HALOPERIDOL AFFECTS GUINEA-PIG CHEWING BURST DURATIONS

Previous investigations have reported that most movement patterns in h umans and other mammalian species are partitioned into 1-5-s units. Th is finding has led to the hypothesis that a highly conservative physio logical system, common among mammalian species, segments ongoing movem ent patterns into 1-5-s 'chunks'. However, to date little or no work h as been done to explore the physiological and neurochemical nature of this segmenting phenomenon, therefore, it is unknown whether the same evolutionarily conservative mechanism controls partitioning of all mov ement patterns. The literature suggests that central dopamine plays a key role in this 1-5-s partitioning. If this is so, then dopamine bloc kers should result in significant alterations in the 1-5-s segmentatio n of mammalian movement patterns. To test this hypothesis, the current study determined whether the neuroleptic haloperidol significantly af fected guinea pig chewing burst durations, which reportedly average 1- 3 s and are therefore considered to manifest this partitioning phenome non. Seven male albino guinea pigs received daily 0.5 mg/kg i.m. halop eridol injections, and three male albino guinea pigs received comparab le saline injections (controls). After either 3 or 11 weeks, injection s were stopped, and 1 week thereafter the animals were starved for 24 h and then videotaped singly in an experimental arena. Animals inevita bly fed on alfalfa pellets during the taping session, and the chewing bursts that occurred while the animals fed were timed. The results sho wed that control animals' chewing bursts had durations similar to thos e previously reported for free-roaming, non-drug-treated guinea pi,os. However, haloperidol-treated guinea pigs' chewing bursts were signifi cantly more variable in duration (p=0.0013) than those of matched cont rol animals. Inspection of the data from individual animals revealed t hat two haloperidol-treated animals had abnormally short chewing burst durations, whereas three haloperidol-treated animals had abnormally l ong chewing burst durations. The fact that haloperidol treatment was a ssociated with either abnormally short or long chewing burst durations is reminiscent of neuroleptic-induced human movement disorders, which reportedly range from a 'paucity of movement' to 'perseverant movemen ts'. This suggests that intact central dopaminergic systems may play a n important role in modulating the duration of mammalian movement patt erns, which normally ranges 0.2-5 s.