Biomedical subjects

G F Gebhart

Publications and source records attributed to G F Gebhart.

At least 37 records · Page 2Linked to original sources

PubMed2003

Gastric ulcers reduce A-type potassium currents in rat gastric sensory ganglion neurons.

Voltage-dependent potassium currents are important contributors to neuron excitability and thus also to hypersensitivity after tissue insult. We hypothesized that gastric ulcers would alter K(+) current properties in primary sensory neurons. The rat stomach was surgically exposed, and a retrograde tracer (1,1'-dioctadecyl-3,3,3,3'-tetramethylindocarbocyanine methanesulfonate) was injected into multiple sites in the stomach wall. Inflammation and ulcers were produced by 10 injections of 20% acetic acid (HAc) in the gastric wall. Saline (Sal) injections served as control. Nodose or T9-10 dorsal root ganglia (DRG) cells were harvested and cultured 7 days later to record whole cell K(+) currents. Gastric sensory neurons expressed transient and sustained outward currents. Gastric inflammation significantly decreased the A-type K(+) current density in DRG and nodose neurons (Sal vs. HAc-DRG: 82.9 +/- 7.9 vs. 46.5 +/- 6.1 pA/pF; nodose: 149.2 +/- 10.9 vs. 71.4 +/- 11.8 pA/pF), whereas the sustained current was not altered. In addition, there was a significant shift in the steady-state inactivation to more hyperpolarized potentials in nodose neurons (Sal vs. HAc: -76.3 +/- 1.0 vs. -83.6 +/- 2.2 mV) associated with an acceleration of inactivation kinetics. These data suggest that a reduction in K(+) currents contributes, in part, to increased neuron excitability that may lead to development of dyspeptic symptoms.

4-Aminopyridine↗

PubMed2003

Arylacetamide kappa-opioid receptor agonists produce a tonic- and use-dependent block of tetrodotoxin-sensitive and -resistant sodium currents in colon sensory neurons.

We have previously reported that U50,488 [(trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]benzeneacetamide] enantiomers contribute to visceral antinociception by a nonopioid receptor-mediated blockade of sodium currents in colon sensory neurons. The present experiments were undertaken to examine the effect of arylacetamide kappa-opioid receptor agonists (kappa-ORAs) U50,488 and EMD 61,753 [(N-methyl-N-[1S)-1-phenyl)-2-(13S))-3-hydroxypyrrolidine-1-yl)-ethyl]-2,2-diphenylacetamide HCl] on tetrodotoxin-sensitive (TTX-S) and -resistant (TTX-R) sodium currents, and the mechanism of their sodium channel-blocking actions. Whole cell patch-clamp experiments were performed on colon sensory neurons from the S1 dorsal root ganglion identified by content of retrograde tracer 1.1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine metanesulfonate. The concentration-response curves of U50,488 and EMD 61,753, for tonic inhibition of total, TTX-S, and TTX-R sodium currents were similar (EC50 values for U50,488 and EMD 61,753 were 8.4 +/- 1.69 and 1.2 +/- 1.78 microM, respectively). In contrast, the peptide kappa-ORA dynorphin was without effect in these experiments. U50,488 (10 microM) shifted the voltage dependence of steady-state inactivation curves for total, TTX-S, and TTX-R currents to more negative potentials. Inhibition was present at holding potentials of -100 to -20 mV. After the tonic block elicited by 10 microM U50,488, repetitive stimulation with 5-ms depolarizing pulses at a frequency of 3 Hz further enhanced the inhibition of total, TTX-R, and TTX-S currents by 43.8 +/- 4.9, 46.2 +/- 4.9, and 40 +/- 3.2%, respectively. These results demonstrate that arylacetamide kappa-ORAs nonselectively inhibit voltage-evoked sodium currents in a manner similar to local anesthetics, by enhancing closed-state inactivation and induction of use-dependent block.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed2003

Nonopioid actions of U50,488 enantiomers contribute to their peripheral cutaneous antinociceptive effects.

