The term laterale parvozellulare Zone (Formatio reticularis) refers to one of three parts of the reticular formation of the brainstem subdivided longitudinally on the basis of histochemical stains for neurotransmitters and related enzymes, connectivity, cytoarchitecture and function as well as conventional stains for Nissl substance and myelin. It is located in the brainstem lateral to the mediane Zone (Formatio reticularis) and the mediale magnozellulare Zone (Formatio reticularis). It is characterized by small cells and includes adrenergic, cholinergic and noradrenergic cell groups, such as the locus ceruleus ( Schiebler-1999 ).