Electrical amygdala kindling.

This unit describes a method of electrical amygdala kindling in the rat. This procedure requires mastery of stereotaxic electrode implantation which is not covered in the current unit. Also, the investigator must have a sound knowledge of electronics and computing. The text gives instructions on how to render rats epileptic, how to determine the effects of compounds in kindled rats, and how to analyze the data. Results with three reference substances are illustrated. These substances are used in the clinic and give robust results in kindling.

Comparison of the phenotype of NK1R-/- mice with pharmacological blockade of the substance P (NK1 ) receptor in assays for antidepressant and anxiolytic drugs.

The phenotype of NK1R-/- mice was compared with that of acute pharmacological blockade of the tachykinin NK1 receptor on sensorimotor function and in assays relevant to depressive illness and anxiety. The dose range for L-760735 and GR205171 that was associated with functional blockade of central NK1 receptors in the target species was established by antagonism of the behavioural effects of intracerebroventricular NK1 agonist challenge in gerbils, mice and rats. The caudal grooming and scratching response to GR73632 was absent in NK1R-/- mice, confirming that the receptor had been genetically ablated. There was no evidence of sedation or motor impairment in NK1R-/- mice or following administration of L-760735 to gerbils, even at doses in excess of those required for central NK1 receptor occupancy. In the resident-intruder and forced swim test, the behaviour of NK1R-/- mice, or animals treated acutely with L-760735 or GR205171, resembled that seen with the clinically used antidepressant drug fluoxetine. However, the effects of GR205171 were not clearly enantioselective in mice. In contrast, although NK1R-/- mice also exhibited an increase in the duration of struggle behaviour in the tail suspension test, this was not observed following pharmacological blockade with L-760735 in gerbils or GR205171 in mice, suggesting that this may reflect a developmental alteration in the knockout mouse. There was no effect of NK1 receptor blockade with L-760735 in guinea-pigs or GR205171 in rats, or deletion of the NK1 receptor in mice, on behaviour in the elevated plus-maze test for anxiolytic activity. These findings extend previous observations on the phenotype of the NK1R-/- mouse and establish a broadly similar profile following acute pharmacological blockade of the receptor. These studies also serve to underscore the limitations of currently available antagonists that are suitable for use in rat and mouse behavioural assays.

Models for assessing antipsychotics: antagonism of amphetamine-induced hyperactivity and stereotypies in mice.

All classical antipsychotics, such as chlorpromazine and haloperidol, have potent dopamine receptor-blocking properties. This unit describes the rat anti-Thy-1.1 model of acute proliferative glomerulonephritis for the study of chronic renal insufficiency. A procedure is detailed for the induction of glomerulonephritis in rats as well as measurement of daily urinary excretion of protein, which is a convenient, primary screening tool. The unit also provides methods for assessment of glomerular filtration rate and effective renal plasma flow in anesthetized rats with anti-Thy-1.1-induced renal insufficiency.

Vigilance-controlled quantified EEG in safety pharmacology.

The vigilance-controlled quantified EEG can be used either as a safety, or as a discovery pharmacology procedure. Put strategically into the preclinical development process of a drug, it can be useful for making the decision about the future research direction to be taken. The experimental approach described in this unit is based on the rat EEG. Even though there are considerable differences in function and structure between human and rat brain, the EEG response to psychoactive drugs and convulsants is similar in the two species. Thus, the rat EEG is generally a reliable predictor for human CNS drug effects.

Rodent models of depression: forced swimming and tail suspension behavioral despair tests in rats and mice.

Rodents forced to swim in a narrow space from which there is no escape will, after an initial period of vigorous activity, adopt a characteristic immobile posture, making only those movements necessary to keep their heads above the water. It was hypothesized that immobility reflected the animals' having learned that escape was impossible and their having given up hope. Immobility was therefore given the name "behavioral despair". Immobility was subsequently found to be reduced by a wide range of clinically active antidepressant drugs. This simple behavioral procedure has since become a useful test for screening novel antidepressants in rats and is presented in this unit. An equivalent procedure in the mouse is also described along with a "dry" version of the test where immobility is induced simply by suspending the mouse by the tail.

