SB-224289--a novel selective (human) 5-HT1B receptor antagonist with negative intrinsic activity

1. Human 5-HT1B (h5-HT1B) and human 5-HT1D (h5-HT1D) receptors show remarkably similar pharmacology with few compounds discriminating the receptors. We report here on a novel compound, SB-224289 (1'-Methyl-5-[[2'-methyl-4'-(5-methyl- 1,2,4-oxadiazol-3-yl)biphenyl-4-yl]carbonyl]-2,3,6,7-tetrahydro spiro [furo [2,3-f]indole-3,4'-piperidine] oxalate), which has high affinity for h5-HT1B receptors (pK1=8.16+/-0.06) and displays over 75 fold selectivity for the h5-HT1B receptor over all other 5-HT receptors including the h5-HT1D receptor and all other receptors tested thus far. 2. Functional activity of SB-224289 was measured in a [15S]GTPgammaS binding assay on recombinant h5-HT1B and h5-HT1D receptors expressed in Chinese Hamster Ovary (CHO) cells. SB-224289 displayed negative intrinsic activity at both receptors with higher potency at h5-HT1B receptors. SB-224289 caused a rightward shift of agonist concentration response curves consistent with competitive antagonism and generated affinities comparable with those obtained from competition radioligand receptor binding studies. 3. SB-224289 potentiated [3H]5-HT release from electrically stimulated guinea-pig cerebral cortical slices to the same extent as as the non-selective 5-HT1 antagonist methiothepin. SB-224289 also fully reversed the inhibitory effect of exogenously superfused 5-HT on electrically stimulated release. 4. Using SB-224289 as a tool compound, we confirm that in guinea-pig cerebral cortex the terminal 5-HT autoreceptor is of the 5-HT1B subtype.

SB-216641 and BRL-15572--compounds to pharmacologically discriminate h5-HT1B and h5-HT1D receptors

Despite only modest homology between h5-HT1B and h5-HT1D receptor amino acid sequences, these receptors display a remarkably similar pharmacology. To date there are few compounds which discriminate between these receptor subtypes and those with some degree of selectivity, such as ketanserin, have greater affinity for other 5-HT receptor subtypes. We now report on two compounds, SB-216641 (N-[3-(2-dimethylamino) ethoxy-4-methoxyphenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-(1,1'-biphenyl)-4-carboxamide) and BRL-15572 3-[4-(3-chlorophenyl) piperazin-1-yl]-1,1-diphenyl-2-propanol), which display high affinity and selectivity for h5-HT1B and h5-HT1D receptors, respectively. In receptor binding studies on human receptors expressed in CHO cells, SB-216641 has high affinity (pKi = 9.0) for h5-HT1B receptors and has 25-fold lower affinity at h5-HT1D receptors. In contrast, BRL-15572 has 60-fold higher affinity for h5-HT1D (pKi = 7.9) than 5-HT1B receptors. Similar affinities for these compounds were determined on native tissue 5-HT1B receptors in guinea-pig striatum. Functional activities of SB-216641 and BRL-15572 were measured in a [35S]GTPgammaS binding assay and in a cAMP accumulation assay on recombinant h5-HT1B and h5-HT1D receptors. Both compounds were partial agonists in these high receptor expression systems, with potencies and selectivities which correlated with their receptor binding affinities. In the cAMP accumulation assay, results from pK(B) measurements on the compounds again correlated with receptor binding affinities (SB-216641, pK(B) = 9.3 and 7.3; BRL-15572, pK(B) = <6 and 7.1, for h5-HT1B and h5-HT1D receptors respectively). These compounds will be useful pharmacological agents to characterise 5-HT1B and 5-HT1D receptor mediated responses.

