B. Costall

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.

Effects of the 5-HT3 receptor antagonist, GR38032F, on raised dopaminergic activity in the mesolimbic system of the rat and marmoset brain.

1 The ability of the selective 5‐HT3 receptor antagonist GR38032F to reduce raised mesolimbic dopaminergic activity was studied in behavioural experiments in the rat and marmoset. 2 GR38032F injected into the nucleus accumbens (0.01–1 ng) or peripherally (0.01–1 mg kg−1 i.p.) inhibited the locomotor hyperactivity caused by the acute intra‐accumbens injection of amphetamine (10 μg) in the rat. Similar treatments with sulpiride and fluphenazine also inhibited the amphetamine‐induced hyperactivity. 3 The peripheral administration of GR38032F (0.001–0.1 mg kg−1 i.p., b.d.) during a 13 day period of dopamine infusion (25 μg 24 h−1) into the nucleus accumbens of the rat reduced the dopamine‐induced hyperactivity response to control (vehicle infused) levels. Locomotor activity remained at control levels after discontinuing the dopamine/GR38032F treatment regimen. 4 The hyperactivity caused by the infusion of dopamine into the rat nucleus accumbens was also inhibited by fluphenazine (0.01‐0.05 mg kg−1 i.p., b.d.), but locomotor activity was suppressed to levels below control values and a rebound hyperactivity occurred after discontinuation of the dopamine/fluphenazine treatment regimen. 5 The discontinuation of a concomitant 13 day intra‐accumbens infusion of dopamine with haloperidol, 0.01 mg kg−1 i.p. t.d.s., caused a rebound hyperactivity. This hyperactivity was suppressed by GR38032F (0.001‐0.1 mg kg−1 i.p.). 6 The unilateral infusion of dopamine (25 μg 24 h−1, 13 days) into the left amygdala of rats having right hemispheric dominance (as measured in a turn preference test) caused locomotor hyperactivity. Intraperitoneal administration of GR38032F (0.1–100 μg kg−1) or fluphenazine (0.025‐0.1 mg kg−1), and the intra‐amygdaloid injection of GR38032F (0.1–100 ng) or fluphenazine (25–500 pg), either into the infused or non‐infused side, inhibited the dopamine‐induced locomotor hyperactivity. 7 Marmosets receiving bilaterial infusions of dopamine (25 μg 24 h−1 for 13 days) into the nucleus accumbens also exhibited increased locomotor activity. GR38032F (0.1‐1.0 μg kg−1 t.d.s.), reduced the hyperactivity to control levels with no rebound hyperactivity following the discontinuation of the dopamine/GR38032F treatment regimen. Fluphenazine (0.01–2.5 mg kg−1 i.p., t.d.s.) also inhibited the hyperactivity, but locomotor activity was reduced to values below control levels and a rebound hyperactivity followed the discontinuation of the dopamine/fluphenazine treatment. 8 It is concluded that the 5‐HT3 receptor antagonist GR38032F, and the neuroleptic agents fluphenazine, sulpiride and haloperidol, can reduce raised mesolimbic dopaminergic activity in the rat and marmoset. GR38032F is distinguished from the dopamine receptor antagonists by, firstly, its ability to return the hyperactivity response to control values, without excessive suppression of locomotion even on enhanced dosage regimes and, secondly, by the lack of rebound hyperactivity following abrupt discontinuation of its treatment.

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.

The role of telencephalic dopaminergic systems in the mediation of apomorphine-sterrotyped behaviour

Abstract The electrolytic brain lesion technique was utilised in a systematic evaluation of the role of dopaminergic areas of the rat telencephalon in the mediation of stereotyped behaviour by apomorphine, the effects of the lesions being assessed both during the acute and chronic stages following their induction. After bilateral lesion of the ascending dopaminergic fibres in the lateral hypothalamus rats exhibited hypokinesia and mild catalepsy and, both in the acute and chronic stages following these lesions, the normal dose-dependent stereotypic effect of apomorphine was markedly reduced or abolished. An even greater reduction was observed after pallidectomy although lesion of the caudate-putamen was without effect. Destruction of the ascending dopaminergic fibers to the mesolimbic system caused a reduction in the intensity of apomorphine stereotypy during the acute and chronic stages. A similar reduction was observed after lesion of the tuberculum olfactorium or nucleus accumbens septi, although the effect was less marked following the latter lesions. Stereotypy was also reduced, both during the acute and chronic stages following ablation of the nucleus amygdaloideus centralis, but was not modified by lesion of the stria terminalis. These studies indicate that both extrapyramidal and mesolimbic dopaminergic systems are involved with the mediation of stereotyped behaviour by apomorphine, the degree of involvement of the two systems with the different components of stereotyped behaviour being clearly differentiated. Since lesion of the dopaminergic pathways was virtually as effective in reducing or abolishing the apomorphine effect as lesson of the dopaminergic areas themselves, the possibility that apomorphine may modify pre- as well as post-synaptic mechanisms is considered.

