Effect of chronic administration of alprazolam and adinazolam on clonidine- or apomorphine-induced aggression in laboratory rodents.

The activity of chronic (3 weeks) treatment with the triazolobenzodiazepines, alprazolam and adinazolam, on clonidine- and apomorphine-induced aggression were studied. Adinazolam, like desipramine, potentiated aggression induced by clonidine while diazepam and alprazolam completely abolished it. In the apomorphine-induced aggression, adinazolam suppressed both aggressivity and stereotypy, while diazepam slightly potentiated it. Alprazolam did not modify the effect of aggression induced by apomorphine. On the whole, while adinazolam seemed to develop an activity closer to that of a classical antidepressant like desipramine, alprazolam appeared to be more similar to the benzodiazepines on clonidine-induced aggression in mice. Compared to desipramine and diazepam, adinazolam left these two effects induced by apomorphine almost unchanged. The experiments performed showed differences between the profiles of action of the two triazolobenzodiazepines studied.

The comparison of benzodiazepine derivatives and serotonergic agonists and antagonists in two animal models of anxiety.

The present paper compares the effects of different serotonergic agonists and antagonists with benzodiazepine derivatives in two animal models of anxiety; the Vogel's and the open-field tests. In the Vogel's conflict test, both diazepam and midazolam produced an anti-punishment action. The drugs 8-OH-DPAT (0.025 and 0.05 mg/kg), buspirone (0.62 mg/kg), gepirone and ipsapirone (0.3 and 0.62 mg/kg, respectively) increased punished intake of water. Ritanserin disinhibited the behaviour of rats at the doses of 2.5 and 5.0 mg/kg and ICS 205-930 (0.001 and 0.01 mg/kg) exerted a marked increase in punished drinking, while ondansetron was active only after the largest dose (1.5 mg/kg). In the open-field test, all drugs increased the number of entries into the central area, as well as the time spent in the central sector of the open-field. The present data indicate similar but not identical spectra of pharmacological sensitivity of both ethologically-oriented and conflict tests, for various classes of anxiolytic drugs. The 5-HT1A receptor agonists and 5-HT2 receptor antagonist have been shown to have similar anxiolytic-like profile to the benzodiazepines but in a narrower dose-range. The 5-HT3 receptor antagonists appeared to be unique in respect to their very strong anti-emotional activity (ICS 205-930), devoid of any clear-cut general inhibitory properties upon locomotion.

Serotonergic innervation of the hippocampus and nucleus accumbens septi and the anxiolytic-like action of midazolam and 5-HT1A receptor agonists.

An involvement of serotonergic innervation of the hippocampus (HP) and the nucleus accumbens septi (NAS) in anxiolytic activity of benzodiazepine midazolam and 5-HT1A receptor agonists was studied in two different animal models of anxiety. Injection of midazolam (10.0 and 20.0 micrograms) or 8-OH-DPAT (0.5 and 1.0 micrograms) into the hippocampus increased punished consumption of water in the Vogel conflict test. Buspirone given at 0.1, 0.5 and 1.0 microgram was ineffective in the Vogel test, while at 5.0 micrograms it enhanced shock-induced suppression of drinking. In the open-field test midazolam (0.01 and 0.1 microgram), 8-OH-DPAT (0.1, 0.5 and 1.0 microgram) and buspirone (2.5 and 5.0 micrograms) increased the number of entries into the central part of the open-field and the time spent in the central sector. Depletion of 5-HT had no influence on the anxiolytic-like effect in the open-field test of intrahippocampally-administered 8-OH-DPAT (0.5 microgram), but the drug tended to increase motor activity in lesioned animals. Midazolam and buspirone injected into the NAS did not have an anxiolytic effect in the Vogel test. A small increase in punished drinking was observed after 8-OH-DPAT (1.0 and 2.5 micrograms). Following intra-NAS injection, midazolam, 8-OH-DPAT and buspirone all failed to produce any marked anxiolytic-like effect in the open-field test. It appears that the hippocampus, rather than the NAS, is involved in mediating anxiolytic-like effects of 5-HT1A receptor agonists. Hippocampal postsynaptic 5-HT1A receptors may account for the anti-emotional influence of this group of drugs. The results indicate some similarities in the psychotropic profile of 5-HT1A receptor agonists and midazolam.

Serotonergic innervation of the hippocampus and nucleus accumbens septi and the anxiolytic-like action of the 5-HT3 receptor antagonists.

