[Two-year outcomes of selective laser trabeculoplasty in open-angle glaucoma and ocular hypertension]. / Résultats à deux ans de la trabéculoplastie sélective au laser dans le glaucome à angle ouvert et l'hypertonie oculaire.

BACKGROUND: Selective laser trabeculoplasty (SLT) is a relatively new treatment strategy for the treatment of glaucoma. Its principle is similar to that of argon laser trabeculoplasty (ALT), but may lead to less damage to the trabecular meshwork. METHODS: We assessed the 2-year efficacy of SLT in a noncomparative consecutive case series. Any adult patient either suspected of having glaucoma or with open-angle glaucoma, whose treatment was judged insufficient to reach target intraocular pressure (IOP), could be recruited. IOP and number of glaucoma treatments were recorded over 2 years after the procedure. RESULTS: Our sample consisted of 44 consecutive eyes of 26 patients, aged 69+/-8 years. Eyes were treated initially on the lower 180 degrees . Three of them were retreated after 15 days on the upper 180. Fourteen eyes had ocular hypertension, 17 primary open-angle/normal-tension glaucoma, 11 pseudoexfoliation (PEX) glaucoma, and two pigmentary glaucoma. Thirty-six eyes had previously been treated and continued to be treated with topical anti-glaucoma medication, ten had had prior ALT, nine iridotomy, and 12 filtering surgery. The 2-year-follow up could not be completed for eight eyes because they needed filtering surgery. In the remaining 36 eyes, IOP decreased by a mean of 17.2%, 3.3 mmHg, (19.2+/-4.7 to 15+/-3.6 mmHg) after 2 years (p<0.001). As a secondary outcome, the number of glaucoma treatments decreased from 1.44 to 1.36 drops/patient. Other results according to subgroups of patients are analyzed: the greatest IOP decrease occurred in eyes that had never been treated with anti-glaucoma medication or with PEX glaucoma. SLT was probably valuable in a few eyes after filtering surgery; however, the statistical power of the study was not strong enough to draw a firm conclusion. When expressed in survival curves after 2 years, however, only 48% and 41% of eyes experienced a decrease of more than 3 mmHg or more than 20% of preoperative intraocular pressure, respectively. CONCLUSION: SLT decreases IOP somewhat for at least 2 years without an increase in topical glaucoma treatment. However, it cannot totally replace topical glaucoma treatment. In the future, patient selection should be improved to decrease the cost/effectiveness ratio.

[Proliferative diabetic retinopathy: vitreo-retinal complications are often related to insufficient retinal photocoagulation]. / Rétinopathie diabétique vasoproliférante: complications vitréorétiniennes et photocoagulation rétinienne incomplète.

INTRODUCTION: Panretinal photocoagulation proved to be effective in preventing complications related to vasoproliferative diabetic retinopathy. Surgery is most often a last resort in cases of recurrent or persistent vitreous hemorrhage or retinal detachment. The aim of our study is to point out that eyes requiring surgery for complications related to vasoproliferative diabetic retinopathy are often insufficiently photocoagulated. PATIENTS AND METHODS: Retrospective analysis of operating protocols and surgical results for a series of 39 eyes of 36 patients with complications of vasoproliferative diabetic retinopathy. RESULTS: The mean age at the intervention was 57 years. Eighty-five percent of the eyes had a vitreous hemorrhage, 17% a retinal detachment. Eighty-five percent of the eyes had undergone a partial retinal photocoagulation before surgery. All eyes underwent a vitrectomy with segmentation of fibrovascular membranes. In 85% of the eyes studied, endolaser photocoagulation was necessary, sometimes even in the mid-periphery. After 39+/-26 months of postoperative follow-up, 97% of eyes showed improvement of the anatomical state of the retina and improvement or stabilization of visual acuity. CONCLUSION: Our results confirm the benefit of vitreoretinal surgery in complications related to vasoproliferative diabetic retinopathy. Moreover, it should be emphasized that complications requiring surgery often result from incomplete preoperative photocoagulation. To be effective, photocoagulation has to destroy more than 35% and up to 50% of photoreceptors. An intraoperative laser extension can reduce the risk of regrowth of fibrovascular membranes.

