Sentence:  Pretreating rats with α-methyl-ρ-tyrosine (30 mg/kg i.p. at -4 h) to interrupt the synthesis of catecholamines antagonized pivoting and <WSD>retropulsion</WSD> induced by levallorphan (50 mg/kg i.p.) (WRAY 1973) but, surprisingly, not lateral head movements and pivoting elicited by cyclazocine (3 mg/kg s.c.) (BUCKETT and SHAW 1975). 
Meaning of the word marked with <WSD> tags:  (medicine) An abnormal tendency to step backwards, as if trying to recover one's balance, sometimes seen in disorders such as Parkinson's Disease.