Excitation of Mouse Superficial Dorsal Horn Neurons by Histamine and/or PAR-2 Agonist: Potential Role in Itch

Recent studies have suggested the existence of separate transduction mechanisms and sensory pathways for histamine and nonhistaminergic types of itch. We studied whether histamine and an agonist of the protease-activated receptor (PAR)-2, associated with nonhistaminergic itch, excite murine dorsal horn neurons. Single units were recorded in superficial lumbar dorsal horn of adult ICR mice anesthetized with pentobarbital. Unit activity was searched using a small intradermal hindpaw injection of histamine or the PAR-2 agonist SLIGRL-NH2. Isolated units were subsequently challenged with intradermal histamine followed by SLIGRL-NH2 (each 50 μg/1 μl) or reverse order, followed by mechanical, thermal, and algogenic stimuli. Forty-three units were classified as wide dynamic range (62%), nociceptive specific (22%), or mechano insensitive (16%). Twenty units gave prolonged (mean, 10 min) discharges to intradermal injection of histamine; 76% responded to subsequent SLIGRL-NH2, often more briefly. Units additionally responded to noxious heat (63%), cooling (43%), topical mustard oil (53%), and intradermal capsaicin (67%). Twenty-two other units gave prolonged (mean, 5 min) responses to initial intradermal injection of SLIGRL-NH2; 85% responded to subsequent intradermal histamine. They also responded to noxious heat (75%), mustard oil (93%), capsaicin (63%), and one to cooling. Most superficial dorsal horn neurons were excited by both histamine and the PAR-2 agonist, suggesting overlapping pathways for histamine- and non–histamine-mediated itch. Because the large majority of pruritogen-responsive neurons also responded to noxious stimuli, itch may be signaled at least partly by a population code.

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Superficial Dorsal Horn Neurons Identified by Intracutaneous Histamine: Chemonociceptive Responses and Modulation by Morphine

Journal of Neurophysiology ◽

10.1152/jn.2000.84.2.616 ◽

2000 ◽

Vol 84 (2) ◽

pp. 616-627 ◽

Cited By ~ 50

Author(s):

Steven L. Jinks ◽

E. Carstens

Keyword(s):

Dorsal Horn ◽

Dynamic Range ◽

Mustard Oil ◽

Mechanical Stimuli ◽

Superficial Dorsal Horn ◽

Neuronal Responses ◽

Noxious Heat ◽

Morphine Concentration ◽

Dorsal Horn Neurons ◽

Low Concentrations

We have investigated whether neurons in superficial laminae of the spinal dorsal horn respond to intracutaneous (ic) delivery of histamine and other irritant chemicals, and thus might be involved in signaling sensations of itch or chemogenic pain. Single-unit recordings were made from superficial lumbar dorsal horn neurons in pentobarbital sodium–anesthetized rats. Chemoresponsive units were identified using ic microinjection of histamine (3%, 1 μl) into the hindpaw as a search stimulus. All superficial units so identified [9 nociceptive-specific (NS), 26 wide-dynamic-range (WDR)] responded to subsequent ic histamine. A comparison group of histamine-responsive deep dorsal horn neurons ( n = 16) was similarly identified. The mean histamine-evoked discharge decayed to 50% of the maximal rate significantly more slowly for the superficial (92.2 s ± 65.5, mean ± SD) compared with deep dorsal horn neurons (28.2 s ± 11.6). In addition to responding to histamine, most superficial dorsal horn neurons were also excited by ic nicotine (22/25 units), capsaicin (21/22), topical mustard oil (5/6), noxious heat (26/30), and noxious and/or innocuous mechanical stimuli (except for 1 unit that did not have a mechanosensitive receptive field). Application of a brief noxious heat stimulus during the response to ic histamine evoked an additive response in all but two cases, followed by transient depression of firing in 11/20 units. Intrathecal (IT) administration of morphine had mixed effects on superficial dorsal horn neuronal responses to ic histamine and noxious heat. Low morphine concentrations (100 nM to 1 μM) facilitated histamine-evoked responses (to >130% of control) in 9/24 units, depressed the responses (by >70%) in 11/24, and had no effect in 4. Naloxone reversed morphine-induced effects in some but not all cases. A higher morphine concentration (10 μM) had a largely depressant, naloxone-reversible effect on histamine responses. Responses of the same superficial neurons to noxious heat were facilitated (15/25), reduced (8/25), or unaffected (2/25) by low morphine concentrations and were depressed by the higher morphine concentration. In contrast, deep dorsal horn neuronal responses to both histamine and noxious heat were primarily depressed by low concentrations of morphine in a naloxone-reversible manner. These results indicate that superficial dorsal horn neurons respond to both pruritic and algesic chemical stimuli and thus might participate in transmitting sensations of itch and/or chemogenic pain. The facilitation of superficial neuronal responses to histamine by low concentrations of morphine, coupled with inhibition of deep dorsal horn neurons, might underlie the development of pruritis that is often observed after epidural morphine.

