Neuroscience research
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Neuroscience research · Apr 2001
Tetrodotoxin-resistant conductivity and spinal effects of cutaneous C-fibre afferents in the rat.
The effect of the sodium channel blocking agent tetrodotoxin (TTX) on signal processing in afferent fibres of dorsal roots was tested in Sprague-Dawley rats. TTX applied to the dorsal roots L4-L6 blocked the fast afferent volleys from the sural nerve, which was stimulated electrically with supramaximal strength for A-fibres. Afferent C-fibre compound action potentials (CAPs) elicited by electrical stimulation of the dorsal root L5 peripherally from the TTX block or by electrical stimulation of the sural nerve likewise disappeared from the recording. ⋯ During TTX block, C-fibre potentials could also be recorded from dorsal root filaments after stimulation of the sural nerve or the dorsal root L5 peripherally of the TTX-block. The results suggest that in the axonal membrane of cutaneous C-afferents, both TTX sensitive and TTX-resistant voltage gated sodium channels exist, the latter being responsible for the propagation of signals in a portion of C-fibres after TTX application. The TTX-resistant portion of the afferent potential does not seem to contribute much to the afferent C-fibre CAP before TTX application, but its central effects seem to be overproportionally strong.
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Neuroscience research · Apr 2001
Ultrastructural localization of brain-derived neurotrophic factor in rat primary sensory neurons.
In a previous study we have shown that brain-derived neurotrophic factor (BDNF) is present in a subpopulation of small- to medium-sized sensory neurons in the dorsal root ganglia (DRG) and is anterogradely transported in both the peripheral and central processes. Within the spinal cord, BDNF is localized to varicosities of sensory nerve terminals in laminae I and II of the dorsal horn. This study raised the question of whether BDNF is localized in synaptic vesicles of the afferent nerve terminals. ⋯ Double labelling experiments at the light microscopic level showed that 55% of BDNF immunoreactive neurons in DRG are colocalized with CGRP and many nerve terminals in laminae I and II of the spinal cord contained both BDNF and CGRP immunoreactivities. The results of double labelling at the ultrastructural level showed that most BDNF-ir (immunoreactive) nerve terminals contained CGRP or the low affinity neurotrophin receptor, p75, but not vice versa. These results point to the conclusion that BDNF may be released in parallel with neurotransmitters from nerve terminals in the spinal cord from a subpopulation of nociceptive primary afferents.