The Journal of comparative neurology
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Phox2b is required for development of the peripheral autonomic nervous system and a subset of cranial nerves and lower brainstem nuclei. Phox2b mutations in man cause diffuse autonomic dysfunction and deficits in the automatic control of breathing. Here we study the distribution of Phox2b in the adult rat hindbrain to determine whether this protein is selectively expressed by neurons involved in respiratory and autonomic control. ⋯ In adult rats, Phox2b is neither a comprehensive nor a selective marker of hindbrain autonomic pathways. This marker identifies a subset of hindbrain neurons that control orofacial movements (dorsomedial spinal trigeminal nucleus, pontine peritrigeminal neurons), balance and auditory function (vestibulocochlear efferents), the eyes, and both divisions of the autonomic efferent system. Phox2b is virtually absent from the respiratory rhythm and pattern generator (VRC and dorsolateral pons) but is highly expressed by neurons involved in the chemical drive and reflex regulation of this oscillator.
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The reorganizations of the overall intrinsic glutamatergic and gamma-aminobutyric acid (GABA)-ergic hippocampal networks as well as the time course of these reorganizations during development of pilocarpine-induced temporal lobe epilepsy were studied with in situ hybridization and immunohistochemistry experiments for the vesicular glutamate transporter 1 (VGLUT1) and the vesicular GABA transporter (VGAT). These transporters are particularly interesting as specific markers for glutamatergic and GABAergic neurons, respectively, whose expression levels could reflect the demand for synaptic transmission and their average activity. ⋯ This is illustrated by a recovery of VGLUT1 immunoreactivity in the inner molecular layer and an increased VGLUT1 immunolabeling in the CA1-CA3 dendritic layers. These data indicate that an increased activity of remaining GABAergic interneurons occurs during the latent period, in parallel with the loss of vulnerable glutamatergic and GABAergic neurons preceding the reorganization of glutamatergic networks.
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Correspondence between the nerve composition and the functional characteristics of its fiber populations is not always evident. To investigate such correspondence and to give a systematic picture of the morphology of the rat hind limb nerves, extensive morphometric study was performed on the sciatic nerve, its founding dorsal and ventral spinal roots, and its major branches. Nerve histology was examined in semithin sections via microscopic image analysis. ⋯ It is anticipated that morphological parameters established in this study would advance the development of neural prostheses in humans. The proximodistal correspondences among the fiber populations of different nerves were established by parametric statistical comparisons. The proposed approach provides a conceptual framework for understanding the comparative anatomy of the peripheral nerves and spinal roots and can be further applied in other species.
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Periglomerular (PG) cells in the rodent olfactory bulb are heterogeneous anatomically and neurochemically. Here we investigated whether major classes of PG cells use gamma-aminobutyric acid (GABA) as a neurotransmitter. In addition to three known subtypes of PG cells expressing tyrosine hydroxylase (TH), calbindin D-28k (CB), and calretinin (CR), we identified a novel PG cell population containing the GABAA receptor alpha5 subunit. ⋯ In addition, CB-, CR-, and TH-positive dendrites were apposed to GABAA receptor clusters containing the alpha1 or alpha3 subunits, which are found in mitral and tufted cells, and the alpha2 subunit, which is expressed by PG cells. Together, these findings indicate that all major subtypes of PG cells are GABAergic. In addition, they show that PG cells provide GABAergic input to the dendrites of principal neurons and are interconnected with other GABAergic interneurons, which most likely are other PG cells.
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The actions of Reelin in neuronal positioning in the developing cortex and cerebellum are relayed by Src-family kinase (SFK)-mediated phosphorylation of Dab1. Biochemical studies show that after phosphorylation Dab1 binds to an adaptor protein, CrkL. Whether CrkL is important for Reelin signaling in vivo is unknown, because crkl(-/-) embryos die before cortical development is complete. ⋯ These results show that tyrosine phosphorylation of Dab1 by SFKs is required for Reelin-regulated SPN positioning. In addition, we found that SPN migration in crkl(-/-) showed a partial reeler phenotype, suggesting a partial loss of response of SPN to Reelin signaling. These results suggest a role for CrkL in the Reelin signaling pathway to control neuronal migration.