[Seroepidemiological study of brucellosis in a rural endemic area]

BACKGROUND

This study investigated the prevalence of Brucella spp. antibodies in the general population in the Health Area of Tremp (Region of Pallars Jussà, Lleida). It also identified the risk factors with the presence of these.

PATIENTS AND METHODS

A total of 346 (191 men and 155 women) were studied. Information about the sex, age, location, the personal and familiar antecedents of brucellosis, occupational risk, contact with the animals and the consumption of non-hygienic dairy products was recorded. The estimation of the seroprevalence was carried out by the ELISA IgG test. The association of independent variables with the presence of antibodies was assessed by the Coombs to Brucella and the ELISA IgG tests. It was assessed by using the calculation of the analysis variance.

RESULTS

The personal antecedents, the contact with the animals and the occupational risk all showed a statistically significant relation (p < 0.05) with the Coombs and ELISA IgG tests. The familiar antecedents showed a significant relation with the ELISA IgG. The consumption of dairy products and the location showed no statistically significant relation. A seroprevalence was obtained among the researched population of 11.9%, the maximum occurred in Isona surgery (25.6%) and the minimum in Tremp (9.8%).

CONCLUSIONS

The seroprevalence is high and the epidemiological profile associated with the fact of being seropositive is associated with the profession of the study subject and it coincides with de infection mechanisms present in the area.

Vertebral and rib sarcoidosis: long-term clinical remission with methotrexate

We describe a patient with bilateral hilar lymphadenopathy shown on a chest radiograph and supraclavicular lymphadenopathy. Biopsy of a supraclavicular lymph node showed non-caseating granulomas. A diagnosis of sarcoidosis was made and no treatment was given. One year later she complained of cervical and lumbar pain and decreasing strength of the right hand. Magnetic resonance imaging of the spine showed multiple lesions within the vertebral bodies of six vertebrae, and thoracic computed tomography showed partial destruction of the first right rib. A biopsy of the second lumbar vertebra demonstrated non-caseating granulomas. Corticosteroid treatment was unsuccessful and long-term remission of the symptoms was achieved with a weekly low dose of methotrexate.

[Efficacy of hygienic and dietary therapy in coronary patients with isolated hypoalphalipoproteinemia]

OBJECTIVE

Hypoalphalipoproteinemia (HA) is a relatively frequent disorder found in patients with coronary artery disease (CAD). It is associated to a greater risk of suffering recurrent coronary episodes and of mortality caused by this disease.

METHODS

We selected 60 patients with previous CAD and isolated HA (HDLc concentration < 0.9 mmol/L, and desirable lipidic profile) that were consecutively seen in a specialized lipid clinic. Subjects were randomly included in the two groups of cases (group of intervention) and controls. Cases were treated with non-pharmacological measures which included changes in lifestyle and dietary habits. Control subjects were referred to their general practitioners in order to receive conventional medical care.

RESULTS

It was demonstrated a significant increase in the HDLc concentration in both groups, being greater the improvement in the group of intervention, but the differences in the increase in the HDLc between both groups were not significant. Fibrinogen was lower in the patients of the group of intervention, especially in those patients that gave up smoking.

CONCLUSION

Changes in lifestyle and dietary habits are useful to correct the low HDLc plasma levels and to reduce fibrinogen levels in those patients with CAD and HA.

Excitotoxicity, synaptic repair, and functional recovery in the mammalian cochlea: a review of recent findings

