6-cyano-7-nitroquinoxaline-2-3-dione and cesium-chloride

The globus pallidus plays a significant role in motor control under both health and pathological states. Recent studies have revealed that hyperpolarization-activated cyclic nucleotide-gated (HCN) channels occupy a critical position in globus pallidus pacemaking activity. Morphological studies have shown the expression of HCN channels in the globus pallidus. To investigate the in vivo effects of HCN channels in the globus pallidus, extracellular recordings and behavioral tests were performed in the present study. In normal rats, micro-pressure ejection of 0.05mM ZD7288, the selective HCN channel blocker, decreased the frequency of spontaneous firing in 21 out of the 40 pallidal neurons. The average decrease was 50.4±5.4%. Interestingly, in another 18 out of the 40 pallidal neurons, ZD7288 increased the firing rate by 137.1±27.6%. Similar bidirectional modulation on the firing rate was observed by a higher concentration of ZD7288 (0.5mM) as well as another HCN channel blocker, CsCl. Furthermore, activation of HCN channels by 8-Br-cAMP increased the firing rate by 63.0±9.3% in 15 out of the 25 pallidal neurons and decreased the firing rate by 46.9±9.4% in another 8 out of the 25 pallidal neurons. Further experiments revealed that modulation of glutamatergic but not GABAergic transmission may be involved in ZD7288-induced increase in firing rate. Consistent with electrophysiological results, further studies revealed that modulation of HCN channels also had bidirectional effects on behavior. Taken together, the present studies suggest that HCN channels may modulate the activity of pallidal neurons by different pathways in vivo.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; 8-Bromo Cyclic Adenosine Monophosphate; Action Potentials; Animals; Cardiotonic Agents; Cesium; Chlorides; Excitatory Amino Acid Antagonists; Globus Pallidus; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; Male; Mice; Mice, Inbred C57BL; Neurons; Posture; Pyrimidines; Rats; Rats, Wistar; Subthalamic Nucleus; Valine; Wakefulness

Fast inhibitory synaptic transmission in the medial vestibular nucleus (MVN) is mediated by GABA(A) receptors (GABA(A)Rs) and glycine receptors (GlyRs). To assess their relative contribution to inhibition in the MVN, we recorded miniature inhibitory postsynaptic currents (mIPSCs) in physiologically characterized type A and type B MVN neurons. Transverse brain stem slices were prepared from mice (3-8 wk old), and whole cell patch-clamp recordings were obtained from visualized MVN neurons (CsCl internal; Vm = -70 mV; 23 degrees C). In 81 MVN neurons, 69% received exclusively GABA(A)ergic inputs, 6% exclusively glycinergic inputs, and 25% received both types of mIPSCs. The mean amplitude of GABA(A)R-mediated mIPSCs was smaller than those mediated by GlyRs (22.6 +/- 1.8 vs. 35.3 +/- 5.3 pA). The rise time and decay time constants of GABA(A)R- versus GlyR-mediated mIPSCs were slower (1.3 +/- 0.1 vs. 0.9 +/- 0.1 ms and 10.5 +/- 0.3 vs. 4.7 +/- 0.3 ms, respectively). Comparison of type A (n = 20) and type B (n = 32) neurons showed that type A neurons received almost exclusively GABA(A)ergic inhibitory inputs, whereas type B neurons received GABA(A)ergic inputs, glycinergic inputs, or both. Intracellular labeling in a subset of MVN neurons showed that morphology was not related to a MVN neuron's inhibitory profile (n = 15), or whether it was classified as type A or B (n = 29). Together, these findings indicate that both GABA and glycine contribute to inhibitory synaptic processing in MVN neurons, although GABA dominates and there is a difference in the distribution of GABA(A) and Gly receptors between type A and type B MVN neurons.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Bicuculline; Biotin; Cesium; Chlorides; Drug Interactions; Electric Impedance; Electric Stimulation; Excitatory Amino Acid Antagonists; Female; GABA Antagonists; gamma-Aminobutyric Acid; Glycine; In Vitro Techniques; Male; Membrane Potentials; Mesylates; Mice; Mice, Inbred C57BL; Neural Inhibition; Neurons; Patch-Clamp Techniques; Sodium Channel Blockers; Synaptic Transmission; Tetrodotoxin; Vestibular Nuclei

