Biomedical subjects

Fernando Peña

Publications and source records attributed to Fernando Peña.

13 recordsLinked to original sources

PubMed2006

Gasping activity in vitro: a rhythm dependent on 5-HT2A receptors.

Many rhythmic behaviors are continuously modulated by endogenous peptides and amines, but whether neuromodulation is critical to the expression of a rhythmic behavior often remains unknown, particularly in mammals. Here, we address this issue in the respiratory network that was isolated in spontaneously rhythmic medullary slice preparations from mice. Under control conditions, the respiratory network generates fictive eupneic activity. We hypothesized previously that this activity depends on two types of pacemaker neurons. The bursting properties of one pacemaker rely on the persistent sodium current (INa(p)) and are insensitive to blockade of calcium channels with cadmium (CI-pacemakers), whereas bursting mechanisms of a second pacemaker are sensitive to cadmium (CS-pacemakers) and the calcium-dependent nonspecific cation current blocker flufenamic acid. During hypoxia, fictive eupneic activity is supplanted by the neural correlate of gasping, which is proposed to depend only on CI-pacemakers. Because CI-pacemakers require endogenous activation of 5-HT2A receptors, we tested the hypothesis that 5-HT2A receptor activation is critical for gasping. Here, we demonstrate that fictive gasping and CI-pacemaker bursting were selectively eliminated by the 5-HT2A receptor antagonist piperidine or ketanserin. Neither 5-HT2A antagonist eliminated bursting by CS-pacemakers and ventral respiratory group (VRG) population activity. However, this VRG activity was very different from eupneic activity. In the presence of 5-HT2A antagonists, VRG activity was eliminated by flufenamic acid and could not be reliably restored by adding substance P. These data support the hypothesis that two types of pacemaker bursting mechanisms underlie fictive eupnea, whereas only one burst mechanism is critical for gasping.

Action Potentials↗

PubMed2006

Epileptiform activity induced by pharmacologic reduction of M-current in the developing hippocampus in vitro.

PURPOSE: Benign familial neonatal convulsions (BFNCs), an inheritable epilepsy that occurs in neonates but not in adults, is caused by hypofunctional mutations in genes codifying for the M-type K+ current. In an attempt to develop an in vitro model of this disease, we tested whether blocking M-current with linopirdine induces epileptiform activity in brain slices from animals of different ages. METHODS: Horizontal hippocampus-entorhinal cortex slices were obtained from neonatal (1-2 weeks after birth) and adult (8-9 weeks after birth) rats. Extracellular field recordings of the CA1 region were performed. After recording control conditions, linopirdine was added to the bath, and field activity was recorded continuously for 3 h. 4-Aminopyridine, a drug commonly used to induce epileptiform activity in vitro, was used as a control for our experimental conditions. RESULTS: Bath perfusion of linopirdine induced epileptiform activity only in slices from neonatal rats. Epileptiform activity consisted of interictal-like and ictal-like activity. In slices from adult rats, linopirdine induced erratic interictal-like activity. In contrast, 4-aminopyridine was able to induce epileptiform activity in slices from both neonatal and adult rats. CONCLUSIONS: We demonstrated that blockade of M-current in vitro produces epileptiform activity with a developmental pattern similar to that observed in BNFCs. This could be an in vitro model that can be used to study the cellular mechanisms of epileptogenesis and the developmental features of BFNCs, as well as to develop some therapeutic strategies.

4-Aminopyridine↗

PubMed2006

Breathing generation and potential pharmacotherapeutic approaches to central respiratory disorders.

Breathing is generated and controlled by a brainstem neuronal network. Both intrinsic and synaptic interactions are involved in respiratory rhythm generation and their contribution is state-dependent, changing with hypoxia and the neuromodulatory state. Cellular mechanisms involved in acute or chronic pathological conditions are still unknown. A dysfunction in the neuronal network that controls breathing may be involved in several respiratory disorders such as central sleep apnea, sudden infant death syndrome, congenital hypoventilation, and in some clinical conditions that produce breathing dysfunction such as drug-induced respiratory depression, obesity hypoventilation syndrome, etc. Despite the fact that several drugs are currently used to treat these diseases, the probable effects of this pharmacotherapy on the central rhythm generator and on other neuronal networks related with breathing control is poorly understood. Here, we review the current pharmacological approaches in the treatment of respiratory disorders, such as acetazolamide, theophylline, aminophylline, progesterone, nitric oxide. Possible effects of these drugs on the central respiratory network are discussed and putative therapeutic targets for the development of future pharmacological therapies suggested.

Animals↗

PubMed2005

Mecp2 deficiency disrupts norepinephrine and respiratory systems in mice.

