H Sun

Publications (4)6.76 Total impact

• Article: The physiological role of pre- and postsynaptic GABA(B) receptors in membrane excitability and synaptic transmission of neurons in the rat's dorsal cortex of the inferior colliculus.

  H Sun, S H Wu
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  ABSTRACT: In the inferior colliculus (IC), GABAergic inhibition mediated by GABA(A) receptors has been shown to play a significant role in regulating physiological responses, but little is known about the physiological role of GABA(B) receptors in IC neurons. In the present study, we used whole-cell patch clamp recording in vitro to investigate the effects of activation of GABA(B) receptors on membrane excitability and synaptic transmission of neurons in the rat's dorsal cortex of the inferior colliculus (ICD). Repetitive stimulation of GABAergic inputs to ICD neurons at high frequencies could elicit a slow and long-lasting postsynaptic response, which was reversibly abolished by the GABA(B) receptor antagonist, CGP 35348. The results suggest that postsynaptic GABA(B) receptors can directly mediate inhibitory synaptic transmission in ICD. The role of postsynaptic GABA(B) receptors in regulation of membrane excitability was further investigated by application of the GABA(B) receptor agonist, baclofen. Baclofen hyperpolarized the cell, reduced the membrane input resistance and firing rate, increased the threshold for generating action potentials (APs), and decreased the amplitude of the AP and its associated after-hyperpolarization. The Ca2+-mediated rebound depolarization following hyperpolarization and the depolarization hump at the beginning of membrane depolarization were also suppressed by baclofen. In voltage clamp experiments, baclofen induced inward rectifying K+ current and reduced low- and high-threshold Ca2+ currents, which may account for the suppression of membrane excitability by postsynaptic GABA(B) receptors. Application of baclofen also reduced excitatory synaptic responses mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, and inhibitory synaptic responses mediated by GABA(A) receptors. Baclofen increased the ratios of 2nd/1st excitatory and inhibitory postsynaptic currents to paired-pulse stimulation of the synaptic inputs. These results suggest that fast glutamatergic and GABAergic synaptic transmission in ICD can be modulated by presynaptic GABA(B) receptors.
  Neuroscience 05/2009; 160(1):198-211. · 3.38 Impact Factor
• Article: Modification of membrane excitability of neurons in the rat's dorsal cortex of the inferior colliculus by preceding hyperpolarization.

  H Sun, S H Wu
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  ABSTRACT: The inferior colliculus (IC) is among the largest nuclei in the central auditory system and is considered to be a major integration center in the auditory pathway. To understand how IC contributes to auditory processing, we investigated the effects of preceding hyperpolarization on membrane excitability and firing behavior of neurons located in the dorsal cortex of the inferior colliculus (ICD). We made whole-cell patch clamp recordings from ICD neurons (n=96) in rat brain slices. We classified ICD neurons into three types, i.e. sustained-regular, sustained-adapting and buildup, according to their responses to depolarizing current injection. Nearly 91% of the neurons had sustained firing throughout the period of current injection, showing either regular or adapting pattern. About 9% of the neurons exhibited a buildup pattern, in which sustained firing started after a long delay. Rebound depolarization and spikes after hyperpolarization were seen in 51.7% of the sustained neurons, but were not seen in buildup neurons. When depolarizing current was preceded by a hyperpolarizing current, various forms of the modification on membrane excitability were observed. For non-rebound neurons, the membrane excitability was either suppressed or unchanged after pre-hyperpolarization. The first spike latency lengthened in neurons whose firing changed to a buildup pattern, shortened in those whose firing changed to a pauser pattern, and remained unchanged in those whose discharge pattern remained sustained. For rebound neurons, the firing rate decreased in neurons whose firing pattern was changed to onset or pauser, increased in neurons whose firing was changed to adapting, or remained unchanged in neurons whose firing became irregular. The first spike latency was shortened in all the rebound cells. The results suggest that intrinsic membrane properties can play an important role in integration of excitatory and inhibitory inputs and thereby in determination of the output of ICD neurons.
  Neuroscience 07/2008; 154(1):257-72. · 3.38 Impact Factor
• Article: Modification of membrane excitability of neurons in the rat's dorsal cortex of the inferior colliculus by preceding hyperpolarization

