Intrathecally administered cholera toxin blocks allodynia and hyperalgesia in persistent pain models.

In persistent pain, the spinal cord concentration of the opioid peptide dynorphin increases dramatically, yet the function of dynorphin remains unknown. If prodynorphin expression could be manipulated in vivo, it might be possible to determine what role dynorphin plays in persistent pain. Previous work in our laboratory showed that prodynorphin expression is regulated through the cyclic adenosine monophosphate pathway. Therefore, we attempted to enhance prodynorphin expression in the spinal cord of rats by stimulating adenylate cyclase with cholera toxin; however, contrary to our hypothesis, intrathecally administered cholera toxin did not enhance prodynorphin expression. Rather, cholera toxin suppressed the increase in prodynorphin produced by inflammation. Cholera toxin also inhibited the allodynia and hyperalgesia associated with inflammation and nerve injury. Interestingly, the antiallodynic and antihyperalgesic actions of cholera toxin were reversed with the opioid receptor antagonist, naloxone. These findings suggest that cholera toxin enhances or unmasks an endogenous opioid pathway to produce its antiallodynic and antihyperalgesic effects. Furthermore, these data indicate that the suppression of the inflammation-induced increase in spinal cord prodynorphin is caused by the opioid-mediated decrease in the nociceptive stimulus.     

Stimulation of the nucleus paraventricularis thalami suppresses scratching and biting behaviour of arthritic rats and exerts a powerful effect on tests for acute pain

In 20 arthritis-sensitive Wistar rats, an electrode was implanted in the paraventricular thalamic nucleus (PV). In the tail-flick and hot-plate test, PV was stimulated continuously for a period of 30 min, during which every 5 min either a tail-flick or hot-plate test was performed. Stimulation of PV induced important prolongations of the reaction times on tail-flick and hot-plate tests. However, there was no significant correlation between the results of the two tests. The effect of stimulation was immediate and did not outlast the stimulation period. PV stimulation did not give rise to tolerance, either within the stimulation period of 30 min, or during the successive testing days. After the termination of these acute pain tests, rats were inoculated with Mycobacterium butyricum. All animals developed polyarthritis. PV stimulation had a profound suppressive effect on the scratching and biting behaviour displayed by the animals. This reduction in scratching and biting behaviour was specific for PV stimulation since stimulation of another target, the ventrolateral thalamic nucleus (4 animals), had no effect on these behaviours. The attenuation of the scratching and biting behaviour was not a result of a general motor impairment, since other behaviours increased (running and sniffing) or did not change. There was no significant correlation between the results of scratching behaviour with those of the tail-flick and hot-plate test.     

Intrathecally administered gabapentin inhibits formalin-evoked nociception and the expression of Fos-like immunoreactivity in the spinal cord of the rat

In the present study, we investigated the effects of intrathecal gabapentin on nociceptive behaviors and the numbers of spinal Fos-like immunoreactive (Fos-LI) neurons evoked by injection of 0.25 to 2.5% formalin in the hindpaw of the rat. Pretreatment with gabapentin dose dependently decreased flinches and weighted pain scores in phase 2, but not phase 1, at each concentration of formalin. The highest dose of gabapentin (100 microgram) shifted the EC(50) values of formalin for both flinches and weighted pain scores to the right by 2.5-fold, suggesting that formalin was perceived to be significantly less noxious. Gabapentin also decreased phase 2 behaviors when administered after formalin but was only one third as potent. Unlike its inhibition of formalin-evoked nociceptive behaviors, the effect of gabapentin on the expression of Fos-like immunoreactivity in the spinal cord was highly dependent on the concentration of formalin. Intrathecal pretreatment with 100 microgram of gabapentin did not decrease the numbers of Fos-LI neurons evoked by 0.5% formalin, yet this dose decreased the numbers of Fos-LI neurons in laminae I-II and VII-X of rats that received 1.25% formalin and uniformly decreased by 50% the numbers of Fos-LI neurons in all laminae of rats that received 2.5% formalin. These latter findings suggest that gabapentin neither nonselectively decreases the excitability of spinal cord neurons nor uniformly inhibits the release of all neurotransmitters from primary afferent terminals. Rather, its effects may be preferential for those neurotransmitters released by higher, more noxious concentrations of formalin and for conditions in which there is a greater induction of central sensitization.     

