Effects of chemotherapeutic agents 5-fluorouracil and methotrexate alone and combined in a mouse model of learning and memory.
BACKGROUND
The concern that adjuvant cancer chemotherapy agents cause cognitive impairment in a significant number of patients has been expressed by patients and healthcare providers, but clinical studies have yielded conflicting results to date.


OBJECTIVE
We directly tested two commonly used chemotherapeutic agents in a mouse model of learning and memory.


METHODS
In the present study, mice were conditioned to respond for a liquid reinforcer (Ensure solution) in the presence of an audible tone on day 1 as a measure of acquisition and were then required to perform the same response on day 2 as a measure of retrieval and retention. Methotrexate and 5-fluorouracil were administered prior to the day 1 session.


RESULTS
Methotrexate (1.0-32 mg/kg) alone failed to alter mean latency acquisition, retrieval, or reinforced response rates. Similar to scopolamine, a known amnesic in this assay, 5-fluorouracil (3-75 mg/kg) failed to alter response rates or acquisition latency on day 1 but significantly altered latency to retrieve a previously learned response on day 2. In combination, 3.2 mg/kg methotrexate plus 75 mg/kg 5-fluorouracil significantly increased day 1 and day 2 acquisition and retrieval latencies without altering response rates or motivation to respond as measured by progressive ratio responding.


CONCLUSIONS
Taken together, these data demonstrate that 5-fluorouracil causes increased latencies for retrieval of previously learned behavioral responses and that combination of chemotherapeutic agents may produce greater delays than either agent alone, including when neither agent alone does so.
Foley
John J
JJ
Department of Pharmaceutical Sciences, Temple University School of Pharmacy, 3307 North Broad Street, Philadelphia, PA 19140, USA.
Raffa
Robert B
RB
Walker
Ellen A
EA
D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D003216:Conditioning, Operant / Q000187:drug effects; D004347:Drug Interactions; D005472:Fluorouracil / Q000494:pharmacology*; D005502:Food; D007274:Injections, Intraperitoneal; D007858:Learning / Q000187:drug effects*; D008297:Male; D008568:Memory / Q000187:drug effects*; D008727:Methotrexate / Q000494:pharmacology*; D051379:Mice; D009042:Motivation; D018727:Muscarinic Antagonists / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D012055:Reinforcement Schedule; D012201:Reward; D012601:Scopolamine / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology
D000964:Antimetabolites, Antineoplastic; D018727:Muscarinic Antagonists; D010879:Piperazines; D017366:Serotonin Receptor Agonists; D012601:Scopolamine; C015068:1-(3-chlorophenyl)piperazine; D005472:Fluorouracil; D008727:Methotrexate