Sex differences in the influence of body mass index on anatomical architecture of brain networks.

BACKGROUND/OBJECTIVES: The brain has a central role in regulating ingestive behavior in obesity. Analogous to addiction behaviors, an imbalance in the processing of rewarding and salient stimuli results in maladaptive eating behaviors that override homeostatic needs. We performed network analysis based on graph theory to examine the association between body mass index (BMI) and network measures of integrity, information flow and global communication (centrality) in reward, salience and sensorimotor regions and to identify sex-related differences in these parameters. SUBJECTS/METHODS: Structural and diffusion tensor imaging were obtained in a sample of 124 individuals (61 males and 63 females). Graph theory was applied to calculate anatomical network properties (centrality) for regions of the reward, salience and sensorimotor networks. General linear models with linear contrasts were performed to test for BMI and sex-related differences in measures of centrality, while controlling for age. RESULTS: In both males and females, individuals with high BMI (obese and overweight) had greater anatomical centrality (greater connectivity) of reward (putamen) and salience (anterior insula) network regions. Sex differences were observed both in individuals with normal and elevated BMI. In individuals with high BMI, females compared to males showed greater centrality in reward (amygdala, hippocampus and nucleus accumbens) and salience (anterior mid-cingulate cortex) regions, while males compared to females had greater centrality in reward (putamen) and sensorimotor (posterior insula) regions. CONCLUSIONS: In individuals with increased BMI, reward, salience and sensorimotor network regions are susceptible to topological restructuring in a sex-related manner. These findings highlight the influence of these regions on integrative processing of food-related stimuli and increased ingestive behavior in obesity, or in the influence of hedonic ingestion on brain topological restructuring. The observed sex differences emphasize the importance of considering sex differences in obesity pathophysiology.

The use of gastric electrical signals for algorithm for automatic eating detection in dogs.

Food ingestion increases fundic impedance (FI) and reduces antral slow wave rate (SWR). Our aim was to determine if such changes can be integrated into an algorithm for automatic eating detection (AED). When incorporated in implantable medical devices, AED can time treatment to food intake without need for patient input. Four dogs were implanted with fundic and antral electrodes, connected to an implantable recording device. Changes in FI and SWR induced by fixed meals of different weights were determined, and were used to build an AED algorithm. Its performance was then tested on the same animals given an ad libitum access to food. The effects of gastric balloon distension and nitroglycerin on SWR and FI were also tested. Fixed meals reduced SWR in a weight-dependent manner, R(2) = 0.936, P < 0.05 baseline compared to 50, 100, 200 and 400 g. Meals increased FI above baseline in a weight-dependent manner; R(2) = 0.994, P < 0.05 baseline compared to 200 and 400 g. During ad libitum intake, the AED algorithm detected 86% of all meals > or =15 g. Gastric distension reduced SWR and increased FI. Nitroglycerin reduced SWR. AED, using changes in FI and gastric SWR is feasible. Changes in FI and SWR are induced primarily by the presence of food in the stomach.

Circadian patterns of gastric electrical and mechanical activity in dogs.

Gastric motor function assessment, in humans and animals, is typically performed for short recording periods. The aim of this article was to monitor gastric electrical and motor activity in the antrum and fundus simultaneously, for long periods, using a new implantable system. Ten dogs were implanted with fundic and antral electrodes for assessment of impedance and electrical activity. Dogs were studied while in cages, for periods of 22-26 h. From late evening and until feeding on the next day, slow wave (SW) rhythm demonstrated a distinct pattern of intermittent pauses (mean duration = 22.8 +/-4.1 s) that delineated groups of SW's. Phasic increases in fundic tone were seen mostly in association with SW pauses, and were highly correlated with antral contractions, R(2) = 0.652, P < 0.05. The SW rate (events per minute) in the postprandial period, fasting and night time was 4.2 +/- 0.2, 5 +/- 0.2 and 4.7 +/- 0.3, respectively, P < 0.05 postprandial vs other periods. Antral and fundic mechanical activities were highly correlated during fasting, particularly at night. This novel method of prolonged gastric recording provides valuable data on the mechanical and electrical activity of the stomach, not feasible by current methods of recording. During fasting, fundic and antral motor activities are highly correlated and are associated with periodic pauses in electrical activity.

