Seena Mathew - Published Work
Modulation of vesicle release by presynaptic kainate receptors imaged by FM1-43 multiphoton microscopy in acute brain slices
by S. MATHEW, L. POZZO-MILLER, J.
We have previously shown that activation of kainic acid receptors (KARs) produces an increase in the frequency of miniature inhibitory postsynaptic currents (mIPSCs) in the prefrontal cortex (PFC) without changing their amplitude, suggesting a presynaptic mechanism of action. To address this question directly, we combined multiphoton excitation laser scanning microscopy with FM1-43 dye staining to directly visualize vesicle release from presynaptic terminals in acute slices of PFC. High potassium-induced depolarization was used to load the total recycling pool of vesicles with FM1-43. Presumptive inhibitory terminals were identified by their distribution around pyramidal neuron somata in a “calyx” fashion. Destaining was induced by afferent fiber stimulation using either constant 10Hz stimulation, or a “natural” pattern that consisted of stimulus intervals extracted from cortical spike firings recorded in vivo. The average frequency, total number (1200), and intensity of applied stimuli were kept constant. The rate of FM1-43 destaining was significantly increased by 250nM kainate (control: 0.012 +/- 0.002 s-1, vs. KA: 0.031 +/- 0.003 s-1; p<0.05), indicating an increase in release probability. Intriguingly, this effect of KA was even larger when “natural” patterned stimulation was used for FM1-43 destaining (control: 0.023 +/- 0.001 s-1, vs. KA: 0.065 +/- 0.005 s-1; p<0.01). We conclude that kainate acts presynaptically to increase vesicle release from presumptive inhibitory terminals. Since this effect is enhanced during a “natural” stimulus pattern, the activation of presynaptic KARs may include frequency-dependent mechanisms.
Program No. 336.18/I10. 2006 Atlanta, GA: Society for Neuroscience, 2006.
2006 Copyright by the Society for Neuroscience all rights reserved.