Criptosporidiosis. Una infección rara en el trasplante renal / Cryptosporidiosis. A rare infection in renal transplantation

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[Fever and cavitary infiltrate in a renal transplant recipient]. / Receptora de trasplante renal con fiebre y neumonía cavitada.

Aspergillus infection is a rare but devastating complication following organ transplantation with high mortality rate. Aspergillus fumigatus is the most common cause of invasive aspergillosis. This fungus is present in the environment worldwide. Aspergillus infection is mainly acquired by inhalation of spores and several nosocomial infections in transplant recipient have been associated with construction work at hospitals. Risk factors for invasive aspergillosis include administration of steroid boluses, history of cytomegalovirus infection, neutropenia and prolonged antibiotic use after transplantation. Successful treatment depends on three factors: early diagnosis, aggressive antifungal therapy and decrease or removal of immunosuppression. Amphotericin deoxycholate has been the standard treatment for many years but lipid preparations for amphotericin are now used due to their significantly fewer adverse effects. A number of new antifungal drugs are now being developed including new azoles such as voriconazol and echinocandin. Invasive aspergillosis has a high mortality rate more than 95% when cerebral dissemination is demonstrated. We report the case of a 47 years old woman who received a cadaveric renal graft and developed pulmonary aspergillosis with fulminant cerebral dissemination two months later. The diagnosis of pulmonary aspergillosis was by culture isolation obtained from bronchioalveolar lavage. Removal of immunosuppresive agents and liposomal amphotericin B therapy were started shortly after admission. Brain CT scan performed on the 12th day showed cerebral dissemination. The recipient died two days later. Our patient had several risk factors such as the administration of steroid boluses and cytomegalovirus infection. Invasive aspergillosis must be always included in the differential diagnosis of fever and pulmonary disease in the renal transplant recipient.

Receptora de trasplante renal con fiebre y neumonía cavitada / Fever and Cavitary infiltrate in renal transplant recipient

Las infecciones fúngicas constituyen una causa poco frecuente de infección en el trasplante renal pero con una elevada mortalidad. La aspergilosis invasiva representa la segunda causa de infección fúngica en estos pacientes. Se adquiere por inhalación de esporas, su incidencia está en estrecha relación con factores ambientales, constituye una infección nosocomial en el trasplante renal, y se asocia a obras hospitalarias y a contaminación por los sistemas de ventilación. Los factores de riesgo en el paciente trasplantado para el desarrollo de la infección incluyen la neutropenia prolongada, la coinfección por virus como el citomegalovirus y la administración de altas dosis de esteroides. El pronóstico es muy grave con una mortalidad que oscila entre el 75-95% según las diversas series, siendo incluso mayor del 95% si existe afectación cerebral. El éxito del tratamiento depende de la precocidad del diagnóstico, la agresividad del tratamiento y la reducción o retirada de la inmunosupresión. El antifúngico clásico utilizado es la anfotericina B, últimamente sustituida por su forma liposomal debido a la menor incidencia de efectos secundarios. Actualmente existen nuevos azoles, como la equinocandina y el voriconazol, que constituyen un tratamiento útil de forma primaria. Se presenta el caso de una mujer de 47 años que recibió un trasplante renal de cadáver dos meses antes y desarrolló una aspergilosis pulmonar con diseminación cerebral inmediata y fulminante. La paciente presentaba como factores de riesgo el haber recibido altas dosis de esteroides y una infección por citomegalovirus. La enferma recibió tratamiento con anfotericina B liposomal y retirada precoz de la inmunosupresión, pero falleció poco después del diagnóstico de su afectación cerebral. La aspergilosis invasiva debe incluirse en el diagnóstico diferencial de fiebre y afectación pulmonar en el paciente con trasplante renal (AU)

