The effects of parachlorophenylalanine and stimulus intensity on open-field test measures in rats

An inhibitor of 5-hydroxytryptamine synthesis, p-chlorophenylalanine (PCPA), or an inert saline solution was administered intraperitoneally to rats. At maximum depletion of serotonin (72 hr after injection), the rats were tested in the standard, four-day open-field test. A further four days of testing in the open field in which the sound level was raised from the standard 78 to 93 dB showed that, while PCPA increased defaecation in both sexes and under both sound levels, the controls increased defaecation at the higher level stimulus intensity, whereas PCPA-injected rats defaecated less. Parachlorophenylalanine increased ambulation in males on the first day of open-field testing but not in females. On the remaining seven days of testing PCPA markedly reduced ambulation in females but did not affect ambulation in males. Across-trial habituation of neither the defaecation nor the ambulation measure was influenced by PCPA.