Auditory and visual stimuli evoke a synchronised activation of sympathetic, respiratory and motor outputs after disinhibition of midbrain colliculi

Abstract

The midbrain colliculi are involved in cardiovascular and behavioural responses to threatening stimuli. Disinhibition of this area can evoke spontaneous synchronized sympathetic and respiratory responses in anesthetized rats. This raised the question as to whether naturalistic stimuli can generate such responses. In urethane‐anesthetized, paralysed, vagotomised and artificially ventilated rats, abrupt sound (n=7) or bright light (n=5) generated synchronised bursts of activity in sympathetic (309 ± 30 or 217 ± 38%), phrenic (60 ± 18 or 43 ± 15 bpm), and sciatic (17 ± 4 or 15 ± 3%) nerve activities and blood pressure (30 ± 4 or 31 ± 8 mmHg) after disinhibition of ventral sites in superior and inferior colliculi. The onsets of the sympathetic, respiratory and sciatic responses following auditory or light stimuli occurred within a time period of <50 msec. Simultaneous multi‐sensory stimulation evoked an enhanced response. Blockade of the dorsomedial hypothalamus (DMH), dorsolateral periaqueductal grey (dlPAG) or cuneiform nucleus using muscimol did not affect the responses. Our findings show that neurons in the colliculi can generate synchronised cardiovascular, respiratory and behavioural responses triggered by a sudden auditory or visual stimulus. The output pathways from the colliculi do not depend on synapses within the DMH, dlPAG or cuneiform nucleus.Supported by NHMRC 1028183 and 570912 and by Capes.