The principal cells of the chick tangential nucleus are vestibular nucleus neurons participating in the vestibuloocular and vestibulocollic reflexes. In birds and mammals, spontaneous and stimulus-evoked firing of action potentials is essential for vestibular nucleus neurons to generate mature vestibular reflex activity. The emergence of spike-firing pattern and the underlying ion channels were studied in morphologically-identified principal cells using whole-cell patch-clamp recordings from brain slices of late-term embryos (embryonic day 16) and hatchling chickens (hatching day 1 and hatching day 5). Spontaneous spike activity emerged around the perinatal period, since at embryonic day 16 none of the principal cells generated spontaneous action potentials. However, at hatching day 1, 50% of the cells fired spontaneously (range, 3 to 32 spikes/s), which depended on synaptic transmission in most cells. By hatching day 5, 80% of the principal cells could fire action potentials spontaneously (range, 5 to 80 spikes/s), and this activity was independent of synaptic transmission and showed faster kinetics than at hatching day 1. Repetitive firing in response to depolarizing pulses appeared in the principal cells starting around embryonic day 16, when <20% of the neurons fired repetitively. However, almost 90% of the principal cells exhibited repetitive firing on depolarization at hatching day 1, and 100% by hatching day 5. From embryonic day 16 to hatching day 5, the gain for evoked spike firing increased almost 10-fold. At hatching day 5, a persistent sodium channel was essential for the generation of spontaneous spike activity, while a small conductance, calcium-dependent potassium current modulated both the spontaneous and evoked spike firing activity. Altogether, these in vitro studies showed that during the perinatal period, the principal cells switched from displaying no spontaneous spike activity at resting membrane potential and generating one spike on depolarization to the tonic firing of spontaneous and evoked action potentials.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Apamin; Bicuculline; Cesium; Chick Embryo; Chlorides; Dose-Response Relationship, Radiation; Drug Combinations; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; GABA Antagonists; In Vitro Techniques; Lysine; Neurons; Sodium Channel Blockers; Strychnine; Tetrodotoxin; Vestibular Nuclei

The electrical field application technique has revealed that the electrotonic length of the distal apical dendrites of hippocampal CA1 pyramidal neurones is long compared to the rest of the cell. This difference may be due to an asymmetrical distribution of channels responsible for the leak conductance in distal and proximal membrane segments. One such conductance, the hyperpolarization-activated cation current, I(h), is reported to display an increasing density with distance from the soma along the apical dendrite. Such asymmetry of I(h) could be a major cause of the increased electrotonic length of the distal apical dendrite. In the present study we found that blockade of I(h), by bath application of Cs(+) (3 mM) or ZD7288 (20 microM), reduced the electrical field-induced transmembrane polarization (TMP) in the distal apical dendrites. In some neurones the polarization reversed polarity, reflecting a movement of the indifference point (site of zero polarization) from the distal dendrites, across the recording site to a more proximal position. These effects were more pronounced when Cs(+) and ZD7288 were applied locally to the distal apical dendrites. Bath application of another antagonist of leak conductance, Ba(2+) (1 mM), also decreased the average field-induced polarization. This latter effect, however, did not reach statistical significance. These data suggest that I(h) is partly responsible for the distal location of the indifference point, and indicate that an elevated activity of I(h) contributes to the relatively increased electrotonic length of the most distal part of the apical dendrites.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Barium Compounds; Cesium; Chlorides; Dendrites; Electromagnetic Fields; Electrophysiology; Excitatory Amino Acid Antagonists; Hippocampus; Ion Channels; Male; Pyramidal Cells; Pyrimidines; Rats; Rats, Wistar

1. Neuronal activity results in local elevation of extracellular K+ concentration ([K+]o). 2. Using the patch-clamp technique in the whole-cell configuration, we investigated whether extracellular K+ activates non-voltage-operated Ca2+ channels in pyramidal cells cultured from rat embryonic hippocampi. 3. K+ (12 mM) reversibly activated a sustained inward current at a holding potential of -100 mV. Membrane conductance and variance of noise were significantly increased by K+. This current could be observed at membrane potentials negative to +60 mV. 4. Inhibitors of inward rectifier K+ channels and hyperpolarization-induced cation current reduced the current only at potentials negative to -50 mV. 5. The K+-induced current was activated in Na+-free but not in Ca2+-free medium, did not depend on cytosolic [Cl-], and was blocked by Cd2+ but not by organic channel inhibitors. 6. Half-maximal activation of the current (at -100 mV) was attained at [K+]o approximately 20 mM. 7. The current is similar to Igl, a K+-induced Ca2+ current described in glomerulosa cells. It was also present in pyramidal cells from prefrontal cortex but not in hippocampal bipolar and glial cells. 8. Activation of K+-induced Ca2+ current may elevate cytoplasmic [Ca2+] at [K+]o levels which are insufficent to activate voltage-dependent Ca2+ channels.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Barium Compounds; Cadmium; Calcium; Calcium Channel Blockers; Calcium Channels; Cells, Cultured; Cesium; Chlorides; Excitatory Amino Acid Antagonists; Female; Fetus; Hippocampus; Ion Channel Gating; Nifedipine; omega-Conotoxin GVIA; Patch-Clamp Techniques; Peptides; Potassium; Prefrontal Cortex; Pregnancy; Pyramidal Cells; Rats; Rats, Wistar; Sodium; Tetrodotoxin