The spontaneous time-dependent contraction and relaxation of the arteries (vasomotion) has been observed extensively in a wide variety of tissues and species, from bat wings to human skin. Although is widely accepted the existence of rhythmic variations in the blood flow with mean oscillatory frequency about 6-11 per minute, little is known about the mechanisms responsible for this phenomenon, its characteristics, and its physiological significance. In this work we studied vasomotion properties of thalamic microvasculature in the anaesthetised cat (isofluorane or alpha-chloralose) during spontaneous and visual driven activity, and correlated it with neuronal activity.

Vasomotion was estimated from oxyhemoglobin measurements using spectrophotometry. Vasomotion was observed spontaneously in 35% of the recordings during isofluorane anaesthesia, the average frequency of oscillation was 0.16Hz. In those recordings neuronal activity could be classified as tonic. Visual stimulation evoked normal responses in the cell, disrupted vasomotion, and increased oxyhemoglobin levels similarly to non-vasomotion periods.

During chloralose anaesthesia vasomotion was observed in 100% of recordings, appearing about 30 minutes after injection, with a continuous frequency peak at 0.14Hz, associated with a decrease in basal levels of oxyhemoglobine (41%). The strongest effect was observed within 2 hours from the injection. During this period cell typical fired in burst mode and neither oxyhemoglobin levels nor vasomotion characteristics were modified during visual stimulation.

These results suggest the existence of a mechanism of vasomotion related to GABA (A) receptors which might have important implications regarding the protocols of anaesthesia used for studying neuronal responses. Supported: MECBFU2005-00502