Acetylcholine receptor subunit homomer formation requires compatibility between amino acid residues of the M1 and M2 transmembrane segments.

The neuronal nicotinic acetylcholine receptor (nAChR) subunits alpha3 and alpha7 have different assembly behavior when expressed in heterologous expression systems: alpha3 subunits require other subunits to assemble functional nAChRs, whereas alpha7 subunits can produce homomeric nAChRs. A previous analysis of alpha7/alpha3 chimeric constructs identified a domain comprising the first putative membrane-spanning segment, M1, as essential to homomeric assembly. The present study dissected further this domain, identifying three amino acid residues, which are located at the most intracellular third of the M1 transmembrane segment, as important in the assembly of homomers. Moreover, formation of homooligomeric complexes seems to require a compatible accommodation between this region and certain residues of the second transmembrane segment, M2. Thus, compatibility between defined domains of the M1 and M2 transmembrane segments appears as a determinant factor governing homomer association of nAChR subunits.

A residue in the middle of the M2-M3 loop of the beta4 subunit specifically affects gating of neuronal nicotinic receptors.

An aspartate residue in the M2-M3 loop of neuronal nicotinic receptor alpha7 subunits is a major determinant of the channel functional response. This residue is conserved in most beta4 subunits, e.g. human and rat, but not in others, e.g. bovine. We have used these differences to examine the mechanism by which this residue alters the functional properties of alpha3beta4 receptors. Having ruled out an effect on the macroscopic binding ability of the agonist, the level of receptor expression, or the single channel conductance, the results suggest that receptors lacking that residue have a deficient coupling between binding and gating.

Elastoviscous substances with analgesic effects on joint pain reduce stretch-activated ion channel activity in vitro.

Activation by noxious mechanical stimuli of sensory nerve fibres that signal joint pain takes place through stretch-activated ion channels, which open in response to increased membrane tension. It has been suggested that the analgesic effect of hyaluronan solutions used for intra-articular treatment of joint pain in humans are mediated by a reduction of the sensitivity of mechanosensory ion channels of nociceptive nerve terminals. We have investigated whether cross-linked hyaluronan solutions (hylans) of different elastoviscosities modify the response characteristics of stretch-activated ion channels of Xenopus laevis oocytes. Patch-clamp recordings on intact oocytes and in excised membrane patches (outside-out and inside-out configurations) were performed in Barth's solution (control condition) and after exposure to hylans of different elastoviscosities. For mechanical stimulation, monitored suction was applied through the microelectrode and the activity of stretch-activated channels was recorded. The activity of stretch-activated channels was significantly reduced in the presence of high elastoviscous hylan A (0.8% polymer content, molecular weight 6M) and of a mixture of hylan A (90% by weight) and hylan B (10% by weight), 0.9% total polymer content, a clinically used hylan product. In contrast, solutions of hylan A with the same chemical composition but reduced elastoviscosity (0.8% polymer content, molecular weight 96000) were found ineffective. It is concluded that stretch-activated channels have a decreased mechanical sensitivity in the presence of elastoviscous solutions of hylan, but not in the presence of non-elastoviscous solutions of hylan of the same concentration. These data suggest that the analgesic effects of intra-articular injections of elastoviscous solutions of hylans are due to a reduction of the sensitivity to mechanical forces of stretch-activated channels present in the membrane of joint mechanonociceptors.

[Measuring visual field loss by automated perimetry in chronic glaucoma stabilized by trabeculectomy]. / Evolution du champ visuel en périmétrie automatisée dans le glaucome chronique équilibré par trabéculectomie.

The progression of field loss was determined by Humphrey Automated threshold perimetry in the short and intermediate term after surgical trabeculectomy for chronic glaucoma: mean indices (MD, PSD et FOV) were studied before and after normalisation of the intraocular pressure. Risk factors such as secondary glaucoma, previous visual field defects and cardiovascular risk factors were significantly correlated to poor or bad progression of field loss: the mean variation of MD = +1.23 dB +/- 2.84 (p < 1.5%), the mean variation of PSD = 0.50 dB +/- 1.37 (p < 6%), but the mean variation of FOV was not significant; so 36% of field defects were improved, 42% were stabilized and 22% were aggravated. When the risk factors were absent, 86% of field losses were stabilised but when cardiovascular factors were present, only 64% were stabilised. These risk factors can also be used to ascertain the prognosis of post-surgical progression of visual field, as already shown in previous reports. Automated threshold perimetry was useful to study the visual field progression with standardized and reliable numerical parameters, allowing statistical computerised management of the patients with glaucoma.