Besides its fast excitatory properties, glutamate is known to have neurotoxic properties when released in large amounts or when incompletely recycled. This so-called excitotoxicity is involved in a number of acute and/or degenerative forms of neuropathology such as epilepsy, Alzheimer's, Parkinson's, stroke, and retinal ischemia. In the cochlea, excitotoxicity may occur in two pathological conditions: anoxia and noise trauma. It is characterized by a two-step mechanism: (1) An acute swelling, which primarily depends on the AMPA/kainate type of receptors, together with a disruption of the postsynaptic structures (type I afferent dendrites) resulting in a loss of function. Within the next 5 days, synaptic repair may be observed with a full or a partial (acoustic trauma) recovery of cochlear potentials. (2) The second phase of excitotoxicity, which may develop after strong and/or repetitive injury, consists of a cascade of metabolic events triggered by the entry of Ca2+, which leads to neuronal death in the spiral ganglion. Ongoing experiments in animals, tracking the molecular basis of both these processes, presages the development of new pharmacological strategies to help neurites to regrow and reconnect properly to the IHCs, and to prevent or delay neuronal death in the spiral ganglion. Human applications should follow, and a local (transtympanic) strategy against cochlear excitotoxicity may, in the near future, prove to be helpful in ischemic- or noise-induced sudden deafness, as well as in the related tinnitus.

Morphological and molecular changes in the inner hair cell region of the rat cochlea after amikacin treatment

This study investigates the morphological and molecular changes that occur in the inner hair cell area of the rat cochlea following aminoglycoside treatment. Rats were injected daily with 500 mg/kg of amikacin between postnatal day 9 (PND9) and PND16. Cochleae were examined at PND16 to PND120 using both scanning and transmission electron microscopy and molecular fluorescent labeling. The inner hair cells showed obvious signs of apoptosis in response to amikacin treatment and most of them were missing by one week after the end of the aminoglycoside exposure period. Concomitantly, the epithelium became scarred as the surrounding supporting cells expanded and filled the space vacated by the missing IHCs. The mid-basolateral region of these modified supporting cells was surrounded by many afferent and efferent terminals. However, these cells expressed neither calbindin nor SNAP25, proteins that are both expressed by IHCs in the normal, untreated organ of Corti in the rat. In addition, these supporting cells remained attached to the basal lamina by a thin cytoplasmic process. The supporting cells surrounding the inner hair cells therefore appear unable to convert directly into inner hair cells following aminoglycoside induced hair-cell loss but may be able to provide trophic support for the remaining afferent and efferent neurites.

Mild presentation of systemic lupus erythematosus in elderly patients assessed by SLEDAI. SLE Disease Activity Index

OBJECTIVE

Systemic lupus erythematosus (SLE) predominantly affects young patients. SLE starting in later life has a clinical presentation different than in younger patients. We have used the SLE Disease Activity Index (SLEDAI) to explore the relationship between age of onset and disease activity.

METHODS

We selected all patients controlled in our hospital at the moment of clinical diagnosis of SLE (100 patients; 85 females and 15 males). They were classified in two groups: those with early onset (>50 y) and those with late onset (>50 y) based on their age at the moment of clinical diagnosis of SLE.

RESULTS

In 12 patients the onset of SLE was >50 y (10 females and two males; mean age 59 y). The early onset patients had significantly higher SLEDAI values at the presentation and during the first year of disease with respect to elderly patients. Antibodies to DNA and hypocomplementemia were detected more often in younger patients.

CONCLUSION

Our results confirm using SLEDAI, that the lupus of the elderly patients is a distinct clinical subgroup with a milder course of disease.

[Regenerative potential of the sensory epithelium of the mammalian organ of Corti after poisoning with ototoxic antibiotics]

Cochlear sensory hair cells are very sensitive to noxious influences such as ageing, noise and ototoxic drugs. Whereas lost auditory hair cells are replaced by new hair cells in the avian and lower vertebrates, cochlear sensory hair cells do not regenerate in mammals. Recently, we have observed transient atypical cells in the cochlea of amikacin intoxicated rats. We have related their presence to an attempt at sensory hair cell neodifferentiation. The aim of the present study was to i) investigate the mechanisms responsible for sensory hair cell losses during the intoxication and the subsequent appearance of atypical cells, ii) characterise the phenotype of these atypical cells and iii) evaluate the influence of cochlear immaturity in such an attempt at sensory hair cells neo-differentiation.

Löfgren's syndrome revisited: a study of 186 patients

PURPOSE

To evaluate the clinical features, the results of noninvasive tests and biopsies, and the outcome of patients with Löfgren's syndrome.

