Effects of scopolamine on antipredator defense reactions in wild and laboratory rats

Uncertainty and anxiety: Evolution and neurobiology

Anxiety is a complex phenomenon: Its eliciting stimuli and circumstances, component behaviors, and functional consequences are only slowly coming to be understood. Here, we examine defense systems from field studies; laboratory studies focusing on experimental analyses of behavior; and, the fear conditioning literature, with a focus on the role of uncertainty in promoting an anxiety pattern that involves high rates of stimulus generalization and resistance to extinction. Respectively, these different areas provide information on evolved elicitors of defense (field studies); outline a defense system focused on obtaining information about uncertain threat (ethoexperimental analyses); and, provide a simple, well-researched, easily measured paradigm for analysis of nonassociative stress-enhanced fear conditioning (the SEFL). Results suggest that all of these-each of which is responsive to uncertainty-play multiple and interactive roles in anxiety. Brain system findings for some relevant models are reviewed, with suggestions that further analyses of current models may be capable of providing a great deal of additional information about these complex interactions and their underlying biology.

Revisiting the role of anxiety in the initial acquisition of two-way active avoidance: pharmacological, behavioural and neuroanatomical convergence

Two-way active avoidance (TWAA) acquisition constitutes a particular case of approach -avoidance conflict for laboratory rodents. The present article reviews behavioural, psychopharmacological and neuroanatomical evidence accumulated along more than fifty years that provides strong support to the contention that anxiety is critical in the transition from CS (conditioned stimulus)-induced freezing to escape/avoidance responses during the initial stages of TWAA acquisition. Thus, anxiolytic drugs of different types accelerate avoidance acquisition, anxiogenic drugs impair it, and avoidance during these initial acquisition stages is negatively associated with other typical measures of anxiety. In addition behavioural and developmental treatments that reduce or increase anxiety/stress respectively facilitate or impair TWAA acquisition. Finally, evidence for the regulation of TWAA acquisition by septo-hippocampal and amygdala-related mechanisms is discussed. Collectively, the reviewed evidence gives support to the initial acquisition of TWAA as a paradigm with considerable predictive and (in particular) construct validity as an approach-avoidance conflict-based rodent anxiety model.

Tests of unconditioned anxiety - pitfalls and disappointments

The plus-maze, the light-dark box and the open-field are the main current tests of unconditioned anxiety for mice and rats. Despite their disappointing achievements, they remain as popular as ever and seem to play an important role in an ever-growing demand for behavioral phenotyping and drug screening. Numerous reviews have repeatedly reported their lack of consistency and reliability but they failed to address the core question of whether these tests do provide unequivocal measures of fear-induced anxiety, that these measurements are not confused with measures of fear-induced avoidance or natural preference responses - i.e. discriminant validity. In the present report, I examined numerous issues that undermine the validity of the current tests, and I highlighted various flaws in the aspects of these tests and the methodologies pursued. This report concludes that the evidence in support of the validity of the plus-maze, the light/dark box and the open-field as anxiety tests is poor and methodologically questionable.

Maladaptation to mental stress mitigated by the adaptive immune system via depletion of naturally occurring regulatory CD4+CD25+ cells

Peripheral cellular immunity was recently shown to play a critical role in brain plasticity and performance. The antigenic specificity of the participating T cells, however, was not investigated, and nor was their relevance to psychological stress. Here we show, using a mouse model, that adaptive immunity mitigates maladaptation to the acute psychological stress known to trigger abnormal behaviors reminiscent of human post-traumatic stress disorder. Assessment of behavioral adaptation (measured by the acoustic startle response and avoidance behavior) in mice after their exposure to predator odor revealed that maladaptation was several times more prevalent in T cell-deficient mice than in their wild-type counterparts. A single population of T cells reactive to central nervous system (CNS)-associated self-protein was sufficient to endow immune-deficient mice with the ability to withstand the psychological stress. Naturally occurring CD4+CD25+ regulatory T cells were found to suppress this endogenous anti-stress attribute. These findings suggest that T cells specific to abundantly expressed CNS antigens are responsible for brain tissue homeostasis and help the individual to cope with stressful life episodes. They might also point the way to development of immune-based therapies for mental disorders, based either on up-regulation of T cells that partially cross-react with self-antigens or on weakening of the activity of regulatory T cells.

