Journal of Neurophysiology, Vol 75, Issue 5 2167-2173, Copyright © 1996 by APS

ARTICLES

Intracellular blockade of inhibitory synaptic responses in visual cortical layer IV neurons

S. M. Dudek and M. J. Friedlander
Neurobiology Research Center, University of Alabama at Birmingham 35294-0021, USA.

1. Inhibitory postsynaptic potentials (IPSPs) evoked by stimulation at the white-matter/layer VI border were recorded intracellularly from visual cortical layer IV neurons maintained in vitro. These IPSPs, typically not apparent at resting membrane potentials, were measured at membrane potentials 15-25 mV depolarized from resting levels. The effects of two chloride channel blockers on these IPSPs were investigated. 2. 4,4'-Dinitro-stilbene-2,2'-disulfonic acid (DNDS) was found to inhibit IPSPs as it diffused into the postsynaptic cell from an intracellular micropipette, leaving only the presumed pure excitatory postsynaptic potential (EPSP) component of the evoked compound PSP. Input resistance, resting membrane potential, spike accommodation, and EPSPs at resting membrane potentials were not significantly affected. 3. A novel chloride channel blocker 5,11,17,23-tetrasulfonato-25,26,27,28-tetramethoxy-calix[4]a rene (TS-TM-calix[4]arene) was found to potently inhibit IPSPs recorded at depolarized membrane potentials. The TS-TM-calix[4]arene, similar to DNDS, did not affect input resistance, resting membrane potential, spike accommodation, and EPSPs at resting membrane potentials. 4. To confirm that DNDS and TS-TM-calix[4]arene were indeed blocking IPSPs, similar experiments were performed on monosynaptic IPSPs evoked by stimulation of layer V in the presence of 2-amino-5-phosphonovaleric acid (APV) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Both DNDS and TS-TM-calix[4]arene were effective in blocking monosynaptic IPSPs. 5. Consistent with the notion that DNDS and TS-TM-calix[4]arene block IPSPs by inhibiting gamma-aminobutyric acid-A (GABAA) receptor channels, the decrease in input resistance caused by extracellular application of muscimol was also significantly inhibited by intracellular use of these compounds. 6. These data suggest that DNDS and TS-TM-calix[4]arene applied intracellularly may be useful for the study of the function of GABAA-mediated synaptic inhibition of cortical neurons. Because only neurons impaled by the recording electrodes are influenced by the drugs, this method offers an advantage over extracellular application of GABAA blockers in that entire networks of neurons are not influenced.

This article has been cited by other articles:

				B. Jiang, M. Trevino, and A. Kirkwood Sequential Development of Long-Term Potentiation and Depression in Different Layers of the Mouse Visual Cortex J. Neurosci., September 5, 2007; 27(36): 9648 - 9652. [Abstract] [Full Text] [PDF]

				R. Khanbabaie, A. S. Mahani, and R. Wessel Contextual Interaction of GABAergic Circuitry With Dynamic Synapses J Neurophysiol, April 1, 2007; 97(4): 2802 - 2811. [Abstract] [Full Text] [PDF]

				S. P. Perrett, S. M. Dudek, D. Eagleman, P. R. Montague, and M. J. Friedlander LTD Induction in Adult Visual Cortex: Role of Stimulus Timing and Inhibition J. Neurosci., April 1, 2001; 21(7): 2308 - 2319. [Abstract] [Full Text] [PDF]

				B. J. Hefti and P. H. Smith Anatomy, Physiology, and Synaptic Responses of Rat Layer V Auditory Cortical Cells and Effects of Intracellular GABAA Blockade J Neurophysiol, May 1, 2000; 83(5): 2626 - 2638. [Abstract] [Full Text] [PDF]

				G. Gonzalez-Burgos, G. Barrionuevo, and D. A. Lewis Horizontal Synaptic Connections in Monkey Prefrontal Cortex: An In Vitro Electrophysiological Study Cereb Cortex, January 1, 2000; 10(1): 82 - 92. [Abstract] [Full Text] [PDF]

				K. Harsanyi and M. J. Friedlander Transient Synaptic Potentiation in the Visual Cortex. I. Cellular Mechanisms J Neurophysiol, March 1, 1997; 77(3): 1269 - 1283. [Abstract] [Full Text] [PDF]

				K. Harsanyi and M. J. Friedlander Transient Synaptic Potentiation in the Visual Cortex. II. Developmental Regulation J Neurophysiol, March 1, 1997; 77(3): 1284 - 1293. [Abstract] [Full Text] [PDF]