Estudio neurofisiológico y comportamental del efecto de la hipoxia hipobárica sobre el rendimiento cognitivo submáximo en ratones y su implicación en el balance del sistema colinérgico

Programa de Doctorado en NeurocienciasEl ambiente de alta montaña se caracteriza por un descenso en la presión parcial de oxigeno.produciendo condiciones de hipoxia hipobárica en los organismos sometidos a él en los que puede generar déficits cognilivos y cambios en la cinemática de los potenciales sinápticos generados en la vía talámico-cortical. Los déficits en aprendizaje y memoria pueden ser mitigados. Incluso prevenidos totalmente.a través de la aclimatación a altura simulada. y la consiguiente hipoxia hipobárica, en condiciones reales o simuladas. El objeto principal de esta Tesis Doctoral es estudiar la repercusión de esta aclimatación sobre el rendimiento cognitivo en condiciones normales y en altitud. La aclimatación a hipoxia hipobárica en ratones puede producir mejores rendimientos en pruebas comportamentales realizadas en condiciones normales de presión, sison de una complejidad suficiente para que hagan esperar rendimientos submáximos.Estos déficits y mejoras cognitivas están muy ligados al sistema cofinérgico en las mismas estructuras que sustentan al aprendizaje y la memoria. De esta manera, la sintesis y la degradación de la acetilcolina varían en función de una exposición aguda, o de una aclimatación a las citadas condiciones.en estructuras que componen este sistema. como son el septum medial, el hipocampo, y otras porciones de la corteza cerebral.Universidad Pablo de Olavide. Centro de Estudios de Postgrad

Disease-specific monoclonal antibodies targeting glutamate decarboxylase impair GABAergic neurotransmission and affect motor learning and behavioral functions

Autoantibodies to the smaller isoform of glutamate decarboxylase (GAD) can be found in patients with type 1 diabetes and a number of neurological disorders, including stiff-person syndrome, cerebellar ataxia and limbic encephalitis. The detection of disease-specific autoantibody epitopes led to the hypothesis that distinct GAD autoantibodies may elicit specific neurological phenotypes. We explored the in vitro/in vivo effects of well-characterized monoclonal GAD antibodies. We found that GAD autoantibodies present in patients with stiff person syndrome (n = 7) and cerebellar ataxia (n = 15) recognized an epitope distinct from that recognized by GAD autoantibodies present in patients with type 1 diabetes mellitus (n = 10) or limbic encephalitis (n = 4). We demonstrated that the administration of a monoclonal GAD antibody representing this epitope specificity; (1) disrupted in vitro the association of GAD with γ-Aminobutyric acid containing synaptic vesicles; (2) depressed the inhibitory synaptic transmission in cerebellar slices with a gradual time course and a lasting suppressive effect; (3) significantly decreased conditioned eyelid responses evoked in mice, with no modification of learning curves in the classical eyeblink-conditioning task; (4) markedly impaired the facilitatory effect exerted by the premotor cortex over the motor cortex in a paired-pulse stimulation paradigm; and (5) induced decreased exploratory behavior and impaired locomotor function in rats. These findings support the specific targeting of GAD by its autoantibodies in the pathogenesis of stiff-person syndrome and cerebellar ataxia. Therapies of these disorders based on selective removal of such GAD antibodies could be envisioned.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Role of Reuniens Nucleus Projections to the Medial Prefrontal Cortex and to the Hippocampal Pyramidal CA1 Area in Associative Learning

We studied the interactions between short- and long-term plastic changes taking place during the acquisition of a classical eyeblink conditioning and following high-frequency stimulation (HFS) of the reuniens nucleus in behaving mice. Synaptic changes in strength were studied at the reuniens-medial prefrontal cortex (mPFC) and the reuniens-CA1 synapses. Input/output curves and a paired-pulse study enabled determining the functional capabilities of the two synapses and the optimal intensities to be applied at the reuniens nucleus during classical eyeblink conditioning and for HFS applied to the reuniens nucleus. Animals were conditioned using a trace paradigm, with a tone as conditioned stimulus (CS) and an electric shock to the trigeminal nerve as unconditioned stimulus (US). A single pulse was presented to the reuniens nucleus to evoke field EPSPs (fEPSPs) in mPFC and CA1 areas during the CS-US interval. No significant changes in synaptic strength were observed at the reuniens-mPFC and reuniens-CA1 synapses during the acquisition of eyelid conditioned responses (CRs). Two successive HFS sessions carried out during the first two conditioning days decreased the percentage of CRs, without evoking any long-term potentiation (LTP) at the recording sites. HFS of the reuniens nucleus also prevented the proper acquisition of an object discrimination task. A subsequent study revealed that HFS of the reuniens nucleus evoked a significant decrease of paired-pulse facilitation. In conclusion, reuniens nucleus projections to prefrontal and hippocampal circuits seem to participate in the acquisition of associative learning through a mechanism that does not required the development of LTP

Experimental design.

<p>(A) EMG recording electrodes were implanted in the orbicularis oculi (O.O.) muscle of the upper left eyelid. In addition, bipolar stimulating electrodes were implanted on the ipsilateral supraorbital nerve for presentation of unconditioned stimulus (US). The conditioned stimulus (CS) consisted of a tone delivered from a loudspeaker located 30 cm from the animal's head. Animals were also implanted with stimulating electrodes in the thalamic reuniens nucleus and with recording electrodes in the medial prefrontal cortex (top diagram) or the hippocampal CA1 area (bottom diagram). (B–D) Photomicrographs illustrating the location of recording electrodes in the mPFC (B) and in the hippocampal CA1 area (D), as well as the stimulation (C) site (arrows). Calibration bars 500 µm. Abbreviations: D, L, M, V, dorsal, lateral, medial, and ventral. E, A schematic representation of the conditioning paradigm, illustrating CS and US stimuli, and the moment at which a single pulse (100 µs, square, biphasic) was presented to the reuniens nucleus (St. Reu.). An example of an EMG record from the orbicularis oculi (O.O.) muscle obtained from the 9th conditioning session is illustrated, as well as an extracellular record of hippocampal activity from the same animal, session, and trial. Note the fEPSPs evoked by the pulse presented to the reuniens nucleus.</p

Effects of two HFS sessions on the reuniens-CA1 and reuniens-mPFC synapses.

<p>(A, B) Evolution of fEPSPs evoked in the PFC (A) and in the CA1 area (B) by paired-pulse stimulation of reuniens nucleus before and after two HFS sessions. Each animal was presented with two HFS sessions (see shaded areas) each consisting of five 200 Hz, 100 ms trains of pulses at a rate of 1/s. This protocol was presented six times, at intervals of 1 min. The 100 µs, square, biphasic pulses used to evoke LTP were applied at the same intensity used for the single pulse presented following HFS presentation. The evolution of LTP was checked using a pair of pulses (1st, black circles; 2nd, white circles) with an interstimulus interval of 40 ms. Recording was carried out for 72 h. Note that fEPSP amplitudes evoked by the 1st and the 2nd pulses reached values below baseline following the two HFS sessions for both synapses. *, <i>P</i><0.05 for fEPSPs evoked by the 1st pulse; #, <i>P</i><0.05 for fEPSPs evoked by the 2nd pulse.</p