Intrathecally administered endotoxin or cytokines produce allodynia, hyperalgesia and changes in spinal cord neuronal responses to nociceptive stimuli in the rat.

Inflammatory processes occurring within the central nervous system (CNS) can produce 'illness induced behaviours' which include fever, sleep and the development of allodynia and hyperalgesia. Here we demonstrate the effects of the pro-inflammatory mediators, bacterial endotoxin, and rat recombinant interleukin 1 beta (rrIL-1 beta) or tumour necrosis factor-alpha (rrTNF alpha) on the integration of somatosensory information at the single neuronal level, via recordings from wide-dynamic range neurones in the dorsal horn of the spinal cord in anaesthetized rats. Intrathecal administration of E. coli lipopolysaccharide (LPS, 10 and 100 microg, i.t.) enhanced the activity of dorsal horn neurones, including facilitation of neuronal post-discharge. Intrathecal administration of IL-1 beta (5-5000 pg) or TNF-alpha (5-5000 pg) enhanced dorsal horn neuronal responses, including the acute responses to C-fibre stimulation, wind-up and post-discharge, however, the effects of IL-1 beta were more robust than those of TNF alpha. Intrathecal administration of IL-1 beta (1-1000 pg) also leads to the development of mechanical allodynia and hyperalgesia. On the other hand intrathecal application of TNF alpha did not produce changes in sensitivity to mechanical stimuli. Changes in the activity of spinal wide-dynamic range neurones induced by local inflammation may provide a pathomechanism for the clinical pathology of central pain syndrome, which can accompany CNS disease or acute CNS injury.     

Partial medial meniscectomy produces osteoarthritis pain-related behaviour in female C57BL/6 mice

Murine models of osteoarthritis (OA) provide a potentially powerful tool to elucidate mechanisms responsible for OA pain. However, few studies have examined pain behaviours in relevant OA models in mice. We have therefore characterized the time course and pharmacological sensitivities of pain-related behaviours in a model of OA in C57Bl/6 mice induced by partial medial meniscectomy. Progressive degenerative joint damage developed in a time-dependent manner and was first detected 4 weeks after surgery. Pain was assessed by monitoring weight bearing, mechanical hyperalgesia, cold allodynia, mechanical allodynia and vocalisation in response to knee compression for 12 weeks postsurgery. No significant weight-bearing deficits were observed during the course of the study. Significant mechanical allodynia was present in the ipsilateral hind limb from 9 weeks after surgery. Hind limb mechanical hyperalgesia and cold allodynia, and increased vocalisation in response to knee compression developed in the ipsilateral limb in 2 phases. An early phase of hypersensitivities lasted for up to 3 weeks and was reversed by treatment with a nonsteroidal anti-inflammatory drug (NSAID), diclofenac. Pain then resolved for several weeks, followed by a second phase of NSAID-insensitive pain after 7 weeks postsurgery. During this phase, all pain behaviours could be reversed by morphine. In contrast, other analgesic drugs (paracetamol, gabapentin, and tramadol) had selective effects on only 1 or 2 modalities. Pain levels fluctuated during the second phase, with transient periods of reduced pain. At these times, underlying hypersensitivities could be unmasked by administration of naloxone, indicating that reduced pain was due to endogenous opioids.     