The roles of hippocampus (HP) and the nucleus accumbens septi (NAS) in the anxiolytic activity of two 5-HT3 receptor antagonists were studied in two animal models of anxiety, in rats. Injection of tropisetron (0.005 and 0.01 microgram) or ondansetron (1.0 and 2.5 micrograms) into the hippocampus increased punished consumption of water in the Vogel conflict test. In the open field test neither 5-HT3 receptor antagonists had anxiolytic-like effects. Tropisetron (0.01 and 0.025 microgram) injected into the NAS caused a marked increase in punished drinking, while ondansetron (0.01-15.0 micrograms) had no effect. In the open field test, tropisetron (0.001, 0.005 and 0.01 microgram) and ondansetron (1.0 and 2.5 micrograms) given to the NAS increased the number of entries into the central part of the open-field, and the time spent in the central sector of the arena. Depletion of 5-HT significantly enhanced the anxiolytic-like effect of intra-NAS-injected tropisetron in the open field, at the dose of 0.005 microgram. Moreover, 5,7-DHT lesions produced a tendency to increase motor activity in tropisetron-treated rats. Both hippocampal and accumbens 5-HT3 receptors seem to contribute to the anxiolytic-like effects of 5-HT3 antagonists in the Vogel test. It also appears that this effect of 5-HT3 receptor antagonists is related to their action on postsynaptic 5-HT3 receptors within the NAS, and depends on the functional state of the 5-HT innervation ascending from the raphe nuclei. Thus, the present data add more arguments for the more specific involvement of this limbic nucleus in emotional control.

Comparison of the potency, kinetics and voltage-dependency of a series of uncompetitive NMDA receptor antagonists in vitro with anticonvulsive and motor impairment activity in vivo.

The amino-adamantane derivatives memantine (1-amino-3,5-dimethyladamantane) and amantadine (1-amino-adamantane) are relatively low affinity, uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonists which have been used clinically in the treatment of dementia and Parkinson's disease respectively for several years without serious side effects. The aim of this study was to test whether memantine, amantadine and other low affinity uncompetitive NMDA receptor antagonists also have better therapeutic indices than high affinity antagonists in preclinical models of epilepsy by assessing the potency, kinetics and voltage-dependency of open channel blockade for a series antagonists in vitro and comparing these effects to anticonvulsive and motor impairment activity in vivo. The compounds tested were memantine, amantadine, 14 other amino-adamantanes, (+)-MK-801, ketamine, dextrorphan, dextromethorphan and phencyclidine. The offset kinetics of open-channel blockade assessed with whole cell patch clamp recordings from cultured superior colliculus neurones were highly correlated to potency i.e. the less potent antagonists showed faster unblocking kinetics (Koff, r = 0.904). Although, onset kinetics as assessed by Kon were not correlated to potency (r = 0.023), tau on estimated at IC50 is perhaps a more meaningful measure of onset kinetics at equieffective concentrations and was also well correlated to potency (r = -0.863). All amino-adamantanes tested were strongly voltage-dependent. There was also a good correlation between the in vitro potencies of uncompetitive NMDA receptor antagonists assessed with patch clamp recordings and displacement of equilibrium [3H](+)-MK-801 binding and their in vivo activity against maximal electroshock (MES) and pentylenetetrazol (PTZ) induced tonic convulsions and NMDA-induced lethality in mice. Memantine and four other amino-adamantanes with somewhat lower potency and faster blocking kinetics had better therapeutic indices (ED50 rotarod and traction reflex over ED50 in MES-induced convulsions; TI = 2-4) than substances with higher affinity such as ketamine, dextrorphan and (+)-MK-801 (TI < 2). However, amantadine and several other amino-adamantanes with lower potency than memantine actually had poorer therapeutic indices (TI < or = 0.5) which may have been due to additional actions at other ion channels or receptors at the doses necessary to protect against seizures. In fact, ED50 in the MES test was negatively-correlated to therapeutic indices (traction r = -0.790, rotarod r = -0.797) i.e. the less potent uncompetitive antagonists had worse therapeutic indices. The data from the present study do not lend support to the idea that low affinity, open channel NMDA receptor blockers are also effective in models of epilepsy at doses having little effect on physiological processes. It should be stressed that these data do not contradict the known therapeutic safety of memantine and amantadine in dementia and Parkinson's disease respectively. Thus the good clinical profile of memantine in dementia has been attributed not only to its fast blocking/unblocking kinetics but also to its strong voltage-dependency. These biophysical properties may allow therapeutically-relevant concentrations to block chronic, low level pathological activation of NMDA receptors whilst leaving their synaptic activation intact. Precisely these properties may also underlie the poor therapeutic indices seen in the present study on antiepileptic activity due to the synaptic nature of both seizures and normal glutamatergic transmission.

