Behavioral consequences of antidepressant treatment in rodents

Short-term antidepressant treatment has long-lasting effects, and reverses stress-induced decreases in bone features in rats

Antidepressants are among the most-prescribed class of drugs in the world and though weight gain is a common outcome of antidepressant treatment, that effect is not well understood. We employed an animal model comprised of 2 weeks of chronic restraint stress with antidepressant treatment, followed by diet-induced obesity. We showed that short-term antidepressant treatment had long-lasting effects, not only leading to weight gain, but also enhancing trabecular and cortical bone features in rats; therefore, weight gain in this model was different from that of the classic diet-induced obesity. Late in the post-restraint recovery period, antidepressant-treated animals were significantly heavier and had better bone features than saline-treated controls, when assessed in the distal femoral metaphysis. The propensity to gain weight might have influenced the rate of catch-up growth and bone allometry, as heavier animals treated with fluoxetine also had enhanced bone features when compared to non-stressed animals. Therefore, short-term antidepressant treatment ameliorated the long-term effects of stress on body growth and bone. Growth and bone structural features were associated with leptin levels, and the interaction between leptin levels and antidepressant was significant for bone mineral content, suggesting that short-term antidepressants in the context of long-term diet-induced obesity modified the role of leptin in bone formation. To our knowledge this is the first study reporting that short-term antidepressant treatment has long-lasting effects in restoring the effects of chronic stress in body weight and bone formation. Our findings may be relevant to the understanding and treatment of osteoporosis, a condition of increasing prevalence due to the aging population.

Animal Models of Depression and Drug Delivery with Food as an Effective Dosing Method: Evidences from Studies with Celecoxib and Dicholine Succinate

Multiple models of human neuropsychiatric pathologies have been generated during the last decades which frequently use chronic dosing. Unfortunately, some drug administration methods may result in undesirable effects creating analysis confounds hampering model validity and preclinical assay outcomes. Here, automated analysis of floating behaviour, a sign of a depressive-like state, revealed that mice, subjected to a three-week intraperitoneal injection regimen, had increased floating. In order to probe an alternative dosing design that would preclude this effect, we studied the efficacy of a low dose of the antidepressant imipramine (7 mg/kg/day) delivered via food pellets. Antidepressant action for this treatment was found while no other behavioural effects were observed. We further investigated the potential efficacy of chronic dosing via food pellets by testing the antidepressant activity of new drug candidates, celecoxib (30 mg/kg/day) and dicholine succinate (50 mg/kg/day), against standard antidepressants, imipramine (7 mg/kg/day) and citalopram (15 mg/kg/day), utilizing the forced swim and tail suspension tests. Antidepressant effects of these compounds were found in both assays. Thus, chronic dosing via food pellets is efficacious in small rodents, even with a low drug dose design, and can prevail against potential confounds in translational research within depression models applicable to adverse chronic invasive pharmacotherapies.

Chronic serotonin-norepinephrine reuptake transporter inhibition modifies basal respiratory output in adult mouse in vitro and in vivo

Respiratory disturbances are a common feature of panic disorder and present as breathing irregularity, hyperventilation, and increased sensitivity to carbon dioxide. Common therapeutic interventions, such as tricyclic (TCA) and selective serotonin reuptake inhibitor (SSRI) antidepressants, have been shown to ameliorate not only the psychological components of panic disorder but also the respiratory disturbances. These drugs are also prescribed for generalized anxiety and depressive disorders, neither of which are characterized by respiratory disturbances, and previous studies have demonstrated that TCAs and SSRIs exert effects on basal respiratory activity in animal models without panic disorder symptoms. Whether serotonin-norepinephrine reuptake inhibitors (SNRIs) have similar effects on respiratory activity remains to be determined. Therefore, the current study was designed to investigate the effects of chronic administration of the SNRI antidepressant venlafaxine (VHCL) on basal respiratory output. For these experiments, we recorded phrenic nerve discharge in an in vitro arterially-perfused adult mouse preparation and diaphragm electromyogram (EMG) activity in an in vivo urethane-anesthetized adult mouse preparation. We found that following 28-d VHCL administration, basal respiratory burst frequency was markedly reduced due to an increase in expiratory duration (T(E)), and the inspiratory duty cycle (T(I)/T(tot)) was significantly shortened. In addition, post-inspiratory and spurious expiratory discharges were seen in vitro. Based on our observations, we suggest that drugs capable of simultaneously blocking both 5-HT and NE reuptake transporters have the potential to influence the respiratory control network in patients using SNRI therapy.

