Binding of [³H]cholecystokinin in the ventromedial hypothalamus modulated by an afferent brainstem projection but not by ovarian steroids

The ventromedial nuclei (VMN) of the hypothalamus are innervated by cholecystokinin-immunoreactive (CCK-IR) fibers originating in the dorsal parabrachial nuclei (PBS). They also contain high levels of receptors for CCK and binding of [¹²⁵I]CCK to these receptors is modulated by estrogen. In the present study, we show that unilateral lesion of the PBS increases the binding of the sulphated octapeptide of [³H]cholecystokinin ([³H]CCK) within the ipsilateral VMN of the hypothalamus, but not within other brain nuclei that contain receptors for CCK. Thus, CCK fibers originating in the PBS selectively innervate the VMN and CCK receptors within the VMN are postsynaptic to parabrachial afferents. However, treatment of ovarietomized rats with estradiol benzoate and progesterone did not affect the binding of [³H]CCK in the VMN, even after lesion of the parabrachial afferents.