D1 dopamine receptor agonist (SKF-38393) induction of Fos immunoreactivity in progestin receptor-containing areas of female rat brain.

Injection of dopamine or dopamine receptor subtype agonists facilitates the expression of lordosis in estrogen-primed female rats. The D1 receptor specific agonist, SKF-38393, facilitates lordosis in estradiol-primed female rats via a process that requires progestin receptors. Based on these data, neuronal response to the D1 receptor agonist SKF-38393 was assessed by expression of the immediate early gene protein, Fos. In the first experiment we examined the modulation of Fos expression by D1 agonists in progestin receptor-containing areas of estradiol-primed female rat brain. In the second experiment we examined if there are progestin if there are progestin receptor-containing cells that respond to stimulation of D1 receptors with increased Fos expression. Ten to 14 days following ovariectomy and stereotaxic surgery, animals were injected with 5 micrograms estradiol benzoate. Forty eight h later they were injected intracerebroventricularly with 100 ng of SKF-38393 or saline. One h following injection animals were perfused, and brain sections immunostained for Fos protein. Results from the first experiment suggest that SKF-38393 increased the total number of Fos immunoreactive cells in the mid-ventromedial hypothalamic nucleus/ventrolateral portion (VMHVL), the caudal VMHVL, the paraventricular hypothalamic nucleus and the caudate putamen. In the medial preoptic area, the rostral VMHVL and the arcuate hypothalamic nucleus, there was a significant increase in the number of darkly stained Fos-immunoreactive cells following the SKF-38393 treatment. In the second study, SKF-38393 increased the number of progestin receptor-containing cells which contained Fos immunoreactivity in the caudal VMHVL. The results suggest potential sites of action for the facilitation of sexual behavior by centrally administered D1 agonists.