Neuroscience research
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Neuroscience research · Aug 2009
Thiamylal antagonizes the inhibitory effects of dorsal column stimulation on dorsal horn activities in humans.
In humans, peripheral somatosensory information converges upon dorsal horn neurons in the spinal cord, which can be recorded from the dorsal epidural space as spinal cord potentials (SCPs) following segmental dorsal root stimulation (SS) employing epidural catheter electrodes. Antidromic action potentials and descending inhibition from the dorsolateral funiculus may contribute to SCPs following dorsal column stimulation (DCS). Effects of thiamylal (2.5-7.5 mg/kg, i.v.) on SCPs evoked by independent DCS or SS were compared with those evoked by simultaneous DCS and SS (DCS/SS). ⋯ In awake subjects, N and P potentials produced by simultaneous DCS/SS were significantly smaller than the sum of independent responses. Thiamylal anesthesia antagonized this inhibition; responses to simultaneous DCS/SS were larger than the sum of independent responses. These results suggest that in wakefulness DCS inhibits dorsal horn neuron activity in the lumbar spinal cord, while thiamylal antagonizes DCS-induced inhibition in dose-dependent fashion.
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Neuroscience research · Mar 2009
Prefrontal and medial temporal contributions to episodic memory-based reasoning.
Episodic memory retrieval and reasoning are fundamental psychological components of our daily lives. Although previous studies have investigated the brain regions associated with these processes separately, the neural mechanisms of reasoning based on episodic memory retrieval are largely unknown. Here, we investigated the neural correlates underlying episodic memory-based reasoning using functional magnetic resonance imaging (fMRI). ⋯ In addition, activations predominant in the linking process between the two were found in the left dorsal and right ventral PFC. These findings suggest that episodic memory-based reasoning is composed of at least three processes, i.e., reasoning, episodic memory retrieval, and linking processes between the two, and that activation of both the PFC and MTL is crucial in episodic memory-based reasoning. These findings are the first to demonstrate that PFC and MTL regions contribute differentially to each process in episodic memory-based reasoning.
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Neuroscience research · Jan 2009
Comparative StudyEffects of intrathecal administration of newer antidepressants on mechanical allodynia in rat models of neuropathic pain.
Antidepressants, especially tricyclic antidepressants (TCAs) are widely used for the treatment of various types of chronic and neuropathic pain. The antinociceptive effects of TCAs are, however, complicated. Therefore, two kinds of newer antidepressants whose functions have been more fully clarified were selected, milnacipran, a serotonin and noradrenaline reuptake inhibitor (SNRI) and paroxetine and fluvoxamine, which are selective serotonin reuptake inhibitors (SSRIs). ⋯ The intrathecal administration of milnacipran had an antiallodynic effect in both CCI and STZ-induced diabetic rats in a dose-dependent manner. On the other hand, the intrathecal administration of either paroxetine or fluvoxamine elicited little antiallodynic effect in CCI rats, while both SSRIs had antiallodynic effects in the STZ-induced diabetic rats in a dose-dependent manner. These results indicate a considerable difference to exist in the development and/or maintenance between these two animal models of neuropathic pain and suggest that each of these three antidepressants may be effective for the treatment of diabetic neuropathic pain.
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Neuroscience research · Dec 2008
Neuroanatomical and neurochemical organization of projections from the central amygdaloid nucleus to the nucleus retroambiguus via the periaqueductal gray in the rat.
The periaqueductal gray (PAG)-nucleus retroambiguus (NRA) pathway has been known to be involved in the control of vocalization and sexual behavior. To know how the amygdaloid complex influences the PAG-NRA pathway, here we first examined the synaptic organization between the central amygdaloid nucleus (CeA) fibers and the PAG neurons that project to the NRA by using anterograde and retrograde tract-tracing techniques in the rat. After ipsilateral injections of biotinylated dextran amine (BDA) into the CeA and cholera toxin B subunit (CTb) into the NRA, the prominent overlapping distribution of BDA-labeled axon terminals and CTb-labeled neurons was found ipsilaterally in the lateral/ventrolateral PAG, where some of the BDA-labeled terminals made symmetrical synaptic contacts with somata and dendrites of the CTb-labeled neurons. ⋯ After BDA injection into the lateral/ventrolateral PAG, BDA-labeled fibers were distributed mainly in and around the NRA within the medulla oblongata. Using a combined retrograde tracing and in situ hybridization technique, we further demonstrated that more than half of the CeA neurons labeled with Fluoro-Gold (FG) injected into the lateral/ventrolateral PAG were positive for glutamic acid decarboxylase 67 mRNA and that the vast majority of PAG neurons labeled with FG injected into the NRA expressed vesicular glutamate transporter 2 mRNA. The present results suggest that the glutamatergic PAG-NRA pathway is under the inhibitory influence of the GABAergic CeA neurons.
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Neuroscience research · Nov 2008
Contribution of TRPV1 to the bradykinin-evoked nociceptive behavior and excitation of cutaneous sensory neurons.
Bradykinin (BK), a major inflammatory mediator, excites and sensitizes nociceptor neurons/fibers, thus evoking pain and hyperalgesia. The cellular signaling mechanisms underlying these actions have remained unsolved, especially in regard to the identity of channels that mediate acute excitation. Here, to clarify the contribution of transient receptor potential vanilloid 1 (TRPV1), a heat-sensitive ion channel, to the BK-evoked nociceptor excitation and pain, we examined the behavioral and physiological BK-responses in TRPV1-deficient (KO) mice. ⋯ BK clearly increased intracellular calcium in cultured dorsal root ganglion (DRG) neurons of TRPV1-KO mice, although the incidence of BK-sensitive neurons was reduced. BK has been reported to activate TRPA1 indirectly, yet a considerable part of BK-sensitive DRG neurons did not respond to a TRPA1 agonist, mustard oil. These results suggest that BK-evoked nociception/nociceptor response would not be simply explained by activation of TRPV1 and A1, and that BK-evoked nociceptor excitation would be mediated by several ionic mechanisms.