Akiyama T, Tominaga M, Davoodi A, Nagamine M, Takamori K, Carstens MI, Carstens E (2014) Spinal antinociceptive effect of gastrin releasing peptide (GRP) via GABAergic inhibitory interneurons expressing the GRP receptor (GRPR). Neuroscience 2014 Abstracts 158.02. Society for Neuroscience, Washington, DC.

Summary: GRPR-expressing dorsal horn neurons signal itch. We investigated a role for such neurons in modulating the spinal neurotransmission of mechanical and heat pain in mice. In behavioral studies, we measured heat and mechanical paw withdrawal thresholds using Hargreaves and von Frey assays, respectively. Mice received intrathecal (it) administration of one of following (5 µL volume); bombesin (6.2 pmol), GRP (0.1 nmol), and GRPR antagonists RC-3095 (0.03 nmol) and BW2258U89 (1.5 nmol). It administration of bombesin or GRP significantly reduced both heat and mechanical withdrawal thresholds with a maximal effect 10 min post-administration. In contrast, it administration of RC-3095 and BW2258U89 significantly increased both heat and mechanical withdrawal thresholds with a maximal effect 10 min post-administration. Mice treated with it bombesin-saporin to ablate GRPR-expressing spinal neurons exhibited reduced heat and mechanical withdrawal thresholds. It GRP failed to elicit heat and mechanical hyperalgesia in these mice. In electrophysiological recordings from superficial lumbar dorsal horn neurons, either bombesin or RC-3095 was spinally applied during responses elicited by noxious mechanical or heat stimulation of the cutaneous receptive field on the hindpaw. Bombesin increased both noxious mechanical- and heat-evoked activity in bombesin-sensitive neurons, while RC-3095 decreased noxious heat-evoked activity. In bombesin-insensitive neurons, bombesin decreased both noxious mechanical- and heat-evoked activity, while RC-3095 increased both. We additionally employed a double-label strategy to investigate if GRPR-expressing dorsal horn neurons coexpressed GABA, a molecular marker of inhibitory interneurons. Approximately 10% of GRPR-positive neurons were immunopositive for GABA. These results indicate that a subset of GRPR-expressing neurons function as interneurons in a circuit that suppresses nociceptive transmission in the dorsal horn. Noxious mechanical and heat stimuli activate GRPR-expressing dorsal horn neurons. A GABAergic subset of these may serve as inhibitory interneurons that contribute to inhibition of spinal neurons signaling heat and mechanical pain. Alternatively, GRPR-expressing neurons may drive other subsets of inhibitory interneurons. The antinociceptive circuit described here can be activated by pruritogens. We propose that the relative activity in antinociceptive and antipruritic circuits within the dorsal horn modulates itch- and pain-signaling ascending neurons to result in the perception of itch or pain.

Related Products: Bombesin-SAP (Cat. #IT-40)

Akiyama T, Tominaga M, Takamori K, Carstens M, Carstens E (2014) Role of spinal bombesin-responsive neurons in nonhistaminergic itch. J Neurophysiol 112:2283-2289. doi: 10.1152/jn.00409.2014

Summary: Recent papers have demonstrated that pruritogen-evoked scratching behavior is reduced or eliminated by intrathecal injection of Bombesin-SAP (Cat. #IT-40). In this work the authors build on those data by investigating if spinal neurons that are responsive to pruritogens administered intradermally are also responsive to a spinal infusion of bombesin. Through the use of intradermal chloroquine injections, spinal superfusion of bombesin, and noxious pinch, the overlap of neurons processing itch and nociception was examined. The results demonstrate that chloroquine- and bombesin-sensitive neurons are involved in the transmission of itch, and that these are a separate neuronal population from those involved in nociception.

Related Products: Bombesin-SAP (Cat. #IT-40)

Zhao Z, Wan L, Liu X, Huo F, Li H, Barry D, Krieger S, Kim S, Liu Z, Xu J, Rogers B, Li Y, Chen Z (2014) Cross-inhibition of NMBR and GRPR signaling maintains normal histaminergic itch transmission. J Neurosci 34:12402-12414. doi: 10.1523/JNEUROSCI.1709-14.2014

Summary: After itch detection, the itch pathway moves through an array of G-protein coupled receptors and transient receptor potential channels in dorsal root ganglion neurons into dorsal horn neurons which integrate and transduce these signals, sending them to the somatosensory cortex. The purpose of this work is to clarify whether gastrin-releasing peptide (GRP) or B-type natriuretic peptide regulates histaminergic itch. Several strains of knockout mice received 200, 300, or 400 ng intrathecal injections of bombesin-SAP (Cat. #IT-40). Blank-SAP (Cat. #IT-21) was used as a control. The data further define the respective functions of the neuromedin B receptor and GRP receptor in itch, and reveals a working relationship between the different interneuron populations.

