Neuronal localization of cholecystokinin mRNA in the rat brain by using in situ hybridization histochemistry

The distribution of cholecystokinin (CCK) mRNA in the rat brain was determined by means of in situ hybridization histochemistry. Our results demonstrate a widespread distribution of neurons containing CCK mRNA throughout the rat brain. Hybridization-positive neurons were distributed throughout the neocortex, olfactory bulb, claustrum, amygdala, the dentate gyrus and hippocampus proper, and several subnuclei of the thalamus and the hypothalamus. The most abundant and most heavily labeled neurons were found in the endopiriform/piriform cortex, tenia tecta, and the ventral tegmental area. The distribution of neurons positive for CCK mRNA paralleled that of CCK-like immunoreactive neurons. These results detail the distribution of CCK mRNA and clearly identify the existence of CCK-synthesizing neurons in regions such as the paraventricular and supraoptic nuclei of the hypothalamus, where the presence of CCK cell bodies was previously uncertain.