cAMP signaling through protein kinase A and Epac2 induces substance P release in the rat spinal cord.

Using neurokinin 1 receptor (NK1R) internalization to measure of substance P release in rat spinal cord slices, we found that it was induced by the adenylyl cyclase (AC) activator forskolin, by the protein kinase A (PKA) activators 6-Bnz-cAMP and 8-Br-cAMP, and by the activator of exchange protein activated by cAMP (Epac) 8-pCPT-2-O-Me-cAMP (CPTOMe-cAMP). Conversely, AC and PKA inhibitors decreased substance P release induced by electrical stimulation of the dorsal root. Therefore, the cAMP signaling pathway mediates substance P release in the dorsal horn.

Mechanisms of μ-opioid receptor inhibition of NMDA receptor-induced substance P release in the rat spinal cord.

The interaction between NMDA receptors and μ-opioid receptors in primary afferent terminals was studied by using NMDA to induce substance P release, measured as neurokinin 1 receptor internalization. In rat spinal cord slices, the μ-opioid receptor agonists morphine, DAMGO and endomorphin-2 inhibited NMDA-induced substance P release, whereas the antagonist CTAP right-shifted the concentration response of DAMGO. In vivo, substance P release induced by intrathecal NMDA after priming with BDNF was inhibited by DAMGO.

Sustained Suppression of Hyperalgesia during Latent Sensitization by μ-, δ-, and κ-opioid receptors and α2A Adrenergic Receptors: Role of Constitutive Activity.

Unlabelled: Many chronic pain disorders alternate between bouts of pain and periods of remission. The latent sensitization model reproduces this in rodents by showing that the apparent recovery ("remission") from inflammatory or neuropathic pain can be reversed by opioid antagonists. Therefore, this remission represents an opioid receptor-mediated suppression of a sustained hyperalgesic state.

BDNF released during neuropathic pain potentiates NMDA receptors in primary afferent terminals.

NMDA receptors in primary afferent terminals can contribute to hyperalgesia by increasing neurotransmitter release. In rats and mice, we found that the ability of intrathecal NMDA to induce neurokinin 1 receptor (NK1R) internalization (a measure of substance P release) required a previous injection of BDNF. Selective knock-down of NMDA receptors in primary afferents decreased NMDA-induced NK1R internalization, confirming the presynaptic location of these receptors.

Chronic stress-induced changes in pro-inflammatory cytokines and spinal glia markers in the rat: a time course study.

Background/aims: Spinal glia activation has been proposed as one mechanism underlying visceral hyperalgesia in a rodent model of chronic stress. In order to assess the possible role of changes in circulating cytokines and in blood-spinal cord barrier (BSCB) permeability in spinal glia activation, we studied the time course of peripheral and spinal pro-inflammatory cytokines and of spinal and satellite glia markers in response to repeated water avoidance (WA) stress.

Methods: Spinal cords and dorsal root ganglion cells (DRGs) were collected from control rats, rats exposed to 1-hour WA, or 1-hour WA daily for 5 days or 1-hour WA daily for 10 days.

Role of astrocytes and altered regulation of spinal glutamatergic neurotransmission in stress-induced visceral hyperalgesia in rats.

Glutamate (Glu) is the primary excitatory neurotransmitter in the central nervous system and plays a critical role in the neuroplasticity of nociceptive networks. We aimed to examine the role of spinal astroglia in the modulation of glutamatergic neurotransmission in a model of chronic psychological stress-induced visceral hyperalgesia in male Wistar rats. We assessed the effect of chronic stress on different glial Glu control mechanisms in the spinal cord including N-methyl-d-aspartate receptors (NMDARs), glial Glu transporters (GLT1 and GLAST), the Glu conversion enzyme glutamine synthetase (GS), and glial fibrillary acidic protein (GFAP).

Behavioral differences among C57BL/6 substrains: implications for transgenic and knockout studies.

