Rat oxytocin receptor in brain, pituitary, mammary gland, and uterus: Partial sequence and immunocytochemical localization

Partial complementary DNAs of an oxytocin (OT) receptor were cloned from rat brain and uterus. The complementary DNAs encoded for the same amino acid sequence, which showed a high degree of homology with the human and porcine uterine OT receptors, except for a region in the third intracellular loop. Antibodies were raised against nonoverlapping sequences of the third intracellular loop of this rat OT receptor. Using these antisera, OT receptor expression was demonstrated in the brain, pituitary, mammary gland, and uterus by immunocytochemistry. In the brain, several areas including the ventromedial hypothalamus, the bed nucleus of the stria terminalis, the ventral pallidum, the paraventricular nucleus, and the dorsal part of the supraoptic nucleus, demonstrated OT-receptor immunoreactivity. However, no immunoreactivity was detected in two areas of the brain known to contain dense OT-binding sites by receptor autoradiography studies: the ventral hippocampus and the central nucleus of the amygdala. In the pituitary, both the anterior and posterior lobes were positive for OT receptor immunoreactivity, whereas the intermediate lobe was negative. These results demonstrate that the same receptor type is expressed in both peripheral OT target tissues and the brain, and also suggest the possibility that a different OT receptor subtype may be present in some areas of the brain.