Long-term body weight outcomes of antidepressant-environment interactions

Both obesity rates and antidepressant use have escalated in the last 20 years. Most people who start antidepressant treatment discontinue it on their own. Meanwhile, obesity rates continue to increase. To test the hypothesis that antidepressant use is a risk factor for obesity, even after long-term discontinuation, we developed a novel animal paradigm consisting of short-term exposure to stress and antidepressants, followed by long-term high-fat diet. We show here that recurrent restraint stress (RRS)-related weight loss is recovered 2 weeks after the end of stress in young growing rats receiving a high-fat diet. It is noteworthy that animals that received short-term antidepressant treatment with either imipramine or fluoxetine during 7 days of RRS showed behavioral evidence of antidepressant effects. When exposed to a high-fat diet after stress and when antidepressant treatment had ended, the animals had significant increases in caloric intake, body weight (BW) and size from 17 to 22 weeks following antidepressant discontinuation when compared with (control) RRS animals treated with saline and fed with a high-fat diet. These data are consistent with the previously described phenomenon of time-dependent sensitization, and support the notion that enduring effects of short-term antidepressant treatment become manifest on a long-term basis after antidepressant discontinuation, during conditions of high stress followed by high-fat intake. Analyses of open field and body size measurements obtained in a small subset of animals show that animals previously exposed to antidepressant had no deficits in locomotor activity and were larger. Antidepressant exposure may therefore be a covert, insidious and enduring risk factor for obesity, even after discontinuation of antidepressant treatment. Our data support the concept of persistent, long-term effects of pharmacological-environment interactions on BW regulation.

Comparison of the behavioural pharmacology of the Lister-Hooded with 2 commonly utilised albino rat strains

The use of animal models (particularly rats) in research for developing drugs for central nervous system diseases is well validated. However a range of strains are often utilised in these models. The Lister-Hooded (LH) strain is beginning to be increasingly used in preclinical investigations. Thus, the objective of the present study was to investigate the comparative behavioural pharmacology of this strain, with the two most widely used rat strains, namely the Sprague-Dawley (SD), and Wistar (W) strains. The tests used were the forced swim test (FST) for antidepressants, the amphetamine-locomotor activity test for antipsychotics, the elevated plus maze (EPM) for anxiolytics, as well as tests of general locomotor activity using home cage monitoring (HCM) and the open field test. Continuous HCM revealed a significantly higher daily activity and lower nocturnal activity for LH compared to the other strains; there were no strain-related differences in the open field test. In the FST, there were no strain differences in immobility time and a similar magnitude of desipramine-induced reduction in immobility across strains. In the locomotor activity test, control LH rats showed significantly higher activity whilst significant amphetamine-induced hyperactivity was seen only with the LH and W strains. In the EPM, control LH rats had a significantly larger percentage of open arm entries, whilst only the SD strain displayed a significant diazepam-induced increase in this parameter. These findings suggest that strain variation can cause markedly different results in behavioural pharmacological tests where locomotor activity plays a significant role, and should be taken into account when selecting a strain for evaluating the behavioural effects of psychotropic drugs. Such differences in locomotor activity in the LH strain could be accounted for by an altered diurnal pattern in this strain.

Antidepressant treatment and rodent aggressive behaviour

This review examines two 'ethologically relevant' rodent models, the resident-intruder and social hierarchy paradigms, that are sensitive to chronic antidepressant treatment (including repeated electroconvulsive shock). These models of rodent social and agonistic behaviour demonstrate that acute and chronic treatment with antidepressant drugs (regardless of their acute pharmacological activity) induce diametrically opposite changes in rodent aggressive behaviour. The common ability of chronic antidepressant treatment to increase rodent aggression (which in turn results in increased hierarchical status in closed social groups) most likely reflects the increased assertiveness and associated externalization of emotions (indicative of increased extrapunitive aggression) expressed during recovery from depressive illness. Finally, findings that relate observed behavioural changes to underlying neurochemical changes are briefly reviewed in terms of adaptive mechanisms in the rodent central nervous system induced by antidepressants, and also with respect to suicide ideation and panicogenic responses observed in some patients at the onset of treatment with selective serotonin reuptake inhibitors for affective disorders.

