Effects of metergoline and quipazine on locomotor activity of rats in novel and familiar environments

Dissociating effects of spatial learning from locomotor activity for ouabain-induced bipolar disorder-like rats

Whether ouabain, a Na+ - and K+-activated adenosine triphosphatase inhibitor, mimics cognitive impairments that can be dissociated from motor effects in the bipolar disorder-like animal model remains unclear. Ouabain and the vehicle aCSF were microinjected into the left lateral ventricle immediately, after 4h, and after 24h. The results showed that (a) locomotion responses of the Immediate group were significantly decreased compared to those of the aCSF group, particularly the first five minutes. (b) The ouabain-treated rats have longer latency and total distance traveled in the water maze task; however, the velocity was not affected for the ouabain group. (c) The analysis of covariance showed that the latency time (but not the total distance traveled and velocity) of the ouabain group was more impaired than that of the aCSF group, regardless of omitting total distance traveled and cross movement in the open field test. The latency might be more sensitive than the distance traveled and the velocity for assessing spatial learning. Dissociating the spatial learning from the movement may allow testing drug treatments of cognitive deficits independent of locomotor effects associated with bipolar disorder.

Stimulant effects of apomorphine and (+)-amphetamine in rats with varied habituation to test environment

The stimulants (+)-amphetamine and apomorphine are known to increase motility and induce stereotypy in rats. The present study examined the effects of an habituation period immediately prior to injection on these stimulant effects. Male Wistar rats received doses of either drug including 0, 0.01, 0.1, 0.25, 1.0, 2.0 and 4.0 mg/kg in a random order. Activity was assessed in 6 automated chambers where horizontal and vertical activity were tabulated hourly for 4 hours. Initially all rats had equal exposure to the chambers over 5 days. In the subsequent drug phase, habituated rats were placed in the chambers for the 1-hr period prior to each injection whereas non-habituated rats were in their home cages at the corresponding time. (+)-Amphetamine stimulated horizontal activity, although under either condition the effect was not seen until the second hour post-injection, but lasted until the fourth hour. Vertical activity was similarly enhanced, but with habituation there was a significant stimulant effect in the first hour as well. With apomorphine the habituation period resulted in an absence of a significant stimulant effect. Non-habituated rats showed a significant stimulant effect with the highest dose only on vertical activity in the first hour and a stimulant effect with horizontal activity in the second hour. It is suggested that the relative novelty of the environment affected the behavioral response to apomorphine but not to (+)-amphetamine. Furthermore, the activating effects accompanying drug administration should be taken into account as a factor affecting responses to drugs. Such environmental factors may be of particular importance when considering drugs with a short duration of action.

Stimulant effects of (+)-amphetamine are influenced by methodological variables

1. The locomotor effects of (+)-amphetamine were examined in two groups of rats placed in chambers of different sizes. 2. Prior to drug exposure, rats in large chambers were more active, as measured on a rating scale. 3. Under amphetamine, ratings discriminated the 2.5 mg/kg dose from both saline and 0.25 mg/kg without observed differences between the latter two. Scores recorded automatically in the large chambers showed enhanced horizontal activity with both doses, although they did not differ amongst themselves. 4. Methodological variables, including the size of apparatus and recording technique may influence observed effects of amphetamine, and suggest these variables be taken into account when studying drug effects.

Behavioural effects produced in mice infected with venezuelan equine encephalomyelitis virus

Pixuna, a strain of intermediate virulence of venezuelan equine encephalomyelitis virus, was inoculated intracranially to 24-day-old mice. Signs of encephalitis were present in 60% of the animals between 6 and 9 days with a maximum at 7 days postinoculation. The rest of the infected mice did not show clinical signs of encephalitis. In order to study the functional state of serotonergic systems a series of tests susceptible to modifications by serotonin activity were carried out. Locomotor activity was measured in an open field test. Virus-inoculated animals presented a variety of changes in their locomotor behavior at various days postinoculation with respect to the sham-inoculated group, however, they were not significant. Central serotonergic function was examined by the production of the serotonergic syndrome with the receptor agonist, 5-methoxy-N,N-dimethyltryptamine and the precursor, 5-hydroxytryptophan, both administered 4 days after the inoculation. The dose of the agonists was established by a prior drug-response analysis. Intensity of the syndrome was significantly higher in infected mice than in the sham-inoculated group only in 5-methoxy-N,N-dimethyltryptamine-treated animals. The behaviour in the swim test was also measured. Duration of immobility was much shorter in infected than in control mice. The decrease in central serotonin turnover previously reported might be responsible for the modification in locomotor behaviour and for the supersensitivity of serotonin receptors observed in infected mice.

Dopamine-beta-hydroxylase inhibitors, feeding and locomotor activity: reinstatement of feeding following central norepinephrine

The effects of two dopamine-beta-hydroxylase (DBH) inhibitors, FLA-63 and fusaric acid (FA) on feeding behaviour and locomotor activity were examined. In Experiment 1 activity was measured over 7 hr in 48 rats treated with FLA-63 (0, 1.25, 2.50, 5.00 mg/kg) or FA (0, 20.0, 40.0, 80.0 mg/kg). While FA produced no significant effect on activity, FLA-63 produced an increase at the highest doses. In Experiment 2 the same doses of the two DBH inhibitors were administered to 48 rats and food intake over 7 hr was measured; both FA and FLA-63 produced decreases in food intake. In a third experiment, rats were stereotaxically implanted with microinjection guide cannulae extending to the ventromedial hypothalamus and, following peripheral treatment with either 5.0 mg/kg FLA-63, 40 mg/kg FA, or their respective vehicles were injected centrally with morphine (5.3 nmoles in 0.5 microliter), norepinephrine (NE; 60 nmoles in 0.5 microliter for the FLA-63 pre-treated group and 30 nmoles in 0.5 microliter for the FA pre-treated group) or saline. Central NE was found to reinstate feeding only in the hr following injection in both groups, while morphine reinstated feeding only in the FA group and only in the third hr following injection. Results support the involvement of hypothalamic NE in feeding.

The effects of quipazine and fluoxetine on extinction of a previously-reinforced operant response in rats

Previous studies have shown that treatments that reduce serotonergic neurotransmission lead to enhanced responding during extinction. To evaluate the generality of this effect, the present study examined the effects of the serotonin agonists, quipazine and fluoxetine on responding in extinction. In Experiment 1, 72 rats were trained to lever press on a continuous reinforcement schedule for 5 30-min sessions. Four sessions of extinction followed; 30-min prior to each, 3 groups (n = 16) received quipazine (0, 1.0, 5.0 mg/kg) and 3 groups (n = 8) received fluoxetine (0, 1.0, 5.0 mg/kg). The 5.0 mg/kg dose of quipazine resulted in a significant reduction in responding on day 1; the lower dose of quipazine and both doses of fluoxetine were without significant effect. In Experiment 2, 3 similarly trained groups (n = 8) received either saline or quipazine (5.0 mg/kg) prior to each extinction session; additionally, one quipazine group was injected twice with the 5.0 mg/kg dose in its home cage several days before the beginning of extinction. The results of the drug-naive quipazine group replicated those of that group from Experiment 1 whereas the drug-experienced group showed no significant effect of quipazine in extinction. The results suggested that prior drug experience could modify the effects of quipazine on behaviour. Apart from this drug novelty effect the lack of significant effect of either quipazine or fluoxetine suggested that the effects of manipulations believed to increase and decrease serotonin functioning on responding in extinction may not be symmetrical. These results may be understood with reference to the hypothesis that serotonin plays a role in tuning out or reducing responsiveness to nonreinforced or irrelevant stimuli.