Anxiolytic-like effects of the prototypical metabotropic glutamate receptor 5 antagonist 2-methyl-6-(phenylethynyl)pyridine in rodents.

Recently, selective and systemically active antagonists for the metabotropic glutamate 5 receptor (mGlu(5)) were discovered, and the most potent derivative was found to be MPEP (2-methyl-6-(phenylethynyl)pyridine). Given the high expression of mGlu(5) receptors in limbic forebrain regions, it was decided to evaluate the anxiolytic potential of MPEP. After an acute oral administration, MPEP attenuated the anxiety-dependent variable in a variety of well established anxiety test paradigms. In rats, MPEP (10, 30, and 100 mg/kg) increased punished responses in the Geller-Seifter test, but none of these effects reached statistical significance. MPEP significantly increased the ratio (open/total arm entries; 0.1, 1, and 10 mg/kg), the number of open arm entries (0.1, 1, and 10 mg/kg), as well as time spent on open arm (0.1 and 1 mg/kg) in the elevated plus maze test. Furthermore, MPEP (0.3 and 1 mg/kg) significantly increased the time spent in social contact in the social exploration test. In mice, MPEP attenuated stress-induced hyperthermia (15 and 30 mg/kg) and decreased the number of buried marbles in the marble burying test (7.5 and 30 mg/kg). Finally, MPEP (0.01, 0.1, 1, 10, and 100 mg/kg) was tested on spontaneous locomotor activity in mice, and only a dose of 100 mg/kg significantly reduced vertical activity; no effect was seen on horizontal activity. MPEP (7.5, 15, and 30 mg/kg) was ineffective on d-amphetamine-induced (2.5 mg/kg) locomotor activity in mice and prepulse inhibition in rats (1, 3, or 10 mg/kg). Thus, these findings indicate that MPEP exhibits anxiolytic-like effects and low risks for sedation and psychotomimetic side-effects in rodents.

Reboxetine: a pharmacologically potent, selective, and specific norepinephrine reuptake inhibitor.

BACKGROUND: Reboxetine is a potent antidepressant, with efficacy comparable to that of imipramine, desipramine, and fluoxetine, and has improved side-effect profile. The basis of its efficacy and improved tolerability is sought through studies of reboxetine in a number of pharmacological models of depression. METHODS: Pharmacological selectivity for uptake systems was defined by uptake and binding assays for the three monoamine uptake sites. Specificity was determined in 39 different receptor and 6 enzyme assays. In vivo selectivity was defined by measurement of neuronal firing rates in the locus coeruleus, dorsal raphe, and substantia nigra. Reserpine-induced blepharospasm and hypothermia, clonidine-induced hypothermia, defined reboxetine's in vivo pharmacology. Reboxetine's antidepressant potential was evaluated behaviorally by the tail-suspension test, forced swimming, and the DRL72 operant responding test. RESULTS: Reboxetine is a potent, selective, and specific norepinephrine reuptake inhibitor (selective NRI) as determined by both in vitro and in vivo measurements. Unlike desipramine or imipramine, reboxetine has weak affinity (Ki > 1,000 nmol/L)for muscarinic, histaminergic H1, adrenergic alpha1, and dopaminergic D2 receptors. In vivo action of reboxetine is entirely consistent with the pharmacological action of an antidepressant with preferential action at the norepinephrine reuptake site. Reboxetine showed an antidepressant profile in all tests of antidepressant activity used. Significant decreases in immobility were observed in the tail suspension test and behavioral despair test. Increased efficiency in responding was observed in the DRL72 test. CONCLUSIONS: Reboxetine is a potent, selective, and specific noradrenergic reuptake inhibitor. It has a superior pharmacological selectivity to existing tricyclic antidepressants and selective serotonin reuptake inhibitors when tested in a large number of in vitro and in vivo systems. Given the pharmacological profile, reboxetine is expected to be a selective and potent tool for psychopharmacological research. The use of reboxetine in the clinic will also help clarify the role norepinephrine plays in depression.