GR127935 acts as a partial agonist at recombinant human 5-HT1D alpha and 5-HT1D beta receptors

In this study we have investigated the functional activity of GR127935 (2-methyl-1,2,4 oxadiazol-3-yl)-biphenyl-[4-carboxylic acid 4-methoxy-3-(4-methyl-piperazine-1-yl]-amide) at human 5-HT1D alpha and 5-HT1D beta receptors which have been expressed in a Chinese Hamster Ovary (CHO) cell line. Using [35S] GTP gamma S binding to cell membranes as a measure of receptor-G protein coupling. GR127935 showed partial agonist activity in both 5-HT1D alpha and 5-HT1D beta receptor expressing cells (Emax: 29 and 31% above basal control; pEC50: 8.6 and 9.7, respectively). GR127935 also acted as a potent antagonist at the 5-HT1D alpha (app. pA2 8.5) and 5-HT1D beta (app. pA2 9.1) receptors. From studies measuring cAMP accumulation in cultured CHO cells GR127935 also displayed partial agonism, as well as acting as a potent antagonist at the 5-HT1D alpha receptors which stimulate cAMP levels and 5-HT1D beta receptors which inhibit cAMP levels (app. pA2 8.6 and 9.7, respectively). The 5\-HT1-like receptor antagonist methiothepin showed negative intrinsic activity at both receptors in the [35S]GTP gamma S binding assay only. From studies using the receptor alkylating agent EEDQ (N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline) the 5-HT1D alpha cell line displayed a lack of receptor reserve but it was evident in the 5-HT1D beta cell line. In previous studies we have also shown that agonist stimulation of 5-HT1D alpha receptors increases cAMP levels which may be due to high receptor expression. Further investigation using up to 1 microM EEDQ to reduce 5-HT1D alpha receptor number did not reveal an underlying inhibitory adenylyl cyclase response. In conclusion, GR127935 acts as a partial agonist, as well as a potent antagonist, at the human 5-HT1D alpha and 5-HT1D beta receptors when expressed in CHO cells.

Cochlear histopathologic characteristics following long-term implantation. Safety studies in the young monkey

OBJECTIVE

To evaluate the safety of cochlear implantation in children 2 years of age or younger using a non-human primate model.

DESIGN

Histopathologic study.

SUBJECTS

Five macaque monkeys.

INTERVENTION

A commercially produced electrode array was implanted for 3 years.

RESULTS

Histologic examination demonstrated the biocompatibility of the scala tympani electrode array. Limited soft-tissue growth and new bone growth were observed in the lower basal turn. There was no evidence of intracochlear infection. Evidence of minimal insertion trauma was seen. Hair cell loss was, in general, confined to the region of the electrode array, with normal hair cell populations toward the apex, although there was evidence of hair cell preservation adjacent to the array. At least 20% of spiral ganglion cells were preserved even in regions with a smaller proportion of hair cells.

CONCLUSIONS

Even after extended periods of implantation, the electrode array is well tolerated, and there is substantial preservation of neural elements.

Titanium-anchored prostheses in otology

In the late 1970s, Per-Ingvar Branemark and coworkers in Goteberg, Sweden, successfully introduced osseointegrated titanium implants into clinical practice. They had achieved the previously elusive goal of producing stable, secure percutaneous implants anchored in underlying cortical bone. Two applications of these implants to otology were obvious: (1) to provide a coupling for bone-conduction hearing aids and (2) to provide fixation points for anchoring of auricular prostheses. Before describing the current state of these clinical applications and considering future potential uses, the authors review the basis for titanium osseointegration.

Characterization of a descending system that enables crossed group II inhibitory reflex pathways in the cat spinal cord

