Analysis of the actions of 5-hydroxytryptamine on the rabbit isolated vagus nerve

Summary Depolarization and reduction in the C fibre compound action potential (C spike) in response to 5-HT were recorded simultaneously from rabbit isolated vagus nerve. 5-HT (0.1–100 mol/l) was applied either as single concentrations or cumulatively and EC₅₀ and IC₅₀ values measured from individual concentration-response curves. The EC₅₀ values for depolarization (cumulative curves: 2.33, 1.64–3.33 mol/l, geometric means and 95% confidence limits, n = 31; non-cumulative curves: 3.99, 2.89 – 5.52 mol/l, n = 9) were significantly higher than IC₅₀ values for C spike reduction (cumulative curves: 1.25, 0.91–1.74 mol/l, n = 30; non-cumulative curves: 1.41, 0.72–2.76 mol/l, n = 8). Complex effects on the C spike were observed, suggesting a susceptible group of C fibres and a 5-HT-resistant component to the C fibre action potential. The motor nerve C fibres in the vagus nerve appear insensitive to 5-HT, whereas the sensory C fibres were sensitive to 5-HT. Phenylbiguanide had a similar selective effect on the C spike, while the depolarizing agents, 1,1-dimethyl-4-phenylpiperazinium (DMPP) and gamma-aminobutyric acid (GABA) did not. Cumulative concentration-response curves for depolarization and C spike reduction could be repeated reproducibly if an interval of 90 min was left between determinations. Up to 6 curves could be generated from one preparation. The 5-HT uptake inhibitor, citalopram (0.1 and 1 mol/l), had no effect on cumulative concentration-response curves. Concentration-response curves from pooled data, when 5-HT was applied non-cumulatively, showed higher maxima for both depolarization and C spike reduction compared to similar curves for cumulative application of increasing concentrations of 5-HT. It is concluded that although the two actions of 5-HT on the rabbit vagus nerve (depolarization, C spike reduction) closely parallel each other in respect of their cumulative and non-cumulative concentration-response curves, the repeatability of concentration-response curves, and, as reported in a companion paper, blockade by metoclopramide or BRL 43694 and involvement of 5-HT₃ receptors, some differences remain which may or may not indicate an independent genesis of the two responses.Send offprint requests to D. I. Wallis at the above address     

Isolated intrathoracic injury with air bag use

The restrained (air bag and seatbelt) driver of a vehicle involved in a high-speed motor-vehicle accident sustained a tear of the thoracic aorta with no signs of external injury. Air bag deployment may mask significant internal injury, and a high index of suspicion is warranted in such situations.     

Characterisation of the contractile activity of eletriptan at the canine vascular 5-HT1B receptor

The functional activity of eletriptan ((R)-3-(1-methyl-2-pyrrolidinylmethyl)-5-[2-(phenylsulphonyl )ethyl]- 1 H-indole) at the contractile serotonin (5-hydroxytryptamine; 5-HT) '1B-like' receptor in dog isolated saphenous vein and basilar artery was investigated. Eletriptan, like 5-HT and sumatriptan potently contracted saphenous vein (pEC50: 6.3, 6.9 and 6.1, respectively) and basilar artery (pEC50 7.2, 7.5 and 6.8, respectively). The maximum responses evoked by eletriptan was, unlike sumatriptan, significantly lower than that to 5-HT (intrinsic activity saphenous vein: eletriptan 0.57, 5-HT 1.0, sumatriptan 0.85; basilar artery: eletriptan 0.77, 5-HT 0.98, sumatriptan 0.89). Contractions evoked by eletriptan were antagonised by the 5-HT1B/1D receptor antagonist GR125743 (N-[4-methoxy-3-(4-methyl piperazin-1-yl)phenyl]-3-methyl-4-(4-pyridyl)benzamide) with pA2 values of 9.1 in saphenous vein and 9.4 in basilar artery. Affinity estimates (pKA) for 5-HT and sumatriptan determined from receptor alkylation studies in saphenous vein were 6.6 and 6.3, respectively, compared to the apparent equilibrium dissociation constant (pKp) for eletriptan of 6.8. The rank order of relative intrinsic efficacies (epsilon) was 5-HT > sumatriptan > eletriptan. Thus, eletriptan required greater receptor occupancy (4.4-fold) to evoke an equivalent contraction to 5-HT and sumatriptan in dog isolated saphenous vein. These data demonstrate that eletriptan is a potent partial agonist at the canine vascular 5-HT1B receptor.     

