György Ádám

Right prefrontal activation produced by arterial baroreceptor stimulation: a PET study.

This study was performed to test the hypothesis of greater right hemispheric involvement in the processing of baroreceptor stimuli. Carotid sinus baroreceptors were stimulated by rhythmically decreasing air pressure in a neck chamber, and under control conditions the thorax was stimulated in a similar manner. Changes in regional cerebral blood flow (rCBF) were measured by PET. Baroreceptor stimulation resulted in rCBF increase in the right anterior–inferior prefrontal cortex (Brodmann areas (BA) 10/44/47) and bilaterally in BA 6/8. We conclude that in at least some stages of baroreceptor information processing the right hemisphere plays a greater role than the left hemisphere.

Visceroceptive control of operant behavior in rats.

Abstract The effect of non-contingent visceral stimulation as well as the possibility of the discrimination of non-painful gastrointestinal stimuli was examined in an operant situation in rats. The animals were submitted to surgery and prepared with chronic isolated intestinal loops, chronically implanted gastric electrodes or tubing in order to enable the administration of visceroceptive stimuli of different intensities in the course of an operant conditioning procedure. It was shown that visceral stimuli above the behavioral threshold level, those causing startle reactions, orienting or motor responses, result in differential effects. Thus the discrimination of the presence or of the absence of gastrointestinal stimulation can be demonstrated in rats using the operant conditioning technique.

The influence of monocular viewing on heart period variability.

Monocular viewing seems to differentially activate the cerebral hemispheres. Viewing with only one eye is accompanied by a relatively greater activation of the contralateral hemisphere. In this study heart periods were measured during binocular, left and right monocular viewing in 29 right-handed males. Power spectral analysis of heart period variability showed that the amount of heart rate fluctuations in the 0.07-0.13 Hz frequency range (the mid-frequency peak of the spectrum) depends on the viewing eye. Only viewing with the left eye produced a significant increase of the mid-frequency peak. It is known that sympathetic activity contributes strongly to the mid-frequency component of the heart rate. Therefore, it is concluded that the effects of left monocular viewing result in an increased sympathetic influence on the sinoatrial node.

Thresholds of behavioral reactions evoked by intestinal and skin stimuli in rats

Abstract The behavioral changes depending on the intensity of intestinal and skin stimuli were studied in rats. The reactions to the electric stimulation of the gut mucosa as well as of the abdominal skin were classified into four categories. The thresholds were calculated by interpolation from intensity-frequency curves. The behavioral effects of the external and the internal stimulation have been compared. The appropriate criteria for evaluating the thresholds and the consequences of the sigmoid shape of the curves were also discussed.

Modulation by GABAB and delta opioid receptors of neurally induced responses in isolated guinea-pig taenia coli and human colonic circular muscle

The GABA-ergic and opioid modulation of neurally induced muscle responses was studied in isolated guinea-pig taenia coli and human colonic circular muscle, using identical field stimulation parameters (rectangular pulses of 0.5 ms duration, 9 V x cm(-1) intensity, trains of 3 pulses at 0.5 Hz, repeated every 1/3/5 min). The stimulation-induced contractions were inhibited in both preparations by GABA and baclofen; the IC50 values in human colonic circular muscle were approximately 100 and 31.0 microM, respectively. In guinea-pig taenia coli, the inhibition by 10(-4) M GABA was dose-dependently reversed by 10(-4)-10(-3) M of GABA(B) receptor antagonist CGP 35348; antagonism by phaclofen was less effective in the same concentration range. In human colonic circular muscle, inhibition by 3 x 10(-5) M baclofen was fully reversed by 10(-3) M CGP 35348. With the exception of caecum, the delta 2 opioid receptor agonist deltorphin II was a potent inhibitor in human colonic circular muscle. 10(-8) M Deltorphin caused a 74.4 +/- 9.6% (n = 4) inhibition which was reversed by 10(-6) M of delta receptor selective peptide antagonist BOC-Tyr-Pro-Gly-Phe-Leu-Thr(OtBu). Deltorphin II was ineffective in guinea-pig taenia coli even at 10(-6) M; the same concentration caused an 84.3 +/- 7.9 (n = 4) inhibition in human preparations. It is concluded that: 1) GABA-ergic modulatory mechanisms are present both in human colonic circular muscle and guinea-pig taenia coli; 2) the GABA receptors involved are of type B; and 3) delta opioid receptor-mediated modulation functions only in human colonic circular muscle in regions other than the caecum.

