title: Axons giving rise to the palisade endings of feline extraocular muscles display motor features.
abstract: Palisade endings are nerve specializations found in the extraocular muscles (EOMs) of mammals, including primates. They have long been postulated to be proprioceptors. It was recently demonstrated that palisade endings are cholinergic and that in monkeys they originate from the EOM motor nuclei. Nevertheless, there is considerable difference of opinion concerning the nature of palisade ending function. Palisade endings in EOMs were examined in cats to test whether they display motor or sensory characteristics. We injected an anterograde tracer into the oculomotor or abducens nuclei and combined tracer visualization with immunohistochemistry and α-bungarotoxin staining. Employing immunohistochemistry, we performed molecular analyses of palisade endings and trigeminal ganglia to determine whether cat palisade endings are a cholinergic trigeminal projection. We confirmed that palisade endings are cholinergic and showed, for the first time, that they, like extraocular motoneurons, are also immunoreactive for calcitonin gene-related peptide. Following tracer injection into the EOM nuclei, we observed tracer-positive palisade endings that exhibited choline acetyl transferase immunoreactivity. The tracer-positive nerve fibers supplying palisade endings also established motor terminals along the muscle fibers, as demonstrated by α-bungarotoxin. Neither the trigeminal ganglion nor the ophthalmic branch of the trigeminal nerve contained cholinergic elements. This study confirms that palisade endings originate in the EOM motor nuclei and further indicates that they are extensions of the axons supplying the muscle fiber related to the palisade. The present work excludes the possibility that they receive cholinergic trigeminal projections. These findings call into doubt the proposed proprioceptive function of palisade endings.
authors: Center of Anatomy and Cell Biology, Integrative Morphology Group, Medical University Vienna, A-1090 Vienna, Austria.
authors: Lars
authors: L
authors: Zimmermann
authors: Camilo J
authors: CJ
authors: Morado-Díaz
authors: María A
authors: MA
authors: Davis-López de Carrizosa
authors: Rosa R
authors: RR
authors: de la Cruz
authors: Paul J
authors: PJ
authors: May
authors: Johannes
authors: J
authors: Streicher
authors: Ángel M
authors: ÁM
authors: Pastor
authors: Roland
authors: R
authors: Blumer
mesh_terms: D000010:Abducens Nerve / Q000166:cytology / Q000502:physiology; D000818:Animals; D001369:Axons / Q000502:physiology*; D002038:Bungarotoxins; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D002415:Cats; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D007150:Immunohistochemistry; D009046:Motor Neurons / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D009411:Nerve Endings / Q000502:physiology; D009801:Oculomotor Muscles / Q000294:innervation / Q000502:physiology*; D010275:Parasympathetic Nervous System / Q000502:physiology; D011434:Proprioception / Q000502:physiology; D014276:Trigeminal Nerve / Q000166:cytology
chemical_list: D002038:Bungarotoxins; D002795:Choline O-Acetyltransferase; D015740:Calcitonin Gene-Related Peptide