Haloperidol Affects Guinea Pig Chewing Burst Durations

Abstract

Previous investigations have reported that most movement patterns in humans and other mammalian species are partitioned into 1–5-s units. This finding has led to the hypothesis that a highly conservative physiological system, common among mammalian species, segments ongoing movement patterns into 1–5-s 'chunks'. However, to date little or no work has 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 movement patterns. The literature suggests that central dopamine plays a key role in this 1—5-s partitioning. If this is so then dopamine blockers should result in significant alterations in the 1–5-s segmentation of mammalian movement patterns. To test this hypothesis the current study determined whether the neuroleptic haloperidol significantly affected guinea pig chewing burst durations, which reportedly average 1–3 s and are therefore considered to manifest this partitioning phenomenon. Seven male albino guinea pigs received daily 0.5 mg/kg i.m. haloperidol injections, and three male albino guinea pigs received comparable saline injections (controls). After either 3 or 11 weeks, injections were stopped, and 1 week thereafter the animals were starved for 24 h and then videotaped singly in an experimental arena. Animals inevitably fed on alfalfa pellets during the taping session, and the chewing bursts that occurred while the animals fed were timed. The results showed that control animals chewing bursts had durations similar to those previously reported for free-roaming, non-drug-treated guinea pigs. However, haloperidol-treated guinea pigs chewing bursts were significantly more variable in duration (p =0,0013) than those of matched control animals. Inspection of the data from individual animals revealed that two haloperidol-treated animals had abnormally short chewing burst durations, whereas three haloperidol-treated animals had abnormally long chewing burst durations. The fact that haloperidol treatment was associated 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 movements'. This suggests that intact central dopaminergic systems may play an important role in modulating the duration of mammalian movement patterns, which normally ranges 0.2–5 s.