Vasopressin facilitates glycinergic and GABAergic synaptic transmission in developing hypoglossal motoneurons.

The hypoglossal nucleus of young rats contains vasopressin binding sites and vasopressin can directly excite hypoglossal motoneurons. In addition, indirect evidence suggests that vasopressin can enhance the synaptic input to motoneurons. We have characterized this latter effect by using brainstem slices and whole-cell recordings. We found that, in the presence of blockers of fast glutamatergic transmission, vasopressin strongly facilitated inhibitory synaptic activity. On average, vasopressin caused a six-fold increase in the frequency and a 1.5-fold increase in the amplitude of GABAergic postsynaptic currents. The effect of vasopressin on glycinergic postsynaptic currents was similar in magnitude. Vasopressin did not affect the frequency of GABAergic or glycinergic miniature postsynaptic currents, indicating that the peptide-induced facilitation of inhibitory transmission was mediated by receptors located on the somatodendritic region rather than on axon terminals of presynaptic neurons. The pharmacological profile of these receptors was determined by using d[Cha4]AVP and dVDAVP, selective agonists of V1b and V2 vasopressin receptors, respectively, and Phaa-D-Tyr-(Et)-Phe-Gln-Pro-Arg-Arg-NH2, a selective antagonist of V1a vasopressin receptors. The two agonists had no effect on the frequency of inhibitory postsynaptic currents. By contrast, the antagonist suppressed the vasopressin-induced facilitation of these currents, indicating that the receptors involved were exclusively of the V1a type. Thus, vasopressin exerts a dual action on hypoglossal motoneurons: a direct excitatory action and an indirect action mediated by GABAergic and glycinergic synapses. By virtue of this dual effect, vasopressin could alter the input-output properties of these motoneurons. Alternatively, it could play a role in generating or modulating specific motor patterns.

[The value of multifocal ERG in diagnosis of discrete macular dystrophies]. / Importance de l'ERG Multifocal dans le Diagnostic de Dystrophies Maculaires Discrètes.

BACKGROUND: Multifocal ERG is being extensively applied to numerous retinal disorders. It has gained particular clinical value in retinal disorders developing without morphological alterations. PATIENTS AND METHODS: We investigated a series of 4 patients, aged 10, 18, 29, and 49 years, respectively. When examined, they complained of photophobia and slowly progressive bilateral loss of vision, visual acuity ranging from 0.7 to 0.1. RESULTS: Ophthalmoscopic examination showed no or minimal alterations such as subtle granular changes in the fovea. Photopic-scotopic full-field ERG was normal. Multifocal ERG, in contrast, showed markedly reduced signal amplitudes within the central 10 degrees. CONCLUSIONS: Based on the results of multifocal ERG, we were able in each case to consider with a high degree of probability the diagnosis of progressive foveal cone dystrophy. This is to emphasize the sensitivity of multifocal ERG in disorders affecting primarily the macula, without morphological changes, as cone (-rod) dystrophy, early Stargardt dystrophy, etc. The uttermost advantages of multifocal ERG are its innocuity, its applicability to children and the very early sensitivity to changes in retinal function.

Nicotinic cholinergic activation of magnocellular neurons of the hypothalamic paraventricular nucleus.

