The Journal of comparative neurology
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In the rabbit retina there are two types of horizontal cell (HC). A-type HCs (AHC) are axonless and extensively coupled via connexin (Cx)50 gap junctions. The B-type HC (BHC) is axon-bearing; the somatic dendrites form a second network coupled by gap junctions while the axon terminals (ATs) form a third independent network in the outer plexiform layer (OPL). ⋯ We conclude that in the rabbit retina, Cx57 is only found on BHC-AT processes. Thus, in species where there are two types of HC, different connexins are expressed. The absence of Cx57 labeling in the somatic dendrites of B-type HCs suggests the possibility of an additional unidentified HC connexin in the rabbit.
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Cortical and subcortical inputs to the striatum are functionally highly organized and they obey to some extent striatal patch-matrix topography. Whether this organization is reflected in the density of various glutamatergic endings is unknown. We therefore mapped boutons expressing the vesicular glutamate transporters VGluT1 and VGluT2, together with boutons immunoreactive for vesicular γ-aminobutyric acid (GABA) transporter (VGAT) in patch and matrix throughout the striatum. ⋯ In contrast, VGluT2 showed a global increase in density from lateral to medial and a relatively high density in the ventral striatum. VGAT appeared more evenly distributed in the striatal patch-matrix than the VGluTs, with a tendency of bouton density to increase from medial to lateral. We noted a good correlation between the high VGluT1 bouton density dorsomedially with inputs from dorsal medial prefrontal cortex and related thalamic regions, and the enhanced VGluT2 input ventromedially with input from ventral medial prefrontal cortex and thalamic, amygdaloid, and hippocampal sources.
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This study examined the distribution of γ-aminobutyric acid (GABA)(B) receptors on immunohistochemically identified neurons, and levels of GABA(B(1)) and GABA(B(2)) mRNA, in the L4 and L5 dorsal root ganglia (DRG) of the rat in the absence of injury and 2 weeks after L5 spinal nerve ligation. In uninjured DRG, GABA(B(1)) immunoreactivity colocalized exclusively with the neuronal marker (NeuN) and did not colocalize with the satellite cell marker S-100. The GABA(B(1)) subunit colocalized to >97% of DRG neurons immunoreactive (IR) for neurofilament 200 (N52) or calcitonin gene-related peptide (CGRP), or labeled by isolectin B4 (IB4). ⋯ Ligation also decreased levels of GABA(B(1)) and GABA(B(2)) mRNA in the L5, but not the L4 DRG compared with sham-operated or naïve rats. These findings indicate that the GABA(B) receptor is positioned to presynaptically modulate afferent transmission by myelinated, unmyelinated, and peptidergic afferents in the dorsal horn. Loss of GABA(B) receptors on primary afferent neurons may contribute to the development of mechanical allodynia after L5 spinal nerve ligation.
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Inhibitory and excitatory synaptic inputs onto trigeminal motoneurons play an important role in coordinating jaw movements. Previously, we reported that the phenotype of the inhibitory boutons apposing the somata of jaw-closing (JC) motoneurons changes from γ-aminobutyric acid (GABA)-positive (GABA+) to predominantly glycine-positive (Gly+) during development. In the present study, we investigated the development of inhibitory and excitatory boutons apposing antagonistic jaw-opening (JO) motoneurons (anterior digastric motoneurons) at postnatal day 2 (P2), P11, and P31 in the rat. ⋯ The fraction of GABA+ boutons decreased by 86% and the fraction of GABA+/Gly+ boutons increased by 200% from P11 to P31, suggesting a switch from GABA+ to GABA+/Gly+ phenotype. The fraction of Gly+ boutons remained unchanged. These results indicate that inhibitory synapses onto somata of JO motoneurons exhibit a developmental pattern distinct from that of synapses onto JC motoneurons, which may reflect distinctive maturation of oral motor system.
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Comparative Study
Pre-Bötzinger complex receives glutamatergic innervation from galaninergic and other retrotrapezoid nucleus neurons.
The retrotrapezoid nucleus (RTN) contains CO(2) -responsive neurons that regulate breathing frequency and amplitude. These neurons (RTN-Phox2b neurons) contain the transcription factor Phox2b, vesicular glutamate transporter 2 (VGLUT2) mRNA, and a subset contains preprogalanin mRNA. We wished to determine whether the terminals of RTN-Phox2b neurons contain galanin and VGLUT2 proteins, to identify the specific projections of the galaninergic subset, to test whether RTN-Phox2b neurons contact neurons in the pre-Bötzinger complex, and to identify the ultrastructure of these synapses. ⋯ Their boutons (n = 48) formed asymmetric synapses filled with small clear vesicles. In summary, RTN-Phox2b neurons, including the galaninergic subset, selectively innervate the respiratory pattern generator plus a portion of the dorsolateral pons. RTN-Phox2b neurons establish classic excitatory glutamatergic synapses with pre-Bötzinger complex neurons presumed to generate the respiratory rhythm.