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Y S Chan

Publications and source records attributed to Y S Chan.

113 records · Page 7Linked to original sources
PubMedDate not supplied

Bilateral otolith contribution to spatial coding in the vestibular system.

Recent work on the coding of spatial information in central otolith neurons has significantly advanced our knowledge of signal transformation from head-fixed otolith coordinates to space-centered coordinates during motion. In this review, emphasis is placed on the neural mechanisms by which signals generated at the bilateral labyrinths are recognized as gravity-dependent spatial information and in turn as substrate for otolithic reflexes. We first focus on the spatiotemporal neuronal response patterns (i.e. one- and two-dimensional neurons) to pure otolith stimulation, as assessed by single unit recording from the vestibular nucleus in labyrinth-intact animals. These spatiotemporal features are also analyzed in association with other electrophysiological properties to evaluate their role in the central construction of a spatial frame of reference in the otolith system. Data derived from animals with elimination of inputs from one labyrinth then provide evidence that during vestibular stimulation signals arising from a single utricle are operative at the level of both the ipsilateral and contralateral vestibular nuclei. Hemilabyrinthectomy also revealed neural asymmetries in spontaneous activity, response dynamics and spatial coding behavior between neuronal subpopulations on the two sides and as a result suggested a segregation of otolith signals reaching the ipsilateral and contralateral vestibular nuclei. Recent studies have confirmed and extended previous observations that the recovery of resting activity within the vestibular nuclear complex during vestibular compensation is related to changes in both intrinsic membrane properties and capacities to respond to extracellular factors. The bilateral imbalance provides the basis for deranged spatial coding and motor deficits accompanying hemilabyrinthectomy. Taken together, these experimental findings indicate that in the normal state converging inputs from bilateral vestibular labyrinths are essential to spatiotemporal signal transformation at the central otolith neurons during low-frequency head movements.

Animals↗
PubMedDate not supplied

Differential expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate glutamate receptors in the rat striatum during postnatal development.

Alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA)-type glutamate receptors (GluR1-4) are one of the most important ionotropic glutamate receptors in the striatum, a key region of the basal ganglia. The present study investigated the trend of developmental expression of AMPA receptor subunits in the striatum of rats in different developmental stages, i.e., at postnatal day 7 (PND7), PND21 and adult. Perfuse-fixed striatal sections were used. The expression of AMPA subunits was studied by immunofluorescence and reverse transcriptase-polymerase chain reaction (RT-PCR). RT-PCR revealed that the levels of expression of the GluR1 and GluR3 mRNAs were the same among the age groups. The level of GluR2 mRNA was highest in PND21 rats and lowest in adult. The highest level of GluR4 mRNA was detected in rats at PND7. Similar trends of GluR1, GluR2 and GluR2/3 immunoreactivity expression were observed using commercially available specific antibodies. In addition, a large proportion of parvalbumin-immunoreactive GABAergic interneurons in the striatum were found to display GluR1 immunoreactivity in PND21 and adult rats. In contrast, most of the choline acetyltransferase-immunoreactive cholinergic interneurons were found to display GluR2 immunoreactivity but less GluR1 and no GluR2/3 immunoreactivity in PND21 and adult rats. The present study suggests that there is a distinct pattern of expression of AMPA-type receptor mRNAs and proteins in the rat striatum at different stages of development.

Animals↗
PubMedDate not supplied

Relationship of rostral ventrolateral medullary neurons and angiotensin in the central control of blood pressure.

The rostral ventrolateral medulla (RVL) in the medulla oblongata contains a group of vasomotor neurons that regulate the level of arterial blood pressure. That these spinal-projecting neurons were spontaneously active, cardiac-locked and barosensitive further underlies their important role in generating a tonic sympathoexcitatory outflow. In pentobarbital anesthetized spontaneously hypertensive rats (SHR), the electrophysiological behaviours of these sympathoexcitatory cardiovascular neurons were significantly different from those of normotensive Wistar Kyoto rats (WKY). In SHR, there was an equal occurrence of slow-conducting single discharge units and fast-conducting double discharge units while the vast majority of RVL neurons was single discharge units in WKY. Further, the single discharge units of SHR had a higher firing rate and a more regular discharge pattern than those in WKY. The activity of a subpopulation of these RVL cardiovascular neurons was excited by iontophoretic application of angiotensin II, with the magnitude and duration of the excitation greater in SHR than in WKY. Besides, microinjection of [Sar1, Ile8]-angiotensin II, an angiotensin II antagonist, to RVL caused a greater decrease in the firing rate of a subpopulation of RVL cardiovascular neurons in SHR than in WKY. In both types of rats, the neuronal responses were significantly greater in double discharge units than in single discharge units. This was followed by a subsequent depressor response which was significantly greater in SHR than in WKY. These observations demonstrate that in SHR the altered spontaneous electrophysiological property of sympathoexcitatory neurons in the RVL and their augmented sensitivity to the tonic influence of brain angiotensin may contribute to the manifestation of hypertension in this strain of rats.

Anesthesia, General↗
PubMedDate not supplied

Effects of chronic captopril treatment on the electrical-microstimulation-induced blood pressure changes and electrophysiological properties of cardiovascular neurons in the rostral ventrolateral medulla of the spontaneously hypertensive rat.

The effects of chronic treatment with captopril, an angiotensin-converting enzyme inhibitor, on various properties of the rostral ventrolateral medulla (RVL) were studied in spontaneous hypertensive rats (SHR) given captopril (orally at a dose of 30 mg/kg) or vehicle from the age of 4-5 weeks to 19-20 weeks. In SHR, such a treatment with captopril resulted in an arterial blood pressure similar to that of normotensive Wistar Kyoto rats (WKY). Upon electrical microstimulation of the RVL, the minimal threshold current required to elicit a pressor response in captopril-treated SHR was significantly higher than that observed in SHR. Furthermore, analysis of the discharge pattern of RVL spinal projecting cardiovascular neurons showed a significant difference between captopril-treated and untreated SHR with respect to the proportion of double discharge units and the regularity of single discharge units. These properties of the RVL in captopril-treated SHR were, however, similar to those of WKY. Upon withdrawal of electrical microstimulation, the secondary sustained pressor response characteristic of SHR, but not of WKY, persisted in captopril-treated SHR at a smaller magnitude and a shorter duration. These results indicate that the normalization of arterial blood pressure in SHR upon chronic oral treatment with angiotensin-converting enzyme inhibitor is associated with changes in properties of RVL cardiovascular neurons towards those of WKY. This suggests that brain angiotensin and RVL cardiovascular neurons play interactive roles in the development of hypertension in SHR.

Angiotensin II↗