Distribution of cholecystokinin-immunoreactive cell bodies in the male and female rat: I. Hypothalamus

The hypothalamic distribution of cholecystokinin‐immunoreactive (CCKI) cell bodies in colchicine‐treated male and female rats was studied. Immunoreactive neurons were visualized along the anterior two‐thirds of the third ventricle but were especially numerous in the preoptic periventricular nucleus. Dense aggregations of CCKI cells were found in the anterior magnocellular, posterior magnocellular, medial parvicellular, and posterior parvicellular divisions of the paraventricular nucleus. Both the supraoptic nucleus and the central, cell‐dense part of the dorsomedial nucleus contained large numbers of CCKI cells. CCKI cells in the preoptic periventricular nucleus were more numerous in the female, as was a population of labeled cells in the dorsal medial preoptic area. However, CCKI cell bodies in this part of the medial preoptic area were larger in males than in females. Males had more CCKI cells in the central part, of the medial preoptic nucleus and in the posterior magnocellular subdivision of the paraventricular nucleus. Both males and females had similar numbers of immunoreactive cells in the anterior magnocellular and the parvicellular divisions of the paraventricular nucleus as well as in the anterior hypothalamus, dorsal areas, dorsomedial nucleus, and supramammillary region. These data provide morphological evidence for a sexually differentiated hypothalamic CCKI system.