The European journal of neuroscience
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Using immunohistochemistry and in situ hybridization, we studied changes in expression of some neuropeptides in large and medium-sized neurons in lumbar 4 and 5 rat dorsal root ganglia projecting to the gracile nucleus, in response to peripheral axotomy. Fourteen days after unilateral sciatic nerve transection, many large neurons and some medium-sized neurons in ipsilateral dorsal root ganglia were strongly neuropeptide Y-positive. Galanin-, vasoactive intestinal polypeptide (VIP)- and peptide histidine-isoleucine (PHI)-like immunoreactivities coexisted with neuropeptide Y-like immunoreactivity in some of these neurons. ⋯ Neuropeptide Y-like immunoreactivity colocalized with galanin- or VIP/PHI-like immunoreactivity in some nerve fibres. None of these neuropeptide immunoreactivities could be detected in nerve fibres and terminals in the control or contralateral gracile nucleus. These findings suggest that neuropeptides, in addition to their role in small dorsal root ganglion neurons, may have a function in large and medium-sized dorsal root ganglion neurons projecting to laminae III and IV in the dorsal horn as well as to the gracile nuclei, as a part of their response to peripheral axotomy.
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We have studied the somatotopic reorganization in dorsal horn neurons after a disruption in the normal spatial arrangement of primary sensory axons in adult rats. Muscle afferents were redirected to skin by cutting and cross-anastomosing the hindlimb gastrocnemius nerve (GN) and sural nerve (SN). It has previously been shown that after 10-12 weeks GN afferents innervate the hairy skin of the lateral ankle and calf (previously innervated by SN afferents) and become potentially capable of relaying information on the location and intensity of stimuli applied to the skin. ⋯ Furthermore, for many neurons, receptive fields were formed from inappropriately regrown GN afferents and adjacent intact cutaneous afferents (in the tibial or common peroneal nerves). Therefore, when GN afferents innervate skin in adult animals, they alter their central connectivity in an appropriate manner for their new peripheral terminations, so that an orderly somatotopic representation of the hind limb skin is maintained. We suggest that this plasticity of dorsal horn somatotopy is driven in part by activity-dependent mechanisms.
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The aim of the present work was to determine if noradrenergic neurons of the anterior and the posterior subregions of the locus coeruleus exhibit a difference in reactivity in response to sodium nitroprusside-induced arterial hypotension, and if the pharmacological induction of tyrosine hydroxylase by RU24722 modifies the reactivity of locus coeruleus neurons to this hypotensive stimulus. Previous findings have demonstrated that administration of RU24722 increases the concentration of tyrosine hydroxylase in the rat locus coeruleus by two different mechanisms in the anterior and in the posterior locus coeruleus subregions. The goal of the present study was to measure in vivo the changes in catecholaminergic metabolism in the locus coeruleus after treatment with RU24722 using differential normal pulse voltammetry (DNPV). ⋯ In the RU24722-pretreated rats, there was a 39% increase in tyrosine hydroxylase and dihydroxyphenylacetic acid in the locus coeruleus. The functional reactivity to hypotension measured by DNPV was significantly decreased (P < 0.001) in both the anterior and posterior locus coeruleus subregions with RU24722 treatment. Therefore, this study suggests that the response of locus coeruleus cells to a hypotensive stimulus depends upon the intracellular tyrosine hydroxylase concentration both in the basal condition and during pharmacological induction of tyrosine hydroxylase gene expression.