In the cat, stimulation of group II afferents from hindlimb muscles evokes different crossed reflex actions depending on the integrity of the spinal cord: with the cord intact, extensor motoneurons are inhibited by activation of contralateral group II afferents; after spinal transection, the same stimuli excite these neurons (crossed extension reflex). We have investigated the mechanisms underlying this descending control. To delimit the descending pathway, the effects of funicular lesions of the thoracic cord on the crossed actions on motoneurons were examined. Bilateral lesions of the dorsolateral funiculi abolished the crossed IPSPs as effectively as complete spinal section. If either dorsolateral funiculus was spared, the IPSPs remained. To examine whether serotonergic fibers were involved, the effects of agents selective for 5-hydroxytryptamine (5-HT)1A receptors were examined. After abolishing the crossed IPSPs by spinal transection, systemic administration of the 5-HT1A receptor agonist (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide (8-OH-DPAT; 0.1-1.3 mg/kg, i.v.) restored the crossed inhibition. This effect was antagonized by the selective 5-HT1A receptor antagonist WAY-100135 (0.7-3.7 mg/kg, i.v.). The simplest explanation of these findings is that a serotonergic pathway, descending via the dorsolateral funiculi and acting via 5-HT1A receptors, is involved: with the spinal cord intact, the pathway would be tonically active and thus enable the crossed inhibition. This raises the possibility that a serotonergic pathway is involved in the selection of specific spinal reflex patterns via 5-HT1A receptors.

Swallowing in motor neurone disease

Ninety-two patients with motor neurone disease have been assessed clinically and radiologically for evidence of swallowing problems. At the time of examination, moderate or severe swallowing difficulty was present in 89% of those whose disease had presented as bulbar palsy, in 45% of those in whom the disease began many months before as progressive muscular atrophy and in 29% of those with amyotrophic lateral sclerosis. Patients with more severe swallowing symptoms appeared more likely to have abnormal findings on videofluoroscopy overall. However, not all patients with an abnormal radiological picture had swallowing difficulties. It is suggested that radiological signs should only be used within the context of clinical symptoms and signs in the selection of patients for palliative surgery. Thirteen patients with pseudobulbar symptoms and signs had a cricopharyngeal myotomy performed: two suffered major post-operative complications. However, the satisfaction rate was 89% and we recommend cricopharyngeal myotomy for such patients. Pharyngostomy was performed for seven patients unable to initiate swallowing, six had post-operative complications.

Cochlear implantation in children: labyrinthitis following pneumococcal otitis media in unimplanted and implanted cat cochleas

Pneumococcal otitis media is frequent in young children and could lead to labyrinthitis post-implantation. To assess the risk, and methods of minimizing it by a graft to the round window around the electrode entry point, we have used a cat animal model of pneumococcal otitis media. Twenty-one kittens were used in the study. Thirty-two cochleas were implanted when the kittens were 2 months of age. Fourteen cochleas were implanted without using a graft (12 were available for study); 9 had a fascial graft, and 9 a Gelfoam graft (7 were available for study). The implanted kittens had their bullae inoculated with Streptococcus pneumoniae 2 months after implantation and were sacrificed 1 week later. There were also 9 unimplanted control ears which were inoculated when the animals were 4 months of age. Labyrinthitis occurred in 44% of unimplanted control, 50% of implanted ungrafted, and 6% of implanted grafted (fascia and Gelfoam) cochleas. There was no statistically significant difference between the unimplanted control and the implanted cochleas (p < 0.05). There was, however, a difference between the implanted-ungrafted and implanted grafted cochleas, but not between the use of fascia and Gelfoam to graft the round window entry point. As a result, the data indicates that cochlear implantation does not increase the risk of labyrinthitis following pneumococcal otitis media, but it is desirable to use fascia as a graft to the round window around the electrode entry point.

Nonorganic hearing loss in cochlear implant candidates

Five patients undergoing assessment for cochlear implantation have been found to have a nonorganic hearing loss (pseudohypacusis). This phenomenon has not been reported previously in this patient population. The cases are presented and the causes, detection, and management of this condition are discussed.

Cochlear implantation in young children: histological studies on head growth, leadwire design, and electrode fixation in the monkey model

For safe cochlear implantation in children under 2 years of age, the implant assembly must not adversely affect adjacent tissues or compromise head growth. Furthermore, growth changes and tissue responses should not impair the function of the device. Dummy receiver-stimulators, interconnect plugs, and leadwire-lengthening systems were implanted for periods of 36 months in the young monkey to effectively model the implantation of the young child. The results show that implanting a receiver-stimulator package has no adverse effects on skull growth or the underlying central nervous system. The system for fixing the electrode at the fossa incudis proved effective. There was marked osteoneogenesis in the mastoid cavity, resulting in the fixation of the leadwire outside the cochlea. This study provides evidence for the safety of cochlear implantation in young subjects.