SUBJECTS AND METHODS

Patients diagnosed as having Löfgren's syndrome at a university hospital in Barcelona, Spain, from 1974 to 1996, were prospectively followed. Löfgren's syndrome was defined as the association of erythema nodosum or periarticular ankle inflammation with unilateral or bilateral hilar or right paratracheal lymphadenopathy.

RESULTS

Löfgren's syndrome was diagnosed in 186 patients. The mean age was 37 +/- 11 years, and 157 (85%) were women. In 91 patients (49%), symptoms started during the spring (P < 0.0001). Erythema nodosum, periarticular ankle inflammation, or both were present at onset in 173 patients (93%). At the time of diagnosis, 161 patients (87%) had no respiratory symptoms; 151 (81%) had stage I abnormalities on chest radiograph, 29 (16%) stage II, and 6 (3%) stage 0. Five percent of patients had decreased forced vital capacity, and 15% had decreased carbon monoxide diffusing capacity. Extrathoracic involvement was infrequent. Serum angiotensin-converting enzyme levels were increased in 50% of patients. Gallium-67 scans showed hilar uptake in all the studied patients, but it yielded useful additional diagnostic information only in those with normal chest radiographs or with unilateral hilar lymphadenopathy. The diagnosis was proven with biopsy results in 63% of patients. None of the patients without histologic confirmation were subsequently found to have a diagnosis other than sarcoidosis. In the 133 patients who were followed for a mean of almost 5 years, 11 (8%) continued to have active disease, and 8 (6%) had several recurrences between 18 months and 20 years after a complete resolution. A normal serum angiotensin-converting enzyme level at diagnosis was associated with disease resolution without recurrence.

CONCLUSION

Löfgren's syndrome is usually a self-limiting form of sarcoidosis. Histologic confirmation is not necessary in typical cases. In a small number of patients, the disease may remain active or recur long after its onset, although usually with mild organ dysfunction.

AMPA-preferring glutamate receptors in cochlear physiology of adult guinea-pig

1. The present study was designed to determine which glutamate (Glu) receptors are involved in excitatory neurotransmission at the first auditory synapse between the inner hair cells and the spiral ganglion neurons. 2. The Glu receptors present at the membrane level were investigated on isolated spiral ganglion neuron somata from guinea-pigs by whole-cell voltage-clamp measurements. Glu and AMPA induced a fast onset inward current that was rapidly desensitized, while kainate induced only a non-desensitizing, steady-state current. NMDA induced no detectable current. 3. To further discriminate between the AMPA and kainate receptors present, we used the receptor-specific desensitization blockers, cyclothiazide and concanavalin A. While no effect was observed with concanavalin A, cyclothiazide greatly enhanced the Glu-, AMPA- and kainate-induced steady-state currents and potentiated Glu-induced membrane depolarization. 4. To extrapolate the results obtained from the somata to the events occurring in situ at the dendrites, the effects of these drugs were evaluated in vivo. Cyclothiazide reversibly increased spontaneous activity of single auditory nerve fibres, while concanavalin A had no effect, suggesting that the functional Glu receptors on the somata may be the same as those at the dendrites. 5. The combination of a moderate-level sound together with cyclothiazide increased and subsequently abolished the spontaneous and the sound-evoked activity of the auditory nerve fibres. Histological examination revealed destruction of the dendrites, suggesting that cyclothiazide potentiates sound-induced Glu excitotoxicity via AMPA receptors. 6. Our results reveal that fast synaptic transmission in the cochlea is mainly mediated by desensitizing AMPA receptors.

High disease activity at baseline does not prevent a remission in patients with systemic lupus erythematosus

OBJECTIVE

To evaluate the utility of systemic lupus erythematosus (SLE) initial clinical manifestations and the SLE Disease Activity Index (SLEDAI) for identifying patients who will have a remission.

