Neuroscience research
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Neuroscience research · Oct 2001
Inhibitory effect of histamine on axonal transport in cultured mouse dorsal root ganglion neurons.
Histamine is important in mediating peripheral sensory information such as inflammation, allergic hypersensitivity, and itch. In the present study, using video-enhanced microscopy, we investigated the effect of histamine on axonal transport in cultured dorsal root ganglion (DRG) neurons of the mouse. Application of histamine (100 microM) reversibly reduced the number of particles transported within neurites in both anterograde and retrograde directions. ⋯ Pretreatment with a combination of pyrilamine (1 microM) and thioperamide (1 microM) completely blocked the response to histamine. The H(2)-receptor antagonist cimetidine (1 microM) was ineffective. These results suggest that histamine inhibits axonal transport of cultured mouse DRG neurons via the activation of H(1)- and H(3)-receptors.
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Neuroscience research · Aug 2001
Somatic noxious mechanical stimulation induces Fos expression in the postsynaptic dorsal column neurons in laminae III and IV of the rat spinal dorsal horn.
This study was conducted to ascertain the possible expression of Fos-like immunoreactivity (Fos-LI) in the postsynaptic dorsal column (PSDC) neurons in response to noxious mechanical stimulation of the forepaw glabrous area of normal rats. For this purpose, Fos immunohistochemistry along with Fluoro-Gold (FG) retrograde tracing was utilized. After repeated noxious pinching of the forepaw glabrous area, there was a marked increase in number of Fos-LI neurons in the dorsal horn, including Rexed's laminae III and IV, at C5-T1 spinal cord segments ipsilateral to the stimulation. ⋯ At segment C6 or C7, double-labeled neurons made up about 10% of the PSDC neurons that projected their axons to the cuneate nucleus. Most of the double-labeled neurons appeared fusiform with their primary dendrites projected dorso-ventrally. The present results suggest that the morphologically distinct, subclasses of PSDC neurons in spinal laminae III and IV may contribute to the central transmission of mechanical nociceptive information through the dorsal column into the cuneate nucleus.
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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.
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Neuroscience research · Dec 2000
Is narcolepsy a REM sleep disorder? Analysis of sleep abnormalities in narcoleptic Dobermans.
Narcolepsy is a chronic sleep disorder marked by excessive daytime sleepiness, cataplexy, sleep paralysis, and hypnagogic hallucinations. Since the discovery of sleep onset REM periods (SOREMPs) in narcoleptic patients, narcolepsy has often been regarded as a disorder of REM sleep generation: REM sleep intrudes in active wake or at sleep onset, resulting in cataplexy, sleep paralysis, or hypnagogic hallucinations. However, this hypothesis has not been experimentally verified. ⋯ Stimulation of a cholinoceptive site in the basal forebrain induces a long-lasting attack of cataplexy in narcoleptic dogs; however, bursts of rapid eye movements during this state still occur with a 30 min cyclicity. Sites and mechanisms for triggering cataplexy may therefore be different from those for REM sleep. Cataplexy and a dysfunction in the maintenance of vigilance states, but not abnormal REM sleep generation, may therefore be central to narcolepsy.