Comparative behavioural profile of newer antianxiety drugs on different mazes

Anxiety is associated with diverse range of psychiatric conditions. In the present study, antianxiety effect of fluoxetine, citalopram (SSRI's), gabapentin (antiepileptic drugs), venlafaxine (SNRI), clozapine and resperidone (atypical antipsychotics) and a herbal preparation ashwagandha on elevated zero maze and elevated plus maze paradigms was examined. Anti-anxiety potentials of these drugs were compared with diazepam. The drugs tested i.e. fluoxetine (10 mg/kg), citalopram (10 mg/kg), clozapine (0.25, 0.5, 1 mg/kg), resperidone.(0.5, 1 mg/kg), venlafaxine (4, 8, 16 mg/kg), citalopram (10 mg/kg), fluoxetine (10 mg/kg), gabapentin (10, 20 mg/kg) and ashwagandha (100, 200 mg/kg) significantly increased the number of open arm entries and time spent in open arm. These drugs also decreased the latency to enter in open arm as compared to control in both the paradigms. Present study confirms the antianxiety activity of different newer classes of drugs and found some of them comparable to diazepam in both the elevated zero maze and elevated plus maze paradigm.     

Fluoxetine: A Randomized Clinical Trial in the Maintenance of Weight Loss

Because current weight-reduction treatments have considerable recidivism, a therapy that could help patients maintain weight loss would be of benefit. A six-center, randomized, double-blind trial compared the effects of the specific serotonin uptake inhibitor, fluoxetine hydrochloride, and placebo on maintenance of weight loss. Obese outpatients who had lost ≤3.6 kg after 8 weeks of single-blind fluoxetine 60 mg/day in the qualification phase (N=317 [70.4% of patients entered]; mean ± standard deviation [SD] weight loss, 6.8 ± 2.8 kg) were randomly assigned to fluoxetine 20 mg/day (N=104), fluoxetine 60 mg/day (N=106), or placebo (N=107) for 40 weeks (maintenance phase). Patients received minimal nutrition/dietary counseling. Qualification phase clinic visits were biweekly; maintenance phase visits were monthly for 4 months, then bimonthly for 6 months. Patients treated with fluoxetine 60 mg/day continued to lose weight for 8 additional weeks (16 weeks total; maximum mean ± SD weight loss, 7.2 ± 4.6 kg); those treated with fluoxetine 20 mg/day or placebo began to regain weight. Mean weights remained below baseline values at week 48 (all groups); treatment differences were not statistically significant. Study completion rates were comparable (fluoxetine 20 mg/day, 67.3%; fluoxetine 60 mg/day, 56.6%; placebo, 67.3%; p = 0.175). Among commonly reported adverse events (>10% incidence), only asthenia was reported statistically significantly (p< 0.050) more frequently with fluoxetine than with placebo. Few patients discontinued for any single adverse event. Fluoxetine 60 mg/day was effective for a longer period than fluoxetine 20 mg/day or placebo in maintaining weight loss. Overall, fluoxetine was safe and well tolerated.     

Haloperidol-stomach lesions attenuation by pentadecapeptide BPC 157, omeprazole, bromocriptine, but not atropine, lansoprazole, pantoprazole, ranitidine, cimetidine and misoprostol in mice