The ability of arylacetamide kappa-opioid receptor agonists (kappa-ORAs) to block sodium channels by a nonopioid mechanism has been previously documented. The present experiments were undertaken to test whether two enantiomers of the arylacetamide kappa-ORA (trans)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]benzeneacetamide (U50,488), (+)-(1R,2R)-U50,488 and (-)-(1S,2S)-U50,488, are antinociceptive in the formalin model by a peripheral, nonopioid receptor-mediated mechanism. Although both enantiomers have been previously shown to block sodium channels with comparable potencies, only (-)-(1S,2S)-U50,488 has activity at the kappa-opioid receptor (KOR). In the formalin test, intrapaw administration of U50,488 enantiomers as well as lidocaine exhibited significant dose-related attenuation of formalin-induced flinching behavior. The rank order of potency of the drugs tested was (-)-(1S,2S)-U50,488 > (+)-(1R,2R)-U50,488 > lidocaine. The antinociception produced by lower doses of (-)-(1S,2S)-U50,488 was blocked by intrapaw nor-binaltorphimine as well as by antisense knockdown of the KOR. Such pretreatments, however, did not block the antinociception produced by (+)-(1R,2R) U50,488, lidocaine, or higher doses of (-)-(1S,2S)-U50,488. These data suggest that the sodium channel blocking effects of U50,488 and similar kappa-ORAs can contribute to their peripheral antinociceptive actions.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed2003

Characterization and opioid modulation of inflammatory temporomandibular joint pain in the rat.

PURPOSE: Experimental inflammation of the rat temporomandibular joint (TMJ) is commonly used to study trigeminal nociceptive processing. This study describes spontaneous pain-related behaviors following TMJ inflammation in the rat. The ability of preemptive systemic morphine to attenuate behaviors as well as immediate-early gene expression in the trigeminal nucleus is described. MATERIALS AND METHODS: Adult male Sprague-Dawley rats received an intra-articular injection of mustard oil (0% to 20%, 50 microL) and were observed for behavioral changes. Morphine sulfate (0 to 10 mg/kg SC) was given 30 minutes before mustard oil; this was reversed in one group with naltrexone hydrochloride (5 mg/kg SC). Two hours after injection rats were killed and perfused. Immunohistochemistry for the protein product of the immediate-early gene c-fos was performed, and brain stem sections including the trigeminal subnucleus caudalis were examined for positive nuclei. RESULTS: Mustard oil inflammation of the rat TMJ induces dose-dependent, morphine-sensitive behaviors. Behaviors observed included excessive grooming of the region, a chewing-like behavior, and head shaking. Fos expression in the trigeminal subnucleus caudalis parallels changes in behaviors. Morphine dose dependently attenuates the number of behaviors, as well as Fos expression; this effect is reversed by the micro-opioid receptor antagonist naltrexone. CONCLUSIONS: Mustard oil inflammation of the rat TMJ causes reliable behavioral changes, which may be quantified and, together with Fos expression, used to assess various experimental TMJ treatment modalities.

Analgesics, Opioid↗

PubMed2003

Modulation of visceral hyperalgesia by morphine and cholecystokinin from the rat rostroventral medial medulla.

Using a model of visceral nociception, we examined whether cholecystokinin (CCK) acts as an anti-opioid peptide in the rat rostral ventromedial medulla (RVM). Because such interaction may be affected by inflammation, rats with and without inflamed colons were studied. The visceromotor response to noxious colorectal distension (CRD), quantified electromyographically, was recorded before and after intra-RVM administration of CCK, CCK receptor antagonists, and morphine. Either 50% ethanol/saline (vehicle) or 2,4,6-trinitrobenzenesulfonic acid (TNBS), which inflames the colon, was instilled into the colon 5 days before experiments. Intra-RVM morphine dose-dependently attenuated responses to CRD in intracolonic vehicle-treated rats. In TNBS-treated rats with inflamed colons, responses to CRD were significantly increased and 0.3, 3.0 and 6.0 microg doses of intra-RVM morphine reduced responses to control (i.e. were anti-hyperalgesic); the greatest dose tested (30 microg) further reduced responses to 40% control. In intracolonic vehicle-treated rats, intra-RVM pre-treatment with a selective CCK(B) (but not CCK(A)) receptor antagonist dose-dependently and significantly enhanced the effect of a low dose of morphine. Intra-RVM CCK-8 peptide enhanced responses to CRD in intracolonic vehicle-treated, but not TNBS-treated rats. Intra-RVM naloxone was without effect in intracolonic vehicle-or TNBS-treated rats, suggesting an absence of tonic opioid activity in RVM. These results document a CCK-opioid interaction in RVM, suggesting that colon inflammation leads to tonic activity at CCK(B) receptors in RVM.