Evaluation of a ginkgo biloba extract (EGb 761) in functional tests for monoamine oxidase inhibition.

A standardized extract of ginkgo biloba (EGb 761) was evaluated in functional tests for monoamine oxidase (MAO) inhibition in mice: l-dihydroxyphenylalanine (CAS 59-92-7,1-DOPA) potentiation, tryptamine (CAS 61-54-1) potentiation, 5-hydroxytryptophan (CAS 4350-07-6,5-HTP) potentiation and phenylethylamine (CAS 64-04-0) potentiation. The doses investigated (25, 50 and 100 mg/kg p.o once daily for 5 days) were those known to possess anti-stress properties in other animal models. In contrast to the reference substances investigated (nialamide (CAS 51-12-7), clorgyline (CAS 17780-75-5) and 1-deprenyl (CAS 14611-52-01), EGb 761 did not exhibit any activity indicative of MAO inhibition. It was concluded that MAO inhibition was not the mechanism primarily responsible for EGb 761's anti-stress activity.

Animal models of depression: utility for transgenic research.

The utility of available animal models of depression for transgenic research is reviewed. Criteria for usefulness are non-dependence on a mechanism of action, pharmacological validity, existence of genetic determinants, availability of a mouse version, procedural simplicity, and reproducibility. The following models are reviewed: behavioral despair, tail suspension, learned helplessness, chronic mild stress, olfactory bulbectomy, DRL behavior and conditioned place preference. It is concluded that the behavioral despair and tail suspension models satisfy the criteria most closely. On the other hand, despite its procedural complexity and poor reproducibility, the chronic mild stress model shows high promise for the future.

Broad-spectrum, non-opioid analgesic activity by selective modulation of neuronal nicotinic acetylcholine receptors.

Development of analgesic agents for the treatment of severe pain requires the identification of compounds that are devoid of opioid receptor liabilities. A potent (inhibition constant = 37 picomolar) neuronal nicotinic acetylcholine receptor (nAChR) ligand called ABT-594 was developed that has antinociceptive properties equal in efficacy to those of morphine across a series of diverse animal models of acute thermal, persistent chemical, and neuropathic pain states. These effects were blocked by the nAChR antagonist mecamylamine. In contrast to morphine, repeated treatment with ABT-594 did not appear to elicit opioid-like withdrawal or physical dependence. Thus, ABT-594 may be an analgesic that lacks the problems associated with opioid analgesia.

Effects of piracetam on indices of cognitive function in a delayed alternation task in young and aged rats.

The effects of piracetam (64, 128, and 256 mg/kg PO) on the performance of a delayed alternation in a Skinner Box were investigated. Test sessions consisted of 36 trials during which animals were first presented with a single lever (left or right) followed 5, 10, or 20 s later by two levers. A press on the lever opposite to that presented previously (nonmatching to sample) was rewarded. The number of correct responses and the reaction times to the one- and two-lever presentations were recorded. All animals received all treatments in a balanced order. Aged animals showed clear deficits on all three parameters. Piracetam was without effect on the performance of young animals but dose-dependently decreased the choice reaction times (two levers) in aged animals without affecting the other two parameters. These results suggest that piracetam does not affect short-term memory but may facilitate choice behavior in aged animals.

MK-801 and enantiomers: potential antidepressants or false positives in classical screening models?