Effects of chronic citalopram treatment on central and peripheral spontaneous open-field behaviours in rats

The spontaneous open-field behavioural effects of 10 days of chronic treatment with two clinical doses (10 and 20 mg/kg daily) and one high/toxic dose (100 mg/kg daily) of the selective serotonin reuptake inhibitor citalopram (delivered subcutaneously by implanted osmotic pumps) were examined in rats. Central and peripheral arena locomotor and rearing activities were recorded simultaneously, and the data were assessed during the first hour as well as during the following 24 hr (the latter for effects on the diurnal rhythm). Rats treated with 100 mg/kg daily exhibited lower peripheral locomotor and rearing activities than the other groups during the first test hour. The ratio between central and peripheral activity increased in a dose-dependent non-proportional manner during the first test hour, indicating a general increase in the central arena activity exerted by the rats when treated with citalopram. No major differences were observed between any of the four groups in overall behavioural activities over the 24-hr period. This study indicated that the open-field locomotor and rearing behaviours in normal rats were affected by increasing doses of racemic citalopram, particularly during the first hour of adaptation.

Induction of interleukin-1 beta and interleukin-1 receptor antagonist mRNA by chronic treatment with various psychotropics in widespread area of rat brain

We investigated whether psychotropics orally administered to rats affect levels of interleukin-1 beta (IL-1 beta) and interleukin-1 receptor antagonist (IL-1Ra) mRNA in the hypothalamus, hippocampus, frontal cortex, and brain stem, using a reverse transcription-polymerase chain reaction method. The psychotropics tested were chlorpromazine, haloperidol, imipramine, maprotiline, fluvoxamine, and diazepam. Treatment for 28 days raised the levels of both mRNAs. The increase in IL-1Ra mRNA was 6-112 times larger than that of IL-1 beta mRNA in most brain regions examined. These results suggest that chronic treatment with psychotropics causes greater amplifying effects on IL-1Ra mRNA than IL-1 beta mRNA in the brain.

Effects of chronic imipramine on exploration, locomotion, and food/water intake in rats

Three groups of rats were subjected to 15 daily injections of imipramine (10 or 20 mg/kg) or vehicle control injections, respectively. During the treatment period, both imipramine groups failed to grow while the control group gained weight normally. Both dosages of imipramine suppressed food intake significantly, while water intake was only reduced by 20 mg/kg of imipramine and only during the first 5 days of treatment. Twenty-four hours after the last imipramine injection, the animals were subjected to a test battery designed to demonstrate potential changes in locomotion and/or exploration. While locomotion appeared unaffected by both dosages of imipramine, the group receiving 20 mg/kg of imipramine demonstrated a significantly reduced exploration. The exploration of the group receiving imipramine in the concentration of 10 mg/kg was only marginally changed. The temporal pattern of exploration of the animals receiving 20 mg/kg of imipramine revealed that chronic imipramine treatment was associated with an initial "hyperexploration" followed by an "overhabituation," resulting in an overall reduction of exploration during a 15-min period.

Evaluation of depression in rats exposed to chronic (unpredictable) electric shock

The present study was undertaken to evaluate the applicability of a proposed behavioral stress paradigm as an animal model for depression. Rats were trained to press a lever under a fixed ratio (FR) 5 schedule in a Skinner box for 10 days and were subsequently exposed to a daily regimen of 20 cycles of FR 5 and 10 cycles of variable ratio (VR) 10 for about a week. This exposure resulted in a reduction of the number of lever presses and successful escapes compared to the level achieved after training. In addition, weight gain was significantly suppressed compared with other treatments. Acute and chronic administration of psychotropic drugs (imipramine and chlordiazepoxide) showed that treatment with imipramine increased both the number of lever presses and successful escapes while chlordiazepoxide increased only the number of lever presses. The results suggest that this simplified animal model utilizing chronic unpredictable electric shock may be useful in the study of human depression.