Animals↗

PubMed2003

Nerve growth factor and gastric hyperalgesia in the rat.

We recently demonstrated an association between the development of hyperalgesia and an increase in nerve growth factor (NGF) during gastric inflammation. We hypothesized that block of NGF signalling will blunt injury-induced hyperalgesia. Male Sprague-Dawley rats (300-400 g) were anaesthetized, the stomach was exposed and placed in a circular clamp. Acetic acid (60%) or saline (control) was injected into this area and aspirated 45 s later, resulting in kissing ulcers. A balloon was surgically placed into the stomach and electromyographic responses to gastric distension (GD) were recorded from the acromiotrapezius muscle. Animals received a daily injection of neutralizing NGF antibody or control serum for 5 days. NGF in the stomach wall was measured with an ELISA. The severity of gastric injury was assessed macroscopically and by determination of myeloperoxidase (MPO) activity. Gastric injury enhanced the visceromotor response to GD and increased NGF content. Anti-NGF significantly blunted the development of hyperalgesia and led to a decrease in gastric wall thickness and MPO activity. Increases in NGF contribute to the development of hyperalgesia after gastric injury. This may be partly mediated by direct effects on afferent nerves and indirectly by modulatory effects on the inflammatory response.

Acetic Acid↗

PubMed2003

Role of nerve growth factor in modulation of gastric afferent neurons in the rat.

Recent studies demonstrated that experimental ulcers are associated with changes in the properties of voltage-sensitive sodium currents in sensory neurons. We hypothesized that nerve growth factor (NGF) contributes to these changes. Gastric ulcers were induced by acetic acid injection into the wall of the rat stomach. NGF expression was determined by ELISA and immunohistochemically. Sensory neurons were labeled by injection of a retrograde tracer into the gastric wall. Sodium currents were recorded in gastric sensory neurons from nodose and dorsal root ganglia cultured for 24 h in the presence of NGF or a neutralizing NGF antibody, respectively. Gastric ulcer formation caused a rise in NGF concentration within the gastric wall and an increase in NGF immunoreactivity. Exposure to NGF caused a significant increase in the TTX-resistant sodium current, whereas the TTX-sensitive sodium current remained unchanged. This was associated with an acceleration of the recovery from inactivation in spinal sensory neurons. Production and release of NGF in the gastric wall may contribute to sensitization of primary afferent neurons during gastric inflammation.

Anesthetics, Local↗

PubMed2002

Quantitative assessment and characterization of visceral nociception and hyperalgesia in mice.

Colorectal distension (CRD) is a well-characterized model of visceral nociception, which we adapted to the mouse. CRD reproducibly evoked contractions of the abdominal musculature [visceromotor response (VMR)], which was graded to stimulus intensity. The magnitude of VMR was greater in male C57BL6 and female 129S6 mice than in male 129S6 and B6.129 mice. In 129S6, C57BL6, and B6.129 mice strains, VMR was reduced dose dependently by morphine (1-10 mg/kg) and by the kappa-opioid agonist U-69593 (0.2-2 mg/kg), although U-69593 was significantly less potent in C57BL6 mice. In additional experiments, the VMR was recorded from adult male 129S6 mice before and after intracolonic administration of various irritants. Only 30% ethanol significantly enhanced responses to CRD. The colon hyperalgesia persisted for 14 days and was associated with a significant shift of the morphine dose-response function to the left. We believe this will be a useful model for study of visceral nociception and hyperalgesia, including studies of transgenic mice with mutations relevant to pain.

Analgesics, Opioid↗

PubMed2002

Chronic pain and medullary descending facilitation.

Chronic pain, whether the result of nerve trauma or persistent inflammation, is a debilitating condition that exerts a high social cost in terms of productivity, economic impact and quality of life. Currently available therapies yield limited success in treating such pain, suggesting the need for new insight into underlying mechanism(s). Here, we examine the likelihood that sustained activation of descending modulatory pathways that facilitate pain transmission could underlie some states of chronic pain. Such activation of descending facilitatory pathways might be the result of neuroplastic changes that occur at medullary sites in response to persistent input of pain signals. Understanding the mechanisms of descending facilitation and the spinal effects of such discharge could provide new insights into the modulation of chronic pain.