[Severe Aspergillus keratomycosis treated with itraconazole per os]. / Kératomycose aspergillaire sévère traitée par itraconazole per os.

A case of deep traumatic keratomycosis due to Aspergillus fumigatus with anterior chamber involvement is reported. Corneal perforation was threatening because of the large deep and long standing ulcer. This case emphasizes the difficulties of etiological diagnosis and treatment of keratomycosis. The authors analyse the peculiarities of corneal mycotic abcess and emphasize the importance of corneal cultures; they discuss the most recent therapeutic protocols for these lesions. After a very poor response to conventional antifungal therapy, total and quick recovery was acquired using itraconazole per os and topical Amphotericine B. The efficiency of itraconazole proves its antifungal activity against Aspergillus fumigatus and its good penetration to the deeper layers of the cornea and of the anterior chamber.

[Leber's idiopathic stellate neuroretinitis: about two cases]. / Neuro-rétinite stellaire idiopathique de Leber. A propos de deux cas.

BACKGROUND: Described by Theodore Leber in 1916, this syndrome is characterized by unilateral visual loss, optic disc swelling and a stellate pattern of exudative deposits in the macula. MATERIAL AND METHODS: Two young adults were examined for sudden unilateral visual loss preceded by a flu-like syndrome. Fundus examination revealed a swollen optic disc and a macular star, visualized on fluorescein angiography. Visual field, laboratory tests and cranial and orbital tomodensitometry were performed. RESULTS: Visual field examination showed a centrocecal scotoma. Laboratory tests showed inflammatory syndrome in one case. Serology testing (leptospirosis, cat scratch disease, toxoplasmosis and syphilis, etc.) were negative. Tomodensitometry of the brain and orbits gave normal results. One of the patients was treated with intravenous steroid boluses; the other received no treatment. A few weeks after the beginning of symptoms, the swelling of the optic disc seemed to have declined, leaving the macular star unchanged. CONCLUSION: These two cases typically describe Leber's idiopathic stellate neuroretinitis. The prognosis for visual recovery is usually reported to be excellent, but visual sequelae have been described.

[Prevalence of cognitive deterioration in people over 80-years-old: COGMANLLEU study]. / Prevalencia de deterioro cognitivo en personas mayores de 80 años: estudio COGMANLLEU.

INTRODUCTION: We want to detect the prevalence of cognitive prevalence deterioration in the elderly population of 80-years-old or older, their grade of deterioration and the causal pathogenic entity. DESIGN: a cross-sectional population study, including a first phase of screening and a second one of diagnosis confirmation. STUDY SUBJECTS: a total of 877 elderly people of 80-years-old or older belonging to the basic health care area of Manlleu (Osona, Catalonia midlands). In the first phase, relatives and/or caregivers were interviewed, and the participating subjects underwent a set of tests. Those who obtained 24 points or less on the Mini-Mental State Examination (MMSE) and/or an equal Global Deterioration Scale (GDS) or over 3 were admitted to the second phase. During the second phase, a general and a neurological examination were performed, along with blood tests, cranial computed tomography scan and a neuropsychological study. DSM-IV criteria were used for dementia diagnosis, NINCDS-ADRA criteria for Alzheimer's disease (AD) and NINCS-AIREN for vascular dementia. RESULTS: Half of the people over 80-years-old had cognitive deterioration. One-fourth had dementia. A total of 70.3% of these dementias corresponded to AD (47.2% AD without vascular lesions and 23.1% AD with vascular lesions) and 12% corresponded to vascular dementia. The percentage of other degenerative dementias was 17.6%. Age and gender were observed to be associated to dementia. CONCLUSIONS: The prevalence of dementia in the COGMANLLEU study is similar to other European studies. AE is the most frequent dementia.

[Prepapillary arterial loop and retinal arterial branch occlusion]. / Une boucle artérielle prépapillaire compliquée d'occlusion de branche artérielle rétinienne.

Preretinal arterial loops are congenital vascular anomalies that originate from a main branch of the central retinal artery on the optic disc. These arterial loops are usually unilateral and asymptomatic, but they can be associated with retinal artery branch occlusion. We report one case of inferior temporal retinal artery occlusion in a patient with preretinal arterial loops. Two different mechanisms are thought to be the cause of occlusion: twisting of the loop or thrombosis.

