Chronic low-dose haloperidol effects on self-stimulation rate-intensity functions

Microcatalepsy and disruption of forelimb usage during operant behavior: differences between dopamine D1 (SCH-23390) and D2 (raclopride) antagonists

In an experiment designed to distinguish between the behavioral consequences of treatment with SCH-23390, a D1 dopamine receptor blocker, and raclopride, a D2 antagonist, rats were trained to perform a water-reinforced forelimb operant response. Response rate and the duration of each forelimb contact with the operandum were recorded. In addition, the durations of the rat's visits to the reward well were detected by a photobeam which was blocked by the rat's muzzle as it remained at the reward well. In a between-groups dosing design, separate groups of rats (11-13 rats/group) received SCH-23390 (0, 0.01, 0.02, 0.04, 0.08, 0.12 mg/kg, IP, 30 min) or raclopride (0. 0.05, 0.1, 0.2, 0.4, 0.8 mg/kg, IP, 30 min) for 21 consecutive days. Quantitative analyses indicated that for comparable amounts of operant rate reduction, raclopride had a significantly greater tendency than SCH-23390 to increase the duration of operant responses and to increase the maximum muzzle entry duration (i.e., to induce microcatalepsy). The results support the idea that at relatively low doses D2 antagonism is more likely than D1 antagonism to produce effects identified preclinically with extrapyramidal side effects.

Differentiation of haloperidol and clozapine using a complex operant schedule in the dog

This study aimed to differentiate chronically administered typical (haloperidol) and atypical (clozapine) neuroleptics in the dog using a complex temporal regulation schedule combining operant, voluntary, and involuntary motor parameters. Although clozapine and haloperidol showed some characteristics of neuroleptics, justifying their adherence to the same class of compounds, differences have also been highlighted and compared to the clinical observations. Haloperidol induced catalepsy, tremor, dystony, hyperkinesia, and stereotypy. Subjects produced anticipated responses before any stimulus. Incomplete and delayed responses were also produced. An interpretation in terms of akathisia and anhedonia has been suggested. Clozapine induced tremor, exploration, dystony, and hypersalivation. Subjects produced disinhibitory responses to the negative stimulus and incomplete responses but these latter were submitted to tolerance. The simultaneous presence of tranquilizing and disinhibitory effects has been reported on the clinical potential of clozapine both in cases of positive and negative schizophrenic symptomatologies.

Intracerebral haloperidol potentiates the dorsal immobility response in the rat

The effects of intracerebral microinjections of 4-[4-(4-chlorophenyl)-4-hydroxy-1-piperidinyl]-1-(4- fluorophenyl)-1-butanone (haloperidol) (1.0 microgram, 0.5 microliter) in five regions of the brain were tested on the duration of the dorsal immobility response (DIR) and the cling and bar catalepsy in the rat. The duration of the DIR was significantly potentiated (but not the cling and bar catalepsy) following 2-h postinjection of haloperidol in the caudate putamen, nucleus accumbens, and globus pallidus but not in the substantia nigra pars compacta or cortex. These data further expand the previous evidence of regional variations in dopamine to the effects upon inhibitory behaviors.

Enhanced haloperidol-induced prolactin stimulation with chronic neuroleptic treatment in the rat

Animals were treated either acutely, or chronically for 21 days, with a low dose (0.1 mg/kg) of haloperidol, then sacrificed to obtain trunk blood for radioimmunoassay of prolactin (PRL) level. PRL concentrations on day 21 of chronic treatment were greater than two-fold those produced by acute neuroleptic. Challenge with apomorphine to rats withdrawn for 48 hours revealed similar PRL reductions as a group withdrawn from chronic vehicle injections.