The focus was on haloperidol (central dopamine antagonist)-stomach lesion, a longly described suitable counterpart of dopamine blocker cysteamine-duodenal lesion. In this, the contribution of blockade of central/peripheral dopamine receptors and prostaglandins synthesis, along with influence of antiulcer agents was evaluated in mice. Male NMRI Hannnover mice were sacrificed 24 h after haloperidol (25 mg/kg b.w. i.p., given alone or with saline (haloperidol+saline) (i) or in combination (ii,iii)). Supporting central dopamine predominance for haloperidol stomach lesion induction, co-administration of peripheral dopamine receptor antagonist domperidone (5 mg/kg i.p.) (haloperidol+ domperidone) (ii), or prostaglandin synthesis inhibitor indomethacin (10 mg/kg s.c.) (haloperidol+ indomethacin) (iii) did not aggravate this lesion. (i) In haloperidol+saline challenged mice the lesions were inhibited by co-administration (/kg i.p.) of a gastric pentadecapeptide BPC 157, GlyGluProProProGlyLysProAlaAspAspAlaGlyLeuVal, M.W. 1419 (10 microg, 10 ng, 10 pg, but not 1 pg, 100 fg, 10 fg), bromocriptine (10 mg), omeprazole (10 mg, 100 mg, but not 1 mg). Atropine (10, 100, 200 mg), pirenzepine (10, 100, 200 mg), misoprostol (10, 100, 200 microg), pantoprazole (1, 10, 100 mg), lansoprazole (0.1, 1, 10 mg), cimetidine (10, 100, 200 mg) and ranitidine (10, 100, 200 mg) were not effective. (ii) Dopamine peripheral blockade influence: in haloperidol+domperidone mice, previously effective bromocriptine, pentadecapeptide BPC 157 (10 microg) or omeprazole (10 mg) did not attenuate stomach lesions. (iii) Prostaglandins synthesis blockade effect: in haloperidol+indomethacin mice, previously effective agents, bromocriptine or omeprazole were not active, while BPC 157 effect was only lessened.     

Ultrasonic vocalization in response to unavoidable aversive stimuli in rats: effects of benzodiazepines

The effects of two benzodiazepine derivatives (diazepam, 0.5-1 mg/kg; alprazolam, 1.25-2.5 mg/kg) on ultrasonic calling elicited in adult rats by unavoidable aversive stimuli (footshocks) were investigated. The results show that either diazepam or alprazolam affected the duration of ultrasonic calls. In particular, a significant decrease in the length of ultrasounds was found in the group of animals treated with these benzodiazepines. The effects of diazepam were counteracted by the benzodiazepine-antagonist Ro 15-1788. On the other hand, neither a neuroleptic agent, such as haloperidol (0.5-1 mg/kg), nor an antidepressant, such as desipramine (5-10 mg/kg) influenced the parameters of ultrasonic emission in this experimental situation. The present results suggest that ultrasonic vocalization in response to unavoidable aversive stimuli could be considered as a potential new tool for studying drugs with antianxiety properties.     

Duodenal calcium transporter mRNA expression in stressed male rats treated with diazepam, fluoxetine, reboxetine, or venlafaxine

Chronic stress has been reported to decrease bone density and intestinal calcium absorption, but its underlying mechanism remains elusive. Since long-term exposure to glucocorticoids, major stress hormones from adrenal gland, is known to downregulate the mRNA expression of intestinal calcium transporter TRPV6, the present study aimed to demonstrate whether decreases in mRNA expressions of duodenal calcium transporter genes were observed in male rats subjected to restraint stress for 4?weeks. The results from quantitative real-time PCR showed that restraint stress significantly downregulated the mRNA expressions of apical calcium channels (TRPV6 and Ca(v)1.3), cytoplasmic calcium-binding protein (calbindin-D(9k)), and basolateral calcium pump (PMCA(1b)), but not the expression of TRPV5 or NCX1. The mRNA expressions of paracellular genes, ZO-1, occludin, and claudin-3, were not altered by restraint stress. Since several antidepressant or anxiolytic drugs effectively alleviate stress-induced depressive and anxiety symptoms, we further hypothesized that these drugs may also enhance calcium transporter gene expression in stressed rats. As expected, 4-week daily administration of 10?mg/kg fluoxetine, 10?mg/kg reboxetine, or 10?mg/kg venlafaxine differentially increased calcium transporter mRNA expression in stressed rats, whereas 2?mg/kg diazepam had no such effect. It could, therefore, be concluded that 4-week restraint stress downregulated some important calcium transporter mRNA expression in the duodenal epithelial cells of male rats, which could be prevented by oral administration of fluoxetine, reboxetine, and venlafaxine. The present findings may be applied to help alleviate the stress-induced bone loss and osteoporosis by restoring intestinal calcium absorption to provide calcium for bone formation.     

