Participação do colículo superior e inferior na organização de uma resposta simpática, respiratória e somatomotora sincronizada

Abstract

The superior (SC) and inferior (IC) colliculi are believed to generate immediately cardiovascular and behavioural responses to auditory and visual threatening stimuli. In this study we examined the possibility that there are command neurons within the colliculi that can simultaneously drive sympathetic and respiratory. In urethane-anaesthetized rats, microinjections of bicuculline (50 pmol in 50 nL) into sites within a circumscribed region in the deep layers of the superior colliculus and the central and external nuclei of the inferior colliculus evoked a highly distinctive response characterized by short bursts of renal sympathetic nerve activity (RSNA) and phrenic nerve activity (PNA). The bursts of RSNA and PNA were also accompanied by transient increases in arterial pressure and, in most cases, heart rate. Synchronized bursts of RSNA and PNA were also evoked after neuromuscular blockade, artificial ventilation, and vagotomy and so were not dependent on afferent feedback from the lungs. These findings raised the hypothesis that, under conditions where collicular neurons are disinhibited, co-ordinated cardiovascular, respiratory and somatomotor responses can be evoked by natural environmental sitimuli. In response to natural auditory, visual or somatosensory stimuli, powerful synchronized increases in sympathetic, respiratory and somatomotor activity were generated following blockade of GABAA receptors in a specific region in the midbrain colliculi of anesthetized rats, but not under control conditions. Such responses still occurred after removal of most of the forebrain, including the amygdala and hypothalamus, indicating that the essential pathways mediating these coordinated responses were located within the brainstem. The temporal relationships between the different outputs suggest that they are driven by a common population of command neurons within the colliculi.