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Ricardo Delgado

Publications and source records attributed to Ricardo Delgado.

11 recordsLinked to original sources
PubMed2006

Bridging behavior and physiology: ion-channel perspective on mushroom body-dependent olfactory learning and memory in Drosophila.

An important body of evidence documents the differential expression of ion channels in brains, suggesting they are essential to endow particular brain structures with specific physiological properties. Because of their role in correlating inputs and outputs in neurons, modulation of voltage-dependent ion channels (VDICs) can profoundly change neuronal network dynamics and performance, and may represent a fundamental mechanism for behavioral plasticity, one that has received less attention in learning and memory studies. Revisiting three paradigmatic mutations altering olfactory learning and memory in Drosophila (dunce, leonardo, amnesiac) a link was established between each mutation and the operation of VDICs in Kenyon cells, the intrinsic neurons of the mushroom bodies (MBs). In Drosophila, MBs are essential to the emergence of olfactory associative learning and retention. Abnormal ion channel operation might underlie failures in neuronal physiology, and be crucial to understand the abnormal associative learning and retention phenotypes the mutants display. We also discuss the only case in which a mutation in an ion channel gene (shaker) has been directly linked to olfactory learning deficits. We analyze such evidence in light of recent discoveries indicating an unusual ion current profile in shaker mutant MB intrinsic neurons. We anticipate that further studies of acquisition and retention mutants will further confirm a link between such mutations and malfunction of specific ion channel mechanisms in brain structures implicated in learning and memory.

Animals↗
PubMed2006

Quiescence induced by iron challenge protects neuroblastoma cells from oxidative stress.

The brain uses massive amounts of oxygen, generating large quantities of reactive oxygen species (ROS). Because of its lipid composition, rich in unsaturated fatty acids, the brain is especially vulnerable to ROS. Furthermore, oxidative damage in the brain is often associated with iron, which has pro-oxidative properties. Iron-mediated oxidative damage in the brain is compounded by the fact that brain iron distribution is non-uniform, being particularly high in areas sensitive to neurodegeneration. This work was aimed to further our understanding of the cellular mechanisms by which SHSY5Y neuroblastoma cells adapt to, and survive increasing iron loads. Using an iron accumulation protocol that kills about 50% of the cell population, we found by cell sorting analysis that the SHSY5Y sub-population that survived the iron loading arrested in the G(0) phase of the cell cycle. These cells expressed neuronal markers, while their electrical properties remained largely unaltered. These results suggest that upon iron challenge, neuroblastoma cells respond by entering the G(0) phase, somehow rendering them resistant to oxidative stress. A similar physiological condition might be involved in neuronal survival in tissues known to accumulate iron with age, such as the hippocampus and the substantia nigra pars compacta.

Cell Line, Tumor↗
PubMed2006

Divalent cations as modulators of neuronal excitability: emphasis on copper and zinc.

Based on indirect evidence, a role for synaptically released copper and zinc as modulators of neuronal activity has been proposed. To test this proposal directly, we studied the effect of copper, zinc, and other divalent cations on voltage-dependent currents in dissociated toad olfactory neurons and on their firing rate induced by small depolarizing currents. Divalent cations in the nanomolar range sped up the activation kinetics and increased the amplitude of the inward sodium current. In the micromolar range, they caused a dose dependent inhibition of the inward Na+ and Ca2+ currents (INa and ICa) and reduced de amplitude of the Ca2+-dependent K+ outward current (ICa-K). On the other hand, the firing rate of olfactory neurons increased when exposed to nanomolar concentration of divalent cations and decreased when exposed to micromolar concentrations. This biphasic effect of divalent cations on neuronal excitability may be explained by the interaction of these ions with high and low affinity sites in voltage-gated channels. Our results support the idea that these ions are normal modulators of neuronal excitability.

Action Potentials↗
PubMed2005

Cyclic AMP cascade mediates the inhibitory odor response of isolated toad olfactory receptor neurons.

Odor stimulation may excite or inhibit olfactory receptor neurons (ORNs). It is well established that the excitatory response involves a cyclic AMP (cAMP) transduction mechanism that activates a nonselective cationic cyclic nucleotide-gated (CNG) conductance, accompanied by the activation of a Ca2+-dependent Cl(-) conductance, both causing a depolarizing receptor potential. In contrast, odor inhibition is attributed to a hyperpolarizing receptor potential. It has been proposed that a Ca2+-dependent K+ (K(Ca)) conductance plays a key role in odor inhibition, both in toad and rat isolated olfactory neurons. The mechanism underlying odor inhibition has remained elusive. We assessed its study using various pharmacological agents and caged compounds for cAMP, Ca2+, and inositol 1,4,5-triphosphate (InsP3) on isolated toad ORNs. The odor-triggered K(Ca) current was reduced on exposing the cell either to the CNG channel blocker LY83583 (20 microM) or to the adenylyl cyclase inhibitor SQ22536 (100 microM). Photorelease of caged Ca2+ activated a Cl- current sensitive to niflumic acid (10 microM) and a K+ current blockable by charybdotoxin (20 nM) and iberiotoxin (20 nM). In contrast, photoreleased Ca2+ had no effect on cells missing their cilia, indicating that these conductances are confined to the cilia. Photorelease of cAMP induced a charybdotoxin-sensitive K+ current in intact ORNs. Photorelease of InsP3 did not increase the membrane conductance of olfactory neurons, arguing against a direct role of InsP3 in chemotransduction. We conclude that a cAMP cascade mediates the activation of the ciliary Ca2+-dependent K+ current and that the Ca2+ ions that activate the inhibitory current enter the cilia through CNG channels.

