An ethopharmacological analysis of the behavioral effects of 8-OH-DPAT

Several behaviors associated with the serotonin syndrome have been reported in rats following administration of the 5-HT1A receptor agonist 8-OH-DPAT. The present investigation approached this phenomenon from an ethopharmacological perspective, and provided a detailed temporal analysis of the behavioral effects of this compound over a 2-h period, in both male and female rats in the home cage. In addition, in order to further characterize the nature of the forepaw-treading and locomotor elements, and assess the extent of influence of the physical characteristics of the test arena, this study provided a detailed analysis of these behaviors in both the home cage and a large oval runway. In the initial analysis, the data indicate a distinct chronological sequence of effects following 8-OH-DPAT treatment. For example, "flat back" activity and lower lip retraction were apparent within a few minutes post-injection, the former dissipating after about 30 min and being replaced as the prepotent response by a more general (curved back) locomotor enhancement, while the latter effect remained throughout the 2-h test period. Interestingly, there were reliable gender differences in terms of the onset and disappearance of several behavioral components, with females generally being more rapidly affected, but recovering earlier than males. The detailed analysis of locomotor activity and forepaw treading would suggest that the locomotor syndrome primarily involves forward movement, heavily guided by the physical environment. Furthermore, forepaw-treading would seem only to occur when an animal reaches a barrier and forward movement is briefly interrupted, as no reliable incidence of this behavior was observed in the open area of the test area. Together, these findings provide further characterization of the behavioral syndrome induced by 8-OH-DPAT, and indicate the importance of time post-administration, gender of the subject, and the physical characteristics of the test environment, when considering stereotypical drug effects.