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Substance P enhances excitatory synaptic transmission on spinally projecting neurons in the rostral ventromedial medulla after inflammatory injury
Journal article   Open access   Peer reviewed

Substance P enhances excitatory synaptic transmission on spinally projecting neurons in the rostral ventromedial medulla after inflammatory injury

Liang Zhang and Donna L Hammond
Journal of neurophysiology, Vol.102(2), pp.1139-1151
08/2009
DOI: 10.1152/jn.91337.2008
PMCID: PMC2724368
PMID: 19494188
url
https://doi.org/10.1152/jn.91337.2008View
Published (Version of record) Open Access

Abstract

It has been proposed, but not directly tested, that persistent inflammatory nociception enhances excitatory glutamatergic inputs to neurons in the rostral ventromedial medulla (RVM), altering the activity and function of these neurons. This study used whole cell patch-clamp methods to record evoked excitatory postsynaptic currents (eEPSCs) in spinally projecting RVM neurons from rats injected with saline or complete Freund's adjuvant (CFA) 3-4 days earlier and to examine the role of substance P (SP) in modulating excitatory synaptic transmission. Input-output relationships demonstrated that CFA treatment facilitated fast excitatory glutamatergic inputs to type 1 and type 2 nonserotonergic spinally projecting RVM neurons, but not to type 3 neurons. The facilitation in type 1 and 2 neurons was dependent on neurokinin-1 (NK1) and N-methyl-d-aspartate (NMDA) receptors and prevented by the PKC inhibitor GF109203X. In a subset of neurons from naïve rats, SP mimicked the effects of CFA and increased the potency and efficacy of glutamatergic synaptic transmission. The facilitation was prevented by 10 microM GF109203X, but not by 10 microM KN93, a CaMKII inhibitor. SP (0.3-3 microM) by itself produced concentration-dependent inward currents in most nonserotonergic, but not serotonergic neurons. The present study is the first demonstration, at the cellular level, that persistent inflammatory nociception leads to a sustained facilitation of fast excitatory glutamatergic inputs to RVM neurons by an NK1 and NMDA receptor-dependent mechanism that involves PKC. Further, it demonstrates that the facilitation is restricted to specific populations of RVM neurons that by inference may be pain facilitatory neurons.
 Neural Pathways - drug effects Synaptic Transmission - physiology Maleimides - pharmacology Receptors, N-Methyl-D-Aspartate - metabolism Male Substance P - pharmacology Excitatory Postsynaptic Potentials - drug effects Neural Pathways - physiology Excitatory Postsynaptic Potentials - physiology Neurotransmitter Agents - pharmacology Neurons - physiology Indoles - pharmacology Receptors, Neurokinin-1 - metabolism Synaptic Transmission - drug effects Neurons - drug effects Medulla Oblongata - physiology Medulla Oblongata - drug effects Enzyme Inhibitors - pharmacology Rats Protein Kinase C - antagonists & inhibitors Sulfonamides - pharmacology Calcium-Calmodulin-Dependent Protein Kinase Type 2 - antagonists & inhibitors Rats, Sprague-Dawley Animals Pain - physiopathology Serotonin - metabolism Glutamic Acid - metabolism In Vitro Techniques Benzylamines - pharmacology Inflammation - physiopathology

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