Adenine↗
PubMed2005

Abnormal distribution of E-cadherin and beta-catenin in different histologic types of cancer of the uterine cervix.

OBJECTIVE: The goal of this study was to analyze the cellular distribution and possible alterations of beta-catenin and E-cadherin proteins in different histologic types of uterine cervical cancer and precursor lesions, compared to normal controls. METHODS: We performed an immunochemical staining analysis of the cellular distribution of beta-catenin and E-cadherin proteins in biopsy samples from 20 normal exocervical squamous epithelium, 43 premalignant lesions, and a large series of 126 invasive tumors of different histologic types that included 68 squamous carcinomas, 31 adenosquamous carcinomas, and 27 adenocarcinomas. Statistical significance was evaluated by the chi-square or Fisher's Exact test. RESULTS: We observed beta-catenin abnormally distributed in the cytoplasm of 62% of premalignant lesions and more than 70% of invasive cancers, statistically significant when compared with normal tissue (P < 0.05). Similarly, we found that E-cadherin exhibit a significant abnormal distribution in the cytoplasm of 58% of premalignant lesions (P < 0.05) and in more than 71% of squamous carcinoma and adenosquamous carcinoma when compared with normal tissue (P < 0.05). We found no differences in the distribution of E-cadherin between adenocarcinomas compared with control samples. Interestingly, we found that both, beta-catenin and E-cadherin, were absent in the membrane of nearly 40% premalignant lesions. Nuclear staining of beta-catenin was rarely seen in any cases, contrary to what has been reported for this and other neoplasias. CONCLUSION: Our findings indicate that cellular alterations of both beta-catenin and E-cadherin are frequent in tumors of the uterine cervix of different histologic types, and support a role for these proteins in cervical cancer development.

Adenocarcinoma↗
PubMed2004

Signaling through Gs alpha is required for the growth and function of neuromuscular synapses in Drosophila.

Although synapses are assembled in a highly regulated fashion, synapses once formed are not static structures but continue to expand and retract throughout the life of an organism. One second messenger that has been demonstrated to play a critical role in synaptic growth and function is cAMP. Here, we have tested the idea that signaling through the heterotrimeric G protein, Gs, plays a coincident role with increases in intracellular Ca(+2) in the regulation of adenylyl cyclases (ACs) during synaptic growth and in the function of synapses. In larvae containing a hypomorphic mutation in the dgs gene encoding the Drosophila Gs alpha protein, there is a significant decrease in the number of synaptic boutons and extent of synaptic arborization, as well as defects in the facilitation of synaptic transmission. Microscopic analysis confirmed that Gs alpha is localized at synapses both pre- and postsynaptically. Restricted expression of wild-type Gs alpha either pre- or postsynaptically rescued the mutational defects in bouton formation and defects in the facilitation of synaptic transmission, indicating that pathways activated by Gs alpha are likely to be involved in the reciprocal interactions between pre- and postsynaptic cells required for the development of mature synapses. In addition, this Gs alpha mutation interacted with fasII, dnc, and hyperexcitability mutants in a manner that revealed a coincident role for Gs alpha in the regulation of cAMP and FASII levels required during growth of these synapses. Our results demonstrate that Gs alpha-dependent signaling plays a role in the dynamic cellular reorganization that underlies synaptic growth.

Animals↗
PubMed2004

Synaptic vesicle pools and plasticity of synaptic transmission at the Drosophila synapse.