Comparative study of the effect of 3-carboxy-beta-carboline methylamide and diazepam on rat behavior

The effects of benzodiazepine receptor agonist, diazepam, and inverse agonist, FG 7142, were examined. Strong antagonism between FG 7142 (10 mg/kg) and diazepam (1 mg/kg) activity was revealed in the open field test. On the other hand, both FG 7142 and diazepam inhibited isolation-induced intraspecies aggressive behaviour of rats. FG 7142 also reduced interspecies aggression of mouse-killing rats. The findings suggest that both diazepam and FG 7142 have antiaggressive properties in the isolation-induced aggression model, which are mediated by benzodiazepine receptors of the central nervous system.     

Maternal Aggression and Litter Size in the Female House Mouse

It has been commonly argued that, in house mice, female post-partum fighting against a male intruder functions to protect the offspring from infanticide. The aim of this study was to test the hypothesis that maternal aggression is actually related to pup defence and, specifically, according to parental investment theory, that its intensity should increase with litter size. 60 nulliparous albino female mice were mated and randomly assigned to four experimental groups in which litters were culled at birth to 0, 4, 8, or 12 pups, respectively. On day 8 after delivery all females were tested for maternal aggression against a stranger adult male conspecific (5-min exposure). No aggression occurred in the group in which all pups had been removed. In the other groups, the proportion of females displaying overt aggression increased with litter size. Several scores of female agonistic behaviour (proportion of females displaying overt aggression, total attacking time, frequency of tail rattling) were significantly higher for the females rearing 8 and 12 pups than for the females rearing 4 pups. Aggressive behaviour of females rearing 12 pups was not significantly higher than that of females rearing 8 pups. No male committed infanticide. These results support the hypothesis that rodent maternal aggression is strictly related to offspring defence and are consistent with the theoretical prediction that, the costs of the defence being equal and the gain in fitness increasing with litter size, the intensity of maternal defence of the young should increase with their number.     

Nursing posture is elicited rapidly in maternally naive, haloperidol-treated female and male rats in response to ventral trunk stimulation from active pups

Maternal responsiveness in rats can be induced in virgin females and males, without hormonal priming, following several days of cohabitation with pups. Because antagonism of dopamine (DA) facilitates nursing behavior in lactating rats, the response of nonlactating, maternally naive rats to effective stimulation of the ventral trunk (ventrum) from pups following similar treatment was investigated. Lactating dams, virgin females and males, both intact and gonadectomized, were treated with a catalepsy-inducing dose of haloperidol (5 mg/kg), a DA receptor antagonist, and tested with hungry pups 1 hr later. Subjects were placed over 8 pups and postures assessed every 3 min for 30 min. The nursing posture occurred in most subjects. Lactating and nonlactating females were similar in occurrence of the nursing crouch, though the intensity was somewhat higher in the former; females scored higher than males in terms of likelihood and intensity of crouching; and there was no effect of gonadectomy. The nursing posture was not elicited in intact virgin females if the stimulus pups were anesthetized or if the subjects were treated with saline instead of haloperidol. There were no sex differences in onset or intensity of catalepsy in response to the dose of haloperidol used. These results suggest that the nursing posture occurs reflexively, is not directly dependent upon ovarian hormones, and is diminished by the effects of androgens, prior and current.     