Aspergillus infection is a rare but devastating complication following organ transplantation with high mortality rate. Aspergillus fumigatus is the most common cause of invasive aspergillosis. This fungus is present in the enviroment worldwide. Aspergillus infection is mainly acquired by inhalation of spores and several nosocomial infections in transplant recipient have been associated with construction work at hospitals. Risk factors for invasive aspergillosis include administration of steroid boluses, history of cytomegalovirus infection, neutropenia and prolonged antibiotic use after transplantation. Successful treatment depends on three factors: early diagnosis, agressive antifungal therapy and decrease or removal of immunosuppression. Amphotericin deoxycholate has been the standard treatment for many years but lipid preparations for amphotericin are now used due to their significantly fewer adverse effects. A number of new antifungal drugs are now being developed including new azoles such as voriconazol and echinocandin. Invasive aspergillosis has a high mortality rate more than 95% when cerebral dissemination is demonstrated. We report the case of a 47 years old woman who received a cadaveric renal graft and developed pulmonary aspergillosis with fulminant cerebral dissemination two months later. The diagnosis of pulmonary aspergillosis was by culture isolation obtained from bronchioalveolar lavage. Removal of immunossupresive agents and liposomal amphotericin B therapy were started shortly after admission. Brain CT scan performed on the 12th day showed cerebral dissemination. The recipient died two days later. Our patient had several risk factors such as the administration of steroid boluses and cytomegalovirus infection. Invasive aspergillosis must be always included in the differential diagnosis of fever and pulmonary disease in the renal transplant recipient (AU)

[Diffuse lymphoproliferative disease after renal transplantation and its relation with Epstein-Barr virus. Experience at one center]. / La enfermedad linfoproliferativa difusa postrasplante renal y su relación con el virus Epstein-Barr. Experiencia de un centro.

Post-transplant lymphoproliferative disorders (PTLD) are a group of heterogeneous lymphoid proliferations in chronic immunosuppressed recipients which appear to be related to Epstein Barr Virus (EBV). Receptor EBV seronegativity, use of antilymphocyte antibodies and CMV disease have been identified as risk factors that may tigger development of PTLD. We have studied the incidence of PTLD and its relationship with EBV in 588 adult renal transplant recipients who were transplanted in our hospital from 1988 to 2001. We have also evaluated the diagnostic and therapeutic methods used, the risk factors and outcome of the patients who developed PTLD. We identified 8 recipients (4 males and 4 females), range from 18 to 67 years (mean age 45.6 years) with a median time between grafting and PTLD of 4.1 years (0.1-7 years), who developed PTLD (1.3%). Only 1 patient received OKT3 and had CMV disease, two of them (25%) had been treated with hight doses of prednisolone, another was EBV seronegative, but the rest of them (50%) had no risk factors. Two patients were diagnosed at autopsy, the diagnosis of 5 was based on the histology of biopsy and the last one by CT scans of chest-abdomen and cytology. The presence of EBV in the lymphoproliferative cells was assessed in 5 out of the 7 studied patients (71.4%). The outcome of our recipients was poor. Five out of 8 patients died shortly after diagnosis as a direct consecuence of PTLD and another of an infectious complication of the treatment (75%). The 2 patients alive started dialysis and 1 of them died 2 years later of a non-related cause. In conclusion, PTLD is a relatively frequent disease with a poor prognosis in renal transplant patients. It seems to have a close relationship with EBV and can develop in the absence of the classical risk factors.

La enfermedad linfoproliferativa difusa postrasplante renal y su relación con el virus Epstein-Barr. Experiencia de un centro / Post-transplant lymphoproliferative disorders and its relationship with epstein barr virus

