2-3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline and 2-amino-5-phosphono-3-pentenoic-acid

Homeostatic maintenance of widespread functions is critically dependent on the activity of the sympathetic nervous system. This activity is generated by the CNS acting on the sole output cells in the spinal cord, sympathetic preganglionic neurons (SPNs). SPNs are subject to control from both supraspinal and spinal inputs that exert effects through activation of direct or indirect pathways. A high proportion of indirect control is attributable to activation of spinal interneurons in a number of locations. However, little is known about the different groups of interneurons with respect to their neurochemistry or function. In this study, we report on a novel group of GABAergic interneurons located in the spinal central autonomic area (CAA) that directly inhibit SPN activity. In situ hybridization studies demonstrated a group of neurons that contained mRNA for glutamic acid decarboxylase (GAD)65 and GAD67 within the CAA. Combining in situ hybridization with trans-synaptic labeling from the adrenal gland using pseudorabies virus identified presympathetic GABAergic neurons in the CAA. Electrical stimulation of the CAA elicited monosynaptic IPSPs in SPNs located laterally in the intermediolateral cell column. IPSPs were GABAergic, because they reversed at the chloride reversal potential and were blocked by bicuculline. Chemical activation of neurons in the CAA hyperpolarized SPNs, an effect that was also bicuculline sensitive. We conclude that the CAA contains GABAergic interneurons that impinge directly onto SPNs to inhibit their activity and suggest that these newly identified interneurons may play an essential role in the regulation of sympathetic activity and thus homeostasis.

Topics: 2-Amino-5-phosphonovalerate; Action Potentials; Animals; Autonomic Fibers, Preganglionic; Axonal Transport; Bicuculline; Chlorides; Electric Stimulation; gamma-Aminobutyric Acid; Glutamate Decarboxylase; Glutamic Acid; Herpesvirus 1, Suid; Homeostasis; In Situ Hybridization; Interneurons; Isoenzymes; Kynurenic Acid; Male; Patch-Clamp Techniques; Quinoxalines; Rats; Rats, Wistar; RNA, Messenger; Spinal Cord; Strychnine

Ionic mechanisms of spontaneous GABAergic events in rat hippocampal slices exposed to 4-aminopyridine. J. Neurophysiol. 78: 2582-2591, 1997. Ion-selective (H+ and K+) microelectrode techniques as well as conventional extra- and intracellular recordings were used to study the ionic mechanisms of propagating spontaneous GABAergic events (SGEs) in rat hippocampal slices exposed to 4-aminopyridine (4-AP, 50-100 mu M). All experiments were made in the presence of antagonists of ionotropic glutamate receptors [10 mu M 6-nitro-7-sulphamoylbenzoquinoxaline-2,3-dione (NBQX) and 40 mu M -2-amino-5-phosphonopentanoic acid (AP5)]. The SGEs were composed of a negative-going change in field potential with a temporally coincident increase (0.7 +/- 0.3 mM; mean +/- SE) in extracellular K+ ([K+]o) and an alkaline transient (0.01-0.08 units) in extracellular pH (pHo) in stratum radiatum of the area CA1. Simultaneous intracellular recordings showed a triphasic hyperpolarization-depolarization-late hyperpolarization response in pyramidal cells. Application of pentobarbital sodium (PB, 100 mu M) decreased the interval between SGEs from a mean value of 35 to approximately 20 s and shortened the period of refractoriness of stimulus-evoked propagating events. This was accompanied by an increase in the amplitude of the field potential response of the [K+]o and the pHo shifts and of the depolarizing phase of the pyramidal-cell response. The SGEs were completely blocked by the gamma-aminobutyric acid-A (GABAA) receptor antagonist, picrotoxin (PiTX; 100 mu M). The amplitudes of the negative-going field potential and of the depolarizing phase of the pyramidal-cell response as well as the ionic shifts associated with SGEs were strongly suppressed in the nominal absence of CO2/HCO-3. There was a five-fold increase in the interevent interval, and propagating SGEs could not be evoked by stimuli given at intervals shorter than approximately 2-3 min. Exposure to inhibitors of carbonic anhydrase, benzolamide (BA; 10 micro M) or ethoxyzolamide (EZA; 50 mu M) fully blocked the alkaline pHo transients and turned them into acid shifts. The poorly membrane-permeant BA had no discernible effect on the other components of the SGEs, but application of EZA had effects reminiscent to those of CO2/HCO-3-free medium. Addition of the GABAA receptor-permeant weak-acid anion, formate (20 mM) reestablished the SGEs that were first suppressed by exposure to the CO2/HCO-3-free medium. No SGEs were seen in th

Topics: 2-Amino-5-phosphonovalerate; 4-Aminopyridine; Animals; Benzolamide; Bicarbonates; Carbonic Anhydrases; Enzyme Inhibitors; Ethoxzolamide; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; gamma-Aminobutyric Acid; Hippocampus; Hydrogen-Ion Concentration; In Vitro Techniques; Male; Models, Neurological; Pentobarbital; Picrotoxin; Pyramidal Cells; Quinoxalines; Rats; Rats, Wistar; Reaction Time; Receptors, GABA-A; Receptors, Metabotropic Glutamate