tetrodotoxin and Chronic-Disease

An increasing number of patients complain to medical institutions about a cough that persists for more than 8 weeks, namely chronic cough. The cough observed in patients with chronic cough is not responsive to conventional antitussive agents such as dihydrocodeine and dextromethorphan, and this is a major clinical problem. The most common pathology of chronic cough in Japan is dry cough. Two causes of dry cough are increased sensitivity of cough receptors (cough hypersensitivity) and increased contraction of bronchial smooth muscle. Among these, the mechanisms of cough hypersensitivity are diverse, and understanding these mechanisms is important for the diagnosis and treatment of chronic cough. In this paper I will review the regulatory mechanisms of cough hypersensitivity, especially the regulation of Aδ fiber excitability by C fibers. Furthermore, the central mechanisms involved cough reflex are discussed in relation to central acting antitussives.

Topics: Animals; Arachidonic Acids; Bradykinin; Chronic Disease; Cough; Endocannabinoids; Guinea Pigs; Humans; Mice; Nerve Fibers, Myelinated; Nerve Fibers, Unmyelinated; Nitric Oxide; Polyunsaturated Alkamides; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid; Receptors, Purinergic P2X4; Respiratory Hypersensitivity; Serotonin; Sodium Channels; Tetrodotoxin; TRPV Cation Channels

Previous studies have shown that 5-HT3-antagonists reduce muscle pain, but there are no studies that have investigated the expression of 5-HT3-receptors in human muscles. Also, tetrodotoxin resistant voltage gated sodium-channels (NaV) are involved in peripheral sensitization and found in trigeminal ganglion neurons innervating the rat masseter muscle. This study aimed to investigate the frequency of nerve fibers that express 5-HT3A-receptors alone and in combination with NaV1.8 sodium-channels in human muscles and to compare it between healthy pain-free men and women, the pain-free masseter and tibialis anterior muscles, and patients with myofascial temporomandibular disorders (TMD) and pain-free controls.. Three microbiopsies were obtained from the most bulky part of the tibialis and masseter muscles of seven and six healthy men and seven and six age-matched healthy women, respectively, while traditional open biopsies were obtained from the most painful spot of the masseter of five female patients and from a similar region of the masseter muscle of five healthy, age-matched women. The biopsies were processed by routine immunohistochemical methods. The biopsy sections were incubated with monoclonal antibodies against the specific axonal marker PGP 9.5, and polyclonal antibodies against the 5-HT3A-receptors and NaV1.8 sodium-channels.. A similar percentage of nerve fibers in the healthy masseter (85.2%) and tibialis (88.7%) muscles expressed 5-HT3A-receptors. The expression of NaV1.8 by 5-HT3A positive nerve fibers associated with connective tissue was significantly higher than nerve fibers associated with myocytes (P < .001). In the patients, significantly more fibers per section were found with an average of 3.8 ± 3 fibers per section in the masseter muscle compared to 2.7 ± 0.2 in the healthy controls (P = .024). Further, the frequency of nerve fibers that co-expressed NaV1.8 and 5-HT3A receptors was significantly higher in patients (42.6%) compared to healthy controls (12.0%) (P < .001).. This study showed that the 5-HT3A-receptor is highly expressed in human masseter and tibialis muscles and that there are more nerve fibers that express 5-HT3A-receptors in the masseter of women with myofascial TMD compared to healthy women. These findings indicate that 5-HT3-receptors might be up-regulated in myofascial TMD and could serve as potential biomarkers of chronic muscle pain.

Topics: Adult; Chronic Disease; Female; Humans; Male; Masseter Muscle; Muscle, Skeletal; NAV1.8 Voltage-Gated Sodium Channel; Nerve Fibers; Receptors, Serotonin, 5-HT3; Sodium Channel Blockers; Temporomandibular Joint Disorders; Tetrodotoxin

Our previous study has shown that chronic heart failure (CHF) reduces expression and activation of voltage-gated sodium (Na(v)) channels in baroreceptor neurons, which are involved in the blunted baroreceptor neuron excitability and contribute to the impairment of baroreflex in the CHF state. The present study examined the role of mitochondria-derived superoxide in the reduced Na(v) channel function in coronary artery ligation-induced CHF rats. CHF decreased the protein expression and activity of mitochondrial complex enzymes and manganese SOD (MnSOD) and elevated the mitochondria-derived superoxide level in the nodose neurons compared with those in sham nodose neurons. Adenoviral MnSOD (Ad.MnSOD) gene transfection (50 multiplicity of infection) into the nodose neurons normalized the MnSOD expression and reduced the elevation of mitochondrial superoxide in the nodose neurons from CHF rats. Ad.MnSOD also partially reversed the reduced protein expression and current density of the Na(v) channels and the suppressed cell excitability (the number of action potential and the current threshold for inducing action potential) in aortic baroreceptor neurons from CHF rats. Data from the present study indicate that mitochondrial dysfunction, including decreased protein expression and activity of mitochondrial complex enzymes and MnSOD and elevated mitochondria-derived superoxide, contributes to the reduced Na(v) channel activation and cell excitability in the aortic baroreceptor neurons in CHF rats.

