The histochemical distribution of the enzyme cytochrome oxidase (CO) was explored in the globus pallidus (GP) of the rat, and it was compared with the distribution of acetylcholinesterase (AChE), another well-known enzyme of the basal ganglia in mammals. This neurochemical research illustrates two prominent findings. In the first place, a regional compartmentalization was detected in the pallidal distribution of CO, in which dorsal territories of the GP exhibited a more abundant presence of this enzyme. In addition, the distribution of this mitochondrial enzyme was not uniform all over those dorsal pallidal territories. Thus, the pallidal concentration of CO was gradually decreasing dorsoventrally and lateromedially, and, sometimes, areas highly stained for CO were intermingled with zones in which this enzyme was less conspicuous. In the second place, the pallidal distribution of AChE was the opposite of that found for CO (i.e. more abundant in ventral and medial territories of the GP). The functional significance of these findings is discussed in the light of the heterogeneous hodological neuroanatomy of the GP of rodents.
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