Transient improvement in cognitive function and synaptic plasticity in rats following cancer chemotherapy

Background: Cancer chemotherapy has been associated with cognitive impairment. Several issues complicate such findings including the patients' health, use of multiple chemotherapeutic agents, and proper assessment of cognition. To control these factors, we conducted cognitive studies in female rats receiving cyclophosphamide or 5-fluorouracil (5FU). Methods: Young (7 months) female Fischer-344 rats received five injections of cyclophosphamide (100 mg/kg), 5FU (150 mg/kg), or saline i.p. every 4 weeks for a total of 18 weeks. Aged (18 months) female Fischer-344 rats were treated with cyclophosphamide (80 mg/kg i.p.) for 16 weeks. After 8 to 10 weeks of recovery, rats were tested in two maze learning tasks, the Morris water maze and the Stone 14-unit T-maze. Neuronal synaptic function was assessed by examining long-term potentiation (LTP) in hippocampal slices obtained from young cyclophosphamide-treated rats. Results: Despite the toxic effects induced by chemotherapy, cyclophosphamide- and 5FU-treated rats showed significantly better maze performance compared with controls. Following 29 to 42 weeks of recovery from chemotherapy, no significant effects were observed on maze performance. In aged rats, cyclophosphamide treatment for 14 weeks also produced toxicity, but no impairment in Stone maze learning after 16 weeks of recovery. When assessed during cyclophosphamide treatment, evidence of impaired LTP emerged; however, with 8 weeks of recovery following five cyclophosphamide treatments, we observed enhanced LTP. Conclusion: Despite toxicity accompanying chemotherapy, no evidence of impaired cognitive performance emerged after recovery. Indeed, following 7 to 9 weeks of recovery, we noted evidence of improved learning and LTP.