Topics: Action Potentials; Animals; Antimycin A; Biophysics; Bridged Bicyclo Compounds, Heterocyclic; Chronic Disease; Disease Models, Animal; Electric Stimulation; Enzyme Inhibitors; Gene Expression Regulation; Heart Failure; Hemodynamics; Humans; Lectins; Male; Mitochondria; Multienzyme Complexes; NADH Dehydrogenase; NAV1.7 Voltage-Gated Sodium Channel; Nodose Ganglion; Patch-Clamp Techniques; Phenanthridines; Pressoreceptors; Rats; Rats, Sprague-Dawley; Rotenone; Sodium Channel Blockers; Sodium Channels; Spectrophotometry; Succinate Dehydrogenase; Superoxide Dismutase; Tetrodotoxin; Transfection

Systemic carbamazepine, a voltage-gated sodium channel blocker, has been reported to dose-dependently reduce inflammatory hyperalgesia. However, the antinociceptive effects of carbamazepine on the spinal cord in inflammatory conditions are unclear. The aim of the present study was to evaluate the antinociceptive effects of carbamazepine on the spinal cord in a chronic inflammatory condition.. In Sprague-Dawley rats, a chronic inflammatory condition was induced by complete Freund's adjuvant (CFA) inoculation into the tail. Tail flick (TF) latencies were measured following intraperitoneal carbamazepine, or intrathecal carbamazepine or tetrodotoxin injection in intact rats and in the chronic inflammatory rats. From the values of TF latency at 60 min after drug injection, the effective dose required to produce 50% response (ED(50)) of each drug was derived.. Carbamazepine attenuated thermal responses with both systemic and intrathecal administration. The effect was more evident in rats with chronic inflammation than in intact rats; the ED(50s) of intraperitoneal carbamazepine in intact and inflamed rats were 12.39 and 1.54 mg/kg, and those of intrathecal carbamazepine were 0.311 and 0.048 nmol, respectively. Intrathecal tetrodotoxin also clearly inhibited the response, with ED(50s) of 1.006 pmol in intact rats and 0.310 pmol in inflamed rats. The relative potencies of intrathecal carbamazepine versus tetrodotoxin for inhibition were approximately 1:150-1:300 in intact and inflamed rats.. These results indicate that the inhibition of voltage-gated sodium channels, at least tetrodotoxin-sensitive channels, may contribute to the antinociceptive effect of carbamazepine on CFA-induced inflammatory pain, since lower doses of intrathecal carbamazepine and tetrodotoxin attenuated thermal responses to a greater extent in inflamed rats than in intact rats.

Topics: Analgesics, Non-Narcotic; Anesthetics, Local; Animals; Arthritis, Experimental; Carbamazepine; Chronic Disease; Dose-Response Relationship, Drug; Freund's Adjuvant; Hypesthesia; Inflammation; Injections, Intraperitoneal; Injections, Spinal; Rats; Rats, Sprague-Dawley; Reaction Time; Sodium Channel Blockers; Spine; Tail; Tetrodotoxin

Several voltage-gated sodium channels are expressed in primary sensory neurons where they control excitability and participate in the generation and propagation of action potentials. Peripheral nerve injury-induced alterations in both tetrodotoxin (TTX)-sensitive and TTX-resistant sodium channels have been proposed to contribute to neuropathic pain caused by such lesion. We herein investigated whether the blockade of TTX-sensitive channels could reduce pain-related behaviors and evoked c-Fos immunoreactivity in rats with neuropathic pain produced by chronic unilateral constriction injury to either the sciatic nerve or the infraorbital nerve. Acute as well as subchronic administration of TTX (1-6 mug/kg s.c.) was found to suppress for up to 3 h allodynia and hyperalgesia in sciatic nerve-ligated rats. In contrast, TTX was only moderately effective in rats with ligated infraorbital nerve. In sciatic nerve-ligated rats, TTX administration prevented the increased c-Fos immunoreactivity occurring in the dorsal horn of the lumbar cord and some supraspinal areas in response to light mechanical stimulation of the nerve-injured hindpaw. The anti-allodynia/antihyperalgesia caused by TTX in these neuropathic rats was promoted by combined treatment with naloxone (0.5 mg/kg s.c.) but unaffected by the 5-HT(1B) receptor antagonist F11648 (0.5 mg/kg s.c.) and the alpha(2)-adrenergic receptor antagonist idazoxan (0.5 mg/kg i.v.). In contrast, the anti-allodynic and anti-hyperalgesic effects of TTX were significantly attenuated by co-administration of morphine (3 mg/kg s.c.) or the cholecystokinin(2)-receptor antagonist CI-1015 (0.1 mg/kg i.p.). These results indicate that TTX alleviates pain-related behaviors in sciatic nerve-lesioned rats through mechanisms that involve complex interactions with opioidergic systems.