In the present experiments, the noncompetitive NMDA antagonist 5-methyl-10,11-dihydroxy-5H-dibenzo(a,d)cyclo-hepten-5,10-imine (MK-801) and its (+) and (-) enantiomers were tested in classical screening models used to detect potential antidepressants. The drug and its enantiomers were active in the tail suspension test (TST). The racemate was also active in the forced swimming test (FST). The effects in these tests occurred, however, at doses with marked stimulant activity. Further investigations (reserpine, apomorphine, and yohimbine tests) could not confirm the suspected antidepressant activity. Other NMDA antagonists--2-amino-7-phosphonoheptanoic acid (AP7), kynurenic acid, and 1-glutamic acid diethylester (GDEE)--showed no activity in the TST. These findings throw doubt concerning the potential antidepressant activity of MK-801 and other NMDA antagonists.

Serotonin: neurotransmitter "a la mode". Report on the Third International I.T.E.M.-LABO symposium on strategies in psychopharmacology: serotonin: animal models and clinical targets.

The recently held Symposium "Serotonin: Animal Models and Clinical Targets" (Paris, 26-28th February 1992) reviewed the present status of new serotonergic drugs. Specific serotonin-uptake inhibitors (citalopram, fluoxetine, fluvoxamine, paroxetine) are now clearly accepted as antidepressants with apparently specific effects on obsessive-compulsive disorder. Available 5-HT1a agonists (buspirone, gepirone, ipsapirone) are somewhat disappointing as anxiolytics but more specific compounds (flesinoxan, S 20499, E 4424) are now in development. Neuroleptics with 5-HT2 antagonist properties (amperozide, clozapine, risperidone), appear to have lower EPS potential than classic neuroleptics but the role of 5-HT2 antagonism in the control of psychotic symptoms remains unclear. 5-HT3 antagonists (ondansetron, tropisetron, zacopride) may have anxiolytic and possibly cognition-enhancing properties but more clinical work is needed. Finally, in the preclinical sphere, electrophysiological, neurochemical, and behavioral approaches have been useful in elucidating mechanisms of action but have been less impressive, particularly behavioral techniques, in predicting clinical activity.

Combined effects of diazepam and melatonin in two tests for anxiolytic activity in the mouse.

The effects of behaviorally nonactive doses of melatonin and diazepam were investigated in two test models for anxiolytics in mice to see whether mutual enhancement could be observed when the two treatments were combined. The test models used were the four plates test and the tail suspension test. In the former test anxiolytics increase the number of punished crossings and in the latter increase the duration of immobility of mice suspended by the tail. In the four plates test combined treatment with melatonin (128 and 256 mg/kg IP) and diazepam (0.5 mg/kg PO) caused a significant increase in the number of punished crossings, whereas each treatment alone was without effect. Similarly, in the tail suspension test, a clear increase in the duration of immobility was observed after combined treatment (256 mg/kg IP melatonin + 0.5 mg/kg PO diazepam), whereas no effects were observed with the individual treatments alone. These results suggest that melatonin can enhance the anxiolytic actions of diazepam.

Behavioral indices of beta receptor subsensitivity after chronic treatment with viloxazine in the mouse.

The aim of the experiments was to determine whether chronic pretreatment with viloxazine decreased the sensitivity of mice to the sedative effects of a beta agonist clenbuterol. Mice were subjected to chronic oral treatment with viloxazine (128 mg/kg twice daily) and then given a single administration of 32 mg/kg PO followed by clenbuterol (0.125 mg/kg IP) before being tested in a standard photocell activity meter. Imipramine, administered at the same doses in the same experimental conditions, was used as a comparison compound. The results showed that chronic but not acute viloxazine decreased the hypoactivity induced by clenbuterol, suggesting the induction of beta receptor subsensitivity. With imipramine the results were in the same direction but less clear. The findings are discussed in terms of the eventual specificity of the viloxazine effect to subsensitivity in beta-2 receptors.

Effects of an extract of Ginkgo Biloba (EGB 761) on "learned helplessness" and other models of stress in rodents.

