Effect of activation of γ-aminobutyric acid B receptors on glutamate release in spinal dorsal horn neurons in rats with diabetic neuropathic pain

Abstract

Objective To explore the effect of activation of γ-aminobutyric acid B (GABAB) receptors on glutamate release in spinal dorsal horn neurons in rats with diabetic neuropathyic pain(DNP). Methods Thirty Sprague-Dawley(SD) male rats(aged 4 weeks,weighing 150 g-170 g) were randomly divided into 2 groups (n=15):Normal rats group (N group),DN rats group (D group).DNP were induced by single intraperitoneal (IP) injection of streptozotocin (STZ,50 mg/kg),and rats in C group received the equal volume saline injection.At 3-4 weeks after STZ or saline intraperitoneal injection,blood glucose level and paw withdraw threshold (PWT) were measured,and the rats were then killed,the lumbar segment of spinal cord (L1-5) was removed for slices preparations.Monosynaptic glutamatergic evoked excitatory postsynaptic currents (eEPSCs) of lamina Ⅱ neurons were recorded by using whole-cell voltage-clamp patch.Bath baclofen (1,10,20,50 μmol/L) was applicated,monosynaptic eEPSCs was recorded before application of baclofen,at 1,10,20,50 μmol/L and wash out 5 min,the inhibitory rate (％) of eEPSCs was compared between two groups (n=15),the effect of CGP55845 (1 pmol/L) on eEPSCs of 50 μmol/L baclofen was analyzed in two groups (n=12). Results The mean blood glucose level was significantly higher in D group than in N group,while PWT in D group was significantly lower than that in N group (P＜0.05).eEPSCs in totally 30 glutamatergic neurons was recorded by electrophysiological recording. (1, 10,20,50 μmol/L) baclofen dose-dependently decreased the amplitude of eEPSCs both in two groups,the significant decrease of the amplitude inhibitory rate (％) of eEPSCs was observed at 1,10,20,50 μmol/L baclofen both in two groups(P＜0.05),its in D group were significantly decreased compared with N group at above times(P＜0.05) respectively:(47±7) vs (21 ±7 ),(55 ±6) vs (50±6),(92±6) vs (72±9),(95 ±8) vs (88±8).CGP55845 was completely abolished the inhibitory effect of 50 μmol/L baclofen on the amplitude of monosynaptic eEPSCs in lamina Ⅱ neurons both two groups. Conclusions Activation of GABAB receptors effectively inhibits the glutemate neurotransmitter release in the spinal cord dorsal horn neurons,while it's inhibitory role may decrease in rats with diabetic neuropathy. Key words: γ-aminobutyric acid B receptor; Glutematergic; evoked excitatory postsynaptic currents; Spinal dorsal horn; Diabetic; Pain