METHODS

We studied 100 SLE patients (85 females, 15 males) and identified all patients who had remission (defined as at least one continuous year during which lack of disease activity permitted withdrawal of all treatment to suppress general lupus activity of a particular clinical manifestation). Changes in laboratory parameters without clinical activity, thus not requiring treatment, did not invalidate remission. We did not include any patient who had never required treatment. We evaluated the SLEDAI values and the main SLE manifestations at the time of diagnosis of SLE, and also every 3 months during the first year of disease.

RESULTS

Twenty-four of the 100 SLE patients achieved remission that occurred a mean of 64 months after the diagnosis. They remained in remission for a mean of 55 months. There were no statistical differences in SLEDAI values and the initial manifestations (including renal and cerebral) between patients who reached remission and those who did not. The patients who have a higher SLEDAI score take longer to achieve remission.

CONCLUSION

SLE patients with severe initial clinical manifestations and higher SLEDAI values may achieve clinical remission.

Sequential changes in anti-GAL-1 staining of the rat organ of Corti following amikacin exposure

Hair cell loss and a non-functional epithelial reorganization appeared in the organ of Corti after acoustic or toxic damage. Moreover, in the drug damaged organ of Corti, transient atypical cells were recently described with characteristics of both immature hair cells and/or non-sensory epithelial cells. The phenotype of these atypical cells has been now investigated by using the galectine 1 (GAL-1) antibody. In the normal organ of Corti, this antibody recognizes all the epithelial cells except the sensory hair cells and their supporting cells. At PD 21, transient atypical cells were not stained by GAL-1 antibody, suggesting that they were originated from hair cells or their supporting cells. Later, the organ of Corti was substituted by an epithelial scare, GAL-1 stained. This study also emphasizes the particular resistance of the cochlear apex to degeneration after antibiotic intoxication.

Fate of fumonisin B(1) in corn kernel steeping water containing SO(2)

Six 100 ppm fumonisin B(1) (FB(1)) solutions were prepared by dissolving pure standard in six different solvents containing SO(2). Two of the solvents contained 0.2 or 0.4% SO(2) in distilled water. The other four solvents were obtained by steeping corn kernels at 60 degrees C in a 0.2% SO(2) aqueous solution for 6, 12, 24, or 48 h. After the addition of FB(1), all solutions were maintained at 60 degrees C for 7 days. Fumonisin B(1) content in each solution was determined in triplicate by HPLC. Steeping corn kernels in 0.2% solution at 60 degrees C for 6 h seems to be the most effective treatment to decrease the amount of FB(1).

Characterization of atypical cells in the juvenile rat organ of corti after aminoglycoside ototoxicity

Hair cell regeneration is well documented in the inner ear sensory epithelia of lower vertebrates and birds and may occur in the vestibular organs of mammals. By contrast, hair cell loss in the mature mammalian cochlea is considered irreversible. However, recent reports have suggested that an attempt at hair cell regeneration could occur in vivo in aminoglycoside-lesioned cochleas from neonatal rats. After amikacin treatment, atypical cells with apical specialization reminiscent of early differentiating stereocilia are transiently present at the apex of the intoxicated cochleas but fail to differentiate as hair cells in later stages. In the present study, we used electronic microscopy, histochemistry, and confocal microscopy to investigate the cellular rearrangements in the amikacin-lesioned organ of Corti of rat pups. In addition, we used 5-bromo-2'-deoxyuridine immunocytochemistry to determine whether mitotic processes are involved in the formation of the atypical cells. The morphologic and molecular data suggest that atypical cells are not recovering hair cells, but share characteristics of immature hair cells and supporting cells. Proliferative cells were absent from the region occupied by atypical cells, suggesting that the latter did not arise through mitotic processes. Altogether, the present results support the hypothesis that atypical cells arise through direct transformation of some of the supporting cells that reorganize during hair cell degeneration.

Changes in medical education in Spain

In Spain, the lack of homogeneous criteria among medical institutions has led to gaps between medical school, residency, and continuing medical education. The authors describe the background and early history of the Spanish medical education system, early reforms, and the start of modern postgraduate medical education. They discuss the current system, highlighting ongoing concerns about how physicians are trained, including the emphasis on lectures and traditional assessment methods; the focus of faculty on research activities rather than teaching; inadequate assessment of residents; and the lack of coordination among providers of continuing medical education. However, they also highlight ongoing reform efforts, most notably the development of a new medical curriculum that has just begun to be implemented. They conclude with a discussion of the future direction of medical education in Spain, in which the growing movement toward greater unity among European nations is likely to play a large role.

