strychnine and bicuculline-methochloride

Using whole-cell patch-clamp recordings from spinal cord slices of young (10-15 days old) rats, we have characterized and compared the properties of inhibitory synaptic transmission in lamina II and laminae III-IV of the dorsal horn, which are involved in the processing of nociceptive and non-nociceptive sensory information, respectively. All (100%) of laminae III-IV neurons, but only 55% of lamina II neurons, received both gamma-aminobutyric acid (GABA)ergic and glycinergic inputs. The remaining 45% of lamina II neurons received only GABAergic synapses. Neurons receiving only glycinergic synapses were never observed. Among the 55% of lamina II neurons receiving both GABAergic and glycinergic inputs, all displayed a small proportion (approximately 10%) of mixed miniature inhibitory postsynaptic currents (mIPSCs), indicating the presence of a functional GABA/glycine co-transmission at a subset of synapses. Such a co-transmission was never observed in laminae III-IV neurons. The presence of mixed mIPSCs and the differences in decay kinetics of GABAA-type receptor mIPSCs between lamina II and laminae III-IV were due to the endogenous tonic production of 3alpha5alpha-reduced steroids (3alpha5alpha-RS) in lamina II. Stimulation of the local production of 3alpha5alpha-RS was possible in laminae III-IV after incubation of slices with progesterone, subcutaneous injection of progesterone or induction of a peripheral inflammation. This led to the prolongation of GABAergic mIPSCs, but failed to induce the appearance of mixed mIPSCs in laminae III-IV. Our results indicate that, compared with lamina II, inhibitory synaptic transmission in laminae III-IV is characterized by a dominant role of glycinergic inhibition and the absence of a functional GABA/glycine co-transmission.

Topics: Analysis of Variance; Animals; Bicuculline; Carrageenan; GABA Antagonists; gamma-Aminobutyric Acid; Glycine; Glycine Agents; In Vitro Techniques; Inhibitory Postsynaptic Potentials; Male; Neural Inhibition; Patch-Clamp Techniques; Posterior Horn Cells; Progesterone; Progestins; Rats; Rats, Wistar; Spinal Cord; Strychnine; Synapses; Synaptic Transmission

As previously demonstrated, spontaneously firing bulbar inspiratory neurones are periodically inhibited either at the beginning of, or throughout expiration, while bulbar expiratory neurones are inhibited during inspiration. The aim of the present study was to test the hypothesis that amino acids act as transmitters of these periodic inhibitions. The study was performed using iontophoretic applications of drugs on bulbar respiratory neurones. On these neurones GABA and glycine-sensitive sites were identified and differentiated on the basis of the actions of agonist (muscimol) or antagonists (bicuculline, picrotoxin and strychnine). Using competitive antagonists (nipecotic acid, beta-alanine) mechanisms responsible for GABA uptake were found in the close vicinity of respiratory-related neurones. Some but not all types of periodic inhibition were found to be reduced following application of GABA or glycine antagonists. Strychnine was found to reduce periodic inhibitions occurring at the beginning of expiration in inspiratory neurones. GABA antagonists had an effect on those periodic depressions which were prolonged throughout expiration. A different and complementary role of glycine-like and GABA-like systems in central respiratory mechanisms is proposed.

Topics: Alanine; Amino Acids; Animals; Bicuculline; Cats; Glutamates; Glutamic Acid; Glycine; Kinetics; Medulla Oblongata; Methylene Blue; Muscimol; Neurons; Nipecotic Acids; Oxygen Consumption; Picrotoxin; Strychnine

Compounds reported to be GABA antagonists have been studied quantitatively on dorsal funiculus fibres and terminals in the rat cuneate nucleus in vitro. The potencies of the antagonists against the GABA analogue muscimol were determined as pA2 values. Distinction was made between three different sites of antagonist action within the GABA receptor and ionophore complex. Competitive antagonists, presumed to act at the GABA receptor, and their pA2 values were bicuculline (5.98), bicuculline methochloride (5.88), strychnine (5.29) and tubocurarine (4.95). Antagonists which were not competitive and acted predominantly at the 'picrotoxin site' on the ionophore were picrotoxin (6.19), picrotoxinin (6.03), isopropylbicyclophosphate (5.82) and leptazol (2.89). A third type of antagonism was shown by frusemide. Attention is drawn to the picrotoxin site and its likely importance in the regulation of GABA-mediated inhibition by drugs.

Topics: Animals; Bicuculline; Cyclic P-Oxides; Furosemide; GABA Antagonists; In Vitro Techniques; Medulla Oblongata; Organophosphorus Compounds; Pentylenetetrazole; Picrotoxin; Rats; Receptors, Cell Surface; Receptors, GABA-A; Strychnine; Tubocurarine

Extracellular recordings were made from preoptic-anterior hypothalamic neurones with combined recording and iontophoresis electrodes. Short iontophoretic applications of beta-alanine, GABA, glycine and taurine inhibited the discharge of the majority of neurones tested. Bicuculline metho-chloride reversibly and selectively antagonised GABA responses. Strychnine reversibly antagonised beta-alanine, glycine and taurine but not GABA responses. These results suggest the existence of two populations of inhibitory amino acid receptors in the preoptic-anterior hypothalamus. The function of inhibitory amino acids in the rostral hypothalamus was briefly discussed.

Topics: Amino Acids; Animals; beta-Alanine; Bicuculline; Female; gamma-Aminobutyric Acid; Glycine; Hypothalamus; Hypothalamus, Anterior; Neural Inhibition; Neurons; Preoptic Area; Rats; Strychnine; Synaptic Transmission; Taurine