Intrathecal pertussis toxin produces hyperalgesia and allodynia in mice

Pertussis toxin (PTX), which causes the ADP-ribosylation and thereby inactivation of G_i-proteins, has been employed in analgesia testing to elucidate receptors that are coupled to inhibitory G-proteins, such as the mu-opioid receptor. Consistent with previous findings, the antinociceptive effects of morphine (1–10 μg) as measured by tail-flick latency using a 55°C water bath, were blocked by a single intrathecal injection of 0.5 μg PTX 6 days prior to intrathecal morphine administration. In addition, mice treated intrathecally with 0.5 μg of PTX had significantly shorter baseline tail-flick latencies compared with vehicle treated mice using a 55°C water bath when tested 6 days after PTX or vehicle administration. Morphine-induced antinociception was blocked in a dose-dependent manner by PTX with complete blockade of morphine following a 0.3-μg dose of PTX. Further, mice administered 0.1 μg or 0.3 μg PTX intrathecally had significantly shorter tail-flick latencies compared with vehicle injected mice using a 40, 45 or 50°C water bath when tested 7 days after intrathecal injection. Shorter tail-flick latencies were observed at 45°C as early as 48 h after intrathecal administration of 0.03, 0.1 or 0.3 μg PTX and these shorter tail-flick latencies were observed up to 90 days after intrathecal PTX administration. The intrathecal administration of PTX caused hyperalgesia and allodynia that appears similar to the symptoms reported by patients suffering from neuropathic pain, and suggests that deficiencies in inhibitory systems, as compared with increases in excitatory systems, may play a role in the pathophysiology of at least some central or neuropathic pain states.     

Cysteamine produces dose-related bidirectional immunomodulatory effects in mice

The sulfhydryl reducing agent, cysteamine, is known to functionally inactive prolactin and other neurohormones that have been recently shown to play a role as immunomodulators. Cysteamine was administered to mice to evaluate its effects upon immune organ size and mitogen-induced lymphocyte proliferative responses in relation to corresponding effects on the immunomodulatory hormones, prolactin and corticosterone. The lowest dose of cysteamine, 12.5 mg/kg given once per day for 3 consecutive days, produced significant elevations of both concanavalin A-(Con A) and lipopolysaccharide-induced blastogenesis. Serum prolactin levels were also significantly elevated with 12.5 mg/kg cysteamine. By contrast, at 300 and 400 mg/kg, cysteamine significantly reduced Con A and lipopolysaccharide-induced proliferation. This suppression of mitogen-induced proliferative responses was accompanied by marked atrophy of the thymus. Levels of both prolactin and corticosterone in the serum were significantly reduced at 400 mg/kg cysteamine. A positive correlation was observed between serum prolactin levels and Con A-induced proliferation as well as between serum prolactin and corticosterone levels in cysteamine-treated mice. The immunomodulatory effects of cysteamine were not limited to correlative effects on neuroendocrine parameters. A similar pattern of effects was observed following in vitro administration of cysteamine. Low concentrations in vitro (0.1 mM) stimulated Con A-induced proliferation of normal mouse splenocytes, and higher concentrations in vitro (2.0 mM) suppressed proliferation. These studies indicate that, depending upon the dose, cysteamine has bidirectional effects on mitogen-induced proliferation of lymphocytes; these effects are correlated with cysteamine-related alterations in the neuroendocrine status of the animal but may also be observed with direct addition of the drug to stimulated lymphocytes in culture.     

Antinociceptive activity of intrathecally administered cannabinoids alone, and in combination with morphine, in mice.

The antinociceptive effects of various cannabinoids, alone and in combination with opiates, were evaluated in antinociceptive tests in mice. The cannabinoids tested produce marked antinociceptive effects after i.t. administration to mice. The rank order of potency for the drugs using the tail-flick test was levonantradol greater than CP-55,940 = CP-56,667 greater than 11-hydroxy-delta 9-THC greater than delta 9-THC greater than delta 8-THC; dextronantradol was inactive at a dose of 25 micrograms/mouse. Respective ED50 values in the tail-flick test were 0.4, 12.3, 4.2, 15, 45 and 72 micrograms/mouse. Although pretreatment with morphine somewhat enhanced the effects of delta 9-THC, pretreatment of the mice with naloxone (1 mg/kg s.c. or 1 micrograms/mouse i.t.) failed to block the antinociceptive effects of the cannabinoids, indicating that the cannabinoid-induced antinociception does not occur due to direct interaction with the opiate receptor. Pretreatment of mice with 3.13 micrograms/mouse and 6.25 micrograms/mouse of delta 9-THC shifted the ED50 of morphine to 0.15 and 0.05 micrograms/mouse, respectively (a 4-and a 12-fold shift). The shifts in the dose-response curve of the morphine were parallel. Naloxone administration (1 mg/kg s.c.) completely blocked the antinociceptive effects of the combination of 6.25 micrograms of delta 9-THC with morphine. The AD50 for naloxone blockade of the drug combination was 0.24 (0.06-0.94) mg/kg s.c. and the pA2 was 7.7 (6.7-8.9). The pA2 for naloxone blockade of the dimethylsulfoxide-morphine combination was 6.9 (5.7-8.1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Moxonidine, a selective alpha2-adrenergic and imidazoline receptor agonist, produces spinal antinociception in mice.

