Objective: 

Cortical connectivity is considered to be one of the most sensitive parameters for estimating brain function. The aim of this study was to evaluate changes in cortical connectivity induced by nociceptive stimulation during anesthesia, in rats.

Methods: 

In the present study we used Wistar rats (n=5) of about 250–300 gr. Anesthesia was induced and maintained with chloral hydrate, at an anesthetic depth estimated by a median frequency (MEF) of 2 Hz. During the experiment, the brain electrical activity was recorded using electrodes chronically implanted on the dura mater. Two leads were used, frontal and parietal, on each hemisphere. After a 5-min control path, a 1-minute painful stimulus consisting of a mechanical clamp on the left hind paw was applied for three times, at an interval of two minutes. Cortical connectivity was analyzed in the right hemisphere using the median frequency variation (fronto-parietal index) and correlation coefficient. Signal acquisition was made using BIOPAC MP 150 system.

Results: 

During painful stimulation, MEF increased (MEF pain = 3 * MEF control) in both leads, and frontal cortex activation time doubled (2 minutes) compared with the time of painful stimulation (1 minute) and greater than in the parietal cortex. Painful stimulation didn't modify fronto-parietal index and correlation coefficient.

Conclusions: 

Cortical connectivity did not change during painful stimulation at an anesthetic depth estimated by a MEF of 2 Hz, under chloral hydrat anesthesia, but MEF increased in both areas (frontal and parietal).