The functional link between tail-pinch-induced food intake and emotionality and its possible role in stress coping in rats.

Tail pinch facilitates eating in rats. We investigated an unidentified link between tail-pinch-induced eating behavior and individual emotionality in male Sprague-Dawley rats. Anxiety-like behavior was assessed on the elevated plus maze (EPM) and in the open field test (OFT). Tail-pinch-induced eating was observed as follows: After a 30-min habituation period, the tail pinch was applied for 5 min, followed by a 30-min recovery period. During the habituation and recovery periods, rats were allowed to access food ad libitum. During the recovery period, 14 of 24 rats ate more food than during the habituation period. Thus, we named them "high responders" and the others as "low responders". The food intake was significantly greater, while the times spent in the open arms in the EPM and in the center area in the OFT were significantly shorter in high responders than in low responders. This result suggests that the rats consuming more food after mild stress have higher anxiety.

Suppression of Oral Sweet Taste Sensation with Gymnema sylvestre Affects Postprandial Gastrointestinal Blood Flow and Gastric Emptying in Humans.

An oral sweet taste sensation (OSTS) exaggerates digestive activation transiently, but whether it has a role after swallowing a meal is not known. Gymnema sylvestre (GS) can inhibit the OSTS in humans. We explored the effect of the OSTS of glucose intake on gastrointestinal blood flow, gastric emptying, blood-glucose, and plasma-insulin responses during the postprandial phase. Eight participants ingested 200 g (50 g × 4 times) of 15% glucose solution containing 100 mg of 13C-sodium acetate after rinsing with 25 mL of 2.5% roasted green tea (control) or 2.5% GS solution. During each protocol, gastrointestinal blood flow and gastric emptying were measured by ultrasonography and 13C-sodium acetate breath test, respectively. Decreased subjective sweet taste intensity was observed in all participants in the GS group. The time to attain a peak value of blood flow in the celiac artery and gastric emptying were delayed in the GS group compared with the control group. At the initial phase after glucose intake, blood-glucose and plasma-insulin responses were lower in the GS group than those for the control group. These results suggest that the OSTS itself has a substantial role in controlling postprandial gastrointestinal activities, which may affect subsequent glycemic metabolism.

Multisensory interaction mediates the social transmission of avoidance in rats: dissociation from social transmission of fear.

Social interaction enables animals to transmit various types of sensory information that can modulate learned avoidance behavior and fear responses, which are important to survival. We previously reported that, under a passive avoidance paradigm, avoidance behavior is facilitated when a rat observes another rat (demonstrator) receiving a shock when performing a specific behavior. However, the sensory mechanisms underlying this 'social facilitation of avoidance' are not well understood. The present study examined the role of sensory pathways for social transmission of avoidance, focusing on the olfactory and visual systems. The olfactory ability of observer rats was blocked by an intranasal application of ZnSO4, and their visual ability was blocked by an opaque partition placed between observer and demonstrator rats. We found that blocking either olfactory or visual input drastically diminished the social transmission of avoidance. Interestingly the social transmission of fear responses remained intact even when olfactory or visual information was blocked. These results indicate that the social transmission of avoidance is mediated not by any single sensory modality but by multisensory interaction in rats, suggesting a distinct sensory mechanism from that underlying the social transmission of fear.

Effect of preceding exercise on cerebral and splanchnic vascular responses to mental task.

BACKGROUND: To investigate the effect of preceding acute exercise on the peripheral vascular response to a mental task, we measured splanchnic and cerebral blood flow responses to performing a mental task after exercise and resting. METHODS: In the exercise trial, 11 males exercised for 30 min on a cycle ergometer with a workload set at 70% of the age-predicted maximal heart rate for each individual. After a 15-min recovery period, the subjects rested for 5 min for pre-task baseline measurement and then performed mental arithmetic for 5 min followed by 5 min of post-task measurement. In the resting trial, they rested for 45 min and pre-task baseline data was obtained for 5 min. Then mental arithmetic was performed for 5 min followed by post-task measurement. We measured the mean blood velocity in the middle cerebral artery and superior mesenteric artery and the mean arterial pressure. RESULTS: Mean arterial pressure and mean blood velocity in the middle cerebral artery were significantly higher than the baseline during mental arithmetic in both exercise and resting trials. Mean blood velocity in the middle cerebral artery during mental arithmetic was greater in the control trial than the exercise trial. Mean blood velocity in the superior mesenteric artery showed no significant change during mental arithmetic from baseline in both trials. CONCLUSION: These results suggest that acute exercise can moderate the increase in cerebral blood flow induced by a mental task.