Steady-state evoked potentials to amplitude modulated tones in the monkey

A frequency-specific, objective assessment of hearing thresholds is required for use in subjects unable to perform behavioural audiometry. One such method using steady-state evoked potentials (SSEPs) in response to amplitude-modulated tones was evaluated in an experimental animal, the macaque monkey. An amplitude-modulation frequency of 165 Hz was found to produce optimum response detection in the anaesthetised animal. Auditory thresholds determined by a computerised automatic response detection system accurately reflected behavioural thresholds previously described in this species.

Thrombospondin receptor expression in human neutrophils coincides with the release of a subpopulation of specific granules

The extracellular matrix (ECM) protein thrombospondin (TSP) binds specifically to polymorphonuclear leucocyte (PMN) surface receptors and promotes cell adhesion and motility. TSP receptor expression increases 30-fold after activation with the synthetic chemotactic peptide, N-formylmethionyl-leucylphenylalanine (FMLP) or the Ca2+ ionophore A23187, in combination with cytochalasin B. The expression of TSP receptors was correlated with the exocytosis of both specific and azurophil granules. Newly expressed TSP receptors are not derived from easily mobilized specific granules since agents that trigger some specific granule release [phorbol myristate acetate (PMA), FMLP or ionophore A23187 alone] do not increase TSP receptor expression. In this study we used the anion-channel blocker, 4,4'-di-isothiocyanatostilbene-2,2'-disulphonic acid (DIDS) to investigate the source of these newly expressed receptors. When PMNs were exposed to cytochalasin B and FMLP or to cytochalasin B and ionophore A23187 in the presence of 30-100 microM-DIDS, TSP receptor expression increased coincidently with vitamin B12-binding protein release from specific granules. Under these same conditions, the release of the azurophil granule component, myeloperoxidase, was significantly inhibited. Using agonists that cause release of specific granules, or both specific granules and azurophil granules, we determined that DIDS blocked the release of PMA-mobilized specific granules and cytochalasin B plus FMLP- or cytochalasin B plus ionophore A23187-mobilized myeloperoxidase-containing azurophil granules but not specific granules mobilized by cytochalasin B plus FMLP or cytochalasin B plus ionophore A23187. These results suggested that PMNs contain at least two subpopulations of specific granules: one that is easily mobilized, lacks TSP receptors and is inhibitable by DIDS, and one that is difficult to mobilize, contains a large pool of TSP receptors and the release of which is enhanced in the presence of DIDS.

The surgical management of drooling

As with all branches of surgery, selection of the appropriate operative procedure for a particular patient involves careful weighing of all the alternatives and full discussion with the patient and carers. Each of the procedures described has its devotees and detractors. For an individual patient, however, the risks of each, the likely postoperative course and the results of the surgery--both in terms of the expected chance of improvement in drooling and the presence or otherwise of residual scarring or taste--must be balanced to determine the optimum plan for treatment. The long-term results of submandibular duct transposition for drooling in the author's own institution have recently been reported. An initial improvement in the drooling of all patients was maintained for at least two years in 17 of 20 patients. Only two patients experienced complications requiring further surgery (ranulas in each case). It is suggested that these very satisfactory results, achieved without external scarring and without compromising the sense of taste, support the contention that submandibular duct transposition is the surgical treatment of choice for children and young people with cerebral palsy who drool excessively.