La inmunosupresión farmacológica necesaria en el trasplante de órganos facilita el desarrollo de la enfermedad linfoproliferativa difusa postrasplante (ELDP), en cuya patogenia el virus Epstein Barr (VEB) parece determinante. Diversos factores de riesgo han sido identificados, como son la seronegatividad para VEB del receptor, el uso de anticuerpos mono o policlonales y la infección por CMV. Hemos estudiado la incidencia de ELDP y su relación con el VEB en 588 receptores adultos de trasplante renal de cadáver realizados entre 1988 y 2001 en nuestro hospital, con un seguimiento mínimo de 3 meses. Valoramos los factores de riesgo, los métodos diagnósticos empleados, el tratamiento de ELDP y su evolución.Un total de 8 receptores (1,3 por ciento) con una edad media de 45,6 años (18-67 años), 4 varones y 4 mujeres, y con una evolución media postrasplante de 4,1 años (0,17 años), desarrollaron ELDP. Cuatro de ellos (50 por ciento) no presentaban ninguno de los factores de riesgo clásicos descritos, 2 habían sido tratados con dosis altas de esteroides por rechazo agudo, otro era seronegativo para VEB y un caso había recibido OKT3, presentando además una enfermedad por CMV. El diagnóstico de ELDP fue postmortem en 2 pacientes, por TC toraco-abdominal y celularidad en líquido pleural y ascítico en 1 y mediante el estudio histológico de biopsias en los 5 receptores restantes. Se detectó la presencia de VEB en el tejido linfoproliferativo de 5 de los 7 pacientes estudiados (85,7 por ciento). La evolución de nuestros pacientes fue mala ya que 5 de ellos fallecieron por causa directa de la enfermedad y otro por una complicación infecciosa secundaria al tratamiento (75 por ciento). Los 2 pacientes supervivientes reiniciaron diálisis, falleciendo 1 a los 2 años por causa nos relacionada, mientras que el otro está vivo 9 años después. Concluimos que la ELDP es una entidad de muy mal pronóstico. Está asociada de forma significativa al VEB y en la mitad de los casos no se identifican los factores de riesgo clásicos (AU)

Calmodulin binds to K-Ras, but not to H- or N-Ras, and modulates its downstream signaling.

Activation of Ras induces a variety of cellular responses depending on the specific effector activated and the intensity and amplitude of this activation. We have previously shown that calmodulin is an essential molecule in the down-regulation of the Ras/Raf/MEK/extracellularly regulated kinase (ERK) pathway in cultured fibroblasts and that this is due at least in part to an inhibitory effect of calmodulin on Ras activation. Here we show that inhibition of calmodulin synergizes with diverse stimuli (epidermal growth factor, platelet-derived growth factor, bombesin, or fetal bovine serum) to induce ERK activation. Moreover, even in the absence of any added stimuli, activation of Ras by calmodulin inhibition was observed. To identify the calmodulin-binding protein involved in this process, calmodulin affinity chromatography was performed. We show that Ras and Raf from cellular lysates were able to bind to calmodulin. Furthermore, Ras binding to calmodulin was favored in lysates with large amounts of GTP-bound Ras, and it was Raf independent. Interestingly, only one of the Ras isoforms, K-RasB, was able to bind to calmodulin. Furthermore, calmodulin inhibition preferentially activated K-Ras. Interaction between calmodulin and K-RasB is direct and is inhibited by the calmodulin kinase II calmodulin-binding domain. Thus, GTP-bound K-RasB is a calmodulin-binding protein, and we suggest that this binding may be a key element in the modulation of Ras signaling.

Neuronal survival induced by neurotrophins requires calmodulin.

It has been reported that phosphoinositide 3-kinase (PI 3-kinase) and its downstream target, protein kinase B (PKB), play a central role in the signaling of cell survival triggered by neurotrophins (NTs). In this report, we have analyzed the involvement of Ca2+ and calmodulin (CaM) in the activation of the PKB induced by NTs. We have found that reduction of intracellular Ca2+ concentration or functional blockade of CaM abolished NGF-induced activation of PKB in PC12 cells. Similar results were obtained in cultures of chicken spinal cord motoneurons treated with brain-derived neurotrophic factor (BDNF). Moreover, CaM inhibition prevented the cell survival triggered by NGF or BDNF. This effect was counteracted by the transient expression of constitutive active forms of the PKB, indicating that CaM regulates NT-induced cell survival through the activation of the PKB. We have investigated the mechanisms whereby CaM regulates the activation of the PKB, and we have found that CaM was necessary for the proper generation and/or accumulation of the products of the PI 3-kinase in intact cells.

Syndecan-2 expression in colorectal cancer-derived HT-29 M6 epithelial cells induces a migratory phenotype.

