Sharon Pellow

Validation of open: closed arm entries in an elevated plus-maze as a measure of anxiety in the rat

A novel test for the selective identification of anxiolytic and anxiogenic drug effects in the rat is described, using an elevated + -maze consisting of two open arms and two enclosed arms. The use of this test for detecting such drug effects was validated behaviourally, physiologically, and pharmacologically. Rats made significantly fewer entries into the open arms than into the closed arms, and spent significantly less time in open arms. Confinement to the open arms was associated with the observation of significantly more anxiety-related behaviours, and of significantly greater plasma corticosterone concentrations, than confinement to the closed arms. Neither novelty nor illumination was a significant contributor to the behaviour of the rats on the + -maze. A significant increase in the percentage of time spent on the open arms and the number of entries into the open arms was observed only within clinically effective anxiolytics (chlordiazepoxide, diazepam and, less effectively, phenobarbitone). Compounds that cause anxiety in man significantly reduced the percentage of entries into, and time spent on, the open arms (yohimbine, pentylenetetrazole, caffeine, amphetamine). Neither antidepressants nor major tranquilisers had a specific effect. Exposure to a holeboard immediately before placement on the + -maze showed that behaviour on the maze was not clearly correlated either with exploratory head-dipping or spontaneous locomotor activity.

Anxiolytic and anxiogenic drug effects on exploratory activity in an elevated plus-maze: A novel test of anxiety in the rat

The current studies further investigated the effects, in animal models of anxiety, of novel putative anxiolytic and anxiogenic compounds believed to induce their effects by actions at the GABA-benzodiazepine receptor complex. It was expected that the results would also provide further validation for a novel test of anxiety based on the ratio of open to closed arm entries in an elevated plus maze in the rat. The novel putative anxiolytics CL 218,872 (10-20 mg/kg) and tracazolate (5 mg/kg) significantly elevated the percentage of time spent on the open arms of an elevated plus-maze, consistent with their anxiolytic activity in several other animal tests. Also consistent with results from other animal tests, no anxiolytic activity was observed for the phenylquinoline PK 8165 (10-25 mg/kg), the 3,4-benzodiazepine tofisopam (25-50 mg/kg), or buspirone (0.5-20 mg/kg). The benzodiazepine receptor inverse agonists FG 7142 (1-5 mg/kg) and CGS 8216 (3-10 mg/kg) had anxiogenic activity in this test, as did the atypical benzodiazepine Ro 5-4864 (1-5 mg/kg). Interestingly, however, the benzodiazepine receptor antagonists Ro 15-1788 (10-20 mg/kg) and ZK 93426 (5-10 mg/kg) had no anxiogenic activity in this test.

Intrinsic actions of the benzodiazepine receptor antagonist Ro 15-1788

The imidazodiazepine Ro 15-1788 is a benzodiazepine receptor antagonist that was initially reported to be lacking in intrinsic activity in a variety of test situations in which benzodiazepine-like effects can be identified. However, many recent studies have shown that this compound does indeed have intrinsic activity in a variety of behavioural, neurological, electrophysiological and biochemical preparations in both animals and man. The purpose of the present review is firstly to describe these intrinsic actions, and secondly to consider to what extent these intrinsic actions of Ro 15-1788 have implications for current concepts of the functioning of the benzodiazepine receptor.

Selective agonists and antagonists for 5-hydroxytryptamine receptor subtypes, and interactions with yohimbine and FG 7142 using the elevated plus-maze test in the rat.

The effects of some 5‐HT receptor ligands were investigated on measures of anxiety in an elevated plus‐maze test in the rat. Quipazine (2 and 4 mg kg−1), a non‐specific 5‐HT agonist and ritanserin (0ṁ25‐10 mg kg−1), a 5‐HT2 receptor antagonist displayed anxiogenic profiles by reducing both of the measures of anxiety used in this test. Two 5‐HT1A receptor ligands, buspirone (4 and 8 mg kg−1) and ipsapirone (2.5‐10 mg kg−1) and the 5‐HT1 agonist, RU 24969 (0ṁ1875‐1ṁ5 mg kg−1) significantly reduced only the percentage of time spent on the open arms. (‐)‐Propranolol (5 and 10 mg kg−1), a 5‐HT1 receptor antagonist significantly reduced only the percentage of entries made onto the open arms. Metergoline (4 mg kg−1), a non‐specific 5‐HT antagonist displayed anxiolytic effects in this test by increasing both measures of anxiety. The 5‐HT1A receptor agonist, 8‐OH‐DPAT (0ṁ0625‐0dependent manner in25 mg kg−1) had no effect on either of the measures of anxiety. The results from the non‐specific ligands (quipazine and metergoline) are consistent with the theory that a reduction in 5‐HT function reduces anxiety. However, in spite of their more selective effects on 5‐HT receptors the results in this test from the more specific ligands are not consistent with a strong involvement of any single receptor subtype. The interaction studies with yohimbine and FG 7142 (β‐carboline‐3‐carboxylate methylamide) provided no clear evidence for a major role of 5‐HT pathways in the mediation of their anxiogenic effects.

Multiple sites of action for anxiogenic drugs: Behavioural, electrophysiological and biochemical correlations

This review describes animal models of anxiety that are able to identify an anxiogenic drug effect. Evidence is reviewed for the anxiogenic action of several drugs that act at the GABA-benzodiazepine-chloride ionophore complex in the brain. The effects of their combinations with various other drugs thought to act at the same sites are discussed. The classification of these drugs on the basis of their behavioural profiles is compared with their classification based on biochemical and electrophysiological studies.

