Brain research
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Comparative Study
Isoflurane exerts neuroprotective actions at or near the time of severe traumatic brain injury.
Isoflurane improves outcome vs. fentanyl anesthesia, in experimental traumatic brain injury (TBI). We assessed the temporal profile of isoflurane neuroprotection and tested whether isoflurane confers benefit at the time of TBI. Adult, male rats were randomized to isoflurane (1%) or fentanyl (10 mcg/kg iv bolus then 50 mcg/kg/h) for 30 min pre-TBI. ⋯ Rats receiving fentanyl pre- and post-TBI had the worst CA1 neuronal survival of all groups. Our data support isoflurane neuroprotection, even when used at the lowest feasible level before TBI (i.e., when discontinued with recovery to tail pinch immediately before injury). Investigators using isoflurane must consider its beneficial effects in the design and interpretation of experimental TBI research.
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Comparative Study
Defensive-like behaviors and antinociception induced by NMDA injection into the periaqueductal gray of mice depend on nitric oxide synthesis.
Glutamate NMDA receptor activation within the periaqueductal gray (PAG) leads to antinociceptive, autonomic and behavioral responses characterized as the fear reaction. Considering that NMDA receptor triggers activation of neuronal nitric oxide synthase (nNOS), enzyme that produces nitric oxide (NO), this study investigated the effects of intra-PAG infusions of NPLA (Nomega-propyl-L-arginine), an nNOS inhibitor, on behavioral and antinociceptive responses induced by local injection of NMDA receptor agonist in mice. The behaviors measured were frequency of jumping and rearing as well as duration (in seconds) of running and freezing. ⋯ Microinjections of NMDA significantly decreased nociception response and produced jumping, running, and freezing reactions. Intra-dPAG injections of NPLA (0.4 nmol) completely blocked the NMDA effects without affecting either behavioral or nociceptive responses in intra-dPAG saline-injected animals, except for the rearing frequency that was increased by the nNOS inhibitor. These results strongly suggest the involvement of NO within the PAG in the antinociceptive and defensive reactions induced by local glutamate NMDA receptor activation in this midbrain structure.