Members of the heparan sulfate proteoglycan family, the syndecans have emerged as integrators of extracellular signals, such as ECM components or growth factors, that activate cytoplasmic signaling cascades and regulate cytoskeletal functions. Specifically, syndecan-2 has been implicated in various cellular processes, from differentiation to migration, including its participation in cell-cell and cell-matrix adhesion. Here, we focused on the involvement of syndecan-2 in epithelial versus mesenchymal differentiation. Colorectal cancer-derived HT-29 M6 epithelial cells were stably transfected with full-length syndecan-2 cDNA, and the effect on cell morphology, adhesion, and mobility was evaluated. Characteristic features of migratory cells such as loss of intercellular contacts, flatter shape and multiple membrane projections were observed in syndecan-2 transfectants. Western blot analysis of the major component of epithelial adherens junctions, E-cadherin, revealed decreased expression levels. Furthermore, syndecan-2 induced stronger adhesion to collagen type I, specifically inhibited by heparin. This was correlated with an increased ability for migration, as demonstrated by wound healing experiments and transwell assays, without affecting their growth rate. These results indicate that syndecan-2 expression in mucus-secreting HT-29 M6 cells induces differentiation toward a migratory mesenchymal-like phenotype.

PC12 cells have caveolae that contain TrkA. Caveolae-disrupting drugs inhibit nerve growth factor-induced, but not epidermal growth factor-induced, MAPK phosphorylation.

Nerve growth factor (NGF) induces survival and differentiation of the neural crest-derived PC12 cell line. Caveolae are cholesterol-enriched, caveolin-containing plasma membrane microdomains involved in vesicular transport and signal transduction. Here we demonstrate the presence of caveolae in PC12 cells and their involvement in NGF signaling. Our results showed the expression of caveolin-1 by Western blot and confocal immuno-microscopy. The presence of plasma membrane caveolae was directly shown by rapid-freeze deep-etching electron microscopy. Moreover, combined deep-etching and immunogold techniques revealed the presence of the NGF receptor TrkA in the caveolae of PC12 cells. These data together with the cofractionation of Shc, Ras, caveolin, and TrkA in the caveolae fraction supported a role for these plasma membrane microdomains in NGF signaling. To approach this hypothesis, caveolae were disrupted by treatment of PC12 cells with cholesterol binding drugs. Either filipin or cyclodextrin treatment increased basal levels of MAPK phosphorylation. In contrast, pretreatment of PC12 cells with these drugs inhibited the NGF- but not the epidermal growth factor-induced MAPK phosphorylation without affecting the TrkA autophosphorylation. Taken together, our results demonstrate the presence of caveolae in PC12 cells, which contain the high affinity NGF receptor TrkA, and the specific involvement of these cholesterol-enriched plasma membrane microdomains in the propagation of the NGF-induced signal.

Nerve growth factor but not neurotrophin-3 is synthesized by hippocampal GABAergic neurons that project to the medial septum.

Conventional uptake of neurotrophins takes place at axon terminals via specific receptors, and is followed by retrograde transport. Recent studies demonstrated that, with the exception of nerve growth factor, other neurotrophins may be delivered anterogradely to the region containing the receptor expressing neurons. In this study we used a triple labeling method that combines retrograde tract tracing, in situ hybridization and immunocytochemistry to examine whether non-principal cells projecting from the hippocampus to the septum synthesize nerve growth factor. Our results show that, on average, 59% of the horseradish peroxidase-labeled hippocamposeptal nonpyramidal neurons also display nerve growth factor messenger RNA hybridization signal. The ratio was slightly higher in the CA1 stratum oriens and the hilus of the dentate gyrus (64 and 62%, respectively) compared to stratum oriens of the CA3 region (58%). In addition, we demonstrated that many nerve growth factor-positive septally projecting neurons also contain the calcium-binding protein calbindin D-28K, whereas nerve growth factor-negative projecting cells mostly lack this neurochemical marker. In contrast to nerve growth factor, neurotrophin-3 has never been found in hippocamposeptal cells. Hippocamposeptal GABAergic cells are reciprocally connected with the medial septum, thus they are in a key position to regulate nerve growth factor release as a function of the activity level in the septohippocampal system. Furthermore, our results raise the intriguing possibility that nerve growth factor may be transported also in an anterograde manner. Regardless of the direction of transport, the presence of nerve growth factor in hippocamposeptal cells suggests that long distance fast synaptic mechanisms and slow neurotrophin action are coupled in these neurons.

