Papers by Ernesto Mendoza
Learning & Memory, 2009
Procedural memories and habits are posited to be stored in the basal ganglia, whose intrinsic cir... more Procedural memories and habits are posited to be stored in the basal ganglia, whose intrinsic circuitries possess important inhibitory connections arising from striatal spiny neurons. However, no information about long-term plasticity at these synapses is available. Therefore, this work describes a novel postsynaptically dependent long-term potentiation (LTP) at synapses among spiny neurons (intrinsic striatal circuitry); a postsynaptically dependent long-term depression (LTD) at synapses between spiny and pallidal neurons (indirect pathway); and a presynaptically dependent LTP at strionigral synapses (direct pathway). Interestingly, long-term synaptic plasticity differs at these synapses. The functional consequences of these long-term plasticity variations during learning of procedural memories are discussed.
Journal of Neurophysiology, 2007
Projection neurons of the substantia nigra reticulata (SNr) convey basal ganglia (BG) processing ... more Projection neurons of the substantia nigra reticulata (SNr) convey basal ganglia (BG) processing to thalamocortical and brain stem circuits responsible for movement. Two models try to explain pathological BG performance during Parkinson disease (PD): the rate model, which posits an overexcitation of SNr neurons due to hyperactivity in the indirect pathway and hypoactivity of the direct pathway, and the oscillatory model, which explains PD as the product of pathological pattern generators disclosed by dopamine reduction. These models are, apparently, incompatible. We tested the predictions of the rate model by increasing the excitatory drive and reducing the inhibition on SNr neurons in vitro. This was done pharmacologically with bath application of glutamate agonist N-methyl-D-aspartate and GABA A receptor blockers, respectively. Both maneuvers induced bursting behavior in SNr neurons. Therefore synaptic changes forecasted by the rate model induce the electrical behavior predicted by the oscillatory model. In addition, we found evidence that Ca V 3.2 Ca 2ϩ channels are a critical step in generating the bursting firing pattern in SNr neurons. Other ion channels involved are: hyperpolarization-activated cation channels, high-voltage-activated Ca 2ϩ channels, and Ca 2ϩ -activated K ϩ channels. However, although these channels shape the temporal structure of bursting, only Ca V 3.2 Ca 2ϩ channels are indispensable for the initiation of the bursting pattern.
The modulatory effect of D 2 dopamine receptor activation on calcium currents was studied in neos... more The modulatory effect of D 2 dopamine receptor activation on calcium currents was studied in neostriatal projection neurons at two stages of rat development: postnatal day (PD)14 and PD40. D 2 -class receptor agonists reduced whole cell calcium currents by about 35% at both stages, and this effect was blocked by the D 2 receptor antagonist sulpiride. Nitrendipine partially occluded this modulation at both stages, indicating that modulation of Ca V 1 channels was present throughout this developmental interval. Nevertheless, modulation of Ca V 1 channels was significantly larger in PD40 neurons. -Conotoxin GVIA occluded most of the Ca 2ϩ current modulation in PD14 neurons. However, this occlusion was greatly decreased in PD40 neurons. -Agatoxin TK occluded a great part of the modulation in PD40 neurons but had a negligible effect in PD14 neurons. The data indicate that dopaminergic D 2 -mediated modulation undergoes a change in target during development: from Ca V 2.2 to Ca V 2.1 Ca 2ϩ channels. This change occurred while Ca V 2.2 channels were being down-regulated and Ca V 2.1 channels were being up-regulated. Presynaptic modulation mediated by D 2 receptors reflected these changes; Ca V 2.2 type channels were used for release in young animals but very little in mature animals, suggesting that changes took place simultaneously at the somatodendritic and the synaptic membranes. channels that activate Ca 2ϩ -dependent K ϩ currents in neostriatal neurons. Neuroscience 95: 745-752, 2000.
