Cytoarchitectural organization of the parabrachial/Kölliker-Fuse complex in man.

While the parabrachial/Kölliker-Fuse complex has been described in a variety of animal species it has not been characterized in human brainstem. In the present study we investigated fetal and infant brainstems, focusing particularly on the dorsolateral part of the pontine tegmentum, with the aim of defining the precise cytoarchitecture of the medial parabrachial, lateral parabrachial, and Kölliker-Fuse nuclei in man, and analyzing the developmental stages of this complex. In serial sections of 28 human brainstems of subjects aged between 32 gestational weeks and 1 year we made a morphologic and morphometric analysis of the shape and size of the parabrachial/Kölliker-Fuse complex. We observed a homogeneous morphology in all cases, which enabled us to define the structure of the three nuclei. The features of the parabrachial nuclei are largely consistent with those reported in experimental studies. However, the Kölliker-Fuse nucleus appears to be more developed in human beings than in other animal species, showing a greater extension and a more complex structure. The neuronal maturation of these nuclei was seen to occur between the 35th and the 36th gestational weeks.