Intracerebral vascular changes induced by cold pressor test: a model of sympathetic activation.

Cerebral vascular changes seem to play a fundamental role in the pathogenesis of various functional disturbances, (i.e. those suggested for migraine pathogenesis). However the exact role of single regulatory aspects (metabolic-neuronal-mechanic) are not completely understood and easily investigated in man. In particular, the role of autonomic nervous system is widely debated and recently the stimulation of tegmental noradrenergic nuclei (locus coeruleus in particular) has proved capable of inducing, in the animal, both the reduction and the increase of extracerebral blood flow. In order to evaluate the vascular effect of locus coeruleus stimulation in man, we investigated intracerebral vascular changes induced by the cold pressor test (CPT) (a well standardized method for activating both nociceptive and sympathetic pathways) by means of transcranial Doppler sonography. The examinations were performed in 14 healthy controls. CPT induced a constant and evident reduction in mean arterial velocity of the middle cerebral artery. The response was triggered during the first minute following hand immersion in ice water and reached its maximum level by the 3rd minute. Pretreatment with the alfa2-agonist clonidine caused a marked reduction of the cerebrovascular response. These data suggest that: a) intracerebral vascular response induced by CPT may be attributed to a central noradrenergic mechanism (possibly modulated at the locus coeruleus level) and b) transcranial Doppler monitoring of CPT effect is a potential tool for investigating peculiar patterns of functional disturbances of cerebral circulation.