European Journal of Pharmacology, 2001
To know which Ca 2q channel type is the most important for neurotransmitter release at corticostr... more To know which Ca 2q channel type is the most important for neurotransmitter release at corticostriatal synapses of the rat, we tested 2q 2q Ž Ca channel antagonists on the paired pulse ratio. v-Agatoxin TK was the most effective Ca channel antagonist IC s 127 nM; 50 Ž . . maximal effect s 211% with ) 1 mM and Hill coefficients 1.2 , suggesting a single site of action and a Q-type channel profile. Corresponding parameters for Cd 2q were 13 mM, 178% and 1.2. The block of L-type Ca 2q channels had little impact on transmission, 2q 2q
European Journal of Pharmacology, 2003
Population spikes associated with the paired pulse ratio protocol were used to measure the presyn... more Population spikes associated with the paired pulse ratio protocol were used to measure the presynaptic inhibition of corticostriatal transmission caused by A-opioid receptor activation. A 1 AM of [D-Ala 2 , N-MePhe 4 , Gly-ol 5 ]-enkephalin (DAMGO), a selective A-opioid receptor agonist, enhanced paired pulse facilitation by 44 F 8%. This effect was completely blocked by 2 nM of the selective A-receptor antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-NH (CTOP). Antagonists of N-and P/Q-type Ca 2 + channels inhibited, whereas antagonists of potassium channels enhanced, synaptic transmission. A 1 AM of N-conotoxin GVIA, a blocker of N-type Ca 2 + channels, had no effect on the action of DAMGO, but 400 nM N-agatoxin TK, a blocker of P/Q-type Ca 2 + -channels, partially blocked the action of this opioid. However, 5 mM Cs 2 + and 400 AM Ba 2 + , unselective antagonists of potassium conductances, completely prevented the action of DAMGO on corticostriatal transmission. These data suggest that presynaptic inhibition of corticostriatal afferents by A-opioids is mediated by the modulation of K + conductances in corticostriatal afferents. D (J. Bargas). www.elsevier.com/locate/ejphar European Journal of Pharmacology 462 (2003) 91 -98
Neuroscience Letters, 2007
Field recordings were used to determine the influence of ␦-opioid receptor activation on corticos... more Field recordings were used to determine the influence of ␦-opioid receptor activation on corticostriatal synaptic transmission. Application of the selective ␦-opioid receptor agonist, [Tyr-D-Pen-Gly-Phe-D-Pen]-enkephalin (DPDPE, 1 M), decreased the amplitude of the field-excitatory synaptic potential and at the same time increased the paired pulse ratio (PPR) suggesting a presynaptic site of action. This response reversed rapidly when DPDPE was washed and blocked by 1 nM of the selective ␦-receptor antagonist naltrindole. Neither -conotoxin GVIA (1 M) nor -agatoxin TK (400 nM), blockers of N-and P/Q-type Ca 2+ -channels, respectively, nor TEA (1 mM), blocker of some classes of K + -channels, occluded the effects of DPDPE. Instead, 1 mM 4-AP or 400 M Ba 2+ occluded completely the effects of DPDPE. Therefore, the results suggest that the modulation by ␦ opioids at corticostriatal terminals is mediated by transient (K V 4) K + -conductances.
Synapse, 2006
Long term synaptic plasticity has been more extensively studied in excitatory synapses, but it is... more Long term synaptic plasticity has been more extensively studied in excitatory synapses, but it is also a property of inhibitory synapses. Many inhibitory synapses target hippocampal pyramidal neurons of the CA1 region. They originate from several interneuron classes that subdivide the surface area that they target on the pyramidal cell. Thus, many interneurons preferentially innervate the perisomatic area and axon hillock of the pyramidal cells while others preferentially target dendritic branches and spines. Methods to preferentially activate dendritic or somatic inhibitory synapses onto pyramidal neurons have been devised. By using these methods, the present work demonstrates that a stimulation pattern that induces long term potentiation (LTP) in excitatory synapses of the Schaffer collaterals is also capable of inducing distinct types of long term plastic changes in different classes of inhibitory synapses: Induction of long term depression (LTD) was seen in dendritic inhibitory synapses whereas LTP was observed in somatic inhibitory synapses. These findings suggest that inhibitory synapses arising from different interneuron classes may respond to the same stimulus according to their specific plastic potential enabling a spatial combinatorial pattern of inhibitory effects onto the pyramidal cell. Synapse 60:533–542, 2006. © 2006 Wiley-Liss, Inc.
Título del proyecto: Diseño de un proceso de adsorción que utilice materiales lignocelulósicos en... more Título del proyecto: Diseño de un proceso de adsorción que utilice materiales lignocelulósicos en un lecho fluidizado inverso
Título del proyecto: Diseño de un proceso de adsorción que utilice materiales lignocelulósicos en... more Título del proyecto: Diseño de un proceso de adsorción que utilice materiales lignocelulósicos en un lecho fluidizado inverso
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Papers by Ernesto Mendoza