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Responses of Superficial Dorsal Horn Neurons to Intradermal Serotonin and Other Irritants: Comparison With Scratching Behavior

Journal of Neurophysiology ◽

10.1152/jn.00431.2001 ◽

2002 ◽

Vol 87 (3) ◽

pp. 1280-1289 ◽

Cited By ~ 76

Author(s):

Steven L. Jinks ◽

E. Carstens

Keyword(s):

Dorsal Horn ◽

Time Course ◽

Dynamic Range ◽

Neuronal Firing ◽

Whole Body ◽

Mustard Oil ◽

Neural Pathways ◽

Superficial Dorsal Horn ◽

Behavioral Experiments ◽

Dorsal Horn Neurons

Scratching behavior is used to assess itch sensation in animals, but few studies have addressed the relative scratch-inducing capacity of different algesic and pruritic chemicals. Furthermore, central neural mechanisms underlying itch are not well understood. We used electrophysiological and behavioral methods to investigate the ability of several irritant chemicals to excite neurons in the superficial dorsal horn, as well as to elicit scratching, in rats. In anesthetized rats, single neurons in the superficial lumbar dorsal horn, identified by their responsiveness to intracutaneous (ic) histamine, were classified as wide dynamic range (WDR) or nociceptive-specific (NS). Serotonin (5-HT) given ic to the paw excited most (88%) WDR and NS neurons over a prolonged time course (often up to 40 min). 5-HT–evoked responses exhibited significant tachyphylaxis. Most neurons also gave shorter-duration responses to ic capsaicin (92%) and mustard oil (71%). In separate behavioral experiments, significant dose-related hind limb scratching directed at the ic injection site in the back of the neck was elicited by 5-HT over a time course similar to that of evoked neuronal firing. A second 5-HT injection made 40 min later at the same site elicited significantly less scratching. Formalin also elicited scratching that was not dose-related and less than that evoked by 5-HT. 5-HT and Formalin also evoked head or whole-body shakes that were significantly correlated with scratching. Neither histamine, capsaicin, nor vehicle controls elicited significant scratching or shaking. In rats, 5-HT appears to be more pruritogenic than histamine as assessed by scratching and shaking behavior, and excites superficial dorsal horn neurons over a behaviorally relevant time course. However, because most neurons additionally responded to pain-producing stimuli, they are not itch-specific. They might nonetheless contribute to neural pathways that distinguish between pain and itch based on some neural mechanism such as frequency coding.

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Intradermal endothelin-1 excites bombesin-responsive superficial dorsal horn neurons in the mouse

Journal of Neurophysiology ◽

10.1152/jn.00723.2015 ◽

2015 ◽

Vol 114 (4) ◽

pp. 2528-2534 ◽

Cited By ~ 4

Author(s):

T. Akiyama ◽

M. Nagamine ◽

A. Davoodi ◽

M. Iodi Carstens ◽

F. Cevikbas ◽

...