[The involvement of the parenchyma of the central nervous system in Behçet disease]

INTRODUCTION

Behçet disease is a systemic form of vasculitis which presents with neurological symptoms with a frequency varying between 16 and 40%. Involvement of the parenchyma has been found to worsen the prognosis in patients with neuroBehçet (NB).

OBJECTIVE

To review the clinical features and course of patients with NB involving the parenchyma of the central nervous system (CNS).

CLINICAL CASES

Seven patients with Behçet disease and neurological localizing signs were seen in our hospital between 1989 and 1996. The initial diagnosis was of ischemic ictus in five of the seven patients. Both neuroimaging studies and investigation of the cerebrospinal fluid were always pathological in all cases. Vascular studies (arteriography and echo-Doppler of the supra-aortic trunks) were normal. One patient died. Four patients had serious sequelae following treatment.

CONCLUSION

NB should be included in the different diagnosis of ictus. Involvement of the parenchyma of the CNS was accompanied by lymphocytic meningitis, perhaps also leading to a worse functional prognosis.

Cardiovascular risk factors associated with clinically isolated and diffuse atherosclerosis in Spanish patients with coronary artery disease

BACKGROUND

Patients with coronary artery disease (CAD) associated with peripheral (PAD) or cerebrovascular disease (CVD), a condition called diffuse atherosclerosis, have a higher risk of death than patients with isolated CAD. The prevalence of diffuse atherosclerosis and the atherogenic risk factors associated with this condition in our geographic area have not been described previously.

METHODS

A cohort of 2597 patients (62 +/- 10.8 years, 665 women) consecutively admitted at Bellvitge Hospital because of acute coronary syndromes were studied. CAD patients were divided in two groups with diffuse and located atherosclerosis according to whether they had or they had not an associated PAD or CVD. Baseline history, physical data and lipid profile were recorded in each patient according to a standardized questionnaire.

RESULTS

A total of 370 patients (14.2%) had diffuse atherosclerosis. Among them, there were more men and women older than 55 years than among those with isolated CAD. Patients with diffuse atherosclerosis were more frequently hypertensive, diabetic and former smokers than those with isolated CAD (60.5% vs. 49.4%, P < 0.01; 37.4% vs. 24.5%, P < 0.01; and 47% vs. 35.7%, P < 0.01, respectively). There were no significant differences in the mean values of total cholesterol (TC), low-density cholesterol (LDL-C), high-density cholesterol (HDL-C) and triglycerides between both groups of patients, but patients with diffuse atherosclerosis had a lower HDL-C/TC ratio, with borderline statistical significance (0.18 +/- 0.06 vs. 0.19 +/- 0.06, P = 0.06). Using multiple logistic regression analysis, the variables associated with diffuse atherosclerosis in men were age greater than 55 years (OR 1.97, CI 1.33-2.93), hypertension (OR 1.50, CI 1.14-2.20), diabetes (OR 1.78, CI 1.20-2.70), smoking (former smokers) (OR 2.09, CI 1.36-3.24) and HDL-C/TC < 0.20 (OR 1.60, CI 1.18-2.17); and in women hypertension (OR 3.43, CI 1.48-7.94) and diabetes (OR 2.58, CI 1.55-4.80).

CONCLUSIONS

Clinically overt diffuse atherosclerosis is a relatively common disease. Older patients and those with hypertension, diabetes or low HDL-C/TC ratio are more likely to have diffuse atherosclerosis than those without these conditions.

Diagnostic utility of postmortem fine-needle aspiration cultures

BACKGROUND

Microbiological cultures at autopsy have not proved to be very useful. In life, transthoracic and fine-needle aspirations of other tissues have provided better results. The aim of this prospective study was to assess the diagnostic utility of postmortem cultures obtained by fine-needle aspiration puncture (FNAP) of several tissues when punctures were performed in the immediate postmortem period.

