Publications (2)10.43 Total impact
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Article: GABAA receptors increase excitability and conduction velocity of cerebellar parallel fiber axons.
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ABSTRACT: In the adult mammalian brain, GABA(A) receptors (GABA(A)Rs) are responsible for the predominant forms of synaptic inhibition, but these receptors can excite neurons when the chloride equilibrium potential (E(Cl)) is depolarized. In many mature neurons, GABA(A)Rs are found on presynaptic terminals where they exert depolarizing effects. To understand whether excitatory GABA action affects axonal function, we used transverse cerebellar slices to measure the effects of photolysis of caged GABA on the initiation and propagation of compound parallel fiber (PF) action potentials (APs). Photolysis of caged GABA increased the amplitude and conduction velocity of PF APs; GABA reuptake blockers and a positive modulator of GABA(A)Rs enhanced these effects. In contrast, a modulator selective for δ-subunit-containing GABA(A)Rs did not enhance these effects and responsiveness remained in δ(-/-) mice, arguing that δ-subunit-containing GABA(A)Rs are not required. Synaptically released GABA also increased PF excitability, indicating that the mechanism is engaged by physiological signals. A Hodgkin-Huxley-style compartmental model of the PF axon and granule cell body was constructed, and this model recapitulated the GABA-dependent decrease in AP threshold and the increase in conduction velocity, features that were sensitive to E(Cl) and to the voltage dependence of sodium channel inactivation. The model also predicts that axonal GABA(A)Rs could affect orthodromic spike initiation. We conclude that GABA acting on cerebellar PFs facilitates both spike generation and propagation, allowing axons of granule cells to passively integrate signals from inhibitory interneurons and influence information flow in the input layer to the cerebellar cortex.Journal of Neurophysiology 02/2012; 107(11):2958-70. · 3.32 Impact Factor -
Article: Submillisecond optical reporting of membrane potential in situ using a neuronal tracer dye.
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ABSTRACT: A major goal in neuroscience is the development of optical reporters of membrane potential that are easy to use, have limited phototoxicity, and achieve the speed and sensitivity necessary for detection of individual action potentials in single neurons. Here we present a novel, two-component optical approach that attains these goals. By combining DiO, a fluorescent neuronal tracer dye, with dipicrylamine (DPA), a molecule whose membrane partitioning is voltage-sensitive, optical signals related to changes in membrane potential based on FRET (Förster resonance energy transfer) are reported. Using DiO/DPA in HEK-293 cells with diffraction-limited laser spot illumination, depolarization-induced fluorescence changes of 56% per 100 mV (tau approximately 0.1 ms) were obtained, while in neuronal cultures and brain slices, action potentials (APs) generated a Delta F/F per 100 mV of >25%. The high sensitivity provided by DiO/DPA enabled the detection of subthreshold activity and high-frequency APs in single trials from somatic, axonal, or dendritic membrane compartments. Recognizing that DPA can depress excitability, we assayed the amplitude and duration of single APs, burst properties, and spontaneous firing in neurons of primary cultures and brain slices and found that they are undetectably altered by up to 2 microm DPA and only slightly perturbed by 5 microm DPA. These findings substantiate a simple, noninvasive method that relies on a neuronal tracer dye for monitoring electrical signal flow, and offers unique flexibility for the study of signaling within intact neuronal circuits.Journal of Neuroscience 07/2009; 29(29):9197-209. · 7.11 Impact Factor
