Differential contribution of GABAergic and glycinergic components to inhibitory synaptic transmission in lamina II and laminae III-IV of the young rat spinal cord.
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.
Inquimbert
Perrine
P
Université Louis Pasteur, Institut des Neurosciences Cellulaires et Intégratives (INCI), Centre National de la Recherche Scientifique (CNRS), UMR7168, F-67084 Strasbourg, France.
Rodeau
Jean-Luc
JL
Schlichter
Rémy
R
D000704:Analysis of Variance; D000818:Animals; D001640:Bicuculline / Q000031:analogs & derivatives / Q000494:pharmacology; D002351:Carrageenan / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D005998:Glycine / Q000378:metabolism*; D018684:Glycine Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D020671:Posterior Horn Cells / Q000502:physiology*; D011374:Progesterone / Q000494:pharmacology; D011372:Progestins / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000033:anatomy & histology*; D013331:Strychnine / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D018756:GABA Antagonists; D018684:Glycine Agents; D011372:Progestins; D011374:Progesterone; D005680:gamma-Aminobutyric Acid; D002351:Carrageenan; D013331:Strychnine; C006749:bicuculline methochloride; D005998:Glycine; D001640:Bicuculline