M.E. Kelly

Exploration of mice in a black and white test box: Validation as a model of anxiety

The validity of a black and white test box to measure changes in mouse exploratory behaviour relevant to assessment of anxiety was investigated by variation of the illumination within the test box, the use of different strains of mice, holding conditions and drug treatments. The suppression of exploratory activity in the white section caused by bright illumination was antagonised by anxiolytic agents from the benzodiazepine series, buspirone, 5-HT3 receptor antagonists, alcohol, nicotine, morphine and SCH23390. The anxiogenic agent FG7142 exacerbated the behavioural suppression. Black C57/BL/6, brown DBA2 and albino BKW mice were sensitive to the effects of drug treatments, whereas albino Tuck mice were less responsive. It is concluded that the characteristic change in mouse exploratory behaviour caused by anxiolytic agents is to preferentially increase exploratory behaviour in the white aversive section of the black and white test box. It is most consistently shown by (a) an increased time spent in the white section with proportional increases in (b) rearings and (c) ambulation and (d) a delay in the initial transition from the white to the black section.

The potential anxiolytic activity of GR38032F, a 5-HT3-receptor antagonist.

1 The highly selective 5‐HT3‐receptor antagonist, GR38032F, has been tested in five animal models predictive for anxiolytic activity. 2 In the social interaction test in the rat and in a light/dark exploration test in the mouse, GR38032F dose‐dependently released suppressed behaviour without modifying locomotor activity. 3 In the cynomolgus monkey and the marmoset, GR38032F reduced anxiety‐related symptoms without causing sedation. In the marmoset, the effects were clearly dose‐related. 4 GR38032F did not have any detectable activity in the water‐lick conflict test in the rat. 5 We conclude that GR38032F is potentially a very potent anxiolytic agent without sedative, anticonvulsant or hypnotic activity.

Zacopride: anxiolytic profile in rodent and primate models of anxiety.

Abstract— Zacopride, a substituted benzamide derivative, was compared with diazepam in three models of experimental or provoked anxiety. The drugs action (i) in reducing aversion to a brightly lit environment was assessed in mice using a two compartment black and white test box system, (ii) in disinhibiting a suppressed behaviour was measured in the rat social interaction test under high light/unfamiliar conditions and (iii) in antagonizing a defensive response in the marmoset was assessed using the threat of a human presence. Both zacopride and diazepam enhanced exploratory behaviour and social interaction in the mouse and rat models and antagonized the defensive response in the marmoset, zacopride being 100 times more potent than diazepam. It is concluded that the 5‐HT3 receptor antagonist, zacopride, alters rodent and primate behaviour in a manner consistent with that of an anxiolytic agent.

Preclinical pharmacology of ropinirole (SK&F 101468-A) a novel dopamine D2 agonist

These studies characterise the pharmacology of ropinirole, a selective D-2 agonist. High-affinity human caudate binding revealed a Ki for D2 receptors of 2.9 x 10(-8) M with no affinity for D1 at 10(-4) M in the rat. Ropinirole was weakly active at alpha 2-adrenoceptors and 5-HT2 receptors but inactive at 5-HT1, benzodiazepine and gamma-aminobutyric acid receptors or alpha 1 and beta-adrenoceptors. In rodents, ropinirole, like apomorphine, caused biphasic spontaneous locomotor activity and contralateral circling in 6-OHDA-lesioned mice with no tolerance to the latter after 14 days treatment. Amphetamine caused ipsilateral responses in the lesioned mice. Ropinirole did not cause marked stereotypies. In marmosets ropinirole (0.05-1.0 mg/kg SC or 0.1 mg/kg PO) reversed all motor and behavioural deficits induced by MPTP. This response started 10-20 minutes after dosing, and exceeded 2 hours. No tolerance was seen following chronic b.i.d. treatment. Similar results were obtained with 1-dopa plus benserazide; however, 1-dopa always caused emesis, whereas beneficial effects were shown with ropinirole in the absence of this side effect. These results support the continued clinical assessment of ropinirole for the treatment of Parkinsons disease.

