The Influence of Moderate Hypercapnia on Neural Activity in the Anesthetized Nonhuman Primate

Hypercapnia is often used as vasodilatory challenge in clinical applications and basic research. In functional magnetic resonance imaging (fMRI), elevated CO2 is applied to derive stimulus-induced changes in the cerebral rate of oxygen consumption (CMRO2) by measuring cerebral blood flow and blood-oxygenation-level–dependent (BOLD) signal. Such methods, however, assume that hypercapnia has no direct effect on CMRO2. In this study, we used combined intracortical recordings and fMRI in the visual cortex of anesthetized macaque monkeys to show that spontaneous neuronal activity is in fact significantly reduced by moderate hypercapnia. As expected, measurement of cerebral blood volume using an exogenous contrast agent and of BOLD signal showed that both are increased during hypercapnia. In contrast to this, spontaneous fluctuations of local field potentials in the beta and gamma frequency range as well as multiunit activity are reduced by ∼15% during inhalation of 6% CO2 (pCO2 = 56 mmHg). A strong tendency toward a reduction of neuronal activity was also found at CO2 inhalation of 3% (pCO2 = 45 mmHg). This suggests that CMRO2 might be reduced during hypercapnia and caution must be exercised when hypercapnia is applied to calibrate the BOLD signal

Locally resolved stress and strain analysis of sinter-joined micro valves using synchrotron X-ray diffraction and conical slit apertures

For assessing the quality of the joining area as well as researching the influence of joining parameters in combination with different materials, the principal stress components of sinter-joined micro valves were analysed. Transmission experiments have been conducted at the high-energy material science (HEMS) beamline P07 at PETRA III, DESY. Due to the dimensions of the samples, a high spatial resolution of the measurements was required. Of special interest was the distribution of residual stress in the joining area of the valves, which demanded a depth resolved measurement using a conical slit. Strains were deduced from the obtained Debye–Scherrer rings of the {200}, {211}, and {220}-planes of the α/α′-phase involving reference measurements on non-sintered powder of the specimen materials. The grain statistics have been improved by integrating over slices of the diffraction rings and by calculating a mean lattice parameter taking into account all lattice planes. From the strain data, the hydrostatic and the deviatoric stress were calculated for the three dimensional stress state

Locally resolved stress and strain analysis of sinter-joined micro valves using synchrotron X-ray diffraction and conical slit apertures

For assessing the quality of the joining area as well as researching the influence of joining parameters in combination with different materials, the principal stress components of sinter-joined micro valves were analysed. Transmission experiments have been conducted at the high-energy material science (HEMS) beamline P07 at PETRA III, DESY. Due to the dimensions of the samples, a high spatial resolution of the measurements was required. Of special interest was the distribution of residual stress in the joining area of the valves, which demanded a depth resolved measurement using a conical slit. Strains were deduced from the obtained Debye–Scherrer rings of the {200}, {211}, and {220}-planes of the α/α′-phase involving reference measurements on non-sintered powder of the specimen materials. The grain statistics have been improved by integrating over slices of the diffraction rings and by calculating a mean lattice parameter taking into account all lattice planes. From the strain data, the hydrostatic and the deviatoric stress were calculated for the three dimensional stress state

Studies with ketamine and alfentanil following Freund's complete adjuvant-induced inflammation in rats

1. N-Methyl-D-aspartate (NMDA) receptor antagonists suppress inflammatory hyperalgesia and the development of acute opioid tolerance. They may also enhance opioid-induced antinociception, while suppressing postopioid-induced hyperalgesia and opioid-enhanced inflammatory hyperalgesia. 2. The non-competitive NMDA receptor antagonist, ketamine, is a racemic chiral drug; its individual enantiomers have differing affinities for the NMDA receptor. The anaesthetic and antinociceptive potencies of (S)-ketamine are 1.5- and threefold higher, respectively, than those of (R)-ketamine in laboratory rodents. 3. The present study investigated the effects of racemic ketamine and enantiopure (S)-ketamine on inflammatory hyperalgesia in rats, 5 days after intraplantar injection of Freund's complete adjuvant (FCA) into one hind paw. First, racemic or (S)-ketamine was administered alone; second, racemic or (S)-ketamine was administered 30 min after initiation of i.v. infusions of the mu-opioid agonist, alfentanil. 4. Area under the curve (AUC) values for Von Frey paw withdrawal threshold (PWT) versus time curves were significantly increased (P < 0.05) for both inflamed and non-inflamed hind paws by racemic and (S)-ketamine (5 & 10 mg/kg, s.c.). Similarly, AUC values for reduction of hind paw volume versus time were significantly increased (P < 0.05) by racemic and (S)-ketamine (10 mg/kg, s.c.). 5. Alfentanil infusions significantly increased PWT in both hind paws, but neither racemic nor (S)-ketamine (5 mg/kg, s.c.) administered 30 min after initiation of alfentanil infusion produced further increases in PWT. 6. Racemic and (S)-ketamine produced antinociceptive effects in both hind paws, but an antihyperalgesic effect per se was not apparent. Additionally, there was a possible anti-inflammatory effect of both drugs in the inflamed hind paw. These findings complement previous studies in which non-competitive NMDA receptor antagonists suppressed behavioural hyperalgesia. 7. However, racemic and (S)-ketamine did not further enhance alfentanil's antinociceptive effects, although they appeared to prolong alfentanil's antinociceptive effects in the non-inflamed hind paw. These findings suggest that factors such as time-course, frequency and the mode of administration of NMDA receptor antagonists, in addition to the type of antinociceptive model (i.e. inflammatory compared with acute) and the nociceptive testing procedure (i.e. noxious mechanical compared with low threshold stimuli) may influence their effects on opioid-induced antinociception