The Journal of comparative neurology
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Retrograde labeling has been used to identify sensory neurons in the lumbar dorsal root ganglia (DRG) that innervate the rat tibial periosteum, medullary cavity, and trabecular bone. The size, neurochemical profile [isolectin B4 (IB4) binding, substance P (SP), calcitonin gene-related peptide (CGRP), and NF200 immunoreactivity (-IR)], and segmental distribution of sensory neurons innervating each of these bony compartments are reported. After injections of fast blue into the periosteum, medullary cavity, and trabecular bone (epiphysis), retrogradely labeled neurons were observed throughout the ipsilateral (but not contralateral) lumbar DRG. ⋯ The percentage of CGRP-IR neurons innervating bone was significantly lower than the percentage of CGRP-IR neurons innervating skin (ANOVA; P < 0.05). No other significant differences in the neurochemical profiles of neurons labeled from bone vs. skin were observed. The findings of the present study show that the periosteum, medullary cavity, and trabecular bone are all innervated by sensory neurons that have size and neurochemical profiles consistent with a role in nociception.
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The retrotrapezoid nucleus (RTN) contains noncholinergic noncatecholaminergic glutamatergic neurons that express the transcription factor Phox2b (chemically coded or "cc" RTN neurons). These cells regulate breathing and may be central chemoreceptors. Here we explore their ultrastructure and their acid sensitivity by using two novel BAC eGFP-Phox2b transgenic mice (B/G, GENSAT JX99) in which, respectively, 36% and 100% of the cc RTN neurons express the transgene in complete or partial anatomical isolation from other populations of eGFP neurons. ⋯ Terminals on more distal eGFP dendrites formed preferentially asymmetric, presumably excitatory, synapses. In sum, C1 cells are pH insensitive, whereas cc RTN neurons are uniformly acid sensitive. The RTN neurons receive inhibitory and excitatory synaptic inputs and may have unfettered biochemical interactions with glial cells and the local microvasculature.
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To characterize neuronal pathways that release opioid peptides in the rat dorsal horn, multiple-label immunohistochemistry, confocal microscopy, and computerized co-localization measures were used to characterize opioid-containing terminals and cells. An antibody that selectively recognized beta-endorphin labeled fibers and neurons in the ventral horn as well as fibers in the lateral funiculus and lamina X, but practically no fibers in the dorsal horn. An anti-enkephalin antibody, which recognized Leu-, Met-, and Phe-Arg-Met-enkephalin, labeled the dorsolateral funiculus and numerous puncta in laminae I-III and V of the dorsal horn. ⋯ The prodynorphin-positive neurons in the dorsal horn were distinct from neurons expressing mu-opioid receptors, neurokinin 1 receptors, and protein kinase C-gamma. These results show that enkephalins and dynorphins are present in different populations of dorsal horn neurons. In addition, dynorphin is present in some C-fibers.