Possible role of dopamine in the differences in sexual behaviour between Roman High and Low Avoidance rats: behavioral, pharmacological and neurochemical findings

Abstract

POSSIBLE ROLE OF DOPAMINE IN THE DIFFERENCES IN SEXUAL BEHAVIOUR BETWEEN ROMAN HIGH AND LOW AVOIDANCE RATS: BEHAVIORAL, PHARMACOLOGICAL AND NEUROCHEMICAL FINDINGS. Roman High (RHA) and Low Avoidance (RLA) rats display opposite behavioral traits: RHA rats are active copers, impulsive and prone to abuse drugs while RLA rats are reactive copers, hyperemotional and prone to develop depressive-like symptoms. These differences are linked to differences in brain monoamine (mainly dopamine) function and neuroendocrine responses to stress. RHA and RLA rats differ also in sexual behavior, with RHA rats displaying higher motivation and better copulatory performance than RLA rats. Moreover, in the two lines sexual behaviour is differentially influenced by dopamine agonists and antagonists, suggesting a different sensitivity/density of dopamine receptors in brain areas involved in sexual behaviour. Taken together and in keeping with the well known role of dopamine in the modulation of different aspects of sexual behaviour, these findings raise the possibility that the differences observed in sexual behaviour between RHA and RLA rats can be due to differences in brain dopamine transmission. In order to test this hypothesis, naive (never exposed to a receptive female) and sexually experienced (which underwent five copulation tests) RHA and RLA rats implanted with a microdialysis probe aimed at the shell of the nucleus accumbens (NAs), were used in a classical appetitive/consummatory test of sexual behavior, during which copulatory parameters were recorded and dialysate aliquots collected from the NAs for the determination of dopamine by HPLC-ECD. The results show that the higher sexual motivation and better performance of RHA vs. RLA rats occurred concomitantly with a higher dopamine release, as shown by the higher dopamine concentrations found in the NAs dialysate of RHA vs. RLA rats. These differences between the two lines were greater in naive animals and persisted, although attenuated, in experienced animals. These findings confirm that a different mesolimbic dopaminergic tone exists in RHA and RLA rats, which may be responsible, at least in part, for their different copulatory patterns. Moreover, as sexual behaviour is one of the most important sources of natural reward due its importance in the preservation of species, these results, taken together with those that show differences between the two lines in the mesolimbic dopaminergic function after the intake of different natural or addictive rewards (as drugs of abuse), strongly support the validity to use these two rats lines as a model for the study of the genetic, neurochemical and behavioural factors at the basis of individual differences in motivated behaviour and its alterations and their interactions with different classes of stimuli as well