Ezrin links syndecan-2 to the cytoskeleton.

The syndecan family of heparan sulfate proteoglycans is known to associate with the actin cytoskeleton, possibly transducing signals from the extracellular matrix. In the search for proteins that could mediate the association of syndecan-2 with the actin cytoskeleton we found that ezrin, a protein which links membrane receptors to the cytoskeleton, coimmunoprecipitated with syndecan-2 in COS-1 cells. In vitro assays indicated a direct association between the amino-terminal domain of ezrin and the cytoplasmic domain of syndecan-2. Confocal microscopy showed colocalization of ezrin and syndecan-2 in actin-rich microspikes in COS-1 cells. The syndecan-2/ezrin protein complex was resistant to 0.2% Triton X-100 extraction but the syndecan-2/amino-terminal domain of ezrin complex was not, which indicated that carboxi-terminal domain of ezrin is involved in the cytoskeleton anchorage of this protein complex. Additionally we observed that the activation of rhoA GTPase increased syndecan-2 insolubility in 0.2% Triton X-100 and syndecan-2/ezrin association. Taken together, these results indicate that ezrin connects syndecan-2 to the actin cytoskeleton.

Nerve growth factor activation of the extracellular signal-regulated kinase pathway is modulated by Ca(2+) and calmodulin.

Nerve growth factor is a member of the neurotrophin family of trophic factors that have been reported to be essential for the survival and development of sympathetic neurons and a subset of sensory neurons. Nerve growth factor exerts its effects mainly by interaction with the specific receptor TrkA, which leads to the activation of several intracellular signaling pathways. Once activated, TrkA also allows for a rapid and moderate increase in intracellular calcium levels, which would contribute to the effects triggered by nerve growth factor in neurons. In this report, we analyzed the relationship of calcium to the activation of the Ras/extracellular signal-regulated kinase pathway in PC12 cells. We observed that calcium and calmodulin are both necessary for the acute activation of extracellular signal-regulated kinases after TrkA stimulation. We analyzed the elements of the pathway that lead to this activation, and we observed that calmodulin antagonists completely block the initial Raf-1 activation without affecting the function of upstream elements, such as Ras, Grb2, Shc, and Trk. We have broadened our study to other stimuli that activate extracellular signal-regulated kinases through tyrosine kinase receptors, and we have observed that calmodulin also modulates the activation of such kinases after epidermal growth factor receptor stimulation in PC12 cells and after TrkB stimulation in cultured chicken embryo motoneurons. Calmodulin seems to regulate the full activation of Raf-1 after Ras activation, since functional Ras is necessary for Raf-1 activation after nerve growth factor stimulation and calmodulin-Sepharose is able to precipitate Raf-1 in a calcium-dependent manner.

Expression of neurotrophins in hippocampal interneurons immunoreactive for the neuropeptides somatostatin, neuropeptide-Y, vasoactive intestinal polypeptide and cholecystokinin.