Rett syndrome is a severe X-linked neurological disorder in which most patients have mutations in the methyl-CpG binding protein 2 (MECP2) gene and suffer from bioaminergic deficiencies and life-threatening breathing disturbances. We used in vivo plethysmography, in vitro electrophysiology, neuropharmacology, immunohistochemistry, and biochemistry to characterize the consequences of the MECP2 mutation on breathing in wild-type (wt) and Mecp2-deficient (Mecp2-/y) mice. At birth, Mecp2-/y mice showed normal breathing and a normal number of medullary neurons that express tyrosine hydroxylase (TH neurons). At approximately 1 month of age, most Mecp2-/y mice showed respiratory cycles of variable duration; meanwhile, their medulla contained a significantly reduced number of TH neurons and norepinephrine (NE) content, even in Mecp2-/y mice that showed a normal breathing pattern. Between 1 and 2 months of age, all unanesthetized Mecp2-/y mice showed breathing disturbances that worsened until fatal respiratory arrest at approximately 2 months of age. During their last week of life, Mecp2-/y mice had a slow and erratic breathing pattern with a highly variable cycle period and frequent apneas. In addition, their medulla had a drastically reduced number of TH neurons, NE content, and serotonin (5-HT) content. In vitro experiments using transverse brainstem slices of mice between 2 and 3 weeks of age revealed that the rhythm produced by the isolated respiratory network was irregular in Mecp2-/y mice but could be stabilized with exogenous NE. We hypothesize that breathing disturbances in Mecp2-/y mice, and probably Rett patients, originate in part from a deficiency in noradrenergic and serotonergic modulation of the medullary respiratory network.

Animals↗

PubMed2005

Direct olive oil authentication: detection of adulteration of olive oil with hazelnut oil by direct coupling of headspace and mass spectrometry, and multivariate regression techniques.

Control of adulteration of olive oil, together with authentication and contamination, is one of the main aspects in the quality control of olive oil. Adulteration with hazelnut oil is one of the most difficult to detect due to the similar composition of hazelnut and olive oils; both virgin olive oil and olive oil are subjected to that kind of adulteration. The main objective of this work was to develop an analytical method able to detect adulteration of virgin olive oils and olive oils with hazelnut oil by means of its analysis by a headspace autosampler directly coupled to a mass spectrometer used as detector (ChemSensor). As no chromatographic separation of the individual components of the samples exists, a global signal of the sample is obtained and employed for its characterization by means of chemometric techniques. Four different crude hazelnut oils from Turkey were employed for the development of the method. Multivariate regression techniques (partial least squares and principal components analysis) were applied to generate adequate regression models. Good values were obtained in both techniques for the parameters employed (standard errors of prediction (SEP) and prediction residual error sum of squares (PRESS)) to evaluate its goodness. With the proposed method, minimum adulteration levels of 7 and 15% can be detected in refined and virgin olive oils, respectively. Once validated, the method was applied to the detection of such adulteration in commercial olive oil and virgin olive oil samples.

Corylus↗

PubMed2005

Hypoxia-induced changes in neuronal network properties.

Because of their high energetic demand, neurons within the mammalian central nervous system are extremely sensitive to changes in partial pressure of oxygen. Faced with acute hypoxic conditions, an organism must follow a complex and highly dynamic emergency plan to secure survival. Behavioral functions that are not immediately essential for survival are turned off, and critical behaviors (such as breathing) undergo a biphasic response. An augmentation of breathing is initially adaptive, whereas prolonged hypoxic conditions are better served by an energy-saving mode. However, the hypoxic response of an organism depends on many additional factors. Environmental conditions, the animal's age and health, and the pattern (continuous vs intermittent) and duration (chronic vs acute) of hypoxia greatly determine the specific course of a hypoxic response. Different forms of hypoxia can cause pathology or be used as therapy. Therefore, it is not surprising that the hypoxic response of an organism results from widespread and highly diverse reconfigurations of neuronal network functions in different brain areas that are accomplished by diverse hypoxic changes at all levels of the nervous system (i.e., molecular, cellular, synaptic, neuronal, network). Hypoxia-induced changes in synaptic transmission are generally depressive and result primarily from presynaptic mechanisms, whereas changes in intrinsic properties involve excitatory and inhibitory alterations involving the majority of K+, Na+, and Ca2+ channels. This article reviews the response of the nervous system to hypoxia, accounting for all levels of integration from the cellular to the network level, and postulates that a better understanding of the diversity of cellular events is only possible if cellular and network events are considered in a functional and organismal context.

Animals↗

PubMed2004

Substance P-mediated modulation of pacemaker properties in the mammalian respiratory network.