Related Products: Bombesin-SAP (Cat. #IT-40), Blank-SAP (Cat. #IT-21)

Sasaki A, Adhikari S, Andoh T, Kuraishi Y (2013) BB2 bombesin receptor-expressing spinal neurons transmit herpes-associated itch by BB2 receptor-independent signaling. Neuroreport 24(12):652-656. doi: 10.1097/WNR.0b013e32836352d8

Summary: Using a skin rash model created by inoculating mice with human herpes virus, bombesin receptor-expressing spinal neurons were lesioned intrathecally with 400 ng of Bombesin-SAP (Cat. #IT-40). Lesioned animals displayed reduced scratching, but licking (due to pain) was not reduced.

Related Products: Bombesin-SAP (Cat. #IT-40), Blank-SAP (Cat. #IT-21)

Zushida K, Light K, Uchida S, Hevi C, Shumyatsky GP (2012) The GRP peptide and the GRPR-positive interneurons control fear acquisition and extinction. Neuroscience 2012 Abstracts 496.03. Society for Neuroscience, New Orleans, LA.

Summary: The gastrin releasing peptide (GRP) is the marker of the neural circuits relaying fear-related conditioned stimulus (CS) information to the amygdala. The GRP is expressed by principal cells and the GRP-receptor (GRPR) is expressed by interneurons. The GRPR is expressed in the amygdala and hippocampus. To examine the role of the GRPR-positive interneurons in these two brain areas, we performed local injections of the bombesin-saporin (SAP)-toxin, which selectively eliminates the GRPR-expressing cells. The intra-BLA [lateral (LA) and basal nuclei (BA) of amygdala] injection of bombesin-SAP before fear conditioning significantly enhanced cued, but not contextual fear memory. We did not observe any significant effect of post-training intra-BLA injections of bombesin-SAP on fear memory recall. Also, there were no significant effects of bombesin-SAP on acquisition of contextual and cued fear memory in mice injected bombesin-SAP into LA, BA and central amygdala (CeA), respectively. Also, we examined cued fear memory in the GRP knockout mice and found significant enhancement in their cued fear memory. These results support the idea that GRPR-expressing interneurons play an inhibitory role in acquisition of fear memory and suggested inhibitory effect by the GRPR-expressing GABA interneurons on fear memory requires both LA and BA but not CeA.

Related Products: Bombesin-SAP (Cat. #IT-40)

ATS Poster of the Year Winner

Mishra SK, Holzman S, Hoon MA (2012) A nociceptive signaling role for neuromedin B. J Neurosci 32(25):8686-8695. doi: 10.1523/JNEUROSCI.1533-12.2012

Summary: Previous work suggests that neuromedin B (NMB) is involved in nociception. Direct injection of the peptide causes nociceptive sensitization, while NMB antagonists attenuate sensitization in reponse to nerve stimulation with mustard oil. Specific subsets of dorsal horn interneurons were eliminated by administering either 10 μg of the custom conjugate neuromedin B-SAP, 0.13 μg of SSP-SAP (Cat. #IT-11), or 1.3 μg of bombesin-SAP (Cat. #IT-40). Blank-SAP (Cat. #IT-21) was used as a control. The data indicate that NMB may be involved in the perception of thermal sensation, but not mechanical or pruritic sensation.

