Modelo in vitro para el estudio del papel de la unión mesopontina en la generación del sueño de movimientos oculares rápidos y la vigilia / In vitro model for the study of the role of the mesopontine region in rapid eye movement (REM) sleep and wakefulness / Modelo in vitro para o estudo do papel da união mesopontina na geração de sono de movimentos oculares rápidos e da vigília

El estudio de las estrategias neurales para la organización del comportamiento en vertebrados constituye un desafío mayor para la Neurociencia. El avance del conocimiento en este campo depende de manera crítica de la utilización de modelos experimentales adecuados que admitan múltiples niveles de análisis (p.ej: comportamental, circuital, celular, sináptico, molecular) y abordajes multitécnicos. Nos propusimos analizar in vitro una red neural de la unión mesopontina del tronco encefálico críticamente implicada en el control del sueño de movimientos oculares rápidos (S-REM). Pese al cúmulo de evidencias que apoyan el papel desempeñado por esta red en relación al S-REM, los mecanismos celulares y sinápticos que subyacen a este control son poco conocidos y continúan siendo objeto de intensa investigación. Para avanzar en el conocimiento de estos mecanismos, se llevó a cabo la caracterización morfológica y funcional de una rodaja de tronco encefálico de la rata, en la que las estructuras críticas para el control del S-REM, i.e.: núcleos tegmentales laterodorsal y pedúnculopontino, y su proyección al núcleo reticular pontis oralis (PnO), están presentes y son operativas. La inclusión del núcleo motor del trigémino en la rodaja permitió detectar cambios de la excitabilidad de las motoneuronas ante manipulaciones farmacológicas del PnO, representativos de los cambios del tono muscular asociados a maniobras similares realizadas in vivo. La utilización de este modelo in vitro de S-REM, permitirá aportar a la dilucidación de las estrategias neurales que operan en niveles intermedios de organización del SN en mamíferos para la generación y regulación de un estado comportamental.

The study of the neural basis of behavior is a major challenge in Neuroscience. Advancing our knowledge in this field depends, critically, on the use of experimental paradigms that provide multiple levels of analysis, as well as powerful techniques. We have selected, as a model of a neural plan that organizes a complex behavior, a neural network located in the mesopontine junction. This region is thought to be both necessary and sufficient for the generation of rapid eye movement (REM) sleep, although the cellular and synaptic mechanisms involved in the control of this behavioral state at the mesopontine level are still under debate and remain poorly understood. As part of a long term effort to gain insight into these mechanisms, we carried out the morphological and functional characterization of a slice preparation of rat brainstem and we demonstrate that critical structures for the control of REM sleep - the laterodorsal and pedunculopontine tegmental nuclei and their projection to the oral part of the pontine reticular nucleus (PnO) - are present and are operational. The presence of the trigeminal motor nucleus in the slice sought to include in the experimental model a structure capable of expressing changes of the excitability of the motorneurons caused by pharmacological manipulations of the PnO, representative of changes of muscle tone associated with similar maneuvers performed in vivo. The use of this in vitro model of REM sleep will provide critical information to elucidate neural strategies that operate at intermediate levels of central nervous system organization in mammals to control behavioral states.

O estudo de estratégias neurais para a organização do comportamento em vertebrados constitui um desafio maior para a Neurociencia. O avanço do conhecimento nessa área depende criticamente da utilização de modelos experimentais adequados que suportem múltiplos níveis de análise (por exemplo: comportamental, circuital, celular, sináptico e molecular) e abordagens por múltiplas técnicas. Decidiu-se analisar in vitro uma rede neural da união mesopontina do tronco encefálico criticamente envolvida no controle do sono de movimentos oculares rápidos (S-REM). Apesar da riqueza de provas que sustentam o papel desta rede em relação ao S-REM, os mecanismos celulares e sinápticos subjacentes a este controle são pouco conhecidos e permanecem sob intensa investigação. Para avançar no conhecimento desses mecanismos, caracterizou-se morfológica e funcionalmente uma fatia de tronco encefálico de rato, na qual as estruturas críticas para o controle do S-REM, i.e.: núcleos tegmentais laterodorsal e pedunculopontino, e sua projeção para o núcleo reticular pontis oralis (PnO) estão presentes e operantes. A inclusão do núcleo motor do trigêmeo na fatia permitiu detectar mudanças da excitabilidade das motoneuronas provocadas por manipulações farmacológicas do PnO, representativas das alterações do tônus muscular associados com operações semelhantes quando realizados in vivo. A utlização deste modelo in vitro de S-REM permitirá contribuir para a elucidação de estratégias neurais que operam em níveis intermedios de organização do SN de mamíferos para a geração e regulação de um estado comportamental.

On the verge of a respiratory-type panic attack: Selective activations of rostrolateral and caudoventrolateral periaqueductal gray matter following short-lasting escape to a low dose of potassium cyanide.

Intravenous injections of potassium cyanide (KCN) both elicit escape by its own and facilitate escape to electrical stimulation of the periaqueductal gray matter (PAG). Moreover, whereas the KCN-evoked escape is potentiated by CO2, it is suppressed by both lesions of PAG and clinically effective treatments with panicolytics. These and other data suggest that the PAG harbors a hypoxia-sensitive alarm system the activation of which could both precipitate panic and render the subject hypersensitive to CO2. Although prior c-Fos immunohistochemistry studies reported widespread activations of PAG following KCN injections, the employment of repeated injections of high doses of KCN (>60µg) in anesthetized rats compromised both the localization of KCN-responsive areas and their correlation with escape behavior. Accordingly, here we compared the brainstem activations of saline-injected controls (air/saline) with those produced by a single intravenous injection of 40-µg KCN (air/KCN), a 2-min exposure to 13% CO2 (CO2/saline), or a combined stimulus (CO2/KCN). Behavioral effects of KCN microinjections into the PAG were assessed as well. Data showed that whereas the KCN microinjections were ineffective, KCN intravenous injections elicited escape in all tested rats. Moreover, whereas the CO2 alone was ineffective, it potentiated the KCN-evoked escape. Compared to controls, the nucleus tractus solitarius was significantly activated in both CO2/saline and CO2/KCN groups. Additionally, whereas the laterodorsal tegmental nucleus was activated by all treatments, the rostrolateral and caudoventrolateral PAG were activated by air/KCN only. Data suggest that the latter structures are key components of a hypoxia-sensitive suffocation alarm which activation may trigger a panic attack.