Antagonism of behavioural depression produced by clonidine in the Mongolian gerbil: a potential screening test for antidepressant drugs.

The effects of various antidepressant drugs and some other therapeutic agents on the depression of locomotion and exploratory activity induced by clonidine (0.1 mg/kg IP) were investigated in the Mongolian gerbil (Meriones unquiculatus). In parallel experiments, the effect of yohimbine on clonidine-induced sedation was observed. The following behavioral components were analysed: ambulation, rearing and novel object investigation. Yohimbine antagonized the effects of clonidine in a dose-dependent manner. All antidepressants similarly antagonized the effect of clonidine on ambulation but they differed to a greater extent in their potency in counteracting the clonidine action on exploration, particularly the novel object investigation. On the other hand diazepam and neuroleptic agents such as pimozide and flupentixol failed to antagonize the clonidine effects. The antagonism of clonidine-induced behavioral depression might be used in the selection of antidepressants.

A stimulatory effect of intraaccumbens injections of noradrenaline on the behavior of rats in the forced swim test.

Intraaccumbens injections of catecholamines noradrenaline and dopamine, though not of serotonin, stimulated locomotion by rats in an open field, 10-15 min later. Similar effects were observed 5 min after microinjection of apomorphine whereas clonidine only attenuated locomotor activity. On the other hand, intraaccumbens administration of phenylephrine, isoproterenol and quipazine, in doses similar to an effective dose of noradrenaline, did not alter rat open field behavior. The escape-directed activity of rats in the forced swim test (FST) was stimulated 5 min after local administration of noradrenaline, phenylephrine, isoproterenol or apomorphine only. No effects in the FST were observed 15 min after noradrenaline injection or after intracaudate noradrenaline administration. The stimulatory effects of intraaccumbens noradrenaline injection in the FST were antagonized by the local pretreatment of rats with phentolamine, though not with propranolol. Accordingly, it is possible to conclude that both catecholamines, but not serotonin, play complex and probably distinct roles within the nucleus accumbens in the stimulation of activity by rats in the FST and the open field test.

Interaction between accumbens D1 and D2 receptors regulating rat locomotor activity.

The effect of intra-accumbens injections of various dopaminergic agonists and antagonists on the rat locomotor activity has been evaluated in automated open fields. Locomotor stimulation has been observed after local administration of d-amphetamine (10 micrograms), apomorphine (10 micrograms), as well as of solution containing the D1 agonist SKF 38 393 and D2 receptor agonist LY 171 555 (quinpirole) in doses (10 and 4 micrograms, respectively) which were inactive when both drugs were administered separately. On the other hand separate injections of metoclopramide (0.1 microgram) and SCH 23 390 (0.5 microgram) (D2 and D1 receptor antagonists) very potently inhibited animals' locomotor activity. The data indicate that concomitant stimulation of both accumbens D1- and D2-receptor related mechanisms is a necessary condition to increase rat motility. Moreover, it seems that accumbens D1 receptors may be differently involved in the control of facilitatory versus inhibitory motor processes.

A study of the effects of clonidine on the EEG in rats treated with single and multiple doses of antidepressants.

The influence of repeated and single administrations of desipramine, amitryptiline, and mianserin on the EEG effects of clonidine has been investigated in rats implanted with chronic cortical electrodes. Clonidine induced a dose-dependent EEG synchronization in control animals. Signs of behavioral depression occurred after administration of moderate (0.1 mg/kg) and higher (0.2 mg/kg) doses of clonidine. Single doses of desipramine and amitryptiline attenuated the clonidine effect, while mianserine potentiated clonidine-induced synchronization. Antidepressants given once daily for 14 days completely (desipramine and amitryptiline) or partially (mianserin) reduced the effect of clonidine. Antidepressants alone produced only a slight effect on cortical EEG pattern.

Morphine action in grouped and isolated rats and mice.