The aim of the present work was to determine whether paraventricular neurons possess functional acetylcholine nicotinic receptors. Using infrared videomicroscopy and differential interference contrast optics, we performed whole-cell recordings in hypothalamic slices containing the paraventricular nucleus. Acetylcholine, locally applied by pressure microejection in the presence of the muscarinic antagonist atropine, evoked a rapidly rising inward current in paraventricular magnocellular endocrine neurons. This current persisted in the presence of blockers of synaptic transmission. It could be reversibly suppressed by nanomolar concentrations of methyllycaconitine, a selective antagonist of alpha 7-containing nicotinic receptors, but was insensitive to micromolar concentrations of dihydro-beta-erythroidine, an antagonist acting preferentially on non-alpha 7 nicotinic receptors. In addition, the effect of acetylcholine could be mimicked by exo-2-(2-pyridyl)-7-azabicyclo[2.2.1]heptane, a recently synthesized nicotinic agonist specific for alpha 7 receptors. Acetylcholine also desensitized paraventricular nicotinic receptors. Desensitization was pronounced and recovery from desensitization was rapid, consistent with the notion that paraventricular nicotinic receptors contain the alpha 7 subunit. Nicotinic currents could not be evoked in paraventricular parvocellular neurons, suggesting that these neurons are devoid of functional nicotinic receptors. The electrophysiological data were corroborated by light microscopic autoradiography, showing that [(125)I]alpha-bungarotoxin binding sites are present in all the magnocellular divisions of the paraventricular nucleus but are undetectable in other areas of this nucleus. Immunohistochemistry, performed using antibodies directed against vasopressin and oxytocin, indicated that responsiveness to nicotinic agonists was a property of vasopressin as well as of oxytocin magnocellular endocrine neurons, in both the paraventricular and the supraoptic nucleus. We conclude that nicotinic agonists can influence the magnocellular neurosecretory system by directly increasing the excitability of magnocellular neurons. By contrast, they are probably without direct effects on paraventricular parvocellular neurons.

Nicotinic acetylcholine receptors in neonatal motoneurons are regulated by axotomy: an electrophysiological and immunohistochemical study in human bcl-2 transgenic mice.

Motoneuron axotomy was exploited as a model system for studying functional and morphological changes caused in motoneuron cell bodies by peripheral axon injury. Rodent facial motoneurons express functional nicotinic acetylcholine receptors. We have determined the effect of neonatal unilateral facial nerve transection on these receptors by using electrophysiological and immunohistochemical techniques. To avoid rapid apoptotic cell death of axotomized motoneurons, the study was done in mice overexpressing the human bcl-2 transgene. Intact motoneurons responded to acetylcholine by generating a rapidly rising inward current, which was insensitive to methyllycaconitine, a selective antagonist of alpha7-containing nicotinic receptors, but was suppressed by dihydro-beta-erythroidine, a broad-spectrum antagonist. This indicates that mouse facial motoneurons possess nicotinic receptors which are probably devoid of the alpha7 subunit. In striking contrast, axotomized motoneurons displayed little or no sensitivity to acetylcholine. Axotomy did not affect the sensitivity of facial motoneurons to the selective glutamate receptor agonist alpha-amino-3-hydroxy-5-methyl-4-isoxaxolepropionic acid. Immunohistochemical studies revealed that the alpha4 nicotinic receptor subunit was present in intact motoneurons but was undetectable in axotomized motoneurons. By contrast, the beta2 subunit was comparable in intact and axotomized motoneurons. alpha3 immunoreactivity was undetectable, both in intact and in axotomized motoneurons.Thus, mouse facial nicotinic receptors are possibly of the alpha4beta2 type and axotomy interferes negatively with the expression of the alpha4 subunit. By down-regulating nicotinic receptors, peripheral nerve injury may facilitate motoneuron degeneration. Alternatively, nicotinic receptor downregulation and motoneuron degeneration may be independent consequences of peripheral axotomy.

Oxytocin receptor agonists enhance inhibitory synaptic transmission in the rat hippocampus by activating interneurons in stratum pyramidale.