Animals↗

PubMed2002

The pharmacology of gastrointestinal nociceptive pathways.

The principal conscious sensations that arise from the gastrointestinal tract are discomfort and pain. Chronic visceral discomfort and pain are generally managed poorly with currently available pharmacological agents. Receptors and ion channels present on extrinsic visceral primary afferent (sensory) neurons are targets for the development of new pharmacological strategies for control of visceral pain.

Animals↗

PubMed2002

Experimental ulcers alter voltage-sensitive sodium currents in rat gastric sensory neurons.

BACKGROUND & AIMS: Voltage-dependent Na+ currents are important determinants of excitability. We hypothesized that gastric inflammation alters Na+ current properties in primary sensory neurons. METHODS: The stomach was surgically exposed in rats to inject the retrograde tracer 1.1'-dioctadecyl-3,3,3,'3-tetramethylindocarbocyanine methanesulfonate and saline (control) or 20% acetic acid (ulcer group) into the gastric wall. Nodose or thoracic dorsal root ganglia (DRG) were harvested after 7 days to culture neurons and record Na+ currents using patch clamp techniques. RESULTS: There were no lesions in the control and 3 +/- 1 ulcers in the ulcer group. Na+ currents recovered significantly more rapidly from inactivation in nodose and DRG neurons obtained from animals in the ulcer group compared with controls. This was partially a result of an increase in the relative contribution of the tetrodotoxin-resistant to the peak sodium current. In addition, the recovery kinetics of the tetrodotoxin-sensitive current were faster. In DRG neurons, gastric inflammation shifted the voltage-dependence of activation of the tetrodotoxin-resistant current to more hyperpolarized potentials. CONCLUSIONS: Gastric injury alters the properties of Na+ currents in gastric sensory neurons. This may enhance excitability, thereby contributing to the development of dyspeptic symptoms.

Acetic Acid↗

PubMed2002

Facilitation and attenuation of a visceral nociceptive reflex from the rostroventral medulla in the rat.

BACKGROUND & AIMS: Noxious inputs from somatic tissue are subject to biphasic descending modulation from the rostroventral medulla (RVM). In the present study, we investigated descending facilitatory and inhibitory influences from the RVM on a visceral nociceptive reflex. METHODS: The visceromotor response (VMR), a contraction of peritoneal musculature during noxious colorectal distention (80 mm Hg, 20 seconds), was quantified as the integrated electromyogram. RESULTS: At 22 sites in the RVM, electrical stimulation produced biphasic effects, facilitating the VMR at low (5, 10, and 25 microA) and inhibiting it at greater (>50 microA) intensities of stimulation. Electrical stimulation at all intensities tested (5-200 microA) in other sites in the RVM only inhibited (30 sites) or only facilitated (12 sites) the VMR to colorectal distention. Activation of glutamatergic receptors in the RVM replicated the effects of electrical stimulation. Reversible blockage (intraspinal lidocaine injection) or irreversible transection of spinal funiculi revealed that descending facilitatory influences from the RVM were conveyed in the ventrolateral/ventral funiculus, whereas descending inhibitory influences were contained in the dorsolateral funiculi. CONCLUSIONS: Spinal visceral nociceptive reflexes are subject to facilitatory modulation from the RVM, providing the basis for a mechanism by which visceral sensations can be enhanced from supraspinal sites.

Animals↗

PubMed2002

Activation of lamina I spinal cord neurons that express the substance P receptor in visceral nociception and hyperalgesia.