Neuromodulators are integral parts of a neuronal network, and unraveling how these substances alter neuronal activity is critical for understanding how networks generate patterned activity and, ultimately, behavior. In this study, we examined the cellular mechanisms underlying the excitatory action of substance P (SP) on the respiratory network isolated in spontaneously active transverse slice preparation of mice. SP produced a slow depolarization in all recorded inspiratory pacemaker and non-pacemaker neurons. Ion exchange experiments and blockers for different ion channels suggest that the slow depolarization is caused by the activation of a low-threshold TTX-insensitive cationic current that carries mostly Na+. The SP-induced slow depolarization increased tonic discharge in non-pacemaker neurons and primarily enhanced the frequency of bursting in Cd2+-insensitive pacemaker neurons. In the Cd2+-sensitive pacemaker neuron, the burst frequency was not significantly affected, whereas burst duration and amplitude were more enhanced than in Cd2+-insensitive pacemaker neurons. In a subset of non-pacemaker neurons that produced NMDA-dependent subthreshold oscillations, SP caused the production of bursts of action potentials. We conclude that the degree of pacemaker activity in the respiratory network is not fixed but dynamically regulated by neuromodulators such as SP. This finding may have clinical implications for Rett syndrome in which SP levels along with other neuromodulators are decreased in the brainstem.

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PubMed2004

Differential contribution of pacemaker properties to the generation of respiratory rhythms during normoxia and hypoxia.

Pacemaker neurons have been described in most neural networks. However, whether such neurons are essential for generating an activity pattern in a given preparation remains mostly unknown. Here, we show that in the mammalian respiratory network two types of pacemaker neurons exist. Differential blockade of these neurons indicates that their relative contribution to respiratory rhythm generation changes during the transition from normoxia to hypoxia. During hypoxia, blockade of neurons with sodium-dependent bursting properties abolishes respiratory rhythm generation, while in normoxia respiratory rhythm generation only ceases upon pharmacological blockade of neurons with heterogeneous bursting properties. We propose that respiratory rhythm generation in normoxia depends on a heterogeneous population of pacemaker neurons, while during hypoxia the respiratory rhythm is driven by only one type of pacemaker.

Action Potentials↗

PubMed2004

Pacemaker neurons and neuronal networks: an integrative view.

Rhythmically active neuronal networks give rise to rhythmic motor activities but also to seemingly non-rhythmic behaviors such as sleep, arousal, addiction, memory and cognition. Many of these networks contain pacemaker neurons. The ability of these neurons to generate bursts of activity intrinsically lies in voltage- and time-dependent ion fluxes resulting from a dynamic interplay among ion channels, second messenger pathways and intracellular Ca2+ concentrations, and is influenced by neuromodulators and synaptic inputs. This complex intrinsic and extrinsic modulation of pacemaker activity exerts a dynamic effect on network activity. The nonlinearity of bursting activity might enable pacemaker neurons to facilitate the onset of excitatory states or to synchronize neuronal ensembles--an interactive process that is intimately regulated by synaptic and modulatory processes.

Action Potentials↗

PubMed2004

Prevalence of diabetic retinopathy in adult Latinos: the Los Angeles Latino eye study.

OBJECTIVE: To estimate age- and gender-specific prevalence of diabetic retinopathy (DR) and to determine the association of type, duration, and treatment of diabetes with the prevalence of DR in adult Latinos. DESIGN: Population-based cross-sectional study. PARTICIPANTS: Six thousand three hundred fifty-seven Latinos aged 40 years and older from 6 census tracts in Los Angeles, California. METHODS: The study cohort consisted of all self-identified Latinos of primarily Mexican ancestry aged 40 years and older residing in 6 census tracts in La Puente, Los Angeles County, California. All participants diagnosed with diabetes underwent a complete ophthalmologic examination, including stereoscopic fundus photography (7 standard Early Treatment Diabetic Retinopathy Study fields). Photographs were graded in a masked manner using a modified Airlie House Grading System to assess presence and severity of DR. MAIN OUTCOME MEASURES: Prevalence of nonproliferative DR, proliferative DR, and macular edema. RESULTS: Of 1263 participants with definite diabetes mellitus, gradable fundus photographs were available in 1217 participants (96%). Of those 1217 participants, 46.9% had DR. Severe nonproliferative DR and proliferative DR were present in 4.4% and 6.1% of diabetics, respectively. Macular edema was observed in 10.4% and clinically significant macular edema was observed in 6.2% of all diabetics. No age- or gender-related differences were present. After adjusting for duration of diabetes, the prevalence of DR was similar in persons with type 1 and type 2 diabetes. CONCLUSIONS: Our data suggest that the prevalence of DR is high among Latinos of primarily Mexican ancestry. The increase in prevalence of DR with longer duration of diabetes emphasizes the public health importance of early diagnosis and management in Latinos. Further data on incidence and progression are required to understand better the natural history of DR in Latinos.

Adult↗

PubMed2003

Stabilization of bursting in respiratory pacemaker neurons.