alpha2-Adrenergic receptor (AR)-selective compounds produce antihypertensive and antinociceptive effects. Moxonidine alleviates hypertension in multiple species, including humans. This study demonstrates that intrathecally administered moxonidine produces antinociception in mice. Antinociception was detected via the (52.5 degrees C) tail-flick and Substance P (SP) nociceptive tests. Moxonidine was intrathecally administered to ICR, mixed C57BL/6 x 129/Sv [wild type (WT)], or C57BL/6 x 129/Sv mice with dysfunctional alpha2aARs (D79N-alpha2a). The alpha2AR-selective antagonist SK&F 86466 and the mixed I1/alpha2AR-selective antagonist efaroxan were tested for inhibition of moxonidine-induced antinociception. Moxonidine prolonged tail-flick latencies in ICR (ED50 = 0.5 nmol; 0. 3-0.7), WT (0.17 nmol; 0.09-0.32), and D79N-alpha2a (0.32 nmol; 0. 074-1.6) mice. Moxonidine inhibited SP-elicited behavior in ICR (0. 04 nmol; 0.03-0.07), WT (0.4 nmol; 0.3-0.5), and D79N-alpha2a (1.1 nmol; 0.7-1.7) mice. Clonidine produced antinociception in WT but not D79N-alpha2a mice. SK&F 86466 and efaroxan both antagonized moxonidine-induced inhibition of SP-elicited behavior in all mouse lines. SK&F 86466 antagonism of moxonidine-induced antinociception implicates the participation of alpha2ARs. The comparable moxonidine potency between D79N-alpha2a and WT mice suggests that receptors other than alpha2a mediate moxonidine-induced antinociception. Conversely, absence of clonidine efficacy in D79N-alpha2a mice implies that alpha2aAR activation enables clonidine-induced antinociception. When clinically administered, moxonidine induces fewer side effects relative to clonidine; moxonidine-induced antinociception appears to involve a different alpha2AR subtype than clonidine-induced antinociception. Therefore, moxonidine may prove to be an effective treatment for pain with an improved side effect profile.     

A new mutation, gld, that produces lymphoproliferation and autoimmunity in C3H/HeJ mice

A newly discovered autosomal recessive mutation, generalized lymphoproliferative disease (gld), in the C3H/HeJ strain of mice, determines the development of early onset massive lymphoid hyperplasia with autoimmunity. Significant lymph node enlargement is apparent as early as 12 wk of age. By 20 wk, lymph nodes are 50-fold heavier than those of coisogenic C3H/HeJ-+/+ mice. There is a concomitant increase in the numbers of peripheral blood lymphocytes. Analysis of C3H-gld lymph node lymphocyte subsets by immunofluorescence indicates an increase in numbers of B cells, T cells, and null (Thy-1-, sIg-) lymphocytes by 6-, 15-, and 33-fold compared with congeneic control mice. Serologically, gld/gld mice develop antinuclear antibodies (including anti-dsDNA), thymocyte-binding autoantibody, and hypergammaglobulinemia with major increases in several immunoglobulin isotypes. Mutant gld mice live only one-half as long as normal controls (12 and 23 mo, respectively). Interstitial pneumonitis was found in virtually all C3H-gld mice autopsied when moribund. Although immune complexes were detected in the glomerulus by immunofluorescence techniques, only 14% of the autopsied mice had significant lupus-like nephritis. Vascular disease was not found. The pattern of early onset massive lymph node enlargement, hypergammaglobulinemia, and production of antinuclear autoantibodies resembles the basic abnormal phenotype induced by the lpr (lymphoproliferation) mutation. The mutations gld and lpr are not allelic. Linkage studies indicate that gld is located between Pep-3 and Lp on chromosome 1. This new mutation adds another genetically well-defined model to the list of murine lymphoproliferative/autoimmune disorders that may be exploited to gain a clearer understanding of immunoregulatory defects and for identifying common pathogenetic factors involved in systemic autoimmune diseases.     

