotonin stores or occupation of the S2 recognition site since chronic PCPA or acute ketanserin preadministration did not affect the mianserin-induced decreases. The results suggest that mianserin may be acting on other sites which it does not share in common with other S2-antagonists such as ketanserin.

This investigation assessed the relative abilities of three neuroleptics to supersensitize behaviors mediated by the nigrostriatal and mesolimbic dopamine (DA) systems. Rats were treated with either haloperidol, thioridazine, fluotracen or vehicle for 21 days. Stereotypy, in response to DA injection to the striatum, or locomotor activity, in response to DA injection to the nucleus accumbens, were measured after the termination of drug treatment. Pre-treatment with haloperidol enhanced both behavioral responses to central DA injection, while pre-treatment with thioridazine did not enhance either behavior. Pre-treatment with fluotracen enhanced the locomotor response to DA injection to the nucleus accumbens, but did not alter stereotypy after DA injection to the striatum. Neuroleptics differ in their ability to supersensitize the same DA-related behavior, and act selectively to supersensitize behaviors mediated by different DA systems.

Tricyclic antidepressant drugs bind to histamine receptors in rodent and other mammalian tissues. However, a readily accessible, normal human tissue for studies of these drugs has not been available. We showed that freshly isolated human leukocytes can be used for this purpose. Following isolation by dextran sedimentation, leukocytes were incubated for 30 sec. in histamine concentrations from 1.0 nM to 1.0 mM. A dose-related increase in intracellular cyclic AMP was observed. When the cells were preincubated for 10 min. in the tricyclic, nortriptyline, and then challenged with histamine, the concentration of histamine needed for a comparable cyclic AMP increase was elevated 100-fold over non-preincubated cells. These results indicate that the tricyclic drug interacts with histamine receptors on leukocytes, and that these cells may be used for biochemical and clinical studies of these drugs.

Testing for competitive inhibition of sparteine oxidation in the 9000 x g supernatant fraction from human liver provides an in vitro means to identify drugs which can bind to the same form of cytochrome P450 which oxidizes sparteine. There has so far been only two outcomes of this test: either the drug examined competed with sparteine for a common binding site, or it did not inhibit the reaction. The results of such in vitro testing implicated the involvement of guanoxan, nortriptyline, desipramine, imipramine, amitriptyline and chlorpromazine with this enzyme. Amobarbital, tolbutamide and guanethidine in therapeutic concentrations did not interfere with sparteine oxidation by this preparation.

Following a report that nortriptyline was found useful in the control of enuresis in adults, presumably as an anticholinergic, its likely mechanism of action and apparent bladder specificity have now been investigated in vitro. The ratios of anticholinergic potencies (reciprocal of dissociation contents, Ki) for four different tricyclic antidepressants, derived from competitive binding assays with (-)[3H]QNB in tissue homogenates, in the order (human) detrusor muscle/ileal longitudinal muscle/caudate, are as follows: Nortriptyline, 5/4/7; desipramine, 2/1/5/; clomipramine, 4/3/27; amitriptyline, 25/14/56. The apparent selective effect of nortriptyline on the bladder cannot be ascribed to its higher affinity to bladder receptors. Still, this drug is the least discriminatory of the four. Hence, at a given concentration, it is expected to affect tissue embodying a low density receptor pool sooner than tissue having a large receptor reserve. The ratios of the densities of (-)[3H]QNB binding sites in the order detrusor muscle/ileal muscle/cortex is 1/3/5, supporting the present contention. In the guinea-pig, the ratios of the anticholinergic potency in the order bladder/proximal ileum/distal ileum/cortex are as follows: Nortriptyline, 25/5/6/33; desipramine, 8/2/2/14; amitriptyline, 100/14/20/100; clomipramine, 17/3/5/33. Also, the ratios of the densities of binding sites are 1/6/5/2. Hence, data derived from assays in the guinea-pig are not representative of those derived from human tissue.

Early biochemical research on antidepressant treatments provided evidence that the treatments alter catecholaminergic and serotonergic activity. The mechanisms of action proposed by the resulting biogenic amine hypotheses of affective disorders, however, are not consistent with the delayed onset of therapeutic effects of antidepressant treatments nor with the acute effects of more recently developed antidepressant drugs. Recent investigation of chronic antidepressant treatments using ligand binding, electrophysiological, and behavioral techniques have attempted to identify subgroups of receptors that might be affected uniquely and specifically by chronic antidepressant treatments. Such receptor changes have been suggested to form a basis for the mechanism of action of antidepressants. At the present time, however, the data produced by ligand binding experiments and electrophysiological experiments investigating serotonergic functioning do not fit together. In addition, interpretational problems and internal contradictions exist within each of the three bodies of data when straightforward hypotheses regarding a serotonergic role in antidepressant treatment are formulated. In order to clarify the serotonergic role in antidepressant drug and ECS effects the functional significance of observed changes in putative serotonergic receptors must be discovered. Unfortunately, putative receptors identified by ligand binding cannot be directly compared to those identified by electrophysiological techniques, because these two methods require the disassembly of the organism in mutually incompatible ways. In order to prove that either or both techniques do in fact identify functional serotonin receptors, investigators need to proceed both more microscopically and also more globally. Further anatomical and physiological studies are necessary to locate putative receptors and to demonstrate their place in existing serotonergic networks. Further behavioral studies must be done to relate alterations in receptor characteristics to the functioning of the intact organism.

Phenothiazines and tricyclic antidepressants, when added to culture medium, gave rise in several types of cells (C6 rat glioma cells and human fibroblasts), to a decrease in lysosomal sphingomyelinase activity. The effect of chlorpromazine and desipramine was dose dependent, and was observed after 3 hours of incubation with the drugs at concentrations ranging between 1 and 10 microM. In C6 glioma cell cultures, the decrease in sphingomyelinase activity was related to the clinical effectiveness of phenothiazines, tricyclic antidepressants and derivatives. Incorporation of (choline-14C) sphingomyelin showed that the metabolic pathway implying the synthesis of phosphatidylcholine from the hydrolysis of sphingomyelin and/or transfer of phosphorylcholine to phosphatidylcholine was also partially reduced.

The histamine-H1 receptor blocking properties of a number of structurally different antidepressant drugs have been evaluated using a 3H-mepyramine binding assay and a guinea-pig ileum preparation. The tricyclic antidepressants all inhibited the histamine-H1 receptor. Some newer antidepressant drugs, such as zimelidine and nomifensine were devoid of activity while others, such as iprindole and mianserin were very potent. It is concluded that antagonistic effects on the histamine-H1 receptor is not associated with the therapeutic efficacy in depression, but may contribute to the sedative effects of the antidepressant drugs.