Synaptic and endogenous pacemaker properties have been hypothesized as principal cellular mechanisms for respiratory rhythm generation. This rhythmic activity is thought to originate in the pre-Bötzinger complex, an area that can generate fictive respiration when isolated in brainstem slice preparations of mice. In slice preparations, external potassium concentration ([K+]o) is typically elevated from 3 to 8 mm to induce rhythmic population activity. However, elevated [K+](o) may not simply depolarize respiratory neurons but also change rhythm-generating mechanisms by inducing or altering pacemaker properties. To test this, we examined the membrane potential (V(m)) of nonpacemaker neurons and endogenous bursting properties of pacemaker neurons before and after blockade of excitatory and inhibitory synaptic input in 3 mm [K+]o artificial CSF (aCSF). Most pacemaker neurons (82%) ceased to burst in 3 mm [K+]o aCSF after blockade of glutamatergic transmission. In all of these, endogenous bursting was restored on additional blockade of glycinergic and GABAergic inhibition. Thus, bursting properties are suppressed by endogenous synaptic inhibition, the level of which may determine whether network rhythmicity is generated in 3 mm (n = 12) or 8 mm (n = 40) [K+]o aCSF. In 3 mm [K+]o aCSF, synaptically isolated pacemaker neurons (n = 22) continued to burst over a wide range of imposed V(m). Furthermore, the V(m) of synaptically isolated pacemaker neurons was not significantly affected (p = 0.1; n = 10) when [K+]o was changed from 8 to 3 mm, whereas isolated nonpacemakers hyperpolarized (p < 0.001; n = 14). We conclude that respiratory pacemaker neurons possess membrane properties that stabilize their bursting against changes in [K+]o and imposed changes in V(m).

Animals↗

PubMed2002

Endogenous activation of serotonin-2A receptors is required for respiratory rhythm generation in vitro.

Endogenous amines and peptides continuously modulate the activity of neuronal networks and are required even for their normal operation. The respiratory rhythm generator, localized in the pre-Bötzinger complex, is not an exception. This network is modulated by various neurotransmitters, including serotonin (5-HT). In this study, we isolated the respiratory network in brainstem slices and demonstrate that the endogenous activation of 5-HT(2A) is required for the generation of the respiratory rhythm in vitro. At the network level, activation of 5-HT(2A) receptors with 4-iodo-2,5-dimethoxyamphetamine or the 5-HT uptake blocker alaproclate increased the frequency of respiratory activity. Blockade of endogenously activated 5-HT(2A) receptors with three different antagonists decreased the frequency, amplitude, and regularity of respiratory population activity, an effect that was blocked by protein kinase C (PKC) activators. At the cellular level, blockade of 5-HT(2A) receptors reduced the action potential discharge in all examined respiratory neurons, which was associated with a reduction in the fast and the persistent sodium current. Continuous application of 5-HT(2A)-receptor antagonists differentially affected pacemaker neurons. Pacemaker activity was eliminated in cadmium-insensitive pacemaker neurons. In cadmium-sensitive pacemaker neurons, the frequency of pacemaker activity was unaffected and the amplitude of pacemaker bursts was enhanced. It is assumed that cadmium-insensitive pacemakers rely on the persistent sodium current, whereas cadmium-sensitive pacemakers depend on the activation of calcium currents. We conclude that endogenously activated 5-HT(2A) receptors are required for maintaining fictive respiratory activity in the brainstem slice by modulating sodium conductances via a PKC pathway.

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PubMed2002

Okadaic acid induces epileptic seizures and hyperphosphorylation of the NR2B subunit of the NMDA receptor in rat hippocampus in vivo.

Overactivation of N-methyl-D-aspartate (NMDA) glutamate receptors is closely related to epilepsy and excitotoxicity, and the phosphorylation of these receptors may facilitate glutamate-mediated synaptic transmission. Here we show that in awake rats the microinjection into the hippocampus of okadaic acid, a potent inhibitor of protein phosphatases 1 and 2A, induces in about 20 min intense electroencephalographic and behavioral limbic-type seizures, which are suppressed by the systemic administration of the NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cyclohepten-5,10-imine hydrogen maleate and by the intrahippocampal administration of 1-(5-isoquinolinesulfonyl)-2-methylpiperazine, an inhibitor of protein kinases. Two hours after okadaic acid, when the EEG seizures were intense, an increased serine phosphorylation of some hippocampal proteins, including an enhancement of the serine phosphorylation of the NMDA receptor subunit NR2B, was detected by immunoblotting. Twenty-four hours after okadaic acid a marked destruction of hippocampal CA1 region was observed, which was not prevented by the receptor antagonists. These findings suggest that hyperphosphorylation of glutamate receptors in vivo may result in an increased sensitivity to the endogenous transmitter and therefore induce neuronal hyperexcitability and epilepsy.

Animals↗