p-Chloroamphetamine (PCA): Acute and chronic effects on habituation and sensitization of the acoustic startle response in rats

In a series of 6 experiments the effects of p-chloroamphetamine (PCA) on the acoustic startle response in rats were investigated. 15 min after 5 mg/kg PCA startle amplitude was inhibited, 2-15 hr after PCA startle was facilitated. Rate of habituation however was not altered. Both the inhibitory and excitatory effects of PCA were blocked by pretreatment with p-chlorophenylalanine but not by alpha-methyl-p-tyrosine. 24 hr, 1 week and 4 weeks after PCA, initial startle amplitude was unchanged but PCA increased rate of sensitization over successive tone blocks. Increased sensitization was most pronounced at 10 mg/kg and absent at 2.5 mg/kg. The early inhibitory effect of PCA but not the later facilitatory effect was eliminated by reducing the level of background noise. The results suggest that inhibition of startle sensitization is associated with enhanced release of serotonin (5-HT) whereas enhancement of startle sensitization is associated with 5-HT depletion.