The present study determines the analgesic effects of morphine in grouped and isolated rats and mice. Isolated animals developed altered behavioral patterns, including mouse-killing in rats and mutual aggressiveness in mice. The analgesic effect of morphine was tested by tail compression in rats and by the hot plate for mice. Isolated rats developing mouse-killing behavior had a raised pain threshold, while indifferent animals (nonkillers) responded less to morphine. Isolated mice, particularly low aggressors, gave enhanced responses to morphine.

Studies on the effect of lesions of the ventral noradrenergic tract on the antinociceptive action of morphine.

In rats, lesions were placed in the ventral tegmental noradrenergic tract (VT). In some animals lesions also involved the dorsal tegmental noradrenergic tract (DT). Morphine (Mf) analgesia was examined by the tail compression method 8-9 days after lesions. VT lesions produced no changes in Mf activity, while lesions involving VT + DT produced a partial attenuation of the antinoceptive action of Mf. These results suggest that the ascending NA fibres forming the VT are not essential for the antinoceptive effect of Mf.

Lesion of serotonergic neurons antagonizes clonidine induced suppression of avoidance behavior and locomotor activity in rats.

The effects of clonidine on avoidance acquisition and locomotor activity were studied in male Wistar rats with 5,6-dihydroxytryptamine (5,6-DHT) lesions of the median raphe nucleus. Lesioned animals showed marked depletion in forebrain serotonin and 5-hydroxyindole acetic acid concentrations. clonidine (0.2 mg/kg IP in a single daily dose for 6 consecutive days) inhibited avoidance acquisition and reduced locomotor activity in unlesioned rats. In 5,6-DHT rats clonidine failed to produce depressive effect. The resistance of raphe-lesioned rats to clonidine is discussed on the basis of possible interaction between noradrenergic and serotonergic brain systems.

The effect of oxytocin and fragment (MIF-I) on the development of tolerance to hypothermic and hypnotic action of ethanol in the rat.

The daily pretreatment of rats with oxytocin (OXY) or MIF-I prior to ethanol (Et-OH) administration markedly altered the alcohol tolerance when tested on the fifth day of treatment. OXY (800 and 2400 nmole/kg SC) and MIF (800 nmole/kg SC) inhibited the development of tolerance to the hypnotic effect of Et-OH. MIF at this dose also inhibited the tolerance to the hypothermic effect. Only OXY in the dose of 800 nmole/kg suppressed hypothermia in an acute experiment with Et-OH and produced by itself hypothermia after acute administration (2400 nmole/kg). The tolerance to this last effect developed after four days of peptide treatment. The results indicate that OXY and MIF-I can influence the processes of development of tolerance to some central depressive effects of Et-OH in rats.

Inhibition of affective aggression and dominance in rats after thyrotropin-releasing hormone (TRH) microinjection into the nucleus accumbens.

The effect of 10 micrograms TRH injected bilaterally into the nucleus accumbens septi on two models of affective aggression and on dominance in a water-competition task was investigated in pairs of male Wistar rats. TRH significantly suppressed affective shock-induced and apomorphine-induced fighting. It also decreased dominance when administered to dominant rats while no effect was noted upon injection into subordinate animals. The peptide influenced neither water consumption in thirsty rats nor the pain threshold in a hot plate test.

MIF-1 potentiates the action of tricyclic antidepressants in an animal model of depression.

In the present paper, the effect of simultaneous treatment of rats with low doses of MIF-1 and tricyclic antidepressants on rat behavior in the forced swim test was studied. It was found that MIF-1 stimulated in a dose-dependent manner "active" behavior of animals in this paradigm. The effect of MIF-1 appeared to be independent of changes in rats' locomotion in the open field test. The combined treatment of rats with MIF-1 (0.01 mg/kg IP) and amitriptyline (5 mg/kg IP) or desipramine (1.25 mg/kg) IP) significantly stimulated active behavior in the forced swim test above the level obtained with each of the drugs given separately. The present data suggest the potential clinical efficacy of a combined therapy of depressive patients with MIF-1 and small doses of tricyclic antidepressants.

Aggressive behaviour and the central serotonergic systems.

A brief critical review of serotonin involvement in two classes of aggressive behaviour, i.e. affective and predatory aggression, is presented. Special emphasis is put on the differentiation between the role played in aggression by the two ascending serotonergic systems, the mesolimbic and the mesostriatal. It is concluded that only serotonergic neurons from the dorsal raphe nucleus forming the mesostriatal system play an inhibitory role in both classes of aggression. The mesolimbic system does not seem to be directly involved in an aggression modulation. The data suggesting that the dorsal raphe may mediate its inhibitory influence through the medial amygdala is presented and discussed. Finally some attention is given to the problem of serotonin metabolism variability (biorhythm) and its implications in behavioural studies.