Further studies on the action of 5-hydroxytryptamine on lumbar motoneurones in the rat isolated spinal cord

Summary Using the hemisected spinal cord of the neonate rat, the effects of altered external Ca, thyrotrophin-releasing hormone (TRH) and a number of antagonists were tested on depolarizations evoked by 5-hydroxytryptamine (5-HT). Responses of populations of motoneurones were recorded via a ventral root. 5-Hydroxytryptamine depolarizations were not Ca-dependent but were enhanced in amplitude in Ca-free solutions. Raised Mg reversed this enhancement. 5-Hydroxytryptamine depolarizations persisted in the presence of Mn (1.53 mmol/l). TRH depolarized motoneurones; there was no evidence of modulation of 5-HT responses on concurrent application of TRH. Ritanserin (0.1 mol/l) had a modest blocking action on 5-hydroxytryptamine depolarizations reducing the maximum; 1mol/l ritanserin caused a greater antagonism which was unsurmountable (pIC₅₀ 5.2). Ritanserin (0.1 or 1 mol/l) did not depress responses to noradrenaline (NA). Ketanserin (0.1 mol/l) caused a blockade of slow onset, equilibrium with the receptors requiring 1 h. Blockade by 0.01, 0.1 and 1 mol/l ketanserin was concentration-dependent (pIC₅₀ 6.2). Ketanserin 1 mol/l, but not at lower concentrations, depressed noradrenaline responses. Mianserin (0.1 mol/l) also caused a blockade of slow onset; 0.1 or 1 mol/l produced a flattening of the 5-hydroxytryptamine concentration-response curve but did not depress noradrenaline responses (pIC₅₀ 4.7). The pIC₅₀ for spiperone was 8.0. DOI (10–100 mol/l) had no detectable agonist action but at concentrations of 0.01 and 0.1 mol/l it acted as an antagonist. Equilibration with the receptors occurred over 2 h. DOI (0.01 mol/l) depressed 5-hydroxytryptamine but not noradrenaline responses; higher concentrations of DOI also depressed noradrenaline responses. The pharmacological profile of the 5-hydroxytryptamine receptor mediating depolarization of spinal and facial motoneurones suggests that it belongs to the 5-HT_1C-5-HT₂, group of 5-hydroxytryptamine receptors but is not identical to 5-HT_1C or the 5-HT₂ CNS binding sites. Alternatively, the response might arise from a mixed population of 5-HT₁-like and 5-HT₂ receptors. Send offprint requests to D. I. Wallis at the above address     

Screening for complement deficiency in bacterial meningitis

Seventy-seven children with bacterial meningitis were screened for complement deficiency. Both the classical and the alternate pathways were normal in 75 patients. Transiently reduced total haemolytic activity of the classical pathway was documented in a boy with meningococcal meningitis. Total haemolytic activity of both the classical and the alternate pathways were reduced in another patient with pneumococcal meningitis: individual complement components determination indicated predominant activation of the alternate pathway.     

