Psychostimulant-induced behavior as an animal model of obsessive-compulsive disorder: an ethological approach to the form of compulsive rituals

Kappa-opioid agonist U69593 potentiates locomotor sensitization to the D2/D3 agonist quinpirole: pre- and postsynaptic mechanisms

To assess whether the development and expression of behavioral sensitization to the dopamine D2/D3 agonist quinpirole (QNP) is influenced by coadministration of the kappa opioid receptor agonist U69593, rats received every 3-4 days for a total of 10 treatments an injection of U69593 (0.3 mg/kg) together with an injection of either a postsynaptic (0.5 mg/kg) or a presynaptic dose of QNP (0.05 mg/kg); locomotor activity was measured after each treatment. Control rats were injected as appropriate with QNP, U69593, and vehicle/saline. Following chronic treatment, dose-response profiles to QNP were obtained to assess the expression of sensitization; the effect of U69593 on locomotor activity in animals already sensitized to QNP was also assessed. Results showed that cotreatment of U69593 with a postsynaptic dose of QNP doubled the speed and magnitude of sensitization to QNP, while U69593 cotreatment with a presynaptic dose of QNP switched the effects of QNP from locomotor depression to locomotor sensitization. However, U69593 cotreatment with a presynaptic dose of QNP changed a different set of measures of sensitization than did cotreatment with a postsynaptic dose of the dopamine agonist. Together, findings suggest that sensitization to QNP is not a unitary phenomenon but has components that are relatively independent, mediated by distinct pre- and postsynaptic mechanisms and modulated by kappa receptor activity.

Differential effects of clorgyline on sensitization to quinpirole in rats tested in small and large environments

RATIONALE

Cotreatment with clorgyline shifts the development of sensitization to the D2/D3 dopamine receptor agonist quinpirole from locomotion to mouthing, an effect apparently unrelated to the monoamine oxidase inhibition property of clorgyline. This phenomenon was demonstrated in rats examined in small activity chambers. However, like with other psychostimulant drugs, sensitization to quinpirole is modulated by environmental context. It is not known whether the clorgyline cotreatment effect is likewise influenced by the environment.

OBJECTIVE

To determine the generality of the clorgyline effect on behavioral sensitization by evaluating the effects of clorgyline cotreatment on sensitization to quinpirole in two different environments: a small activity chamber and a large open field.

METHODS

Male rats received eight injections of quinpirole (0.5 mg/kg, twice weekly) in an open field or activity chamber; one group in each environment received a constant infusion of clorgyline (1 mg/kg/day via osmotic minipumps) while the other group served as the sham surgery control. For quinpirole injection 7 or 8, rats were tested in the alternate environment.

RESULTS

In activity chambers, clorgyline cotreatment switched sensitization to quinpirole from locomotion to mouthing. In the open field, clorgyline cotreatment increased mouthing and expanded the explored space without a change in path stereotypy or the amount of locomotion compared to treatment with quinpirole alone.

CONCLUSIONS

Structure of the environment can modulate the clorgyline cotreatment effect on behavioral sensitization to quinpirole. The behavioral profiles produced by clorgyline cotreatment in the two environments resembled the behavioral effects observed with quinpirole and D1 agonist cotreatment. It is suggested that clorgyline cotreatment produces a behavioral profile characteristic of enhanced dopamine D1 and D2 receptor costimulation.

Current animal models of obsessive compulsive disorder: a critical review

During the last 30 years there have been many attempts to develop animal models of obsessive compulsive disorder (OCD), in the hope that they may provide a route for furthering our understanding and treatment of this disorder. The present paper reviews current genetic, pharmacological and behavioral animal models of OCD, and evaluates their face validity (derived from phenomenological similarity between the behavior in the animal model and the specific symptoms of the human condition), predictive validity (derived from similarity in response to treatment) and construct validity (derived from similarity in the underlying mechanisms--physiological or psychological).

Development and temporal organization of compulsive checking induced by repeated injections of the dopamine agonist quinpirole in an animal model of obsessive-compulsive disorder

Rats treated chronically with the dopamine D2/D3 receptor agonist quinpirole develop locomotor sensitization and exhibit compulsive checking of specific places in an open-field arena, a behavioral profile that may represent an animal model of obsessive-compulsive disorder. However, it is not known how compulsive checking develops across quinpirole injections nor whether checking behavior possesses a particular temporal structure. Male rats received quinpirole (0.5mg/kg, twice weekly x 10) or an equivalent regimen of saline and were placed in a large open field for 55 min where their behavior was digitally tracked for subsequent analysis of checking behavior using existing and newly developed computer software. Results showed that the measures of compulsive checking did not follow a singular profile across injections: some remained constant and others changed monotonically reaching their near-maximum levels after about 5-7 quinpirole injections. Moreover, results showed that checking behavior was organized into bouts of checking, with the number of bouts, as well as the rate of checking within a bout, increasing across injections to reach near maximal levels after about 5-7 administrations of quinpirole. Finally, quinpirole-treated rats showed a paucity of long inter-bout intervals. These results suggest that (a) compulsive checking emerges from the operation of at least two underlying processes: a regulated process and a process of sensitization that intensifies the performance of checking behavior; and (b) quinpirole treatment may attenuate a sense of satiety that could underlie the compulsive nature of checking. Finally, because key variables measured using the newly developed algorithms showed the expected profile, the present study provides validation for the use of this methodology for the analysis of checking behavior.

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.