Colonic sensitivity in irritable bowel syndrome and normal subjects according to their hemispheric preference and cognitive style.

According to our earlier results, non-painful, weak afferent visceral signals may exert a steady influence on brain processes, including cognitive functions. In the present series colonic impulses of irritable bowel syndrome (IBS) subjects served as a model of chronic impact from the gut. Hemispheric preference, as well as cognitive style of information processing served as indicators of covert changes in brain functions. In twentyone IBS patients and in ten control subjects of both sexes, the thresholds of minimal colonic distension sensitivity has been measured following the determination of hemispheric preference and of advantage in verbal or spatial information processing of the subjects. In IBS patients distension thresholds proved to be higher in verbals than in spatials, whereas in healthy controls the relationship of colonic thresholds and verbal versus, spatial advantage was reversed. Among the normal controls with left hemisphere preference a significantly higher distension threshold has been observed than in those with right hemisphere preference, whereas in the IBS group such threshold-differences were not observable.

Intestinal Afferent Influence on Behavior

Gastroenterology, as the scientific field separated recently from normal and pathological physiology, deals mainly with functions taking place in the alimentary tract itself. Thus, its general principle is inevitably organocentric. In other words, this branch of medicine pays relatively little attention to processes happening outside the main system, especially to such “distant” events as higher nervous or mental phenomena. The merit of contemporary psychophysiology consists in filling the gap between classical physiology of the gastrointestinal tract and experimental psychology.

Satiation evoked by distension of the small intestine in water deprived rats

Abstract Rats with chronic Thiry-Vella fistulae were deprived for 23 hours and studied in a free drinking situation. The intestine was distended or electrically stimulated in some of the sessions compared to non-stimulated and sham-stimulated experiments. The cumulative water intake of every 3 min, and the behaviour at 30 sec intervals were recorded. The intestine distended rats drank considerably less than the non-stimulated controls, and the behaviour characteristic of satiety had occurred earlier. This effect was eliminated by local intestinal Tetracaine infusion but not by the infiltration of the abdominal skin. The possible role of the gut distension in satiation is discussed.

Visceroception, Awareness, and Behavior

Taking into consideration the Sherringtonian classification of receptors, one notes that the power law of psychophysics is absolutely inapplicable to only one class of sensory organs, the visceral receptors; that is, their impulse flow to the brain does not generally evoke any sensation. The title of the present section should be somewhat thought-provoking because it challenges the classical concepts of neurophysiology. Some 15 or 20 years ago, even handbooks and textbooks of sensory physiology refused to recognize visceral sensation as an independent psychophysiological phenomenon.

THE SPECIFIC AND NONSPECIFIC BEHAVIORAL EFFECTS OF INTESTINAL STIMULATION IN RATS

Publisher Summary This chapter discusses the specific and nonspecific behavioral effects of intestinal stimulation in rats. The stimulation affects only the small intestine and not the surrounding viscera. In an experiment described in the chapter, the infiltration of the abdominal skin with Lidocaine did not affect drinking. The animals stimulated by water filled balloon showed characteristic behavior changes depending on the intensity of the stimulation. Weak stimulation increased the orienting activity, which enhanced ambulation and sniffing. In the period of strong stimulation, orienting behavior was also observed but with an altered character. The painful stimulation almost completely abolished orientation; instead, fast ambulation and long freezing periods occurred. The electrical stimulation— whether weak or strong—diminished all activities and strengthened the freezing tendency. The increase in the intensity had only quantitative influence; the decrease of activity was greater than in weakly stimulated rats. The animals appeared to be uncertain about the nature and origin of the unpleasant sensation and chose the natural way of responding, that is, immobilization. The great difference between the efficiency of electrical versus mechanical stimulation in changing the behavior supports the view of different ways of afferent activation.