Our knowledge on the Drosophila neuromuscular synapse is rapidly expanding. Thus, this synapse offers an excellent model for studies of the molecular mechanism of synaptic transmission and synaptic plasticity. Two synaptic vesicle (SV) pools have been identified and characterized using a fluorescent styryl dye, FM1-43, to stain SVs. They are termed the exo/endo cycling pool (ECP), which corresponds to the readily releasable pool (RRP) defined electrophysiologically, and the reserve pool (RP). These two pools were identified first in a temperature-sensitive paralytic mutant, shibire, and subsequently confirmed in wild-type larvae. The ECP participates in synaptic transmission during low frequency firing of presynaptic nerves and locates in the periphery of presynaptic boutons in the vicinity of release sites, while SVs in the RP spread toward the center of boutons and are recruited only during tetanic stimulation. These two pools are separately replenished by endocytosis. Cyclic AMP facilitates recruitment of SVs from the RP to the ECP. Activation of presynaptic metabotropic glutamate receptors recruits SVs from the RP and enhances SV release by elevation of the cAMP level. Memory mutants that have defects in the cAMP/PKA cascade, dunce and rutabaga, exhibit reduced levels of recruitment of synaptic SVs from the RP to the ECP and have limited short-term synaptic plasticity. SV mobilization between the two pools could be a key step for changes in synaptic efficacy. Since a variety of mutants that have distinct defects in synaptic transmission are available for detailed studies of synaptic function, this direction of approach in Drosophila seems promising.

Animals↗
PubMed2004

Cilium-attached and excised patch-clamp recordings of odourant-activated Ca-dependent K channels from chemosensory cilia of olfactory receptor neurons.

It has previously been proposed that a Ca2+-dependent K+ conductance is implicated in the inhibitory odourant response in rat and toad olfactory receptor neurons. Previous whole-cell and single-channel measurements on inside-out excised patches, in addition to immunochemical evidence, indicated the presence of Ca2+-dependent K+ channels in olfactory cilia, the transducing structures of these sensory cells. Ca2+-dependent K+ channels opened in 'on-cilium' membrane patches from C. caudiverbera upon odourant stimulation. Furthermore, after excision in the inside-out configuration, the channel could be opened by micromolar Ca2+, in a Ca2+-dependent fashion, but it was unresponsive to cyclic AMP. We estimated that the Ca2+ concentration in the proximity of a Ca2+-dependent K+ channel within the cilia reaches at least 100 microM during the odour response. The K+ channel displayed a higher selectivity for K+ than for Na+. Our results support a role for this Ca2+-dependent K+ channel in chemotransduction.

Animals↗
PubMed2003

Presence of Ca2+-dependent K+ channels in chemosensory cilia support a role in odor transduction.

Olfactory receptor neurons (ORNs) respond to odorants with changes in the action potential firing rate. Excitatory responses, consisting of firing increases, are mediated by a cyclic AMP cascade that leads to the activation of cationic nonselective cyclic nucleotide-gated (CNG) channels and Ca2+-dependent Cl- (ClCa) channels. This process takes place in the olfactory cilia, where all protein components of this cascade are confined. ORNs from various vertebrate species have also been shown to generate inhibitory odor responses, expressed as decreases in action potential discharges. Odor inhibition appears to rely on Ca2+-dependent K+ (KCa) channels, but the underlying transduction mechanism remains unknown. If these channels are involved in odor transduction, they are expected to be present in the olfactory cilia. We found that a specific antibody against a large conductance KCa recognized a protein of approximately 116 kDa in Western blots of purified rat olfactory ciliary membranes. Moreover, the antibody labeled ORN cilia in isolated ORNs from rat and toad (Caudiverbera caudiverbera). In addition, single-channel recordings from inside-out membrane patches excised from toad chemosensory cilia showed the presence of 4 different types of KCa channels, with unitary conductances of 210, 60, 12, and 29 and 60 pS, high K+-selectivity, and Ca2+ sensitivities in the low micromolar range. Our work demonstrates the presence of K+ channels in the ORN cilia and supports their participation in odor transduction.

Animals↗
PubMed2002

Changes in retinoblastoma gene expression during cervical cancer progression.

The role of tumour suppressor genes in the development of human cancers has been studied extensively. In viral carcinogenesis, the inactivation of suppressor proteins such as retinoblastoma (pRb) and p53, and cellular oncogenes overexpression, such as c-myc, has been the subject of a number of investigations. In uterine-cervix carcinomas, where high-risk human papillomavirus (HPV) plays an important role, pRb and p53 are inactivated by E7 and E6 viral oncoproteins, respectively. However, little is known about the in situ expression of some of these proteins in pre-malignant and malignant cervical tissues. On the other hand, it has also been demonstrated that c-myc is involved in cervical carcinogenesis, and that pRb participates in the control of c-myc gene expression. By using immunostaining techniques, we investigated pRb immunodetection pattern in normal tissues, squamous intraepithelial lesions (SILs) and invasive carcinomas from the uterine cervix. Our data show low pRb detection in both normal cervical tissue and invasive lesions, but a higher expression in SILs. C-Myc protein was observed in most of the cellular nuclei of the invasive lesions, while in SILs was low. These findings indicate a heterogeneous pRb immunostaining during the different stages of cervical carcinogenesis, and suggest that this staining pattern could be a common feature implicated in the pathogenesis of uterine-cervix carcinoma.

Carcinoma in Situ↗