Determining the structure of and the velocity field in prestellar cores is essential to understanding protostellar evolution.} {We have observed the dense prestellar cores L 1544 and L 183 in the $N = 1 to 0$ rotational transition of CN and thcn in order to test whether CN is depleted in the high--density nuclei of these cores.} {We have used the IRAM 30 m telescope to observe along the major and minor axes of these cores. We compare these observations with the 1 mm dust emission, which serves as a proxy for the hydrogen column density.}{We find that while CNjone is optically thick, the distribution of thcnjone intensity follows the dust emission well, implying that the CN abundance does not vary greatly with density. We derive an abundance ratio of $rm [CN]/[hh]=dix{-9}$ in L 183 and 1-3tdix{-9} in L 1544, which, in the case of L 183, is similar to previous estimates obtained by sampling lower--density regions of the core.}{We conclude that CN is not depleted towards the high--density peaks of these cores and thus behaves like the N-containing molecules nhp and hhh. CN is, to our knowledge, the first C--containing molecule to exhibit this characteristic.
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