Keyword(s):

Dorsal Horn ◽

Dynamic Range ◽

Allyl Isothiocyanate ◽

High Threshold ◽

Mechanical Stimuli ◽

Superficial Dorsal Horn ◽

Noxious Heat ◽

Nociceptive Neurons ◽

Endothelin 1 ◽

Dorsal Horn Neurons

Endothelin-1 (ET-1) has been implicated in nonhistaminergic itch. Here we used electrophysiological methods to investigate whether mouse superficial dorsal horn neurons respond to intradermal (id) injection of ET-1 and whether ET-1-sensitive neurons additionally respond to other pruritic and algesic stimuli or spinal superfusion of bombesin, a homolog of gastrin-releasing peptide (GRP) that excites spinal itch-signaling neurons. Single-unit recordings were made from lumbar dorsal horn neurons in pentobarbital-anesthetized C57BL/6 mice. We searched for units that exhibited elevated firing after id injection of ET-1 (1 μg/μl). Responsive units were further tested with mechanical stimuli, bombesin (spinal superfusion, 200 μg·ml−1·min−1), heating, cooling, and additional chemicals [histamine, chloroquine, allyl isothiocyanate (AITC), capsaicin]. Of 40 ET-1-responsive units, 48% responded to brush and pinch [wide dynamic range (WDR)] and 52% to pinch only [high threshold (HT)]. Ninety-three percent responded to noxious heat, 50% to cooling, and >70% to histamine, chloroquine, AITC, and capsaicin. Fifty-seven percent responded to bombesin, suggesting that they participate in spinal itch transmission. That most ET-1-sensitive spinal neurons also responded to pruritic and algesic stimuli is consistent with previous studies of pruritogen-responsive dorsal horn neurons. We previously hypothesized that pruritogen-sensitive neurons signal itch. The observation that ET-1 activates nociceptive neurons suggests that both itch and pain signals may be generated by ET-1 to result in simultaneous sensations of itch and pain, consistent with observations that ET-1 elicits both itch- and pain-related behaviors in animals and burning itch sensations in humans.

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Activation of Superficial Dorsal Horn Neurons in the Mouse by a PAR-2 Agonist and 5-HT: Potential Role in Itch

Journal of Neuroscience ◽

10.1523/jneurosci.6103-08.2009 ◽

2009 ◽

Vol 29 (20) ◽

pp. 6691-6699 ◽

Cited By ~ 64

Author(s):

T. Akiyama ◽

A. W. Merrill ◽

M. I. Carstens ◽

E. Carstens

Keyword(s):

Dorsal Horn ◽

Potential Role ◽

Superficial Dorsal Horn ◽

Dorsal Horn Neurons

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Estrogen rapidly modulates mustard oil-induced visceral hypersensitivity in conscious female rats: a role of CREB phosphorylation in spinal dorsal horn neurons

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00210.2006 ◽

2007 ◽

Vol 292 (1) ◽

pp. G438-G446 ◽

Cited By ~ 9

Author(s):

Ching-Liang Lu ◽

Jen-Chuen Hsieh ◽

Meei-Ling Tsaur ◽

Yn-Ho Huang ◽

Paulus S. Wang ◽

...

Keyword(s):

Dorsal Horn ◽

Single Injection ◽

Mineral Oil ◽

Visceral Hypersensitivity ◽

Female Rats ◽

Mustard Oil ◽

Superficial Dorsal Horn ◽

Colorectal Distension ◽

Dorsal Horn Neurons ◽

Ovx Rats

This study investigated the effect of sex hormones on mustard oil (MO)-induced visceral hypersensitivity in female rats and analyzed possible involved signaling pathways. Female rats, either intact or ovariectomized (OVX), were prepared for abdominal muscle electromyography in response to colorectal distension after intracolonic instillation of MO. The effect of MO intracolonic sensitization was evaluated in intact rats, OVX rats, and OVX rats pretreated with a single injection of 17β-estradiol (E), progesterone (P), E+P, or vehicle. cAMP-responsive element-binding protein (CREB) and phosphorylated CREB (pCREB) were detected in the superficial dorsal horn of L6 and S1 in MO or mineral oil-treated OVX rats with/without colorectal distension and estrogen replacement. The distal colorectum was removed for histological evaluation of inflammatory severity in MO-treated intact or OVX rats. The MO-treated rats had significantly higher visceromotor reflex than controls (enhanced visceral hypersensitivity), whereas OVX eliminated this hypersensitivity. After a single injection of E or E+P, the rats rapidly restored MO-induced visceral hypersensitivity within 2 h. Estrogen also rapidly induced a dose-dependent increase in pCREB expression in the superficial dorsal horn neurons in MO-treated, but not mineral oil-treated, OVX rats. The present study suggests that estrogen can rapidly modulate visceral hypersensitivity induced by MO intracolonic instillation in conscious female rats, which may involve spinal activation of the cAMP response element-mediated gene induction pathway.