Autoregulation in the ocular and cerebral arteries during the cold pressor test and handgrip exercise.

The aim of this study was to determine whether autoregulation exerts similar effects in the ocular and cerebral vessels, which are both branches of the internal carotid artery. Ocular blood flow velocities, cerebral blood flow velocity and blood pressure were measured in 11 subjects during a 2-min resting period, static handgrip exercise (HG) and a cold pressor test (CPT). Blood velocity data for the superior and inferior temporal retinal arterioles (STRA and ITRA, respectively) and the retinal and choroidal vasculature (RCV) were obtained for 4 s during the measurement using laser speckle flowmetry. Mean blood flow velocity in the middle cerebral artery (MCAVmean) was measured by transcranial Doppler ultrasound. The conductance index (CI) of each vessel was calculated by dividing blood flow by mean arterial pressure. Blood flow velocity in the RCV increased by 19 ± 9% from resting baseline level during the CPT (P < 0.05), while blood flow in the STRA, ITRA and MCAVmean did not. The CI of the MCA decreased. The RCV blood flow velocity, ITRA blood flow and MCAVmean increased by 8 ± 1, 9 ± 3 and 11 ± 4%, respectively, during the HG (P < 0.05). Conversely, STRA blood flow remained unchanged. The HG did not significantly change the CI in any of the vessels measured. These findings suggest that cerebral blood flow velocity was maintained during the CPT, but autoregulation does not work well in the RCV during the CPT and HG.

Effects of dynamic exercise and its intensity on ocular blood flow in humans.

Visual performance is impaired when the ocular blood flow decreases, indicating that ocular blood flow plays a role in maintaining visual performance during exercise. We examined the ocular blood flow response to incremental cycling exercise to test the hypothesis that ocular blood flow is relatively stable during dynamic exercise because of its autoregulatory nature. The blood flow in the inferior and superior temporal retinal arterioles (ITRA and STRA, respectively) and retinal and choroidal vessels (RCV), mean arterial pressure, and heart rate (HR) were measured at rest and during leg cycling in nine young and healthy subjects (26 ± 5 years, mean ± SD). Ocular blood flow was measured by laser speckle flowmetry. The exercise intensity was incremented by 30 W every 3 min until the subject was unable to maintain a position appropriate for measuring ocular blood flow. Blood flow data obtained during cycling exercise were categorized based on HR as follows: <100, 100-120, and >120 bpm. Blood flow in the RCV increased with the exercise intensity: by 16 ± 8, 32 ± 13, and 40 ± 19% from baseline, respectively. However, blood flow and vascular conductance in the ITRA and STRA did not change significantly with exercise. These findings demonstrate for the first time that ocular blood flow increases in the retina and choroid, but not in the arterioles, with increasing exercise intensity during dynamic exercise.

Muscle metaboreflex activation by static exercise dilates pupil in humans.

We examined a hypothesis that static exercise and activation of sympathetic activation by metabolically sensitive skeletal muscle afferents (metaboreflex) influence the sympathetic nervous activity modulating pupil diameter. Nine subjects performed 2 min isometric handgrip exercise at 30% maximal voluntary contraction, which was followed by either 2 min of postexercise muscle ischemia (PEMI) in the forearm or no PEMI (control trial). The pupil diameter and mean blood pressure (MAP) increased significantly from rest during exercise in PEMI and control trials (5 ± 1 and 7 ± 1% in diameter; 13 ± 2 and 12 ± 2 mmHg in MAP, respectively). These increases in the diameter and MAP were maintained during PEMI (7 ± 2% and 9 ± 2 mmHg) but not during the recovery period in the control trial (3 ± 2% and 1 ± 2 mmHg). These results demonstrate that static handgrip exercise increases the pupil diameter, and this increase is partly due to the activation of metaboreflex in humans.

Effect of intensity of dynamic exercise on pupil diameter in humans.