Neural gastrointestinal electrical stimulation enhances colonic motility in a chronic canine model of delayed colonic transit.

Neural gastrointestinal electrical stimulation (NGES) induces sequential contractions and enhances emptying in acute canine gastric and colonic models. This study was set to determine (i) the effect of NGES in a chronic canine model of delayed colonic transit and (ii) possible mechanism of action. Four pairs of electrodes were implanted in the distal colon of nine mongrel dogs. Delayed colonic transit was induced by diphenoxylate/atropine and alosetron. Transit was fluoroscopically determined by the rate of evacuation of radiopaque markers, and was tested twice in each dog, in random order, on and off stimulation. Two stimulation sequences, separated by 1 min, were delivered twice a day via exteriorized electrodes. Colonic manometry during stimulation was performed before and after intravenous (i.v.) injection of 1 mg of atropine. Complete evacuation of all markers was significantly shortened by NGES, from 4 days to 2 days, interquartile range 3-4 days vs 2-3 days, respectively, P = 0.016. NGES induced strong sequential contractions that were significantly diminished by atropine: 190.0 +/- 14.0 mmHg vs 48.7 +/- 19.4 mmHg, respectively (P < 0.001). NGES induces strong sequential colonic contractions and significantly accelerates movement of content in a canine model of delayed colonic transit. The effect is atropine sensitive.

Microprocessor-controlled movement of solid gastric content using sequential neural electrical stimulation.

BACKGROUND & AIMS: Gastric electrical stimulation has been attempted for years without much success. The aim of this study was to determine if movement of solid gastric content could be achieved using microprocessor-controlled sequential electrical stimulation. METHODS: The study was performed on 9 anesthetized dogs. The dogs underwent laparotomy, pyloroplasty, and implantation of 4-6 sets of bipolar stainless-steel wire electrodes. Each set consisted of 2-6 electrodes (10 x 0.25 mm, 3 cm apart) implanted circumferentially. The stomach was filled with solid food mixed with plastic pellets, and the process of gastric emptying was monitored. Artificial contractions were produced using microprocessor-controlled phase-locked bipolar trains of 50-Hz rectangular voltage with flexible amplitudes. RESULTS: Using the above stimulating parameters, we were able to produce circumferential gastric contractions that were artificially propagated distally by embedding and phase-locking the stimulating voltage. The number of expelled pellets after the stimulation sessions was significantly higher than the number of pellets emptied during the nonstimulation sessions (P < 0.01). CONCLUSIONS: Microprocessor-controlled electrical stimulation produced artificial peristalsis and markedly accelerated the movement of solid gastric content.

Electrogastrographic impact of multi-site functional gastric electrical stimulation.

Microprocessor-controlled multi-site functional gastric electrical stimulation using synchronized higher frequency (above 25 Hz) bipolar voltages has been suggested as a possible new avenue towards efficient artificial control of gastric motility. However, the effect of this sequential stimulation on gastric electrical activity is unknown. Because of the substantial strength of the invoked sequential contractions, using implanted electrodes to assess gastric electrical activity (GEA) in experimental animals is difficult, if not impossible. Electrogastrography (EGG), the non-invasively obtained recording of GEA, provides an excellent opportunity to study the changes associated with the multi-site functional stimulation. In this study, we investigated 4 unconscious dogs with 4 circumferential sets of subserosally-implanted stimulating electrodes and 4 force transducers attached close to each stimulating electrode set at operation. The abdominal cavity of each dog was closed after the electrode implantations and 3 standard neonatal electrocardiographic electrodes were attached overlying the abdominal projection of the gastric axis. Two-channel EGG recordings were obtained for 1/2 h before any electrical stimulation and during 1/2 h of intensive sequential stimulation. Significant changes were observed in the EGG pattern during stimulation. These changes were quantified and compared to the basal recordings. Our findings indicate that the interrelation between spectral changes in cutaneous EGG and mechanical activity of the stomach could be far more complex than previously speculated.