Separate breeding colonies of C57BL/6 ("B6") mice maintained at the Jackson Laboratories ("J") and NIH ("N") have led to the emergence of two distinct substrains of C57BL/6 mice: C57BL/6J and C57BL/6N. Molecular genetic studies indicate simple sequence-length polymorphisms, single-nucleotide polymorphisms, and copy-number variants among B6 substrains that may contribute to phenotypic differences. We examined differences in motor coordination, pain sensitivity, and conditional fear in the C57BL/6J strain and three N strains: C57BL/6NCrl (Charles River), C57BL/6NTac (Taconic), and C57BL/6NHsd (Harlan Sprague Dawley).

The role of neurokinin 1 receptors in the maintenance of visceral hyperalgesia induced by repeated stress in rats.

Background & Aims: The neurokinin 1 receptors (NK(1)Rs) and substance P (SP) have been implicated in the stress and/or pain pathways involved in chronic pain conditions. Here we examined the participation of NK(1)Rs in sustained visceral hyperalgesia observed in rats exposed to chronic psychological stress.

Methods: Male Wistar rats were exposed to daily 1-hour water avoidance stress (WA) or sham WA for 10 consecutive days.

Experimental colitis modulates the functional properties of NMDA receptors in dorsal root ganglia neurons.

N-methyl-D-aspartate (NMDA) receptors (NMDARs) on spinal afferent neurons regulate the peripheral and central release of neuropeptides involved in the development of hyperalgesia. We examined the effect of experimental colitis on the molecular and functional properties of NMDARs on these neurons. Lumbosacral dorsal root ganglia (DRG) were collected from adult rats 5 days after the induction of colitis for whole cell patch-clamp recording, Western blot analysis, and quantitative RT-PCR.

Repeated exposure to water avoidance stress in rats: a new model for sustained visceral hyperalgesia.

Chronic stress plays an important role in the development and exacerbation of symptoms in functional gastrointestinal disorders. To better understand the mechanisms underlying this relationship, we aimed to characterize changes in visceral and somatic nociception, colonic motility, anxiety-related behavior, and mucosal immune activation in rats exposed to 10 days of chronic psychological stress. Male Wistar rats were submitted daily to either 1-h water avoidance (WA) stress or sham WA for 10 consecutive days.

Electrophysiological characterization of N-methyl-D-aspartate receptors in rat dorsal root ganglia neurons.

In the peripheral nervous system, N-methyl-D-aspartate receptors (NMDAR) expressed on the central and peripheral terminals of primary afferent neurons are involved in nociception. We used single cell imaging of intracellular calcium concentration ([Ca2+]i) and patch clamp techniques to characterize the functional properties of NMDARs on adult rat dorsal root ganglia (DRG) neurons in primary culture and selectively on those innervating the distal colon. In Mg2+-free extracellular solution, rapid perfusion of DRG neurons with 250 microM NMDA and 10 microM glycine caused a significant increase in [Ca2+]i, and elicited inward currents in whole cell patch clamp recordings when the holding potential was -60 mV.

Protease-activated receptor 2 sensitizes the capsaicin receptor transient receptor potential vanilloid receptor 1 to induce hyperalgesia.

Inflammatory proteases (mast cell tryptase and trypsins) cleave protease-activated receptor 2 (PAR2) on spinal afferent neurons and cause persistent inflammation and hyperalgesia by unknown mechanisms. We determined whether transient receptor potential vanilloid receptor 1 (TRPV1), a cation channel activated by capsaicin, protons, and noxious heat, mediates PAR2-induced hyperalgesia. PAR2 was coexpressed with TRPV1 in small- to medium-diameter neurons of the dorsal root ganglia (DRG), as determined by immunofluorescence.

Two N-methyl-D-aspartate receptors in rat dorsal root ganglia with different subunit composition and localization.

N-methyl-D-aspartate (NMDA) receptors in sensory afferents participate in chronic pain by mediating peripheral and central sensitization. We studied the presence of NMDA receptor subunits in different types of primary afferents. Western blots indicated that rat dorsal root ganglia (DRG) contain NR1, NR2B, NR2C, and NR2D but not NR2A.