To test the hypothesis that pupil diameter, which is innervated by the autonomic nervous system, increases with exercise intensity, we determined pupil diameter during incremental exercise in eight healthy subjects. The subjects performed an incremental ergometer exercise in a room illuminated at 90-100 lx. We continuously measured pupil diameter and heart rate before, during, and after the exercise. Pupil diameter increased significantly with exercise intensity (except at the lowest intensity), peaking at 113+/-3% (mean+/-SE) of the diameter during the resting baseline period. The diameter did not differ significantly between the resting baseline and recovery periods. These findings suggest that exercise enlarges pupil diameter and that the magnitude of dilation is related to exercise intensity.

Effects of a mental task on splanchnic blood flow in fasting and postprandial conditions.

We tested the hypothesis that a mental task attenuates the meal-induced vasodilation in the splanchnic vasculature. Ten subjects performed a 5-min colour-word conflict test (CWT) under fasting and postprandial conditions. Subjects in the postprandial condition had ingested solid food with an energy content of 300 kcal (1,255 kJ) before either performing the CWT (mental task trial) or resting (resting control trial). The mean blood velocities (MBV) in the coeliac artery (CA) and superior mesenteric artery (SMA), and the mean arterial pressure (MAP) were measured. The MBV in the CA and SMA were divided by the MAP to assess the vascular conductance (VC). The MBV in the CA and SMA were significantly increased by the CWT under fasting conditions. In the postprandial condition, the MBV in the CA and SMA significantly increased immediately after the meal in both the mental task and resting control trials. The VC in the SMA, but not in the CA, was significantly decreased by the CWT under fasting conditions. In the postprandial conditions, there was no significant difference in the VC in both arteries between mental task and resting control trials. These results suggest that a mental task exerts different effects on the CA and SMA under fasting but not postprandial condition. The vasoconstrictive effect of a mental task on the SMA does not counter the vasodilatory effect of meal ingestion.

Vascular responses to fear-induced stress in humans.

The information about the effect of mental activities on detailed cardiovascular responses is limited, though strong and chronic psychological stressors are risk factors of cardiovascular morbidity and mortality in humans. The responses of vascular resistance (VR) during fear-induced stress was studied by measuring the mean arterial pressure (MAP), heart rate (HR), skin blood flow in the index finger and forehead, limb blood flow in the calf and forearm, and blood flow in the renal and superior mesenteric arteries before, during, and after a period of induced fear. After 2 min of rest, baseline data were acquired from eight subjects, after which they watched a 3-min video that was considered to be frightening. Minute-by-minute data were calculated. The MAP was divided by the blood flow to attain the VR. While a clear steady state was not evident in the stress-induced vascular response, stress significantly increased the MAP and HR (e.g., by 10+/-3 mm Hg and 8+/-3 bpm, respectively, at the 2nd min; mean+/-SEM), and the VR of the forearm and finger skin (e.g., by 80+/-26% and 79+/-28%, respectively, at the 2nd min). The VR increased slightly in the calf and visceral arteries but not in the forehead throughout the stimulation. The variables returned to baseline levels by the 1st min after cessation of the fearful stimulation. These results suggest that fear-induced stress causes vasoconstriction in the forearm and finger.

Chewing and taste increase blood velocity in the celiac but not the superior mesenteric arteries.

To investigate the role of chewing and taste in the meal-induced rapid increase in splanchnic blood flow, we compared the blood flow responses in the celiac artery (CA) and superior mesenteric artery (SMA) to chewing solid food with a chocolate taste (FOOD) and paraffin wax without taste (WAX). After 5 min of baseline measurement, 15 healthy subjects repeated chewing and expectorating the FOOD or WAX every 20 s for 4 min followed by 10 min of recovery measurement. We measured the mean blood velocity (MBV) in the CA and SMA. The baseline MBVs in the CA and SMA did not differ between the FOOD and WAX trials. The MBV in the CA was lower than baseline at the 1st min of chewing in both trials. It was higher than baseline at the 3rd min of FOOD chewing, whereas it did not increase during and after WAX chewing. The MBV in the CA was higher in the FOOD trial than in the WAX trial at the 3rd min of chewing and thereafter. In contrast, the MBV in the SMA did not change throughout the protocols. These results suggest that the taste of food plays a role in meal-induced hyperemia in the CA but not the SMA.

Ambient temperature affects glabrous skin vasculature and sweating responses to mental task in humans.