Using a double detection method, which combines in situ hybridization for the detection of neurotrophin messenger RNA with immunocytochemistry against the neuropeptides somatostatin, neuropeptide Y, vasoactive intestinal polypeptide and cholecystokinin, we have analysed the expression of the neurotrophins, nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3, in distinct populations of neuropeptide-immunoreactive hippocampal interneurons. Nerve growth factor messenger RNA expression was found in subsets of the four subpopulations of neuropeptide-immunoreactive interneurons. The highest degree of co-localization was observed in the neuropeptide-Y-positive cells (up to 70%) and in somatostatin-immunoreactive cells (48%). Only small subsets of cholecystokinin- and vasoactive intestinal polypeptide-positive neurons (21% and 10%, respectively) displayed nerve growth factor hybridization signals. In contrast, expression of neurotrophin-3 messenger RNA was exclusively observed in 26% of neuropeptide-Y-immunoreactive cells. Brain-derived neurotrophic factor hybridization signals were never detected in the neuropeptide-positive hippocampal interneurons. Morphological analysis of neuropeptide-immunoreactive interneurons that express or lack nerve growth factor messenger RNA revealed that most perisomatic inhibitory neurons, such as large vasoactive intestinal polypeptide/ cholecystokinin-immunoreactive cells, showed positive nerve growth factor hybridization signals. In addition, some somatostatin/neuropeptide-Y-immunoreactive interneurons, which are responsible for dendritic inhibition of principal hippocampal neurons, expressed nerve growth factor messenger RNA. In contrast, interneurons specialized to innervate other GABAergic cells, such as small vasoactive intestinal polypeptide-positive cells, lacked nerve growth factor expression. All these data indicate that expression of neurotrophins is differentially regulated in functionally distinct classes of hippocampal interneurons immunoreactive for neuropeptides. We also analysed whether neuropeptide-immunoreactive interneurons expressing neurotrophins were targets of the GABAergic septohippocampal pathway. We used a triple detection method, combining anterograde tracing of this connection, with in situ hybridization for the detection of neurotrophin mRNA, and immunocytochemistry against neuropeptides. Our data showed that the four populations of hippocampal interneurons studied (somatostatin, neuropeptide-Y, vasoactive intestinal polypeptide and cholescystokinin) received GABAergic afferents from the septum. However, no preference for neuropeptide-immunoreactive cells expressing neurotrophins was observed, compared to neuropeptide-positive neurons lacking neurotrophin expression.

Syndecan-2 induces filopodia by active cdc42Hs.

The syndecans, a family of transmembrane heparan sulfate proteoglycans, are ubiquitous molecules whose intracellular function is still unknown. To examine the function of syndecan-2, one of the most abundant heparan sulfate proteoglycan in fibroblasts, we performed transfection studies in COS-1 and Swiss 3T3 cells. Endogenous syndecan-2 colocalized with F-actin in cortical structures. Overexpression of full-length syndecan-2 induced the formation of long filopodia-like structures. These changes correlated with a rearrangement of the actin cytoskeleton, which strongly colocalized with syndecan-2. Overexpression of syndecan-2 lacking the extracellular domain increased the number of microspikes on the cell surface but failed to induce filopodia. Addition of heparin blocked the effect of full-length syndecan-2, suggesting that heparan sulfate chains in the extracellular domain are necessary to induce filopodia. Coexpression of cdc42Hs negative-dominant N17 blocked syndecan-2-induced filopodia and cdc42Hs positive-dominant V12 had a synergic effect. This indicates that active cdc42Hs is necessary for syndecan-2 induction of filopodia. These results provide a link between syndecan-2, actin cytoskeleton, and cdc42Hs.

Expression of nerve growth factor and neurotrophin-3 mRNAs in hippocampal interneurons: morphological characterization, levels of expression, and colocalization of nerve growth factor and neurotrophin-3.

We have investigated the distribution and morphology of hippocampal interneurons that express the neurotrophins nerve growth factor (NGF) and neurotrophin-3 (NT-3) in the rat. For this study, we combined in situ hybridization for the detection of NGF and NT-3 mRNAs and immunocytochemistry against the calcium-binding proteins parvalbumin (PARV), calretinin (CALR), and calbindin (CALB). Whereas the majority of PARV+ interneurons expressed NGF mRNA, only subsets of CALR- and CALB-immunoreactive interneurons (23% and 24%, respectively) displayed NGF hybridization. Most CALB/NGF+ cells were located in the stratum oriens/alveus of the CA3-CA1 regions, suggesting that they may include the population of CALB+, hippocamposeptal, nonpyramidal neurons. Most of the nonspiny CALR/NGF+ neurons were located within or in the vicinity of the pyramidal layer and had faint CALR immunostaining and stellate, thin dendrites. Regarding the spiny CALR-immunoreactive cells, we found that most of these neurons in the hilus were NGF+, whereas only 59% of displayed NGF hybridization in the stratum lucidum of the CA3 region. A small subset of PARV- and CALR-immunoreactive cells expressed NT-3 mRNA (16% and 13%, respectively). NT-3 message was not found in the large basket cells of the dentate gyrus, whereas the distribution and morphology of CALR/NT-3+ cells were similar to those of nonspiny CALR/NGF+ cells. In fact, double in situ hybridization analysis confirmed that most NT-3+ neurons also expressed NGF mRNA, indicating coexpression of both neurotrophins in subpopulations of PARV+ and CALR+ neurons. Moreover, the level of NGF mRNA expression was higher in PARV+ neurons than in CALR- and CALB-immunoreactive interneurons, whereas NT-3 message was expressed similarly in PARV+ and CALR+ neurons. The present findings show a differential expression of NGF and NT-3 mRNAs in subsets of hippocampal interneurons and suggest that the expression of these transcripts depends on factors intrinsic to particular cell types.