Human neutrophil adherence to thrombospondin occurs through a CD11/CD18-independent mechanism

Thrombospondin (TSP), a 450-kDa trimeric glycoprotein secreted by platelets and endothelial cells at sites of tissue injury or inflammation, may play an important role in polymorphonuclear leukocyte (PMN) adherence to blood vessel walls before diapedesis. We have examined the adherence of PMN to TSP and compared it to adherence to other extracellular matrix proteins. PMN adherence to TSP-coated plastic was complete by 60 min with spreading completed by 2 h. The kinetics of adhesion and spreading on TSP were similar to that of vitronectin (VN), laminin (LN), and fibronectin (FN). Activation of PMN with the calcium ionophore A23187 or the chemotactic peptide FMLP increased PMN adherence to LN and FN, but not to TSP or VN, suggesting that PMN activation may differentially regulate expression of TSP and VN receptors as compared to LN and FN receptors. The specificity of PMN adherence to TSP was confirmed by competition with saturating amounts of TSP and inhibition with anti-TSP antibodies. mAb A6.1, which binds to the protease-resistant core of TSP, was the most effective in blocking PMN adherence to TSP. Using TSP proteolytic fragments, we demonstrated that the primary interaction of PMN with TSP was mediated through the 140-kDa COOH-terminal domain. Inasmuch as the 140-kDa fragment of TSP contains an Arg-Gly-Asp sequence similar to the cell recognition site of FN and VN, we determined whether RGDS peptides would inhibit PMN adhesion. RGDS did not significantly inhibit PMN adhesion to TSP, VN, or LN, but reduced PMN adhesion to FN by 50%. To determine if PMN adhesion to TSP was mediated by a beta 2 integrin receptor such as LFA-1, MO-1, or p150,95, we performed adhesion assays using PMN isolated from patients with leukocyte adhesion deficiency that lack beta 2 receptors. Leukocyte adhesion deficiency PMN exhibited normal adherence to TSP. In contrast, adherence to VN, LN, and FN was reduced by 95%. Therefore, adherence to TSP is probably not mediated by a beta 2 integrin receptor. These data contribute to the accumulating evidence that PMN can interact with extracellular matrix proteins through a CD11/CD18-independent process.

Human neutrophil adherence to thrombospondin occurs through a CD11/CD18-independent mechanism

Thrombospondin (TSP), a 450-kDa trimeric glycoprotein secreted by platelets and endothelial cells at sites of tissue injury or inflammation, may play an important role in polymorphonuclear leukocyte (PMN) adherence to blood vessel walls before diapedesis. We have examined the adherence of PMN to TSP and compared it to adherence to other extracellular matrix proteins. PMN adherence to TSP-coated plastic was complete by 60 min with spreading completed by 2 h. The kinetics of adhesion and spreading on TSP were similar to that of vitronectin (VN), laminin (LN), and fibronectin (FN). Activation of PMN with the calcium ionophore A23187 or the chemotactic peptide FMLP increased PMN adherence to LN and FN, but not to TSP or VN, suggesting that PMN activation may differentially regulate expression of TSP and VN receptors as compared to LN and FN receptors. The specificity of PMN adherence to TSP was confirmed by competition with saturating amounts of TSP and inhibition with anti-TSP antibodies. mAb A6.1, which binds to the protease-resistant core of TSP, was the most effective in blocking PMN adherence to TSP. Using TSP proteolytic fragments, we demonstrated that the primary interaction of PMN with TSP was mediated through the 140-kDa COOH-terminal domain. Inasmuch as the 140-kDa fragment of TSP contains an Arg-Gly-Asp sequence similar to the cell recognition site of FN and VN, we determined whether RGDS peptides would inhibit PMN adhesion. RGDS did not significantly inhibit PMN adhesion to TSP, VN, or LN, but reduced PMN adhesion to FN by 50%. To determine if PMN adhesion to TSP was mediated by a beta 2 integrin receptor such as LFA-1, MO-1, or p150,95, we performed adhesion assays using PMN isolated from patients with leukocyte adhesion deficiency that lack beta 2 receptors. Leukocyte adhesion deficiency PMN exhibited normal adherence to TSP. In contrast, adherence to VN, LN, and FN was reduced by 95%. Therefore, adherence to TSP is probably not mediated by a beta 2 integrin receptor. These data contribute to the accumulating evidence that PMN can interact with extracellular matrix proteins through a CD11/CD18-independent process.