Neuroendocrine response to clonidine and 8-OH-DPAT in rats following chronic administration of desipramine or sertraline

1. Rats were administered either desipramine (DMI) or sertraline daily at doses 7.5 mg kg-1 or 10 mg kg-1, i.p., respectively and the effects on the functional state of hypothalamic neuroendocrine control mechanisms assessed by measurements of plasma hormones following acute drug challenge. The effects of treatment on gross behaviour and brain adrenoceptor density were also determined. 2. Both DMI and sertraline caused significant reduction in activity measured as ambulation and rearing at 14 days of treatment. 3. All animals were chronically cannulated after 14 days of treatment and tested for neuroendocrine response to acute i.v. clonidine (50 micrograms kg-1) or 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, 250 micrograms kg-1) after 21 or more days of treatment. 4. Rats treated with DMI but not sertraline showed a virtually complete suppression of the growth hormone (GH) secretion elicited by clonidine in controls, while the secretion of corticosterone was augmented. 5. Treatment with DMI but not sertraline led to a significantly greater 8-OH-DPAT-induced secretion of prolactin than in the control rats, while the plasma concentrations of corticosterone following 8-OH-DPAT were not influenced by either DMI or sertraline treatment. 6. The density (but not the affinity) of cerebral cortical binding of [3H]-dihydroalprenolol was significantly reduced by DMI treatment. 7. These results show that DMI treatment blunted the sensitivity of post-synaptic alpha 2-adrenoceptors, accompanied by complex interactions manifested as increased responsiveness of alpha 1-adrenoceptors and 5-HT1A receptors. Sertraline had no significant neurendocrine effects at a dose which significantly reduced gross activity.

Effects of anxiolytic and antidepressant drugs on long-lasting behavioural deficits resulting from one short stress experience in male rats

Exposure of male Wistar rats to one single session of ten inescapable footshocks induces changes in the behavioural responses to environmental stimuli as measured in the "noise test" 14 days later. Shocked (S) rats showed decreased locomotion and rearing during the first 3 min of exposure to a novel environment compared to control (C) rats. When the 85 dB background noise was switched off a marked immobility response emerged in S rats, concomitant with a further decrease in locomotion and rearing. In response to noise off, C rats showed hardly any immobility and a much smaller reduction in locomotion and rearing compared to S rats. These long-lasting changes in behaviour were not reversed by acute treatment with the antidepressants fluvoxamine (3.0-30.0 mg/kg) and desmethylimipramine (DMI, 2.5-10.0 mg/kg) injected IP 30 min before the noise test on day 14 following the shock session. Chronic treatment (day 1 to day 14) with fluvoxamine or DMI did not reverse the behavioural deficits induced by shock exposure. Diazepam (0.6-5.0 mg/kg) administered acutely only reversed the effects of shock on locomotion during the first 3 min of the noise test. Chronic treatment with diazepam normalized the shock-induced decrease in locomotion and attenuated the rearing decrease during the first 3 min of the test, and partially restored shock-induced changes in behavioural response to switching off the noise. The most potent drug in this study was the 5-HT1A receptor agonist flesinoxan (0.3-3.0 mg/kg).(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic and environmental influences on reactive and spontaneous locomotor activities in rats

Paired groups of rats (derived from divergent, selective breeding or living in divergent environmental conditions) were compared with regard to locomotor activities. Intrapair differences were found to vary non-systematically, depending upon whether the rats were initially exposed to a test-environment with or without a slight environmental modification (reactive activities), or were allowed to habituate extensively to the environment (spontaneous activity). Since the behavioral patterns were found to represent distinct entities, this pointed to the necessity of differentiating clearly between spontaneous and reactive activities and indicated, once again, that both genetic and environmental influences are important in these behaviors and must be taken into account. Accepting and controlling for these variables makes it possible to use the factor of individual differences in laboratory animal behavior to advantage.

Citalopram. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in depressive illness

Citalopram is an antidepressant belonging to a new class of drugs which enhance serotoninergic neurotransmission through potent and selective inhibition of serotonin reuptake. Preliminary trials suggest that its short term therapeutic efficacy is significantly greater than that of placebo and mianserin, and comparable to that of amitriptyline, maprotiline and imipramine. It appears to be a weaker antidepressant agent than clomipramine, but better tolerated. Its elimination half-life of 33 hours permits once daily oral administration. Symptomatic improvement obtained with short term treatment has been maintained when therapy has been extended for up to 1 year; in the few patients studied for this extended period, the relapse rate was lower than with fluvoxamine, fluoxetine or imipramine. Compared to standard antidepressant agents, citalopram is well tolerated. It does not appear to be cardiotoxic, has not been associated with seizures in humans, and is relatively nonsedating. Unlike the tricyclic antidepressants, citalopram has minimal anticholinergic effects. Mild and transient nausea, with or without vomiting, is the most frequent adverse effect--occurring in 20% of patients--and increased perspiration, headache, dry mouth, tremor and insomnia are experienced by 15 to 18% of patients. Citalopram thus offers similar therapeutic efficacy and a more favourable tolerability profile than the tricyclic antidepressants. Preliminary data suggest that it may be particularly useful in patients who cannot tolerate the anticholinergic or cardiovascular side effects of tricyclic antidepressants and in those for whom sedation is not indicated.