Role of the putative transmembrane segment M3 in gating of neuronal nicotinic receptors.

The involvement of some structural domains in the gating of the neuronal nicotinic acetylcholine receptor (AChR) was studied by expressing functional alpha7/alpha3 chimeric subunits in Xenopus oocytes. Substitution of the M3 transmembrane segment in the alpha7 subunit modifies the kinetic properties of the chimeric AChRs as follows: (a) a 6-fold reduction in the maximal current evoked by nicotinic agonists, (b) a 10-fold decrease in the macroscopic desensitization rate, (c) an increase of almost 1 order of magnitude in the apparent affinity for acetylcholine and nicotine, and (d) a decrease in the affinity for alpha-bungarotoxin. Computer simulations showed that the first three effects could be accounted for by a simple kinetic model in which chimeric AChRs presented a smaller ratio of the gating rates, beta/alpha, and a slightly slower desensitization rate. It is concluded that the M3 domain influences the gating of neuronal AChRs.

Gating of alpha3beta4 neuronal nicotinic receptor can be controlled by the loop M2-M3 of both alpha3 and beta4 subunits.

Previous studies have shown that the gating mechanism of alpha3beta4 neuronal nicotinic receptors is affected by a residue in the middle of the M2-M3 loop of the beta4 subunit. We have extended the study of the same location to the alpha3 subunit. Bovine alpha3beta4 receptors were mutated in position 268, substituting the residue present in wild-type receptors, i.e. leucine in alpha3 and asparagine in beta4, for an aspartate. Wild-type and mutated alpha3 and beta4 subunits were combined to form four different receptors. We have measured macroscopic currents in Xenopus oocytes elicited by nicotine, and related them to surface receptor expression measured with an epibatidine-binding essay. We also obtained single-channel recordings of the receptors to study their kinetic behaviour. The results were analysed in terms of an allosteric model with three states. We found that the effect of the mutation in the alpha3 subunit on the gating of the receptor was similar to the corresponding mutation in the beta4 subunit. The effect when both subunits were mutated was additive, suggesting that the contribution of each subunit to the gating mechanism is independent.

Multiple roles of the conserved key residue arginine 209 in neuronal nicotinic receptors.

We have examined the role of a highly conserved arginine (R209), which flanks the M1 transmembrane segment of nAChRs, in the biogenesis and function of neuronal nAChRs. Point mutations revealed that, in alphaBgtx-sensitive neuronal alpha7 nAChRs, the conserved arginine is required for the transport of assembled receptors to the cell surface. By contrast, R209 does not play any role in the transport of assembled alpha-Bgtx-insensitive neuronal alpha3beta4 nAChRs to the cell surface. However, a basic residue at this position of alpha3 and beta4 subunits is necessary for either synthesis, folding, or assembly of alpha3beta4 receptors. Moreover, electrophysiological experiments revealed that in alpha3beta4 receptors the conserved arginine of the alpha3 subunit is involved in either coupling agonist binding to the channel or regulating single channel kinetics.

Neuronal nicotinic acetylcholine receptors on bovine chromaffin cells: cloning, expression, and genomic organization of receptor subunits.

Neuronal nicotinic acetylcholine receptors from bovine adrenomedullary chromaffin cells play a primary role in triggering catecholamine secretion. In the present study, their constituent subunits were characterized. In addition to the alpha 3 subunit, which we have previously cloned, the presence of alpha 5 and beta 4 but not of beta 2 subunits was detected by reverse transcription-PCR analysis of mRNA from adrenal medulla. In situ hybridization indicated that alpha 3, alpha 5, and beta 4 subunits are coexpressed in all chromaffin cells. The primary structure of alpha 5 and beta 4 subunits was determined and functional receptors were obtained upon coinjection of subunit cRNAs into Xenopus oocytes. In contrast to other beta 4-containing nicotinic receptors, the ones formed by the bovine beta 4 subunit are insensitive to the agonist cytisine. Finally, we characterized the intergenic region of alpha 3 and alpha 5 subunits, which together with the beta 4 subunit, form a gene cluster in rats and chickens. RNase assays and the existence of overlapping cDNAs indicate that, in the bovine genome, the alpha 3 and alpha 5 genes overlap at their 3' ends. This fact is probably due to inefficient transcription termination, as a result of weak polyadenylation signals.