Expert opinion
The trigemino-cardiac reflex: a view to the future

After the trigemino-cardiac reflex (TCR) was first described by the senior author in 1999 [1], it resolved one of the great problems and mysteries in neurosurgery. In the meantime, several other groups have published their results about the TCR, but there still remain a lot of questions about this reflex that are currently unresolved. Our group has recently published an important update of the current knowledge of the TCR [2]. In the following, we will shed light on future research aspects of the TCR.
Of course, skull base surgery has made great advances during the last years [3], but additionally the TCR has substantially contributed to the positive development of this young surgical discipline. However, it is best known that education has a great influence on the outcome of cardiovascular events, the TCR being an example [4], so it is important that every neuroscientist knows about the TCR and its treatment, and is continuously informed about new knowledge regarding the TCR. Despite the importance and strength of the TCR there is little information about the cellular mechanisms and brainstem pathways that constitute this reflex [5]. Stimulation of trigeminal fibres evokes a powerful excitatory and polysynaptic pathway to cardiac vagal neurons [6], and this pathway is endogenously modulated and differentially enhanced, and depressed, by serotonin (5-HT1A and 5-HT2 respectively) receptors [7]. Brainstem 5-HT systems are involved in the protective responses to hypoxia recruits a 5-HT pathway to cardiac vagal neurons that activates 5-HT3 receptors on cardiac vagal neurons to maintain parasympathetic cardiac activity during hypoxia. The TCR is one of the known endogenous physiological neuroprotective mechanisms against ischaemia [5]. The TCR is an example of these protective physiological entities [5, 8, 9] and may be part of a group of related responses generally defined as “oxygen-conserving reflexes” [5]. Within seconds after the initiation of such a reflex, there is powerful and differentiated activation of sympathetic nerves and consequently primary cerebrovascular vasodilatation [5]. By this physiological response, adjustments of the systemic and cerebral circulations are initiated to change the cerebral blood flow in a manner that is not yet understood [5]. TCR, hibernation and ischaemic tolerance appear to involve at least partially similar physiological mechanisms [2, 9], because most of the signals, transducers and effectors that...


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