Ondansetron inhibits a behavioural consequence of withdrawing from drugs of abuse

The ability of the selective 5-HT3 receptor antagonist ondansetron to influence the behavioural consequences of withdrawal from chronic treatment with ethanol, nicotine or cocaine was investigated in the light/dark exploration test in the mouse and social interaction test in the rat. In both tests acute and chronic (7 days) treatments with ondansetron (0.01-1.0 microgram.kg-1 IP) disinhibited suppressed behaviour; withdrawal from chronic treatment (0.1 mg/kg IP b.i.d.) did not exacerbate the behavioural suppression. Chronic treatment for 14 days with ethanol (8% w/v in the drinking water), nicotine (0.1 mg/kg b.i.d.) or cocaine (1.0 mg/kg b.i.d.) released suppressed behaviour in the mouse and rat tests. Behavioural suppression was increased following withdrawal from ethanol, nicotine and cocaine. The administration of ondansetron (0.01 mg/kg IP b.i.d.) during the period of ethanol, nicotine and cocaine withdrawal prevented the exacerbation in suppressed behaviour. It is concluded that ondansetron potently reduces behavioural suppression during acute and chronic treatments in the rodent models, does not cause a rebound exacerbation of behavioural suppression following withdrawal, and is a highly effective inhibitor of the increased behavioural suppression following withdrawal from the drugs of abuse: ethanol, nicotine and cocaine.

Neuroanatomical sites of action of 5-HT3 receptor agonist and antagonists for alteration of aversive behaviour in the mouse.

1 The cerebral topography of the action of diazepam and the action of the 5‐hydroxytryptamine 5‐HT3 receptor antagonists GR38032F and ICS 205–930 in attenuating an aversive response was studied in the mouse. 2 Mice which had been cannulated to allow drug injection into the dorsal and median raphe nuclei, the amygdala, nucleus accumbens or caudate‐putamen were placed in a two compartment black (dimly illuminated) and white (brightly illuminated) test box. Measurements were made of the time spent, rearing and line crossings in the two sections and the latency of initial movement from the white to the black area. 3 The injection of diazepam (0.1–10 ng), GR38032F (0.01–1.0 ng) and ICS 205–930 (1.0–10 ng) into the dorsal raphe nucleus and amygdala, and the injection of diazepam (0.1–10 ng) into the median raphe nucleus, reduced an aversive response to the brightly illuminated white area, delaying the initial movement into the black section and increasing the time spent, rearings and line crossings in the white area. Concomitantly such activities were decreased in the black section. 4 The injection of the 5‐HT3 agonist 2‐methyl‐5‐hydroxytryptamine (0.1–10 ng) into the dorsal raphe nucleus and amygdala caused the opposite response, decreasing the time taken to move into the black section and increasing the time spent, rearings and line crossings in the black section, decreasing such activities in the white area. 5 The 5‐HT3 agonist and antagonists showed little or no effect following injection into the median raphe nucleus and there were no changes in exploratory behaviour following their injection, or injection of diazepam, into the nucleus accumbens or caudate‐putamen. 6 It is concluded that in the mouse the cerebral topography of action of GR38032F and ICS 205–930 in attenuating an aversive response follows that of diazepam in the dorsal raphe nucleus and amygdala but that diazepam may have additional effects mediated via the median raphe nucleus.

Sites of action of ondansetron to inhibit withdrawal from drugs of abuse.

The cerebral site of action of the selective 5-HT3 receptor antagonist ondansetron to influence the behavioural consequences of withdrawal from subchronic treatment with diazepam, ethanol, nicotine or cocaine was studied in the light/dark exploration test in the mouse. The aversive response to the light compartment of the test box was reduced during a subchronic treatment with peripherally administered diazepam, ethanol, nicotine and cocaine, but was exacerbated following withdrawal from the 4 treatments. The behavioural consequences of withdrawal from diazepam (10 mg/kg IP b.i.d. 14 days), ethanol (8%/w/v drinking water for 14 days), nicotine (0.1 mg/kg IP b.i.d. 14 days) or cocaine (1.0 mg/kg IP b.i.d. 14 days) were antagonised by ondansetron injected into the amygdala and dorsal raphe nucleus (1-10 ng); injections of ondansetron (10 ng) into the median raphe nucleus, the nucleus accumbens and striatum were ineffective. It is concluded that the amygdala and dorsal raphe nucleus may be sites of action for ondansetron to antagonise the aversive behaviour caused by withdrawal from 4 common drugs of abuse in a mouse model, and that 5-HT projections from the dorsal raphe nucleus may be involved in aversive behaviour.

