Altered thalamocortical functional connectivity by propofol anesthesia in rats.

Anesthesia, a state of profound central nervous system suppression, involves a sequence of events that is still not well understood. In the present study, we examined the action of propofol (a sedative-hypnotic drug commonly used as anesthetic) on thalamocortical functional connectivity in rats by using functional connectivity magnetic resonance imaging (fcMRI) with a 3.0-tesla MR scanner. Intraperitoneal injections of propofol (80 or 160 mg/kg) were administered to Sprague-Dawley rats. Synchronized low-frequency fluctuations (LFF) of blood oxygen level-dependent (BOLD) signals were found between the thalamic and somatosensory cortices (S1/S2) after administration of 80 mg/kg propofol. However, after application of 160 mg/kg propofol, synchronized LFF of BOLD signals disappeared. These observations indicate that thalamocortical connectivity may play an important role in propofol anesthesia. We also observed that regionally specific long-range correlations of spontaneous low-frequency physiological fluctuations in BOLD signals may be present across somatosensory networks of the brain in the absence of external stimulation. However, our experiment suggests that fcMRI can be used to investigate brain networks that exhibit correlated fluctuations.