Abstract
Cholecystokinin (CCK) is a peptide found in both gut and brain. Although numerous studies address the role of brain CCK postnatally, relatively little is known about the ontogeny of CCK expression in the central nervous system (CNS). Recent work revealed that CCK modulates olfactory axon outgrowth and gonadotropin-releasing hormone-1 (GnRH-1) neuronal migration, suggesting that CCK may be an important factor during CNS development. To further characterize the developmental expression of CCK in the nervous system, in situ hybridization experiments were performed. CCK mRNA expression was widely distributed in the developing mouse brain. As early as E12.5, robust CCK expression is detected in the thalamus and spinal cord. By E17.5, cells in the cortex, hippocampus, thalamus and hypothalamus express CCK. In addition, CCK mRNA was also detected in the external zone of the median eminence where axons of the neuroendocrine hypophysiotropic systems terminate. Our study demonstrates that CCK mRNA is expressed prenatally in multiple areas of the CNS, many of which maintain CCK mRNA expression postnatally into adult life. In addition, we provide evidence that regions of the CNS known to integrate hormonal and sensory information associated with reproduction and the GnRH-1 system, expressed CCK already during prenatal development.