Brain research
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The aim of the present study was to investigate whether local application of octreotide, an analogue of somatostatin, suppresses the glutamate-evoked activities of Adelta and C primary afferent fibers innervating dorsal hairy skin of the rat in vivo. The single unit activity of Adelta and C afferent fibers was recorded in isolated filaments from the dorsal cutaneous branches of the T9-T12 spinal nerves. Changes in discharge relative to baseline during injection of glutamate (0.3mM, 10microL) into the receptive field with pretreatment by octreotide (20microM, 10microL) were compared with injection after pretreatment with normal saline. ⋯ The discharge rates during injection of glutamate after octreotide pretreatment were significantly lower than after normal saline pretreatment. The suppressive effect of octreotide was reversed by the somatostatin receptor antagonist cyclo-somatostatin. These results suggest that interactions between excitatory amino acid and inhibitory neuropeptides may contribute to sensory signaling in the peripheral nervous system.
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This study was performed to determine whether spinal GABAergic systems mediate the relieving effects of low frequency electroacupuncture (EA) on cold allodynia in a rat tail model of neuropathic pain. For neuropathic surgery, the right superior caudal trunk was resected at the level between the S1 and S2 spinal nerves innervating the tail. Two weeks after the nerve injury, the intrathecal catheter was implanted. ⋯ EA stimulation at ST36 significantly inhibited the cold allodynia sign, whereas EA at non-acupoint and plain acupuncture at ST36 (without electrical stimulation) did not show antiallodynic effects. Intrathecal administration of gabazine or saclofen blocked the relieving effects of ST36 EA stimulation on cold allodynia. These results suggest that spinal GABA(A) and GABA(B) receptors mediate the suppressive effect of low frequency EA on cold allodynia in the tail neuropathic rats.
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Disruption of the blood-brain barrier (BBB) and/or the blood-cerebrospinal fluid barrier (BCSFB) is thought to be one of the major pathophysiological consequences of meningitis and contributes to the development of adverse neurological outcomes. In order to clarify this hypothesis further, we sequentially quantified the permeability of these barriers with magnetic resonance imaging (MRI) contrast enhancement using gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA) in rats with various experimentally-induced meningitis. Meningeal inflammation was elicited by an intracisternal injection of interleukin (IL)-1beta, prostaglandin (PG) E(2), or lipopolysaccharide (LPS). ⋯ On the other hand, no significant changes in signal intensity of the brain parenchymal areas due to IL-1beta injection were observed. The findings suggest that the permeability of the BCSFB can be evaluated quantitatively by calculating the GER. MRI with Gd-DTPA provides a useful method to monitor the change in the permeability to the brain barriers.
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Distinct expression of cold receptors (TRPM8 and TRPA1) in the rat nodose-petrosal ganglion complex.
TRPM8 and TRPA1 are cold-activated transient receptor potential (TRP) cation channels. TRPM8 is activated by moderate cooling, while TRPA1 is activated by extreme, noxious cold temperatures. These cold receptors are expressed in different subpopulations of primary afferent neurons. ⋯ We retrogradely labeled cranial nerve X with Fast Blue (fluorescent dye) and found TRPM8 transcripts in the jugular-vagal ganglion but not the NG neurons. TRPA1 transcripts were not detected in TRPM8-expressing neurons but were present in the subpopulation of TRPV1-expressing visceral sensory neurons. Taken together, these findings support that in the vagal system the expression of cold-activated TRP channels differs between nodose- and jugular-ganglion neurons suggesting different mechanisms of cold-transduction and that the TRPA1 distribution is consistent with its proposed function as a cold-sensing receptor in the visceral system.
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The effect of subcutaneous injection of glutamate on the mechanical sensitivity of rat facial cutaneous mechanoreceptors was examined. Individual facial mechanoreceptors were recorded in the trigeminal ganglion of anesthetized Sprague-Dawley rats. An electronic von Frey hair was used to measure the mechanical threshold (MT) of the afferent fibers at baseline and following subcutaneous injection of glutamate (0, 0.01, 0.1, 1M; 10microl) or glutamate (0, 0.1M) plus the competitive N-methyl-d-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonovalerate (APV; 0.01M). ⋯ APV blocked the mechanical sensitization of the afferent fibers treated by glutamate 0.1M in both sexes with a lower effect in females at a 10-20minute post-injection. Subcutaneous injection of glutamate mechanically sensitizes rat facial cutaneous mechanoreceptors through activation of peripheral NMDA receptors. Peripheral NMDA receptor antagonists may be considered for craniofacial pain.