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

INVOLVEMENT 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, and their sexual behavior differentially influenced by dopamine agonists and antagonists [1; 2]. Together with the well known role of dopamine in sexual behavior, these findings suggest that the sexual differences between RHA and RLA rats may be due to differences in dopamine neurotransmission. 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 concentration 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, and provide insights into the differences among individuals in the neural basis of motivated behaviours and their relationship with vulnerability to abuse natural and/or drug rewards or to develop depressive disorders.