Pharmacokinetics of systemically administered cocaine and locomotor stimulation in mice

Cocaine and its metabolites were measured in plasma and brain from mice injected i.p. with cocaine and monitored for spontaneous locomotor behavior. Cocaine concentrations in the brain reached peak values within 5 min after administration of cocaine. At all time points between 5 and 60 min the concentrations of cocaine in the brain were 7-fold higher, on the average, than those in plasma. The opposite was true for the concentrations of benzoylecgonine; brain to plasma ratios of benzoylecgonine were approximately 0.1 from 5 to 30 min after i.p. cocaine injection. After i.p. injection of either 10 or 25 mg/kg of cocaine, cocaine disappeared from plasma and brain with a half-life of 16 min and benzoylecgonine disappeared from plasma with a half-life of 62 min. There was good correspondence between locomotor stimulation and concentration of cocaine in the brain measured at 12, 22 and 32 min after i.p. administration of 25 mg/kg of cocaine. Among individual animals there was a significant correlation between their locomotor stimulation and their brain cocaine concentration, indicating that differences in cocaine levels in the brain between animals contribute to their different behavioral response; however, the correlation analysis also indicated the role of other factors determining the locomotor response to cocaine.     

Amineptine, a tricyclic antidepressant, inhibits the mitochondrial oxidation of fatty acids and produces microvesicular steatosis of the liver in mice

Microvesicular steatosis of the liver has been reported in two subjects receiving amineptine (a tricyclic antidepressant metabolized by beta-oxidation of its acyl chain). A similar disease is observed after ingestion of drugs which inhibit hepatic mitochondrial fatty acid beta-oxidation, or in subjects with various inborn defects in this metabolic pathway. We therefore determined the effects of amineptine on the mitochondrial oxidation of fatty acids in mice. In vitro, the formation of beta-oxidation products during incubation of palmitic acid with mouse liver mitochondria and the various cofactors necessary for beta-oxidation was inhibited by 27, 33, 46 and 57% respectively, in the presence of 0.25, 0.5, 1 and 2 mM of amineptine. Inhibition was reversible. Tricarboxylic acid cycle activity, assessed by the in vitro formation of [14C]CO2 from [1-14C]acetyl coenzyme A by mouse liver mitochondria, was inhibited by 22, 23, 47, 54, 60 and 62%, respectively, in the presence of 0.0625, 0.125, 0.25, 0.5, 1 and 2 mM of amineptine. In vivo, administration of amineptine, 0.5 and 0.75 mmol.kg-1, inhibited by 70 and 84%, respectively, the exhalation of [14C] CO2 during the first 3 hr after the administration of a tracer dose of [U-14C]palmitic acid. Administration of amineptine, 0.0625, 0.25, 0.5 or 1 mmol.kg-1, 6 hr before the measurement, increased hepatic triglycerides by 73, 139, 295 and 320%, respectively. After 1 mmol.kg-1, accumulation of hepatic triglycerides was maximum at 24 hr, reaching 5-fold the control value; liver histology at that time showed microvesicular steatosis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interleukin 1 administration in mice produces hypoferremia despite neutropenia.

