Más allá del generador central de patrones: modulación por aminas de las vías neuronales de toma de decisiones que descienden del cerebro de la sanguijuela medicinal.

The biological mechanisms of behavioral selection, as it relates to locomotion, are far from understood, even in relatively simple invertebrate animals. In the medicinal leech, Hirudo medicinalis, the decision to swim is distributed across populations of swim-activating and swim-inactivating neurons descending from the subesophageal ganglion of the compound cephalic ganglion, i.e. the brain. In the present study, we demonstrate that the serotonergic LL and Retzius cells in the brain are excited by swim-initiating stimuli and during spontaneous swim episodes. This activity likely influences or resets the neuromodulatory state of neural circuits involved in the activation or subsequent termination of locomotion. When serotonin (5-HT) was perfused over the brain, multi-unit recordings from descending brain neurons revealed rapid and substantial alterations. Subsequent intracellular recordings from identified command-like brain interneurons demonstrated that 5-HT, especially in combination with octopamine, inhibited swim-triggering neuron Tr1, as well as swim-inactivating neurons Tr2 and SIN1. Although 5-HT inhibited elements of the swim-inactivation pathway, rather than promoting them, the indirect and net effect of the amine was a reliable and sustained reduction in the firing of the segmental swim-gating neuron 204. This modulation caused cell 204 to relinquish its excitatory drive to the swim central pattern generator. The activation pattern of serotonergic brain neurons that we observed during swimming and the 5-HT-immunoreactive staining pattern obtained, suggest that within the head brain 5-HT secretion is massive. Over time, 5-HT secretion may provide a homeostatic feedback mechanism to limit swimming activity at the level of the head brain.

Resumen tomado de PubMed (NCBI) para el registro citado, en el idioma original. La versión de referencia es la de la publicación original.

El resumen se deja sin traducir para conservar la redacción original de los autores.

El estudio examina en la sanguijuela medicinal cómo las aminas modulan la decisión de nadar. Los estímulos que inician la natación activan las células LL y Retzius serotoninérgicas del cerebro, y la 5-HT altera las neuronas descendentes. La serotonina, sobre todo junto con octopamina, inhibe Tr1, Tr2 y SIN1, y reduce sostenidamente la descarga de la neurona de compuerta 204. Los autores sugieren que la masiva liberación de 5-HT en el cerebro cefálico puede limitar la natación como retroalimentación homeostática.

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