Visceral analgesia induced by acute and repeated water avoidance stress in rats: sex difference in opioid involvement.

BACKGROUND: Chronic psychological stress-induced alterations in visceral sensitivity have been predominantly assessed in male rodents. We investigated the effect of acute and repeated water avoidance stress (WAS) on the visceromotor response (VMR) to colorectal distension (CRD) and the role of opioids in male and cycling female Wistar rats using a novel non-invasive manometric technique. METHODS: After a baseline VMR (1st CRD, day 0), rats were exposed to WAS (1 h day(-1) ) either once or for four consecutive days, without injection or with naloxone (1 mg kg(-1) ) or saline injected subcutaneously before each WAS session. KEY RESULTS: The VMR to CRD recorded on day 1 or 4 immediately after the last WAS was reduced in both females and males. The visceral analgesia was mainly naloxone-dependent in females, but naloxone-independent in males. In non-injected animals, on days 2 and 5, VMR was not significantly different from baseline in males whereas females exhibited a significant VMR increase at 60 mmHg on day 5. Basal CRD and CRD on days 1, 2, and 5 in both sexes without WAS induced similar VMR. CONCLUSIONS & INFERENCES: When monitored non-invasively, psychological stress induces an immediate poststress visceral analgesia mediated by an opiate signaling system in females while naloxone-independent in males, and hyperalgesia at 24 h after repeated stress only in females. These data highlight the importance of sex-specific interventions to modulate visceral pain response to stress.

Brain mapping of digestive sensations elicited by cortical electrical stimulations.

The aim of the study was to obtain a comprehensive map of cortical areas from where digestive sensations during intracerebral electrical stimulations (ES) in epileptic patients are elicited. Direct cortical ESs were performed in 339 medically intractable epileptic patients selected to presurgical evaluation using chronically stereotaxically implanted intracerebral electrodes and audio-video-EEG monitoring system. Digestive sensations were electrically induced on 723 different anatomical sites in 172 subjects (51%). According to the exclusion criteria, the final analysis includes 174 relevant stimulations evoked in 87 patients. The reported sensations referred predominantly to the upper part of the digestive tract including the epigastria and area over the periumbilical (n = 83; 48%), retrosternal (n = 17; 10%), pharyngeal (n = 31; 18%) and oral (n = 18; 10%) regions. The temporal pole (BA 38), hippocampus, amygdala and anterior cingulate cortex (ACC; BA 24/BA 32) were the typical anatomical locations connected with epigastric sensations. Retrosternal sensations were preferentially related to the ACC, while oro-pharyngeal sensations were most related to the suprasylvian opercular cortex and the insula. Cortical ESs are followed by a great variability of induced digestive and associated symptoms corresponding to a widely distributed cortical network of visceral sensation processing, in which the limbic and paralimbic structures play a critical role.

Testing of visceral sensitivity.

Under normal circumstances most of the visceral input to the central nervous system is not perceived consciously. Visceral hypersensitivity associated with altered reflex activity seems to be a common pathophysiological mechanism in functional gastrointestinal disorders. Investigation of visceral sensitivity in humans is based on distension tests using barostat, or tensostat more recently. Tensostat may allow better standardization of distending stimuli, regardless of the capacity or compliance of the organ being tested. Other techniques include transmucosal electrical nerve stimulation, and chemical or thermal stimulation. Measurement of the responses to gut stimuli is based on the evaluation of conscious perception or objective responses, such as reflex activity or central processes. Recently, the assessment of the central responses has become available due to a variety of new brain imaging techniques. Several factors are thought to influence the results of visceral sensitivity studies: age, gender, physiological factors (postprandial testing) as well as psychological factors (stress, hypnosis, hypervigilance phenomenon). Technical conditions for performing tests like distension protocols may considerably affect the perception of sensory thresholds. Various mediators and pharmacological agents, in particular those acting on serotonin receptors, affect the sensory function of the gastrointestinal tract, and some of them have therapeutic potential in the treatment of visceral hypersensitivity.