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A Subset of Palisade Endings Only in the Medial and Inferior Rectus Muscle in Monkey Contain Calretinin

Lienbacher, K;Ono, S;Fleuriet, J;

Summary diagram describing the possible innervation pattern of the global layer in the medial and inferior rectus muscle based on the present findings: Motoneurons within the oculomotor nucleus (nIII) correspond to motoneurons of skeletal muscles and target the twitch muscle fibers by a single en plaque endplate (SIF) (_black_). Two histochemically different sets of palisade endings (PE) and multiple en grappe endings were found in the medial and inferior rectus muscle. This includes one group of calretinin (CR)-positive (_red_) and CR-negative (_blue_) palisade and multiple endings, respectively. Two populations of neurons are present in the C-group targeting the nontwitch muscle fibers, a CR-positive and a CR-negative group. The present study could not determine whether PEs and multiple endings form an anatomic entity or originate from different neuronal groups within the C-group, or whether both forms are present in parallel. Therefore, in theory, four populations of neurons in the C-group can be anticipated: CR-positive neurons giving rise to palisade endings and multiple en grappe endings (_filled neuron soma_), CR-positive neurons providing only multiple endings (_open neuron soma_), and the respective populations for CR-negative neurons including their nerve endings. The CR-positive innervation unique to the medial and inferior rectus muscle may represent an additional specialized more excitable set of neurons targeting nontwitch muscle fibers required for eye alignment in convergence. [Summary diagram describing the possible innervation pattern of the global layer in the medial and inferior rectus muscle based on the present findings: Motoneurons within the oculomotor nucleus (nIII) correspond to motoneurons of skeletal muscles and target the twitch muscle fibers by a single en plaque endplate (SIF) (black). Two histochemically different sets of palisade endings (PE) and multiple en grappe endings were found in the medial and inferior rectus muscle. This includes one group of calretinin (CR)-positive (red) and CR-negative (blue) palisade and multiple endings, respectively. Two populations of neurons are present in the C-group targeting the nontwitch muscle fibers, a CR-positive and a CR-negative group. The present study could not determine whether PEs and multiple endings form an anatomic entity or originate from different neuronal groups within the C-group, or whether both forms are present in parallel. Therefore, in theory, four populations of neurons in the C-group can be anticipated: CR-positive neurons giving rise to palisade endings and multiple en grappe endings (filled neuron soma), CR-positive neurons providing only multiple endings (open neuron soma), and the respective populations for CR-negative neurons including their nerve endings. The CR-positive innervation unique to the medial and inferior rectus muscle may represent an additional specialized more excitable set of neurons targeting nontwitch muscle fibers required for eye alignment in convergence.] View Original [/data/Journals/IOVS/937150/i1552-5783-59-7-2944-f08.png]Download Slide [/downloadimage.aspx?image=/data/Journals/IOVS/937150/i1552-5783-59-7-2944-f08.png&sec=190625657&ar=2684289&imagename=]