Role of serotonin2 receptors in regulating aggressive behavior

Quipazine and pirenperone , the drugs interacting with serotonin2 -receptors, more readily displaced 3H-spiroperidol from its binding sites in the frontal cortex than in the striatum. Pirenperone (0,07-0,3 mg/kg), antagonist of serotonin2 -receptors, selectively decreased the intensity of apomorphine aggressiveness. The antiaggressive action of haloperidol (0,01-0,2 mg/kg) was in correlation with its antistereotypic activity. Long-term administration of naloxone (0,5; 15,0 mg/kg), together with apomorphine (0,5 mg/kg) reduced the number of head-twitches caused by quipazine (2,5 mg/kg). The administration of quipazine 48 hours after the last injection of naloxone and apomorphine caused spontaneous aggressiveness that did not differ from apomorphine aggressiveness. Intracerebroventricular injection of cholecystokinin tetrapeptide (CCK-4) markedly enhanced the foot-shock aggression. The same dose of CCK-4 also decreased the intensity of quipazine (2,5 mg/kg) head-twitches. Compared to haloperidol, pirenperone was a more selective antagonist of CCK-4. After long-term apomorphine treatment (0,5 mg/kg during 10 days, twice daily), the effect of CCK-4 on aggressive behaviour was markedly enhanced. It is possible that two subtypes of serotonin2 -receptors exist in the brain and have opposite action on the aggressive behaviour. CCK-4 may play the role of an endogenous modulator of sensitivity of serotonin2 -receptors involved in the control of aggressiveness.     

The comparative effects of propofol, thiopental, and diazepam, administered intravenously, on pentylenetetrazol seizure threshold in the rabbit.

The anticonvulsant effects of propofol, thiopental, and diazepam, administered intravenously, on pentylenetetrazol (PTZ) seizure threshold were studied and compared in the rabbit. The PTZ seizure threshold determined in various rabbit groups during the control phase of conducted experiments, was found to be in the range of 10.1 +/- 2.0 to 13.5 +/- 3.7 mg/kg. Intravenous administration of comparable doses of propofol, thiopental, and diazepam resulted in marked and significant increases in PTZ seizure threshold. At all administered doses (1.25-10.0 mg/kg), propofol was found to be more effective than thiopental in increasing the PTZ threshold dose. However, the anticonvulsant effects of diazepam were more marked than those of propofol, except at a dose of 10 mg/kg where both agents exhibited equipotent activities. These data demonstrate that propofol enjoys a considerable degree of anticonvulsant activity in the rabbit. This anticonvulsant action is greater than that of thiopental at doses ranging from 2.5 to 10 mg/kg and equipotent with diazepam at the 10 mg/kg dose.     

Short-term tolerance to morphine: effects of diazepam, phenobarbital, and amphetamine

Short-term tolerance to morphine, which can be demonstrated in as little as 3 hours after a single administration of the opiate, was examined in animals chronically pretreated with diazepam, phenobarbital, or amphetamine. Tail-flick latency in mice and changes in plasma corticosterone in rats were the parameters tested in these experiments. Rats primed with either saline or morphine, 10 mg/kg, were injected 3 hours subsequently with morphine, 5 mg/kg. Those primed with saline showed the characteristic plasma corticosterone elevation following morphine, when serial blood samples were examined, whereas those previously treated with morphine did not. Mice were primed with saline or either of two doses of morphine, 30 or 100 mg/kg, 3.5 hours prior to estimation of tail-flick latency and ED50 determinations. Mice primed with either dose of morphine had significantly higher ED50's than those primed with saline. Chronic treatment with diazepam or amphetamine in either species did not significantly alter short-term tolerance development by either parameter. However, with phenobarbital pretreatment, the plasma corticosterone response was attenuated and short-term tolerance to morphine's analgesic effects did not occur. Further studies in morphine-pelleted mice showed that analgesic tolerance occurred similarly in all groups. This suggests that barbiturates may delay the process.     

Clopheline-induced aggression in mice: role of genotype and the dopaminergic system

Clophelin (CLO) in a dose 10 mg/kg induced aggressive behaviour in mice significantly dependent of genotype. Pretreatment with flupentixol and haloperidol inhibited or blocked CLO-evoked aggression in high-aggressive mice. Apomorphine administered with CLO enhanced aggression in low-aggressive mice. Stimulation of D2 receptors by bromocriptine failed to change CLO-induced aggression. It was suggested that dopamine system was involved in CLO-aggression through D1 receptors.     

