Chronic administration of typical, but not atypical neuroleptics induce persisting alterations in rest-activity cycles in rats

Relationship of orofacial movements to behavioural repertoire as assessed topographically over the course of 6-month haloperidol treatment followed by 4-month withdrawal

RATIONALE

Late-onset vacuous chewing movements (VCMs) arise in a significant proportion of rats treated chronically with conventional antipsychotic drugs. Given their common action to block dopamine D2-like receptors, VCMs may be related to changes in dopaminergic function; if so, other typical dopamine-mediated behaviours might be altered also.

OBJECTIVE

To examine this hypothesis, behavioural repertoire was studied topographically over the course of chronic treatment and withdrawal.

METHODS

Animals were injected with haloperidol decanoate 28 mg/kg IM, or vehicle, every 3 weeks for 27 weeks, and then maintained without treatment for a further 18 weeks. Immediately before each injection and during withdrawal, VCMs and other topographies of behaviour were assessed.

RESULTS

In both control and haloperidol-treated rats, exploratory behaviours declined over the study, indicating habituation effects. Conversely, VCMs emerged after 6 weeks of treatment with haloperidol and persisted after withdrawal; VCM and locomotion were not related, indicating that in treated rats, increased VCMs are not an artifact of reduced locomotion. Treated animals with VCMs evidenced increases in buccal tremor and grooming behaviour relative to those without VCMs, although no clear relationship to the emergence of VCMs was established; there were no material differences in any other topographies of behaviour.

CONCLUSION

The effect of long-term treatment with haloperidol to induce VCMs is not reflected in fundamental changes in dopamine-mediated behavioural topography but, rather, appears to affect neural mechanisms involved in orofacial movement preferentially.

A silicone pellet for continuous cocaine: comparison with continuous amphetamine

An inexpensive silicone pellet is described for the continuous administration of cocaine for up to 5 days. Rats implanted with this pellet show minimal skin irritation and go through distinct behavioral stages, with an initial period of hyperactivity followed by motor stereotypies. Then, at 3-4 days after implantation, a variety of hallucinogen-like ("late-stage") behaviors appear, including limb flicks, sudden startle responses, and repetitive mid-air grasping movements. Compared to continuous d-amphetamine, continuous cocaine induces decreased motor stereotypies but heightened "late-stage" behaviors.

Comparison of chronic administration of haloperidol and the atypical neuroleptics, clozapine and raclopride, in an animal model of tardive dyskinesia

Rats were administered haloperidol, clozapine, raclopride, or no drug for either 28 days or 8 months and then withdrawn from drug treatment for 3 weeks. Oral movements were repeatedly recorded, both by a human observer and by a computerized video analysis system which determined mouth openings and closings, or computer-scored movelets (CSMs). Four weeks of neuroleptic administration produced no changes in CSMs in any drug-treated group. Long-term administration induced distinctively different patterns of oral activity in the three drug groups, both in number of CSMs and the form of these movements. The oral movements which developed in the haloperidol-treated rats fit a previously described syndrome of late-onset oral dyskinesias which increased upon drug withdrawal. The clozapine- and raclopride-treated rats did not show the increased oral movements seen in the haloperidol animals, but each exhibited uniquely different CSM characteristics compared to controls. The results from this rodent model imply that haloperidol, but not clozapine or raclopride, produces late-onset oral dyskinesias in rats that fit the pattern expected for tardive dyskinesia.