Topics: Anesthetics, Local; Animals; Chronic Disease; Cranial Nerve Diseases; Drug Therapy, Combination; Hyperalgesia; Immunohistochemistry; Lumbar Vertebrae; Male; Neuralgia; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Sciatic Neuropathy; Spinal Cord; Tetrodotoxin; Time Factors

Hyperpolarization-activated cyclic nucleotide-gated cation channels (HCN channels) have large influences upon neuronal excitability. However, the participation of spinal HCN channels in chronic pain states, where pathological conditions are related to altered neuronal excitability, has not been clarified. Intraperitoneally (i.p.) or intrathecally (i.t.) administered ZD7288, a selective blocker of Ih channels, reduced thermal and mechanical hypersensitivity in mice under neuropathic conditions induced by the partial ligation of the sciatic nerve, while no analgesic effect was observed in naïve animals. Moreover, in the mouse formalin test, ZD7288 (i.p. and i.t.) reduced the licking/biting behavior observed during the second phase without affecting the first phase. To further explore the pain-modulatory action of spinal HCN channels, whole-cell patch clamp recordings were made from the visually identified substantia gelatinosa neurons in adult mouse spinal cord slices with an attached dorsal root, and A-fiber- and/or C-fiber-mediated monosynaptic excitatory postsynaptic currents (EPSCs) were evoked by electrical stimulation of the L4 or L5 dorsal root using a suction electrode. Bath-applied ZD7288 reduced A-fiber- and C-fiber-mediated monosynaptic EPSCs more preferentially in slices prepared from mice after peripheral nerve injury. In addition, ZD7288 reduced the frequency of miniature EPSCs without affecting their amplitude in cells receiving monosynaptic afferent inputs, indicating that it inhibits EPSCs via presynaptic mechanisms. The present behavioral and electrophysiological data suggest that spinal HCN channels, most likely at the primary afferent terminals, contribute to the maintenance of chronic pain.

Topics: Animals; Cardiotonic Agents; Chronic Disease; Cyclic Nucleotide-Gated Cation Channels; Disease Models, Animal; Dose-Response Relationship, Drug; Excitatory Postsynaptic Potentials; Hyperalgesia; In Vitro Techniques; Male; Membrane Potentials; Mice; Mice, Neurologic Mutants; Nerve Fibers; Pain Measurement; Patch-Clamp Techniques; Presynaptic Terminals; Pyrimidines; Sciatica; Sodium Channel Blockers; Spinal Cord; Tetrodotoxin

A recent study of our group has shown that in the segments L4 and L5 of the rat, the synaptic field potentials (SFPs) evoked by tetrodotoxin-resistant (TTX-r, presumably nociceptive) muscle afferents differ in size and peak location from those of cutaneous afferents from the same body region [Lambertz D, Hoheisel U, Mense S. Distribution of synaptic field potentials induced by TTX-resistant skin and muscle afferents in rat segment L4 and L5. Neurosci Lett 2006;409:14-8]. Here, we investigated the influence of a muscle inflammation on the distribution of SFPs of TTX-r afferent fibres from muscle and skin in the thoracic and lumbar spinal cord. During a TTX block of the dorsal roots L3-L6, a skin nerve (sural, SU) or a muscle nerve (gastrocnemius-soleus, GS) were electrically stimulated at an intensity supramaximal for unmyelinated afferents and the SFPs recorded with tungsten microelectrodes. In control (non-inflamed) rats, the largest SFPs evoked by TTX-r GS afferents were recorded in laminae IV-VI with a maximum in segment L4, whereas the largest SU-induced SFPs were more superficially located with a maximum in L3. In chronic myositis animals, SFPs induced by GS TTX-r fibres exhibited significant decreases in lamina IV-VI of Th 12 and L5 as well as in lamina VII of L5. In contrast, SFPs evoked by SU TTX-r afferents showed significant increases in lamina IV-VI in L1 and in lamina VII in L4. The results demonstrate that a chronic myositis has a strong influence also on the synaptic effects of nociceptive afferents from the skin, which may explain the subjective cutaneous sensations during a pathological alteration of muscle.