Dynamics of level of randomness of electrogastrograms can be indicative of gastric electrical uncoupling in dogs.

Gastric electrical uncoupling is the lack of electrical synchronization in different parts of the stomach. The aim of this study was to investigate the impact of gastric electrical uncoupling on the level of randomness of canine electrogastrograms (EGG). Electrogastrograms were obtained from 11 unconscious acute dogs. Gastric electrical uncoupling was produced surgically by performing two consecutive circumferential cuts through the entire thickness of the gastric muscle layer. Three separate 1/2-hr eight-channel bipolar EGGs were obtained from each dog in the basal state and after each cut. The signals were amplified using amplifiers with a flexible frequency range, digitized with 10-Hz sampling frequency, and 4.27-min portions of the digital EGGs were subjected to a turning point test for randomness. The number of turning points (NTPs) was determined from successive time intervals calculated from all EGG channels. Distributions of NTPs were calculated for each dog. An average NTPs (ANTP) for each dog in a given state (basal, after the first cut, and after the second cut) was calculated from the ANTPs of all channels. In six of 11 dogs the ANTP were greater after the first cut. The number rose to nine of 11 dogs after the second cut. In only 45% of the dogs were the ANTP distributions significantly different (P < 0.01) after the first cut (sensitivity 45%). After the second cut the sensitivity rose to 64%. In two specific EGG channels NTP distribution was significantly different (P < 0.01) in nine of 11 dogs (sensitivity: 82%) after the second cut. The dynamics of the level of randomness in EGG can be indicative of severe gastric electrical uncoupling. Some EGG channel configurations are more sensitive than others in recognizing gastric electrical uncoupling.

Microprocessor controlled movement of liquid gastric content using sequential neural electrical stimulation.

BACKGROUND: Gastric electrical stimulation has been attempted for several years with little success. AIMS: To determine whether movement of liquid gastric content could be achieved using microprocessor controlled sequential electrical stimulation. METHODS: Eight anaesthetised dogs underwent laparotomy and implantation of four sets of bipolar stainless steel wire electrodes. Each set consisted of two to six electrodes (10x0.25 mm, 3 cm apart) implanted circumferentially. The stomach was filled with water and the process of gastric emptying was monitored. Artificial contractions were produced using microprocessor controlled phase locked bipolar four second trains of 50 Hz, 14 V (peak to peak) rectangular voltage. In four of the dogs four force transducers were implanted close to each circumferential electrode set. In one gastroparetic patient the effect of direct electrical stimulation was determined at laparotomy. RESULTS: Using the above stimulating parameters circumferential gastric contractions were produced which were artificially propagated distally by phase locking the stimulating voltage. Averaged stimulated gastric emptying times were significantly shorter than spontaneus emptying times (t1/2 6.7 (3.0) versus 25.3 (12.9) minutes, p<0.01). Gastric electrical stimulation of the gastroparetic patient at operation produced circumferential contractions. CONCLUSIONS: Microprocessor controlled electrical stimulation produced artificial peristalsis and notably accelerated the movement of liquid gastric content.

Electrogastrography: a noninvasive technique to evaluate gastric electrical activity.

Electrogastrography (EGG) is the recording of gastric electrical activity (GEA) from the body surface. The cutaneous signal is low in amplitude and consequently must be amplified considerably. The resultant signal is heavily contaminated with noise, and visual analysis alone of an EGG signal is inadequate. Consequently, EGG recordings require special methodology for acquisition, processing and analysis. Essential components of this methodology involve an adequate system of digital filtering, amplification and analysis, along with minimization of the sources of external noise (random motions of the patient, electrode-skin interface impedance, electrode bending, obesity, etc) and a quantitative interpretation of the recordings. There is a close relationship between GEA and gastric motility. Although it has been demonstrated that EGG satisfactorily reflects internal GEA frequency, there is not acceptable correlation with gastric contractions or gastric emptying. Many attempts have been made to relate EGG 'abnormalities' with clinical syndromes and diseases; however, the diagnostic and clinical value of EGG is still very much in question.