Effects of psychotropic agents on Sidman avoidance response in good- and poor-performing rats

Individual response profiles of male Wistar rats in animal models for anxiety and depression

Previous work has shown that systematic individual differences between male Wistar rats can be detected in tasks like the elevated plus-maze, or the open field. Here, we investigated whether individual profiles of anxiety, as measured with the plus-maze, may predict behavioral response profiles in other tasks where anxiety, aversion, or depressive behaviors are important. Male Wistar rats were initially screened: (A) in an open field; and (B) in an elevated plus-maze. Based on their plus-maze behavior, that is, the time spent in the open arms, the animals were divided into two subgroups with either 'low' or 'high' anxiety (LA or HA) levels. These subgroups were exposed to other experimental anxiety paradigms, namely object burying and two-way active avoidance, and an animal model of depression, the forced swim test. In the plus-maze, the percentage of time spent on, and the number of entries into the open arms were lower in HA than in LA rats. In the object burying task, HA rats showed more burying behavior of Tabasco-coated marbles, and in the active avoidance task, they showed slower acquisition of avoidance learning and higher escape latency as compared to LA rats. Finally, LA and HA rats behaved similarly in the forced swim test; however, the percentage changes of immobility time between test days 1 and 2 were negatively correlated to open field behavior, namely locomotor activity and center entries. On the other hand, the frequencies of rearing in the open field, which can also gauge functional differences between rats (for example responsiveness to novelty, psychomotor activation), were not substantially related to the behavioral profiles in the tests of anxiety and depression. These results show that individual differences of anxiety in the plus-maze can be predictive of behavior in other anxiety models, but not in forced swim test, indicating that they may be determined partly by similar functional and physiological mechanisms.

Diazepam impairs place learning in native but not in maze-experienced rats in the Morris water maze

Anxiolytic benzodiazepines have been shown to impair place learning in the Morris water maze. However, a clear-cut demonstration of a direct and specific effect on mnemonic processes has not yet been offered. In the present study, the effects of diazepam on place navigation in the Morris water maze were studied in rats. Three conditions were examined: learning, reversal learning and learning after familiarisation of animals with the maze. In view of the anxiolytic and sedative properties of diazepam, appropriate doses of the drug, i.e. those that produced an anxiolytic effect but no major motor impairment, were initially selected in the water-lick conflict and rotarod tests, respectively. Doses of 2.5 and 5 mg/kg PO increased punished drinking in the water-lick conflict test without significantly decreasing rotarod performance. These doses were then used to assess the effects of diazepam on spatial behaviour. Diazepam, at both doses, impaired place learning in behaviourally naive rats. Such an effect appeared to be transient: diazepam-treated rats eventually reached control performance. Moreover, analysis of the probe trial at the end of training revealed adoption of a spatial strategy to locate the submerged platform. Neither reversal learning nor learning after familiarisation was affected. These results do not replicate previous findings in the Morris water maze and provide some evidence that the diazepam-induced place learning deficit may be primarily anxiolytic in nature.

Animal models for the study of anti-anxiety agents: a review

Animal models for the study of anxiolytic agents are reviewed and evaluated according to pharmacological and behavioral criteria. Although there are important exceptions, in general, most early animal models have not provided a reliable basis for identifying compounds with potential anxiolytic action, or for delineating the mechanisms of anxiolytic drug action. The possibility that phylogenetically 'prepared' forms of defensive learning might serve as a basis for the study of anxiolytic agents is introduced.

Effects of phosphatidylserine on avoidance relearning in rats (preliminary observations)

During six learning sessions in a shuttle-box avoidance situation, male Sprague-Dawley rats show two kinds of learning efficiency which allow for dividing them in the subgroups of high-responding (HR) and low-responding (LR) animals. The effect of phosphatidylserine, a pharmacologically active phospholipid obtained from bovine brain, has been studied on the relearning phase of these two populations of rats. Chronic administration of phosphatidylserine (15 mg/kg i.p. for 30 days) significantly increased the avoidance performances of LR animals, without changing those of HR rats. The results obtained suggest that the different behavioral response to the phosphatidylserine treatment may depend on the pre-drug baseline of avoidance learning capability and on the effect that the drug exerts on some brain neurotransmitter metabolism.