Topics: Anesthetics, Local; Animals; Chronic Disease; Drug Resistance; Evoked Potentials, Somatosensory; Male; Muscle, Skeletal; Myositis; Nerve Fibers, Myelinated; Nerve Fibers, Unmyelinated; Neurons, Afferent; Rats; Rats, Sprague-Dawley; Skin; Tetrodotoxin

The recovery of persistent inward currents (PICs) and motoneuron excitability after chronic spinal cord transection is mediated, in part, by the development of supersensitivity to residual serotonin (5HT) below the lesion. The purpose of this paper is to investigate if, like 5HT, endogenous sources of norepinephrine (NE) facilitate motoneuron PICs after chronic spinal transection. Cutaneous-evoked reflex responses in tail muscles of awake chronic spinal rats were measured after increasing presynaptic release of NE by administration of amphetamine. An increase in long-lasting reflexes, known to be mediated by the calcium component of the PIC (CaPIC), was observed even at low doses (0.1-0.2 mg/kg) of amphetamine. These findings were repeated in a reduced S2 in vitro preparation, demonstrating that the increased long-lasting reflexes by amphetamine were neural. Under intracellular voltage clamp, amphetamine application led to a large facilitation of the motoneuron CaPIC. This indicates that the increases in long-lasting reflexes induced by amphetamine in the awake animal were, in part, due to actions directly on the motoneuron. Reflex responses in acutely spinal animals were facilitated by amphetamine similar to chronic animals but only at doses that were ten times greater than that required in chronic animals (0.2 mg/kg chronic vs. 2.0 mg/kg acute), pointing to a development of supersensitivity to endogenous NE in chronic animals. In summary, the increases in long-lasting reflexes and associated motoneuron CaPICs by amphetamine are likely due to an increased release of endogenous NE, which motoneurons become supersensitive to in the chronic stages of spinal cord injury.

Topics: Adrenergic Uptake Inhibitors; Amphetamine; Anesthetics, Local; Animals; Anterior Horn Cells; Chronic Disease; Disease Models, Animal; Dose-Response Relationship, Drug; Electric Stimulation; Electromyography; Female; In Vitro Techniques; Membrane Potentials; Muscle Contraction; Norepinephrine; Patch-Clamp Techniques; Rats; Rats, Sprague-Dawley; Skin; Spasm; Spinal Cord Injuries; Tetrodotoxin

Peripheral nerve injury increases spontaneous action potential discharge in spinal dorsal horn neurons and augments their response to peripheral stimulation. This "central hypersensitivity, " which relates to the onset and persistence of neuropathic pain, reflects spontaneous activity in primary afferent fibers as well as long-term changes in the intrinsic properties of the dorsal horn (centralization). To isolate and investigate cellular mechanisms underlying "centralization," sciatic nerves of 20-day-old rats were subjected to 13-25 days of chronic constriction injury (CCI; Mosconi-Kruger polyethylene cuff model). Spinal cord slices were then acutely prepared from sham-operated or CCI animals, and whole cell recording was used to compare the properties of five types of substantia gelatinosa neuron. These were defined as tonic, irregular, phasic, transient, or delay according to their discharge pattern in response to depolarizing current. CCI did not affect resting membrane potential, rheobase, or input resistance in any neuron type but increased the amplitude and frequency of spontaneous and miniature excitatory postsynaptic currents (EPSCs) in delay, transient, and irregular cells. These changes involved alterations in the action potential-independent neurotransmitter release machinery and possible increases in the postsynaptic effectiveness of glutamate. By contrast, in tonic cells, CCI reduced the amplitude and frequency of spontaneous and miniature EPSCs. Such changes may relate to the putative role of tonic cells as inhibitory GABAergic interneurons, whereas increased synaptic drive to delay cells may relate to their putative role as the excitatory output neurons of the substantia gelatinosa. Complementary changes in synaptic excitation of inhibitory and excitatory neurons may thus contribute to pain centralization.

Topics: Animals; Chronic Disease; Constriction, Pathologic; Electrophysiology; Excitatory Postsynaptic Potentials; Membrane Potentials; Nerve Fibers, Myelinated; Nerve Fibers, Unmyelinated; Neurons; Neurons, Afferent; Patch-Clamp Techniques; Rats; Rats, Sprague-Dawley; Sciatic Nerve; Substantia Gelatinosa; Tetrodotoxin