Setting apart the affected: the use of behavioral criteria in animal models of post traumatic stress disorder

Post-traumatic stress disorder (PTSD) affects about 20-30% of exposed individuals. Clinical studies of PTSD generally employ stringent criteria for inclusion in study populations, and yet in animal studies the data collection and analysis are generally expressed as a function of exposed vs nonexposed populations, regardless of individual variation in response. Prior data support an approach to animal models analogous to inclusion criteria in clinical studies. This series of studies sought to assess prevalence rates of maladaptive vs adaptive responses determined according to a more stringent approach to the concept of inclusion/exclusion criteria (cutoff behavioral criteria-CBC), consisting of two successive behavioral tests (elevated plus maze and acoustic startle response tests). The rats were exposed to stressors in two different paradigms; exposure to a predator and underwater trauma. The prevalence rates of maladaptive responses to stress in these two distinct models dropped over time from 90% in the acute phase to 25% enduring/maladaptive response at 7 days, to remain constant over 30 days. As setting the affected individuals apart from the unaffected approximates clinical studies, it might also help to clarify some of the pending issues in PTSD research.

The Mouse Defense Test Battery: pharmacological and behavioral assays for anxiety and panic

The Mouse Defense Test Battery was developed from tests of defensive behaviors in rats, reflecting earlier studies of both acute and chronic responses of laboratory and wild rodents to threatening stimuli and situations. It measures flight, freezing, defensive threat and attack, and risk assessment in response to an unconditioned predator stimulus, as well as pretest activity and postthreat (conditioned) defensiveness to the test context. Factor analyses of these indicate four factors relating to cognitive and emotional aspects of defense, flight, and defensiveness to the test context. In the Mouse Defense Test Battery, GABA(A)-benzodiazepine anxiolytics produce consistent reductions in defensive threat/attack and risk assessment, while panicolytic and panicogenic drugs selectively reduce and enhance, respectively, flight. Effects of GABA(A)-benzodiazepine, serotonin, and neuropeptide ligands in the Mouse Defense Test Battery are reviewed. This review suggests that the Mouse Defense Test Battery is a sensitive and appropriate tool for preclinical evaluation of drugs potentially effective against defense-related disorders such as anxiety and panic.

Elevated T-maze as an animal model of memory: effects of scopolamine

The elevated T-maze (ETM) is a putative model for the assessment of anxiety and memory in rodents. This study was designed to further evaluate the utility of the ETM in the study of memory processes. We compared the performance of rats in the ETM, the water maze (WM) and the two-way avoidance task (TWA), after pretreatment with scopolamine (SCO; 0.3 or 1.2 mg/kg i.p.). In the ETM, rats were first trained to meet the criterion of remaining inside the enclosed arm for 300 seconds. Seventy-two hours after training, a retrieval test session was performed. At the lower dose, SCO impaired performance in the retrieval session on all three tasks, whereas in the training session an effect was noted only on the WM task. At the higher dose, SCO impaired the performance of rats in the training sessions for ETM and WM, but not TWA. In a fourth experiment using the elevated plus-maze, SCO showed anxiolytic-like effects at the higher dose only. In conclusion, the effects of SCO in rats submitted to the ETM were dose dependent, with the lower dose exerting a selective effect detected only on retrieval, whereas the higher dose induced motor effects that disrupted inhibitory avoidance acquisition, resulting in impaired retrieval. The results are discussed in terms of the utility of the ETM in the study of drug effects and the neurobiological mechanisms underlying anxiety, learning and memory.

Concurrent administration of subeffective doses of scopolamine and MK-801 produces a short-term amnesia for the elevated plus-maze in mice

Amnesic properties of scopolamine, a muscarinic receptor antagonist, and MK-801, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, were evaluated in mice by means of the elevated plus-maze test. In this test, transfer latency, the time mice took to move from the open arm to the enclosed arm, was used as an index of learning and memory. The 3-day pretreatment training dramatically decreased transfer latencies. On the 4th day, the retention trial was performed 30 min after the intraperitoneal injection of scopolamine (Experiment 1) or MK-801 (Experiment 2). The doses of 0.25 and 0.5 mg/kg of scopolamine as well as the doses of 0.1, 0.15, 0.2 and 0.4 mg/kg of MK-801 significantly prolonged the transfer latency as compared with both that in the saline-treated group and that measured on the 3rd day. In Experiment 3, subthreshold doses of these two drugs given in combination (which were ineffective when given alone: scopolamine 0.25 mg/kg, MK-801 0.075 mg/kg) significantly prolonged the transfer latency on the fourth day. However, an amnesic effect of scopolamine plus MK-801 was transient. On the 5th day, no differences in the transfer latency were found. This finding clearly indicates that there is a close relationship between cholinergic and glutamatergic systems and that both systems play an important role in a spatial orientation of mice on the elevated plus-maze.