Avoidance learning during antidepressant withdrawal in mice

Shuttle-box avoidance acquisition, locomotor activity and density of adrenoreceptors in the cerebral cortex have been evaluated, in CD-1 mice, during withdrawal from repeated treatment with desipramine or mianserin (5 or 14 daily injections of antidepressant drug, 10 mg kg-1). Withdrawal from mianserin did not produce any behavioural or neurochemical change. Mice withdrawn from desipramine exhibited avoidance facilitation, when training started 24 h (but not 72 or 120 h) after the last injection. Locomotor activity was not affected and no change was found in the density of beta-adrenoreceptors. An up-regulation of alpha 2- and, to a lesser extent, of alpha 1-adrenoreceptors, occurred 72 h following desipramine withdrawal. However, the assessment of the role played by these neurochemical changes in the avoidance facilitation observed during withdrawal from the antidepressant treatment requires further study.

Intensity and precision of circadian wheel running in three outbred rat strains

The laboratory rat is widely used in many areas of neurobiologic and behavioral research. However, studies of circadian activity rhythms have usually employed other rodent species whose activity patterns are more amenable to measurement in the circadian paradigm. Nevertheless, the rat may be the optimal choice in certain investigations of circadian function because of the wealth of data on the neuroanatomy and neuropharmacology of this species. This study was undertaken to determine whether choice of rat strain could affect the quality of measured circadian activity data. Intensity of wheel running (wheel revolutions per day), precision of onset, and longevity of consistently interpretable running records were assessed in three common outbred rat stains, Long-Evans, Wistar, and Sprague-Dawley. Long-Evans rats showed greater intensity of wheel running while entrained and at four and eight weeks of free running in constant darkness. There was no difference in precision of running onset among the three strains. Thus, use of the Long-Evans strain, with its greater intensity of wheel running and similar precision of activity onset, may confer advantages in studies involving measurement of circadian activity rhythms in the rat.

Neurobehavioral studies of forced swimming: the role of learning and memory in the forced swim test

1. Immobility in the forced swim test ("behavioral despair test") has often been regarded as an animal model of despair or depression. 2. Behavioral studies of forced swimming ("behavioral despair") are reviewed and compared with certain behavioral effects of exposure to inescapable shock (i.e., "learned helplessness"). 3. Exposure to inescapable shock clearly impairs subsequent coping responses. However, detailed behavioral studies of forced swimming indicate that immobility during forced swimming is not a failure of coping but instead reflects a relatively successful coping strategy that employs energy conserving behaviors. 4. Certain neurobiological studies of forced swimming are reinterpreted in light of the behavioral evidence that immobility during forced swimming reflects effects of learning and memory rather than effects of despair or depression. 5. Some implications for future neurobehavioral studies of forced swimming and uncontrollable shock are discussed.

Effect of anxiolytics and antidepressants on extinction and negative contrast

Anxiolytics, particularly the benzodiazepines and barbiturates tend to retard, but not prevent, extinction, promote recovery from negative contrast, and elevate S- responding in discrimination training. Anxiolytics, administered during acquisition, tend to eliminate the partial reinforcement extinction effect, but this result is substantially influenced by parametric considerations. Behaviors that are energized in extinction may have a different pharmacological profile than behaviors that decline. Conclusions regarding the effects of antidepressants must be more tentative but, in general, acutely administered antidepressants are relatively ineffective in all of these paradigms. However, antidepressants may enhance the efficiency of responding on DRL schedules whereas anxiolytics tend to disrupt such behavior.