Effects of captopril and SQ29,852 on anxiety-related behaviours in rodent and marmoset.

The abilities of the ACE inhibitors captopril and SQ29,852 to modify aversive behaviour was compared to the effects of diazepam in the light/dark exploration test in the mouse, the elevated plus maze and social interaction test in the rat, and in anxiety-related behaviours induced by human threat in the marmoset. In the four tests the acute administration of captopril, SQ29,852 and diazepam had the same profiles of action to reduce aversive responding. This was also observed during chronic administration with the three agents in the mouse. However, withdrawal from a chronic treatment with diazepam precipitated a syndrome of increased aversion, whereas withdrawal from treatment with captopril and SQ29,852 was uneventful, values waning to control levels. Withdrawal from treatment with ethanol, nicotine and cocaine also enhanced aversive responding. Treatment with captopril and SQ29,852 antagonised the behavioural consequences of withdrawal from treatment with diazepam and nicotine and SQ29,852 also blocked the consequences of withdrawal from ethanol and cocaine. It is concluded that captopril and SQ29,852 have an anxiolytic profile of action in 3 species, that cessation of treatment is not associated with a withdrawal syndrome, that the ACE inhibitors cross tolerate with diazepam and can antagonise the behavioural consequences of withdrawal from treatment with drugs of abuse.

Actions of buspirone in a putative model of anxiety in the mouse.

Abstract— In a two‐compartment box divided into a dark area and a brightly illuminated white area, mice taken from a dark environment showed aversion to the light and exhibited preference for exploratory rearings and line crossings in the black area. The peripheral administration of buspirone, and its injection into the dorsal raphe nucleus, lead to an increased time spent in the white area associated with enhanced exploratory behaviour with a decreased incidence of rearings and line crossings in the black section. In contrast, the injection of 5‐hydroxytryptamine and 2‐methyl‐5‐hydroxytryptamine into the dorsal raphe nucleus increased exploratory behaviour in the black section with decreased activity in the white area: the effects of 2‐methyl‐5‐hydroxytryptamine were antagonized by buspirone administered peripherally. Ritanserin, methysergide, metergoline and cyproheptadine failed, in non‐sedative doses, to influence exploratory behaviour in the two‐compartment system and ritanserin and methysergide also failed to antagonize the effects caused by 2‐methyl‐5‐hydroxytryptamine. It is concluded that in the mouse model the ability of buspirone to reduce the aversive response to a brightly illuminated area may reflect an anxiolytic action, that the dorsal raphe nucleus may be an important locus of action, and that the effects of buspirone may reflect an interaction at 5‐hydroxytryptamine receptors.

The differential activities of R(+)- and S(−)-zacopride as 5-HT3 receptor antagonists

R(+)- and S(-)-zacopride were assessed as potential 5-HT3 receptor antagonists in behavioural and biochemical tests. The S(-)isomer was more potent than the R(+)isomer to antagonise the hyperactivity induced by the injection of amphetamine or the infusion of dopamine into the nucleus accumbens in the rat. In contrast, the R(+)isomer was more potent to reduce the aversive behaviour of mice to a brightly illuminated environment and in a marmoset human threat test, to facilitate social interaction in rats, to increase performance in a mouse habituation test and prevent a scopolamine-induced impairment, and to antagonise the inhibitory effect of 2-methyl-5-hydroxytryptamine to reduce [3H]acetylcholine release in slices of the rat entorhinal cortex. In binding assays, [3H]S(-)-zacopride and [3H]R(+)-zacopride labelled homogenous populations of high-affinity binding sites in the rat entorhinal cortex, R(+)-zacopride compete for a further 10 to 20% of the binding of [3H]R(+)/S(-)-zacopride or [3H]R(+)-zacopride in excess of that competed for by (S)(-)-zacopride. It is concluded that both isomers of zacopride have potent but different pharmacological activities, with the possibility of different recognition sites to mediate their effects.