David Eilam

Home base behavior of rats (Rattus norvegicus) exploring a novel environment

When rats are placed in a novel environment, they alternate between progression and stopping: in the course of a session they stop briefly in many places, but in one or two places they also stop for very long periods. The place in which they stay for the longest cumulative time is defined as the rats home base. In this place the incidences of grooming and of rearing are high and often the highest. In addition, the number of visits to the home base is typically the highest. Some rats establish a secondary base with similar properties to those of the main home base. The location of the base influences the mode of progression throughout the environment: progression away from base is slower and includes more stops than progression back. It is suggested that this paradigm may be used for the analysis of the spatial organization of locomotor behavior in neuroscience research.

Quinpirole Induces Compulsive Checking Behavior in Rats: A Potential Animal Model of Obsessive-Compulsive Disorder (OCD)

Rats treated chronically with the dopamine agonist quinpirole (0.5 mg/kg, twice weekly x 10) met 5 criteria for performance of compulsive checking. Specifically, in a large open-field with single small objects in 4 of 25 locales, quinpirole rats revisited two places/objects excessively often and rapidly, compared with other locations in the environment or saline controls. They performed a ritual-like set of behavioral acts at these two places/objects and stopped in relatively few locales before returning to the preferred places/objects. Finally, they shifted their behavior to a new location when the object was moved there. Clomipramine (10 mg/kg, daily) postponed but did not prevent the development of the quinpirole effect. Quinpirole-induced compulsive checking may be an exaggeration of normal checking of home site in rats. Results suggest an animal model of obsessive-compulsive disorder and a role for dopamine in this disorder.

Stopping behavior: constraints on exploration in rats (Rattus norvegicus)

In the absence of an obvious reference place, rat locomotor behavior in a novel environment appears haphazard. In previous work, one or two places termed home bases, were shown to stand out from all the other places in the environment in terms of the behaviors performed in them and in terms of their behavioral stability. We use home base location as a reference place for rat movement in locale space, by defining an excursion as a trip starting at a home base and ending at the next stop at a home base. We then establish the uniform distribution as an appropriate model for the number of stops per excursion. This way we show that there is an intrinsic upper bound on the number of times a rat stops during an excursion. As a rat leaves the home base, home base attraction increases with every additional stop performed by it, first slowly and then fast. This cumulative process of attraction may be concluded after each stop, as long as the number of stops does not exceed an intrinsic upper bound; once the upper bound is reached, the rat concludes that excursion and returns to base. The sessions upper bound does not increase with the size of the explored area.

Die hard: A blend of freezing and fleeing as a dynamic defense—implications for the control of defensive behavior

Freezing, fleeing or fighting back are general defensive responses in many taxa. These defenses are mutually exclusive, since a prey cannot simultaneously flee and fight, or freeze and flee. Each of these defenses by itself is rudimentary and probably cannot provide a completely effective means to elude predation. Freezing is efficient only if employed before the prey is spotted by the predator, otherwise the prey becomes a stationary, easy to catch target. In fleeing, the prey can move directly away and maximize its distance from the predator, move toward the predator to confine it to a single clashing point, or dodge sideways to evade the attack. Prey can also run in a straight path that is efficient against slow or distant predators, or in a zigzag path that is efficient when a raptor is close or fast. In all, freezing and fleeing constitute together a complex and flexible defensive response, and are probably controlled by different motor systems that are inter-connected to allow fast switching between these behaviors, as required for an effective and versatile response.

Open-field behavior withstands drastic changes in arena size

Individual voles were tested on successive days under increasing, decreasing, or randomly changing arena size. Locomotor behavior was adjusted to arena size by (i) preserving the same level of activity, (ii) taking longer but less frequent trips in smaller arenas in contrast to taking more frequent yet shorter trips in the larger arenas, and (iii) moving in the entire space available for exploration in the smaller arenas in contrast to remaining along the walls of the open field in the larger arenas. The effect of testing order was minimal, probably being related to increased novelty under increasing arena size, as opposed to habituation under decreasing arena size, when parts of the same area were re-explored. These behavioral changes averaged up to a two-fold difference compared with the larger six-fold change in the perimeter and 44-fold change in the area of the open field. The modest change in open-field behavior indicates that it has a solid spatio-temporal structure that withstands extensive environmental changes. This behavioral stability and consistency further validates studies of pharmacological, neurological, and genetic preparations that use behavior in a small open field as representation of the general pattern of behavior.