METHODS

Comparative analysis was performed between FNAP cultures and those obtained in life and by conventional autopsy. All adult autopsied patients who died at a general teaching hospital in a 3-year period were included. Clinical data, microbiological cultures before death, and pathologic data from autopsies of all patients were recorded, as were results of FNAP performed after death from the heart, right lower lung, liver, spleen, and other areas suspicious for infection. Cultures from the same sites were made at autopsy. Microorganisms were isolated and defined as infectious agents, colonizers, or contaminants according to standard criteria.

RESULTS

Ninety-two patients (59 men, 33 women) were included in the study; patients had a mean age of 67.7 years. There were five main diagnostic groups: neoplastic (n = 25), digestive (n = 15), respiratory (n = 14), circulatory (n = 10), and infectious diseases (n = 10). Infection was suspected in 47 patients (51.3%). Autopsy was performed 12 hours after death or later in 61% of patients. No significant differences were found in terms of contamination or colonization in relation to time between death and FNAP, time between death and autopsy, or microorganisms isolated. The sensitivity of FNAP and autopsy with respect to the isolation of infective microorganisms was similar (80.9% vs 87%), but FNAP was more specific (66.7% vs 44.4%). Age, sex, time between death and FNAP, clinical diagnosis, cause of death, and antimicrobial therapy did not influence the results significantly. Blood cultures gave the best results (specificity 84.4%) [corrected].

CONCLUSIONS

Fine-needle aspiration puncture performed in the immediate postmortem period adds relevant microbiological information to the clinicopathologic picture and provides higher specificity than autopsy cultures. Blood cultures are especially useful. When difficulties are associated with autopsy examination or in cases of selected clinical conditions, FNAP can be an effective tool for the postmortem diagnosis of infection.

Excitotoxicity and repair of cochlear synapses after noise-trauma induced hearing loss

Guinea-pigs were exposed to a traumatic sound inducing up to 80 dB hearing loss. Beside the well described mechanical damage to outer hair cells, a total disruption of inner hair cell (IHC)-auditory nerve synapses was acutely observed within the traumatized area. To test the hypothesis that synaptic damage is due to an excessive release of glutamate by the IHCs, we examined the protective effect of the glutamate antagonist kynurenate on noise-induced hearing loss. The high degree of protection observed with kynurenate attests that dendritic damage is an important component in noise-induced hearing loss. Moreover, we demonstrate that a synaptic repair mechanism occurring within the first few days post-exposure is partly responsible for the recovery of temporary threshold shifts after an acoustic trauma.

Impact on the immune system of undetectable plasma HIV-1 RNA for more than 2 years

OBJECTIVE

To investigate the impact of prolonged HIV suppression on the immune system by analysing the expression of several lymphocyte surface markers in a group of HIV-1-infected patients who maintained undetectable HIV-1 RNA levels for more than 24 months.

PATIENTS AND METHODS

The study included a highly selected group of nine HIV-1-infected asymptomatic subjects and seven HIV-1-seronegative controls. The inclusion criteria of HIV-1-infected patients was to have plasma HIV-1 RNA levels below 20 (1.3 log10) copies/ml for at least 24 months while under antiretroviral treatment with nucleoside analogues. The patient population was retrospectively taken from a cohort of 1418 treated subjects. Mean initial absolute CD4+ T-cell count and percentage were 468+/-234 x 10(6)/l (range, 202-935 x 10(6)/l) and 25+/-6% (range, 16-33%), respectively. Plasma HIV-1 RNA quantification was determined using a standard and ultrasensitive reverse transcriptase polymerase chain reaction assay. Median HIV-1 RNA plasma level before antiretroviral treatment was 3.14 log10 copies/ml (range, 1.74-3.73 log10 copies/ml). Two or three-colour immunophenotyping was performed on whole blood and frozen peripheral blood mononuclear cells by flow cytometry.