Spinal lamina I neurons expressing the substance P receptor (SPR) have been shown to play a role in the transmission of somatic inflammatory and neuropathic pain. To evaluate their involvement in visceral nociception in both the noninflamed and inflamed colon, we examined the expression and ligand-induced internalization of the SPR in the rat spinal cord after distention of the noninflamed colon and in rats with inflammation induced by intracolonic instillation of zymosan (3 hours). In the noninflamed animal, acute noxious but not non-noxious colorectal distention induced SPR internalization in lamina I neurons at the thoracolumbar (T13) and lumbosacral (S1) spinal levels, whereas SPR internalization was not detected in lamina I neurons at spinal lumbar segment L4. Although zymosan-induced colorectal inflammation alone did not induce SPR internalization in lamina I neurons, there was an increased number of SPR-expressing lamina I neurons showing SPR internalization in segments T12 through S2 of the spinal cord after colorectal distention. These results show that acute noxious visceral stimuli induce activation of spinal lamina I neurons expressing the SPR and, that after visceral inflammation, there is a marked increase in both the number and rostrocaudal extent of lamina I SPR neurons activated in response to both normally non-noxious and noxious distention of the colon.

Journal Article↗

PubMed2002

Gastric hyperalgesia and changes in voltage gated sodium channel function in the rat.

Potential peripheral mechanisms that might contribute to the development of visceral hypersensitivity and ultimately to the altered sensations that characterise functional gastrointestinal disorders were examined by developing experimental models of gastric hyperalgesia. A direct link between alteration in behaviour and potential mechanisms of increased excitability of the gastric afferent innervation was found.

Acetic Acid↗

PubMed2002

Models of gastric hyperalgesia in the rat.

Despite the prevalence of dyspepsia, nonhuman models for study of gastric hyperalgesia are limited. We thus characterized responses to gastric distension (GD) in the absence of and after two different gastric insults. A balloon was surgically placed into the stomach, and electromyographic responses to GD were recorded from the acromiotrapezius muscle at various times after balloon placement. Rats received either 20% acetic acid (HAc) or saline injections into the stomach wall or 0.1% iodoacetamide (IA) in drinking water. Responses to GD were monotonic with increasing distending pressure (10-80 mmHg) and were reproducible from days 3-14 after balloon implantation. Both HAc injection and IA ingestion led to increased responses to GD (i.e., gastric hyperalgesia), which, in the case of HAc, persisted for 60 days after HAc treatment. HAc injection produced ulcers in all treated animals; IA ingestion produced no lesions. Myeloperoxidase activity significantly increased after HAc but not saline injection or IA ingestion. In the awake, unrestrained rat, visceromotor responses to GD are quantifiable, reliable, and reproducible. Significantly enhanced responses to GD were apparent in two models of gastric insult, both of which may be useful for the study of the mechanisms of gastric hyperalgesia.

Acetic Acid↗

PubMed2002

Modulation of noxious and non-noxious spinal mechanical transmission from the rostral medial medulla in the rat.

Modulatory influences on spinal mechanical transmission from the rostral medial medulla (RMM) were studied. Noxious stimulation, produced by von Frey-like monofilaments, and non-noxious stimulation, produced by a soft brush, was applied to the glabrous skin of the hind foot. At 28 sites in RMM, electrical stimulation facilitated responses to noxious mechanical stimulation at low intensities (5-25 microA) and inhibited responses of the same neurons at greater intensities (50-100 microA) of stimulation. At 24 and 9 other sites in RMM, stimulation at all intensities only inhibited or only facilitated, respectively, responses to noxious mechanical stimulation of the hind foot. Stimulus-response functions to mechanical stimulation were shifted leftward by low intensities and decreased by high intensities of stimulation. Inhibitory influences were found to descend in the dorsolateral funiculi; facilitatory effects were contained in the ventral spinal cord. Descending modulation of non-noxious brush stimulation revealed biphasic facilitatory-inhibitory effects (9 sites in RMM), only inhibitory effects (14 sites) and only facilitatory effects (8 sites). The effects of electrical stimulation were replicated by intra-RMM administration of glutamate; a low concentration (0.25 nmol) facilitated and a greater concentration (2.5 nmol) inhibited spinal mechanical transmission, providing evidence that cells in RMM are sufficient to engage descending influences. Descending modulatory effects were specific for the site of stimulation, not for the spinal neuron, because modulation of the same neuron was different from different sites in RMM. These results show that spinal mechanical transmission, both noxious and non-noxious, is subject to descending influences, including facilitatory influences that may contribute to exaggerated responses to peripheral stimuli in some chronic pain states.

Animals↗

PubMed2002

Acute effect of an incision on mechanosensitive afferents in the plantar rat hindpaw.