Defense system psychopharmacology: an ethological approach to the pharmacology of fear and anxiety

Defensive behaviors comprise a set of flexible and adaptive responses to threatening situations and stimuli. In semi-natural situations affording a wide variety of responses, defensive behaviors change over time in response to information about the presence of danger, acquired through risk assessment activities. Two test batteries, a Fear/Defense Test Battery (F/DTB) measuring defensive behaviors to present, approaching predators, and an Anxiety/Defense Test Battery (A/DTB) measuring reactions to potential threat, have been used in conjunction with administration of potentially anxiolytic drugs. Results suggest that the F/DTB behaviors are not systematically responsive to anxiolytics. However, on the A/DTB, anxiolytic benzodiazepines produce a profile of effects primarily involving risk assessment activities. Very similar profiles of effect are seen also with some 5-HT1A compounds, alcohol, imipramine and MK-801, but not for a variety of additional compounds. A consistent pattern of gender differences are obtained with the A/DTB, with females more defensive than males. These results indicate that particular patterns of defensive behaviors may provide a very appropriate animal model for the analysis of pharmacological effects on anxiety.

Ondansetron, gender and antipredator defensive behaviour

The 5-HT(3) receptor antagonist ondansetron has provided a somewhat equivocal profile in a number of animal models of anxiety. The present study assessed the effects of this compound in two ethological test batteries. The Fear/Defense Test Battery (F/DTB) and the Anxiety/Defense Test Battery (A/DTB) have been developed to investigate antipredator defensive reactions in rats. The F/DTB measures behavioural reactions of wild- trapped rats to human threat, while the A/DTB assesses behavioural responding in laboratory rats as a consequence of exposure to a domestic cat, and to cat odour per se. Ondansetron (0.001-0.10 mg/kg) failed to provide any reliable and consistent profile of anxiety/fear reduction in either test battery. In addition to the elucidation of drug effects, previous studies have provided clear evidence of gender differences with female rats showing higher levels of defensiveness than males in the A/DTB. Until now, no such differences have been observed with wild-trapped rats in the F/DTB. Thus, the present study indicated a clear gender difference with females exhibiting greater defensiveness. This finding is discussed with reference to the general decrease in defensiveness of the first generation animals compared with their wild-trapped parents.

MK-801 produces a reduction in anxiety-related antipredator defensiveness in male and female rats and a gender-dependent increase in locomotor behavior

The present study investigated the effects of the non-competitive NMDA antagonist MK-801 (0.04-0.16 mg/kg), on antipredator defensive reactions of male and female rats in three paradigms comprising the Anxiety/Defense Test Battery (A/DTB). In order to facilitate interpretation of data from the above study, the behavioral effects of the compound were also assessed in the non-threatening environment of the home cage. The data indicate a marked gender difference in the locomotor effects of the compound with females, but not males, showing a dose-dependent increase in general locomotor activity, a decrease in freezing, and a loss of balance at the highest dose, in both non-threatening and threatening contexts. The behavioral profile for males in the A/DTB included decreased orientation to and proxemic avoidance of the cat stimulus or stimulus site, and increased transits and eating in the cat situation. Contacts with the cat odor stimulus were increased, as was normal, curved back, locomotion in this test. In the absence of non-specific locomotor effects for males, this profile for the A/DTB provides convincing evidence for anxiety/fear reduction with MK-801. While locomotor effects tended to mask the putative anxiolytic properties of the compound in females, evidence remains from behavioral changes not attributable to a locomotor influence to indicate anxiety/fear reduction in this sex.