Oxytocin probably plays a role as a neurotransmitter/neuromodulator in the hippocampus of the rat. Oxytocin binding sites are present in the subiculum and CA1 region and oxytocin can excite a class of CA1 nonpyramidal neurons. In the present work we characterized the effect of oxytocin on hippocampal synaptic transmission. Whole-cell recordings were obtained from pyramidal neurons, in conditions of nearly symmetrical chloride concentrations. The selective oxytocin receptor agonist, [Thr4,Gly7]-oxytocin (TGOT), caused an increase in the frequency and amplitude of spontaneous inhibitory postsynaptic currents (IPSCs) in virtually all neurons. These peptide-enhanced IPSCs were blocked by bicuculline, but not by strychnine, and reversed near 0 mV, indicating that they were mediated by gamma-aminobutyric acid (GABA)A receptors. On average, TGOT caused a nearly threefold increase in the frequency and almost a doubling in the amplitude of spontaneous IPSCs. TGOT did not influence the frequency and the amplitude of miniature IPSCs or spontaneous excitatory postsynaptic currents (EPSCs), and had no effect on evoked IPSCs. The peptide did not affect the basic membrane properties of pyramidal neurons or their GABA sensitivity. Thus, TGOT facilitated inhibitory transmission by exerting an excitatory action on the soma and/or dendrites of GABAergic interneurons. Extracellular recordings were performed in interneurons located in various hippocampal strata. Their sensitivity to TGOT was compared to that of substance P (SP). Interneurons in stratum pyramidale were excited both by TGOT and by SP. By contrast, stratum radiatum interneurons responded to SP but not to TGOT. In stratum oriens, half of the interneurons responded to SP, but only a minority to TGOT. Thus, oxytocin-responsive interneurons appear to be preferentially located in close vicinity of pyramidal neurons.

Magnocellular neurons of the rat supraoptic nucleus are endowed with functional nicotinic acetylcholine receptors.

Acetylcholine can stimulate the release of vasopressin. In organ-cultured hypothalamo-neurohypophyseal systems, acetylcholine enhanced vasopressin release by acting in or near the supraoptic nucleus Extracellular recordings suggested that acetylcholine can increase supraoptic neuron excitability. These effects could be mimicked, in part, by nicotine or blocked by nicotinic antagonists, suggesting that they might be mediated by nicotinic acetylcholine receptors. Autoradiography indicated that alpha-bungarotoxin binding sites are present in the supraoptic nucleus; however, neither acetylcholine nor nicotine binding sites could be detected. Thus, the existence, let alone the nature, of nicotinic receptors in the supraoptic nucleus has so far remained elusive. The present work attempts to determine: (i) whether functional nicotinic receptors are present in this nucleus; (ii) whether they are located on neurosecretory magnocellular cells or at presynaptic sites; (iii) what their pharmacological and biophysical properties are; (iv) whether they influence the activity of all or only part of supraoptic neurons. Whole-cell recordings were performed in hypothalamic slices or in acutely dissociated supraoptic neurons and the effect of nicotinic agonists was tested under voltage-clamp conditions. Autoradiography was done in coronal hypothalamic sections, using [3H]epibatidine and [125I]alpha-bungarotoxin as ligands. Our results indicate that supraoptic neurons possess functional nicotinic receptors containing the alpha7 subunit.

A scorpion alpha-like toxin that is active on insects and mammals reveals an unexpected specificity and distribution of sodium channel subtypes in rat brain neurons.

Several scorpion toxins have been shown to exert their neurotoxic effects by a direct interaction with voltage-dependent sodium channels. Both classical scorpion alpha-toxins such as Lqh II from Leiurus quiquestratus hebraeus and alpha-like toxins as toxin III from the same scorpion (Lqh III) competitively interact for binding on receptor site 3 of insect sodium channels. Conversely, Lqh III, which is highly toxic in mammalian brain, reveals no specific binding to sodium channels of rat brain synaptosomes and displaces the binding of Lqh II only at high concentration. The contrast between the low-affinity interaction and the high toxicity of Lqh III indicates that Lqh III binding sites distinct from those present in synaptosomes must exist in the brain. In agreement, electrophysiological experiments performed on acute rat hippocampal slices revealed that Lqh III strongly affects the inactivation of voltage-gated sodium channels recorded either in current or voltage clamp, whereas Lqh II had weak, or no, effects. In contrast, Lqh III had no effect on cultured embryonic chick central neurons and on sodium channels from rat brain IIA and beta1 subunits reconstituted in Xenopus oocytes, whereas sea anemone toxin ATXII and Lqh II were very active. These data indicate that the alpha-like toxin Lqh III displays a surprising subtype specificity, reveals the presence of a new, distinct sodium channel insensitive to Lqh II, and highlights the differences in distribution of channel expression in the CNS. This toxin may constitute a valuable tool for the investigation of mammalian brain function.