The effects of triazolobenzodiazepines in two animal tests of anxiety and in the holeboard

1 In addition to possessing anti‐anxiety activity in man, triazolobenzodiazepines have been reported to have antidepressant and antipanic properties. In this they differ from classical 1,4‐benzodiazepines that have only anti‐anxiety activity. The purpose of the present study was to examine the effects of the triazolobenzodiazepines in two animal tests of anxiety and in the holeboard, to see whether clear differences could be observed between them and the 1,4‐benzodiazepines. 2 After acute administration, U‐43,465 (16 mg kg−1) had a significant anxiolytic effect in the social interaction test. Neither adinazolam (1–3.5 mg kg−1) nor alprazolam (0.125‐2 mg kg−1) had a significant effect. It is suggested that this is because, with adinazolam and alprazolam, doses at which anxiolytic effects can be observed are close to those at which sedative effects can be observed. 3 U‐43,465 (8–16 mg kg−1) and alprazolam (1–2 mg kg−1) had significant anxiolytic effects in the elevated plus‐maze test of anxiety. 4 U‐43,465 (8–32 mg kg−1), adinazolam (0.5‐5 mg kg−1) and alprazolam (0.2‐2.0 mg kg−1) caused dose‐related reductions in exploratory head‐dipping, locomotor activity and rearing in the holeboard. 5 In general the results seen in the three tests with the triazolobenzodiazepines alprazolam and adinazolam were similar to those seen with classical 1,4‐benzodiazepines. With U‐43,465, however, an anxiolytic effect was observed in the social interaction test after acute treatment; chronic treatment is required to see an effect with classical 1,4‐benzodiazepines. In this U‐43,465 resembles the effects of several novel non‐benzodiazepine putative anxiolytic compounds that are believed to have less sedative potential than the benzodiazepines.

Are the anxiogenic effects of yohimbine mediated by its action at benzodiazepine receptors

Yohimbine, which has activity both at alpha 2-adrenoreceptors and benzodiazepine receptors in the CNS, had an anxiogenic action (1.25-2.5 mg/kg) in the social interaction test in rats. This effect was reversed by the alpha 2-adrenoceptor agonist clonidine (0.01 mg/kg), but not by the benzodiazepine receptor agonist chlordiazepoxide (5-10 mg/kg) or the antagonist Ro 15-1788 (10 mg/kg). These results suggest that the anxiogenic effects of yohimbine are not attributable to its low affinity effects at benzodiazepine receptors but to its alpha 2-adrenoceptor antagonist activity.

Effects of the β-carboline, FG 7142, in the social interaction test of anxiety and the holeboard: Correlations between behaviour and plasma concentrations

The behavioural effects of the beta-carboline FG 7142 were investigated in the social interaction test of anxiety and the holeboard test of exploration and locomotor activity. FG 7142 (5-20 mg/kg) produced a significant decrease in the time spent in social interaction by pairs of rats, without an accompanying decrease in motor activity. This anxiogenic effect was highly correlated with the plasma concentrations of FG 7142 for the rats receiving 5 and 10 mg/kg doses, but not for those receiving the 20 mg/kg dose. In the holeboard, FG 7142 had no effect on exploratory head-dipping at the doses tested, but selectively reduced locomotor activity and the number of rears. The profile of FG 7142 in these tests is compared with those of the beta-carbolines, B-CCE and B-CCP.

The effects of putative anxiogenic compounds (FG 7142, CGS 8216 and Ro 15-1788) on the rat corticosterone response

The effects of FG 7142, CGS 8216 and Ro 15-1788, three compounds that are believed to produce anxiety by an action at benzodiazepine receptors in the CNS, are investigated on the plasma corticosterone concentrations in the rat both in the home cage and after exposure to novelty stress. FG 7142 (5 mg/kg) and CGS 8216 (10 mg/kg), but not Ro 15-1788 (4 or 10 mg/kg) increased basal corticosterone levels in the home cage, and all three compounds potentiated the increase in corticosterone concentrations observed after exposure to a novel environment. The relationship between the effects of drugs on corticosterone concentrations and on anxiety is considered in the light of these results.

The sedative effects of CL 218,872, like those of chlordiazepoxide, are reversed by benzodiazepine antagonists

The effects of CL 218,872, initially classified as a non-sedative anxiolytic, were investigated and compared with those of chlordiazepoxide in the holeboard. The ability of two drugs that antagonise the effects of benzodiazepines, CGS 8216 and Ro 15-1788, to reverse the effects of CL 218,872 and chlordiazepoxide were also investigated, to see whether their effects might be mediated via benzodiazepine receptors. CL 218,872 (10 mg/kg) was found to be significantly sedative in both mice and rats (i.e., both locomotor activity and head-dipping were significantly decreased). In mice, the effects of CL 218,872 and of chlordiazepoxide were very similar over a range of doses, except that the stimulatory effect seen with low doses of chlordiazepoxide on head-dipping just failed to reach significance with CL 218,872. This study is in agreement with recently published results from different tests showing that sedative effects can be obtained with doses of CL 218,872 that are low and not much higher than those leading to anxiolysis. The sedative effects of both CL 218,872 (10 mg/kg) and chlordiazepoxide (20 mg/kg) were significantly reversed by RO 15-1788 (10 and 20 mg/kg) and CGS 8216 (10 mg/kg), suggesting that their effects are mediated via benzodiazepine receptors. The increase in head-dipping seen with chlordiazepoxide (2.5 mg/kg) was also reversed by RO 15-1788 and CGS 8216.