Upregulation of BDNF mRNA expression in the barrel cortex of adult mice after sensory stimulation.

Upregulation of brain-derived neurotrophic factor (BDNF) mRNA expression by neuronal activity has been reported in cultured hippocampal cells and in different in vivo excitotoxic paradigms. The aim of the present study was to determine whether sensory stimulation of the whisker-to-barrel pathway alters BDNF mRNA expression in the cortex and, if so, to evaluate the specificity of this effect. To this end, a set of mystacial whiskers was unilaterally stimulated by mechanical deflection, and the expression of BDNF mRNA was analyzed in the barrel cortex by in situ hybridization (ISH) using a 35S-labeled antisense BDNF riboprobe and emulsion autoradiography. A clear-cut and specific upregulation of the BDNF mRNA expression was found at the level of the somatosensory cortex after the increased peripheral stimulation. In the barrel cortex of control mice, BDNF mRNA was present in a few cells in layers II/III and VI, whereas it was almost undetectable in layer IV. After 6 hr of whisker stimulation, increased levels of BDNF mRNA were found in layers II to VI of the contralateral barrel cortex. In layer IV, BDNF upregulation was confined to the barrels corresponding to the stimulated follicles. ISH combined with immunocytochemistry against the three calcium-binding proteins parvalbumin, calretinin, and calbindin-D28K revealed that BDNF mRNA-expressing cells do not belong to the GABAergic cell population of the barrel cortex. The present results support a role for BDNF in activity-dependent modifications of the adult cerebral cortex.

Expression of NGF and NT3 mRNAs in hippocampal interneurons innervated by the GABAergic septohippocampal pathway.

We used in situ hybridization for the detection of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin 3 (NT3) mRNAs combined with immunocytochemistry against the calcium-binding proteins parvalbumin (PARV), calbindin 28k (CALB), and calretinin (CALR) to determine the expression of neurotrophins in functionally distinct subsets of hippocampal interneurons. Most PARV-immunoreactive neurons in the hippocampus were NGF mRNA-positive (82%), which corresponds to 71% of NGF-positive neurons in the hippocampus proper and in the dentate gyrus (excluding granule cells). In contrast, only a subset of CALB- and CALR-immunoreactive interneurons (24% and 23%, respectively) displayed hybridization signals for NGF. Small subsets of PARV- and CALR-positive cells expressed NT3 mRNA, but we did not find hippocampal interneurons expressing BDNF mRNA. These results show that NGF and NT3 genes are differentially regulated in distinct subsets of GABAergic cells, and these interneurons are a major source of NGF production in the hippocampus. We also addressed whether hippocampal interneurons expressing neurotrophins were targets of the GABAergic septohippocampal pathway. We developed a triple-labeling method that combines anterograde tracing of this pathway by means of Phaseolus vulgaris leucoagglutinin injections, with in situ hybridization for the detection of neurotrophins, and immunocytochemistry for calcium-binding proteins. Virtually every PARV-positive neuron innervated by GABAergic septohippocampal baskets expressed NGF mRNA (86%), whereas 39-59% of CALR- and CALB-positive interneurons that were contacted by GABAergic septohippocampal axons showed NGF gene expression. A small subset of NT3 mRNA-expressing interneurons was also innervated by septohippocampal baskets. These findings show that the GABAergic septohippocampal pathway preferentially terminates on interneurons expressing NGF mRNA, suggesting that this neurotrophic factor might be involved in the specification of this connection and in its maintenance and normal function in the adult brain.