Stereotyped behaviour patterns and hyperactivity induced by amphetamine and apomorphine after discrete 6-hydroxydopamine lesions of extrapyramidal and mesolimbic nuclei

Changes in stereotyped sniffing, biting and hyperactivity induced by apomorphine and D-amphetamine in the rat were determined after bilateral 6-hydroxy-dopamine (6-OHDA) lesions (8-16 micron/4micron6) of the extrapyramidal caudate-putamen (CP) (anterior and centre), globus pallidus (GP) and substantia nigra (SN), the mesolimbic nucleus (ACB), tuberculum olfactorium (TUO) and central amygdaloid nucleus (ACE). Lesions were also induced in the medial forebrain bundle in the lateral hypothalamus (LH). The 6-OHDA lesions of the CP reduced amphetamine biting but not sniffing or hyperactivity. Centrally placed 6-OHDA failed to modify any response to apomorphine but anterior locations reduced apomorphine biting. Both lesion locations led to a 45-65% reduction in striatal dopamine (DA) content, but the anterior location also involved depletions of mesolimbic DA. 6-OHDA lesions of the GP reduced striatal DA by 62% but initially potentiated before reducing both apomorphine and amphetamine biting. These lesions also potentiated amphetamine hyperactivity but other parameters were unmodified. The LH and SN lesions reduced striatal and mesolimbic DA by 75-80% and potentiated apomorphine biting. The LH lesions reduced amphetamine biting and hyperactivity but the SN lesions initially potentiated these responses. 6-OHDA lesions of the ACB reduced the DA content of this nucleus by 72% but had little effect on the TUO: these lesions reduced the duration of amphetamine hyperactivity and potentiated apomorphine biting. In contrast, equally selective lesions of the TUO (80% DA depletion) enhanced the locomotor activity response to both apomorphine and amphetamine; apomorphine biting was also increased but other parameters were unmodified. Lesions of the ACE depleted amygdaloid DA by at least 80% and reduced or abolished apomorphine and amphetamine biting in the chronic stage. The results indicate that the sites for mediation of sterotyped sniffing, biting or hyperactivity are not the same for apomorphine and amphetamine, and that each behavioural state involves the functioning of more than one DA-containing area.

The psychopharmacology of 5-HT3 receptors

The review presents evidence that 5-HT3 receptors within the brain may contribute to the control of behavior. 5-HT3 receptor antagonists GR38032F, zacopride, ICS 205-930 and other agents are very potent in reducing mesolimbic dopamine hyperactivity caused by the injection of amphetamine or infusion of dopamine into the rat nucleus accumbens and amygdala, and the ventral striatum of the marmoset. Such actions are distinguished from those of neuroleptic agents by a failure to reduce normal levels of activity or to induce a rebound hyperactivity after discontinuation of treatment. Indeed, the 5-HT3 receptor antagonists can prevent the neuroleptic-induced rebound hyperactivity. Further evidence that 5-HT3 receptors moderate limbic dopamine function is shown by their ability to reduce both the behavioral hyperactivity and changes in limbic dopamine metabolism caused by DiMe-C7 injection into the ventral tegmental area. The 5-HT3 receptor antagonists also have an anxiolytic profile in the social interaction test in the rat, the light/dark exploration test in the mouse, the marmoset human threat test and behavioral observations in the cynomolgus monkey. They differ from the benzodiazepines by an absence of effect in the rat water lick conflict test and a withdrawal syndrome. Importantly, the 5-HT3 receptor antagonists are highly effective to prevent the behavioral syndrome following withdrawal from treatment with diazepam, nicotine, cocaine and alcohol. Intracerebral injection techniques in the mouse indicate that the dorsal raphe nucleus and amygdala may be important sites of 5-HT3 receptor antagonist action to inhibit aversive behavior. Studies with GR38032F indicate an additional effect in reducing alcohol consumption in the marmoset. The identification and distribution of 5-HT3 receptors in the brain using a number of 5-HT3 receptor ligands, [3H]65630, [3H]zacopride and [3H]ICS 205-930 correlates between studies, and the 5-HT3 recognition sites in cortical, limbic and other areas meet the criteria for 5-HT3 receptors to mediate the above behavioral effects. Thus the use of 5-HT3 receptor antagonists reveals an important role for 5-hydroxytryptamine in the control of disturbed behavior in the absence of effect on normal behavior. The profile of action of the 5-HT3 receptor antagonists has generated a major clinical interest in their potential use for schizophrenia, anxiety and in the control of drug abuse.

Thyroid hormones, brain function and cognition: a brief review.