An unusually severe phenotype for familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is a dominantly inherited predisposition to the development of many hundreds to thousands of adenomatous polyps of the colon. The mean age of onset is around 15 years, symptoms may arise in the third decade, and the median age for the development of colonic cancer is 35-40 years. Prophylactic colectomy reduces the risk of death from colorectal cancer to such an extent that late sequelae such as upper gastrointestinal tumours have become the main cause of mortality in appropriately managed patients. The age at which colonic surveillance begins reflects the natural history of the disease. Onset of polyp formation and cancer in childhood is very unusual, but has recently been associated with a specific mutation at codon 1309 in exon 15 where a more severe phenotype is sometimes observed. The case histories of two families are reported in which there is childhood onset of polyps in the youngest generation and in one case a carcinoma, in whom mutations have been identified in exon 11 of the APC gene. Several other affected relatives were diagnosed at ages ranging from 5-48 years, some already with a cancer at the time of first screening. Since the aim of screening for colonic polyps is prevention of colonic cancer, family members at risk should be offered genetic assessment and direct mutation testing where this is possible, usually in the early teens. In the absence of a genetic test (the situation in about one third of families) or in a known gene carrier, annual colonoscopy examination is advised from the same age. Clinicians should take note of the family history and be prepared to consider much earlier intervention if symptoms occur in a child with a family history of FAP. Where childhood onset of polyps has occurred, other children at risk in the family must be offered earlier genetic testing and endoscopic surveillance.

     

Identification of differentially expressed genes in aflatoxin B1- treated cultured primary rat hepatocytes and Fischer 344 rats

Aflatoxin B1 (AFB1), a mutagen and hepatocarcinogen in rats and humans, is a contaminant of the human food supply, particularly in parts of Africa and Asia. AFB1-induced changes in gene expression may play a part in the development of the toxic, immunosuppressive and carcinogenic properties of this fungal metabolite. An understanding of the-role of AFB1 in modulating gene regulation should provide insight regarding mechanisms of AFB1-induced carcinogenesis. We used three PCR- based subtractive techniques to identify AFB1-responsive genes in cultured primary rat hepatocyte RNA: differential display PCR (DD-PCR), representational difference analysis (RDA) and suppression subtractive hybridization (SSH). Each of the three techniques identified AFB1- responsive genes, although no individual cDNA was isolated by more than one technique. Nine cDNAs isolated using DD-PCR, RDA or SSH were found to represent eight genes that are differentially expressed as a result of AFB1 exposure. Genes whose mRNA levels were increased in cultured primary rat hepatocytes after AFB1 treatment were corticosteroid binding globulin (CBG), cytochrome P450 4F1 (CYP4F1), alpha-2 microglobulin, C4b-binding protein (C4BP), serum amyloid A-2 and glutathione S-transferase Yb2 (GST). Transferrin and a small CYP3A-like cDNA had reduced mRNA levels after AFB1 exposure. Full-length CYP3A mRNA levels were increased. When liver RNA from AFB1-treated male F344 rats was evaluated for transferrin, CBG, GST, CYP3A and CYP4F1 expression, a decrease in transferrin mRNA and an increase in CBG, GST, CYP3A and CYP4F1 mRNA levels was also seen. Analysis of the potential function of these genes in maintaining cellular homeostasis suggests that their differential expression could contribute to the toxicity associated with AFB1 exposure.      

How to use a nasopharyngeal prong in Pierre Robin sequence

Pierre Robin sequence (PRS) describes a small mandible with retrognathia, an elevated and posteriorly positioned tongue, and an associated U-shaped cleft palate. The retracted tongue may obstruct the airway leading to respiratory failure, with failure to thrive and adverse neurodevelopmental outcomes if not addressed. If the airway obstruction cannot be overcome with conservative measures, there are non-surgical and surgical options. A nasopharyngeal prong (NPP) is a non-surgical, temporary treatment that avoids the complications inherent in an operation, especially given the natural history of mandibular growth and improved airway obstruction in PRS. Although the use of a prong requires training, support, and follow up, it effectively bypasses the obstruction in the majority of children with PRS, and allows the child to outgrow the airway obstruction until the prong is no longer required. On average, the prong can be removed between 6 and 12 months of age.