RESULTS

A significant increase was noted in CD4+ lymphocyte counts at the end of the study in HIV-1-positive patients. In addition, the CD4: CD8 ratio rose significantly with respect to baseline, although it remained lower than in the controls. CD45RA+ and CD45RO+ population percentages did not differ between groups. A significant rise in CD45RA+ T cells was observed. Analysis of T-cell activation measuring the expression of human leukocyte antigen-DR and CD25 did not differ between groups. The proportion of CD8+ lymphocytes that were CD28+ was similar in both groups at the end of the follow-up. T-cell receptor Vbeta subfamily analysis showed that an expansion of the T-cell receptor repertoire might occur in these patients.

CONCLUSION

Patients who maintain undetectable viral load for prolonged periods of time with antiretroviral therapy may achieve a partial immune restoration of the immune system. Our results suggest that treatment of patients at early stages of HIV infection is warranted.

Antisense oligonucleotides to the GluR2 AMPA receptor subunit modify excitatory synaptic transmission in vivo

In the brain, fast wxcitatory synaptic transmission is mostly mediated by the alpha-amino-3-hydroxy-5-methyl-isoxazole-propionic acid (AMPA) subtype of the glutamate receptors. Molecular cloning has revealed that four subunits, GluR1, GluR2, GluR3, and GluR4 form heteromeric receptors with high affinity for AMPA. Because antagonists and agonists do not discriminate between individual AMPA receptor subunits, we decided to use antisense oligonucleotides to block the expression of the GluR2 subunit within the receptor complex in adult animals. In the present study, we exploited several advantages afforded by the guinea pig cochlea to determine whether an antisense oligonucleotide directed to the mRNA of the GluR2 subunit could modify primary auditory neurotransmission. While a random probe with the same base composition had no effect, a GluR2 antisense oligonucleotide, continuously delivered into the cochlea, transiently reduced the compound action potential and diminished spontaneous activity of single auditory nerve fibers. Although antisense oligonucleotides penetrated a variety of cells, their effect could be physiologically localized to a single site of GluR2 antisense probe action, the primary auditory neuron. Subunit specificity of this effect was confirmed by a significant reduction in GluR2/3, but not GluR4 immunoreactivity in primary auditory neurons. Besides being the first demonstration that transient knockout of GluR2 subunit in adult animal modifies excitatory synaptic transmission in vivo, these results support the use of the antisense strategy as a powerful tool for blocking expression of any gene in the cochlea.

Glutamate-induced Co2+ uptake in rat auditory brainstem neurons reveals developmental changes in Ca2+ permeability of glutamate receptors

Ca2+ influx through glutamate receptors (GluRs) is thought to play a crucial part in developmental processes and neuronal plasticity. Here we have examined the spatiotemporal distribution of Ca2+-permeable GluRs in auditory brainstem neurons of the rat from birth to adulthood, using the cobalt-staining technique of Pruss and collaborators. In slices of young adult rats, 1 mM glutamate evoked intense cobalt uptake in subsets of neurons in the ventral cochlear nuclei, the medial nucleus of the trapezoid body, the lateral and the medial superior olive, and the lateral lemniscal nuclei. Neurones in the central nucleus of the inferior colliculus, and thalamic auditory nuclei appear to express few, if any, Ca2+-permeable GluRs. Thus, in adults, Ca2+-permeable GluRs are present in neurons of almost all main relay stations of the auditory brainstem. During development, cobalt-stained cells first appeared at about hearing onset (at postnatal day 12 [P12]). At P16, staining levels were highest and the pattern of distribution was already adult-like. The staining intensity slightly declined during the fourth postnatal week. In contrast, Ca2+-permeable receptors were detected in the external cortex of the inferior colliculus as early as P4. Our results show that auditory neurons, characterized by a high temporal precision in neuronal activity, display Ca2+-permeable GluRs. Because Ca2+ permeability appears at about the onset of hearing and is highest during the following 2 weeks, Ca2+ influx through GluRs is likely to be implicated in remodelling processes occurring during this ontogenetic period.