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Innocuous warming enhances peripheral serotonergic itch signaling and evokes enhanced responses in serotonin-responsive dorsal horn neurons in the mouse

Journal of Neurophysiology ◽

10.1152/jn.00703.2016 ◽

2017 ◽

Vol 117 (1) ◽

pp. 251-259 ◽

Cited By ~ 4

Author(s):

T. Akiyama ◽

M. Nagamine ◽

A. Davoodi ◽

M. Ivanov ◽

M. Iodi Carstens ◽

...

Keyword(s):

Dorsal Root Ganglion ◽

Dorsal Horn ◽

Dorsal Root ◽

Ganglion Cells ◽

Underlying Mechanism ◽

Intradermal Injection ◽

Evoked Responses ◽

Superficial Dorsal Horn ◽

Dorsal Horn Neurons ◽

Temperature Controlled

Itch is often triggered by warming the skin in patients with itchy dermatitis, but the underlying mechanism is largely unknown. We presently investigated if warming the skin enhances histamine- or serotonin (5-HT)-evoked itch behavior or responses of sensory dorsal root ganglion (DRG) cells, and if responses of superficial dorsal horn neurons to innocuous warming are enhanced by these pruritogens. In a temperature-controlled environmental chamber, mice exhibited greater scratching following intradermal injection of 5-HT, but not histamine, SLIGRL, or BAM8-22, when the skin surface temperature was above 36°C. Calcium imaging of DRG cells in a temperature-controlled bath revealed that responses to 5-HT, but not histamine, were significantly greater at a bath temperature of 35°C vs. lower temperatures. Single-unit recordings revealed a subpopulation of superficial dorsal horn neurons responsive to intradermal injection of 5-HT. Of these, 58% responded to innocuous skin warming (37°C) prior to intradermal injection of 5-HT, while 100% responded to warming following intradermal injection of 5-HT. Warming-evoked responses were superimposed on the 5-HT-evoked elevation in firing and were significantly larger compared with responses pre-5-HT, as long as 30 min after the intradermal injection of 5-HT. Five-HT-insensitive units, and units that either did or did not respond to intradermal histamine, did not exhibit any increase in the incidence of warmth sensitivity or in the mean response to warming following intradermal injection of the pruritogen. The results suggest that 5-HT-evoked responses of pruriceptors are enhanced during skin warming, leading to increased firing of 5-HT-sensitive dorsal horn neurons that signal nonhistaminergic itch. NEW & NOTEWORTHY Skin warming often exacerbates itch in patients with itchy dermatitis. We demonstrate that warming the skin enhanced serotonin-evoked, but not histamine-evoked, itch behavior and responses of sensory dorsal root ganglion cells. Moreover, serotonin, but not histamine, enhanced responses of superficial dorsal horn neurons to innocuous warming. The results suggest that skin warming selectively enhances the responses of serotonin-sensitive pruriceptors, leading to increased firing of serotonin-sensitive dorsal horn neurons that signal nonhistaminergic itch.

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Responses of Rat Spinal Dorsal Horn Neurons to Intracutaneous Microinjection of Histamine, Capsaicin, and Other Irritants

Journal of Neurophysiology ◽

10.1152/jn.1997.77.5.2499 ◽

1997 ◽

Vol 77 (5) ◽

pp. 2499-2514 ◽

Cited By ~ 84

Author(s):

E. Carstens

Keyword(s):

