Neuroscience
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A selective GABA(B) receptor agonist, baclofen, is known to suppress neuropathic pain. In the present study, we investigated the effect of baclofen on the excitability of trigeminal root ganglion (TRG) neurons by using the whole cell and perforated patch-clamp recording techniques. Under voltage-clamp (V(h)=-60 mV), voltage-dependent K(+) currents were recorded in the small diameter TRG neurons (<30 microm) and isolated by blocking Na(+) and Ca(2+) currents with appropriate ion replacement. ⋯ Application of baclofen reduced action potential duration evoked by a depolarization current pulse. These results indicated that activation of GABA(B) receptors inhibits the excitability of rat small diameter TRG neurons and this inhibitory action is mediated by potentiation of voltage-dependent K(+) currents. We therefore concluded that modification of nociceptive transmission in the trigeminal system by activation of GABA(B) receptors occurs at the level of small TRG neuron cell bodies and/or their primary afferent terminals, which are potential targets of analgesia by baclofen.
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Comparative Study
Expression of axon guidance molecules and their related genes during development and sexual differentiation of the olfactory bulb in rats.
Axon guidance molecules and related proteins such as semaphorin 3A, neuropilin-1, plexin-1, netrin-1, growth-associated protein, olfactory marker protein, cypin and collapsin response mediator proteins guide the development of neural circuits in the olfactory bulb. In this study, transcriptions of these genes were examined in the olfactory bulb of female, male and neonatal testosterone propionate-treated female rats at the ages of 2, 5, 10, 15, 20, 25, 30 and 45 days. The semaphorin 3A, neuropilin-1, growth-associated protein and collapsin response mediator protein 1-5 genes were expressed significantly higher during the early development stages than in adulthood while the opposite is true for the olfactory marker protein. ⋯ A late effect of the neonatal testosterone propionate treatment on netrin-1, growth-associated protein, olfactory marker protein, collapsin response mediator proteins 1, 3, 4 and cypin gene expression was observed. The expression profiles of collapsin response mediator proteins and their related genes in the developing olfactory bulb confirmed most studies on the relationship between collapsin response mediator proteins and development in the brain. Sex differences of semaphorin 3A, neuropilin-1 as well as collapsin response mediator protein 3 at the early development stage and the late effect of neonatal testosterone propionate treatment on the expressions of netrin-1, growth-associated marker protein, cypin and collapsin response mediator proteins 1, 3 and 5 genes may indicate a possible role of these molecules on sexual differentiation of the olfactory bulb.
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The median raphe nucleus is involved in controlling and maintaining hippocampal activity through its projection to inhibitory neurons in medial septum and hippocampus. It has been shown that anterogradely axonal-traced fibers originating in the median raphe nucleus project onto calbindin-containing neurons in hippocampus and parvalbumin-containing neurons in medial septum. Parallel immunohistochemistry studies showing serotonin fibers contacting calbindin- and parvalbumin-positive neurons have led to the assumption that raphe fibers projecting on these types of neurons are mainly serotonergic. ⋯ By use of triple immunofluorescence-labeling we analyzed the serotonergic content of the biotin dextran amine-labeled fibers contacting parvalbumin- and calbindin-positive neurons. Surprisingly, we found a significant non-serotonergic projection from both dorsal and median raphe nuclei onto calbindin- and parvalbumin-containing interneurons in septum and hippocampus, with a preference in hippocampus for projecting onto calbindin-positive neurons. These results indicate that the raphe nuclei may exert their control on hippocampal and septal activity not only through a serotonergic projection, but also through a significant non-serotonergic pathway.
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Leptin is a 16 kDa hormone that is produced by adipose tissue and has a central effect on food intake and energy homeostasis. The ability of leptin to cross the blood-brain and blood-cerebrospinal fluid (CSF) barriers and reach or leave the CNS was studied by the bilateral in situ brain perfusion and isolated incubated choroid plexus techniques in the rat. Brain perfusion results indicated that [(125)I]leptin reached the CNS at higher concentrations than the vascular marker, confirming that [(125)I]leptin crossed the brain barriers. ⋯ Studies using the incubated rat choroid plexus model found that [(125)I]leptin could cross the apical membrane of the choroid plexus to leave the CSF. However, this movement was not sensitive to unlabelled human leptin or specific transport inhibitors/modulators (including probenecid, digoxin, deltorphin II, progesterone and indomethacin). This study supports the concept of brain-barrier regulation of leptin distribution to the CNS, and highlights an important link between leptin and the cerebellum.
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It was previously shown that tyrosine hydroxylase (TH) immunoreactivity in the terminals of the lateral efferents of the cochlea is decreased by acoustic trauma and that sound preconditioning counteracted this decrease [Hear Res 174 (2002) 124]. Here we identify those neurons in the lateral olivocochlear system (LOC) in the brainstem that regulates the peripheral expression of TH in the cochlea. By employing retrograde tracing techniques, dextran-labeled neurons were found predominantly in the ipsilateral LOC system including lateral superior olive (LSO), and the surrounding periolivary regions (dorsal periolivary nucleus [DPO], dorsolateral periolivary nucleus [DLPO], lateral nucleus of trapezoid body [LNTB]). ⋯ Sound conditioning protected against the decrease of TH immunolabeling by acoustic trauma and increased the fiber staining for TH in the LSO and DLPO, but not in the DPO or the LNTB. These results provide evidence that TH positive neurons are present in the LOC system in the guinea-pig. It is now demonstrated that protection against acoustic trauma by sound conditioning has a central component that is governed by TH in the LSO and the surrounding periolivary DLPO region.