Cholinergic and Nadph-δ neurons in the pedunculopontine and laterodorsal tegmental nuclei of human and nonhuman primates.

The brainstem pedunculopontine (PPN) and laterodorsal tegmental (LDTg) nuclei are involved in multifarious activities, including motor control. Yet, their exact cytoarchitectural boundaries are still uncertain. We therefore initiated a comparative study of the topographical and neurochemical organization of the PPN and LDTg in cynomolgus monkeys (Macaca fascicularis) and humans. The distribution and morphological characteristics of neurons expressing choline acetyltransferase (ChAT) and/or nicotinamide adenine dinucleotide phosphate diaphorase (Nadph-δ) were documented. The number and density of the labeled neurons were obtained by stringent stereological methods, whereas their topographical distribution was reported upon corresponding magnetic resonance imaging (MRI) planes. In both human and nonhuman primates, the PPN and LDTg are populated by three neurochemically distinct types of neurons (ChAT-/Nadph-δ+, ChAT+/Nadph-δ-, and ChAT+/Nadph-δ+), which are distributed according to a complex spatial interplay. Three-dimensional reconstructions reveal that ChAT+ neurons in the PPN and LDTg form a continuum with some overlaps with pigmented neurons of the locus coeruleus, dorsally, and of the substantia nigra (SN) complex, ventrally. The ChAT+ neurons in the PPN and LDTg are -two to three times more numerous in humans than in monkeys but their density is -three to five times higher in monkeys than in humans. Neurons expressing both ChAT and Nadph-δ have a larger cell body and a longer primary dendritic arbor than singly labeled neurons. Stereological quantification reveals that 25.6% of ChAT+ neurons in the monkey PPN are devoid of Nadph-δ staining, a finding that questions the reliability of Nadph-δ as a marker for cholinergic neurons in primate brainstem.

Anatomical variants of the rectus femoris motor innervation.

Adult periacetabular osteotomy (PAO) was originally performed through the classic Smith-Petersen approach for optimal operative visibility and acetabular fragment correction. Evolution towards an abductor-sparing technique significantly lowered the post-operative morbidity. The rectus-sparing approach represents a step further, but the innervation of the rectus femoris is theoretically more at risk. Although the topographic anatomy of the femoral nerve has been well described, it was never studied with specificity to surgical landmarks. The femoral nerve's spatial relation with the anterior-inferior iliac spine (AIIS) and the amount of possible dissection in the rectus femoris and iliopsoas interval is uncertain. Seven formalin-preserved human cadaveric specimens without history of inguinal injury or surgery were dissected using the distal limb of an iliofemoral approach. The level of entry of motor innervation was measured and number of branches to the rectus femoris was noted. The average longitudinal distance from the AIIS to the first motor nerve to the rectus femoris was 8.6 ± 1.4 cm. The number of branches varied between 1 and 4 with the most common innervation pattern being composed of two segments. Dissection medial to the rectus femoris should not be carried out further than 7 cm distal to the AIIS and stretching of that interval during surgical exposure should be done cautiously. The clinical efficiency of the rectus-sparing approach should be studied further in order to confirm its advantage over the classic direct anterior approach. The study provides a better understanding of the localization and the anatomical variations of the structures encountered at the level of and below the AIIS. It also assesses the relative risk of denervation of the rectus femoris during PAO through the rectus-sparing approach. The authors recommend that the dissection medial to the rectus femoris should be carried out no further than 7 cm distal to the AIIS and stretching of that interval during surgical exposure should be done cautiously.