Differential regulation of the expression of nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3 mRNAs in adult rat brain after intrahippocampal injection of quinolinic acid.

Intrahippocampal injection of the endogenous excitotoxin quinolinic acid (QUIN) induces seizures together with local, delayed neurodegeneration in specific cell layers. In situ hybridization histochemistry was used to study the spatio-temporal pattern of expression of neurotrophins (NTFs) after this treatment. As in other excitatory paradigms, nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) mRNA levels increased dramatically and transiently in dentate gyrus after the administration of 120 nmol of QUIN to the left hippocampus. BDNF, but not NGF, mRNA also increased in the hippocampal pyramidal cell layer, mainly in the CA1 field. Neurotrophin-3 (NT3) mRNA levels decreased in dentate gyrus, practically disappeared around 12 h after the insult and returned to basal levels four days later. A very different pattern of expression of NTFs was found locally: (a) upregulation of NGF and BDNF mRNAs expression was prevented in a spherical region of 1-2 mm diameter around the injection site, (b) a delayed increase in NT3 mRNA levels, beginning at 12 h and lasting for at least 4 days after the administration of QUIN, was found in the same region, in cell layers showing neurodegeneration. Pretreatment with the non-competitive NMDA antagonist MK-801 (2 mg/kg, 30 min before the insult), partially blocked the increase in both BDNF and NGF mRNAs, as well as the decrease in NT3, in the contralateral hippocampus. However, this treatment did not prevent the QUIN-induced local downregulation of NGF and BDNF. Treatment with the AMPA/kainate antagonist NBQX (30 mg/kg, 15 and 5 min before, and 10 min after the insult) did not influence the effect of QUIN upon NGF or BDNF mRNA levels, although it partially prevented the hippocampal contralateral decrease in NT3 mRNA. In conclusion, the present study strongly supports previous work concerning different regulation of BDNF/NGF respect to NT3 in seizure inducing paradigms. Moreover, the different and to some extent opposite regulation of NTFs in the hippocampal region contiguous to the injection site, respect to the remaining hippocampus, suggests a differential regulation of NTFs in QUIN-induced neurodegenerative and seizural processes. Finally, our pharmacological data, (i) show that the upregulation of NGF and BDNF mRNAs, indirectly induced by QUIN, is not mediated by AMPA receptors, and (ii) suggest other effects for QUIN, apart from the stimulation of NMDA receptors.

Neuronal death and neurotrophin gene expression: long-lasting stimulation of neurotrophin-3 messenger RNA in the degenerating CA1 and CA4 pyramidal cell layers.

Neurotrophin-3 has been characterized as the product of a gene cloned by homology with nerve growth factor and brain-derived neurotrophic factor. Recombinant neurotrophin-3, like nerve growth factor and brain-derived neurotrophic factor, has been shown to enhance survival and differentiation of specific neuronal populations in vitro. However, little is known about its function and regulation in vivo. Both brain-derived neurotrophic factor and nerve growth factor messenger RNAs increased in adult rat brain, in a wide range of excitatory paradigms. In contrast, neurotrophin-3 messenger RNA decreased in some of them. Neurotrophin-3 is the most highly expressed neutrophic factor in immature areas of the central nervous system. However, no stimulation of its expression in the mature central nervous system, either in physiological or pathological conditions, has been described to date. This behaviour suggests that neurotrophin-3 could be involved in biological roles different from the prototypes nerve growth factor and brain-derived neurotrophic factor. Excitatory amino acid receptor-mediated neurotoxicity (excitotoxicity) is believed to contribute to neuronal loss in a wide range of neurodegenerative conditions (for a review, see Ref. 17). Moreover, locally increased levels of the endogenous excitotoxin quinolinic acid may be involved in the natural development of neurodegenerative diseases. The unilateral intrahippocampal injection of 120 nmol of quinolinic acid induced seizures together with local neurodegeneration in specific cell layers. In situ hybridization histochemistry was used to analyse the spatiotemporal pattern of expression of neurotrophin-3. As in other excitotoxic paradigms, neurotrophin-3 messenger RNA clearly decreased, nearly disappearing, in the contralateral hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)