Related Products: NMB-SAP (Cat. #IT-70), SSP-SAP (Cat. #IT-11), Bombesin-SAP (Cat. #IT-40), Blank-SAP (Cat. #IT-21)

Han N, Zu JY, Chai J (2012) Spinal bombesin-recognized neurones mediate more nonhistaminergic than histaminergic sensation of itch in mice. Clin Exp Dermatol 37(3):290-295. doi: 10.1111/j.1365-2230.2011.04314.x

Summary: The authors administered 400 ng of Bombesin-SAP (Cat. #IT-40) to the lumbar spinal subarachnoid space of rats and evaluated the distribution of Fos-positive cells in the dorsal horn after stimulation. Saporin (Cat. #PR-01) was used as a control. The results demonstrate that the neurons eliminated by Bombesin-SAP are critical to both acute and chronic itch pathways, although they have more effect on nonhistaminergic sensation.

Related Products: Bombesin-SAP (Cat. #IT-40), Saporin (Cat. #PR-01)

Liu XY, Liu ZC, Sun YG, Ross M, Kim S, Tsai FF, Li QF, Jeffry J, Kim JY, Loh HH, Chen ZF (2011) Unidirectional cross-activation of GRPR by MOR1D uncouples itch and analgesia induced by opioids. Cell 147(2):447-458. doi: 10.1016/j.cell.2011.08.043

Summary: Recent work has begun to define the different pathways used by itch and pain. This study was designed to investigate whether opioids cause the itch sensation by gastrin releasing peptide receptor activation. Mice received intrathecal injections of bombesin-SAP (Cat. #IT-40) in order to investigate the coexpression of various signaling molecules in the spinal cord. Blank-SAP (Cat. #IT-21) was used as a control. The data suggest that opioid-induced itch is independent of opioid analgesia, and is controlled through a mu-opioid receptor isoform.

Related Products: Bombesin-SAP (Cat. #IT-40), Blank-SAP (Cat. #IT-21)

Jeffry J, Kim S, Chen ZF (2011) Itch signaling in the nervous system. Physiology (Bethesda) 26(4):286-92. doi: 10.1152/physiol.00007.2011

Summary: This review examines recent work done to elucidate the molecular mechanisms behind the sensation of itch. The progress of mouse genetics has allowed the field to move beyond clinical and physiological studies, toward a better understanding of the signaling involved in nonhistaminergic itch. One study discussed used bombesin-SAP (Cat. #IT-40) in mice to ablate GRPR-positive neurons in the dorsal horn. This lesion reduced scratching in response to pruritogens, but did not affect pain behavior‚ indicating that pain and itch use entirely different pathways.

Related Products: Bombesin-SAP (Cat. #IT-40)

Li C, Back S, Lee J, Baek SK, Na H (2010) Gastrin-releasing peptide receptor in the spinal cord mediates mechanical allodynia following nerve injury. Neuroscience 2010 Abstracts 176.2/OO4. Society for Neuroscience, San Diego, CA.

Summary: Gastrin-releasing peptide receptor (GRPR) has been suggested as an itch-specific gene in the spinal cord (Sun et al., Nature, 2009). They described that selective ablation of GRPR-expressing lamina I neurons led to deficits in itch-related scratching behaviors without any effects on pain behaviors including nerve injury-induced mechanical allodynia. It has been known that two types of mechanical allodynia, such as static and dynamic allodynia, can be detectable in neuropathic patients, and may be mediated by distinct mechanisms. In the present study, we investigated the role of spinal GRPR in each of static and dynamic allodynia using both rat- and mouse-tail models of neuropathic pain. Bombesin-saporin (bombesin-sap) was administered intrathecally to ablate spinal GRPR-expressing neurons. Scratching behaviors evoked by pruritogenic agents, such as serotonin and chloroquine, and physiological pain behaviors were analyzed before nerve injury. Static or dynamic allodynia was assessed by the application of von Frey filaments to the tail or brushing the tail with a filament, respectively. RC3095, a GRPR antagonist, was given intrathecally to see its effects on static and dynamic allodynia in neuropathic rats. Bombesin-sap treatment resulted in reduction of GRPR-immunoreactive cells in lamina I of spinal dorsal horn and scratching deficits. Physiological pain behaviors of these animals were not different from those of control animals. Following the partial injury of tail-innervating nerves, animals treated with bombesin-sap exhibited comparable dynamic allodynia to control one. However, they failed to manifest static allodynia during the entire experimental period. In addition, RC3095 relieved static, but not dynamic, allodynia. These findings suggest that spinal GRPR mediates nerve injury-induced static mechanical allodynia as well as itching sensation in normal state.

Related Products: Bombesin-SAP (Cat. #IT-40)