Tolerance in the anxiolytic profile following repeated administration of diazepam but not buspirone is associated with a decrease in the responsiveness of postsynaptic 5-HT-1A receptors

To understand the role of serotonin (5-hydroxytryptamine; 5-HT)-1A receptors in the treatment of anxiety and the development of tolerance to benzodiazepines the present study was designed to monitor the responsiveness of postsynaptic 5-HT-1A receptors following repeated administration of diazepam and buspirone. Results show that tolerance in the anxiolytic profile is produced following repeated administration (2 weeks) of diazepam (2 mg/kg) but not buspirone (0.5 mg/kg). The behavioral effects of 8-OH-DPAT at a dose of 0.25 mg/kg were monitored 3 days after repeated administration of saline or buspirone or diazepam. The results show that 8-OH-DPAT elicited forepaw treading was smaller in repeated diazepam but not repeated buspirone injected rats, while hyperlocomotive effects of 8-OH-DPAT were smaller in both repeated buspirone and repeated diazepam injected rats. The results suggest that postsynaptic 5-HT-1A receptor-dependent responses were attenuated following long-term administration of diazepam but not buspirone. Role of 5-HT-1A receptors in the development of tolerance to the anxiolytic effects of diazepam but not buspirone is discussed.     

Thermoregulatory, motor, behavioural, and nociceptive responses of rats to 3 long-acting neuroleptics

We investigated physiological effects of intramuscular injections of the following 3 long-acting neuroleptics commonly used in wildlife management: haloperidol (0.05, 0.1, and 0.5 mg/kg body mass), zuclopenthixol acetate (0.5, 1, and 5 mg/kg), and perphenazine enanthate (1, 3, and 10 mg/kg), in a rat model. Body temperature and cage activity were measured by intra-abdominal telemeters. Nociceptive responses were assessed by challenges to noxious heat and pressure. Haloperidol (0.5 mg/kg) produced a significant nocturnal hypothermia (p < 0.05) and decreased nighttime cage activity and food intake. Zuclopenthixol (5 mg/kg) significantly decreased nighttime body temperature and cage activity and, at 1 mg/kg and 5 mg/kg, significantly decreased food intake 5-17 h after injection (p < 0.05). Perphenazine (10 mg/kg) significantly decreased nighttime body temperature and cage activity and, at all doses, significantly decreased food intake 5-17 h after injection (p < 0.05). Significant analgesic activity was evident in rats given 5 mg/kg zuclopenthixol up to 40 h after injection, and 10 mg/kg perphenazine from 48 to 96 h after injection (p < 0.0001). Zuclopenthixol (5 mg/kg) and perphenazine (10 mg/kg) had significant antihyperalgesic activities at 16 h postinjection and 24-48 h postinjection, respectively (p < 0.0001). Haloperidol had no significant antinociceptive activity at doses tested. Motor function was impaired in rats given 0.5 mg/kg haloperidol, 5 mg/kg zuclopenthixol and 10 mg/kg perphenazine. Effects of long-acting neuroleptics on body temperature, feeding, and activity were short-lasted and should not preclude their use in wildlife. Antinociceptive actions were longer-lasting, but were nonspecific, and we recommend additional analgesics for painful procedures during wildlife management.     

A study of the action of anticonvulsant drugs on an experimental model of epilepsy

Repeated electrical low intensity stimulation of various regions of the brain has been shown to induce epileptic seizure activity. This experimental model of epilepsy has been used in our laboratory in rats. Male rats, anaesthetized with nembutal (20 mg/kg, i.p.) and ketalar (60 mg/kg, i.p.) were implanted stereotaxically with electrodes in the dorsal hippocampus and neocortex and received 2 hours stimulation sessions via the hippocampal electrodes (1 sec, 60 Hz, 200-800 microA) one stimulus per minute, during which electrographical and behavioral seizures were induced. The effect of anticonvulsant drugs was tested on this model: phenobarbital (40 mg/kg) reduced the quantity of epileptic electrographic activity and abolished the behavioral aspects of the seizures; diphenylhydantoin (20 mg/kg) reduced the quantity of epileptic electrographic activity, but had no effect on the behavioral component of the seizures; diazepam (6 mg/kg) only blocked the behavioral component of the seizures leaving the animal stuporous and immobile, but the electrographical component was unaffected; carbamazepine (10 mg/kg) had no effect on the electrographical epileptic seizures and reduced the behavioral aspects, but to a lesser extent than diazepam.     

