The chemical architecture of the rat's periaqueductal gray based on acetylcholinesterase histochemistry: a quantitative and qualitative study

Abstract

The chemoarchitecture of the periaqueductal gray has been extensively studied, based on acetylcholinesterase reaction and comparing it to other chemical markers. We have divided the periaqueductal gray into four main longitudinal columns, namely dorsomedial, dorsolateral, lateral and ventrolateral. We also identified the dorsal midline column, the supraoculomotor cap and the juxta-aqueductal ring. The acetylcholinesterase gave rise to a strong reaction in the outer half of the lateral column, the outer half of the dorsomedial column, the supraoculomotor cap and the ventral half of the juxta-aqueductal ring. This labeling was in part complementary to that of the NADPH diaphorase and allowed the lateral column to be differentiated from the ventrolateral column. However, the inner half of both lateral and ventrolateral columns displayed the same chemical properties including acetylcholinesterase, tyrosine hydroxilase and serotonin. Thus, from the chemical view, these inner halves should be considered as one different region. Finally, the juxta-aqueductal ring was composed of two clearly different halves, i.e. dorsal and ventral. The dorsal half did not show any clear differences from the above columns and was negative for acetylcholinesterase, NADPH diaphorase and tyrosine hydroxilase, while the ventral half was clearly different from the lateral and ventrolateral columns and displayed a positive reaction to all those chemical markers. From these results, we strongly suggest the use of acetylcholinesterase histochemistry as a tool for accurate parcellation of the periaqueductal gray.