To determine whether the hypoferremic response to inflammation requires neutrophils, we administered human recombinant IL-1 to mice made neutropenic with cyclophosphamide. With single intraperitoneal injections of IL-1 the plasma iron concentrations decreased significantly in mice with either normal neutrophil counts or neutropenia. After single injections transferrin concentrations were not significantly changed, but the decrease in serum iron lowered mean transferrin saturations from a baseline of 45 to 24-30% in nonneutropenic mice, and from 99 to 70-77% in neutropenic mice. Similar changes were observed after intraperitoneal injections of Escherichia coli. 4-d continuous infusions of IL-1 also led to reductions in serum iron concentrations, but transferrin concentrations doubled. The combination of a decrease in serum iron and an increase in transferrin concentration after chronic infusion in neutropenic mice led to a greater decline in mean transferrin saturations, from a baseline of 110 to 25%. In mice not given cyclophosphamide, chronic IL-1 infusion was associated with a reduction in mean hemoglobin concentrations from 14.7 to 13.5 g/dl, consistent with restricted availability of iron for erythropoiesis associated with low saturation of transferrin. We conclude that IL-1 can decrease the serum iron despite profound peripheral neutropenia and that transferrin in a positive acute phase reactant in the mouse.     

Influence of genotype, dose and sex on pruritogen-induced scratching behavior in the mouse

Itch features considerable interindividual variability in humans, and initial studies using animal models have demonstrated a likely role of genetic factors in mediating such variability. In an attempt to systematically study genetic mediation of itch in the mouse such that gene identification by linkage mapping might be achieved, we examined scratching behavior induced by histamine and chloroquine in mice of 11 inbred mouse strains. Multiple chloroquine drug doses were used, revealing the existence of inverted-U dose-response relationships in every strain, allowing us to determine strain-dependent peak scratching behavior over the entire dose range. Peak chloroquine-induced scratching varied by 2.5-fold in this set of strains; scratching behavior shows moderate heritability in the mouse. The present data also reveal, for the first time, significant sex differences in pruritogen-induced scratching behavior, with female mice scratching an average of 23% more than males. Finally, a comparison of the strain means obtained here with previously collected data using nociceptive assays revealed a suggestive negative genetic correlation between chloroquine-induced itch and thermal pain, such that strains sensitive to pain are resistant to itch and vice versa. This finding may have implications both for our understanding of itch pathophysiology and for the identification of itch-related genes.     

Determination and characterization of the antinociceptive activity of intraventricularly administered acetylcholine in mice.

Antinociceptive activity of intraventricularly administered acetylcholine was quantitated in mice by the tail-flick and phenylquinone tests. Acetylcholine was administered intraventricularly under light ether anesthesia in a 5 mul volume of sterile saline and mice were retested 10 minutes after the operation. A dose-response curve was established for acetylcholine (ED50 equals 7.3 mug) which was potentiated by intraventricular neostigimine and blocked by intraperitoneal atropine, but not by atropine methyl nitrate or mecamylamine. The antinociceptive effect of morphine was potentiated by intraventricularly administered acetylcholine. The acetylcholine-induced antinocieption was blocked by five narcotic antagonists in the same rank order of potency in which they antagonized the effects of morphine. However, the stereo-specificity of two narcotic antagonists, pentazocine and cylcazocine, was reversed in blocking acetylcholine and morphine-induced antinociception. The results of this study have established a phenomenon of acetylcholine-induced antinociception and identified the central, muscarinic nature of this response. In addition, several experiments have demonstrated similarities between this phenomenon and morphine-induced antinociception. These data implicate the possible involvement of central cholinergic mechanisms in the antinociceptive action of morphine.     

Amiodarone inhibits the mitochondrial beta-oxidation of fatty acids and produces microvesicular steatosis of the liver in mice