The tetrodotoxin-resistant voltage-gated sodium channel (VGSC) Na(v)1.8 is expressed predominantly by damage-sensing primary afferent nerves and is important for the development and maintenance of persistent pain states. Here we demonstrate that muO-conotoxin MrVIB from Conus marmoreus displays substantial selectivity for Na(v)1.8 and inhibits pain behavior in models of persistent pain. In rat sensory neurons, submicromolar concentrations of MrVIB blocked tetrodotoxin-resistant current characteristic of Na(v)1.8 but not Na(v)1.9 or tetrodotoxin-sensitive VGSC currents. MrVIB blocked human Na(v)1.8 expressed in Xenopus oocytes with selectivity at least 10-fold greater than other VGSCs. In neuropathic and chronic inflammatory pain models, allodynia and hyperalgesia were both reduced by intrathecal infusion of MrVIB (0.03-3 nmol), whereas motor side effects occurred only at 30-fold higher doses. In contrast, the nonselective VGSC blocker lignocaine displayed no selectivity for allodynia and hyperalgesia versus motor side effects. The actions of MrVIB reveal that VGSC antagonists displaying selectivity toward Na(v)1.8 can alleviate chronic pain behavior with a greater therapeutic index than nonselective antagonists.

Topics: Animals; Chronic Disease; Conotoxins; Female; Ganglia, Spinal; In Vitro Techniques; Male; NAV1.8 Voltage-Gated Sodium Channel; Nerve Tissue Proteins; Neurons; Oocytes; Pain; Rats; Rats, Sprague-Dawley; Recombinant Proteins; Sodium Channel Blockers; Sodium Channels; Tetrodotoxin; Xenopus laevis

(1) Increased vascular resistance in chronic heart failure (CHF) has been attributed to stimulated neurohumoral systems. However, local mechanisms may also importantly contribute to set arterial tone. Our aim, therefore, was to test whether pressure-induced myogenic constriction of resistance arteries in vitro--devoid of acute effects of circulating factors--is increased in CHF and to explore underlying mechanisms. (2) At 12 weeks after coronary ligation-induced myocardial infarction or SHAM-operations in rats, we studied isolated mesenteric arteries for myogenic constriction, determined as the active constriction (% of passive diameter) in response to stepwise increase in intraluminal pressure (20 - 160 mmHg), in the absence and presence of inhibitors of potentially involved modulators of myogenic constriction. (3) We found that myogenic constriction in mesenteric arteries from CHF rats was markedly increased compared to SHAM over the whole pressure range, the difference being most pronounced at 60 mmHg (24+/-2 versus 4+/-3%, respectively, P<0.001). (4) Both removal of the endothelium as well as inhibition of NO production (L-N(G)-monomethylarginine, 100 micro M) significantly increased myogenic constriction (+16 and +25%, respectively), the increase being similar in CHF- and SHAM-arteries (P=NS). Neither endothelin type A (ET(A))-receptor blockade (BQ123, 1 micro M) nor inhibition of perivascular (sympathetic) nerve conduction (tetrodotoxin, 100 nM) affected the myogenic response in either group. (5) Interestingly, increased myogenic constriction in CHF was fully reversed after angiotensin II type I (AT(1))-receptor blockade (candesartan, 100 nM; losartan, 10 micro M), which was without effect in SHAM. In contrast, neither angiotensin-converting enzyme (ACE) inhibition (lisinopril, 1 micro M; captopril, 10 micro M) or AT(2)-receptor blockade (PD123319, 1 micro M), nor inhibition of superoxide production (superoxide dismutase, 50 U ml(-1)), TXA(2)-receptor blockade (SQ29,548, 1 micro M) or inhibition of cyclooxygenase-derived prostaglandins (indomethacin, 10 micro M) affected myogenic constriction. (6) Sensitivity of mesenteric arteries to angiotensin II (10 nM - 100 micro M) was increased (P<0.05) in CHF (pD(2) 7.1+/-0.4) compared to SHAM (pD(2) 6.2+/-0.3), while the sensitivity to KCl and phenylephrine was not different. (7) Our results demonstrate increased myogenic constriction in small mesenteric arteries of rats with CHF, potentially making it an i

Topics: Angiotensin II; Angiotensin II Type 1 Receptor Blockers; Animals; Benzimidazoles; Biphenyl Compounds; Bridged Bicyclo Compounds, Heterocyclic; Captopril; Chronic Disease; Coronary Vessels; Disease Models, Animal; Endothelium-Dependent Relaxing Factors; Endothelium, Vascular; Fatty Acids, Unsaturated; Heart; Heart Failure; Hydrazines; Imidazoles; Indomethacin; Lisinopril; Losartan; Male; Mesenteric Arteries; Nitric Oxide; omega-N-Methylarginine; Pyridines; Rats; Rats, Wistar; Receptor, Angiotensin, Type 1; Renin-Angiotensin System; Superoxide Dismutase; Sympathetic Nervous System; Tetrazoles; Tetrodotoxin; Vascular Resistance