The purpose of this study was to examine which primary afferent fibers are sensitized to mechanical stimuli after an experimental surgical incision to the glabrous skin of the rat hindpaw. Afferent fibers teased from the L(5) dorsal root or the tibial nerve were recorded in anesthetized rats. The mechanical response properties of each fiber were characterized before and 45 min after an incision (or sham procedure) within the mechanical receptive field. Sensitization is characterized by an expansion of the mechanical receptive field, an increase in background activity, an increase in response magnitude, or a decrease in response threshold. After incision, the background activity and response properties of Abeta-fibers (n = 9) to mechanical stimuli were unchanged. Four of 13 mechanosensitive Adelta-fibers exhibited sensitization after the incision; response threshold decreased, response magnitude increased, or receptive field size increased. Background activity of Adelta-fibers was not increased by the incision. Sensitization was observed in 4 of 18 mechanosensitive C-fibers 45 min after the incision. Background activity of C-fibers was not increased by the incision. In a group of mechanically insensitive afferent fibers (MIAs), 3 of 7 Adelta-fibers and 4 of 10 C-fibers sensitized 45 min after incision. Response threshold was decreased in only 2 of 17 MIAs; receptive field size increased in 7 of 17 MIAs. Abeta-fibers did not sensitize after the incision, and only 8 of 31 (26%) mechanosensitive Adelta- and C-fibers gave evidence of sensitization. In a group of MIA Adelta- and C-fibers, a greater percentage of 17 fibers studied (41%) were sensitized after incision. In this model, the principal effect of an incision, when examined 45 min after the insult, is an increase in receptive field size of the afferents, particularly those characterized as MIAs. To the extent that the mechanical hyperalgesia characterized in the same model is initiated in the periphery, it would appear that spatial summation of modestly increased response magnitude is important to the development of hyperalgesia.

Acute Disease↗

PubMed2002

Characterization of Adelta- and C-fibers innervating the plantar rat hindpaw one day after an incision.

Primary hyperalgesia after tissue injury is suggested to result from sensitization of primary afferent fibers, but sensitization to mechanical stimuli has been difficult to demonstrate. In the companion study, sensitization of mechano-responsive Adelta- and C-fibers did not explain pain behaviors 45 min after an incision in the rat hindpaw. In the present study, we examined mechanical response properties of Adelta- and C-fibers innervating the glabrous skin of the plantar hindpaw in rats 1 day after an incision or sham procedure. In behavioral experiments, median withdrawal thresholds to von Frey filaments were reduced from 522 mN before to 61 mN 2 and 20 h after incision; median withdrawal thresholds after sham procedure were stable (522 mN). Responses to a nonpunctate mechanical stimulus were increased after incision. In neurophysiological experiments in these same rats, 67 single afferent fibers were characterized from the left tibial nerve 1 day after sham procedure (n = 39) or incision (n = 28); electrical stimulation was used as the search stimulus to identify a representative population of Adelta- and C-fibers. In the incision group, 11 fibers (39%) had spontaneous activity with frequencies ranging from 0.03 to 39.3 imp/s; none were present in the sham group. The median response threshold of Adelta-fibers was less in the incision (56 mN, n = 13) compared with sham (251 mN, n = 26) group, mainly because the proportion of mechanically insensitive afferents (MIAs) was less (8 vs. 54% after sham procedure). Median C-fiber response thresholds were similar in incised (28 mN, n = 15) and sham rats (56 mN, n = 13). Responsiveness to monofilaments was significantly enhanced in Adelta-fibers 1 day after incision; stimulus response functions of C-fibers after incision and after sham procedure did not differ significantly. Only Adelta-fibers but not C-fibers sensitized to the nonpunctate mechanical stimulus. The size of receptive fields was increased in Adelta- and C-fibers 1 day after incision. The results indicate that sensitization of Adelta- and C-fibers is apparent 1 day after incision. Because sensitization of afferent fibers to mechanical stimuli correlated with behavioral results, sensitization may contribute to the reduced withdrawal threshold after incision. Spontaneous activity in Adelta- and C-fibers may account for nonevoked pain behavior and may also contribute to mechanical hyperalgesia by amplifying responses centrally.

Animals↗