Presence of functional neuronal nicotinic acetylcholine receptors in brainstem motoneurons of the rat.

In mammals, nicotinic acetylcholine receptors (nAChRs) play a crucial role in motor control. Muscle-type nAChRs mediate synaptic excitation of skeletal muscle by motoneurons, and nAChRs are present on Renshaw cells, where they produce recurrent inhibition of spinal motoneurons. We asked whether nAChRs are also present in motoneurons. Whole-cell recordings were performed on various motor nuclei in brainstem slices of young rats. Neurons were visualized using infrared (IR) videomicroscopy. Acetylcholine (ACh) or the nicotinic agonist, epibatidine, were delivered by pressure microinjection. Facial (VII), hypoglossal (XII) and vagal (X) motoneurons responded to ACh by generating a fast inward current. In VII motoneurons, the ACh effect was mimicked by epibatidine, and nicotine induced a slow inward current and desensitized the ACh-evoked current. In VII and XII motoneurons, the ACh-evoked current was blocked by the nicotinic antagonist dihydro-beta-erythroidine (DHbetaE), but was unaffected by methyllycaconitine (MLA), an alpha7-specific antagonist. By contrast, the ACh-induced current in X motoneurons was sensitive to MLA. Current-voltage relationships indicated that the currents mediated by either alpha7-containing (X) or non-alpha7-containing (VII, XII) nAChRs displayed inward rectification. In accordance with the electrophysiological data, autoradiography revealed that VII, X and XII nuclei of young rats contained binding sites for [3H]epibatidine; binding sites for [125I]alpha-bungarotoxin, a selective ligand of alpha7-containing nAChRs, were present in X nucleus but were almost undetectable in VII and XII nuclei. Thus, brainstem motoneurons of young rats possess functional nAChRs. They could promote fast synaptic coupling between motoneurons, and thus play a role in somatic and visceral motor functions.

Vasopressin and oxytocin action in the brain: cellular neurophysiological studies.

During the last two decades it has become apparent that vasopressin (VP) and oxytocin (OT), in addition to playing a role as peptide hormones, also act as neurotransmitters. Morphological studies and electrophysiological recordings have shown a close anatomical correlation between the presence of these receptors and the neuronal responsiveness to VP or OT. These compounds have been found to affect membrane excitability in neurons located in the hippocampus, hypothalamus, lateral septum, brainstem, spinal cord and superior cervical ganglion. Sharp electrode intracellular and whole-cell recordings, done in brainstem motoneurons, have revealed that VP and OT can directly affect neuronal excitability by opening non-specific cationic channels. These neuropeptides can also influence synaptic transmission, by acting either postsynaptically or upon presynaptic target neurons or axon terminals. Whereas in some hypothalamic neurons OT appears to mobilize intracellular calcium, as revealed by calcium imaging techniques, in the brainstem the action of this neuropeptide is mediated by a second messenger which is distinct from the second messenger activated in peripheral target cells. Future studies should be aimed at elucidating the properties of the cationic channels responsible for the neuronal action of VP and OT, at identifying the brain-specific second messengers activated by these neuropeptides and at determining whether endogenous VP and OT can exert neuronal effects similar to those elicited by exogenous neuropeptides.

Identification of four epitopes in hepatitis C virus core protein.

We identified four epitopes in hepatitis C virus core protein by using the algorithm of Jameson and Wolf. G15V (amino acids [aa] 31 to 45) appears to be the immunodominant epitope, since it was able to detect antibodies to the core protein in all 40 patients and in 44 of 45 recombinant immunoblot assay-confirmed positive blood donors. This epitope is associated with a low frequency of false-positive results, as found with 522 negative blood donors. A strong reactivity was also observed with the Q15V epitope (aa 7 to 21), although this was associated with low specificity. Occasional reactivity to the R15P (aa 49 to 63) and P15R (aa 99 to 113) epitopes was observed. Q15V and G15V detected antibodies to core protein earlier than the other two epitopes.