Behavioral evidence implicating dopamine in sensorimotor arousal and norepinephrine in the sedative effects of antidepressant drugs

The effects of acute and chronic antidepressant treatment on acoustic startle were evaluated in three experiments. Administration of 2.5-10.0 mg/kg desipramine, amitriptyline, and nortriptyline depressed acoustic startle responding after repeated sensory stimulation. In contrast to the tricyclic drugs, the serotonin reuptake inhibitor zimelidine increased acoustic startle, and inhibition of dopamine reuptake following acute nomifensine and bupropion administration did not influence startle reactivity in the doses examined. The response reducing effects of desipramine and amitriptyline persisted following chronic exposure to these drugs, and these findings were discussed in relation to the inhibitory actions of the tricyclics on locus coeruleus neurons. A second major finding in this study was that animals challenged with d-amphetamine during desipramine and amitriptyline withdrawal showed a facilitated startle response. Enhanced startle reactivity to amphetamine was also observed following long-term exposure to iprindole, and a withdrawal hyperactivity of acoustic startle was evident after chronic treatment with amoxapine, bupropion, and nomifensine. These results agree with evidence that repeated administration of antidepressants increases dopamine neurotransmission which modulates sensorimotor arousal.

The apparent antinociceptive effect of desipramine and zimelidine in the tail flick test in rats is mainly caused by changes in tail skin temperature

Tricyclic antidepressants have shown antinociceptive properties in some, but not in all, animal studies using the tail flick test. Tail flick latency has been found to be strongly negatively correlated to tail skin temperature with its highest correlation found when the temperature is measured close to the heated spot. The selective 5-HT reuptake inhibitor zimelidine, as well as the noradrenaline reuptake inhibitor desipramine, increased tail flick latencies. However, this increase could largely be explained by a concomitant reduction in tail skin temperature. The highest dose of desipramine investigated (25 mg/kg) seemed to possess antinociceptive properties in this test also after correction for the fall in tail skin temperature. Lower doses of desipramine (5 and 15 mg/kg) and zimelidine (5, 20 and 30 mg/kg) were either inactive or their effect on tail flick latency could be explained by the fall in tail skin temperature. The apparent antinociceptive effect of zimelidine in the tail flick test thus seems to be due to an effect on tail skin temperature. Desipramine also seems to have its main effect due to a similar mechanism; however, the highest dose of desipramine used induced significant antinociception.

An open field study of antidepressant drugs

Eight psychotropic drugs, mainly acting on the catecholaminergic systems, were investigated in an open field setting. All drugs but one showed a significant reduction in overall activity over time. Only piribedil at 32 mg/kg showed an increase, while 2 mg/kg showed a decrease over time. Amineptine and nomifensine significantly increased and salbutamol significantly decreased both ambulation and rearing with dose. For viloxazine, metapramine, piribedil and piracetam no significant dose effects were revealed at the doses tested. It is concluded that no clear correlation between clinically reported antidepressant efficacy and the selected open field variables can be demonstrated. However, some of the dopaminergic drugs have substantial activating properties, which might render them dependence-producing properties.

Effects of desipramine on rat behavior are prevented by concomitant treatment with ethanol

Ethanol prevents the decrease of the number of beta-adrenoceptors in the cerebral cortex induced by chronic treatment of rats with desipramine. The activation of the adenylate cyclase, the second messenger, by beta-adrenergic agonists is reduced somewhat less than after treatment with desipramine alone. The present paper examined the hypothesis that ethanol inhibits the neuronal adaptation to desipramine chronic treatment at the functional level as well. Desipramine reduced exploratory behavior (crossings, rearings) as did ethanol. Combined treatment attenuated the effect of desipramine. Cognitive performance was investigated using an active avoidance paradigm. Desipramine-treated rats did not learn the task in contrast to control animals. Again, combination treatment with ethanol improved the ability of the rats to perform the task. The activity of cerebral beta-adrenergic mechanisms was assessed by injection of salbutamol, a beta-adrenoceptor agonist in rats pretreated with 5-hydroxytryptophan (5-HTP). The augmentation of the 5-HTP-induced wet dog shake behavior by salbutamol was observed in all animals independent of the chronic treatment. However, rats treated with desipramine were less active than those treated with tap water or ethanol. The effect of desipramine in the presence of a high concentration of salbutamol was attenuated by ethanol. The observed increase of the number of wet dog shakes correlates with the function of these receptors. In two paradigms, spontaneous motility and apomorphine-induced hypothermia, ethanol did not affect the action of desipramine. It is noteworthy that desipramine acted in both situations within a short time period (minutes to hours). The findings strongly suggest that ethanol can prevent adaptive changes in the brain induced by chronic treatment with the antidepressant desipramine. This is of special interest since the adaptation of beta-adrenoceptors is thought to be critical for the antidepressant efficacy of various therapeutic interventions applied in psychiatric practice.