Behavioral microanalysis of spatial delayed alternation performance: rehearsal through overt behavior, and effects of scopolamine and chlordiazepoxide

Rats were trained in an operant spatial delayed alternation task utilizing retention intervals from 2 to 32 s. In addition to response accuracy, operations of the levers during the retention intervals were recorded and analyzed. Animals were tested following the administration of the muscarinic antagonists scopolamine hydrobromide and methylbromide, and the benzodiazepine receptor agonist chlordiazepoxide. In vehicle-treated animals, the relative number of correct responses and correct rehearsal operations (operation of the forthcoming correct lever during retention intervals) varied with the length of the retention intervals, and these measures were correlated. The response rate for rehearsal operations increased with the length of the retention intervals. It is speculated that the delay-dependent increase in response rate reflects an effect of delayed reward that was also associated with a delay-dependent increase in the tendency to alternate between levers. The effects of delay on the accuracy of rehearsal operations may have contributed to the delay-dependent correct responding. Scopolamine hydrobromide (0.01, 0.03, 0.1, 0.3 mg/kg) and methylbromide (0.1, 0.3 mg/kg) impaired correct responding, but did not seem to interfere with the relative number of correct rehearsal operations. As only the presentation of the panel light indicated trial onset, it is speculated that the cholinergic receptor blockade resulted in an increase in the probability of a repositioning response that was triggered by light onset. Chlordiazepoxide (1, 3, 5, 10 mg/kg) did not affect behavioral performance. These results suggest that in tasks that allow the development of rehearsal operations, delay-dependent response accuracy does not represent a sufficient condition for conclusions on task demands on memory.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for differential effects of 8-OH-DPAT on male and female rats in the Anxiety/Defense Test Battery

The Proxemics/Activity test and the Eat/Drink test, two components of the Anxiety/Defense Test Battery, were developed to measure defensive reactions to situations associated with a natural predator (cat). In the present studies the behavioral effects of 8-OH-DPAT treatment (0.01-1.0 mg/kg, SC) were entirely consistent with anxiety/fear reduction. These effects included an increase in time spent near the cat compartment, and a complimentary decrease in time spent farthest from this compartment, together with an increase in transits and locomote behavior. 8-OH-DPAT (1.0 mg/kg) also increased eat frequencies and durations (highly preferred food) both during and following cat presentation, without influencing drinking. This finding is discussed with reference to previous findings with 8-OH-DPAT in studies assessing both food intake and anxiolysis. Interestingly, 8-OH-DPAT was more potent in a majority of its effects in female subjects, a finding consistent with recent neurochemical data. These findings provide important behavioral evidence for a sexual differentiation in 5-HT function, and support the case for greater emphasis on female subjects in animal models of anxiety.

"Paradoxical" effects of morphine on antipredator defense reactions in wild and laboratory rats

In a Fear/Defense Test Battery, measuring defensive reactions to a present, approaching and contacting predator, the highest dose of morphine tested (7.5 mg/kg) reliably reduced vocalization to dorsal contact, to vibrissae stimulation, and to an anesthetized conspecific in laboratory-bred wild R. norvegicus. Except for a dose-dependent reduction in flinch/jump reactions to dorsal contact (taps), other defensive behaviors (flight, freezing, etc.) were not reliably altered by morphine treatment (0, 1.0, 2.5, 7.5 mg/kg). Vocalization responses to vibrissae stimulation in wild-trapped R. rattus were reliably increased following naloxone (1.0 and 10.0 mg/kg) administration, lending support for opiate receptor involvement in the mediation of defensive vocalization. In the Anxiety/Defense Test Battery, measuring defensive reactions to situations associated with a predator (cat) or with cat odor, laboratory rats showed no decrease in defensive behavior with morphine (0, 1.0, 5.0 mg/kg). In direct contrast to the above findings, the effects of morphine treatment in this test battery suggested a generalized increase in defensiveness to noncontacting and nonpainful threat stimuli. These effects included a decrease in time spent near the cat compartment, with a complementary increase in time spent at maximum distance, a decrease in transits between these sections, an increase in crouching, and a decrease in grooming and rearing. This pattern of results suggests that morphine may have two opposing effects on defensive behavior, a generalized enhancement, together with a more specific reduction of responses to tactile or painful stimulation. A very widespread pattern of reliable sex or sex x drug effects in the Anxiety/Defense Test Battery was in good agreement with previous reports of sex differences in these tests, with females generally more defensive than males. Consonant with previous findings, no reliable sex differences were found with the Fear/Defense Test Battery, although several values approached an acceptable level of statistical significance.