  H. Sun, S.H. Wu
  [show abstract] [hide abstract]
  ABSTRACT: The inferior colliculus (IC) is among the largest nuclei in the central auditory system and is considered to be a major integration center in the auditory pathway. To understand how IC contributes to auditory processing, we investigated the effects of preceding hyperpolarization on membrane excitability and firing behavior of neurons located in the dorsal cortex of the inferior colliculus (ICD). We made whole-cell patch clamp recordings from ICD neurons (n=96) in rat brain slices. We classified ICD neurons into three types, i.e. sustained-regular, sustained-adapting and buildup, according to their responses to depolarizing current injection. Nearly 91% of the neurons had sustained firing throughout the period of current injection, showing either regular or adapting pattern. About 9% of the neurons exhibited a buildup pattern, in which sustained firing started after a long delay. Rebound depolarization and spikes after hyperpolarization were seen in 51.7% of the sustained neurons, but were not seen in buildup neurons. When depolarizing current was preceded by a hyperpolarizing current, various forms of the modification on membrane excitability were observed. For non-rebound neurons, the membrane excitability was either suppressed or unchanged after pre-hyperpolarization. The first spike latency lengthened in neurons whose firing changed to a buildup pattern, shortened in those whose firing changed to a pauser pattern, and remained unchanged in those whose discharge pattern remained sustained. For rebound neurons, the firing rate decreased in neurons whose firing pattern was changed to onset or pauser, increased in neurons whose firing was changed to adapting, or remained unchanged in neurons whose firing became irregular. The first spike latency was shortened in all the rebound cells. The results suggest that intrinsic membrane properties can play an important role in integration of excitatory and inhibitory inputs and thereby in determination of the output of ICD neurons.
  Neuroscience.
• Article: The physiological role of pre- and postsynaptic GABAB receptors in membrane excitability and synaptic transmission of neurons in the rat's dorsal cortex of the inferior colliculus

  H. Sun, S.H. Wu
  [show abstract] [hide abstract]
  ABSTRACT: In the inferior colliculus (IC), GABAergic inhibition mediated by GABAA receptors has been shown to play a significant role in regulating physiological responses, but little is known about the physiological role of GABAB receptors in IC neurons. In the present study, we used whole-cell patch clamp recording in vitro to investigate the effects of activation of GABAB receptors on membrane excitability and synaptic transmission of neurons in the rat's dorsal cortex of the inferior colliculus (ICD). Repetitive stimulation of GABAergic inputs to ICD neurons at high frequencies could elicit a slow and long-lasting postsynaptic response, which was reversibly abolished by the GABAB receptor antagonist, CGP 35348. The results suggest that postsynaptic GABAB receptors can directly mediate inhibitory synaptic transmission in ICD. The role of postsynaptic GABAB receptors in regulation of membrane excitability was further investigated by application of the GABAB receptor agonist, baclofen. Baclofen hyperpolarized the cell, reduced the membrane input resistance and firing rate, increased the threshold for generating action potentials (APs), and decreased the amplitude of the AP and its associated after-hyperpolarization. The Ca2+-mediated rebound depolarization following hyperpolarization and the depolarization hump at the beginning of membrane depolarization were also suppressed by baclofen. In voltage clamp experiments, baclofen induced inward rectifying K+ current and reduced low- and high-threshold Ca2+ currents, which may account for the suppression of membrane excitability by postsynaptic GABAB receptors. Application of baclofen also reduced excitatory synaptic responses mediated by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, and inhibitory synaptic responses mediated by GABAA receptors. Baclofen increased the ratios of 2nd/1st excitatory and inhibitory postsynaptic currents to paired-pulse stimulation of the synaptic inputs. These results suggest that fast glutamatergic and GABAergic synaptic transmission in ICD can be modulated by presynaptic GABAB receptors.
  Neuroscience.