Injured dorsal root ganglion (DRG) neurons often develop adrenergic sensitivity. To investigate the mechanisms of this phenomenon, the effects of norepinephrine (NE) on membrane potential of large- and medium-sized A-type neurons from chronically compressed DRG were recorded electrophysiologically in vitro. NE induced a depolarization in both control (26/36) and injured (56/62) neurons, whereas the incidence and amplitude of NE-induced depolarization in the injured neurons were significantly higher than that in controls. Following NE-induced depolarization, a subthreshold membrane potential oscillation (SMPO) was triggered or enhanced that initiated or increased repetitive firing in a fraction of injured neurons (15/56). After the SMPO was selectively abolished by application of tetrodotoxin (TTX), NE-induced depolarization failed to produce repetitive firing, even with a greater depolarization. Application of Rp-cAMPS (500 microM), a selective inhibitor of protein kinase A (PKA), decreased both SMPO and repetitive firing evoked by NE application or by intracellular current injection. Conversely, Sp-cAMPS (500 microM), a PKA activator, had a facilitating effect on both the SMPO and the repetitive firing. These results strongly suggest that a PKA mediated triggering and enhancement of SMPO may be responsible for the excitatory effects of NE on sensory neurons in neuropathic rats.

Topics: Animals; Chronic Disease; Cyclic AMP; Differential Threshold; Enzyme Inhibitors; Female; Ganglia, Spinal; Male; Membrane Potentials; Nerve Compression Syndromes; Neurons; Norepinephrine; Oscillometry; Rats; Rats, Sprague-Dawley; Tetrodotoxin; Thionucleotides

The effect of chronic granulomatous inflammation of the intestine was studied on the prejunctional modulation of cholinergic nerve activity in the mouse ileum. Contractions to carbachol (0.01 - 0.3 microM) and to electrical field stimulation (EFS, 0.25 - 8 Hz) of enteric neurons were higher in inflamed ileum as compared to control ileum. However, when the neurally-mediated contractions to EFS were expressed as percentage of the direct smooth muscle contraction to carbachol, the responses to EFS were similar in control and inflamed ileum. Atropine (1 microM) abolished all contractions to EFS and carbachol in control and inflamed ileum. DMPP (3 - 30 microM), a nicotinic receptor agonist, induced concentration-dependent contractions that were more pronounced in inflamed ileum as compared to control ileum. Hexamethonium (100 microM), a nicotinic receptor blocker, significantly inhibited the contractions to EFS in inflamed ileum but not in control ileum. In control ileum, histamine (10 - 100 microM) and the histamine H(1) receptor agonist HTMT (3 - 10 microM) inhibited the contractions to EFS concentration-dependently without affecting the contractions to carbachol. The inhibitory effect of histamine and HTMT was prevented by the histamine H(1) antagonist mepyramine (5 - 10 microM) but not by the H(2)- and H(3)-receptor antagonists cimetidine and thioperamide (both 10 microM). In chronically inflamed ileum however, histamine (10 - 100 microM) and HTMT (3 - 10 microM) failed to inhibit the contractions to EFS. The histamine H(2) and H(3) receptor agonists dimaprit and R(-)-alpha-methylhistamine did not affect the contractions to EFS in control and inflamed ileum. The alpha(2)-receptor agonist UK 14.304 (0.01 - 0.1 microM) inhibited the contractions to EFS in control and inflamed ileum without affecting the contractions to carbachol. The effect of UK 14.304 was reversed by the alpha(2)-receptor antagonist yohimbine (1 microM). The inhibitory effect of UK 14.304 on contractions to EFS was of similar potency in control and inflamed ileum. Our results suggest that the prejunctional modulation of cholinergic nerve activity by nicotinic and histaminic H(1) receptors is disturbed during chronic intestinal inflammation whereas the modulation by alpha(2)-receptors is preserved. Such a disturbance of cholinergic nerve activity may contribute to the motility disturbances that are often observed during chronic intestinal diseases in humans.

Topics: Adrenergic Agonists; Adrenergic alpha-2 Receptor Agonists; Adrenergic alpha-2 Receptor Antagonists; Adrenergic Antagonists; Animals; Brimonidine Tartrate; Carbachol; Cholinergic Agents; Cholinergic Agonists; Cholinergic Antagonists; Chronic Disease; Dimethylphenylpiperazinium Iodide; Dose-Response Relationship, Drug; Electric Stimulation; Granuloma; Hexamethonium; Histamine; Histamine Agonists; Histamine Antagonists; Ileum; In Vitro Techniques; Male; Mice; Muscle Contraction; Neuromuscular Junction; Peroxidase; Quinoxalines; Receptors, Histamine; Schistosoma mansoni; Schistosomiasis mansoni; Synaptic Transmission; Tetrodotoxin