Long-term results of submandibular duct transposition for drooling

This study examines the long-term results and morbidity of submandibular duct transposition in drooling children. Twenty-two patients, aged 3 to 18 years, with neurological dysfunction and excessive drooling underwent submandibular duct transposition between 1984 and 1987. In January 1990, 20 patients were reviewed. Their degree of drooling pre-operatively, immediately post-operatively and currently was assessed. The rate of improvement and the occurrence of complications were noted. Drooling was 'much better' in the early post-operative period in 17 of the 20 patients, and this improvement was invariably noted within three weeks. In the three other patients drooling was 'better'. Deterioration occurred in only three patients over the entire follow-up period. Complications all occurred in the first 18 months following surgery; they consisted of salivary retention cysts in four and transient submandibular gland swelling in a fifth patient.

Pharyngeal pouch carcinoma: two unusual cases

Two patients with carcinomata arising in pharyngeal pouches are reported. In one, the tumour was detected preoperatively by a contrast radiographic study. In the second the lesion was a carcinoma in situ. The English literature is reviewed with reference to these two unusual features.

Effects of oestradiol cypionate on spontaneous and oxytocin-stimulated postpartum myometrial activity in the cow

The effects of oestradiol cypionate (ECP) on spontaneous and oxytocin-induced postpartum myometrial activity were measured in four cows using strain gauge transducers (SGT). On the first day after parturition, prior to treatment with ECP, myometrial activity consisted mainly of single-peak contractions (mean frequency 9.6/h, mean duration 141.0s, the majority of the contractions being propagated in a tubocervical direction. Injection of ECP (5 mg i.m.) 18 h after parturition led to suppression of coordinated myometrial activity and the development of sustained low amplitude contractions of reduced frequency (mean 2.9/h, P less than 0.01) and increased duration (mean 422.2 s, P less than 0.05), with multiple superimposed small peaks. In addition, all parts of the uterus tended to contract simultaneously. These changes were apparent by 4 h after treatment and persisted until day 5 after parturition. Injection of oxytocin (25 USP units i.v.) at 24 h after parturition stimulated the reappearance of single-peak coordinated contractions. However, pretreatment with ECP did not enhance the myometrial response to oxytocin.

Middle-latency responses. II. Variation among stimulation sites

We investigated the relationship between thresholds of the electrically evoked auditory brain-stem response (EABR) and the electrically evoked middle-latency response (EMLR), and the variation in EMLR thresholds and dynamic ranges with site of stimulation. The EABRs and EMLRs were recorded in albino guinea pigs in response to electrical stimulation at the round window, promontory, scala tympani, and modiolus. The EABR and EMLR thresholds were similar. There was no significant difference between thresholds for round-window and scala tympani stimulation. Amplitude/intensity functions for the EMLR differed with site of stimulation. The EMLR seems to be comparable with the EABR for assessing the electrical excitability of the auditory pathway with less electrical artifact contamination. In this respect, round-window and scala tympani stimulation sites are equally efficacious.

Middle-latency responses. I. Electrical and acoustic excitation

The electrically evoked auditory brain-stem response has been used in the past to assess auditory system function with regard to cochlear prosthesis application. The brief latency of the response makes it susceptible to electrical artifact contamination, and waveform identification is often difficult. As a possible alternative for a noninvasive measure of system excitability, the middle-latency response (MLR), elicited by electrical stimulation, was investigated. Middle-latency responses were recorded in response to acoustic and round-window electrical stimulation in albino guinea pigs. Acoustic and electrically evoked MLR waveforms were similar, as were their respective latency/intensity functions. Amplitude/intensity functions for the electric MLR showed greater variability than acoustically evoked MLR functions. The electric MLR is readily evoked and relatively insensitive to electrical artifact in the guinea pig. It is potentially a useful tool in assessing the integrity of auditory pathways and consequently in the development of diagnostic tests for cochlear implant candidates.