Phencyclidine decreases tickling-induced 50-kHz ultrasound vocalizations in juvenile rats: a putative model of the negative symptoms of schizophrenia?

The objective of the present study was to examine the idea that the decrease in 50-kHz ultrasonic vocalizations elicited by tickling in juvenile rats following the administration of the psychotomimetic drug phencyclidine (PCP) may represent a valid model of the negative symptoms of schizophrenia. Fifty-kilohertz calls in rodents have been suggested to represent an archaic model of human laughter. Our results showed that daily tickling sessions produced a gradual increase in 50-kHz vocalizations, an effect that reached statistical significance from day 3. Administration of PCP (1 mg/kg, intraperitoneally) attenuated the 50-kHz calls induced by 4 consecutive days of tickling. The ability of several clinically effective or potential antipsychotics to reverse the effects of PCP was investigated. The 5-HT1A receptor partial agonist, buspirone (0.3 and 1 mg/kg, intraperitoneally), the dual D2/5-HT1A receptor ligand, SSR181507 (0.5-0.75 mg/kg, intraperitoneally), but not the atypical antipsychotic, aripiprazole (0.1-1 mg/kg, intraperitoneally), the 5-HT2A receptor antagonist, eplivanserin (0.3-3 mg/kg, intraperitoneally), and the GlyT1 inhibitor, SSR103800 (0.3-3 mg/kg, intraperitoneally) significantly attenuated the effects of PCP on 50-kHz calls. Importantly, in animals not treated with PCP, none of the drugs affected 50-kHz calls elicited by a first handling-tickling session, indicating that the action of buspirone and SSR181507 cannot be explained by an intrinsic effect. To investigate further the specificity of these drug effects, we tested the anxiolytic and antidepressant agents, diazepam (0.1-1 mg/kg, intraperitoneally) and fluoxetine (1-10 mg/kg, intraperitoneally), respectively, in this procedure. Neither drug affected tickling-induced 50-kHz calls in naive or PCP-treated rats. In conclusion, the results of the present study confirm that 50-kHz calls elicited by several tickling sessions in rats can be reduced by acute administration of PCP, and that this effect can be reversed by previous administration of compounds with 5-HT1A receptor agonist properties. As evidence for clinical efficacy of both agents on the negative symptoms of schizophrenia is weak or lacking, the current findings do not allow a definite conclusion to be drawn on the validity of this procedure as a model of this aspect of schizophrenia.