Inhibitory influence of dihydroergosine on the aggressiveness of rats and mice

Fifty mg/kg of ergot alkaloid dihydroergosine (DHESN) inhibited the mouse-killing behavior of isolated male rats, while 10 mg/kg did not. This effect of DHESN (50 mg/kg) lasted for 24 hr. When an additional injection of DHESN (50 mg/kg) was given to mouse-killer rats 6 days following the first, the mouse-killing behavior was again inhibited. The effect of the second drug injection also persisted for 24 hr and was accompanied by an increased concentration of 5-HT in the raphe nuclei and hypothalamus and by a decreased concentration of GABA in the olfactory bulbs. DHESN also inhibited aggressiveness in isolated mice. Two hr following the administration of 10 mg/kg DHESN the fighting was inhibited in 46% of pairs tested, while 50 mg/kg abolished it completely. The effect of 50 mg/kg lasted 24 hr. These results, showing the antiaggressive effects of DHESN, support our previous suggestion that DHESN might presumably be a new antidepressant, and suggest that besides the serotoninergic, the GABA-ergic system might also be involved in the modification of behavior induced by this drug.

Long-term effects of inescapable stress on daily running activity and antagonism by desipramine

The behavioral consequences of exposure to stressors such as inescapable shock are usually transitory if testing is conducted in an environment different from that in which the stressor was administered. The behaviors tested have generally been motivated by discrete stimuli in the environment (e.g., activity in reaction to shock) or have been part of homeostatic regulatory mechanisms (e.g., eating). Here we investigated the effects of inescapable shock on a behavior that is not so tightly tied to motivating and reinforcing conditions, daily activity in a familiar home cage/running wheel environment. Rats lived in the wheel environment for 44-85 days before treatment. Inescapable shock produced only a transient reduction of water intake and body weight, but daily running was depressed for 14-42 days (the maximum period studied) depending on the conditions. This long-term effect on activity occurred despite the fact that shock was administered in an environment very different from the animal's home running wheel environment. The activity reduction was reversed by desipramine in a dose dependent fashion. Indeed, the activity of inescapably shocked animals treated with the optimum dose of desipramine exceeded that of control animals undergoing neither stress nor drug treatment. The maximum effect of desipramine required 7 days of treatment. Desipramine did not affect the activity of control subjects.

The effects of chronic antidepressant treatment in an animal model of anxiety

We have examined the anxiolytic activity of acute and chronic antidepressant treatment in an animal model of anxiety involving novelty-suppressed feeding. Rats were food deprived for 48 h, placed into a novel environment containing food, and the latency to begin eating was recorded. Chronic (21 days), but not acute injections of desipramine (DMI; 10 mg/kg) and amitriptyline (AMI; 10 mg/kg) significantly reduced the latency to begin eating compared to controls, but the percentage decrease was not as great as that seen with either acute or chronic treatment with diazepam (2 mg/kg) or adinazolam (20 mg/kg). A time course study indicated that at least 2 weeks of treatment was necessary to observe a significant anxiolytic effect of antidepressants. The anxiolytic effect of the antidepressants was specific to the novel environment, as 2 weeks of treatment with either diazepam or DMI did not influence the latency to begin eating in the home cage. Finally, a single dose of the central benzodiazepine receptor antagonist, Ro15-1788 (20 mg/kg), given 15 min prior to testing, did not block the anxiolytic effects of chronic DMI, while it completely eliminated the effect of chronic diazepam treatment. These data suggest that antidepressants acquire anxiolytic properties following chronic administration and that this effect appears to be independent of the benzodiazepine receptor system.

