Combined mesencephalic and hypothalamic transplants reverse lesion-induced sexual behavior deficits in the male rat.

Studies of sexual behavior in rodent animal models have provided evidence about the relevant role played by the medial preoptic area of the anterior hypothalamus and the central tegmental field within the mesencephalon in the control of this behavior. Bilateral lesions of the anterior hypothalamus or central tegmental field as well as combined unilateral lesions of both these regions result in sexual behavior deficits. Studies using fetal hypothalamic transplants have been shown to reverse sexual behavior deficits induced either by lesions or aging. However, no previous study has evaluated the effect of combined homotopic transplants into both the anterior hypothalamus and the mesencephalon. In the present study male Wistar animals received two electrolytic lesions, one aimed at the ipsilateral medial preoptic area of the anterior hypothalamus and the other at the contralateral central tegmental field. Following these lesions, unilateral homotopic fetal hypothalamic and mesencephalic transplants were placed into the lesioned areas. Sexual behavior recovered gradually and by weeks 14-15 after transplantation, above 90% of animals with bilateral transplants showed mounts, intromissions, and ejaculations. Only animals with viable transplants located within both lesioned areas showed recovery. These results indicate that the behavioral deficits induced by combined unilateral lesions of hypothalamic and mesencephalic regions can be reversed by homotopic fetal transplants and that this recovery could be the result of the restoration of a behavioral relevant circuit between transplants and host brain nuclei separated by as much as 5 mm, which makes this an excellent model to study mechanisms underlying behavioral recovery after transplantation.

Socio-sexual behavior in male rats after lesions of the dorsolateral tegmentum.

The medial preoptic area of the anterior hypothalamus (MPOA/AH) and the dorsolateral tegmentum (DLT) play an important role in the control of sexual behavior. Unilateral lesions of the MPOA/AH (medial preoptic area of the anterior hypothalamus) combined with unilateral lesions of the contralateral DLT result in deficits in male sexual behavior, while bilateral electrolytic lesions of the DLT have similar effects. In the present study, coital and socio-sexual interactions were recorded before and after bilateral electrolytic DLT lesions. Coital behavior was monitored for 15 weeks after surgery and socio-sexual interactions one 1 and 3 weeks after lesion. DLT-lesioned animals showed reduced copulatory behavior throughout the 15 weeks postlesion. This inhibition was associated with changes in exploratory (sniffing), precopulatory (pursuit and genital exploration), and postcopulatory behaviors (self-grooming). No differences were found in the weights of the testicles, prostate and seminal vesicles. These results indicate that lesions of the DLT produced permanent deficits in sexual behavior associated with a generalized modification of sociosexual behavior. These deficits indicate reduced sexual motivation possibly due to the disruption of the output pathway from the MPOA/AH (medial preoptic area of the anterior hypothalamus) to the DLT.