Detection of sensation threshold was achieved by slowly increasing the stimulation pressure until the subject reported the first sensation of balloon inflation. This procedure was repeated three times, and the mean Tipifarnib Transferase value was calculated. The pain detection threshold was determined by continuing to slowly increase the pressure until the subject reported a feeling of pain for the first time. This individualized pressure at pain detection threshold was used throughout the subsequent experiment. The detection of sensory and pain detection threshold also served as preconditioning, thereby avoiding problems associated with the viscoelastic properties of the gut and enabling training of the subjects to help ensure reproducible responses on subsequent stimulations (15, 44).

For safety reasons, the maximum stimulation pressure was limited to 30 psi. If subjects failed to reach pain detection threshold at 30 psi, the subsequent stimulations were delivered at this maximum intensity. Because the balloon was made of nitrile rubber, which is a compliant material, the stimulation pressure inside the balloon (which could not be measured) is partly related to the balloon compliance and partly related to the properties of the rectal wall. Because of this, is not possible to deduct the force applied to the gut wall based on the measured pressure. To test for reproducibility within the same day, two recordings of EEG were performed, separated by 5 min. For each recording, 30 identical phasic rectal stimuli were delivered, each lasting 150 ms with a random interstimulus interval of 12 �� 4 s, equivalent to a mean stimulation frequency of 0.

08 Hz (16). The subject assessed the sensation on the VAS after each stimulus. Following the first recording, there was 5 min of rest (no stimulation) before the second period of stimulation commenced. Data Analysis Cerebral evoked potentials. In both rats and humans, the morphology of the CEP waveforms consisted of a triphasic response characterized as prominent negative (N) and positive (P) peaks numbered in order of occurrence, i.e., N1, P1, etc. The latency (ms) of the cortical responses was measured at the peak of the distinct negative and positive peaks. The cortical amplitude (��V) was measured for the first peak (P1) relative to baseline and for the following peak-to-peak (P1�CN1 and N1�CP2). Rats.

Maximal amplitudes were recorded at the electrode 1.5 mm posterior of bregma and 1.5 mm lateral of the midline, and hence recordings from this electrode were used for further analysis. EEG signals were analyzed in the interval 0�C300 ms after stimulation. Each CEP recorded was manually inspected and the first positive peak was identified and labeled P1. The Entinostat following distinct negative and positive peaks were identified and labeled N1, P2, etc. The amplitude and latency was determined for each peak.