Chronic oral treatment with diltiazem or verapamil decreases isolation-induced activity impairment in elevated plus maze.

Adult male Wistar rats were either socially isolated or group-housed for 6 weeks and then tested in an elevated plus maze. During isolation the rats received either water or two concentrations of the calcium channel inhibitors, diltiazem or verapamil, in drinking solutions (approximately 5 and 10 mg/kg daily). Isolated rats showed a significantly lower total number of arm entries, a lower percentage of open arm entries and negligible time spent therein than did group-housed animals. Verapamil, in the higher dose, prevented that effect of isolation. Treatment with diltiazem brought about a similar tendency, though the effect did not reach statistical significance. Chronic treatment of group-housed rats with either drug failed to influence their behavior in the plus maze. We conclude that certain calcium channel inhibitors may decrease the behavioral deficit in the elevated plus maze that follows chronic social isolation.

Discriminative stimulus properties of ethanol in the rat: effects of neurosteroids and picrotoxin.

Tetrahydrodeoxycorticosterone (5beta-THDOC; 1.3-12.0 mg/kg), a neurosteroid enhancing the GABA(A) receptor-associated chloride conductance, produced predominantly ethanol-appropriate responding (> 80%) in rats trained to discriminate 1.0 g/kg ethanol from saline. However, neither picrotoxin (0.25-1.5 mg/kg), nor dehydroepiandrosterone sulfate (0.01-100.0 mg/kg), a neurosteroid acting as a GABA(A) receptor antagonist, attenuated the stimulus effects of ethanol. These results indicate that: (1) at least certain neurosteroids may produce subjective states similar to these induced by ethanol; (2) blockade of the GABA(A) receptor-associated channel does not eliminate the ethanol interoceptive cue in rats.

Brain neurotransmitter systems mediating behavioral deficits produced by inescapable shock treatment in rats.

The effect of inescapable footshock (IS) upon rats' motor activity (the open field and forced swim tests) was studied in rats subjected to drugs, and neurotoxin treatments, affecting their central neurotransmitter systems. The agonists of GABA-receptor complex, dopamine, noradrenaline and serotonin neuronal systems, as well as the cholinergic antagonist, partially reversed motor suppression induced by IS, while the dopamine agonist, chlorpromazine, and the cholinergic antagonist, physostigmine, potentiated it. The effects of chemical lesions of the brain monoaminergic neurons with p-chlorophenylalanine (pCPA), N-chloro-ethyl-2,2-bromo-benzylamine (DSP-4), 6-hydroxydopamine (6-OHDA) and 5,7-dihydroxytryptamine (5,7-DHT) were more complex, depending upon the extent of monoamine depletion, and the kind of test applied. It is concluded that a decrease in the brain noradrenergic, serotonergic, dopaminergic and GABAergic neuronal activity, as well as the central cholinergic hyperactivity, might contribute to the behavioral suppression after IS. Thus the central mechanisms of behavioral deficits produced by IS involve multiple neurotransmitter systems, and the analysis of their role in more complicated behavioral patterns must also take into account changes in animals' baseline and stimulated motor activity.

Modification of behavioral response to intra-hippocampal injections of noradrenaline and adrenoceptor agonists by chronic treatment with desipramine and citalopram: functional aspects of adaptive receptor changes.

The present study investigated the effects of acute and of chronic treatment with desipramine (DI) and citalopram (CT) on the alterations in rat behavior in the open field and in the forced swim tests produced by intra-hippocampal microinjections of noradrenaline (NA) and adrenoceptor agonists. Chronic but not acute treatment with DI potentiated the stimulatory effects of NA on the rats' behavior in the open field test and in the forced swim test as well as revealed the excitatory effect of microinjections of phenylephrine at a dose producing insignificant changes when given alone. The depressive effects of clonidine in the open field test were antagonized by acute DI administration and reversed by chronic DI. No characteristic changes in the isoproterenol-induced increase in rat locomotion were observed following chronic DI since the antagonistic interaction was found after both acute and chronic DI pretreatment. Chronic though not acute administration of CT produced effects in the forced swim test similar to those of DI, i.e. excitatory effects of phenylephrine and clonidine on behavior. The data indicate a potentiation of excitatory processes in the brain limbic structure, probably mediated via alpha 1-adrenoceptors.