Conditional tolerance to haloperidol-induced catalepsy is not caused by striatal dopamine receptor supersensitivity

The purpose of this study was to determine if non-pharmacological stimuli influence behavioural tolerance to haloperidol via striatal postsynaptic dopamine receptors. Rats received daily haloperidol and saline in two different environments for a period of 28 days. After this conditioning period half of the rats received haloperidol in the haloperidol-associated environment, whereas the other half received haloperidol in the saline-associated environment. All rats were tested for catalepsy and at the end of the last catalepsy test, striatal DOPAC, HVA and ACh were determined. Only the rats tested in the haloperidol-associated environment were behaviourally tolerant to haloperidol. In contrast, both groups were biochemically tolerant to haloperidol. These results indicate that environmental cue factors govern the development of behavioural tolerance to haloperidol, rather than biochemical factors (striatal DA super-sensitivity). In addition, these factors do not exert their influence on behavioural tolerance via striatal DA receptors.