Synaptic excitation in the dorsal nucleus of the lateral lemniscus : Whole-cell patch-clamp recordings from rat brain slice

• Published in: Neuroscience 1997-06, Vol.78 (3), p.815-827
• Main Authors: FU, X. W, BREZDEN, B. L, KELLY, J. B, WU, S. H
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Action Potentials - physiology; Animals; Biological and medical sciences; Central nervous system; Electric Stimulation; Electrophysiology; Fundamental and applied biological sciences. Psychology; Geniculate Bodies - physiology; Geniculate Bodies - ultrastructure; Glycine - pharmacology; Glycine Agents - pharmacology; In Vitro Techniques; Inferior Colliculi - physiology; Inferior Colliculi - ultrastructure; Magnesium - pharmacology; Membrane Potentials - physiology; Neural Pathways - physiology; Neural Pathways - ultrastructure; Neurons - physiology; Neurons - ultrastructure; Patch-Clamp Techniques; Pons - physiology; Pons - ultrastructure; Rats; Receptors, N-Methyl-D-Aspartate - agonists; Receptors, N-Methyl-D-Aspartate - antagonists & inhibitors; Strychnine - pharmacology; Synapses - physiology; Synapses - ultrastructure; Vertebrates: nervous system and sense organs
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/s0306-4522(96)00580-5

The synaptic events underlying the excitation of neurons in the rat's dorsal nucleus of the lateral lemniscus were studied by whole-cell patch-clamp recordings in a brain slice preparation of the auditory midbrain. Both current-clamp and voltage-clamp data were obtained with the brain slice submerged in artificial cerebrospinal fluid. The rats were between 21 and 35 days of age at the time the recordings were made. Synaptic responses were evoked by a bipolar stimulating electrode placed on the lateral lemniscus just ventral to the dorsal nucleus. To eliminate glycinergic inhibitory responses, all physiological data were gathered with 0.5 microM strychnine added to the saline bath. Under current-clamp conditions, excitatory postsynaptic potentials could be subdivided into early and late components. The early component produced a single, highly reliable, short-latency spike and the later component produced a more variable, long-latency spike or train of spikes. The non-N-methyl-D-aspartate antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione, completely blocked the early excitatory postsynaptic potential and its associated action potential. The N-methyl-D-aspartate antagonist, D,L-2-amino-5-phosphonovaleric acid, blocked the later excitatory postsynaptic potential and its action potentials. Typically, both early and late excitatory postsynaptic potentials could be recorded from the same cell, but the early excitatory postsynaptic potential was evoked at lower stimulus levels and had a larger amplitude than the later excitatory postsynaptic potential. Under voltage-clamp conditions, dorsal nucleus of the lateral lemniscus neurons responded to stimulation of the lateral lemniscus with excitatory postsynaptic currents. Outward excitatory postsynaptic currents were recorded with holding potentials that depolarized the cell membrane and inward currents were seen when the cell was hyperpolarized. The current-voltage (I-V) relation of the early peak portion of the excitatory postsynaptic current was nearly linear, whereas the I-V relation of the later excitatory postsynaptic current (12 ms after the peak) was non-linear over the range between -50 and - 100 mV. The outward excitatory postsynaptic current consisted of an early current that was selectively blocked by 6-cyano-7-nitroquinoxaline-2,3-dione and a later current that was blocked by D,L-2-amino-5-phosphonovaleric acid. In artificial cerebrospinal fluid with normal concentrations of Mg2+, the inward excitatory po