Conditioned lever-press avoidance response in mice: acquisition processes and effects of diazepam

Acquisition of conditioned lever-press avoidance behavior on a continuous avoidance schedule (response-shock interval = 30 s and shock-shock interval = 5 s) and on a discrete avoidance schedule (intertrial interval = 25 s and duration of the warning presentation = 5 s with an escape contingency) in dd mice was investigated. When the behavioral baseline had stabilized, the effects of diazepam on avoidance behaviors were examined. About 60% and 80% of the mice achieved criterion levels of avoidance behavior under continuous avoidance (shock rate being less than 0.5/min) and discrete avoidance (avoidance rate being higher than 75%), respectively. Diazepam (0.5--4 mg/kg SC) dose-dependently impaired avoidance behavior of mice which had a low baseline shock rate and a high baseline avoidance rate under continuous and discrete avoidances, respectively. The changes in avoidance behavior in mice after diazepam were almost identical with those previously found in rats.

Conditioned defensive burying: a new paradigm for the study of anxiolytic agents

Behavioral paradigms that have been designed to mimic forms of learning that are important for the survival of animals in the wild, rather than to minimize the contributions of adaptive predispositions, may prove to be particularly useful for studying the behavioral effects of drugs. In the present experiments, the propensity of rats to bury sources of aversive stimulation was disrupted in a dose-dependent fashion by a single injection of the anxiolytic drug, diazepam. This suggested that the conditioned defensive burying paradigm could prove to be a valuable addition to the paradigms available for studying anxiolytic effects. Supporting this view were two additional observations. First, the relative potencies of diazepam, chlordiazepoxide, and pentobarbital in the burying paradigm compared favorably with their relative potencies in clinical settings. Second, the effects of anxiolytics on conditioned burying appeared to be dissociable from the effects of other drugs that disrupt this behavior.

Rat strain differences in the acquisition of conditioned avoidance responses and in the effects of diazepam

Adult male albino rats of three strains--Wistar, Sprague-Dawley and Holtzman--were trained to press a lever to avoid electric shocks under Sidman-type (R-S interval-20 sec; S-S interval=5 sec) and discriminated avoidance (ITI-15 sec; warning duration=5 sec) schedules, and the acquisition processes of avoidance responses, and the properties of behavioral baselines were investigated. Under both schedules, Wistar strain rats, though showing poorer results than the other two in the beginning, rapidly progressed with the repetitive training, and finally displayed excellent and stable performances. Srague-Dawley strain rats were poorer in performances, with delayed acquisition and prolonged warm-up effect in the within-session performance. The results of Holtzman strain rats ranked between the two. After the establishment of stable behavioral baselines under both schedules, 0.5, 1.0 and 2.0 mg/kg of diazepam were given subcutaneously, and it was found that in Wistar and Holtzman strain rats, the avoidance responses were inhibited together with increase of delivered shocks in parallel to the doses. In Sprague-Dawley strain rats, however, the avoidance responses were conversely improved with 0.5 and 1.0 mg/kg, while such tended to be inhibited with 2.0 mg/kg, with marked concomitant ataxia. As definite strain differences in avoidance response were demonstrated herein, selection of the most appropriate strain should be made when designing behavioral experiments.

Morphine enhancement of shuttle avoidance prevented by alpha-methyltyrosine

Rats were given 6 days of training (180 trials) to make a two-way (shuttle) avoidance response. "Poor performers" making less than 50% avoidances in the 6th block of 30 tials were given drug treatments on the next 2 days. Both morphine sulfate (15 mg/kg) and d-amphetamine sulfate (1 mg/kg) increased the avoidance level by 70-100%. Prior treatment with alpha-methyltyrosine (50 mg/kg) prevented the effects of both drugs. Nalorphine hydrochloride (5 mg/kg) also blocked the effect of morphine. The action of alpha-methyltyrosine to block enhancement of avoidance is taken to indicate that this effect of morphine is attributable to a catecholamine-dependent excitatory component of its activity profile.

Analytical study of acquisition on free-operant avoidance response for evaluation of psychotropic drugs in rats

Systematic research was performed on the acquisition of free-operant (Sidman-type) avoidance response, which is widely used for the study of psychotropic drugs, with the following results: When the training session was fixed at 2 hours once daily, shock-shock (S-S) interval at 5 seconds, and response-shock (R-S) interval variable-20, 30 and 60 seconds, the acquisition speed of the response was almost constant independent of the R-S interval, about 6 sessions being always required. When the S-S and R-S intervals were constantly 5 and 30 seconds, respectively and the length of one session was varying-1, 2 and 4 hours, the behavioral baseline was established after about 6 sessions independently of the length of the session. Thus the cumulative time for the acquisition was shortest when one session was 1 hour long, and longest when it was 4 hours long. There was a linear relation with negative inclination between the logarithm of mean numbers of shock delivered per sessions and the number of sessions. In rapid and exact training of animals for the evaluation of drug effects, one session of an hour per day is adequate. In the evaluation of drug effects on the acquisition process, observation of the shift in logarithmic value of shocks delivered is recommended.