Topics: Animals; Chronic Disease; Drug Resistance; Ion Channel Gating; Ligation; Lumbosacral Region; NAV1.7 Voltage-Gated Sodium Channel; NAV1.8 Voltage-Gated Sodium Channel; Neurons, Afferent; Neuropeptides; Oligodeoxyribonucleotides, Antisense; Pain; Pain, Intractable; Peripheral Nerve Injuries; Peripheral Nerves; Rats; Sodium Channels; Spinal Nerves; Tetrodotoxin

The properties of bladder afferent neurons in L6 and S1 dorsal root ganglia of adult rats were evaluated after chronic bladder inflammation induced by 2 week treatment with cyclophosphamide (CYP; 75 mg/kg). Whole-cell patch-clamp recordings revealed that most (70%) of the dissociated bladder afferent neurons from control rats were capsaicin sensitive, with high-threshold long-duration action potentials that were not blocked by tetrodotoxin (TTX; 1 microM). These neurons exhibited membrane potential relaxations during voltage responses elicited by depolarizing current pulses and phasic firing during sustained membrane depolarization. After CYP treatment, a similar proportion (71%) of bladder afferent neurons were capsaicin sensitive with TTX-resistant spikes. However, the neurons were significantly larger in size (diameter 29.6 +/- 1.0 micrometer vs 23.6 +/- 0.8 micrometer in controls). TTX-resistant bladder afferent neurons from CYP-treated rats exhibited lower thresholds for spike activation (-25.4 +/- 0.5 mV) than those from control rats (-21.4 +/- 0.9 mV) and did not exhibit membrane potential relaxation during depolarization. Seventy percent of TTX-resistant bladder afferent neurons from CYP-treated rats exhibited tonic firing (average 12.3 +/- 1.4 spikes during a 500 msec depolarizing pulse) versus phasic firing (1.2 +/- 0.2 spikes) in normal bladder afferent neurons. Application of 4-aminopyridine (1 mM) to normal TTX-resistant bladder afferent neurons mimicked the changes in firing properties after CYP treatment. The peak density of an A-type K+ current (IA) during depolarizations to 0 mV in TTX-resistant bladder afferent neurons from CYP-treated rats was significantly smaller (42.9 pA/pF) than that from control rats (109.4 pA/pF), and the inactivation curve of the IA current was displaced to more hyperpolarized levels by approximately 15 mV after CYP treatment. These data suggest that chronic inflammation induces somal hypertrophy and increases the excitability of C-fiber bladder afferent neurons by suppressing IA channels. Similar electrical changes in sensory pathways may contribute to cystitis-induced pain and hyperactivity of the bladder.

Topics: 4-Aminopyridine; Action Potentials; Animals; Chronic Disease; Cyclophosphamide; Cystitis; Female; Ganglia, Spinal; Membrane Potentials; Nerve Fibers; Neurons, Afferent; Patch-Clamp Techniques; Rats; Rats, Sprague-Dawley; Tetrodotoxin; Urinary Bladder

In an ex situ organ perfusion system, that of the isolated nonrecirculating joint perfusion of rat small intestine and liver, insulin infused into the portal vein increased intestinal glucose absorption. This insulin action against the bloodstream can be blocked by TTX, indicating a propagation of the insulin signal via hepatoenteral nerves, which conforms with previous studies with atropine and carbachol. Insulin action could also be mimicked by dibutyryl cAMP (DBcAMP) acting directly on the absorptive enterocytes. Because autonomic neuropathy is a common late complication of diabetes mellitus, the possible impairment of these nerves in the diabetic state was studied in streptozotocin-diabetic rats. In the isolated joint intestine-liver perfusion, glucose was applied as a bolus into the lumen; its absorption was measured in the portal vein. In 5-day diabetic as well as in control rats, portal insulin, arterial carbachol, and arterial DBcAMP increased intestinal glucose absorption. In 3-mo diabetic rats portal insulin and arterial carbachol failed to stimulate glucose absorption, whereas arterial DBcAMP still did so, indicating an undisturbed function of the absorptive enterocytes. The lack of an effect of portal insulin and arterial carbachol and the unchanged action of DBcAMP in the chronically diabetic rats indicated that the signaling chain via the hepatoenteral nerves was impaired, which is in line with a diabetic neuropathy.