Compulsive checking behavior of quinpirole-sensitized rats as an animal model of Obsessive-Compulsive Disorder(OCD): form and control

BackgroundA previous report showed that the open field behavior of rats sensitized to the dopamine agonist quinpirole satisfies 5 performance criteria for compulsive checking behavior. In an effort to extend the parallel between the drug-induced phenomenon and human obsessive-compulsive disorder (OCD), the present study investigated whether the checking behavior of quinpirole rats is subject to interruption, which is an attribute characteristic of OCD compulsions. For this purpose, the rats home-cage was placed into the open field at the beginning or the middle of a 2-hr test.ResultsIntroduction of the home-cage reduced checking behavior, as rats stayed inside the cage. After 40 min, checking resurfaced, as quinpirole rats exited the home-cage often. An unfamiliar cage had no such effects on quinpirole rats or saline controls.ConclusionsChecking behavior induced by quinpirole is not irrepressible but can be suspended. Results strengthen the quinpirole preparation as an animal model of OCD compulsive checking.

Dynamics of behavioral sensitization induced by the dopamine agonist quinpirole and a proposed central energy control mechanism

The study characterizes the process of sensitization induced by intermittent administrations of quinpirole (0.5 mg/kg) in rats in a large open field. Sensitization was found to be self-limiting, with all measures of behavior reaching a plateau after the tenth twice-weekly injection. Kinetics of sensitization were a simple hyperbolic function of the number of drug injections for some measures (speed of locomotion, length of locomotor bouts) but showed positive co-operativity for others (distance travelled, duration of locomotion, frequency of stops, route stereotypy), suggesting potentiation of the effect by preceding injections. The pace of sensitization varied for different behaviors: locomotor speed changed fastest in the early portion of chronic treatment; stereotypy of route changed primarily during the late phase; mouthing did not sensitize. Sensitization evolved by a cascade of changes that included: advancing the onset of locomotor activation; prolonging the duration of locomotion; establishing new maxima of observable responses; altering the mode of locomotion; raising speed, rate and length of locomotor bouts; and increasing stereotypy of travel. These observations do not substantiate the prediction that development of behavioral sensitization is associated with emergence of disorganized activity and/or fractionation of response chains. Instead, it is proposed that development of sensitization may represent a build-up and strengthening of performance, reflecting enhanced central control of energy expenditure stimulated by repeated injections of quinpirole. Furthermore, it is suggested that for at least one response, the maximum observable amount of locomotion, development of sensitization requires only D2 stimulation, independent of D1 tone.

Exploration and predation models of anxiety: Evidence from laboratory and wild species

The current article addresses several issues within the context of issues within the context of modeling human anxiety disorders in the laboratory. First, evidence is presented to support the suggestion that behavior in exploration models of anxiety may be motivated by apprehension relating to intraspecific encounters rather than interspecific, predator/prey interactions, which has consequences for the interpretation of findings generated using these tests. Second, data are reviewed concerning the use of stimuli indicating the presence of a predator in the context of anxiety modeling, and it is suggested that tests involving the reactions of animals following exposure to such stimuli may be more closely related to pathologic anxiety mechanisms than tests employing observations during contact with these stimuli. Third, comparative studies, using wild-caught rodents, are outlined that show that, although there are similarities in the defensive strategies adopted by these animals in response to the call of an owl, there are also important differences. Finally, the suggestion is made that the distance-dependent-defense-hierarchy may be of important heuristic value in the interpretation of these data and that, perhaps more significantly, it may also provide a mechanism that allows animal defensive strategies and human anxiety disorders to be placed within the same conceptual framework.

Rituals, stereotypy and compulsive behavior in animals and humans

From a survey of the behavior of animals in the wild, in captivity, under the influence of psychoactive drugs and in a model of obsessive-compulsive disorder (OCD), we identify that the behavioral repertoire invariably includes motor rituals, and that such rituals are performed at a few specific locations/objects in the environment with an orderly transition amongst locations/objects. The concept and parameters of this stable organization of rituals in time and space were used to analyze rituals of OCD patients, compared with control individuals performing the same actions (e.g. car locking). It was found that human rituals also converged to a few places/objects where repetitive acts were performed in a regular order, with the acts in OCD patients overlapping with those of control individuals. Across a very diverse range of animals and conditions, motor rituals are thus characterized by their close linkage to a few environmental locations and the repeated performance of relatively few acts. Such similarity in form may reflect a similarity in the mechanisms that control motor rituals in both animals and humans.

Sand rats see the light: short photoperiod induces a depression-like response in a diurnal rodent.

The present study examined the effect of simulated change in day length on the behavior of a diurnal rodent, the fat sand rat (a species of gerbil). Animals were housed under a short photoperiod (5/19 light/dark cycle) for 3 weeks and compared with controls living under a 12/12 light/dark cycle. All sand rats then underwent the forced swim test for depression-like behavior, and the open-field test for overall activity. Sand rats exposed to the short photoperiod displayed a significantly earlier sinking in the swim test, but there was no difference between their open-field activity compared with controls. Taking these responses as indicative of depression-like behavior, we suggest that a short photoperiod may induce affective-like changes, and that the sand rat may thus offer an appropriate animal model to explore the effect of photoperiod on normal, and perhaps also abnormal, seasonal mood changes (e.g., SAD), which in humans is a prevalent disorder, with winter depression episodes and spring/summer remissions.