The Journal of comparative neurology
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A serial forebrain pathway in the songbird brain plays a critical role in vocal learning; Area X of the parolfactory lobe (X) projects to the medial portion of the dorsolateral nucleus of the anterior thalamus (DLM), which in turn projects to the lateral magnocellular nucleus of the anterior neostriatum (IMAN). Lesions of this pathway in juvenile birds disrupt vocal development, whereas identical lesions in adult birds do not influence the production of already learned song. During the course of vocal learning, IMAN undergoes a phase of massive neuronal loss, whereas the neuronal population of X more than doubles. ⋯ We found that DLM axons arrive within lMAN by 15 days of age, prior to both the loss of neurons from lMAN and the onset of vocal production. The volume of anterograde DiI label over lMAN did not change between 15 and 20 days of age, but this volume more than doubled between 20 and 35 days of age. During this phase of exuberant growth, anterograde label matched the dorsal border of lMAN but extended beyond all other borders of lMAN into a surrounding "shell" of parvicellular neurons.(ABSTRACT TRUNCATED AT 250 WORDS)
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We have used anti-nerve growth factor (anti-NGF) [corrected] administration to study the NGF dependency of the reinnervation of denervated skin by sympathetic nerves in the adult rat. Sympathetic pilomotor fields were revealed by electrical stimulation of selected dorsal cutaneous nerves; the affected skin rapidly assumed a "gooseflesh" appearance, sharply demarcated from surrounding unstimulated skin. Examined 2-5 days after section of neighboring nerves, the "isolated" pilomotor field of the spared nerve was found to be coextensive with an area of amine-fluorescent fibers that were associated with pilomotor muscles and blood vessels. ⋯ During such NGF deprivation, fluorescent regenerating fibers were visualized in the nerve trunk. We conclude that even though the regenerating and collaterally sprouting sympathetic fibers probably utilise the same degenerating dermal pathways to reach and functionally reinnervate the same denervated targets, only the collateral sprouting of the uninjured axons is dependent upon endogenous NGF. These findings extend the results described earlier for nociceptive fibers, and suggest that the contrasting dependencies upon growth factors of sprouting and regeneration might apply throughout the adult nervous system.
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The cortical connections of two vestibular fields [parieto-insular vestibular cortex (PIVC) and area 3aV] were studied in the squirrel monkey (Saimiri sciureus) by means of retrograde tracer techniques. Small iontophoretic or pressure injections of horseradish peroxidase (HRP), wheat-germ-HRP, Nuclear Yellow, and Fast Blue were administered to the cytoarchitectonic areas Ri (PIVC), 3aV, the parieto-temporal association area T3, the granular insula (Ig), and the rostral part of area 7 (7ant). The injection sites were physiologically characterized by means of microelectrode recordings and vestibular, optokinetic, or somatosensory stimulation: Area Ri is the region of the parieto-insular vestibular cortex (PIVC) as defined in macaques. ⋯ The cortical system for processing vestibular information about head-in-space movement consists mainly of the reciprocally interconnected areas PIVC and 3aV, and most likely of border regions of area 2 and 7ant. This "inner cortical vestibular circuit" also receives signals from two other cortical sensory systems, the somatosensory-proprioceptive system mediated by the primary somatosensory cortex and the visual movement system (optokinetic or visual flow signals). These visual movement signals reach PIVC via area 19 and area T3.(ABSTRACT TRUNCATED AT 400 WORDS)
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Comparative Study
Comparative molecular neuroanatomy of cloned GABAA receptor subunits in the rat CNS.
gamma-Aminobutyric acidA (GABAA) receptors in the mammalian central nervous system (CNS) are members of a family of ligand-gated ion channels consisting of heterooligomeric glycoprotein complexes in synaptic and extrasynaptic membranes. Although molecular cloning studies have identified 5 subunits (with approximately 40% amino acid homology) and isoforms thereof (approximately 70% homology), namely alpha 1-6, beta 1-4, gamma 1-3, delta, and rho, the subunit composition and stoichiometry of native receptors are not known. The regional distribution and cellular expression of GABAA receptor messenger RNAs (mRNAs) in the rat CNS have now been investigated by in situ hybridization histochemistry with subunit-specific 35S-labelled oligonucleotide probes on adjacent cryostat sections. ⋯ In addition, beta 1, beta 3, gamma 1, and delta mRNAs were also uniquely expressed in restricted brain regions. Moreover, in the spinal cord, alpha 1-3, beta 2,3, and gamma 2 mRNAs were differently expressed in Rexed layers 2-9, with alpha 2, beta 3, and gamma 2 transcripts most prominent in motoneurons of layer 9. Although differential protein trafficking could lead to the incorporation of some subunits into somatic membranes and others into dendritic membranes, some tentative conclusions as to the probable composition of native proteins in various regions of the CNS may be drawn.(ABSTRACT TRUNCATED AT 400 WORDS)