Amiodarone has been shown to produce microvesicular steatosis of the liver in some recipients. We have determined the effects of amiodarone on the mitochondrial oxidation of fatty acids in mice. In vitro, the formation of 14C-acid-soluble beta-oxidation products from [U-14C]palmitic acid by mouse liver mitochondria was decreased by 92% in the presence of 125 microM amiodarone and by 94% in the presence of 125 microM N-desethylamiodarone. Inhibition due to 100 or 150 microM amiodarone persisted in the presence of 5 mM acetoacetate, whereas acetoacetate totally relieved inhibition due to 15 microM rotenone. In vivo, exhalation of [14C]CO2 from [U-14C]palmitic acid was decreased by 31, 40, 58 and 78%, respectively, in mice receiving 19, 25, 50 and 100 mg.kg-1 of amiodarone hydrochloride 1 hr before the administration of [U-14C]palmitic acid. One hour after 100 mg.kg-1, the exhalation of [14C]CO2 from [1-14C]palmitic acid, [1-14C]octanoic acid or [1-14C]butyric acid was decreased by 78, 72 and 53%, respectively. Exhalation of [14C]CO2 from [1-14C]palmitic acid was normal between 6 and 9 hr after administration of 100 mg.kg-1 of amiodarone hydrochloride, but was still inhibited by 71 and 37%, 24 and 48 hr after 600 mg.kg-1. Twenty four hours after the latter dose of amiodarone, hepatic triglycerides were increased by 150%, and there was microvesicular steatosis of the liver. We conclude that amiodarone inhibits the mitochondrial beta-oxidation of fatty acids and produces microvesicular steatosis of the liver in mice.     

5‐HT3 receptors antagonists reduce serotonin‐induced scratching in mice

Serotonin (5‐hydroxytryptamine, 5‐HT) acts as a pruritogen in humans and animals, but the mechanisms of action through that serotonin induces itch response have not been extensively discovered. In our study, we attempted to investigate the role of 5‐HT3 receptors in scratching behavior due to intradermal serotonin injection. Intradermal injection of serotonin (14.1–235 nmol/site) into the nape of the neck of mice was performed to elicit itch. Scratching behavior was evaluated by measuring the number of bouts during 60 min after injection. We evaluated the effect of intraperitoneal pretreatment with ondansetron and tropisetron (0.1, 0.3, and 1 mg/kg) on itch induced by serotonin. Also, intradermal ondansetron and tropisetron at doses 50, 100, and 200 nmol/site were concurrently administrated with serotonin. Serotonin produced a significant enhancement in scratching at dose 141 nmol/site. Concurrent administration of ondansetron (50, 100, and 200 nmol/site) and tropisetron (100 and 200 nmol/site) with serotonin reduced scratching activity compared to the animals that only received serotonin. Also, pretreatment with intraperitoneal ondansetron and tropisetron (0.3 and 1 mg/kg) 30 min before serotonin attenuated the itch response. We showed that the scratching induced by intradermal serotonin is mediated by 5‐HT3 receptors subtype. It can be concluded that 5‐HT3 may play a role in mediating serotonin‐associated itch responses, and we introduce 5‐HT3 receptors as possible targets for antipruritic agents.     

Partial deficiency of thyroid transcription factor 1 produces predominantly neurological defects in humans and mice

Three genes, TTF1, TTF2, and PAX8, involved in thyroid gland development and migration have been identified. Yet systematic screening for defects in these genes in thyroid dysgenesis gave essentially negative results. In particular, no TTF1 gene defects were found in 76 individuals with thyroid dysgenesis even though a deletion of this gene in the mouse results in thyroid and lung agenesis and defective diencephalon. We report a 6-year-old boy with predominant dyskinesia, neonatal respiratory distress, and mild hyperthyrotropinemia. One allele of his TTF1 gene had a guanidine inserted into codon 86 producing a nonsense protein of 407, rather than 371, amino acids. The mutant TTF1 did not bind to its canonical cis-element or transactivate a reporter gene driven by the thyroglobulin promoter, a natural target of TTF1. Failure of the mutant TTF1 to interfere with binding and transactivation functions of the wild-type TTF1 suggested that the syndrome was caused by haploinsufficiency. This was confirmed in mice heterozygous for Ttf1 gene deletion, heretofore considered to be normal. Compared with wild-type littermates, Ttf1(+/-) mice had poor coordination and a significant elevation of serum thyrotropin. Therefore, haploinsufficiency of the TTF1 gene results in a predominantly neurological phenotype and secondary hyperthyrotropinemia.