Physiology & behavior
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Physiology & behavior · Jan 1999
Clinical TrialAn examination of the effects of isoenergetic intragastric infusions of pure macronutrients on cold pain perception in healthy human volunteers.
Our previous study demonstrated that meals, particularly when rich in fat, significantly reduced the pain induced by the cold pressor stimulus in healthy human subjects. To determine the mechanisms involved, the aim of this study was to bypass the taste and cognitive component of food and to investigate the scope of these analgesic effects with direct intragastric infusion of pure macronutrients in a group of 16 healthy human volunteers (eight male and eight female) on the response to cold-induced pain. All subjects underwent the cold pressor test (CPT) on three occasions in a counterbalanced order: before and after intragastric intubation and infusion of isoenergetic fat (10% intralipid), carbohydrate (CHO-maltodextrin), and a control infusion of isotonic saline. ⋯ The CPT was carried out four times on each test day, once before intubation, and 0.5, 1.5, and 2.5 h after intragastric infusion. Radial pulse and blood pressure measurements and visual analogue scales of mood/emotional state were carried out before and after each CPT. There were no significant differences in pain scores between the three test conditions, suggesting that by bypassing the cognitive and taste component of eating, the trigger for any postingestive analgesic effects of food are lost.
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Physiology & behavior · Jan 1999
Unilateral block of NMDA receptors in the amygdala prevents predator stress-induced lasting increases in anxiety-like behavior and unconditioned startle--effective hemisphere depends on the behavior.
Lasting increases in anxiety-like behavior (ALB) in the elevated plus-maze are produced by a single 5-min exposure of a rat to a cat. Rats become more anxious in the plus-maze for up to 3 weeks after the exposure. The first study in this series demonstrated that blockade of NMDA receptors in rats with MK-801, AP7, or CPP, given systemically 30 min prior to exposure to a cat prevents the increase in ALB assessed 1 week later in the elevated plus-maze. ⋯ The data also suggest that the right amygdala action is "downstream" from the left amygdala contribution. These findings are consistent with the view that NMDA receptors are involved in initiation, but not maintenance, of neural changes mediating lasting increases in anxiety following severe stress. Finally, the findings of the importance of the right amygdala in stress-induced enhancement of the startle response provides neurobiological face validity to predator stress as a model of aspects of posttraumatic stress disorder.