Dorsal Horn ◽

Spinal Dorsal Horn ◽

Dynamic Range ◽

Mustard Oil ◽

High Threshold ◽

Dorsal Horn Neurons ◽

Spinal Dorsal ◽

Range Type ◽

The Mean ◽

Spinal Dorsal Horn Neurons

Carstens, E. Responses of rat spinal dorsal horn neurons to intracutaneous microinjection of histamine, capsaicin, and other irritants. J. Neurophysiol. 77: 2499–2514, 1997. To investigate the spinal processing of cutaneous pruritic and algesic stimuli, single-unit recordings were made from wide-dynamic-range-type lumbar spinal dorsal horn neurons in pentobarbital-sodium-anesthetized rats. Neuronal responses were recorded to mechanical and noxious thermal stimuli, as well as to microinjection (1 μl) of histamine (0.01–10% = 9 × 10−1–9 × 10−4 M), capsaicin (0.1% = 3.3 × 10−3 M), or other algesic chemicals into skin within the receptive field via intracutaneously placed needles. Most (84%) of the 89 neurons responded to intracutaneous (ic) microinjection of histamine with a brief phasic discharge followed by an afterdischarge of variable (s to min) duration. Ten minutes after ic microinjection of histamine (but not NaCl), there was a significant increase in the mean area of the low-threshold (but not high-threshold) portion of unit mechanical receptive fields. However, responses to graded pressure stimuli were not significantly affected after histamine. Responses did not exhibit significant tachyphylaxis when histamine microinjections were repeated at 5- or 10-min intervals. Unit responses significantly increased in a dose-related manner to microinjection of histamine at concentrations ranging across 4 orders of magnitude. Within 30 s after ic microinjection of the H1 antagonist cetirizine, unit responses to ic histamine delivered at the same skin site were significantly attenuated. Unit responses to histamine, as well as to noxious thermal stimulation, were significantly reduced after systemic administration of morphine (3.5 mg/kg ip) in a naloxone-reversible manner. Application of a mechanical rub, scratch, or a noxious heat stimulus during the unit's ongoing response to ic histamine produced a brief and marked excitation, often followed by a period of reduced ongoing discharge. Unit responses to histamine were markedly suppressed by electrical stimulation in the midbrain periaqueductal gray. Most (79%) histamine-responsive units tested also responded to ic microinjection of capsaicin. After the initial microinjection of capsaicin, subsequent responses to histamine and capsaicin microinjections were significantly reduced. Units also responded to ic ethanol (capsaicin vehicle) in a dose-related manner, and showed tachyphylaxis to repeated ic ethanol at 80% but not at 8%. The mean response to 80% ethanol was significantly smaller than to 0.1% capsaicin. All units tested also responded to topical application of mustard oil (50%) and ic serotonin (30 μg). The results are discussed in terms of theories that attempt to reconcile psychophysical and clinical observations of pain and itch sensation.

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Spinal Excitatory Dynorphinergic Interneurons Contribute to Burn Injury-Induced Nociception Mediated by Phosphorylated Histone 3 at Serine 10 in Rodents

International Journal of Molecular Sciences ◽

10.3390/ijms22052297 ◽

2021 ◽

Vol 22 (5) ◽

pp. 2297

Author(s):

Angelika Varga ◽

Zoltán Mészár ◽

Miklós Sivadó ◽

Tímea Bácskai ◽

Bence Végh ◽

...

Keyword(s):

Dorsal Horn ◽

Elevated Level ◽

Burn Injury ◽

Projection Neurons ◽

Superficial Dorsal Horn ◽

Noxious Heat ◽

Dorsal Horn Neurons ◽

Histone 3 ◽

Nociceptive Processing

The phosphorylation of serine 10 in histone 3 (p-S10H3) has recently been demonstrated to participate in spinal nociceptive processing. However, superficial dorsal horn (SDH) neurons involved in p-S10H3-mediated nociception have not been fully characterized. In the present work, we combined immunohistochemistry, in situ hybridization with the retrograde labeling of projection neurons to reveal the subset of dorsal horn neurons presenting an elevated level of p-S10H3 in response to noxious heat (60 °C), causing burn injury. Projection neurons only represented a small percentage (5%) of p-S10H3-positive cells, while the greater part of them belonged to excitatory SDH interneurons. The combined immunolabeling of p-S10H3 with markers of already established interneuronal classes of the SDH revealed that the largest subset of neurons with burn injury-induced p-S10H3 expression was dynorphin immunopositive in mice. Furthermore, the majority of p-S10H3-expressing dynorphinergic neurons proved to be excitatory, as they lacked Pax-2 and showed Lmx1b-immunopositivity. Thus, we showed that neurochemically heterogeneous SDH neurons exhibit the upregulation of p-S10H3 shortly after noxious heat-induced burn injury and consequential tissue damage, and that a dedicated subset of excitatory dynorphinergic neurons is likely a key player in the development of central sensitization via the p-S10H3 mediated pathway.

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