Striatal D-2 dopamine agonist binding sites fluctuate during the rat estrous cycle

Striatal D-2 dopamine (DA) antagonist and agonist binding sites were measured during the rat estrous cycle and compared to ovariectomized (OVX) rats. Dopaminergic D-2 antagonist binding sites were constant during the estrous cycle while agonist binding sites show a rapid and significant decrease of the ratio of high to low D-2 agonist binding sites from proestrus AM (PAM) to diestrus 1 (D1) and return to OVX value in diestrus 2 (DII). Thus, physiological fluctuations of hormones as occur during the estrous cycle can modulate extrahypothalamic biogenic amine activity, namely striatal DA systems which are not involved in the control of hormone secretion.