Ro 15-1788 antagonizes the discriminative stimulus effects of diazepam in rats but not similar effects of pentobarbital

The benzodiazepine antagonist properties of Ro 15-1788 were evaluated in rats trained to discriminate between saline and either 1.0 mg/kg of diazepam or 10 mg/kg of pentobarbital in a two-choice discrete-trial shock avoidance procedure. When administered alone, 1.0 mg/kg of diazepam and 10 mg/kg of pentobarbital produced comparable amounts of drug-appropriate responding (> 84%), whether rats were trained to discriminate between diazepam or pentobarbital and saline. Ro 15-1788 (3–32 mg/kg, p.o.), administered 10 min before diazepam or pentobarbital, produced a dose-related blockade of the discriminative effects of diazepam in both groups of rats, but was completely ineffective in blocking the discriminative effects of pentobarbital. The dose-effect curve for the discriminative effects of diazepam was shifted to the right in a parallel fashion 3- and 13-fold by 10 and 32 mg/kg of Ro 15-1788, respectively, indicating that Ro 15-1788 acts as a surmountable, competitive antagonist of diazepam. When administered alone, Ro 15-1788 (32–100 mg/kg, p.o.) produced primarily saline-appropriate responding, although 100 mg/kg of Ro 15-1788 produced drug-appropriate responding in one out of eight rats. When administered orally 30 min after diazepam, Ro 15-1788 (32 mg/kg) completely reversed within 10 min the discriminative effects of diazepam. The blockade of diazepam's discriminative effects by 32 mg/kg of Ro 15-1788 appeared to last at least as long (approximately 2 hr) as the effects of diazepam alone.     

Neonatal exposure to endocrine active compounds or an ERbeta agonist increases adult anxiety and aggression in gonadally intact male rats

Endocrine active compounds (EACs) have been shown to influence a number of reproductive endpoints but less is known about how they might affect other hormone dependent behaviors including anxiety and aggression. Recent evidence suggests that these effects may be mediated through the beta form of the estrogen receptor (ERbeta). Using male Long Evans rats, we sought to determine how neonatal exposure to EACs affects anxiety and aggression in adulthood. Anxiety was assessed using the elevated plus maze and aggression was assessed 8 weeks later using the resident intruder test. To gain insight into which ER subtype (ERalpha vs ERbeta) might be mediating these effects we used agonists specific for ERalpha (1,3,5-tris(4-Hydroxyphenyl)-4-propyl-1H-pyrazole (PPT)) or ERbeta (Diarylpropionitrile (DPN)) as additional treatment groups. For these experiments the synthetic EAC bisphenol-A (BPA) and the phytoestrogen metabolite equol (EQ) were used. Male neonates were injected with either 0.05 ml sesame oil (control), 50 microg estradiol benzoate (EB), 1 mg/kg DPN, 1 mg/kg PPT, 50 microg/kg BPA, or 10 mg/kg EQ daily for 4 days beginning on the day of birth (PND 0). Compared to the oil treated controls, significantly fewer open arm entries were made by the males neonatally treated with DPN, EQ, or BPA. The DPN and EQ treated males were also more aggressive compared to the controls. These findings suggest that neonatal exposure to EACs with agonistic activity on ERbeta may influence affective behavior in adulthood, including anxiety and aggression.     

