The effects of acute and repeated pyridostigmine bromide administration onresponse acquisition with immediate and delayed reinforcement

This experiment was designed to assess the effects of acute and repeated ad ministration of pyridostigmine bromide (a carbamate with prophylactic and t herapeutic uses) on response acquisition. Experimentally naive, male Spragu e-Dawley rats were exposed to a situation in which lever presses were eithe r immediately followed by food-pellet presentation or after a 16-s resettin g delay. Different groups of rats received either one acute administration of pyridostigmine bromide (10 mg/kg, by gavage) or repeated pyridostigmine administration for 7 days (1.5 mg/kg/day, by gavage). Other groups were tre ated with distilled water for the same period of time. Both acute and repea ted pyridostigmine bromide administration decreased serum cholinesterase le vels by approximately 50%, but neither treatment affected brain cholinester ase levels in our assay. Acute and repeated drug administration produced th e same behavioral effects. Subjects exposed to the 0-s delay conditions obt ained many more food pellets than those exposed to the 16-s delay condition s. Administration of pyridostigmine bromide delayed the onset of responding in some, but not all, of the subjects in the treated groups, independent o f the delay condition to which they were exposed. Many more responses were observed on an inoperative lever during the 16-s delay conditions than duri ng the 0-s delay conditions, especially during the 16-s belay condition in which subjects had received acute vehicle administration. Whether or not th ese effects of small doses of pyridostigmine bromide on response acquisitio n are of central or peripheral origin will need to be determined in future studies, as response acquisition in the present experiment may have been af fected by pyridostigmine's effects on gastrointestinal functioning and/or m otor activity. (C) 1999 Elsevier Science Inc.