In addition to their role in cellular metabolic activity, thyroid hormones (THs), also regulate neural development; the central nervous system is particularly dependent on TH for normal maturation and function. Specifically, there appears to be extensive inter-reliance between TH and acetylcholine (Ach), nerve growth factor and hippocampal function. These associations led us to investigate the possible effects of thyroxine (L-T4) on performance of a spatial learning task, where cholinergic activity and hippocampal function are known to be important. Groups of rats (n=20) received saline (controls) or L-T4 at 2.5 or 5mg/kg daily for 4 days as a sub-chronic treatment, or 0, 5 or 10mg/kg doses administered every third day for 28 days prior to testing as a chronic regimen. Rats were assessed in a water maze for their ability to find a submerged or visible platform. Forty minutes prior to water maze testing, half the animals in each group received 1mg/kg scopolamine to elicit a cognitive deficit. Following testing, rats were decapitated, blood samples taken, and the frontal cortex and hippocampus were dissected out for acetylcholinesterase (AChE) assay. The results showed that L-T4 treatment, administered both sub-chronically and chronically, significantly enhanced the ability of rats to learn a spatial memory task, compared with controls. Moreover, both short-term and long-term L-T4 treatment reduced the cognitive-impairing effects of scopolamine. Improvements in performance were shown to occur alongside significantly increased cholinergic activity in frontal cortex and in the hippocampus of treated animals. These findings demonstrate an augmentative effect of L-T4 upon cognitive function, possibly mediated by an enhancement of cholinergic activity. The results support previous findings of a relationship between L-T4 and acetylcholine, and underscore possible mechanisms by which disorders of thyroid function may be associated with cognitive decline.

Catalepsy and circling behaviour after intracerebral injections of neuroleptic, cholinergic and anticholinergic agents into the caudate-putamen, globus pallidus and substantia nigra of rat brain

Abstract Haloperidol, arecoline and atropine were injected in various combinations into the caudate-putamen, globus pallidus and substantia nigra. Unilateral injections of haloperidol or arecoline into the caudate-putamen, globus pallidus or substantia nigra induced an ipsilateral circling behaviour, the globus pallidus being the most sensitive and the substantia nigra the least sensitive to this effect. Atropine induced a contralateral circling behaviour after injection into the caudate-putamen or globus pallidus and in each case potentiated the ipsilateral circling of haloperidol and arecoline when injected into the opposite nucleus. The injection of atropine into the same caudate-putamen as haloperidol or arecoline inhibited the ipsilateral circling induced by the latter drugs. Catalepsy was observed after haloperidol injections into the caudate-putamen and globus pallidus, the latter nucleus being the most sensitive. Catalepsy was not observed after arecoline injection into any of the nuclei considered. The bilateral injection of atropine into the caudate-putamen and globus pallidus did not modify the catalepsy induced by peripheral administration of haloperidol or arecoline but intranigral atropine markedly potentiated the cataleptic effects of these drugs. Results are discussed in terms of cholinergic and dopaminergic mechanisms within the extrapyramidal system.

The actions of nicotine and cocaine in a mouse model of anxiety

The acute administration of nicotine (0.01-1.0 mg/kg IP) to the mouse increased the time spent and rearings and line crossings in the aversive brightly illuminated white area of a two compartment white/black test box, with a corresponding decrease in the black. This profile of change was maintained during twice daily administration (0.1 mg/kg IP) for 14 days. Eight to 96 hr following withdrawal of nicotine (14-day treatment), the behavioural profile was reversed to a preference for the black area: by 240 hr values had returned to control levels. In contrast to the effects of nicotine, an acute injection of cocaine (0.1-10 mg/kg IP) exacerbated the aversive response to the white area. However, similarly to nicotine, the administration of cocaine (1.0 mg/kg IP) twice daily for 14 days reduced the aversion to the white area and exacerbated the response following cocaine withdrawal. The effects of nicotine and cocaine to reduce and enhance responsiveness to the aversive properties of the white area are discussed in terms of an anxiolytic and anxiogenic response and the possibility of a serotonergic involvement.

Differentiation of the dopamine mechanisms mediating stereotyped behaviour and hyperactivity in the nucleus accumbens and caudate-putamen

A number of dopamine agonists were applied intracerebrally to the nucleus accumbens and caudate‐putamen of rat in an attempt to differentiate the dopamine mechanisms in these nuclei which mediate hyperactivity and stereotyped behaviour. The major effect of dopamine was to induce hyperactivity from the nucleus accumbens and stereotypy from the caudate‐putamen; N‐n‐propyl‐norapomorphine induced hyperactivity and stereotypy from the nucleus accumbens whilst apomorphine induced a marked stereotypy from the caudate‐putamen, modest stereotypy from the nucleus accumbens and no hyperactivity. In contrast to apomorphine, 2‐(NN‐dipropyl)amino‐5,6‐dihydroxy TN‡ induced a more marked stereotypy from the nucleus accumbens and, again, no hyperactivity. The major effect of 2‐(NN‐diethyl)amino‐5,6‐dihydroxy TN was to cause an intense hyperactivity from the nucleus accumbens and marked stereotypy from the caudate‐putamen whilst the primary amine, 2‐amino‐5,6‐dihydroxy TN induced hyperactivity and stereotypy from both areas. The marked hyperactivity and stereotyped responses were inhibited by haloperidol, but not by α‐ or β‐blockers. These data would indicate that there may be different dopamine mechanisms in the nucleus accumbens and caudate‐putamen for the mediation of hyperactivity and stereotyped behaviour.