We compared responses in heart rate (HR), mean blood pressure (MAP), sweating rate (SR), sweating expulsion (SwE), and skin vascular conductance (VC) to mental task among different ambient temperature (Ta) conditions, i.e., 12, 16, 20, and 24 degrees C. Seven subjects (27+/-5 yrs, 64+/-14 kg) underwent a 2-min color word conflict test (CWT) after 2 mins of baseline data acquisition following a 20-min resting period. All subjects wore long sleeve shirts and long pants. The skin blood flow was measured with a laser Doppler probe on the left index finger pulp to calculate skin VC, and the SR and sweating expulsion (SwE) were measured with a ventilated capsule on the left thenar. CWT significantly increased the HR and MAP, while there was no significant effect of Ta on the magnitudes of these responses. CWT significantly decreased the skin VC when the Ta was 24 degrees C, whereas it significantly increased the skin VC when the Ta was 12 or 16 degrees C. CWT significantly increased SR and SwE in all Ta conditions, and the SwE was greater in warmer conditions. These findings suggest that different ambient temperatures induce different responses in finger skin vasculature to mental task, implying the independent response of cutaneous vasomotor tone and sweat glands in glabrous skin to mental task.

Blood flow responses in celiac and superior mesenteric arteries in the initial phase of digestion.

Blood flow (BF) responses in the celiac artery (CA) and superior mesenteric artery (SMA) during and immediately after a meal are poorly understood. We characterized postprandial BF responses in these arteries in the initial phase of digestion. After a baseline measurement in the overnight fasting state, healthy subjects ingested solid food (300 kcal) and water ad libitum within 5 min (4.6 +/- 0.2 min, means +/- SE), and then rested for 60 min in the postprandial state. Mean blood velocities (MBVs) in CA (n = 7) and SMA (n = 9) and mean arterial pressure (MAP) were measured throughout the procedure. The MAP was divided by the MBV to yield the resistance index (RI). The MBV in CA and SMA started increasing within a minute after beginning the meal. The MBV in CA rapidly reached its peak increase (60 +/- 8% change from baseline) at 5 +/- 1 min after the start of the meal, whereas the MBV in SMA gradually reached its peak increase (134 +/- 14%) at 41 +/- 4 min after the start of the meal, reflecting a decrease in the RI for both CA and SMA. These findings suggested an earlier increase in CA and SMA MBV, implying that the increase of BF in some parts of the small intestine precedes the arrival of chyme.

The limited effect of breathing frequency on blood velocity measurements in renal and superior mesenteric arteries.

Breathing including abdominal movement could affect the blood velocity (BV) measurement in the visceral arteries. The present study investigated the effect of breathing frequency on the renal artery (RA) and superior mesenteric artery (SMA) BV measurements. We measured mean arterial pressure (MAP), heart rate (HR) and BV in the RA and SMA using the Doppler technique at different respiratory frequencies. Nine subjects performed breath-holding (<40 s), and spontaneous and controlled breathings at a constant rate of 12, 15 and 20 breaths min(-1). The breathing frequency did not significantly affect the BV in either artery. The BVs at these frequencies were not significantly different from those during spontaneous breathing and breath-holding. There were no significant differences in MAP and HR among trials. This result suggests that the effect of breathing frequency adopted in this study could be neglected in the RA and SMA measurements.

Vasoconstriction and blood flow responses in visceral arteries to mental task in humans.

The vascular responses to mental task in visceral arteries in humans have not been elucidated. We observed the responses in the renal (RA) and superior mesenteric (SMA) arteries to mental stress, using simultaneous pulsed and echo Doppler ultrasound flowmetry. Nine healthy females performed a computerized colour word conflict test (CWT) for 3 min. The mean blood velocity (MBV) in the right RA and SMA, heart rate (HR) and blood pressure were measured. The mean arterial pressure (MAP) was divided by the flow velocity to assess the vascular resistance (VR). The CWT significantly increased the MAP, HR and VR in both arteries from the first minute. During the CWT, flow in the RA decreased significantly at the third minute relative to baseline, while flow in the SMA showed no significant change from the first to the third minute. The degree of vasoconstriction in the RA bed was greater than that in the SMA bed. These results suggest that the mental task causes vasoconstriction in visceral arteries, and imply that it induces differential blood flow and vascular responses in visceral arteries.