Topics: Acute Disease; Animals; Autonomic Nervous System; Bucladesine; Carbachol; Chronic Disease; Cyclic AMP; Diabetes Mellitus, Experimental; Glucose; In Vitro Techniques; Insulin; Intestinal Absorption; Kidney; Liver; Male; Portal Vein; Rats; Rats, Wistar; Signal Transduction; Tetrodotoxin

Despite the susceptibility of immature neurons to seizures, there are few models of epilepsy in the developing brain. By taking advantage of activity-dependent developmental changes in young neurons, we have developed a novel model of chronic epilepsy in cultured hippocampal slices. Incubating slices in tetrodotoxin (TTX) for at least 1 week produced significant changes in the electrical activity and appearance of CA1 pyramidal neurons. Extracellular recordings revealed multiple population spikes, and, in whole-cell recordings, evoked synaptic potentials lasting hundreds of milliseconds with many superimposed action potentials were present. Spontaneous firing with burst-like discharges was also evident. These changes were secondary to increased AMPA-receptor-mediated responses and decreased GABA(A) receptor events. Altered membrane properties involved increased expression of T-type Ca(2+) channels which are normally down-regulated in these neurons. TTX-treated neurons also showed abnormal dendritic branching. This model of chronic epilepsy in developing hippocampal neurons demonstrated many changes at the membrane, cellular and synaptic level that may provide new insights into the nature of epileptogenesis in the young brain.

Topics: Animals; Animals, Newborn; Calcium Channels, T-Type; Chronic Disease; Electrophysiology; Epilepsy; Hippocampus; In Vitro Techniques; Neurons; Rats; Rats, Wistar; Reaction Time; Receptors, AMPA; Receptors, GABA-A; Synaptic Transmission; Tetrodotoxin

Portal-systemic encephalopathy (PSE) is associated with an increased brain tissue turnover of serotonin (5-HT). Despite increased 5-HT metabolism, brain 5-HT release in rats with a portacaval shunt (PCS) seems to be unaltered. Although this may indicate that the overall 5-HT output is unaltered in PSE, it is also possible that the 5-HT release pattern might be altered in some way. In the present study, the potassium-evoked frontal neocortical release of 5-HT was studied in experimental chronic PSE. KCI (60 mM) produced marked increases in the 5-HT output compared with basal values both in PCS and sham rats. Simultaneously, the KCI challenge resulted in significant elevations in the 5-HT release of PCS compared with sham. In Ca2+-free medium, the difference between PCS and sham rats in the KCl-evoked release of 5-HT was abolished. In the presence of TTX (1 mM), both groups displayed increased extracellular 5-HT levels. Again, a difference with higher amplitude of the 5-HT release in PCS compared with sham was evident. It is concluded that in experimental chronic PSE an augmented neocortical 5-HT release compared with the normal in vivo situation is available. The possible mechanism(s) responsible for the difference in neocortical 5-HT output between PCS and sham-operated rats in response to the KCl-challenge is discussed.

Topics: Animals; Body Weight; Calcium; Chronic Disease; Extracellular Space; Frontal Lobe; Hepatic Encephalopathy; Hydroxyindoleacetic Acid; Liver; Male; Microdialysis; Neurons; Organ Size; Potassium Chloride; Rats; Rats, Sprague-Dawley; Serotonin; Tetrodotoxin

The effect of chronic ischemia on the electrical properties of human cardiac tissue is not well understood.. Membrane potentials were studied using microelectrode techniques in isolated human ventricular tissues obtained from nonischemic (n = 17) or chronically ischemic (n = 7) myocardium. In normal Tyrode's solution, resting potential (Vr) was lower in ischemic (-70.1 +/- 2.12 mV) than in nonischemic muscles (-77.6 +/- 0.93 mV; mean +/- SEM; P < 0.05). In high [K]o (> 10 mM) media, Vr was of similar magnitude in both types of tissue (in 21.6 mM [K]o, Vr was -53.1 +/- 2.24 mV in nonischemic and -49.6 +/- 2.03 mV in ischemic preparations; n = 7 each; P > 0.05). Lowering [K]o caused persistent hyperpolarization in nonischemic muscles, but caused depolarization in chronically ischemic preparations (in 2.7 mM [K]o, Vr was -84.9 +/- 2.74 mV and -61.7 +/- 7.72 mV, respectively; n = 7; P < 0.05). Pinacidil (100 microM) normalized the response of chronically ischemic preparations to [K]o. Action potentials (APs) from nonischemic tissues varied in shape and could show aberrations. Epinephrine (1.5 microM) and 4-aminopyridine (3 mM) increased the AP duration, while butanedione monoxime (20 mM) and tetrodotoxin (1 microM) shortened it. In chronically ischemic muscles, the AP was characterized by the absence of a plateau and the presence of a slow phase of final repolarization.. The differential effect of low [K]o on the resting membrane potential of nonischemic and chronically ischemic tissues suggests a change in the properties or the regulation of background K+ channels during chronic ischemia.

Topics: 4-Aminopyridine; Action Potentials; Chronic Disease; Diacetyl; Epinephrine; Heart; Humans; In Vitro Techniques; Membrane Potentials; Middle Aged; Myocardial Ischemia; Potassium; Tetrodotoxin