Antidepressant-like effect of 17beta-estradiol: involvement of dopaminergic, serotonergic, and (or) sigma-1 receptor systems

17beta-estradiol has been reported to possess antidepressant-like activity in animal models of depression, although the mechanism for its effect is not well understood. The present study is an effort in this direction to explore the mechanism of the antidepressant-like effect of 17beta-estradiol in a mouse model(s) of behavioral depression (despair behavior). Despair behavior, expressed as helplessness to escape from a situation (immobility period), as in a forced swim test in which the animals are forced to swim for a total of 6 min, was recorded. The antiimmobility effects (antidepressant-like) of 17beta-estradiol were compared with those of standard drugs like venlafaxine (16 mg/kg, i.p.). 17beta-estradiol produced a U-shaped effect in decreasing the immobility period. It had no effect on locomotor activity of the animal. The antidepressant-like effect was comparable to that of venlafaxine (16 mg/kg, i.p.). 17beta-estradiol also exhibited a similar profile of antidepressant action in the tail suspension test. When coadministered with other antidepressant drugs, 17beta-estradiol (5 microg/kg, i.p.) potentiated the antiimmobility effect of subeffective doses of fluoxetine (5 mg/kg, i.p.), venlafaxine (2 mg/kg, i.p.), or bupropion (10 mg/kg, i.p.), but not of desipramine (5 mg/kg, i.p.) or tranylcypromine (2 mg/kg, i.p.), in the forced swim test. The reduction in the immobility period elicited by 17beta-estradiol (20 microg/kg, i.p.) was reversed by haloperidol (0.5 mg/kg, i.p.; a D(2) dopamine receptor antagonist), SCH 23390 (0.5 mg/kg, i.p.; a D(1) dopamine receptor antagonist), and sulpiride (5 mg/kg, i.p.; a specific dopamine D(2) receptor antagonist). In mice pretreated with (+)-pentazocine (2.5 mg/kg, i.p.; a high-affinity sigma-1 receptor agonist), 17beta-estradiol (5 microg/kg, i.p.) produced a synergistic effect. In contrast, pretreatment with progesterone (10 mg/kg, s.c.; a sigma-1 receptor antagonist neurosteroid), rimcazole (5 mg/kg, i.p.; another sigma-1 receptor antagonist), or BD 1047 (1 mg/kg, i.p.; a novel sigma-1 receptor antagonist) reversed the antiimmobility effects of 17beta-estradiol (20 microg/kg, i.p.). Similarly, in mice pretreated with a subthreshold dose of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, a 5-HT1A serotonin receptor agonist), 17beta-estradiol (5 microg/kg, i.p.) produced an antidepressant-like effect. These findings demonstrate that 17beta-estradiol exerted an antidepressant-like effect preferentially through the modulation of dopaminergic and serotonergic receptors. This action may also involve the participation of sigma-1 receptors.     

Behavioral evidence for dopaminergic supersensitivity after chronic haloperidol

Chronic administration for 16 days of haloperidol (in increasing doses up to 20 mg/kg/day) results in a supersensitivity of dopamine receptors. This supersensitivity is manifested by an enhanced stereotypy and aggression in response to small, otherwise ineffective, doses of apomorphine. Maximum aggression is observed 7 days after the last dose of haloperidol when 2.5 mg/Kg of apomorphine is administered. In addition, “wet shakes”, reminiscent of withdrawal from morphine, are observed in these animals after the cessation of the haloperidol administration. These shakes are blocked by morphine. These results may be interpreted to mean that “wet shakes” and drug induced aggression are the results of hyperactivity of the dopaminergic system.     

Differential effects of acute and chronic haloperidol treatment on striatal and nigral 3, 4-dihydroxyphenylacetic acid (DOPAC) levels

Chronic treatment of rats with haloperidol (4 weeks, 0.5 or 1 mg/kg) resulted in a significant attenuation of the large DOPAC rise seen in the corpus striatum after acute treatment. This tolerance effect was observed both shortly following termination of chronic treatment and on challenge with a low dose (0.1 mg/kg) of the drug 6–8 days later. In contrast, acute haloperidol treatment resulted in only a small and nonsignificant elevation of DOPAC levels in the substantia nigra, while chronic treatment caused a larger and significant increase in levels of the metabolite. Moreover, the latter effect was also observed in response to haloperidol challenge 6–8 days after discontinuation of drug treatment. The differential pattern of response in these two brain regions is discussed in relation to possible mechanisms mediating striatal tolerance and to recent observations regarding changes in nigral dopamine cell firing after chronic haloperidol treatment.