Long-lasting effects of chronic chlorimipramine treatment of rats on exploratory activity on a hole-board, and on immobility in the forced swimming test

The study concerned the effects of acute and chronic clomipramine administration to male rats on exploratory activity in a novel environment (hole-board) and on immobility in the forced swimming test. Acute clomipramine administration did not alter either exploratory activity on a hole-board as measured 3 or 20 h after drug administration, or immobility in the forced swimming test as measured 20 h after drug administration. Approximately 20 h after the last injection of clomipramine, the rats chronically treated with the drug showed reduced exploratory activity on the hole-board. In contrast, chronic clomipramine treatment significantly increased the activity in the forced swimming test. The effects of the drug on exploratory and forced swimming activities persisted for 14 days after the cessation of clomipramine administration. These data indicate that chronic clomipramine administration exerted profound and long-lasting effects on central nervous system function. The long-lasting action of the drug on behaviour in the forced swimming test might explain the long-term beneficial effect of antidepressant drugs in counteracting behavioral depression.

Chronic imipramine effects on exploratory behavior in rats

Approximately 100 days old hooded rats, socially isolated or group-housed since weaning, received 15 daily IP injections of isotonic saline, 10 mg/kg or 20 mg/kg of imipramine HCl. Following their last injection, the rats' active choices of a novel environment, frequencies of rearing and grooming, and cells entered in an exploration box were recorded. The drug treatment reduced rearing, ambulation and (for isolated rats only) grooming, but had no effect on novelty choices. There was a significant weight loss with the higher dose and (for males only) with social isolation during the drug treatment period. While imipramine reduced grooming in isolated but not group-housed rats, there were no other interactions between the two forms of treatment. It was concluded that, in spite of its sedative action on motor activity, chronic imipramine did not alter curiosity about a novel environment.

Effects of chronic amitriptyline and desipramine on food intake and body weight in rats

Long-term treatment with tricyclic antidepressant drugs (TCAs) can induce excessive body weight gain in a significant proportion of patients. Such weight gains, which appear to be largely independent of clinical improvement, are in many cases severe enough to interfere with continuation of treatment. In efforts to model this effect in experimental animals, seven experiments were performed in which two commonly used TCAs, amitriptyline and desipramine, were administered chronically to rats. Despite manipulations of drug dosages (2.5 mg-17 mg/kg), route of administration (intraperitoneal, subcutaneous, oral; daily injections vs. continuous release from osmotic pumps), diet composition and palatability (regular Purina Chow pellets or powder with or without added high fat and high carbohydrate sources; high vs. low protein diets) and animal sex and housing conditions (single vs. group housing), chronic TCA treatment was never observed to increase daily food intake or rates of body weight gain. Desipramine treatment invariably caused decreased food intake and weight loss. Amitriptyline treatment either caused no change in food intake and body weight or slightly reduced levels in comparison to vehicle-treated controls. However, both amitriptyline- and desipramine-treated rats showed a potentiation of acute caloric intake after a single systemic injection of the glucoprivic agent 2-deoxy-D-glucose. These results are considered against the background of human clinical observations. Possible reasons for the differences between human and animal data are discussed.

Interaction between chronic stress and clomipramine treatment in rats. Effects on exploratory activity, behavioral despair, and pituitary-adrenal function

The interaction between the effects of chronic electrical tail shock and clomipramine (CMI) on exploratory activity, behavioral despair and pituitary-adrenal function was studied in adult male rats. Both CMI and shock administered alone significantly reduced exploratory activity in a novel environment (holeboard). Neither interaction nor additive effects were observed when the two treatments were combined. In contrast, chronic shock increased the immobility in the forced swimming test (behavioral despair) and this effect was completely prevented by concomitant CMI administration. Pituitary-adrenal function was not significantly influenced by any of the treatments. The results indicate that: (a) chronic CMI treatment prevented some but not all behavioral changes caused by chronic shock, and (b) no interaction with basal and stress levels of pituitary-adrenal hormones was observed.

The effects of tricyclic and 'atypical' antidepressants on spontaneous locomotor activity in rodents

With the exception of amineptin, buproprion and nomifensine all tricyclic and 'atypical' antidepressants have been reported to reduce spontaneous motor activity in rodents, after both acute and chronic administration. However, with the diversity of chemical actions of these drugs it is unlikely that a single neurochemical mechanism is underlying this one behavioral effect. These widespread sedative effects have implications for interpreting behavioral changes in other test situations, since sedation generally occurs at doses that fall within the dose-range effective in other tests. We also review the effects on spontaneous motor activity of withdrawal from chronic antidepressant treatment.