Study of the formation and distribution of the ansa cervicalis and its clinical significance

The ansa cervicalis is a neural loop in the neck. It is formed by the union of two main nerve roots -i.e., superior and inferior- derived from the ventral rami of the cervical nerves. The aim of this study was to explore the anatomical variations of the ansa cervicalis with a view to preventing accidental injury during surgical procedures. Fifty formalin-fixed cadavers were dissected bilaterally for the ansa cervicalis, in which abnormalities were observed in three cadavers. In one cadaver, the ansa cervicalis was absent and the strap muscles of the neck received their innervations from the vagus nerve. Two cadavers displayed an ansa cervicalis formed by the superior root, which branched out from the vagus nerve instead of the hypoglossal nerve. In recent years, there has been an abundance of techniques utilizing the ansa cervicalis to reinnervate the paralyzed larynx. Because of its proximity to major nerves and vessels of the neck, a good understanding of the topography and morphology of this loop is essential. Any variation in the course, contributing roots or branching pattern of the ansa cervicalis, potentially modifies and complicates the course of procedures relating to this nerve (AU)

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Extrinsic GABAergic innervation of developing neocortical layer 1 in organotypic slice co-cultures.

Afferents from the zona incerta (ZI) of the ventral thalamus contribute to the dense, transient gamma-aminobutyric acid (GABA)ergic fiber plexus in layer 1 of the developing rodent somatosensory cortex. Incertocortical axons contact the distal apical dendrites of postmigratory cortical pyramidal cells. Although recent work has shown that these GABAergic incertocortical fibers are likely to provide widespread fast synaptic excitation of pyramidal cells in layers 2-6 during peak periods of cortical synaptogenesis, little is known about the mechanisms by which these axons project to the neocortex and are confined to layer 1. Here we characterize organotypic slice co-cultures in which a region of embryonic diencephalon containing the ZI is maintained adjacent to a region of embryonic somatosensory cortex. Diencephalic explants from transgenic mice expressing enhanced green fluorescent protein (EGFP) enabled direct visualization of diencephalocortical connections. Isochronic co-cultures exhibited diencephalocortical fiber ingrowth immunoreactive for both GABA and the presynaptic vesicle-associated protein synaptophysin that was restricted to neocortical layer 1. This pattern of lamina-specific diencephalocortical ingrowth occurred irrespective of placement of the afferent explant, and persisted in the absence of action potential activity and GABA(A) receptor activation. Heterochronic co-cultures containing older cortex demonstrated that the cortical explants remain permissive for lamina-specific ingrowth through the first postnatal week. Organotypic slice cocultures provide a system in which to study the mechanisms underlying the layer 1-specific ingrowth of extrinsic GABAergic inputs to the perinatal neocortex.