The effects of repeated oral administration of an extract of Ginkgo Biloba (EGB 761) on various behavioral models of stress in rodents were investigated. The models in rats included "learned helplessness," shock-suppressed licking (Vogel conflict test) and forced swimming-induced immobility ("behavioral despair"). The models in mice included shock-suppressed exploration (four plates test), spontaneous exploration (staircase test) and food consumption in a novel situation (emotional hypophagia). Further tests in rats examined the effects of EGB 761 on memory (passive avoidance test) and responsiveness to shock to determine whether the preventive effects observed with EGB 761 in the learned helplessness procedure were due either to drug-induced impairment of memory or to reduced shock sensitivity. In all experiments EGB 761 was administered over 5 days at daily doses of 50 and 100 mg/kg PO. In some experiments (Vogel test, four plates test, staircase test, emotional hypophagia) the effects of acute administration were also investigated. The results showed that repeated administration of EGB 761 (50 and 100 mg/kg/day) before exposure to unavoidable shock (preventive treatment) clearly reduced the subsequent avoidance deficits in the learned helplessness procedure but was less effective when first administered after "helplessness" induction (curative treatment). EGB 761 did not affect performance in the passive avoidance task or alter the animals' response to electric shock, suggesting that the effects observed in the learned helplessness procedure were not due to impaired memory or reduced shock sensitivity. Anxiolytic-like activity was also seen in the emotional hypophagia test in mice where repeated administration of EGB 761 increased the amount of food consumed.(ABSTRACT TRUNCATED AT 250 WORDS)

Absence of amnesia induction in mice with hydroxyzine in comparison with three other minor tranquillizers.

Hydroxyzine (Atarax) was compared with three traditional anxiolytics (diazepam, meprobamate, triazolam) for potential amnesic activity in a step-through passive avoidance task in the mouse. The doses investigated were: hydroxyzine (4, 8 and 16 mg/kg); diazepam (0.25, 0.5 and 1 mg/kg); meprobamate (8, 16 and 32 mg/kg); triazolam (0.0015, 0.003 and 0.006 mg/kg). The doses investigated were chosen on the basis of prior experiments for not having sedative effects as measured in a photo-cell activity meter. All drugs were administered i.p. 30 min before the first trial of the passive avoidance task. The compounds were also investigated for eventual analgesic activity using the hot plate test. The results indicated that hydroxyzine up to sedative doses was devoid of amnesic activity, whereas clear signs of amnesia were induced by diazepam, meprobamate and triazolam at doses at least 8 times lower than those which reduced spontaneous motor activity. None of the compounds showed analgesic activity in the hot plate test suggesting that the signs of amnesia observed in the passive avoidance test were not due to reduced sensitivity to aversive stimulation.

Specificity of piracetam's anti-amnesic activity in three models of amnesia in the mouse.

The effects of piracetam on the amnesias induced by scopolamine, diazepam and electroconvulsive shock (ECS) were studied in a passive avoidance procedure in the mouse and compared with the interactions of piracetam with the major behavioral effects of these treatments, namely scopolamine-induced hyperactivity, diazepam-induced release of punished behavior (Four Plates Test) and ECS-induced convulsions. Amnesia was induced by injecting scopolamine or diazepam (1 mg/kg, IP) 30 minutes before or applying ECS immediately after the first session (S1) of the passive avoidance task. Piracetam was studied at 3 doses (512, 1024 and 2048 mg/kg) administered PO 60 minutes before S1. Retention was measured 24 hours later (S2) in the absence of any treatment. Piracetam dose-dependently attenuated the memory deficits induced by the three amnesic treatments but did not affect either scopolamine-induced hyperactivity, diazepam-induced release of punished behavior or ECS-induced convulsions. These results point to the specificity of piracetam's anti-amnesic activity and, in particular, suggest that piracetam can suppress the memory disturbances induced by diazepam without affecting diazepam's anxiolytic activity. The test battery employed would therefore seem highly suitable for evaluating the potential nootropic activity of novel compounds.